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  • 1
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    Supporting Global Numerical Optimization of Rational Functions by Generic Symbolic Convexity Tests (2010)
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    Publikationsdatum: 2020-12-11
    Beschreibung: Convexity is an important property in nonlinear optimization since it allows to apply efficient local methods for finding global solutions. We propose to apply symbolic methods to prove or disprove convexity of rational functions over a polyhedral domain. Our algorithms reduce convexity questions to real quantifier elimination problems. Our methods are implemented and publicly available in the open source computer algebra system REDUCE. Our long term goal is to integrate REDUCE as a workhorse'' for symbolic computations into a numerical solver.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 2
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    Fault-Tolerant and Decentralized Lease Coordination in Distributed Systems (2010)
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    Publikationsdatum: 2016-06-30
    Beschreibung: Applications which need exclusive access to a shared resource in distributed systems require a fault-tolerant and scalable mechanism to coordinate this exclusive access. Examples of such applications include distributed file systems and master/slave data replication. We present Flease, an algorithm for decentralized and fault-tolerant lease coordination in distributed systems. Our algorithm allows the processes competing for a resource to coordinate exclusive access through leases among themselves without a central component. The resulting system easily scales with an increasing number of nodes and resources. We prove that Flease ensures exclusive access, i.e. guarantees that there is at most one valid lease at any time.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 3
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    Robust Tail Assignment (2010)
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    Publikationsdatum: 2020-08-05
    Beschreibung: We propose an efficient column generation method to minimize the probability of delay propagations along aircraft rotations. In this way, delay resistant schedules can be constructed. Computational results for large-scale real-world problems demonstrate substantial punctuality improvements. The method can be generalized to crew and integrated scheduling problems.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 4
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    State Trajectory Compression for Optimal Control with Parabolic PDEs (2010)
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    Publikationsdatum: 2022-01-07
    Beschreibung: In optimal control problems with nonlinear time-dependent 3D PDEs, full 4D discretizations are usually prohibitive due to the storage requirement. For this reason gradient and quasi-Newton methods working on the reduced functional are often employed. The computation of the reduced gradient requires one solve of the state equation forward in time, and one backward solve of the adjoint equation. The state enters into the adjoint equation, again requiring the storage of a full 4D data set. We propose a lossy compression algorithm using an inexact but cheap predictor for the state data, with additional entropy coding of prediction errors. As the data is used inside a discretized, iterative algorithm, lossy coding maintaining an error bound is sufficient.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 5
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    A simple mathematical model of the bovine estrous cycle: follicle development and endocrine interactions (2010)
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    Publikationsdatum: 2020-03-11
    Beschreibung: Bovine fertility is the subject of extensive research in animal sciences, especially because fertility of dairy cows has declined during the last decades. The regulation of estrus is controlled by the complex interplay of various organs and hormones. Mathematical modeling of the bovine estrous cycle could help in understanding the dynamics of this complex biological system. In this paper we present a mathematical model of the bovine estrous cycle that includes the processes of follicle and corpus luteum development and the key hormones that interact to control these processes. Focus in this paper is on development of the model, but also some simulation results are presented, showing that a set of equations and parameters is obtained that describes the system consistent with empirical knowledge. Even though the majority of the mechanisms that are included are only known qualitatively as stimulatory or inhibitory effects, the model surprisingly well features quantitative observations made in reality. This model of the bovine estrous cycle could be used as a basis for more elaborate models with the ability to study effects of external manipulations and genetic differences.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 6
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    Rapid Learning for Binary Programs (2010)
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    Publikationsdatum: 2022-03-14
    Beschreibung: Learning during search allows solvers for discrete optimization problems to remember parts of the search that they have already performed and avoid revisiting redundant parts. Learning approaches pioneered by the SAT and CP communities have been successfully incorporated into the SCIP constraint integer programming platform. In this paper we show that performing a heuristic constraint programming search during root node processing of a binary program can rapidly learn useful nogoods, bound changes, primal solutions, and branching statistics that improve the remaining IP search.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 7
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    Dynamic routing at different layers in IP-over-WDM networks -- Maximizing energy savings (2010)
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    Publikationsdatum: 2020-08-05
    Beschreibung: We estimate potential energy savings in IP-over-WDM networks achieved by switching off router line cards in low-demand hours. We compare three approaches to react on dynamics in the IP traffic over time, FUFL, DUFL and DUDL. They provide different levels of freedom in adjusting the routing of lightpaths in the WDM layer and the routing of demands in the IP layer. Using MILP models based on three realistic network topologies as well as realistic demands, power, and cost values, we show that already a simple monitoring of the lightpath utilization in order to deactivate empty line cards (FUFL) brings substantial benefits. The most significant savings, however, are achieved by rerouting traffic in the IP layer (DUFL), which allows emptying and deactivating lightpaths together with the corresponding line cards. A sophisticated reoptimization of the virtual topologies and the routing in the optical domain for every demand scenario (DUDL) yields nearly no additional profits in the considered networks. These results are independent of the ratio between the demand and capacity granularities, the time scale and the network topology, and show little dependency on the demand structure.
    Schlagwort(e): ddc:620
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 8
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    Models for Line Planning with Transfers (2010)
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    Publikationsdatum: 2020-08-05
    Beschreibung: We propose a novel integer programming approach to transfer minimization for line planning problems in public transit. The idea is to incorporate penalties for transfers that are induced by “connection capacities” into the construction of the passenger paths. We show that such penalties can be dealt with by a combination of shortest and constrained shortest path algorithms such that the pricing problem for passenger paths can be solved efficiently. Connection capacity penalties (under)estimate the true transfer times. This error is, however, not a problem in practice. We show in a computational comparison with two standard models on a real-world scenario that our approach can be used to minimize passenger travel and transfer times for large-scale line planning problems with accurate results.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 9
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    Adaptive Timestep Control for the Contact-Stabilized Newmark Method (2010)
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    Publikationsdatum: 2016-06-09
    Beschreibung: The aim of this paper is to devise an adaptive timestep control in the contact--stabilized Newmark method (CONTACX) for dynamical contact problems between two viscoelastic bodies in the framework of Signorini's condition. In order to construct a comparative scheme of higher order accuracy, we extend extrapolation techniques. This approach demands a subtle theoretical investigation of an asymptotic error expansion of the contact--stabilized Newmark scheme. On the basis of theoretical insight and numerical observations, we suggest an error estimator and a timestep selection which also cover the presence of contact. Finally, we give a numerical example.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 10
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    Railway capacity auctions with dual prices (2010)
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    Publikationsdatum: 2020-08-05
    Beschreibung: Railway scheduling is based on the principle of the construction of a conflict-free timetable. This leads to a strict definition of capacity: in contrast with road transportation, it can be said in advance whether a given railway infrastructure can accommodate - at least in theory - a certain set of train requests. Consequently, auctions for railway capacity are modeled as auctions of discrete goods -- the train slots. We present estimates for the efficiency gain that may be generated by slot auctioning in comparison with list price allocation. We introduce a new class of allocation and auction problems, the feasible assignment problem, that is a proper generalization of the well-known combinatorial auction problem. The feasible assignment class was designed to cover the needs for an auction mechanism for railway slot auctions, but is of interest in its own right. As a practical instance to state and solve the railway slot allocation problem, we present an integer programming formulation, briefly the ACP, which turns out to be an instance of the feasible assignment problem and whose dual problem yields prices that can be applied to define a useful activity rule for the linearized version of the Ausubel Milgrom Proxy auction. We perform a simulation aiming to measure the impact on efficiency and convergence rate.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 11
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    Solving Optimal Control Problems with the Kaskade 7 Finite Element Toolbox (2010)
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    Publikationsdatum: 2022-01-07
    Beschreibung: This paper presents concepts and implementation of the finite element toolbox Kaskade 7, a flexible C++ code for solving elliptic and parabolic PDE systems. Issues such as problem formulation, assembly and adaptivity are discussed at the example of optimal control problems. Trajectory compression for parabolic optimization problems is considered as a case study.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 12
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    Aggregation Methods for Railway Networks (2010)
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    Publikationsdatum: 2020-08-05
    Beschreibung: In this paper a bottom-up approach of automatic simplification of a railway network is presented. Starting from a very detailed, microscopic level, as it is used in railway simulation, the network is transformed by an algorithm to a less detailed level (macroscopic network), that is sufficient for long-term planning and optimization. In addition running and headway times are rounded to a pre-chosen time discretization by a special cumulative method, which we will present and analyse in this paper. After the transformation we fill the network with given train requests to compute an optimal slot allocation. Then the optimized schedule is re-transformed into the microscopic level and can be simulated without any conflicts occuring between the slots. The algorithm is used to transform the network of the very dense Simplon corridor between Swiss and Italy. With our aggregation it is possible for the first time to generate a profit maximal and conflict free timetable for the corridor across a day by a simultaneously optimization run.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 13
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    Merging solutions of non-linear algebraic systems (2010)
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    Publikationsdatum: 2020-12-11
    Beschreibung: In solving large polynomial algebraic systems that are too big for standard Gröbner basis techniques one way to make progress is to introduce case distinctions. This divide and conquer technique can be beneficial if the algorithms and computer programs know how to take advantage of inequalities. A further hurdle is the form of the resulting general solutions which often have unnecessarily many branches. In this paper we discuss a procedure to merge solutions by dropping inequalities which are associated with them and, if necessary, by re-parametrizing solutions. In the appendix the usefulness of the procedure is demonstrated in the classification of quadratic Hamiltonians with a Lie-Poisson bracket $e(3)$. This application required the solution of algebraic systems with over 200 unknowns, 450 equations and between 5000 and 9000 terms.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 14
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    A Dynamical Systems Approach for Static Evaluation in Go (2010)
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    Publikationsdatum: 2020-12-11
    Beschreibung: In the paper arguments are given why the concept of static evaluation (SE) has the potential to be a useful extension to Monte Carlo tree search. A new concept of modeling SE through a dynamical system is introduced and strengths and weaknesses are discussed. The general suitability of this approach is demonstrated. A Remark: Among users of the Internet Go server KGS the abbreviation SE is used for 'Score Estimator'. Although different from 'Static Evaluation' a score estimator is easily obtained from static evaluation by adding up probabilities of chains to be alive at the end of the game or points to be owned by White or Black
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 15
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    Classification of integrable quadratic Hamiltonians on e(3) (2010)
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    Publikationsdatum: 2020-12-11
    Beschreibung: Linear Poisson brackets on e(3) typical of rigid body dynamics are considered. All quadratic Hamiltonians of Kowalevski type having additional first integral of fourth degree are found. Quantum analogs of these Hamiltonians are listed.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 16
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    Classification of integrable super-systems using the SsTools environment (2010)
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    Publikationsdatum: 2020-12-11
    Beschreibung: A classification problem is proposed for supersymmetric %scaling\/-\/in\-va\-ri\-ant evolutionary PDE that satisfy the assumptions of nonlinearity, nondegeneracy, and homogeneity. Four classes of nonlinear coupled boson\/-\/fermion systems are discovered under the weighting assumption $|f|=|b|=|D_t|=\oh$. The syntax of the \Reduce\ package \SsTools, which was used for intermediate computations, and the applicability of its procedures to the calculus of super\/-\/PDE are described.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 17
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    N=2 supersymmetric a=4-KdV hierarchy derived via Gardner's deformation of Kaup-Boussinesq equation (2010)
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    Publikationsdatum: 2020-12-11
    Beschreibung: We consider the problem of constructing Gardner's deformations for the $N{=}2$ supersymmetric $a{=}4$--\/Korteweg\/--\/de Vries equation; such deformations yield recurrence relations between the super\/-\/Hamiltonians of the hierarchy. We prove the non\/-\/existence %P.~Mathieu's Open problem on constructing for of supersymmetry\/-\/invariant %Gardner's deformations that %solutions, retract to Gardner's formulas for the KdV equation %whenever it is assumed that, under the %respective component reduction. % in the $N{=}2$ super\/-\/field. the solutions . At the same time, we propose a two\/-\/step scheme for the recursive production of the integrals of motion for the $N{=}2$,\ $a{=}4$--\/SKdV. First, we find a new Gardner's deformation of the Kaup\/--\/Boussinesq equation, which is contained in the bosonic limit of the super\/-\/%$N{=}2$,\ $a{=}4$--\/SKdV hierarchy. This yields the recurrence relation between the Hamiltonians of the limit, whence we determine the bosonic super\/- /Hamiltonians of the full $N{=}2$, $a{=}4$--\/SKdV hierarchy.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 18
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    The Quickest Path to the Goal (2010)
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    Publikationsdatum: 2020-08-05
    Beschreibung: We provide an introduction into the mathematics of and with paths. Not on the shortest, but hopefully on an entertaining path!
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 19
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    Linienoptimierung - reif für die Praxis? (2010)
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    Publikationsdatum: 2020-08-05
    Beschreibung: Wir stellen in dieser Arbeit ein mathematisches Optimierungsmodell zur Bestimmung eines optimalen Linienplans vor, das sowohl die Fahrzeiten und die Anzahl der Umstiege berücksichtigt als auch die Kosten des Liniennetzes. Dieses Modell deckt wichtige praktische Anforderungen ab, die in einem gemeinsamen Projekt mit den Verkehrsbetrieben in Potsdam (ViP) formuliert wurden. In diesem Projekt wurde der Linienplan 2010 für Potsdam entwickelt. Unsere Berechnungen zeigen, dass die mathematische Optimierung in nichts einer "Handplanung" des Liniennetzes nachsteht. Im Gegenteil, mit Hilfe des Optimierungsprogramms ist es möglich, durch Veränderung der Parameter mehrere verschiedene Szenarien zu berechnen, miteinander zu vergleichen und Aussagen über minimale Kosten und Fahrzeiten zu machen.
    Schlagwort(e): ddc:510
    Sprache: Deutsch
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  • 20
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    Positions in the Game of Go as Complex Systems (2010)
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    Publikationsdatum: 2020-12-11
    Beschreibung: The paper gathers evidence showing different dimensions of the game of Go: the continuous and discrete nature of the game and different types of relations between state variables happening on ultra local, local, regional, and global scales. Based on these observations a new continuous local model for describing a board position is introduced. This includes the identification of the basic variables describing a board position and the formulation and solution of a dynamical system for their computation. To be usable as a static evaluation function for a game playing program at least group-wide (regional)aspects will have to be incorporated.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 21
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    Railway Track Allocation by Rapid Branching (2010)
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    Publikationsdatum: 2020-08-05
    Beschreibung: The track allocation problem, also known as train routing problem or train timetabling problem, is to find a conflict-free set of train routes of maximum value in a railway network. Although it can be modeled as a standard path packing problem, instances of sizes relevant for real-world railway applications could not be solved up to now. We propose a rapid branching column generation approach that integrates the solution of the LP relaxation of a path coupling formulation of the problem with a special rounding heuristic. The approach is based on and exploits special properties of the bundle method for the approximate solution of convex piecewise linear functions. Computational results for difficult instances of the benchmark library TTPLIB are reported.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 22
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    Optimizing the Simplon Railway Corridor (2010)
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    Publikationsdatum: 2020-08-05
    Beschreibung: This paper presents a case study on a railway timetable optimization for the very dense Simplon corridor, a major railway connection in the Alps between Switzerland and Italy. Starting from a detailed microscopic network as it is used in railway simulation, the data is transformed by an automatic procedure to a less detailed macroscopic network, that is sufficient for the purpose of capacity planning and amenable to state-of-the-art integer programming optimization methods. In this way, the macroscopic railway network is saturated with trains. Finally, the corresponding timetable is re-transformed to the microscopic level in such a way that it can be operated without any conflicts among the slots. Using this integer programming based micro-macro aggregation-disaggregation approach, it becomes for the first time possible to generate a profit maximal and conflict free timetable for the complete Simplon corridor over an entire day by a simultaneous optimization of all trains requests. This also allows to to undertake a sensitivity analysis of various problem parameters.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 23
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    Analysis of a multi-scale asymptotic model for internal gravity waves in a moist atmosphere (2010)
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    Publikationsdatum: 2016-06-09
    Beschreibung: The thesis presents the analysis of a reduced model for modulation of internal gravity waves by deep convective clouds. The starting point for the derivation are conservation laws for mass, momentum and energy coupled with a bulk micro-physics model describing the evolution of mixing ratios of water vapor, cloud water and rain water. A reduced model for the identified scales of the regime is derived, using multi-scale asymptotics. The closure of the model employs conditional averaging over the horizontal scale of the convective clouds. The resulting reduced model is an extension of the anelastic equations, linearized around a constant background state, which are well-known from meteorology. The closure of the model is achieved purely by analytical means and involves no additional physically motivated assumptions. The essential new parameter arising from the coupling to a micro-physics model is the area fraction of saturated regions on the horizontal scale of the convective clouds. It turns out that this parameter is constant on the employed short timescale. Hence the clouds constitute a constant background, modulating the characteristics of propagation of internal waves. The model is then investigated by analytical as well as numerical means. Important results are, among others, that in the model moisture (i) inhibits propagation of internal waves by reducing the modulus of the group velocity, (ii) reduces the angle between the propagation direction of a wave-packet and the horizontal, (iii) causes critical layers and (iv) introduces a maximum horizontal wavelength beyond which waves are no longer propagating but become evanescent. The investigated examples of orographically generated gravity waves also feature a significant reduction of vertical momentum flux by moisture. The model is extended by assuming systematically small under-saturation, that is saturation at leading order. The closure is similar to the original case but requires additional assumptions. The saturated area fraction in the obtained model is no longer constant but now depends nonlinearly on vertical displacement and thus on vertical velocity.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: doctoralthesis , doc-type:doctoralThesis
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  • 24
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    A Constraint Integer Programming Approach for Resource-Constrained Project Scheduling (2010)
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    Publikationsdatum: 2022-03-14
    Beschreibung: We propose a hybrid approach for solving the resource-constrained project scheduling problem which is an extremely hard to solve combinatorial optimization problem of practical relevance. Jobs have to be scheduled on (renewable) resources subject to precedence constraints such that the resource capacities are never exceeded and the latest completion time of all jobs is minimized. The problem has challenged researchers from different communities, such as integer programming (IP), constraint programming (CP), and satisfiability testing (SAT). Still, there are instances with 60 jobs which have not been solved for many years. The currently best known approach, lazyFD, is a hybrid between CP and SAT techniques. In this paper we propose an even stronger hybridization by integrating all the three areas, IP, CP, and SAT, into a single branch-and-bound scheme. We show that lower bounds from the linear relaxation of the IP formulation and conflict analysis are key ingredients for pruning the search tree. First computational experiments show very promising results. For five instances of the well-known PSPLIB we report an improvement of lower bounds. Our implementation is generic, thus it can be potentially applied to similar problems as well.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 25
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    Coupling Meshbased and Meshfree Methods by a Transfer Operator Approach (2010)
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    Publikationsdatum: 2023-11-03
    Beschreibung: In contrast to the well known meshbased methods like the finite element method, meshfree methods do not rely on a mesh. However besides their great applicability, meshfree methods are rather time consuming. Thus, it seems favorable to combine both methods, by using meshfree methods only in a small part of the domain, where a mesh is disadvantageous, and a meshbased method for the rest of the domain. We motivate, that this coupling between the two simulation techniques can be considered as saddle point problem and show the stability of this coupling. Thereby a novel transfer operator is introduced, which interacts in the transition zone, where both methods coexist.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 26
    Digitale Medien
    Digitale Medien
    Fluorescence correlation spectroscopy. I. Conceptual basis and theory (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1-27 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We describe a method for determining chemical kinetic constants and diffusion coefficients by measuring the rates of decay of spontaneous concentration fluctuations. The equilibrium of the system is not disturbed during the measurement. We measure the number of molecules of a specified type in a defined open volume as a function of time and compute the time course of the deviations from the thermodynamic mean concentration. The method is based on the principle that the rates of decay of spontaneous microscopic fluctuations are determined by the same phenomenological rate coefficients as those of macroscopic departures from equilibrium which result from external perturbations. Hence, an analysis of fluctuations yields the same chemical rate constants and diffusion coefficients as are measured by conventional procedures. In practice the number of the specified molecules is measured by a property such as absorbance or fluorescence which is specific and sensitive to chemical change. The sample volume is defined by a light beam which traverses the cell. As the molecules appear in or disappear from the light beam, either due to diffusion or chemical reaction, their concentration fluctuations give rise to corresponding fluctuations of the intensity of absorbed or emitted light. This paper presents the theory needed to derive chemical rate constants and diffusion coefficients from these fluctuations in light intensity. The theory is applied to three examples of general interest: pure diffusion in the absence of chemical reaction; the binding of a small rapidly diffusing ligand to a larger slowly diffusing macromolecule; and a unimolecular isomerization. The method should be especially useful in studying highly cooperative systems, relatively noncooperative systems with intermediate states closely spaced in free energy, small systems, and systems not readily subject to perturbations of state.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130102
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  • 27
    Digitale Medien
    Digitale Medien
    Molecular mobility of polypeptides containing proline as determined by 13C magnetic resonance (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 97-114 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The molecular conformations and dynamics of poly(L-prolyl), poly(hydroxyl-L-prolyl), poly(L-prolyl-glycyl), poly(hydroxyl-L-prolyl), and poly(glycyl-glycyl-L-prolyl-glycyl), in aqueous solution, have been studied using 13C pulse Fourier transform nmr spectroscopy. From a measurement of the intensities of major and minor resonances in the spectra of the copolypeptides, it was determined that 15-20% of the glycyl-prolyl and glycyl-hydroxyprolyl peptide bonds are cis. Effective rotational correlation times (τeff), obtained from measurements of spin-lattice relaxation times (T1) of individual backbone and side-chain carbons, demonstrated that backbone reorientation is approximately isotropic for the five polypeptides and is characterized by correlation times of ca. 0.3-0.6 nanoseconds as a result of rapid segmental motion. In a given polypeptide glycyl and pyrrolidine residues were found to have the same backbone correlation times, but backbone carbon τeff values did decrease as the glycyl content of the peptides increased. A semi-quantitative analysis of Cβ, Cγ, and Cδ correlation times suggests that rapid ring motion in both prolyl and hydroxyprolyl involves primarily Cγ and Cβ, with the prolyl ring being more mobile than the hydroxyprolyl ring.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130106
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  • 28
    Digitale Medien
    Digitale Medien
    Comment on “rotational relaxation of macromolecules determined by dynamic light scattering” (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 237-238 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No. Abstract.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130117
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  • 29
    Digitale Medien
    Digitale Medien
    Flexibility of DNA (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 217-226 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A model for the flexibility of DNA is proposed that is based on discrete variations in the direction of propagation in going from one subunit to the next. Expansion of the local free energy in terms of the local bending gives a Gaussian distribution function. The assumption of the independence of local bends on neighbors lead to very simple formulae for the persistence length and the characteristic ratio. Emphasis, however, is placed on the application of the formulae for molecules of finite size where the persistence length and C∞ are not defined. The formulae are worked out for two models, which should serve as limits for the real physical situation.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130115
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  • 30
    Digitale Medien
    Digitale Medien
    Dispersion effect on turbidimetric size measurement (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 735-743 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: If dispersion effects are not taken into account, the dimensions of particles in suspension estimated from spectrophotometric data (slope of the log OD versus log λ plot) are too low. By measuring dispersion curves for the medium and for the suspension, a consistent estimate of the size of latex particles of different diameter is obtained from the OD data.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130408
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  • 31
    Digitale Medien
    Digitale Medien
    13C nmr study of the helix-coil transition of poly-N5-(3-hydroxypropyl)-L-glutamine (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 765-768 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The helix-coil transition of poly-N5-(3-hydroxypropyl)-L-glutamine in methanol-water solutions has been observed using 13C nuclear magnetic resonance. Two signals appear in the α-CH region in the course of the transition; this is in contrast with previous proton magnetic resonance experiments carried out on this polymer in the same solvent system.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130411
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  • 32
    Digitale Medien
    Digitale Medien
    The V amylose-H2O system: Structural changes resulting from hydration (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 779-790 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: X-ray diffraction and stereochemical analyses were used to study the hydrated structure of the helical amylose polymorph having a fiber repeat spacing of 8 Å. Intensity calculations using computer models confirmed six as the number of residues per turn and supported the space group P212121. Both diffraction intensity and stereochemical methods indicate the suitability of residue G3 from the potassium acetate complex of cyclohexaamylose as opposed to residues with longer O(4)-O(1) vectors. Comparison of the present results with those obtained for V amylose dehydrate indicated no major conformational differences between the two helix skeletons. A net helical rotation of approximately 30° accompanied the hydrate-dehydrate transition and the rotational position in the hydrate allowed packing that was less close. Hydration water molecules were not located; noncarbohydrate peaks on the electron density maps were primarily due to Fourier series termination errors.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130413
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  • 33
    Digitale Medien
    Digitale Medien
    A circular dichroism study of the primary structures of three crab satellite DNA's rich in A:T base pairs (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 843-852 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We have measured the circular dichroism spectra and have obtained melting curves for samples of purified satellite DNA's from three species of crab, Cancer borealis, Gecarcinus lateralis, and Callinectes sapidus. Although all three satellite DNA's have the same density in neutral CsCl, their circular dichroism spectra and melting and reassociation characteristics are different, as are other properties of these DNA's. The circular dichroism spectra are analyzed to give estimates of nearest-neighbor frequencies. We estimate that about 90% of the Cancer borealis satellite DNA and over 80% of the Gecarcinus lateralis satellite DNA consist of d(AT)n:d(AT)n sequences, while the serially repeating unit of the Callinectes sapidus satellite DNA may not contain any extended d(AT)n:d(AT)n sequences. The results from the circular dichroism spectra for the Cancer borealis, Gecarcinus lateralis, and the Callinectes sapidus satellite DNA's are in agreement with base composition analyses, which give 2.4, 8, and 25% G+C, respectively, for these DNA's.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130417
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  • 34
    Digitale Medien
    Digitale Medien
    Thermodynamic aspects of the gelatinization and swelling of crosslinked starch (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 879-890 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Samples of epichlorohydrin crosslinked potato starch were prepared by using a high ratio of starch to water and alkali concentration below the gelatinization level. This yielded crosslinked samples that were partially crystalline, and where the number of crosslinks could be varied between 1 and 20 crosslinks per 100 anhydroglucose units. The degree of swelling varied regularly with degree of crosslinking, and the molecular weight between crosslinks Mc as derived from swelling data in a good swelling agent compared favorably with Mc derived from chemical analysis.From the heat of gelatinization of the crosslinked starches, as observed in a differential scanning calorimeter, for gelatinization in glycerol, water, and dimethylsulfoxide, a model for the gel state of the crosslinked starch is proposed. It is concluded that the entropy of melting is the determining factor in establishing the temperature of gelatinization.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130504
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  • 35
    Digitale Medien
    Digitale Medien
    The interaction of β-cyclodextrin with dinucleoside phosphates (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 909-917 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Circular dichroism studies of the interaction of β-cyclodextrin with a series of eight dinucleoside phosphates, and with 3′-AMP are reported. From results with ApU and ApA, it is shown that β-cyclodextrin binding is sensitive to dinucleoside stacking in approximately the same way as optical measures of stacking. Some qualitative uses of β-cyclodextrin binding are suggested, based on the fact that the change in the CD spectrum caused by cyclodextrin binding is unique to each of the dinucleosides studied. Hoffman and Bock have previously suggested the use of β-cyclodextrin as a probe of nucleic acid structure. Their work indicated that only binding to adenosine and inosine would have to be considered. The present paper shows that binding to other bases cannot be neglected, and will impose serious restrictions on the use of β-cyclodextrin as a structural probe.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130507
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  • 36
    Digitale Medien
    Digitale Medien
    Synthesis of a novel fluorescent polyriboadenylic acid analog by polynucleotide phosphorylase (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 987-993 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Poly(1,N6-etheno-2-aza-adenylic acid) [poly(2-aza-εA)] was synthesized from 1,N6-etheno-2-aza-adenosine 5′-diphosphate (2-aza-εADP) and Escherichia coli polynucleotide phosphorylase. The values Km = 1.02 mM, V = 1.06 μmol hr-1 enzyme unit-1 were found for the polymerization reaction. In contrast to polyadenylic acid, this novel fluorescent polymer has a random structure in solution. The application of the 2-aza-εADP for localization of polynucleotide phosphorylase was also described.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130513
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  • 37
    Digitale Medien
    Digitale Medien
    Synthesis and optical studies of L-methionine oligopeptides in solution (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1011-1022 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A series of L-methionine oligomers [BOC-(Met)n-OMe] (n = 2-7) and the corresponding diastereomeric di- and tripeptides were synthesized using the mixed anhydride method. Oligomers prepared in this manner were optically pure and were obtained in reasonable yield. Preliminary optical examination of the peptides suggests that secondary structures may begin forming in the pentamer or hexamer in trifluoroethanol. BOC-(Met)4-OMe and BOC-(Met)5-OMe were also synthesized using an insoluble resin containing BOC-L-methionine as the nitrophenol active ester.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130515
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  • 38
    Digitale Medien
    Digitale Medien
    Sequential oligopeptides. Conformational studies of the oligopeptides and a polypeptide with the repeating sequence L-norvalyl-glycyl-L-proline (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1067-1078 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Conformational studies of a series of oligopeptides (from the tripeptide to the octadecapeptide) with the repeating sequence L-norvalyl-glycyl-L-proline and a polytripeptide with this sequence are reported. By means of chiroptical techniques, unordered conformations are found for all oligopeptides in water, trifluoroethanol, and ethylene glycol and for the water-insoluble polymer in trifluoroethanol. In ethylene glycol the polymer assumes a collagen-like structure. Infrared studies indicate that all the oligomers, in contrast to the polymer, are unordered in the solid state.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130519
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  • 39
    Digitale Medien
    Digitale Medien
    The thermal induced helix - β transition of poly(Nε-methyl-L-lysine) and poly(Nδ-ethyl-L-ornithine) in aqueous solution (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1109-1116 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Uncharged poly(Nε-methyl-L-lysine) (PMLL) and its isomer, poly(Nδ-ethyl-L-ornithine) (PELO), in alkaline solution (pH ca. 12) undergo a helix-to-β transition upon mild heating at 50°C or higher in a manner similar to that of poly(L-lysine) (PLL). The rate of conversion follows the order: PMLL 〈 PELO 〈 PLL. The helix can be regenerated upon cooling near zero degrees, for instance, after more than 12 hr at 2°C. At concentrations less than 0.02% the β form is intramolecular, but at higher concentrations both intra- and intermolecular β forms are generated. Poly(Nδ-methyl-L-ornithine) (PMLO), an isomer of PLL, behaves like poly(L-ornithine); uncharged PMLO in alkaline solution is partially helical and becomes disordered at elevated temperatures.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130604
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  • 40
    Digitale Medien
    Digitale Medien
    Side-chain effect on conformation of ionizable polypeptides in aqueous solution (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1161-1171 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In order to study the effect of side-chain length on the conformation of polypeptides, conformational changes of various ionic polypeptides with various lengths of side chain, poly-Nε-glutaryl-L-lysine (PGL), poly-Nδ-glutaryl-L-ornithine (PGO), poly-Nε-succinyl-L-lysine (PSL), and poly-Nδ-succinyl-L-ornithine (PGO), were investigated by ORD, potentiometric titration, and dilatometric measurements in aqueous solution. The results of optical rotation and potentiometric titration measurements indicate strongly that the α-helix stability increases in the sequence PSO 〈 PSL ∼ PGO 〈 PGL, which corresponds to increased side-chain length. The volume change associated with the helix-coil transition also increased in the above sequence. This series of polymers seems to be more hydrophobic compared with poly-L-glutamic acid or poly-L-lysine, as suggested from the values of enthalpy and entropy changes for coil-helix transitions.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130608
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  • 41
    Digitale Medien
    Digitale Medien
    Conformational change of poly-Nε-glutary-L-lysine and poly-Nε-succinyl-L-lysine in aqueous salt solutions (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1195-1203 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The conformational changes of poly-Nε-glutaryl-L-lysine (PGL) and poly-Nε-succinyl-L-lysine (PSL) in various salt solutions were studied by use of ORD and potentiometric titration measurements. The addition of alkali metal salts to the fully ionized PGL or PSL solution caused helix formation. The helical content of the polymers increases in the following sequences: at salt concentration 0-2 M, CsCl 〈 KCl 〈 LiCl 〈 NaCl; and at 2-3 M, LiCl 〈 CsCl 〈 KCl ∼ NaCl. The preferential binding of the solvent components with various alkali metal salts of PGL or PSL was measured in LiCl, NaCl, and KCl solutions by means of equilibrium dialysis and differential refractometry. It was found that with increasing salt concentration, the polymers were preferentially hydrated in NaCl and KCl soultions; however the salt was preferentially bound to the polymers in LiCl solution. Such preferential binding was suggested to be closely related to conformational change. The addition of CaCl2 to polymer solutions led to the stabilization of the helical structure of PGL or PSL.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130611
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  • 42
    Digitale Medien
    Digitale Medien
    Dispersion equation and polarizability of bovine serum albumin from measurements of refractive indices (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1261-1267 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Refractive indices of bovine serum albumin solutions in saline and in 2-chloro ethanol are measured for the spectral region 1770-10000 Å by a reflectance method. A procedure for the determination of a dispersion formula for binary mixtures is developed and applied. The electronic polarizability of bovine serum albumin is determined and is found to be almost independent of the solvent and concentration. Hence it follows that the electronic polarizability of bovine serum albumin is almost independent of the molecular environment.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130616
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  • 43
    Digitale Medien
    Digitale Medien
    Masthead (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974) 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130701
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  • 44
    Digitale Medien
    Digitale Medien
    Structure of aggregates and helix-coil transition of polypeptides by dielectric measurements. II. Poly-D,L-phenylalanine and poly-β-benzyl-L-aspartate in chloroform-dichloroacetic acid mixturesResults presented at Makromolekulares Kolloqium, Freiburg, Germany, February 1971. (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1309-1316 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The dielectric absorption of poly-DL-phenylalanine and poly-γ-benzyl-L-aspartate (PLAB) was measured in very dilute solutions to determine the type of molecular association and to locate the helix-coil transition. Both polypeptides were present as associated helices in chloroform. The mode of aggregation, which was determined by measuring the dipole moment and the critical frequency, did not depend on the polarity of the side chain but rather on that of the solvent.In both polymers, the dissociation of the aggregates in chloroform was observed on addition of small amounts of dichloroacetic acid; further addition of the acid lead to the helix-coil transition.No second region of dielectric absorption that might be related to the kinetics of the transition was found during the helix-coil transition of PBLA.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130703
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  • 45
    Digitale Medien
    Digitale Medien
    Molecular conformation of polysaccharides in solution. Changes in the optical rotation and in the elution pattern of gel filtration (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1357-1366 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Molecular conformation of some polysaccharides in aqueous solution in evidenced by changes in the optical rotation and in the elution pattern of gel filtration. The changes in the specific rotation against that in water are expressed as a molar conformational value [K]D21: -495° for colominic acid in 1.0 N NaOH solution, and -180° for hyaluronate (HA), +85° for corneal keratin sulfate, and +234° for amylose in 8 M urea solution. The gel filtration of amylose and HA dissolved in 8 M urea solution shows elution patterns distinctly different from those dissolved in water. The phenomena are attributable to a molecular conformational transition of polysaccharide molecules in aqueous solution.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130707
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  • 46
    Digitale Medien
    Digitale Medien
    Conformation and packing analysis of polysaccharides and derivatives. I: MannanDedicated to Professor E. Husemann on the occasion of her 65th birthday. (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1127-1139 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A previously described procedure for simultaneous optimization of bond lengths and angles was used to test different models for mannan I. Potential hydrogen bonds and the glycosidic angle were included in the optimization. A conformational model with bifurcated intramolecular hydrogen bonds of the type observed in the methyl cellobioside methanol complex showed the best agreement with available exprerimental data. The coordinates of this model were provided by computer calculations. The available X-ray data, however, were not sufficient for selecting this model; rather, ir data were necessary to furnish the needed information. The different conformational models tested all showed an almost constant virtual bond length O(1)-O(4) of the β-pyranose residue. This was in contrast to the previously obtained results for the α-pyranose residues.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130606
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  • 47
    Digitale Medien
    Digitale Medien
    Frequency dependence of the proton magnetic relaxation in aqueous solutions of haemoproteins (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1187-1193 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The longitudinal proton magnetic relaxation times T1 were measured for ferri (met)-and carbonmonoxy-bovine haemoglobin and equine myoglobin in 0.1 M KH2PO4 aqueous solutions near pH 6 at 5°C and 35°C from 1.5- to 60-MHz Larmor frequencies. It is concluded that the correlation time τC for the dipole-dipole interaction of electron and nuclear spins is in fact the electron (ferric) spin relaxation time τS being close to 1.5 × 10-10 sec for both metHb and metMb at 5°C. At 35°C the paramagnetic relaxation rates are not determined solely by the relaxation of protons exchanging from the haem pocket with bulk solvent. Hence, τC at 35°C cannot be calculated from the dispersion data obtained at this temperature. The relevance of this for the determination of interspin distances r is discussed.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130610
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  • 48
    Digitale Medien
    Digitale Medien
    Solvent effects on the orientaion of naphthalene rings in the side chain of poly-γ-1-naphthylmethyl-L-glutamate (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1213-1222 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The orientation of naphthalene rings in the side chain of poly-γ-1-naphthylmethyl-L-glutamate (PNLG) in mixed solvents of dichoroethane (DCE) and hexafluoroisopropanol (HFIP) has been studied together with its conformation by infrared, circular dichroism, and fluorescence spectra. The CD pattern of PNLG varies with the solvent composition while it maintains the α-helical conformation. The fluorescence spectra of PNLG in solution show excimer emission of the naphthalene chromophores. The ratio of intensity of the excimer emission to that of the normal fluorescence decreases as the HFIP component in the solvent increases. It is suggested that the naphthalene rings in the side chain of α-helical PNLG are more rigidly orientated in the solvents of higher HFIP ratio.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130613
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  • 49
    Digitale Medien
    Digitale Medien
    Optical rotatory properties of L-cystine conformational isomers. Theoretical analysis (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1269-1290 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The near ultraviolet chiroptical properties of L-cystine conformational isomers are examined on a static, “one-electron” model in which the disulfide moiety is the chromophoric group and the atoms of the L-alanyl fragments are treated as perturbers. The zeroth order chromophoric wave functions are calculated on a semiempirical molecular orbital model in which excited states are constructed in the virtual orbital-configuration interaction approximation. The perturbing environment is represented by point charges located at the atomic centers of the L-alanyl fragments. Chromophore-perturber interactions are expressed as charge-multipole moments with only the charge-dipole and charged-quadrupole terms being retained in the calculations. Vicinal contributions to the rotatory strengths of the five lowest energy disulfide transitions are computed for 30 conformational isomers of the L-cystine dizwitterion. The results provide support for the view that vicinal or peripheral effects can account entirely for the observed near ultraviolet (λ 〉 230 nm) chiroptical properties of L-cystine and its derivatives and that these properties are diagnostic of conformational features external to the disulfide moiety.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130617
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  • 50
    Digitale Medien
    Digitale Medien
    A demonstration of two-component behaviour of the circular dichroic spectra of poly(L-tyrosine, 3-bromo-L-tyrosine) in trimethylphosphate (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1341-1346 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The circular dichroic spectrum of poly(Tyr,TyrBr) in trimethylphosphate from 180 to 320 nm is found to be a linear function of composition from 25 to 68% TyrBr, and the spectra of the Tyr and TyrBr components are resolved. For Tyr the resolved spectrum is in agreement with available CD spectra of poly(Tyr). These results are interpreted to mean that the side-chain conformations of Tyr and TyrBr are not affected by the other component, and that for Tyr the conformation is the same as in poly(Tyr). It is also concluded that poly(Tyr,TyrBr) is helical with the same helix sense as poly(Tyr). The restrictions on the side-chain conformations are discussed, and it is suggested that the Tyr and TyrBr side chains are all in the same χ1 region.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130705
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  • 51
    Digitale Medien
    Digitale Medien
    Calculations of the circular dichroism of double-helical nucleic acids. I. Effects involving π → π* transitions (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1377-1389 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The circular dichroism of double-helical nucleic acids was calculated as a function of geometry using the theory of Tinoco and Johnson. This theory does not include contributions of near ultraviolet transitions that are not π → π* in nature. The calculated circular dichroism shows a strong dependence on the distance of base pairs from the helix axis and the tilt of the base pair. Smaller dependences are predicted for the propeller-like twist of a base pair and for variation of the angular increment per base pair. Moderately good agreement between calculated and many experimentally observed spectra could be generated.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130709
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  • 52
    Digitale Medien
    Digitale Medien
    Collagenase induced changes in the circular dichroism spectrum of collagen (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1427-1434 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The maximum at 220 nm in the circular dichroism spectrum of native collagen solution changed to a negative value after heat denaturation or collagenase hydrolysis. The enzyme induced rate of CD change at 220 nm was shown to be first order in collagen concentration. The specific rate constant k is actually a combined rate constant kfast and kslow in which the ratio kf/ks is 4.1. The initial rates were linear with respect to enzyme concentration, and the Km was found to be 5.5 × 10-7 M. The rate of ultraviolet hyperchromicity at 220 nm on collagen hydrolysis was determined. The kfast was the same as that obtained by CD. The kf/ks ratio was 4.6. Both methods may be readily used to assay for collagenase activity.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130713
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  • 53
    Digitale Medien
    Digitale Medien
    Crystal and molecular structure of the amylose-DMSO complex (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1461-1482 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The crystal and molecular structure of the complex of amylose with dimethyl sulfoxide has been studied by a combination of stereochemical analysis, potential energy, and X-ray diffraction methods. The complex crystallizes in a pseudotetragonal unit cell with a = b = 19.17 Å and c (fiber axis) = 24.39 Å, with two antiparallel chains per unit cell and space group P212121. The amylose chain is a left-handed 61(1.355) helix with three turns per crystallographic repeat. The O(6) rotational position is approximately gt. Dimethyl sulfoxide is located inside the helix with one DMSO molecule for every three glucose residues. An additional four DMSO molecules and eight water molecules each are located in the large interstices between chains, and it is the interaction of these molecules with the helix that results in the pseudotetragonal chain packing. The interstitial DMSO is the source of the previously reported additional layer lines, which are not consistent with the 8.13-Å amylose repeat distance. The final R factor for the layers with amylose contribution to the structure factors was 0.29, while the overall R factor was 0.35. The stereochemical packing analysis provided suitable phasing models for the subsequent X-ray refinement.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130716
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  • 54
    Digitale Medien
    Digitale Medien
    On the electric polarization of DNA (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1549-1556 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Dielectric dispersion of DNA was studied in the frequency range 100 Hz-100 kHz at four different temperatures (6-30°C). The dielectric increment ε0-ε∞ increased with the rise of temperature. The relaxation time, on the other hand, decreased. Both the increase in dielectric increment and the decrease in relaxation time could not be explained on the basis of the counterion polarization theory. Dipole moment was estimated from Kirkwood theory. It was found to decrease systematically with temperature. Even at 0°C there was a dipole moment of 104D.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130804
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  • 55
    Digitale Medien
    Digitale Medien
    Intramolecular distances determined by energy transfer. Dependence on orientational freedom of donor and acceptor (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1573-1605 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The dependence of Förster long-range resonance energy transfer efficiency on the orientational freedom of donor D and acceptor A molecules attached to a macromolecular substrate is examined. The usefulness of polarized emission measurements in determining the mutual orientation as well as the degree of orientational freedom of D and A and thereby deriving maximum and minimum values for the D-A separation from the transfer efficieny is demonstrated.
    Zusätzliches Material: 20 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130807
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  • 56
    Digitale Medien
    Digitale Medien
    Water sorption on deoxygenated hemoglobins CC, SC, SS, AS, and AA (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1653-1659 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Five human hemoglobins whose genetic relationship to one another involves one set of alleles, hemoglobins CC, SC, SS, AS, and AA, were studied in the deoxygenated form within a McBain gravimetric sorption system at 28°C. Water was used as the adsorbate at relative vapor pressures ranging from 0.11 to 0.39. The results of this study are reported and compared with a similar study on the ferric form of these same five hemoglobins. For both forms of hemoglobin studied, a slight increase was measured in the number of polar sites accessible to H2O vapor for those genotypes in which the substituent in the sixth position from the N terminus of the two β chains had a positively charged side chain, i.e., hemoglobin C. Those samples containing hemoglobin S (less soluble in the deoxy form) show an increased BET monolayer coverage in the deoxy as compared to the ferric form. For each genotype, the deoxygenated form had more polar sites accessible to H2O vapor than its ferric form. This finding is in agreement with an increase in the size of the central cavity as shown by crystallographic analysis.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130811
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  • 57
    Digitale Medien
    Digitale Medien
    Helix-coil transition in nucleoprotein. Effect of ionic strength on thermal denaturation of polylysine-DNA complexes (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1681-1697 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Thermal denaturation of direct-mixed and reconstituted polylysine-DNA complexes in 2.5 × 10-4 M EDTA, pH 8.0 and various concentrations of NaCl has been studied. For both complexes, increasing ionic strength of the solution raises Tm, the melting temperature of free base pairs. The linear dependence of Tm on log Na+ indicates that the concept of electrostatic shielding on phosphate lattice of an infinitely long pure DNA by Na+ can be applied to short free DNA segments in a nucleoprotein. For a direct-mixed polylysine-DNA complex, the melting temperature of bound base pairs Tm′ remains constant at various ionic strengths. On the other hand, the Tm′ in a reconstituted polylysine-DNA complex is shifted to lower temperature at higher ionic strength. This phenomenon occurs for reconstituted complex with long polylysine of one thousand residues or short polylysine of one hundred residues. It is shown that such a decrease of Tm′ is not due to a reduction of coupling melting between free and bound regions in a complex when the ionic strength is raised. It is also not due to intermolecular or intramolecular change from a reconstituted to a direct-mixed complex. It is suggested that this phenomenon is due to structural change on polylysine-bound regions by ionic strength. It is suggested further that Na+ may replace water molecules and bind polylysine-bound regions in a reconstituted complex. Such a dehydration effect destabilizes these regions and lowers Tm′. This explanation is supported by circular dichroism (CD) results.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130813
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  • 58
    Digitale Medien
    Digitale Medien
    Theoretical investigation of semiconductive properties in proteins. I. Electrical conductivity, charge carrier mobilities, and free paths in β-polyglycine (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1731-1737 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Theoretical values are reported for the specific conductivity, charge carrier mobilities, and delocalized free paths in β-polyglycine using the parallel-chain pleated sheet conformation and the all-valence electron energy band structure obtained previously. The mobilities are found to be much larger along the polypeptide backbones than in the direction of the hydrogen bonds. This indicates a mechanism of conduction in which the former path is favored for electronic delocalization. The preexponential factor of the specific conductivity obtained theoretically agrees well with experimental results.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130905
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  • 59
    Digitale Medien
    Digitale Medien
    Critical chain length for helix formation in L-methionine oligopeptides (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1747-1750 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The circular dichroism of a series of L-methionine oligopeptides [BOC-(Met)n-OMe] was examined in trifluoroethanol and hexafluoroacetone sesquihydrate. The results indicate that the trimer through the hexamer exists predominantly in disordered conformations in these solvents. An abrupt change in the CD pattern at the heptamer in trifluoroethanol suggests that L-methionine oligopeptides begin forming helices at this chain length.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130907
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  • 60
    Digitale Medien
    Digitale Medien
    The state of water on hydrated collagen as studied by pulsed NMR (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1767-1776 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The spin-lattice relaxation time (T1) of water adsorbed on collagen fibers was determined at six frequencies and temperatures varying from 25° to -80°C. Care was taken to eliminate the contributions to the signal of protons other than those in the adsorbed water. Quantitative calculations were made on T1 and the results were compared with the experimental data. It is suggested that a maximum of about 0.50-0.55 g water per g collagen forms a hydration layer, which cannot be frozen down to -90°C and exhibits a distribution of motional correlation times. For collagen samples containing a larger quantity of adsorbed water, the additional water molecules behave like ordinary isotropic water, having a single correlation time and a freezing temperature of about -10°C.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130910
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  • 61
    Digitale Medien
    Digitale Medien
    Raman studies of nucleic acids. XII. Conformations of oligonucleotides and deuterated polynucleotides (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1821-1845 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Laser Raman spectra of the trinucleoside diphoshate ApApA and dinucleoside phosphates ApU, UpA, GpC, CpG, and GpU are reported and discussed. Assignments of conformationally sensitive frequencies are-facilitated by comparison with spectra reported here of poly(rA), poly(rC), and poly(rU) in deuterium oxide solutions. The significant spectral differences between ApU and UpA, and between GpC and CpG, reveal that the sequence isomers have nonidentical conformations in aqueous solution. In UpA at low temperature the bases are stacked and the backbone conformation is similar to that found in ordered polynucleotide structures and RNA. In ApU no base stacking can be detected and the backbone conformation differs from that found in UpA, both in the orientation of phosphodiester linkages and in the internal conformation of ribose. At the conditions employed neither ApU nor UpA exhibits base pairing in aqueous solutions. In both GpC and CpG the bases are stacked and the phosphodiester conformations are similar to those encountered for UpA and RNA. However, major differences between spectra of GpC and CpG indicate that the geometries of stacking and ribosyl conformations are different. In GpC the Raman data favor the formation of hydrogen bonded dimers containing GC pairs. Protonation of C in GpC is sufficient to eliminate the ordered conformation detected by Raman spectroscopy. Despite the ordered backbone conformation evident in GpU, this dinucleoside apparently contains neither stacked nor hydrogen bonded bases at the conditions employed here. The Raman data also confirm the stacking interactions in ApApA, poly(rA), and poly(rC) but suggest that the backbone conformation in poly(rC) differs qualitatively from that found in most ordered polynucleotide structures and is thermally more stable. The present results demonstrate the sensitivity of the Raman technique to sequence-related structural differences in oligonucleotides and provide additional spectra-structure correlations for future conformational studies of RNA by laser Raman spectroscopy.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130914
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  • 62
    Digitale Medien
    Digitale Medien
    Masthead (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974) 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360131001
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  • 63
    Digitale Medien
    Digitale Medien
    Assignment of the proton nmr chemical shifts of the T—N3H and G—N1H proton resonances in isolated AT and GC Watson-Crick base pairs in double-stranded deoxy oligonucleotides in aqueous solution (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1943-1964 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The 300-MHz proton nmr spectra (between 11 and 14 ppm) of a series of double-stranded deoxy oligonucleotides of known sequence have been recorded in H2O solution. These resonances have been assigned to the G—N1H and T—N3H protons of specific base pairs from an evaluation of the temperature dependence of the ring NH linewidths and from the selective ring NH chemical shift changes on actinomycin-D binding. The deoxy oligonucleotides exist predominantly in the DNA-B conformation as evaluated from antibiotic binding studies. Ring-current calculations have been utilized to evaluate the up-field shifts of the G—N1H and T—N3H protons in Watson-Crick base pairs due to the ring currents from the pyrimidine and purine rings of nearest neighbor base pairs in regular DNA-B- and RNA-A-type helices. The perturbations on these up-field ring-current contributions that arise from twisting and tilting a base pair adjacent to the ring NH under study have been evaluated and found to change the calculated chemical shift by ±0.6 ppm for twist and tilt distortions of 〈30°C in a single adjacent base pair. A knowledge of the experimentally assigned ring NH chemical shifts of specific base pairs in known sequences of double-stranded deoxy oligonucleotides coupled with the ring-current tables for the DNA-B helical structure permit the assignment of 13.6 ± 0.1 ppm and 14.6 ± 0.2 ppm for the G—N1H proton of an isolated GC base pair and the T—N3H proton of an isolated AT base pair, respectively.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360131003
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  • 64
    Digitale Medien
    Digitale Medien
    Fluorescence correlation spectroscopy. II. An experimental realization (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 29-61 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: This paper describes the first experimental application of fluorescence correlation spectroscopy, a new method for determining chemical kinetic constants and diffusion coefficients. These quantities are measured by observing the time behaviour of the tiny concentration fluctuations which occur spontaneously in the reaction system even when it is in equilibrium. The equilibrium of the system is not disturbed during the experiment. The diffusion coefficients and chemical rate constants which determine the average time behaviour of these spontaneous fluctuations are the same as those sought by more conventional methods including temperature-jump or other perturbation techniques. The experiment consists essentially in measuring the variation with time of the number of molecules of specified reactants in a defined open volume of solution. The concentration of a reactant is measured by its fluorescence; the sample volume is defined by a focused laser beam which excites the fluorescence. The fluorescent emission fluctuates in proportion with the changes in the number of fluorescent molecules as they diffuse into and out of the sample volume and as they are created or eliminated by the chemical reactions. The number of these reactant molecules must be small to permit detection of the concentration fluctuations. Hence the sample volume is small (10-8 ml) and the concentration of the solutes is low (∼ 10-9 M). We have applied this technique to the study of two prototype systems: the simple example of pure diffusion of a single fluorescent species, rhodamine 6G, and the more interesting but more challenging example of the reaction of macromolecular DNA with the drug ethidium bromide to form a fluorescent complex. The increase of the fluorescence of the ethidium bromide upon formation of the complex permits the observation of the decay of concentration fluctuations via the chemical reaction and consequently the determination of chemical rate constants.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130103
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  • 65
    Digitale Medien
    Digitale Medien
    Circular dichroism studies on the polymerization of N-carboxy α-amino acid anhydride (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 129-138 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The D and L copolymerizations of N-carboxy γ-benzyl glutamate anhydride (NCA) were carried out in a homogeneous solution with various D/L ratios, initiated by either n-butylamine or sodium methoxide, and were followed directly by circular dichroism (CD) to observe the behavior of the secondary structure of growing polymer molecules. In the n-butylamine system, the difference of the helical content between the righthanded and the lefthanded (Δα-helix) gradually increased as the polymerization proceeded, while in the sodium methoxide system, the Δα-helix had a tendency to decrease during the later stages of the polymerization. These results suggest a difference of the power of stereo-selection of monomer antipodes by the growing chain end between these systems, the stereoselectivity by the growing chain end in the sodium methoxide system being higher than that in the n-butylamine system.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130108
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  • 66
    Digitale Medien
    Digitale Medien
    The effect of temperature and salt concentration on the circular dichroism exhibited by unionized derivatives of L-alanine in aqueous solution (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 169-183 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The circular dichroism of Ac-Ala-NHMe, cyclo(-Ala-Ala-), Ac-Ala-OMe, Ac-Ala-Ala-OMe, and Ac-Ala-Ala-Ala-OMe has been measured in water and in aqueous salt solutions as a function of temperature. Only cyclo(-Ala-Ala-) exhibits circular dichroism which is independent of temperature. Each of the linear derivatives of L-alanine exhibits a positive circular dichroism in the range 208-218 nm at 15°C in water. Heating reduces the intensity of the positive circular dichroism, and only Ac-Ala-OMe retains positive circular dichroism at 75°C in water. Isothermal addition of salts produces changes in the circular dichroism of linear derivatives of L-alanine which resemble those seen on heating. The relative effectiveness of the salts tested, at a concentration of 4M, is LiCl ≤ KCl = NaCl 〈 MgCl2 ≤ CaCl2 ≤ NaClO4. The circular dichroism of cyclo(-Ala-Ala-) is also affected by the salts. Extrapolation of the results obtained with Ac-Ala-OMe, Ac-Ala-Ala-OMe, and Ac-Ala-Ala-Ala-OMe to a long polypeptide with a -CH2R side chain in the L-configuration leads to the conclusion that this polypeptide should exhibit a temperature-dependent salt-sensitive positive circular dichroism between 208 and 218 nm when it exists as a statstical coil.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130111
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  • 67
    Digitale Medien
    Digitale Medien
    Calorimetric investigation of the helix-coil conversion of polyuridylic acid (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 227-235 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The heats of the conformational conversion ΔHc of polyuridylic acid (polyU) in the presence of various cations were determined using a differential scanning microcalorimeter and an isothermal mixing calorimeter. The first method yields a value of ΔHc = 5.2 kcal/mol of base pairs, the second one a value of ΔHc = 6.4 kcal/mol of base pairs. Knowing ΔHc and the maximal slope of the degree of conversion, which was determined from the temperature dependence of the absorbance of polyU solutions at 260 nm, we were able to evaluate the parameter of cooperativity σ. From the relation σ = eΔFstack/RT the stacking free energy ΔFstack could be calculated. Dividing the apparent enthalpy of conversion by the calorimetrically measured enthalpy yields the cooperative length N0 of one helical segment at the midpoint of conversion. The results show that the type of the cation has no influence on the magnitude of ΔHc, whereas the cooperativity of polyU is influenced by the various cations.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130116
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  • 68
    Digitale Medien
    Digitale Medien
    In memoriam: E. Scoffone (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 861-862 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130502
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  • 69
    Digitale Medien
    Digitale Medien
    Dynamic light scattering studies of poly-L-lysine HBr in the presence of added salt (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 903-908 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Clipped autocorrelation functions for the fluctuating intensity of light scattered from dilute solutions of poly-L-lysine in 0.2 M NaBr have been observed over a wide range of time scales down to 1.83 μsec, and over a wide range of pH. Two poly-L-lysine samples of molecular weight 35,000 and 200,000, respectively, were compared to determine the extent of draining of the so-called random-coil configuration. The observed correlation functions were in general very satisfactorily represented by simple translation diffusion of single molecules. At high pH ∼10-10.4, there was evidence of considerable aggregation, but no indication whatsoever of any unusually fast component, as reported recently by Jamieson et al. for poly-L-lysine HBr in the absence of salt.A 30% rise in the diffusion coefficient to a peak at pH 10 parallels the previously reported dip in the intrinsic viscosity, and is interpreted in terms of a more compact structure in that pH region between the coil and helix extremes.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130506
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  • 70
    Digitale Medien
    Digitale Medien
    Studies of deoxyribonucleoproteins progressively depleted of proteins in solutions of various ionic strengths (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 863-877 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The conformation of deoxyribonucleoprotein (DNP) from calf thymus at different stages of deproteinization was studied.The dissociation of the first portion of histone produces no effect on the hydrodynamical and optical behavior of DNP particles. The conformational transition of a macromolecule was observed as soon as the ratio of protein to DNA ≤ 0.9.The effect of ionic strength on the conformation of DNP particles with high protein content was more strongly pronounced than that for DNA. On the contrary, DNP particles depleted of proteins (protein/DNA 〈 0.9) were found to be less sensitive than DNA to the variation of ionic strength. These data imply that the DNP molecules rich in proteins possess a superstructure that is destroyed as the protein/DNA ratio becomes 0.9.The data were analyzed in view of current theories on various model concepts. The most probable model to describe the DNP molecule was chosen by comparing the calculated and experimentally obtained parameters. We believe that DNP is best described as a “compressed coil,” possibly including superhelical regions.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130503
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  • 71
    Digitale Medien
    Digitale Medien
    Synthesis of some amino acids, sugars, and peptides in cold plasma abiotic synthesis of some high-molecular-weight proteid-like structures (V) (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 943-954 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of some high-molecular-weight protenoid structures in radiofrequency cold plasma conditions are discussed. The fractionation results of the raw product and the spectrum of free and protenoid-bound amino acids are given. The uv analysis of these compounds is presented.A protein-forming mechanism that might have existed on the primitive earth is proposed.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130510
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  • 72
    Digitale Medien
    Digitale Medien
    An electron microscopic method for studying nucleic acid-protein complexes. Visualization of RNA polymerase bound to the DNA of bacteriophages T7 and T3Dedicated to the memory of Dr. Jean-Pierre Tranzer. (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 995-1009 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Double-stranded DNA can be readily adsorbed on mica or directly on carbon coated grids from the surface of solutions containing ethidium bromide, actinomine, or propidium diiodide. The DNA molecules are unfolded, well separated, and show a length distribution similar to molecules prepared by protein monolayer techniques.Since the intercalating dyes tested do not lead to an increased apparent diameter of the nucleic acid the method is useful for the study of nucleic acid-protein complexes. As a model, the binding of E. coli RNA polymerase to phage T7 and T3 DNA was examined under different conditions. The enzyme can easily be identified and its position along the DNA molecule can be mapped.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130514
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  • 73
    Digitale Medien
    Digitale Medien
    Sequential oligopeptides. Synthesis and characterization of the oligopeptides and a polypeptide with the repeating sequence L-norvalyl-glycyl-L-proline (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1055-1066 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis and characterization of a series of oligopeptides (from the tripeptide to the octadecapeptide) with the repeating sequence L-norvalyl-glycyl-L-proline and a polytripeptide with this sequence are reported. The oligomers were synthesized step by step using the mixed anhydride method. All the products were chemically and optically pure. The polymer was prepared by the active ester method, using the p-nitrophenyl ester as the polymerizable tripeptide derivative. Good yield of relatively high average molecular-weight polymer was obtained. In the accompanying paper conformational investigations, both in solution and in the solid state, on the oligomers and the polymer are described.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130518
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  • 74
    Digitale Medien
    Digitale Medien
    Synthesis and conformational study of poly(Nδ-carbobenzoxy, Nδ-benzyl-L-ornithine) and poly(Nδ-benzyl-L-ornithine) (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1117-1125 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Poly(Nδ-carbobenzoxy, Nδ-benzyl-L-ornithine) (PCBLO) was prepared by the standard NCA method. PCBLO was converted into poly(Nδ-benzyl-L-ornithine) (PBLO) through decarbobenzoxylation with hydrogen bromide. The monomer Nδ-benzyl-L-ornithine was synthesized by reacting L-ornithine with benzaldehyde, followed by hydrogenation. The conformation of the two polypeptides was studied by optical rotatory dispersion and circular dichroism. PCBLO forms a right-handed helix in helix-promoting solvents. In mixed solvents of chloroform and dichloroacetic acid (DCA) it undergoes a sharp helix-coil transition at 12% (v/v) DCA at 25°C, as compared with 36% for poly(Nδ-carbobenzoxy-L-ornithine) (PCLO). Like PCLO, the helix-coil transition is “inverse,” that is, high temperature favors the helical form. PBLO is soluble in water at pH below 7 and has a “coiled” conformation. In 88% (v/v) 1-propanol above pH (apparent) 9.6 it is completely helical. In 50% 1-propanol the transition pH (apparent) is about 7.4; this compares with a pHtr of about 10 for poly-L-ornithine in the same solvent.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130605
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  • 75
    Digitale Medien
    Digitale Medien
    Interaction of ethidium bromide with DNA. Optical and electrooptical study (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1141-1160 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The binding of ethidium bromide to DNA has been studied by various optical methods. From fluorescence polarization studies, and film, electric linear dichroism, and circular dichroism spectra, we propose assignments of the absorption bands of the dye, which are discussed in connection with wave-mechanical calculations recently reported.The optical activity induced in the dye absorption bands upon binding to DNA was attributed to various origins depending on the electronic transition considered. The visible absorption band displayed a circular dichroism due to the asymmetry of the binding site and independent of the amount of binding. The transition identified at 378 nm from the circular dichroism and electric dichroism observations was thought to be due to a magnetic-dipole transition. It remained constant with increasing amounts of dye bound. The main ultraviolet band showed circular dichroism characteristics corresponding to exciton interactions between dye molecules bound to neighboring sites.The electric dichroism observed for the strongly bound dye molecules indicated that the phenanthridinium ring of ethidium bromide was probably not perfectly parallel to the DNA base planes. When the amount of dye bound to DNA exceeded the maximum amount compatible with the exclusion of adjacent binding sites, the electric dichroism decreased owing to the appearance of externally bound dye molecules with no contribution to the dichroism.Sonicated DNA was used to study the lengthening of the DNA molecule upon complexation. Although the viscosity of the complexes increased with the amount of binding, the rotational diffusion coefficient measured by the electric birefringence relaxation was not detectably affected. The absence of variation in the electric birefringence with the binding indicated that the DNA base stacking remained unaltered.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130607
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  • 76
    Digitale Medien
    Digitale Medien
    Polymerization of optical isomers of phenylalanine N-carboxyanhydride by poly (N-methylalanine) diethylamide (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1205-1212 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In the polymerization of phenylalanine N-carboxyanhydride (NCA) using poly(N-methyl-L-or DL-alanine) diethylamide as initiator, the polymerization rate was L-NCA ≃ D-NCA 〉 DL-NCA. This is a new type of selective polymerization and indicates the incompleteness of earlier investigations to study the asymmetrically selective polymerization without D-NCA. Neither secondary structure nor optical activity of the polymeric initiator is a reason for the selectivity. Hence the cause for the selectivity was sought in the properties of the NCA's in solution. However, the selectivity was not observed in the polymerization initiated by poly(L-phenylalanine) dimethylamide. The importance of the initiator being a secondary amine type was suggested. The experimental results are discussed on the basis of these considerations.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130612
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  • 77
    Digitale Medien
    Digitale Medien
    Conformational stability in dinucleoside phosphate crystals. Semiempirical potential energy calculations for uridylyl-3′-5′-adenosine monophosphate (UpA) and guanylyl-3′,5′-cytidine monophosphate (GpC) (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1243-1259 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Classical potential energy calculations were performed for the dinucleoside phosphates UpA and GpC. Two widely accessible low-energy regions of conformation space were found for the ω′, ω pair. That of lowest energy contains conformations similar to helical RNA, with ω′ and ω in the vicinity of 300° and 280°, respectively. All five experimental observations of crystalline GpC, two of ApU, and the helical fragment of ApApA fall in this range. The second lowest region has ω′ and ω at about 20° and 80°, respectively, which is in the general region of one experimentally observed crystalline conformer of UpA, and the nonhelical region of ApApA.It is concluded that GpC and ApU, which were crystallized as either sodium or calcium salts, are shielded from each other in the crystal by the water of hydration and are therefore free to adopt their predicted in vacuo minimum energy helical conformations. By contrast, crystalline UpA had only 1/2 water per molecule, and was forced into higher energy conformations in order to maximize intermolecular hydrogen bonding.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130615
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  • 78
    Digitale Medien
    Digitale Medien
    Structure of aggregates and helix-coil transition of polypeptides by dielectric measurements. I. Poly-γ-benzyl-L-glutamate in dioxane and dioxane-dichloroacetic acid (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1293-1308 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Dielectric dispersion measurements on poly-γ-benzyl-L-glutamate (PBLG) in dioxane and dioxane-dichloroacetic acid (DCA) mixtures in the frequency range 200 Hz-2 MHz were made in order to study the structure of molecular aggregates. The structure of aggregates is explained on the basis of the variation of dipole moment and relaxation time with degree of aggregation. PBLG was found to form linear head-to-tail-type aggregates in dioxane. These aggregates gradually reduce in size without loosing their α-helical structure during the process of disaggregation obtained by either adding DCA to the solution in dioxane or by heating. It was confirmed that the addition of 30 wt % DCA completely destroys the aggregation of PBLG in dioxane at 30°C. Thermal disaggregation, however, was not complete even at a temperature approaching the boiling point of the solvent.A reaction scheme for aggregation is proposed and equilibrium constants are calculated at various stages of aggregation. The enthalpy of aggregate formation is found to be -3 kcal/mol. Results of optical rotatory dispersion measurements of the helix-coil transition in this system are also presented.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130702
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  • 79
    Digitale Medien
    Digitale Medien
    Solution properties of synthetic polypeptides. XVII. Stability of the α-helical conformation of poly(γ-benzyl L-glutamate) in helicogenic solvents (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1347-1356 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The Zimm-Bragg parameters s and σ were determined for poly(γ-benzyl L-glutamate) (PBLG) in m-cresol and in dimethylformamide (DMF) from ORD data as a function of molecular weight. It was found that, within the temperature range between 10 and 55°C and on the average, s = 1.61 ± 0.1 and √σ = 0.04 ± 0.01 in m-cresol and s = 1.65 ± 0.05 and √σ = 0.045 ± 0.015 in DMF. The values of s in m-cresol decreased with increasing temperature, while the values of σ in the same solvent increased. This result for s suggests that PBLG in m-cresol will undergo a thermal helix-coil transition of normal type. The parameters in DMF showed no appreciable trend to vary with temperature. Aside from the difference between the two solvents, our results are consistent with existing data for various conformation-dependent properties such as light-scattering radius, intrinsic viscosity, and dipole moment, each indicating that the polypeptide chain has some flexibility in helicogenic solvents.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130706
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  • 80
    Digitale Medien
    Digitale Medien
    Calculations of the circular dichroism of double-helical nucleic acids. II. Effects involving n → π* transitions (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1391-1403 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The circular dichroism of double-helical nucleic acids was calculated as a function of geometry, including terms involving n → π* transitions. The “nonbonding” n or σ orbitals were of the azine type, delocalized, but concentrated at the nitrogen atoms of the purines and pyrimidines. Dynamic coupling of the magnetic moments of the n → π* transitions with the electric moments of π → π* transitions generated important terms. Mixing of electric dipole character into n → π* transitions by the static electric field perturbation of the molecule is of lesser importance. The largest contributions of n → π* transitions to the circular dichroism of double-helical nucleic acids are comparable in magnitude to the sum of π → π* terms only for geometries where the circular dichroism is weak. Using both n → π* and π → π* contributions one is able to match experimental and calculated circular dichroism spectra for DNA's over a much wider range of conditions than was possible previously.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130710
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  • 81
    Digitale Medien
    Digitale Medien
    Raman spectral changes induced by side-chain interactions in racemic poly-γ-benzyl glutamate (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1435-1445 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Laser Raman spectra are reported for solid films cast from a series of solutions containing mixtures of right- and left-handed α-helices of poly-γ-benzyl-L- and D-glutamate. Procedures were established for producing spectra that were reproducible in position to ±0.3 cm-1 and in relative intensity to a few percent for features of interest. Spectra for the pure L and pure D polymers were identical, as expected. Several small but definite spectral changes appear in the mixtures, reaching a maximum for the racemic 50:50 mixture. The changes are a shift of -1.4 cm-1 in the amide I peak at 1650.5 cm-1; a shift of about -5 cm-1 in the partially resolved amide III peak at 1291 cm-1; a shift of +2.5 cm-1 in the benzyl peak at 3062.5 cm-1; changes in relative intensity of as much as 50% in several regions; and the marked enhancement of several peaks, particularly that at 254 cm-1. These changes are discussed in terms of side-chain interactions in the packing of right- and left-handed helices.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130714
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  • 82
    Digitale Medien
    Digitale Medien
    Study of the self-diffusion coefficients of cations in the presence of an acidic polysaccharide (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1535-1548 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Self-diffusion coefficient measurements have been applied to the study of Na+, Ca++, and Sr++ in the presence of a linear acidic polysaccharide extracted from cartilage, i.e., chondroitin sulfate. A series of experimental determinations was made with and without supporting electrolytes, and an analysis of experiments involving the separation of the electrostatic interaction terms by an extension of Manning's theory produced results showing the preponderant nature of these electrostatic terms. The specificity of each type of ion or the influence of the pH can be considered merely as higher order corrections with respect to the preceding interactions. Counterion concentration ranges and pH ranges were determined, where either the alkaline-earth counterions become free and hence move with their normal diffusion rate, or these cations are associated with the polyelectrolyte molecule, thus giving a diffusion coefficient similar to that of the macromolecule, or the apparent diffusion coefficients vary between these two extreme diffusion rates as a function of the association equilibria. This variation can be expressed as a function of the linear charge density parameter ξ related to the structure of the polyelectrolyte, the value of which was determined and found in good agreement with published values.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130803
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  • 83
    Digitale Medien
    Digitale Medien
    The calculated circular dichroism of polyproline ii in the polarizability approximation (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1635-1651 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The circular dichroism (CD) spectrum of polyproline II (PPII) has heretofore been moderately well calculated from exciton theory only at the expense of assuming unreasonable chain conformations and accepting a conservative spectrum in the 180-250-nm region (which is not observed). We have incorporated far uv transitions in the polarizability approximation and, together with the π2π* transition, have calculated the resulting correction to the exciton model. This has been accompanied by a modified assignment of the ππ* transition in PPII, and a simultaneous calculation of the absorption and CD spectra of the α-helix, β structure, PPI, and PPII. We obtain good agreement with the observed CD spectrum of PPII in the 180-250-nm region for acceptable chain conformations. In addition, we predict a negative CD into the far uv, in agreement with recent experimental observations. Our calculations also reproduce features of the far uv CD spectrum of the α-helix, and are in agreement with the CD spectra of the β chain and PPI. The calculated CD of the unordered polypeptide chain is not significantly influenced by far uv contributions, indicating that our previous calculation is valid for such a system. These results demonstrate the importance of incorporating far uv transitions in order to achieve an adequate theoretical explanation of the CD spectra of polypeptides.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130810
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  • 84
    Digitale Medien
    Digitale Medien
    Masthead (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974) 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130901
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  • 85
    Digitale Medien
    Digitale Medien
    Hydrodynamic properties of a new plasma expander: Polyhydroxyethylaspartamide (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1721-1729 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The intrinsic viscosity and molecular weight of several samples of polyhydroxyethylaspartamide with differing degrees of polymerization were determined and related, according to the Mark-Howink equation. The a exponent is consistent with a random-coil structure. The average unperturbed dimensions of the polymer, the dimensions in water, and the water-polymer interaction parameter were calculated according to Flory and Fox. The interaction of the polymer with water may explain its good efficacy as a plasma expander, as has previously been demonstrated in biological experiments. The behavior of the molecule in 6 M guanidine hydrochloride solution was also studied: this solvent has a very slight effect on the configuration of the polymer, in contrast with its normal effect on proteins.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130904
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  • 86
    Digitale Medien
    Digitale Medien
    Microcalorimetric investigation of dilute and concentrated solutions and films of the polydeoxynucleotide poly[d(A-T)·d(A-T)] (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1751-1756 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Microcalorimetric heat capacity measurements on dilute and concentrated solutions and films of poly[d(A-T)·d(A-T)] in 2 M sodium chloride have been carried out. Values for enthalpy, entropy, and temperature of the helix-coil transition have been found to depend on the polymer concentration, and to have maxima near 20% (w/w) of polymer. The results are discussed in terms of polynucleotide hydration as one of the structure stabilizing factors.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130908
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  • 87
    Digitale Medien
    Digitale Medien
    Evaluation of kinetic parameters of thermal decomposition of native collagen by thermogravimetric analysis (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1791-1807 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetic parameters associated with the thermal decomposition of native collagen have been obtained by thermogravimetric techniques. In order to achieve this a thermogravimetric analysis was carried out in the temperature range of 25°C to about 1000°C. In this temperature range, it had been found that the differential primary weight loss curve had yielded three distinct peaks for the tendon collagen. The thermal decomposition corresponding to each peak was analyzed to retrieve its kinetic parameters. The peak temperature associated with the first peak decreased as the water content in a sample increased, while that of the second peak was independent of its hydration condition. It is believed that the first and the second peaks are, respectively, results of: (1) dissociation of water from collagen, and (2) of breaking of the collagen molecule itself. The third peak has not been easily identified so far. The activation energy and the order of water decomposition are obtained by various known methods. The results obtained by these different approaches agree reasonably well. The kinetic parameters of second and third peak are also obtained and reported here.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130912
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  • 88
    Digitale Medien
    Digitale Medien
    Recursion relation generation of probability profiles for specific-sequence macromolecules with long-range correlations (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1859-1871 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The problem of calculating detailed probability profiles giving the probability of each unit in the chain to be in the ordered state (and all other average quantities as well including the fraction of strand association) for specific-sequence macromolecules requiring statistical weights that correlate up to the total number of units in the chain (e.g., DNA, collagen) is formulated in terms of recursion relations for appropriate a priori and conditional probabilities, thus generalizing the approach of Lacombe and Simha for nearest-neighbor correlations in specific sequence macromolecules. The technique allows the probability profiles for chains of thousands of units to be calculated in minutes making no approximation in the basic model.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130916
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  • 89
    Digitale Medien
    Digitale Medien
    Studies on poly(L-lysine50, L-tyrosine50)-DNA interaction (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1909-1926 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Interaction between poly(Lys50, Tyr50) and DNA has been studied by absorption, circular dichroism (CD), and fluorescence spectroscopy and thermal denaturation in 0.001M Tris, pH 6.8. The binding of this copolypeptide to DNA results in an absorbance enhancement and fluorescence quenching on tyrosine. There is also an increase in the tyrosine CD at 230 nm. The CD of DNA above 250 nm is slightly shifted to the longer wavelength which is qualitatively similar to, but quantitatively much smaller than, that induced by polylysine binding. At physiological pH the poly(Lys50, Tyr50)-DNA complex is soluble until there is one lysine and one tyrosine per nucleotide in the complex. The same ratio of amino acid residues to nucleotide has also been observed in copolypeptide-bound regions of the complex. The addition of more poly(Lys50, Tyr50) to DNA yields a constant melting temperature, Tm′, for bound base pairs at 90°C which is close to that of polylysine-bound DNA under the same condition. The melting temperature, Tm, of free base pairs at about 60°C on the other hand, is increased by 10°C as more copolypeptide is bound to DNA. As the temperature is raised, both absorption and CD spectra of the complexes with high coverage are changed, suggesting structural alteration, perhaps deprotonation, on bound tyrosine. The results in this report also suggest that intercalation of tyrosine in DNA is unlikely to be the mode of binding.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360130919
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  • 90
    Digitale Medien
    Digitale Medien
    Normal vibrations of cyclic tetraglycine (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 2565-2570 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Normal vibration analysis of cyclic tetraglycine has been carried out employing the Urey-Bradley force field and the vibrational assignments are compared with those in related molecules.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1974.360131213
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  • 91
    Digitale Medien
    Digitale Medien
    Vinyl polymerization by metal complexes, 11Part 10, cf.1.. Formation of polyvinylamine-copper(II) chelatesDedicated to Professor Dr. ICHIRO SAKURADA on his 70th birthday (1974)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 175 (1974), S. 83-93 
    Details
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Um den Mechanismus der Katalyse der Polyvinylamin-Kupfer(II)-Chelate bei der Auslösung der Vinylpolymerisation zu klären, wurden die Stabilitätskonstanten dieser Chelate durch Anwendung einer modifizierten BJERRUMschen Methode gemessen, und die Konzentration der chemischen Spezies wurde auf Grund der Chelattheorie abgeschätzt. Anhand dieser Ergebnisse wurde die Aktivität der Polyvinylamin-Kupfer(II)-Chelate bei der Polymerisation von Acrylnitril und von Methylmethacrylat bei verschiedenen pH-Werten diskutiert.
    Notizen: In order to clarify the mechanism of catalysis of polyvinylamine-copper(II) chelates on the initiation of vinyl polymerizations, stability constants of these chelates were measured by applying a modification of BJERRUM'S method, and each concentration of the chemical species was estimated on the basis of the chelate theory. From these results, the activity of the polyvinylamine-copper(II) chelates for the polymerization of acrylonitrile and methyl methacrylate at different pH values was discussed.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/macp.1974.021750110
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  • 92
    Digitale Medien
    Digitale Medien
    Synthesis of poly[4(5)-vinylimidazole-co-γ-vinyl-γ-butyro-lactone] and its catalytic activity in ester hydrolysisDedicated to Professor Dr. ICHIRO SAKURADA on his 70th birthday (1974)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 175 (1974), S. 119-124 
    Details
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Die Copolymerisation von 4(5)-Vinylimidazol mit γ-Vinyl-γ-butyrolacton wurde in Gegenwart von 2,2′-Azoisobutyronitril oder Benzoylperoxid durchgeführt. Die Initiatoren üben keinen Einfluß auf die Copolymerisationsparameter aus. Diese werden auch von Methanol als Lösungsmittel nicht beeinflußt. Die Copolymerisationsparameter wurden zu r1 = 20,0 ± 0,8 und r2 = 0,030 ± 0,002 bestimmt.Die katalytische Aktivität des Copolymers bei der Hydrolyse von p-Nitrophenylacetat (4) und von 3-Acetoxy-N,N,N-trimethylaniliniumjodid (5) bei pH = 8,0 war über doppelt so groß wie die eines statistischen Terpolymers mit Imidazol-, Carbonsäure- und Hydroxyl-Gruppen.
    Notizen: Copolymerizations of 4(5)-vinylimidazole (1) and γ-vinyl-γ-butyrolactone (2) initiated by 2,2′-azoisobutyronitrile or benzoyl peroxide were carried out. The initiators did not affect the radical reactivity ratio (r). In addition, the reactivity ratio was not influenced by methanol as solvent. The following ratios were obtained r1 = 20,0 ± 0,8 and r2 = 0,030 ± 0,002.The catalytic activity of the copolymers in the hydrolyses of p-nitrophenyl acetate (4) and 3-acetoxy-N,N,N-trimethylanilinium iodide (5) at pH = 8,0 was found to be more than twice as high as that of a random terpolymer containing imidazole, carboxylic acid, and hydroxy moieties.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/macp.1974.021750114
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  • 93
    Digitale Medien
    Digitale Medien
    Influence of the structure of cobalt(III)-poly(4-vinylpyridine) complexes on the electron-transfer reactionDedicated to Professor Dr. ICHIRO SAKURADA on his 70th birthday (1974)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 175 (1974), S. 171-178 
    Details
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Kobalt(III)-Komplexe, die einen Polymer-Liganden enthalten, cis-[Co(en)2PVPCl]Cl2, cis-[Co(trien)PVPCl]Cl2, cis-[Co(en)2PVPBr]Br2, cis-[Co(en)2PVPN3]Cl2 und cis-[Co(en)2-QPVPCl]Cl2 (PVP = Polyvinylpyridin, QPVP = teilweise quaterniertes PVP), wurden dargestellt, und ihre Reduktion mit Ferrosulfat wurde untersucht. Es wurde gezeigt, daß die Komplexbildung mit QPVP durch sterische Faktoren beeinflußt wird, wie durch den Polymerisationsgrad des Polymer-Liganden und die Raumerfüllung der Quaternierungsmittel. Die Quaternierung des Polymer-Liganden selbst zeigte jedoch nur einen geringen sterischen Einfluß auf die Reduktionskinetik. Für die verschiedenen Brückenliganden (X) ergab sich folgende Reihe in bezug auf die Reduktionsgeschwindigkeit von cis-[Co(en)2PVPX]2+:N3 〉 Cl 〉 Br. Die Reduktionsgeschwindigkeit von cis-[Co(en)2PVPCl]2+ ist größer als die von cis-[Co(trien)PVPCl]2+. Die Einflüsse der Brücken- und Nichtbrückenliganden auf die Reduktion sind ähnlich für die Polymer-Komplexe und die monomeren Analoga.
    Notizen: Cobalt(III)-complexes having a polymeric ligand, cis-[Co(en)2PVPCl]Cl2, cis-[Co(trien)-PVPCl]Cl2, cis-[Co(en)2PVPBr]Br2, cis-[Co(en)2PVPN3]Cl2 and cis-[Co(en)2QPVPCl]Cl2 (where PVP = poly(4-vinylpyridine) and QPVP = partially quarternized PVP) were prepared and their reduction with ferrous sulfate was studied. Complex formation with QPVP was shown to be affected by steric factors such as the degree of polymerization and the bulkiness of the quaternizing agents, but the quarternization showed only a small steric influence on the reduction kinetics. The order of the reduction rate of cis-[Co(en)2PVPX]2+ with respect to the bridging ligand X is N3 〉 Cl 〉 Br, and the reduction rate of cis-[Co(en)2PVPCl]2+ is higher than that of cis-[Co(trien)PVPCl]2+. The effects of bridging and non-bridging ligands in the reduction of polymer complexes were the same as those for the monomeric analogues.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/macp.1974.021750118
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  • 94
    Digitale Medien
    Digitale Medien
    Thermodynamic studies based on corresponding states theory for solutions of polystyrene in ethyl methyl ketoneDedicated to Professor Dr. ICHIRO SAKURADA on his 70th birthday (1974)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 175 (1974), S. 197-208 
    Details
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Die FLORYsche Theorie über das Prinzip der übereinstimmenden Zustände für Polymerlösungen wurde geprüft, indem die theoretisch berechneten Parameter mit experimentellen Ergebnissen verglichen wurden. Der osmotische Druck des Systems Polystyrol/Äthylmethylketon wurde für Polymerkonzentrationen zwischen 10 und 30% bei 10 bis 55°C gemessen. Unter Verwendung der Parameter X12 und Q12, die den erhaltenen Daten am besten entsprachen, wurden die berechneten Parameter mit den experimentellen Ergebnissen verglichen. Der Entropie-Parameter ψ1 sowie der Enthalpie-Parameter χH, 1 waren negativ und nahmen mit steigender Temperatur ab. Mit Hilfe der anpassungsfähigen Parameter X12 und Q12 gibt die FLORYsche Theorie die thermodynamischen Größen ziemlich gut wieder, obwohl eine geringe Abweichung von den experimentellen Ergebnissen zu bestehen scheint. Die SHULTZ-FLORYsche Methode zur Bestimmung der Theta;-Temperatur wurde auf der Grundlage dieser Theorie diskutiert.
    Notizen: The polymer solution theory on the corresponding state principle developed by FLORY was examined by comparing the thermodynamic parameters calculated theoretically with experimental results. The osmotic pressure of the polystyrene/ethyl methyl ketone system was determined for solutions of polymer concentrations 10 to 30% at 10 to 55°C. Using X12 and Q12 parameters best fitting to these data, the calculated parameters were compared with experimental results. Both the entropy parameter ψ1 and enthalpy parameter χH, 1 were negative and decreased with increasing temperature. FLORY'S theory elucidates appreciably well the thermodynamic quantities with the use of the adjustable parameters X12 and Q12, but there seems to remain still some disagreement with experimental results. SHULTZ-FLORY'S method for determining the Θ-temperature was discussed based on this theory.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/macp.1974.021750121
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  • 95
    Digitale Medien
    Digitale Medien
    Crystallization of polypeptides in the course of polymerization, 5Part 4, cf.5.. Effect of the steric hindrance on the crystal growth by the side chainsDedicated to Professor Dr. ICHIRO SAKURADA on his 70th birthday (1974)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 175 (1974), S. 283-299 
    Details
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Es wurde der Einfluß der sterischen Hinderung durch Polypeptid-Seitenketten auf den Wachstumsmechanismus von Polypeptidkristallen während der Polymerisation untersucht. Dabei wurden von uns Untersuchungen der Kinetik der heterogenen Polymerisation von L-Valin-LEUCHS-Anhydrid (NCA), L-Isoleucin-NCA und L-Leucin-NCA mit Butylamin als Initiator in Acetonitril und der Strukturen sowie der Morphologie der gebildeten Polymere durchgeführt. In den Anfangsstadien der Polymerisation bildeten sich Oligomere, die in dünnen, bandförmigen Kristallen mit antiparalleler β-Konformation kristallisierten. Die molekularen Anordnungen in den Kristallen wurden mit Hilfe der Elektronenbeugung untersucht. In den späteren Stadien der Polymerisation setzten die gewachsenen Poly(L-valin)- und Poly-(L-iso1eucin)-Ketten die β-Struktur weiter fort, und ihre aktiven Enden wurden in den gebildeten Kristallen eingeschlossen, was ein-Einpendeln des Umsatzes bei einem niedrigen Wert zur Folge hatte. Poly(L-leucin) andererseits schien Kristalle mit gestreckten Ketten zu bilden, die zu einem sehr hohen Umsatz führten. Dies kann nicht ohne die Annahme erklärt werden, daß sich auf den in den Anfangsstadien der Polymerisation gebildeten β-Skelettkristallen α-Helix-Ketten bilden, wie dies im Falle des Poly(L-alanins) bereits früher berichtet wurde.
    Notizen: In order to examine the effect of the steric hindrance by the polypeptide side chains on the growth mechanism of polypeptide crystals in the course of polymerization, we studied kinetics of the heterogeneous polymerization of L-valine N-carboxy anhydride (NCA), L-isoleucine NCA, and L-leucine NCA initiated by butylamine in acetonitrile and the structures and morphologies of the resultant polymers. In the early stages of polymerization, oligomers formed crystallized into thin ribbon-like crystals with the antiparallel β-conformation. The molecular arrangements in the crystals were studied by electron diffractions. In the later stages, the grown chains of poly(L-valine) and poly(L-isoleucine) continued to take the β-structure and their active ends were occluded in the crystals formed, which resulted in the levelling off of the conversion at a low value. On the other hand, poly(L-leucine) seemed to give the extended chain crystal, which made the conversion very high. This can not be accounted for without assuming the formation of β-helical chains onto the β-skeleton crystals formed in the early stages of polymerization as in the case of poly(L-alanine) reported previously.
    Zusätzliches Material: 20 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/macp.1974.021750129
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  • 96
    Digitale Medien
    Digitale Medien
    Mechanochemische Synthesen durch Polykondensation mit Polyestern als Grundsubstanz, 3.Teil 2 cf. Cr. Simionescu, C. Vasikiu Oprea, C. Neguleanu, Buletinul I.P.C. Iasi Fasc. 3-4, 45 (1969). Einige kinetische Aspekte der Mechanochemischen Polykondensation durch Schwingmahlung des Poly(oxyäthylenoxyterephthaloyl)s mit aliphatischen Diaminen (1974)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 175 (1974), S. 371-389 
    Details
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: The kinetics and the mechanism of the mechanochemical polycondensation process of poly(oxyethyleneoxyterephthaloyl) [poly(ethylene terephthalate)] with aliphatic diamines (ethylene- and hexamethylenediamine) were studied. First order kinetics was found and in addition the fact that a very small thermal activation energy is needed and that the diamines can react as radical acceptors.
    Notizen: Kinetik und Mechanismus des mechanochemischen Polykondensationsvorganges von Poly(oxyäthylenoxyterephthaloyl) (Polyäthylenterephthalat) mit aliphatischen Diaminen (äthylen- und Hexamethylendiamin) wurden untersucht. Es wurde gefunden, daß die Reaktion nach einer Kinetik erster Ordnung abläuft, daß eine äußerst geringe thermische Aktivierungsenergie benötigt wird und daß die Diamine als Radikalakzeptoren auftreten können.
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/macp.1974.021750203
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  • 97
    Digitale Medien
    Digitale Medien
    Studies on the mechanism of redox polymerization initiated by N-haloamines and iron(II)Presented at the XXIVth IUPAC-Congress, Hamburg, Germany, September 1973. (1974)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 175 (1974), S. 413-423 
    Details
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Zur Aufklärung des Mechanismus der Redox-Polymerisation von Methylmethacrylat, die die Redox-Startsysteme N-Halogendiäthylamin + Fe2+ und Triäthylamin + Halogen + Fe2+ in wäßrigem Medium unter Lichtausschluß bewirken, wurden die Endgruppen des Polymeren nach der Farbstoff-Verteilungsmethode untersucht. Im Falle von Chlor als Halogen kommt es mit beiden Startsystemen lediglich zum Einbau von Aminogruppen in das Polymere in einem Ausmaß von ca. 1 Endgruppe pro Polymermolekül. Bei Verwendung des Startsystems Triäthylamin + Halogen + Fe2+ liegen darüber hinaus die in das Polymer eingebauten Aminogruppen zu einem großen Teil in quaternärer Form vor. Mit Brom als Halogen findet bei beiden Anregungssystemen lediglich ein Bromeinbau, nicht jedoch ein Einbau von Aminogruppen in das Polymere statt. Die Chlor enthaltenden Startsysteme haben sich für die Herstellung von solchen Polymeren nützlich erwiesen, die eine Aminogruppe nur an einem der beiden Kettenenden besitzen sollen.
    Notizen: The mechanism of the redox polymerization of methyl methacrylate in aqueous medium in the dark was studied for the redox initiator systems N-halodiethylamine + Fe(II) and triethylamine + halogen + Fe(II), by analysis of the polymer end groups using the dye partition method. In the case of chlorine, both these initiator systems incorporate only the amino group into the polymer to an extent of about one group per polymer molecule. The polymers are found to be free from chlorine. Furthermore, a large portion of the total amino groups introduced into the polymer, using the initiator system triethylamine + halogen + Fe(II) are quaternary in nature. In the case of bromine, both the initiator systems introduce only a bromine atom and no amino group into the polymer. The initiator systems containing chlorine prove to be useful for the preparation of polymers containing amino groups at the one end only.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/macp.1974.021750206
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  • 98
    Digitale Medien
    Digitale Medien
    Free radical polymerization of unconjugated dienes, 14.Part 13, cf. Makromol. Chem. 157, 111 (1972). Divinyl ketone in acetone solution at 50°C (1974)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 175 (1974), S. 457-466 
    Details
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Die radikalische Polymerisation des Divinylketons in Aceton bei 50°C wurde untersucht und mit den Resultaten bereits bekannter radikalischer Polymerisationen anderer 1,4-Diene vergl+hen. Es wird gezeigt, daß Divinylketon einer bicyclischen Cyclopolymerisation unterliegt, die derjenigen des Divinyläthers und des Divinylsulfids ähnlich ist. Die Cyclisierungskonstanten werden ermittelt und die Zusammensetzung der Polymere (als lineare, monocyclische und bicyclische Struktureinheiten) als Funktion der Monomerkonzentration, bei welcher die Polymerisation durchgeführt wurde, berechnet.
    Notizen: The free radical polymerization of divinyl ketone at 50°C in acetone solutions was investigated. The results are compared with those already reported for the free radical polymerization of other 1,4-dienes. It is shown that divinyl ketone undergoes bicyclic cyclopolymerization in a similar way as divinyl ether and divinyl sulfide. The cyclization ratios are computed and the polymer composition, in terms of linear, monocyclic and bicyclic structural units, is calculated as a function of the monomer concentration at which the polymerization was carried out.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/macp.1974.021750210
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  • 99
    Digitale Medien
    Digitale Medien
    Über die Bruttokinetik der Thermooxidation von HochdruckpolyäthylenVorgetragen beim XXIV. IUPAC-Kongreß, Hamburg, September 1973. (1974)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 175 (1974), S. 467-481 
    Details
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: The oxidation of molten foils (20μm) from high pressure polyethylene at 157°C and at 650 Torr (= 867 mbar) oxygen pressure was studied and kinetically analyzed for the period of maximum rate.The oxygen uptake, weight increase, and hydroperoxide formation start with a rate different from zero; the initial rate of carbonyl groups and volatile products is practically zero.The absorbed oxygen, except in the initial stage, shows a distribution of the ratio 1:1 between the polymer (predominantly as carbonyl groups) and volatile products (such as water). The average number of C-atoms in the volatile fragments was estimated from kinetic data to be 6 per O-atom.
    Notizen: Die Oxidation von geschmolzenen Folien (20μm) aus Hochdruckpolyäthylen wurde bei 157°C und 650 Torr (= 867 mbar) Sauerstoffdruck untersucht und kinetisch in der Periode der maximalen Geschwindigkeit ausgewertet.Die Sauerstoffaufnahme, die Gewichtszunahme und die Hydroperoxidbildung beginnen mit einer von Null abweichenden Geschwindigkeit; die Anfangsgeschwindigkeit der Bildung von Carbonylgruppen und flüchtigen Produkten ist praktisch Null.Der absorbierte Sauerstoff verteilt sich außer im Anfangsverlauf im Verhältnis 1:1 zwischen dem Polymeren (vorwiegend als Carbonylgruppe) und den flüchtigen Produkten (in Form von Wasser). Die durchschnittliche Anzahl von C-Atomen in den flüchtigen Fragmenten wurde aus kinetischen Daten auf 6 pro O-Atom abgeschätzt.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/macp.1974.021750211
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  • 100
    Digitale Medien
    Digitale Medien
    Copolymer statistics during esterification of syndiotactic poly(methacrylic acid) with diazomethane (1974)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 175 (1974), S. 523-534 
    Details
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Nicht-neutralisierte und neutralisierte, syndiotaktische Poly(methacrylsäure) wird mit Diazomethan partiell verestert. Umsatz und Triadenverteilung der entstenhenden cosyndiotaktischen Methylmethacrylat-Methacrylsäure-Copolymeren und deren Fraktionen werden durch 1H-NMR-Spektroskopie bestimmt. Nicht-neutralisierte Poly(methacrylsäure) ergibt Copolymere, die in bezug auf den Umsatz heterogen sind; ihre Fraktionen zeigen näherungsweise eine BERNOULLI-Verteilung der Triaden. Neutralisierte Poly(methacrylsäure) liefert hingegen homogene Copolymere mit einer innerhalb der Meßgenauigkeit liegenden BERNOULLI-Verteilung der Triaden. Ein kinetischer Nachbargruppeneffekt tritt daher bei der Veresterung mit Diazomethan nicht auf. So hergestellte Copolymere weisen eine einfache konfigurative und kompositive Statistik auf, wie sie durch Copolymerisation der Monomeren bislang nicht hergestellt werden kann. Der Polyelektrolytcharakter der Copolymeren kann durch anschließende, vollständige Veresterung mit einem zweiten Diazoalkan eliminiert werden; die Statistik der so entstehendenen Copolymeren ist mit der der ursprünglichen Copolymeren identisch.
    Notizen: Syndiotactic poly(methacrylic acid) is partially esterified as such or in its neutralized form with diazomethane. The extent of reaction and the triad distribution of the resulting cosyndiotactic methyl methacrylate-methacrylic acid copolymers and their fractions are determined by 1H-NMR spectroscopy. Unneutralized poly(methacrylic acid) yields copolymers which are heterogeneous with respect to conversion, the fractions of the copolymers possessing an approximate BERNOULLIan triad distribution. Neutralized poly(methacrylic acid) results in homogeneous copolymers whose triad distribution is BERNOULLIan within accuracy of measurement. A kinetic neighboring group effect is therefore not operative during the esterification with diazomethane. Copolymers may thus be prepared which are of simple configurational and compositional statistics, not obtainable at present by copolymerization of monomers. The polyelectrolyte character of the copolymers may be eliminated by consecutive, complete esterification with a second diazoalkane, the statistics of the derived copolymers being identical with that of the precursor copolymers.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/macp.1974.021750215
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