Bibliothek

Notizen: The use of multiple scattering techniques combined with a statistical exchange potential for the description of the electronic structure of atoms, molecules, and solids depends strongly on the geometry (muffin tin, overlapping spheres, or cellular potentials) and on the form of the electron gas exchange. In this work we compare only the effects of using different geometries. For that purpose we have done calculations on the hydrogen molecular ion and Hartree-type calculations on the hydrogen molecule so that no exchange effects are involved. To avoid arbitrariness in the choice of the sphere sizes we propose a nonempirical criterion that consists of using the set of radii that will minimize the charge in the interstitial region of the molecule or cluster. Some arguments are given to justify this criterion, and to clarify the differences between cellular, overlapping spheres, and muffin-tin geometries. It is found that the cellular geometry gives a very good description around the equilibrium internuclear distance. However, for most systems of interest, exchange will be present. Thus, we have done, for comparison, the calculation on H2 using Xαβ statistical exchange. It is shown through this calculation that some of the correlation energy may be obtained by redefining the molecular orbitals in terms of non-paired-spins spatial orbitals, this formulation being required to obtain the correct free-atom limit.

Notizen: The theory of the open-and closed-shell restricted Hartree-Fock method is given a unitary group formulation. Both extremum and stability conditions are employed, the former leading to a generalized Brillouin theorem.

Notizen: An improved interaction potential has been devised for diatomic alkali halide molecules. This potential, in addition to similar attraction terms as in the Rittner potential, includes a new exponential for the short-range repulsion. The constant m in the exponential is seen to be well expressible in terms of the parameters of the Rittner potential. The new potential is also correlated with different properties, as for example, effective charges, effective radii, effective principal quantum numbers, etc., of the combining ions. Various spectroscopic constants, viz., the ionic dissociation energy Di, the vibrational-rotational coupling constant αe, the vibrational anharmonicity constant ωexe, as well as two second-order spectroscopic constants γe and βe have been calculated for this and for the Rittner potential. From comparisons between these two potentials, the new one has been observed better than the other.

Notizen: Giving explicit consideration to the lone pairs of the carbonyl oxygen of the amide group it is found that the polarity of the amide group resides essentially in the lone pair. As a confirmation, the lone pairs of the ester group are also found to account for most of its polarity. This localization of amide dipole affects the dipeptide conformation map only in the unallowed regions of the map, but has significant impact on the dipole moment of the dipeptide in different conformations. The experimentally observed dipole moments of dipeptides in solution are in conformity with our assignment of polarity of the amide group.

Notizen: No. Abstract.

Notizen: The geometrical parameters of the ammonia molecule in the lowest-lying triplet state have been estimated by means of the SCF method and by making an extrapolation to take into account electron correlation effects. The planar configuration has been obtained as the most probable geometrical arrangement (3 A2″).

Notizen: A new method for the calculation of electrostatic isopotential maps, based on completely transferable bond orbitals, is proposed. According to the simple form of the potential term the amount of computational work is proportional to the first power of the number of valence electrons. Slater-type atomic orbitals are used to construct the bond orbitals, thus all integrals can be calculated explicitly. The subtilisin charge-relay system is studied as an example. It is found, in agreement with the results of Beppu and Yomosa, that the two protons transfer in a stepwise manner.

Notizen: We report here a summary of a limited CI calculation carried out on the C∞v and D∞h electronically excited states of bifluoride ion. This species is interesting as the prototype of a hydrogen-bonded system. It is determined that the lowest-lying excited states of the system are dissociative and/or autoionizing.

Notizen: The role of some amino acids and metal ions in the catalytic activity of carbonic anhydrase (carbonate dehydratase EC 4.2.1.1) has been investigated. The additional stabilization of the transition state complex was used as the qualitative measure of the effect of molecular surrounding on CO2 hydration reaction calculated within the approximate CNDO/2 approach. The effect of the molecular environment has been simulated by inclusion into the SCF LCAO MO Hamiltonian, a term representing the interaction with a set of point charges and atomic dipoles centered on experimentally determined position of Zn2+ ion and all atoms of histidine 94, 96, 119 and threonine 199, 200 (or histidine 200 in the case of carbonic anhydrase B). The possible molecular mechanism of CO2 hydration inside the active site has been also discussed.

Notizen: Ab initio calculations on the SCF level and with the inclusion of valence shell electron correlation in the IEPA-PNO (independent electron pair approximation with pair natural orbitals), the PNO-CI (pair-natural-orbital configuration interaction) and the CEPA-PNO (coupled electron pair approximation with pair natural orbitals) schemes with Gaussian lobe functions of “double zeta quality” have been performed for the minimum energy path of the insertion of singlet (1A1) methylene to the (1Σg+)H2 molecule to yield methane. The energy was minimized on the SCF level to all geometrical parameters for various values of the “approximate” reaction coordinate. The energy along the reaction path decreases monotonically without a barrier and the curves representing the total energy of the system as a function of approximate reaction coordinates obtained at different levels of approximations have the same shape. From the physical point of view three phases of the reaction can be distinguished (chemically two steps) with different geometrical arrangements and different internal geometries of the partners.

Notizen: The electronic structure of the model hydrogen-bonded systems has been studied at the all-valence level in relation to the charge transfer mechanism. It is concluded that together with the intermolecular proton transfer an electronic charge transport occurs for hydrogen bonds of 2.70-3.00 Å in length, i.e., when the proton motion within the bond is anticipated. For elucidation of transport properties of one-dimensional hydrogen-bonded systems the tunneling-hopping model is preferred instead of the band theory. The importance of the proposed mechanism of the charge transfer for biological processes has been emphasized.

Notizen: Metalloporphyrins perform a variety of functions in nature from the storage and transport of electrons and molecular oxygen to the decomposition of hydrogen peroxide and the activation of oxygen. The chemistry of both the centrally coordinated metal and the porphyrin macrocycle play important roles in these reactions. The use of model systems and metalloporphyrins, other than iron porphyrins, is described for the elucidation of the mechanism of action of the natural systems.

Notizen: The concept of potential surfaces and classification of various types of intermolecular forces are given. The possibilities and the criteria of applicability of modern methods for potential surface calculation at short, intermediate, and long distances are discussed. Special attention is paid to the methods for calculating interactions between large molecules.

Notizen: The present work is devoted to investigation of thermal transitions in the crystals of seven proteins to compare the protein globule stability in crystal and solution. Calorimetry methods, electron and optical microscopy, as well as x-ray diffraction studies are used. It is found that protein crystals do not melt and that the destruction of the crystal lattice is a result of protein globule denaturation within the crystal. It is demonstrated that during the heating of pepsin and DF-trypsin crystals it is possible to observe phase transition of the first order. Equilibrium temperatures of protein denaturation in crystals and in solution coincide. The peculiarities of the crystal state are revealed in the increasing thermal transition cooperativity and the system relaxation period.

Notizen: The new properties of clusters - the polynuclear Fe, Cu, Mo - containing metal-protein complexes have been discussed. The properties arose as a result of strong electron interaction and of the multiorbitals system existence in which the orbitals energetically fall close together. The clusters are characterized by (i) a high electronic capacity, (ii) an ability to multielectronic transfer without essential rearrangement of nuclei configuration, (iii) a high degree of donor-acceptor energetical levels fitting at tunnel transfer, (iv) high possibilities for avoiding of reaction pathways being quantum mechanically forbidded, and (v) an ability to provide smooth reaction energetic relief in coordinated sphere. The analysis of data on spin exchange between paramagnetic centers (binuclear transition-metal complexes, nitroxile biradicals, triplet exited chromophores) showed that in the range of spinexchanged constants Kex = 1014-1 sec -1 of the distances between the centers r = 3-17 Å the approximate relation Kex =1017 exp (-2.3r)sec-1 takes place. This relation may be considered as a criterion of nonspecific electron density transfer through nonconducting medium. The quantitation of exchange triplet-triplet energy migration permits one to estimate the degree of quantum-mechanical electron density penetration through biological matrix. By means of measurement of spin-lattice relaxation rate for oxidized primary donor in bacterial photosynthetic system - bacteriochlorophyll cation (BChl+ ) - it is shown that the distance between BChl+ and primary acceptor (complex FeQ) is about 34 Å. The proposed two-step photoelectron transfer model explains the effective charge separation by relatively slow tunnel recombination of the charges BChl+ FeQ-. As spin and Mössbauer labeling experiments showed the conformation mobility of surrounding protein and membrane matrix with frequency more than 107 sec-1 is required for photoelectron output from primary photosynthetic cell in chromotophores and reaction center to secondary acceptor.

Notizen: Detailed quantum-chemical calculations by means of semiempirical all-valence electrons methods and a generalized (multivariable) rank correlation analysis are the fundamentals of a novel strategy of search for QSAR within homologous series of compounds. The set of molecular parameters (describing the electronic and conformational properties as well as potential interactions of the drugs) is calculated theoretically. Owing to the rank correlation method, no linear model (like LFER) for the dependence of the biological activity upon the molecular parameters is presumed. The computed correlation coefficients are valued by carefully determined levels of statistical significance. Significant correlations are used to predict unknown activities in terms of ranks relative to the basic sample.

Notizen: This paper proposes a method for the generalization of the second quantization operators. The method is based on two main hypotheses: (i) the same form of the correlation operator, which is good for closed-shell systems is chosen and (ii) a system of equations is given to calculate the differences (xk0-xk1), which characterize both attachment and detachment operators.

Notizen: The steric constants Es and ν have the greatest chance of being independent of lipophilic substituent constants. There is a high probability among hydrocarbon substituents that the steric constants correlate with the lipophilic ones, while in the case of polar substituents the probability is low.

Notizen: The model systems of molecular nitrogen fixation [N2 + H]⋅, [N2 + H]+, [N2 + H]-, [N2 + H2], [N2 + H2]+, and [N2 + H2]- were studied by the semiempirical INDO method. The study was based on the formal analogy between the catalytic reactions and the photochemical, radical, and ionic reactions on the other side. Symmetrical and donor-acceptor properties of necessary catalytic systems were proposed using the dependence of energy characteristics and electron structure on reaction coordinate. On the basis of this MO study we have proposed the appropriate symmetry types of catalysts for each of acceptable models of nitrogen fixation. For one of the proposed systems there was realised a model MO computation with explicit inclusion of atoms of transition metals (Fe, V).

Notizen: All equilibrium conformations of a series of N-alkyl-α-alkyl derivatives of noradrenaline and their synthetic precursors - phenylaminoketones - have been calculated. It has been shown that spasmodic changes in bronchodilating activity of the catecholamines, observed with the increase in α-alkyl substituent size, may arise from the difference in the ratio of diastereoisomers produced by reduction of aminoketones.

Notizen: Aromatic polynuclear p-quinones and their derivatives have been studied using their electronic absorption and luminescence spectra and their basicity. The data were used to provide a basis for the study of the relationships between the structure and the spectral characteristics.

Notizen: The spectrum of a two-component solid solution with a nondiagonal disorder is studied in the framework of the average T matrix method. For a one-dimensional system in the nearest-neighbor approximation the criteria for the system parameters are given such that at an in-band resonance, one or two “impurity bands” may be realized, and the corresponding model calculation is performed. In the single-site approximation an expression of the self-energy part of a nondiagonal disordered system Green's function is found taking into account multiple occupancy corrections. The possibility of using it to describe a disordered system excitation spectrum and the calculation of state density moments are discussed.

Notizen: The processes of radiationless conversion in aromatic and heteroaromatic molecules are investigated theoretically. The values of constant rates of internal conversion are calculated. The theoretical estimation of constant rates of S-T conversion aromatic hydrocarbon molecules and in their carbonyl-, thiocarbonyl-, and nitroderivatives and in azaheterocyclic molecules are given. The S-T conversion probability between the states of different orbital nature (nπ* and ππ*) is equal to ca. 1010-1011 sec-1 that is two to four orders higher than the conversion probability between the states of the same orbital nature. It is shown that the process of T-S conversion may be described in the second and in the highest orders of perturbation theory. The luminescent characteristics of molecules are connected with the relative position of electron states of different orbital nature and multiplicity and conversion characteristics.

Notizen: A review of recent theoretical studies of molecules of interest to photosynthesis is given, in which the results of ab initio self-consistent-field plus configuration-interaction studies are discussed. Ground-state and low-lying excited singlet and triplet state descriptions are presented for six molecules, including Mg-porphine, Mg-chlorin, ethyl chlorophyllide a, and their corresponding magnesium-free analogs. The data are then used to rationalize a variety of observed properties, including molecular orbital structure, ionization potentials, chemical reactivity, Franck-Condon transition energies, oscillator strengths, transition polarizations, and other properties. As a result, relatively comprehensive and complete descriptions of the electronic structural features of chlorophyll a and related molecules are obtained, which are in general in good agreement with available experimental data, but which also provide new concepts and reinterpretation of existing data in several instances.

Notizen: Thermodynamics of the melting of a DNA-type macromolecule is studied theoretically. Elements of the macromolecule are able to annex a low-molecular impurity from the solvent (e.g., metal ions). Two models of the annexing of the impurity to the macromolecule are analyzed. It is shown that the concentration dependence of the helix-coil phase transition temperature is describable by a non-monotonic function in the case of certain relations between parameters.

Notizen: Of the two known families of double-stranded DNA conformations, A is stable in less-polar, and B in more-polar solutions. In some water-nonelectrolyte solutions, B to A transition occurs when water activity in the system is near 0.8. In such systems, however, as water-methanol, water-ethylene glycol, etc., B conformation is stable at very low water activity. Hyperfine splitting constant of a spin label (A), a widely used criterion of the solvent polarity, was measured by EPR method in the solutions, in which B to A transition takes place at 25°C. A values in solutions of different compositions are close to each other. A method for quantitative estimation of Van der Waals and hydrogen-bond contributions to A values is proposed. A values in water-methanol solutions show that their polarity is too high for the A form to be stable. Decreasing temperature shifts the B-A equilibrium to the B form, which correlates with increasing polarity of the water-alcohol solutions, as measured by the EPR method. Thus B to A transition is mainly determined by the polarity of the environment, which, in turn, is determined by the ability of the solvent molecules to participate in Van der Waals interactions and hydrogen bonding.

Notizen: The problems connected with the transformations of energy in the living systems are reviewed. Possibility of Bose-Einstein condensation by input of radiant energy over a critical level is considered as a route for overcoming the barriers of activation energy under the conditions of a pump and a thermalizing environment. Molecular force fields constitute the pump. Under our scheme excitons constitute the major fraction of bosons to so condense. Instantaneous dipoles of London theory are then examined as excitons. Lastly an energy packet from a quantized dipolar field is suggested rather than the concept of “conformons.” Questions of charge and of other modes of energy transfer are briefly discussed.

Notizen: It is shown in the present work that a protein globule can mediate the donor-to-acceptor electron transport, when the protein is in the solution or incorporated into the membrane.

Notizen: A quantitative conformational theory of proteins is developed that enables one to predict the native structure of a protein from its amino acid sequence. The theory is based on the following principles: (1) the spatial structure and conformational properties of a protein are predetermined by its amino acid sequence; (2) the native conformation of a protein corresponds to the free energy minimum; (3) all interactions within a protein molecule are specified as short-, mediumy-, and long-range types, interactions of different types being consistent with each other. The role of the short-, medium-, and long-range interactions in the spatial organization of a protein globule is discussed, and a step-by-step analysis of amino acid sequences with gradually increasing lengths is presented. The proposed theory is based on a semiempirical computational method that involves quantitative evaluation of all pairwise atomic interactions within a protein molecule in an aqueous medium. Examples illustrating the suggested approach are presented.

Notizen: Using the Bogolyubov's rate equation from the theory of superfluidity the possibility of Bose condensation of phonons in biological systems and the validity of Fröhlich's hypothesis has been proved. We took into account both the third and the fourth anharmonism in the rate equation. All the processes with active phonons (from one to four) of biological active modes have been investigated. Taking into account these processes the expression for the chemical potential is shown to be changed, but the conditions for Bose condensation of phonons still exist. For the first time we point out the possibility of soliton wave packet propagation in the coherent systems of phonons and photons. The possibility of Bose condensation of excitons in biological systems is also discussed.

Notizen: A free radical was produced enzymatically by incubating benzo(a)pyrene with liver microsomes. This radical, identified as the 6-oxybenzo(a) pyrene radical, was sufficiently reactive to bind covalently with nucleic acid bases. Similar reactive free radicals were produced enzymatically from anthanthrene and 10-aza-benzo(a)pyrene, which are carcinogenic in spite of lacking so-called “bay regions.” Hepatocarcinogens such as 3′-methyl-4-dimethylaminoazobenzene and related compounds, naphthylamines, and 2-acetylaminofluorene yield free radicals after being incubated with liver microsomes. Thus, various kinds of chemical carcinogens are found to be converted to free radicals, suggesting causal significance for the formation of free radicals in chemical carcinogenesis.

Notizen: Size and shape parameters for the core, bonding, and lone electron pairs of the ten-electron hydrides (CH4, NH3, H2O, HF) were determined from ab initio MO wave functions using various Gaussian basis sets. The fundamental features of approximate electron pair loge representation are somewhat more sensitive to the quality of the basis functions than the molecular total energy. The total size of the molecular electron distribution is less affected by basis set variations than its components: the core, bonding, and lone pair sizes. There is an apparent tendency to “preserve” the total size of molecular distribution.

Notizen: We consider the effects of a non-muffin-tin charge density in the multiple-scattering method. The study is carried out by means of a parametrized electronic density, which is used in a variational expression for the energy of the molecular system. We show that, at least in two situations, the parametrized density reproduces the true density very well. In a numerical study of the electronic configuration of the CH4 molecule, we show that the non-muffin-tin density may shift the one-electron energies by as much as 1 eV and the total energy by as much as 1 Ry.

Notizen: For each of HNO, FNO, LiNO, LiON and HF2-, ab initio valence-bond wave functions are reported for the four-electron three-center bonding unit which involves one of the following sets of atomic orbitals: (a) NX σ-bond (X = H, For Li) and oxygen 2pπ′; (b) LiO σ-bond and nitrogen 2pπ′; (c) hydrogen 1s and fluorine 2pσ. Six S = 0 valence-bond structures pertain for this type of bonding unit. For HF2- and FNO, the calculated bond-eigenfunction coefficients for some of these valence-bond structures differ appreciably according to whether the Slater determinants include only the electrons of the four-electron three-center bonding unit, or all of the valence-shell ± inner-shell electrons. For HNO, LiNO, and LiON, the all-electron and all valence-shell electron calculations generate similar sets of bond-eigenfunction coefficients. For each of the nitrosyl systems, the bond-eigenfunction coefficient with largest magnitude is calculated to be that for which zero atomic formal charges occur in the valence-bond structure. Qualitative valence-bond and “increased-valence” descriptions of the bonding are presented.

Notizen: Various electronic indices calculated by the CNDO/s-CI method for uracil, 5-fluorouracil, thymine, and cytosine and the Woodward-Hoffmann rule applied to the photodimerization of these molecules lead us to the following conclusions: (i) decrease of the C5—C6 bond order consequent to excitation is generally correlated with the photodimerization reaction for all the biological pyrimidines; (ii) excited pyrimidine molecules may be nonplanar and the excitation would be delocalized over both the molecules which photodimerize; (iii) electrostatic interactions may play a significant role in the initial stages of the photodimerization reaction; (iv) singlet precursors to the stable triplet photodimers may exist; and (v) electron density does not, in general, increase in the C5—C6 bond in the excited state as compared to the ground state, contradicting the proposals of some earlier workers. Hybrid population densities and σ-bond orders have been calculated for the first time for the molecules. Fluorine in 5-fluorouracil perturbs the hybrid populations as compared to those of uracil mainly in its vicinity.

Notizen: A novel approach is developed for optimizing molecular orbitals within the context of a multiconfiguration self-consistent-field problem. The MCSCF wave function is determined through a sequence of eigenvalue problems in the multiconfiguration space and the single-excitation space. They are used to iteratively improve the natural orbitals, which in turn are related, by successively improved transformations, to the MCSCF orbitals. The mathematical problems arising out of this general concept are solved and the computational implementation is discussed. In many applications the method has proven itself as a powerful approach in forcing rapid convergence. Adaptation to spin and spatial symmetry is maintained throughout and the procedure is applicable to excited states as well as to ground states.

Notizen: The direct dissociation of ethylene into two methylenes is studied along the least motion reaction path by means of an ab initio multiconfiguration self-consistent-field (MCSCF) calculation. All eight configurations arising from those valence orbitals that form the CC bonds, seven of them singlet coupled and one triplet coupled, are taken into account. The HCH bond angle is optimized along the entire reaction path. Separate MCSCF optimizations are carried through for the lowest two states of 1Ag symmetry. The (1Agσ2π2) ethylene ground state dissociates into two (3B1σπ) ground-state methylenes. The (1Agσ2π*2) excited state of ethylene dissociates into two (1A1σ2) excited methylenes. It is established that both these dissociations proceed without any barrier in the energy curve. In the ground state, where orbital symmetry is conserved, the π-bond breaks before the σ-bond, and the calculated heat of reaction agrees within 6 kcal/mol with the experimental value. In the excited state, where orbital symmetry is not conserved, the nonbonded repulsion between methylene σ2 lone pairs is found to blend into the antibonding character of the excited ethylene, yielding an energy curve that is everywhere repulsive. However, the variation of the HCH angle during the dissociation process is not simple, initially it expands and subsequently it contracts. Quantitative analytical approaches are developed which furnish conceptual interpretations of the orbital changes and configurational changes along the reaction path.

Notizen: The semiempirical MINDO/3 method is employed to calculate the energies of various tautomers of model tautomeric compounds -  2-oxo- and 4-oxopyridines and pyrimidines. The results are compared with experimental data in the gas phase, where the solute-solvent interactions not included in theoretical calculations are absent. Although the relative energies obtained by the MINDO/3 method appear to be superior to other semiempirical and ab initio calculations, the accuracy of the method was determined to be as low as 3-4 kcal/mol. It indicates that it is exceedingly difficult to account theoretically for intrinsic stabilities of the tautomers. The importance of various factors influencing calculated free-energy differences is discussed. Particular attention is paid to the problem of geometry optimization.

Notizen: In the usual ab initio method of calculating molecular orbitals, the number of integrals to be evaluated increases as M4, where M is the number of basis functions. In this paper, an alternative method is discussed, where the computation time increases much less violently with the number of basis functions. Matrix elements of the deformation potential are evaluated by Fourier transform methods, while matrix elements of the neutral-atom potential are evaluated by means of transferable integrals. The transferable integrals (moments of the neutral-atom potentials) can be evaluated once and for all and incorporated as input data in computer programs. In an appendix to the paper, a general expansion theorem is discussed. This theorem allows an arbitrary spherically symmetric function to be expanded about another center.

Notizen: Matrix elements of unitary group generators between spin-adapted antisymmetric states are shown to be proportional to spin matrix elements of so-called “line-up” permutations. The proportionality factor is given explicitly as a simple function of the orbital occupation numbers. If one bases the theory on ordered orbital products, the line-up permutations are given a priori. The final formulas have a very simple structure; this is a direct consequence of the fact that the spin functions have been taken to be geminally antisymmetric.

Notizen: The method of optimal relaxation to determine the eigenvalues of symmetric matrices, as proposed by Shavitt, has been adapted to solve the equation-of-motion problem. Matrices Z and Y are obtained by one diagonalization, while matrices A and B remain unchanged. This procedure is particularly useful for high-dimensional or nonorthogonal bases, if one needs only the lowest transition energies.

Notizen: The explicit expressions for the matrix elements of unitary group generators between geminally antisymmetric spin-adapted N-electron configurations in terms of the orbital occupancies and spin factors, given as spin function matrix elements of appropriate orbital permutations, are derived using the many-body time-independent diagrammatic techniques. It is also shown how this approach can be conveniently combined with graphical methods of spin algebras to obtain explicit expressions for the spin factors, once a definite coupling scheme is chosen. This method yields explicit expressions for the orbital permutations defining the spin factors. However, if desired, the explicit determination of line-up permutations can be avoided in this approach, since they are implicitly contained in the orbital diagrams. It also clearly indicates why the geminally antisymmetric spin functions have to be used when a simple formalism is desired.

Notizen: The position and intensity of the absorption bands of a number of chalcone dyes have been calculated on the basis of the free-electron molecular-orbital (FEMO) theory. The three to four absorption maxima of the chalcones are calculated by assuming the molecule to consist of two parts. The hypothetical cleavage is affected at the site of C=O bond such that first and second part of the molecule contains six and eight π electrons, respectively. Each part is then treated as an independent entity and the absorption maxima obtained by the application of joint and continuity condition of Kuhn are in agreement with the experimental values. The perturbation energy correction due to the substituted functional groups with higher electronegativity than carbon have also been made in the absorption maxima. The oscillator strengths corresponding to the values of the absorption maxima have been obtained as well.

Notizen: The effective utilization of hypervirial relations is scrutinized to improve the approximate excited-state functions in the harmonic oscillator system. A new method is presented which simultaneously employs the off-diagonal hypervirial relations with the diagonal hypervirial relation. In order to use these relations effectively, the following points are pointed out: (i) the presented method is useful to get better reasonable results for the excitation energies and the state functions; (ii) the ground state given must satisfy the virial theorem; (iii) in the hypervirial operator used here as xm, the smaller integers of m's present better results; and (iv) the employment of the comparatively small number of trial basis functions of the type exp (-γ|x|) is sufficient for reproducing the exact excited state. Especially among them, condition (ii) plays an important role. Applying all the proposals to the first and the second excited states, one gets a highly improved excitation energy, state function, and other physical quantities (e.g., transition moment and oscillator strength). The presented method is also found to be more effective than the employment of only the off-diagonal hypervirial relations or the method of the scaling operation.

Notizen: Oxygen is generated when aqueous solution of iron (III) tris(2,2′-bipyridyl), Fe(bipy)33+, are brought in contact with catalytic amounts of powdered or colloidal RuO2. The oxygen yield depends strongly on the pH, reaching a maximum between pH 7 and 8 where it corresponds to the stoichiometry of the reaction: The rate of the reaction is so fast that it occurs practically upon dissolution of Fe(bipy)33+ in the aqueous phase. In acidic media (pH 4), no O2 evolution is observed. Instead, Fe(bipy)33+ is converted to an intermediate which in the presence of RuO2 yields O2 upon neutralization.The pH profile of the O2 evolution occuring upon illumination of Ru(bipy)32+ in the presence of the cobalt complex [Co(NH3)5Cl]2+ was also investigated.The surprisingly low energy losses (160 mV) in reaction (1) makes the construction of four quanta water splitting systems feasible.

Notizen: Alkali cation complexation and bilayer transport by the bicyclic decapeptides S,S′-bis-cyclo-glycyl-L-hemicystyl-glycyl-glycyl-L-prolyl (1), S, S′-bis-cyclo-glycyl-L-hemicystyl-glycyl-glycyl-D-prolyl (2), S, S′-bis-cyclo-glycyl-L- hemicystyl-sarcosyl-sarcosyl-L-prolyl (3), and S, S′-bis-cyclo-glycyl-L-hemicystyl-sarcosyl-sarcosyl-D-prolyl (4) were analyzed according to structural, thermodynamic and kinetic criteria; valinomycin was used as a reference ionophoretic system.Structural analysis of peptide 3 with spectroscopic methods showed different conformational arrangements in the bicyclic system depending on its state of complexation. Circular dichroism indicated the presence of a multitude of conformations with differing helicities around the disulfide bridge in both free and complexed states.Thermodynamic analysis by microcalorimetry demonstrated a far lower cation selectivity among the synthetic peptides than displayed by valinomycin. Peptide 3 shows cation affinities of about two orders of magnitude higher than peptide 4, but still much lower than found for the complexes of valinomycin with K+ and Rb+. In contrast to the latter case, the complexation reactions of peptides 3 and 4 are driven by both enthalpy and entropy contributions. Neither peptide 1 and 2 nor the cyclic partial structures of all four peptides displayed significant cation complexation.A kinetic analysis of the K+-complexation by peptide 3 based on the microcalorimetry experiments showed far lower rates of cation exchange for the synthetic peptide than those reported for valinomycin. Transport studies with peptide 3 using artificial lipid bilayer membranes gave negative results. The apparent lack of ionophoretic properties of these synthetic peptides despite their considerable ability to form complexes with cations is discussed in terms of structural parameters.

Notizen: The defensive secretion of the nudibranch Phyllidia varicosa consists of two isocyanosesquiterpenes: the previously described 9-isocyanopupukeanane (1), and its 2-isomer (4), for which we report the structure and properties. The mixture originates with a sponge, Hymeniacidon sp., where it is produced in varying proportions. CD. measurements and X-ray diffraction data establish the absolute configuration of the two metabolites.

Notizen: Synthesis of some branched paraffins of high molecular weightSynthesis and properties of two series of branched paraffins of high molecular weight are described. In the course of the preparation of one of the starting materials the Wolff-Kishner reduction of a sterically hindered ketone, unstable in basic medium, has been elaborated.

Notizen: α-MSH was labelled at its tyrosine2 residue with tritium and iodine. Several synthetic routes were investigated by preparing 13 precursor or mode compounds and 4 different labelled products (via about 40 intermediates). Their melanotropic activity was determined with an in vitro frog skin assay and, for some of the compounds, with a tyrosinase assay. The tritiation was performed on [Tyr(I2)2]α-MSH by catalytic halogen/tritium exchange, yielding α-MSH of high specific radioactivity (34 Ci/mmol) and full biological activity. Iodination was studied in detail using five different techniques. An equimolar chloramine T procedure proved to be the most convenient and reproducible method, resulting in monoiodinated α-MSH containing 99% of the label in position 2. The biological activity was 50% that of α-MSH; the specific radioactivity, determined in a competitive binding assay with a highly specific α-MSH antiserum and [Tyr(I)2]α-MSH as competitor, was 1530 Ci/mmol. The labelling techniques and the bioligical results are discussed.

Notizen: Leucine9-α-melanotropin ([Leu9]α-MSH) was synthesized in homogeneous solution by a fragment condensation approach, and it was assayed for its melanophore-dispersing and its tyrosinase-stimulating activity with a reflectometric in vitro frog skin assay and with cultured mouse melanoma cells, respectively. In both assay systems, parallel log dose-response curves were obtained for ([Leu9)]α-MSH and α-MSH; however, in the frog skin assay the activity of the title compound was 1 middot; 1010 Units/mmol, i.e. 25% of the activity of α-MSH, whereas its tyrosinasestimulating potency was only 1% compared to α-MSH (EC50= 2.5 · 10-7M). This indicates a major difference in the recognition/stimulation process of the receptors of the two cell types.

Notizen: 2-Pyridine sulfenyl chloride (PS-Cl) is a useful reagent for simultaneously deprotecting and activating the mercapto-group of cysteine and of cysteine-peptides preliminary to disufide-bond formation. The S-protecting groups that are amenable to this reaction include trityl, diphenylmethyl, acetamidomethyl, t-butyl, and t-butylsulfenyl.

Notizen: Attempted Synthesis of Nonafulvenes and of NonaheptafulvaleneThe reaction of cyclononatetraenide with α-bromobenzyl acetate (6) as well as with 1,1-dihalodimethylether gives at -50°, instead of the expected cyclononatetraenes, bicyclo[6.1.0]nona-2,4,6-triene derivatives 10d and 16 (Scheme 3 and 5, respectively). It seems that in some cases the well known thermally disrotative valence isomerization of cyclononatetraenes 7 to 3a, 7a-dihydroindenes 8 is much slower than the formation of bicyclo[6.1.0]nona-2,4,6-trienes of the type 10 and 16. This type of reaction hurts the Woodward-Hoffmann rules.Possible precursors of the attractive nonaheptafulvalene are prepared by reaction of acetoxy-tropylium fluoborate (19a) as well as of bromo-tropylium bromide (19b) with lithium-cyclononatetraenide (Scheme 8). So far, the attempted gas-phase pyrolysis of the precursors 21a and 21b failed to give nonaheptafulvalene (5).

Notizen: Kinetic Study of the Distribution of Electrically Neutral Ionophores between a Solvent Polymeric Membrane and an Aqueous PhaseThe kinetic behaviour of a series of ligands in the transfer from a solvent polymeric membrane into a stirred aqueous phase was investigated and compared with theoretical kinetic models. It was found that the transfer of ligands with low lipophilicity was controlled by the diffusion in the membrane phase, and that of ligands with high lipophilicity was controlled by the exchange reaction at the phase boundary and/or the diffusion through the unstirred Nernst diffusion layer. The diffusion coefficients in the membrane decrease drastically on increase of the content of the polymer in the membrane and are nearly independent of the size and lipophilicity of the ligand, whereas the overall transfer coefficient through the boudary region does not depend on the polymer content but decreases with increasing lipophilicity of the ionophore.

Notizen: Preparation of Stilbenyl Derivatives of IsoxazolesSchiff's bases derived from 3- and 5-(p-formylphenyl)-phenylisoxazoles and o- or p-chloroaniline are reacted with various p-tolyl substituted aromatic heterocycles in the presence of dimethylformamide and potassium hydroxide or potassium t-but-oxide to yield the corresponding heterocyclic substituted stilbenes (‘Anil synthesis’). 5-[4-(Chlorphenylimino-methyl)phenyl]-phenylisoxazoles react less readily than the corresponding 3-isomers.

Notizen: Synthesis of a 33-membered Polyaminolactam by Use of the Zip-reactionThe pentaamino lactam derivative 11 was synthesized from the 13-membered tosylaminolactam 2. The prolongation of the side chain was achieved using the phthalimido derivative 3. After removal of the protecting groups the resulting base 11 was treated with KAPA reagent (1,3-propanediamine/potassium-3-aminopropyl-amid). By zip-reaction the 33-membered 13, 17, 21, 25, 29-pentaaza-32-dotriacontanelactam (1) was formed in 85% yield.

Notizen: Influence of imidazole, metal salts and mixtures of imidazole/metal salt on ‘prebiotic’ condensation reactions induced by polyphosphates in aqueous solutionsIn the presence of imidazole, aqueous solutions 0.1 M in glycine and 0.1 M in sodium trimetaphosphate, at pH 8.0-8.6 and room temperature, yield after 14 days up to 3% of triglycine. Addition of Cd2+ or Zn2+ decreases the yields, while Mg2+ increases them slightly.The significance of the systems trimetaphosphate/imidazole and trimetaphosphate/imidazole/magnesium salt in the promotion of ‘prebiotic’ condensation reactions in aqueous solutions, especially the condensation of amino acids, is discussed.

Notizen: Synthesis of 3β-acetoxy-24-aza-24-desoxa-xymalogeninStarting from the pregnenolone-derivative 1 we report the synthesis of the possibly cardiac-active compound 24-aza-24-desoxa-xysmalogenin 15.

Notizen: Cynaratriol, a new guajanolide from Cynara cardunculus L. and C. scolymus L. (Compositae)A new guajanolide given the name cynaratriol (4) was isolated from the leaves of Cynara cardunculus L The structure of 4 and its derivatives 3, 11, 13-triacetylcynaratriol (5) and 3, 13-dibenzoyl-cynaratriol (6) was deduced on the basis of IR.-, 1H-NMR.-, 13C-NMR.- and mass spectroscopic data. 4 is also present in C. Scolymus L. as shown by GC./MS. analysis. The same absolute configuration is suggested for 4 as found for all other Cynara sesquiterpenes.

Notizen: Benzimidazole and benzothiazole sugar derivativesSimple aldehydosugars such as 1 or 2, by reaction with o-phenylenediamine, gave the corresponding benzimidazoles 3 and 4. Whereas the unperturbed α, β-unsaturated aldehydosugar D gave the benzodiazepine E upon treatment with o-phenylenediamine, the formyl-bearing alkenyl acetals 5 and 8 led, in the same conditions, to the benzimidazoles 6 and 9 respectively or, on reaction with o-aminothiophenol, to the benzothiazoles 7 and 10 respectively. This difference in reactivity is explained by the electrondonor ability of the oxygen atom of the alkenyl acetal function as shown by the 13C-RMN. spectra.

Notizen: Use of the Wittig reaction for the synthesis of derivatives of bromoenosuloses and bromoenuronic estersTreatment of 3-O-benzyl (or 3-O-methyl)-1, 2-O-isopropylidene-α-D-xylo-pentodialdo-1, 4-furanoses (2 or 1) with acetylbromomethylidenetriphenylphosphorane (3), benzoylbromomethylidenetriphenylphosphorane (4) or bromoethoxycarbonylmethylidenetriphenylphosphorane (5) gave in good to excellent yields the expected enose (6--11). In all cases but one (8 where some 10% of the E-isomer was formed) the reaction led to the exclusive formation of the Z-isomer whose configuration was established by NMR.

Notizen: 24-Isopropycholesterol (1) and 22-dehydro-24-isopropylcholesterol 2 have been isolated as the only sterols from an Australian sponge of the genus Pseudaxinyssa. Structures have been deduced from spectroscopic data.

Notizen: Mixed acetals 7 of benzeneseleninylacetaldehyde, prepared by a simple 2-step procedure from mono- and bicyclic allylic alcohols 5, undergo benzeneselenenic acid elimination to transient ketene acetals 8 which afford γ, δ-unsaturated esters 9 via the ester Claisen rearrangement (Scheme 2). Under the same conditions selenoxide 7h derived from benzyl alcohol 5h is converted back to benzyl alcohol with the concomitant formation of ethylphenylselenoacetate 12.

Notizen: Thermal Cyclization of α-Alkynones to 2-CyclopentenonesGas phase thermolysis at 600-740° of substituted 1-pentyn-3-ones (α-alkynones), which are easily prepared by acylation of trimethylsilyl acetylenes, leads to substituted 2-cyclopentenones. The intramolecular formation of a new C, C-bond between an acetylenic and a non-activated carbon atom is accompanied by a [1,2]-migration of one of the substituents at the triple bond. This novel ‘-alkynone cyclization’ reaction may be explained by postulating an alkylidene carbene intermediate which inserts into a C,H-bond five carbon atoms away at the non-acetylenic part of the ketone. Several examples demonstrate that the α-alkynone cyclization offers a simple tool for the preparation of certain monocyclic, bicyclic and spiro compounds containing a 2-cyclopentenone moiety.

Notizen: 8-Benzoyl-9-deuterio-naphtho [de-2.3.4]bicyclo [3.2.2]nona-2,6,8-triene (1) rearranged quantitatively in a photochemical di-π-methane-type process to 2-, 6-, and 9-deuteriated 1-benzoyl-naphtho [de-2.3.4]tricyclo [4.3.0.02,9]nona-2, 6-diene (8a-c). The phenylhydroxymethyl analogue 2 underwent a similar regioselective rearrangement to 9a-c. The rearrangement 1 → 8a-c is proposed to proceed along three reaction paths evolving from two primary photochemical processes of naphthylvinyl and vinyl-vinyl bonding (1 → 3 + 6). Evidence for a competition between several paths and involvement of biradical intermediates derives from changes in the isotopomeric composition with temperature, and from laser flash detection (λexc 353 nm) of a transient. The dependence of the quantum yield for product formation from 1 on excitation wavelength and sensitizer triplet energy leads to the conclusion that reaction to the primary biradicals occurs directly from the S1 (n, π*) and T2 (n, π* ) states, and that reaction from T1 (π, π*) and from S2 (π, π*) proceed either directly or via T2.

Notizen: Formation of 4-, 5- and 6-membered heterocycles by ambidoselective cyclization of enolate anionsN-Acylmethyl-N-chloracetyl-2,6-dimethylanilines 4 were cyclized with base to 4-, 5- or 6-membered ring compounds, depending on the substituent R2 (Scheme 2). All products can be rationalized as derived from the intermediate enolate anions a and b. The enolate anion a reacts by intramolecular alkylation to yield either 1, 4-oxazines 5 or azetidines 6 (Schemes 1, 3 and 7). The regioselectivity observed is expected on the basis of the allopolarization principle. The enolate anion b reacts only with formation of a new C—C bond (Scheme 5). Comparison with the behaviour of the 2, 6-unsubstituted anilines 9, 1a and 12, shows a strong dependence not only on electronic but also on steric factors (Scheme 4 and 6).

Notizen: Bacteriochlorophyll aGg and Bacteriopheophytin ap in Photosynthetic Reaction Centers from Rhodospirillum rubrum G-9+In photosynthetically active reaction centers from Rhodospirillum rubrum G-9+, the magnesium complex bacteriochlorophyll a contains geranylgeraniol as the alcohol component, while the metal-free bacteriopheophytin a contains phytol instead. These pigments bacteriochlorophyll aGg (4) and bacteriopheophytin aP (1) were isolated from reaction center preparations in a ratio of 2:1 and (after demetallation of 4) identified as bacteriopheophytin aGg (2), and aP (1) by comparison with authentic samples (UV./VIS., CD. and mass spectra as well as mixed HPLC.).

Notizen: 1H- and 13C-NMR.-spectra of 6-(p-X-phenyl)fulvenesThe 1H- and 13C-NMR.-spectra of a series of 6-(p-X-phenyl)fulvenes 3, measured at 9.39 T (93.9 kgauss), have been analyzed. In these compounds, electronic effects due to the substituent X clearly exert changes in chemical shifts as well as in coupling constants in the 5-membered ring. Small changes in bond length are observed by comparison of the vicinal 1H, 1H-coupling constants, whereas changes in charge densities linearly influence the chemical shifts of C(5), C(2) and C(3).

Notizen: Epoxidation of 3-phenoxycyclohexene 5 with m-chloro-perbenzoic acid gave 6 and 7 in a ratio of 9:1. These two epoxides were heated with a series of amines to give the aminophenoxycyclohexanol derivatives 1 and 2 respectively; in all cases the reaction was regio- and stereospecific. Two methods based on the principle of neighbouring group participation were developed to synthesize the cis-amino alcohols 3 and 4. In the first, the hydroxy group was used to introduce an amine function at the vicinal carbon atom. In the second method, the amino group served as the point of reference and the configuration of the adjacent alcohol function was inverted.

Notizen: Excitation of p-Chloranil (CA) in propylcyanide (PrCN) at room temperature leads to rapid production of 3CA* which decays predominantly to CAH· with kd0 = 1.6 · 105 s-1. Observation of a photoinduced current suggests simultaneous production of CA- formed by electron transfer quenching of 3CA* by the medium. Added naphthalene (NP) quenches 3CA* with kq = 7.0 · 109M-1S-1; NP+ is unambigously identified as product (besides CA-) of the electron transfer process. Dissociation of the ion pair occurs with essentially unit probability. Higher concentrations of NP lead to the formation of (NP)+2. Pertinent spectroscopic parameters established for NP+ under the conditions used are λmax = 685 nm (∊ = 2970) using the known parameters of CA\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{+ \atop \dot{}} $\end{document} as reference. NP+ and CA\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{+ \atop \dot{}} $\end{document} decay by charge annihilation with kr = 4.5 · 109 M-1S-1. The deviation from the diffusion controlled rate constant expected for ionic species, is discussed in view of the spin characteristics of the process. Comparison with two other ion recombination reactions leads to the conclusion that ‘inverted behaviour’ as expected from Marcus' theory does also not show up for backward e--transfer between two ions (produced by forward e--transfer between two neutrals). Residual absorptions in the system are ascribed to CAH·, tentatively proposed to originate from H+-abstraction by CA\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{+ \atop \dot{}} $\end{document} from the solvent. NP+ appears to be a rather stable species with respect to the medium if the latter is meticulously purified.

Notizen: Because of its overall steric resemblance to the phenylalanine analogue, carboranylalanine, the title compound was prepared by the modified Strecker synthesis of Patel & Worsley. The use of (S)-(-)-α-methylbenzylamine in the synthesis, the positive trend of [α]D with increasing protonation, and the thin-layer chromatographic behaviour of synthetic diastereomeric dipeptides are strong indications that the configuration at the asymmetric carbon atom is S (natural L). Its optical purity was ascertained by purification via the quinine and ephedrine salts of t-butoxy-carbonyl-adamantylalanine. The new amino acid shall be used for studies of structure-activity relationships of phenylalanine and leucine residues in biologically active peptides. In addition, a convenient synthesis in excellent yield of the starting material, 2-(1-adamantyl)-ethanal, by Pfitzner-Moffat oxidation of 2-(1-adamantyl)-ethanol is described.

Notizen: N-Deacetylcolchiceine (7), readily available from colchicine (1), was converted into N-trifluoroacetyl-deacetylcolchiceine (8). Methylation of 8 with methyl iodide in the presence of potassium carbonate afforded a mixture of N-trifluoroacetyl-demecolcine (10) and its isomer 11. The mixture of 10 and 11 was detrifluoroacetylated and separated by chromatography to afford demecolcine (2) and isodemecolcine (12). A more practical route to 2 started with 8, and gave N-trifluoroacetyl-deacetylcolchicine (13) and its isomer 14 after O-methylation with diazomethane. N-Methylation of 13 and 14 with methyl iodide and potassium carbonate afforded 10 and 11. The overall yield in the conversion of colchicine (1) into demecolcine (2) via 7, 8 and 13 was 55%.

Notizen: Sugar triazenes and benzotriazinesSeveral triazenylsugars have been prepared, generally in good yields, by treating an amino sugar with a substituted benzenediazonium salt. The triazenylsugars bearing a hydrogen atom on the triazenyl group are acetylated on the nitrogen atom closest to the glycosyl moiety (N(1)), even when the proton exchanged sites between N(1) and N(3). When an acetyl or a methoxycarbonyl group was present in the ortho position of the benzene ring cyclization took place leading to a 3,4-dihydro-4-methylidene-1,2,3-benzo[d]triazine or a 3,4-dihydro-1,2,3-benzo[d]triazin-4-one respectively.

Notizen: Acetoxythallation of (-)-elemol acetate (1b) yields a diacetate 2b which after treatment with lithium aluminium hydride gives (-)-guai-1 (10)-ene-4α, 11-diol (2a). (-)-Elemol (1a) is converted to (-)-selina-4α, 11-diol (9, cryptomeridiol) by hydroxymercuration followed by reductive demercuration. (+)-γg-Elemene (5) similarly yields (+)-selin-7(11)-en-4α-ol (11, juniper camphor). The stereochemistry and mechanism of these metal salt-induced olefinic cyclization and their biogenetic implication are discussed.

Notizen: Antitumor showdomycin analoguesA series of 3-glycosylidenesuccinimides (3) and 3-glycosylidene-1-phenyl-succinimides (5) have been prepared in good yields using a Wittig reaction. In each case, the preponderant, or even the exclusive, isomer formed was E. As expected from orbital considerations, the contribution to the conformational equilibrium of the rotamer whose H—C (γ) and H—C(δ) bonds were antiparallel was low. One of these succinimide derivatives 3a showed interesting anticancer activity, similar to that of the sugar enone C. These compounds probably act as somewhat selective alkylating agents.

Notizen: Different lipophilic β-diketones have been prepared. Some preferably transport Mg2+ and Ca2+ through PVC-based liquid membranes when a pH-gradient is applied across the membrane. A theoretical model is presented that allows a description of potentiometrically determined ion selectivities as well as transport selectivities obtained under zero current and electrodialytic conditions, respectively. The expectations based on this model are in agreement with the experimental evidence presented. Some membrane systems have potentiality for their application in the measurement of water hardness.

Notizen: Methylmercury(II) transfer from two heterocyclic thiones to a wide variety of other ligands and the reverse reaction have been investigated by the temperature-jump method. The reactions are almost diffusion controlled, even when the free energy difference is negligible. The only exceptions are reactions to and from hydroxide. They are about hundred times slower than those with other ligands of comparable stability at zero free energy difference. This is in agreement with the behaviour of hydroxide in other methylmercury(II) exchange reactions. They follow an associative reaction mechanism. An empirical correlation of rate-and equilibrium-constants for atom transfer reactions is proposed. This equation shows some similarities to that of the Marcus type for atom transfer. However, the proposed equation not only describes reactions governed by an associative mechanism, but also those of dissociative type and cases between the two extremes.

Notizen: Carotenoid Glycosyl Esters. The Synthesis of Crocetin-di-(β-D-glucosyl) Ester. A New Method for the Selective Esterification of Unprotected β-D-GlucoseThe naturally occurring crocetin-di-(β-D-glucosyl) ester is easily synthesized by the reaction of crocetin-di-imidazolide or crocetin-di-(1,2,4-triazolide) and unprotected β-D-glucose in pyridine in presence of a base (Scheme 4). Under the described experimental conditions the esterification takes place exclusively at the anomeric C-atom and furthermore produces only the β-anomer. It is the first time that an unprotected carbohydrate has been used for the selective synthesis of glucosyl esters at the anomeric C-atom. This represents the major advantage of this new method.

Notizen: The bis(methylthio)benzenes 3a-3c are oxidized to the methylsulfinyl-methylthiobenzenes 4a-4c on a Pt-anode in good yields.

Notizen: The C,C-bond cleavage which occurs during chromic acid oxidation of t-butylphenylmethanol (1) and 1,2-diphenylethanol (2) to the extent of up to 67% is reduced to 3% for 1 and 13% for 2 when the reaction is run in acetone, and totally suppressed upon co-oxidation of the alcohols 1 and 2 with oxalic acid. Similarly, the yield of 7-norbornanone obtained from 7-norbornanol (7) is raised in going from acetic acid (24%) to acetone (41%) and approaches 100% in the co-oxidation. With the co-oxidation 5-endo-bicyclo [2.1.1]hexanol (3) is converted to the corresponding ketone in 54% yield. Mechanistic implications of these results are discussed.

Notizen: Carbocyclic Compounds from Monosaccharides. 1. Transformations in the Glucose SeriesA method for the preparation of pentasubstituted cyclopentanes from monosaccharides is presented, involving two crucial steps, viz. the reductive fragmentation of 5-bromo-5-deoxyglucosides (such as 10, 17 and 23, see Scheme 3) with Zn or butyl lithium yielding 5,6-dideoxy-hex-5-enoses (such as 11 and 24, see Schemes 3 and 4), and the subsequent cyclization of these hexenoses with N-methyl- or N-(alkoxyalkyl)hydroxylamines (via the corresponding nitrones) to form cyclopentano-isoxazolidines (see Scheme 2). Thus, the glucosides 17 and 23 were converted diastereoselectively and in good yields into the cyclopentano-isoxazolidines 27 and 45 (Schemes 5 and 7), which were characterized by their transformation into various derivatives. 27 and 45 were correlated through the common derivative 62. The configuration of the cyclization products were established by pyrolysis of the N-oxide 65 to the enol ether 67 (Scheme 10).

Notizen: The Bredt olefins bicyclo [3.3.1]non-1-ene (2), bicyclo [4.2.1]non-1 (8)-ene (3), and bicyclo [4.2.1]non-1 (2)-ene (4) react rapidly with 1,3-dipoles such as diazomethane, phenyl azide, and mesitonitrile oxide to yield mixtures of two regioisomeric cycloadducts 10, 11 and 12, respectively. On the contrary, cycloaddition to the comparable monocyclic 1-methyl-(E)-cyclooctene (5) is fairly regioselective. 2-Methylnorborn-2-ene (6) gives one isomer with mesitonitrile oxide (as do less strained olefins), but mixtures with diazomethane and phenyl azide. 1H-NMR. and 13C-NMR. spectra of the cycloadducts are reported. The results are discussed in the light of frontier molecular orbital theory.

Notizen: The aim of the paper is to elucidate the problem of the regular changes in the properties of f-elements represented by the double-double effect. It is pointed out that because of the half-filled shell and double-double effects the f-element properties cannot be plotted as a linear function of the L-quantum number, as suggested by Sinha [1][2].

Notizen: The anomeric effect as a conformation determining factor for 3-cyano-perhydro-1,2-benzoxazinesAn unusual population of conformer II is found by 1H-NMR. spectroscopy in the conformation equilibrium I⇄ II of 1b (Fig. 3) in which the non-bonding nitrogen electronpair is anti-periplanar to the C—CN bond. This finding is interpreted in terms of a generalized anomeric effect operating in the α-cyano-hydroxylamin-ether structural unit.

Notizen: Selective ionophores of extreme lipophilicity for liquid membrane electrodesLipophilic ionophores of the type diether diamides have been prepared. Their lipophilicity is up to 7 orders of magnitude higher than the one of the most lipophilic ion carriers used as selective components in liquid membrane electrodes reported so far. For such ion carriers of extremely high lipophilicity kinetic limitations of the carrier induced ion transfer between aqueous and membrane phase usually dominate and heavily disturb the electromotive behavior of the membrane electrode. These limitations are absent only in those cases where most of the lipophilic segments of the carrier may remain in the membrane phase while the segments with the coordination sites are exposed to the aqueous phase during the transfer process.

Notizen: The values nJ (195Pt, 14N) are shown to be measurable directly from the 195Pt spectrum for a variety of complexes containing nitrogen ligands. The sample temperature can play an important role in determining the width of the 195Pt signal. 195Pt chemical shifts for the complexes trans-[PtCl2(C2H4) (substituted pyridine)] have been measured. Methyl substitution at the 2- and 6-positions produces a relatively large downfield shift.

Notizen: Reactions of oxygenated cobalt(II) complexes. XII. A binuclear μ-peroxodicobalt(III) complex with a macrocyclic bridging ringXI: siehe [1].Singly bridged [(tren) (NH3) CoO2(NH3) (tren)]4+ reacts with excess tren by replacement of NH3 in cis-position to the peroxo group and formation of a new type of doubly bridged μ-peroxo complex. An X-ray structure determination of [(tren)-Co(O2, tren)Co(tren)] (ClO4)4 · 2 H2O showed that the additional tren forms a macrocyclic bridging ring. The conformation of the CoOOCo group is transoid with a dihedral angle of 20°. The crystals are monoclinic with space group P21/c. The lattice constants are a = 9,798, b = 26,385, c = 16,385 Å, β = 110,2° with four formula units in the cell. The final R value is 0,124. ClO4- anions are disordered.The reactions of [(tren)Co(O2, tren)Co(tren)]4+ in aqueous solution are compared with those of [(tren) (NH3) CoO2Co (NH3tren)]4+. In acidic solution the new complex mainly decomposes to CoII and O2. In alcaline medium the bridging tren is replaced by an OH bridge, forming the well characterized doubly bridged [(tren)-Co(O2, OH)Co(tren)]3+. Differing from the singly bridged bis (ammino) complex, the reactions of which show no pH dependency at all, the decomposition of the tren bridged complex is H+-catalyzed. The kinetic data have been interpreted as (i) preceding fast protonation step which is followed by a conformational change of the bridging ring, (ii) acid hydrolysis of a Co-μ-tren bond and (iii) fast cleavage of the Co-OO bond which is labilized by coordinated H2O.

Notizen: The preparation of the nucleophile trans-[RuCl(NO)(1)], where 1 is the bidentate ligand Ph2PCH2C18CH2PPh2, and of the five-coordinate species [RuCl(CO)(NO)(1)], [RuCl(CO)(NO)(Ph2PCH2Ph)2] and [RuCl(NO)(2)(1)] are reported.The crystal structure of [RuCl(CO)(NO)(1)] shows that the coordination around the metal atom is distorted trigonal bipyramidal with the phosphorus atoms in axial positions. The Ru—N—O bond angle is 142.8°. 1H- and 31P-NMR. and \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \nu $\end{document}NO IR.-data for the above complexes are reported and related to the coordination geometry.

Notizen: The rearrangement products obtained upon reduction of 1,6-methano[10]-annulene (1) and its 11-halogen derivatives have been studied by ESR. and, in part, by ENDOR. spectroscopy. These derivatives comprise 11,11-difluoro- (2), 11-fluoro- (3), 11,11-dichloro- (4) and 11-bromo-1,6-methano[10]annulene (5), as well as the 2,5,7,10-tetradeuteriated compounds 2-D4 and 3-D4. The studies of the secondary products in question have been initiated by the finding that the radical anion of 11,11-dimethyltricyclo[4.4.1.01,6]undeca-2,4,7,9-tetraene (12), i.e., the prevailing valence isomer of 11,11-dimethyl-1,6-methano[10]annulene, undergoes above 163 K a rearrangement to the radical anion of 5,5-dimethylbenzocycloheptene (14). A rearrangement of this kind also occurs for the radical anion of the parent compound 1, albeit only above 323 K. The lower reactivity of 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} relative to 12\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} is rationalized by the assumption that the first and rate determining step in the case of 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} is the valence isomerization to the radical anion of tricyclo[4.4.1.01,6]undeca-2,4,7,9-tetraene (1a). In the reducing medium used in such reactions (potassium in 1,2-dimethoxyethane), the final paramagnetic product of 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} is not 5H-benzocycloheptene (15), but the benzotropylium radical dianion (). This product () is also obtained from the radical anions of the halogen-substituted 1,6-methano[10]annulenes, 2 to 5, in the same medium. The temperatures required for the conversion of 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 3\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} into lie above 293 and 243 K, respectively, whereas the short-lived species 4\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 5\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} undergo such a rearrangement already at 163 K. The stability of the four halogen-substituted radical anions thus decreases in the sequence 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} 〉 3\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} 〉 4\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} ≈ 5\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}. Replacement of 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 3\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} by 2-D4\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 3-D4\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}, respectively, leads to 1,4,5,8-tetradeuteriobenzotropylium radical dianion (). Experimental evidence and theoretical arguments indicate that the rearrangements in question are initiated by a loss of one (3\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 5\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}) or two (2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 4\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}) halogen atoms. Such a reaction step must involve the intermediacy of the radical 19 · (see below) which rapidly isomerizes to the benzotropylium radical 16:. Support for the transient existence of 19. is provided by the thermolysis of 1,6-methano [10]annulene-11-t-butylperoxyester (6) which yields 16. in a temperature dependent equilibrium with a mixture of its dimers (162).In the hitherto unreported ESR. spectra of 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}. and 3\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}, the coupling constants of the ring protons differ considerably from the analogous values for the radical anions of other 1,6-bridged [10]annulenes. These differences strongly suggest that the fluoro-substitution substantially affects the character of the singly occupied orbital.

Notizen: On ultraviolet irradiation of the cyclopent-2-enyl methyl ketones 1a-c at -54° ≤ t ≤ 139°, photo-CIDNP. effects of the starting ketones, the 1,3-acetyl shifted isomers (2), and radical disproportionation and combination products (4-7) were observed. These effects show a unique dependence of the polarization phase on temperature which is a novel feature in photo-CIDNP. studies. The results of the investigation, which also included experiments using triplet quenchers, triplet sensitizers and radical scavengers, are rationalized in terms of Schemes 2 and 3.α-Cleavage is a major excited-state reaction of 1a-c on direct irradiation. Temperature-activated α-cleavage (kaS(t)) to the radical pair R · · R′1 and intersystem crossing (kisc) to the T2 state are among the competing S1 deactivation processes. The T2 state in turn cleaves (kaT2) to R · · R′3 A ‘low-temperature range’ with kisc ≫ kaS(t) and a ‘high-temperature range’ with kaS(t) ≫ kisc exhibiting preferential reactivity from the T2 and S1 states, respectively, can be defined for all three β,γ-unsaturated ketones 1a-c.

Notizen: Spiro-β-lactams from [2+2]-Cycloaddition of Ketenes to IminolactonesIminolactones (‘Isoimides’) derived from maleic anhydride and amines are shown to react with various ketenes in a [2+2]-cycloaddition mode. Either preformed ketenes or the combination acid chloride/tertiary amine can be used as reagent. The reaction products have been assigned the spiro-β-lactam structure. Unsubstituted ketene is inert under the reaction conditions. It is possible to synthesize the spiro-β-lactams in a one-pot procedure, starting from a mixture of maleic anhydride/amine and excess dialkylketene.

Notizen: The disilane/disilylmethane rearrangement of an optically active disilanyl sulfide 9B was used to prepare an optically active disilylalkene 10 whose absolute configuration was established by X-ray analysis of the bromo derivative 13 (P21, a = 7.847 (3) Å, b = 9.487 (3) Å, c = 20.010 (8) Å, β = 82.28° (3), Z = 2). Acylation of 10 furnished an optically active ketone 14, which was degraded to 16, a compound of known absolute configuration. The enantiomeric excess of 10 was determined by alkylation with an optically active lithium compound and that of 14 by an optically active NMR.-shift reagent. The SE′ reaction 10 → 14 was thus shown to proceed with 94% (97% syn/3% anti) stereoselectivity.