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  • 1980-1984  (413)
  • 1920-1924
  • 1905-1909
  • Biochemistry
  • Industrial Chemistry and Chemical Engineering
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Acta neuropathologica 65 (1984), S. 99-109 
    ISSN: 1432-0533
    Keywords: Lipidosis ; Brain ; Human ; Gaucher disease ; Morphology ; Biochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The Norrbottnian type of Gaucher disease is characterized by infantile or juvenile onset and variable degrees of neurological symptoms, some of which develop only after splenectomy. A full neuropathological description of this type of Gaucher disease has not been reported previously. The brains of five patients were examined morphologically and biochemically. All presented typical accumulations of glucosylceramide storing cells in the adventitia of vessels in the cerebral and cerebellar sub-cortical white matter (s.c.w.m.). There were differences between the five cases with regard to the accumulation of adventitial storage cells and to the fatty acid pattern of the glucosylceramide isolated from the s.c.w.m., which implicate that the accumulation of glucosylceramide in adventitial cells in the brain is dependent on the generalized lipid storage process and enhanced by splenectomy. Loss of neurones and myelin was noted in the vicinity of accumulations of storage cells in two cases. The five cases whowed varying degrees of nerve cell loss, satellitosis and neuronophagia. Lipofuscin with simple and complex lipids but no glycolipids could be demonstrated in neurones light-microscopically. Utrastructural examination revealed inclusion bodies with bilayers in neurones of the cerebral and cerebellar cortex, dentate nucleus and pons. Because of the bilayered structure of Gaucher cell inclusions the bilayers in neurones are assumed to be formed by glucosylceramide. The fatty acid composition of glucosylceramide isolated from cerebral cortex in all cases suggested that cerebral gangliosides were its main precursor. The highest levels of psychosine (glucosylsphingosine) were seen in the cases with the most advanced nerve cell loss. The morphological and biochemical findings indicate that the neuronopathic process is associated with accumulation of glucosylceramide and psychosine in neurones.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 123 (1984), S. 140-151 
    ISSN: 1615-6102
    Keywords: Biochemistry ; Cell wall ; Chitin ; Cytochemistry ; Glomus epigaeum ; Spore
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The cell wall of the spore ofGlomus epigaeum Daniels and Trappe, which has fibrillar subunits regularly arranged in arcs, was studied ultrastructurally and biochemically. The periodic acid/thiocarbohydrazide/silver proteinate (PATAg) reaction for polysaccharide location (Thiéry 1967) and the silver methenamine reaction for protein location (Swift 1968) were performed on whole spores, progressively alkaline-extracted and autoclaved spores, and untreated and alkaline-extracted cell wall fractions. The cytochemical results and those obtained from frozen sections indicated that the fibrils forming the main structure of the outer and inner wall consist of chitin. Quantitative determinations showed that chitin is the most important component (47%) of the alkali-insoluble residue and represents 27.2% of the whole cell wall fraction. It occurs predominantly as the acetylated form. Cytochemical and biochemical observations showed that the matrix surrounding the fibrils is made of alkali-soluble, PATAg positive polysaccharides (4.98% of the whole cell wall fraction). Monomers were identified by gas liquid chromatography as being γ-lactone of glucuronic acid, and glucose, rhamnose and mannose. Alkali-soluble proteins are an important part of the matrix, being spread mostly throughout the inner wall and constituting a large portion (55.1 %) of the alkali-soluble fraction. From the results we derive a model in which the chemical components are interconnected to build up a macromolecular network, in agreement with electron-microscopic observations.
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  • 3
    ISSN: 1615-6102
    Keywords: Insect midgut ; Lipid absorption ; Cytology ; Biochemistry ; Radioactive oleic acid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Voluntary uptake of triolein, margarine, and lipid-rich natural food (Tubifex) by fasting dragonfly larvae (Aeshna cyanea) led to heavy accumulations of lipid absorption droplets in the enterocytes within 2 days, while subsequent lipid clearance of the midgut epithelium took several weeks depending on the ingested lipid load. No endocytotic lipid uptake was observed after application of a molecular-dispersed fat dye. The smallest lipid droplets first appeared in the subapical groundplasm of the enterocytes and showed a reversible increase in size on their way towards the base. Lipid droplets were also observed at appropriate intervals after oral administration of oleic acid, after feeding margarine in the cold, and after injection of triolein into the isolated midgut. Comparative biochemical analysis after triolein feeding evidenced release of lipase and hydrolytic liberation of FA from TG in the midgut lumen, as well as time-dependent accumulations of TG in the midgut epithelium and of DG in the hemolymph. Oral injection of [14C] oleic acid was followed by its rapid absorption into the midgut epithelium, where it was utilized for the synthesis of MG and esterification to DG and TG. Discharge of radioactive lipid into the hemolymph occurred in the form of FA and DG, while the rectal fat body showed approximately equal labeling of the FA, DG, and TG fractions.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 37-43 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Iterative numerical analysis methods, similar to those used for ray tracing in electron and ion guns, have been employed to calculate the electrical potential distribution in the vicinity of the orifice of an electrical sensing zone (esz) instrument. In particular, the electrical potential across the mouth of the orifice is considered and the effects of numerically bevelling the sharp peripheral edge are demonstrated.The results support the empirical equation: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm d}\phi {\rm /d}x \sim 1 + \alpha '\{(r/R)/(1 - r/R)\} ^{\beta '} $$\end{document} for the axial component of the potential gradient, dφ/dx, at the mouth of the orifice expressed as a function of the radial distance, r, from the centre of the orifice of radius R; α′ and β′ are empirical constants. This equation was derived from previously reported experimental data on relative shifts and heights of artefact peaks apparent on the coarse side of size distributions measured via the esz method on a series of latex copolymers.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 143-152 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper deals with the influence of particle shape and particle size distribution on the fluidisation behaviour of granular activated carbon in the aqueous phase. Methods for relating the degree of expansion, as a function of liquid velocity, to particle shape and particle size distribution are discussed and tested. Two different types of activated carbon, both containing irregularly shaped particles but with differences in shape, are used to test the models discussed. A tentative method which takes into account the influence of water temperature on fluidisation behaviour is proposed.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 171-177 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Experimental methods to determine minimum sintering temperatures of a variety of granules such as polymers, glass, coal, inorganic salts, etc. are presented. These methods include the use of a dilatometer in which the contraction-dilation characteristics of a small sample is measured, a differential scanning calorimeter test and an Instron machine by which yield strengths are measured. It is clearly shown that for the majority of materials studied, the different methods give similar values for the minimum sintering temperature but that the dilatometer experiment is the simplest as well as the most reliable method. Since the minimum sintering temperature is always less than the solid's melting point, an efficient method of measuring this temperature is very important for all fluidizable granules subjected to high temperatures. The danger of agglomeration during fluidization increases tremendously at temperatures higher than minimum sintering and therefore special precautions must be taken to avoid defluidization under these conditions.
    Additional Material: 15 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 14-21 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Mandelbrot has extended the concept of classical dimensional description of physical systems to include fractional values which describe the ruggedness of a structure. Thus if one has a dimension of 1.2 one knows that one is dealing with a line which fills space more efficiently than a line which has dimension of 1.1. A mathematical curve which exhibits ideal fractal structure has the same appearance when viewed at any level of scrutiny. Kaye and co-workers applied the concept of fractal mathematics to the description of the boundaries of fineparticle profiles. As demonstrated in this communication a natural fractal boundary in contrast with an ideal fractal can exhibit different fractal structures over different ranges of scrutiny. As a consequence one should always report the scale of scrutiny employed when examining the fractal structure of natural boundaries. Data is presented demonstrating the fractal/euclidean boundary structure manifest by aluminum shot fineparticles examined at various levels of scrutiny. The relationship between fractal descriptors of fineparticle boundaries and the Fourier analysis of geometric signature waveforms for describing the structure of fineparticles is explored. Data presented by Flook on the physical significance of the various co-efficients of a Fourier analysis of a signature waveform is correlated with the fractal description of the ruggedness of a profile.
    Additional Material: 11 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 45-52 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Three general types of commercial particle sizing instruments have been tested with redispersed fly ash and devolatilised coal char in the size range 0.5 to 5 μm. Results are compared with volume-equivalent diameters obtained by Coulter Counter. Single-particle light-scattering counters are found to oversize fly ash, primarily because of the irregular particle shape, but generally to undersize the strongly absorbing char particles. The Malvern sizer, based on Fraunhofer diffraction analysis, grossly oversizes fly ash dispersed in water, probably because most of the particles are too small for the Fraunhofer approximation to be valid; results for carbon char are closer to the expected values, although results for particles dispersed in air and in water show some disagreement. The Aerodynamic Particle Sizer undersizes irregular particles substantially, probably because of increased drag resulting from the irregular shape and tumbling motion of these particles.
    Additional Material: 9 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 137-142 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Deep-sea manganese nodules must be potentially valuable one of the most mineral resources containing several economically valuable metal elements. Manganese minerals in the nodules are regarded principally as todorokite and δ-MnO2. The todorokite phase is porous and enriched in copper and nickel, while the porous δ-MnO2 phase is enriched in cobalt. Porosity and adsorption as well as dissolution characteristics have been observed for each constituent mineral. Furthermore the pore diffusion coefficient has been calculated. Moreover, the zeta potential of each constituent mineral has been measured in order to evaluate the electrochemical property. This has been applied successfully to the selective concentration of copper and nickel bearing or cobalt bearing minerals in deep-sea manganese nodules.
    Additional Material: 8 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 153-160 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Over the past few years, laser diffraction spectrometry has become a very important method of particle size analysis. Typical features include the large measuring range, the simplicity of operation and the speed with which analyses can be carried out. The principle of measurement and the set-up of three commerical instruments are described.The following points are discussed, with reference to examples:-Relevant parameters, such as particle shape, shape of distribution curve or dispersion, bution curve or dispersion,-reproducibility, comparison of the results obtained with different types of apparatus between one another and with other, analytical methods, and-on-line use of the instruments for the measurement of dynamic processes, eg. flocculation and dispersion processes.Operating experience gained with six instruments over a number of years is discussed.The measuring method which is described here is in a stage of rapid development and dissemination. It is for this reason that recent improvements and new developments cannot be dealt with here. For example, an apparatus named Helos from Sympatec GmbH, Remlingen, has appeared on the market. The external appearance of the instruments marketed by the Malvern and Leeds and Northrup companies has changed somewhat.The author's practical experience (in some instances extremely wide-ranging) with these devices is presented here in summary form.
    Additional Material: 18 Ill.
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  • 11
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 74-77 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The evaluation of particle size distributions of comminution products often shows that the experimental distributions cannot be represented by one of the well-known functions (GGS, RRSB, log-normal distributions). Although in some cases a more or less satisfactory approximation to one of these functions can be made, a physically meaningful interpretation is generally impossible. Using the frequency curve, it can often be shown that mixed distributions, represented by several statistical assemblies, do exist. In this paper the progeny size distributions of quartzite formed by slow compression comminution of single grains and particle beds as well as of the comminution products of a roller mill are interpreted as superpositions of several statistical assemblies each of which can be represented by a truncated log-normal distribution.
    Additional Material: 6 Ill.
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  • 12
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An apparatus is described for the fast and automatic measurement of the grain size distribution of sand ranging from 0 to 4 mm. A sample of sand continuously introduced at a rate of 30 g/min is separated by the apparatus into seven fractions of 0-0.063, 0.063-0.125, 0.125-0.25, 0.25-0.5, 0.5-1, 1-2, and 2-4 mm. The amount of sand in each of these fractions is determined and the results are given in time intervals of 1 minute. The sand is separated in a separation chamber through which water streams in a horizontal laminar flow. The samples are separated according to their settling velocities. The four coarse fractions descend to the bottom of the chamber. They are collected and weighed under water. The three fine fractions remain suspended in three effluent water streams. The quantity of sand is measured in flow cells by absorption of laser light. Control of the system as well as the collection and processing of the measured data are done by means of an electronic control unit and a microcomputer.
    Additional Material: 3 Ill.
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  • 13
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 96-101 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The principle of an instantaneous reading, respirable dust, photometer and its application are described. The instrument measures the infrared light (940 nm wavelength) scattered on airborne particles under a mean scattering angle of 70°. Its open measuring chamber, which is insensitive to daylight, is filled with total dust. The photometer reading, however, is calibrated in terms of mass concentration of respirable dust by means of a gravimetric respirable dust sampler. Experiments carried out with monodisperse test aerosols and with real dusts confirm the instrument's principle. The photometer values obtained for real dusts can be linearly converted into mass values of respirable dust as long as ultra-fine or ultra-coarse dusts are excluded. In several practical cases an increased flux of scattered light is compensated for by a higher density of the dust material.
    Additional Material: 7 Ill.
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  • 14
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 112-116 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The application of a new LDA method which simultaneously measures the size and velocity of small water droplets in the spray cone of a fan type water nozzle is described. As the phase difference between adjacent photomultipliers responding to signals from a fringe mode LDA is linearly proportional to the diameter of the spherical particle in the measuring volume, the new instrument allows, for long distances between the optical devices and the measuring volume in the spray, non-invasive measurements and from these the correlation of size and velocity of the individual droplet in order to establish two-dimensional distributions. From the new LDA instrument one receives definite information about the volume-flow concentration in the measuring point of an enclosed flow situation.
    Additional Material: 5 Ill.
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  • 15
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 7-13 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In the application and the development of on-line methods for particle size analysis one has to distinguish three principally different problem areas:aallocation and preparation of a representative sample,banalysis of the sample,cevaluation of the results.Methods and problems connected with these areas will be discussed in this paper. Some of the methods available for rapid response analysis of particle size distributions mark the beginning of a new era of particle size analysis. One has to recognize however that a uniform solution of the problems of on-line particle size analysis is extremely difficult if not impossible to find. The boundary conditions vary to such an extent that similar methods or combinations of methods can rarely be used in different cases. Since instrument manufacturers will in most cases not be able to adopt their instruments to different industrial applications, specialists will have to solve the problem. One has to recognize, however, that not all of the steps described in this paper have been investigated to an extent which renders possible appropriate solutions. There is still room for improvement.
    Additional Material: 9 Ill.
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  • 16
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 32-36 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Most existing theories of the response of electrical sensing zone particle size analysers, for instance of the type Coulter Counter®, predict that a significant deviation from sizing linearity will occur at and above some 40% of the aperture diameter. Practical experience, at least for the only test models available - latex spheres - shows that this is not the case in practice. Linear particle response up to 80% of the aperture diameter has been established, confirming the prediction recently made by Scarlett in a new response theory.
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  • 17
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 59-65 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: It has been shown that the projected area of a rotating fineparticle can be used to construct a signature waveform which is descriptive of some aspects of the three-dimensional morphology of a fineparticle. If the fineparticle is rotated systematically about two mutually independent axes, through two sets of 90 degrees rotations, the signature waveform can be related to the surface area of the convex hull. It could be that the convex hull of a fineparticle is related to its fluid dynamic behaviour and its ability to modify the effective viscosity of a fluid in its suspension. This type of significance of different types of Cauchy signature waveforms are discussed. The concept of three-dimensional signature waveforms is extended to cover the structural shape waveform and the fractal waveforms which, respectively, describe the spatial structure and the ruggedness of a fineparticle profile. The possible utilization of all three types of waveforms to describe in a complete manner the three-dimensional structure of a rugged fineparticle is discussed.
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  • 18
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 89-95 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: While editing the first issues of Particle Characterization it has been recognized by the editors that the papers submitted differ widely in the representation of data and in the nomenclature chosen to characterize such common variables as particle size, different equivalent particle diameters, average particle sizes, cumulative and density values of a distribution etc. In oder to make papers published in this Journal more readily assimilable and graphs representing particle size analysis data instantly recognizable by using agreed upon standardized nomenclature the following paper has been submitted by one of the editors. It was first presented at the Harold Heywood Memorial Symposium, September 1974, at the University of Technology, Loughborough, U. K.
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  • 19
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 108-111 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In optical particle counters the calibration function describing the relationship between the amplitude of the scattered light pulses and particle size depends on several parameters. In this paper, several calibration methods are discussed. As an example, the calibration of an optical particle counter (HC-15, Polytec GmbH & Co., Waldbronn, FRG) is demonstrated, using real aerosols with unknown particle shape and refractive index, and a precollector with known collection efficiency. The error analysis, when performed together with the results of an indirect check of the obtained calibration curve, provide evidence that this method yields good calibration curves for the aerosol being measured. The method is then applied to obtain the calibration curves for quartz dust, ash from a fluidized bed combustor and coal dust.
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  • 20
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Particle Technology is a broad and multidisciplinary subject of great importance but diffuse in definition. In this paper a view is presented of the underlying science and its technological applications. In particular a structured subject is dependent upon characterization techniques from which predictions can be made. In this paper the interrelationship between macroscopic and microscopic characterization is discussed. The standardisation and development of the microscopic techniques, particle analysis, is identified as the key to the development of the whole subject.
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  • 21
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    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 66-73 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Besides the knowledge of material constants of the homogeneous phases of a disperse system, a good understanding of its geometrical properties is necessary for describing physical processes. In order to characterize the shape of the interface between solids and pore space with respect to the irregularities in all orders of magnitude, the fractal dimension has proved to be an informative parameter. By this study the theory of fractal dimensions, in three-dimensional space originally limited to topological curves, surfaces and volumes, is extended into physical properties like specific surface, tortuosity, porosity and formation factor with “physical” dimensions -1 or 0 as an exponent of the unit of length. The typical properties of the true fractals are transferable to some of these derived parameters. This leads to power laws describing the dependence of the particular measure on the resolution length. With special models, which seem to be of widespread validity in nature, petrophysical considerations lead to further power laws for the rest of the physical parameters, dependent on discrete length parameters such as grain radius and pore radius. By determination of the exponents of such independent power laws, a better particle characterization is possible, as the fractal dimension of the surface alone may be misleading, especially when the grain size of the particles is not uniform.
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  • 22
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Measured drop-size distributions are presented which were obtained by the atomization of water with hollow-cone nozzles. The drop-size distributions were determined using a scatteredlight particle size counting analyser at various locations in the droplet cone. These local distributions change systematically from the cone's axis to its border. To acquire the drop-size distribution of all the drops the local distributions have to be superimposed. The spatial mass flow distribution in the cone can be calculated from these measurements.
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  • 23
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: New types of equipment for measuring the tensile strength of a powder bed, based on the Warren Spring type of split cell, have been developed by the authors and are reported in this paper. The main modification is an extension of the range of the porosity of the powder bed to be tested by improving the sliding mechanism of the split cell. Three versions of the modified equipment are introduced and explained, and the reduction of the sliding friction and the stability of the split cell at a high compression range are shown. The results obtained with beds of a wide porosity range are presented in a new equation for the adhesion force of a powder bed.
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  • 24
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    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 167-170 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Fluid classification methods for particle size analysis are based on the concept of cut size. The particles suspended in a fluid are passed through several separation stages, of progressively finer cut-size, so that each stage collects a fraction of the feed solids in the same way as each screen in a stack of sieves.There is an inherent error involved in the data reduction, which often leads to a poor comparison between the results of fluid classification and sedimentation, although both in principle measure the equivalent Stokes' diameter.This paper investigates the problem and attributes the above mentioned error to the difference between the equiprobable size and the analytical cut size. The paper presents a simple correlation which relates the analytical cut size and the equiprobable size if both the measured size distribution and the grade efficiency curve of the separator follow, approximately, log-normal functions. The usefulness of the correlation is exemplified in the case of the Bahco analyser. Measured grade efficiency curves for each separation stage provide the necessary data for the above mentioned correction and this is then applied to examples of practical particle size analysis.
    Additional Material: 2 Ill.
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  • 25
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    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 22-27 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: For some time studies have been made relating the values obtained from simple shape description to bulk powder properties. More recently the detailed mathematical description of particle outline has become possible and quite powerful techniques have been developed. These techniques may be used for the regeneration by computer of the shape and, more importantly, for studies relating shape to individual particle behaviour and to bulk powder properties. Quite inadequate attention has been directed to the task of obtaining from the laboratory sample of the bulk powder a representative sample of shapes without bias. In this communication the considerations to be included in the sampling procedure are reviewed and a possible solution to the problems posed is presented.
    Additional Material: 1 Ill.
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  • 26
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    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 28-31 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The currently used methods of sample preparation are examined and found to be unsatisfactory in case of counting methods for particle size analysis. It is the purpose of this paper to review the results of investigations of two different measuring principles (light extinction and electrical resistance change) by use of the same signal handling equipment. The commonly used techniques and units are compared with regard to the resulting density distributions of particle size below 0.25 mm. The final conclusions including recommendations to the use of ultrasonic treatment and to improvements of the sampling and the sample-feeding units are valid for all counting methods.
    Additional Material: 8 Ill.
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  • 27
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    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 53-58 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: When performing particle size analysis by scattered light, coincidences in the measuring volume of optical particle counters not only cause too small a particle concentration to be measured, but also a size distribution to be obtained which is systematically shifted towards coarser particle sizes. It is pointed out in this paper how this shift can be precalculated when the true distribution is given. The results show under which conditions a correction of the measured distribution is indispensable.
    Additional Material: 4 Ill.
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  • 28
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    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 78-84 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The classification of powders into groups possessing specific behavioural identities has long been recognized as desirable. This has been approached by describing different powders using two variables and plotting the data on a scatter diagram. The property of interest is then inferred from a powder's position on the scatter diagram. Unfortunately, a powder's behaviour is rarely adequately described by only two variables. To describe a powder more fully requires more variables and this presents a problem in interpretation. Cluster analysis refers to a range of techniques for interpreting multivariate data sets and is used in many fields. This paper describes cluster analysis and considers the method and potential of its application to particle technology. By way of an illustration, a cluster analysis has been performed on twenty-seven powders resulting in groups recognizable by their characteristic fluidisation and flow properties. It is concluded that cluster analysis could be a powerful tool in predictive and analytical work in the field of particle technology.
    Additional Material: 1 Ill.
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  • 29
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    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 102-107 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In this paper a new electrical conductivity technique for the measurement of bubble size and velocity is presented. This measuring system is able not only to estimate size and velocity of particles (bubbles and droplets in liquids) but also to give complete information on the space related motion of particles. Thus a significant improvement is achieved in the accuracy of measurement.By using the simultanous measurement of both: bubble sizes and volumetric hold up of the dispersed phase, one is able to calculate the local interfacial area. In the first part of this paper the measuring system, its properties and limits are illustrated. In the second part results obtained in a bubble column will be presented.
    Additional Material: 9 Ill.
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  • 30
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    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 1 (1984), S. 121-126 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: It is often necessary to carry out sedimentation analysis of powders, consisting of two or more components, which differ in some physical properties. By means of theoretical studies of twocomponent systems the systematic errors of the measured particle size distributions were analysed for the case that differences exist in the following combinations of properties:-particle size distribution D(x) and solid density ϱs-D(x) and mass absorption coefficient μm-D(x) and ϱs and μmUsing real systems (SiO2 + Fe2O3, Al2O3 + SiO2, Al2O3 + Fe2O3) the partial and total errors were estimated and compared with the results obtained with a Sedigraph. Differences in the density of the components often result in negligible errors, even for the system SiO2 + Fe2O3, if the mass portion of one component is below about 10%. For the total error the differences of μm and D(x) are decisive. Its value is below 1% if the mass portion of the slightly absorbing component is 〈5% or if the strongly absorbing component is 〈1%.
    Additional Material: 10 Ill.
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  • 31
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    Particle and Particle Systems Characterization 1 (1984), S. 127-131 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Combined gravitational and centrifugal sedimentation analysis was studied using a Sedigraph X-ray sedimentometer and a Ladal pipette centrifuge. The test powders were talc, calcite and lead oxide. The purpose of the study was to examine the possibilities of extending the sedimentation analysis towards finer sizes by the use of centrifugal force. All the test samples could be analysed down to 0.04-0.05 μm by the combined sedimentation procedure with reasonable accuracy and the results were matched to give a uniform distribution. It was also shown to be preferable to present the size analysis data in a log-probability scale, as it gives the means to easily distinguish materials with different particle size characteristics and to estimate the actual distribution by a statistical function.
    Additional Material: 5 Ill.
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  • 32
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    Particle and Particle Systems Characterization 1 (1984), S. 161-166 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Numerous unit operations in particle technology require that dry powders are fed into a system with as little fluctuation as possible in flow rate and velocity and that the powder is dispersed in flowing air. A feeding and dispersing system has been developed which allows mass throughputs between 0.1 and 20 kg/h. It has been used as a feeder unit for dry particle size analysis from diffraction patterns.
    Additional Material: 12 Ill.
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  • 33
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab initio crystal orbital calculations have been performed on regular polyethylene chains applying basis sets of minimal and double-zeta quality. Relative stabilities of periodic all-trans, all-gauche, and alternating trans-gauche conformers have been evaluated, including extensive geometry optimization. Potential curves for a simultaneous rotation around C—C single bonds from the all-trans to the all-gauche conformation have been computed applying the rigid-rotor approximation, the flexible-rotor approximation, and an additional reoptimization of C—C distances. A rigid-rotor potential curve from the all-trans to the alternating trans-gauche conformation has been computed as well. Results obtained are compared with ab initio calculations on butane and pentane and with semiempirical and empirical force-field studies on polyethylene.
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  • 34
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    Journal of Computational Chemistry 5 (1984), S. 64-71 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The degrees of conformational freedom of poly L-D β-helical chain are analyzed consistent with the helical parameters of gramicidin A structure. From conformational energy calculations, “helical librations” that can be sustained by this structure are described and the energy of libration as a function of the cavity size is presented. Two different modes of conformational change are identified corresponding to librations of all L-D-peptide units or all D-L-peptide units while retaining the helical parameters. Such helical librations are considered relative to conformational perturbations due to the presence of an ion in the channel.
    Additional Material: 6 Ill.
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  • 35
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    Journal of Computational Chemistry 5 (1984), S. 84-88 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The use of symmetry coordinates (SC) in geometry optimization is discussed. A computer program incorporating the use of sc, together with analytical calculation of the gradient and quadratic acceleration, is described. Also reported are careful test results on a series of small molecules and typical results with a long series of molecules up to quite large size (40-60 atoms).
    Additional Material: 2 Ill.
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  • 36
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    Journal of Computational Chemistry 5 (1984), S. 89-103 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A technique to generate electrostatic contours on a steric surface is presented and applied to the presentation of molecules that interact with DNA. A set of electrostatic points at predetermined values along with their derivatives are obtained on the steric contours as they are generated. The steric contours are generated in a set of parallel planes. Points with given electrostatic values are then connected between and within the contours mathematically with a Taylor's expansion and two rules: the first to tentatively line up points that can be connected, and the second to check to insure that the remaining points can be connected. This method insures that contours will not cross by requiring that a possible connection of two points leaves an even number of remaining points for each electrostatic value in isolated regions of unused points bounded by points that have already been connected. The hidden line algorithm used previously to draw molecules in a space-filling model within the context of steric contours is applied to the complete problem of the presentation of a molecule bound to DNA with steric contours in parallel planes, and with electrostatic contours drawn on this steric surface.
    Additional Material: 13 Ill.
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  • 37
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    Journal of Computational Chemistry 5 (1984), S. 115-121 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Analysis of a Gaussian potential function suitable for modeling degenerate bending vibrations in weakly bound molecular complexes is presented. Approximate eigenvalues and eigenvectors are obtained by application of perturbation theory. Comparison to the “exact” eigenvalues obtained via a numerical solution shows that the first- and higher-order perturbation corrections are consistent with variational principles.
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  • 38
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    Journal of Computational Chemistry 5 (1984), S. 170-174 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: An algorithm is described for generating atomic Cartesian coordinates of conformations of macrocyclic molecules possessing exact rotational or rotation-reflection symmetries. A fragment representing the asymmetric unit of the molecule is suitably oriented in space, and then a symmetry operator is applied to generate the initial coordinates of the molecule. An empirical force field of interatomic interactions is used to generate equilibrium conformations. Results of calculations performed on two cyclic polylactones and one crown ether using this approach are given. They reveal that symmetric conformations of these molecules are often preferred. Since the latter conformations are probably responsible for the specialized properties of these molecules, this method should facilitate doing theoretical studies on these kinds of compounds.
    Additional Material: 1 Ill.
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  • 39
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    Journal of Computational Chemistry 5 (1984), S. 182-185 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The principles of a new method, the method of zero determinants, are described which can be used for the determination of the number of exponentials in accurate, multiexponential decay curves, as well as for the smoothing of multiexponential experimental data. It is based on the idea that the determinant of an overdetermined data matrix for accurate data is zero. The method is not limited by mathematical approximations, and thus uncovers the decay curve hidden in the data set.
    Additional Material: 1 Ill.
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  • 40
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    Journal of Computational Chemistry 5 (1984), S. 197-199 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Group equivalents which are useful for converting energies derived from ab initio calculations into enthalpies of formation have been obtained. They allow ΔHf to be estimated from 6-31G* energies with an uncertainty on the order of ±2 kcal/mol.
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  • 41
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    Journal of Computational Chemistry 5 (1984), S. 207-215 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The effect of different exponents, Slater, Burns, Clementi, and Best Limited Molecular Orbital (BLMO) on the approximate one-electron property expectation values from minimum basis-set calculations is reported for Roothaan-Hartree-Fock (RHF), neglect of diatomic differential overlap (NDDO), and maximum overlap method (MOM) calculations on FH, CO, and LiH.
    Additional Material: 2 Ill.
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  • 42
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    Journal of Computational Chemistry 5 (1984), S. 225-229 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Changes of electronic charge distribution following the lowest singlet n-π* transitions of benzaldehyde, benzamide, benzoic acid, the phthalaldehydes, pyridine, and the diazines have been examined using the CNDO-S/CI method. A Singlet n-π* transition is found as a general rule to direct electronic charges to the para position of the atom in the ring that carries the lone pair or to which the substituent carrying the lone pair is attached.
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  • 43
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    Journal of Computational Chemistry 5 (1984), S. 261-262 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Additional Material: 2 Tab.
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  • 44
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    Journal of Computational Chemistry 5 (1984), S. 241-247 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Previous investigators have shown that statistical mechanical averages for configuration-dependent physical properties of long unperturbed polyoxyethylene chains are sensitive to the gauche-trans energy difference for rotation about C—C bonds. Agreement between theory and experiment could be obtained only by significant adjustment of this energy away from values predicted by semiempirical conformational energy computations. The present work examines the success of MM2 in evaluating conformational properties of long unperturbed polyoxyethylene chains. Calculations are performed which identify the rotational isomers, and their energies, for the indicated bonds in CH3OCH2CH2O—CH2—CH2—OCH2CH2OCH3. These energies are used to assign statistical weights utilized in the configuration partition function for a rotational isomeric state chain with symmetric threefold interdependent rotations. The customary generator matrix scheme is employed to evaluate the mean-square unperturbed end-to-end distance, mean-square unperturbed dipole moment, and their temperature coefficients. Contrary to computational schemes employed previously, MM2 is found to provide an estimate of the gauche-trans energy difference for rotation about C—C which is in harmony with the known dimensions and dipole moments of the unperturbed polymer. MM2 also provides good estimates for most of the other parameters required in the rotational isomeric state treatment. A notable exception is provided by the gauche-trans energy difference for rotation about the C—O bond. This energy difference is overestimated by MM2.
    Additional Material: 1 Ill.
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  • 45
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    Journal of Computational Chemistry 5 (1984), S. 272-279 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Various algorithms for evaluating nonbonded interactions in molecular dynamics (MD) simulations of macromolecular systems are considered, and a combination of two techniques using a space grid for finding neighbor atoms is proposed. The application of grid search techniques to nonrectangular periodic systems is discussed. Finally, the computing time required by different algorithms is compared on a Cray-1 vector processing computer as well as on a CDC Cyber 170/760 sequential computer. Neighbor list techniques turn out to be faster than the grid search techniques for the systems considered here. However, storage requirements may exclude the use of neighbor list techniques for large systems. Finally, MD of complex macromolecular systems turned out to be about 4-14 times faster on a Cray-1 than on a Cyber 170/760.
    Additional Material: 2 Ill.
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  • 46
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    Journal of Computational Chemistry 5 (1984), S. 280-287 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A computer program is described which evaluates the second-order Møller-Plesset energy using the integral list formed by HONDO 5. In this program use may be made of full molecular symmetry for most common point groups, even if they contain two-dimensional representations. The algorithm for the integral transformation may also be applied to other methods beyond Hartree-Fock. Some numerical results and timings are presented.
    Additional Material: 1 Ill.
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  • 47
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    Journal of Computational Chemistry 5 (1984), S. 571-575 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Classical conformational analysis was applied to the study of the variation of heats of formation (HOF) and geometrical parameters of small-ring propellanes. As expected, the calculated HOF is the smallest for [4,4,4] propellane I and the largest for [2,2,2]propellane X. In spite of the different trends exhibited by the strain energy components, the calculated HOF values may be reproduced within a simple additivity scheme. The calculated bridgehead-bridgehead bond length is the longest for [2,2,2]propellane (1.655 Å), lowers with increasing molecular size, and is equal to 1.558 Å for [4,4,4]propellane. In agreement with experimental findings the latter value is significantly larger than the standard value of 1.54 Å typical for unstrained hydrocarbons. Other calculated geometrical parameters as well as HOF values cannot be compared with experimental and/or theoretical results since there is a lack of reliable experimental data. Surprisingly, [2,2,2]propellane was found to be more flexible than the less strained bicyclo[2,2,2]octane.
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  • 48
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    Journal of Computational Chemistry 5 (1984), S. 581-588 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Three newly defined information theoretic topological indices, namely “degree complexity (Id),” “graph vertex complexity (HV),” and “graph distance complexity (HD)” along with three other information indices have been used to study their discriminating power of 45 trees and 19 monocyclic graphs. It is found that the newly defined indices have satisfactory discriminating power while HD has been found to be the only index to discriminate all the graphs studied.
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  • 49
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    Journal of Computational Chemistry 5 (1984), S. 589-597 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The formula for the first derivative of the MCSCF energy with respect to a nuclear coordinate is reviewed. The efficient utilization of symmetry in programs employing symmetry-adapted basis functions is described: Advantages that are also obtained for higher derivatives and for gradients of nonself-consistent wave functions are briefly discussed. Using CASSCF wave functions, the method is applied to the question of nonlinearity in the heavy atom chain of propadienone (CH2CCO).
    Additional Material: 3 Ill.
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  • 50
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    Journal of Computational Chemistry 5 (1984), S. 606-611 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The transition states involved in the hetero-Diels-Alder reactions of acrylaldehyde-ethylene and butadiene-formaldehyde systems were characterized using an efficient method of locating a saddle point on the energy surface of two coordinates calculated with MINDO/3 method. It has been shown that parallel transition and rotation of the conjugate coordinate frame lead to the reaction and orthogonal coordinate system on the hyperbolic paraboloid energy surface. It was concluded that the method we adopted is similar to the “X-method” but is much simpler to apply to real reaction systems.
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  • 51
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    Journal of Computational Chemistry 5 (1984) 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
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  • 52
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    Journal of Computational Chemistry 5 (1984), S. 24-34 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We consider the problem of predicting the mode of binding of a small molecule to a receptor site on a protein. One plausible approach, given a rigid molecule and its geometry, is to search directly for the orientation in space that maximizes the degree of contact. The computation time required for such a naive procedure is proportional to n3m3, where n is the number of points in the site where binding can occur, and m is the number of atoms in the ligand. We give an alternative, combinatorial approach, in which only “contact-no-contact” criteria are considered. We relate this problem to the well-known combinatorial problem of finding cliques in a graph and show that we can use a solution to the clique problem not only to solve our original problem, but also the problem of avoiding energetically unfavorable matches. Our experience with this method indicates that the computation time required is proportional to nm2.8, with a lower constant of proportionality than that of the naive procedure.
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  • 53
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    Journal of Computational Chemistry 5 (1984), S. 35-43 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Semiempirical molecular orbital calculations by the MNDO method are reported for sulfur rings and chains S3 through S8, for the corresponding dications, S22+ through S82+, and for S4+. The MNDO method seems quite successful in predicting the geometries of neutral catenated sulfur molecules, even the unusual bond-length alternation and extent of coplanarity in cyclo-S7. In contrast to hydrocarbon rings, for which its prediction of strain is erratic, MNDO is consistent in its calculated strain energies in small cyclosulfur rings; unfortunately all the strain energies are overestimated by 70%. As a consequence of this error, the method must be considered unreliable in its predictions of structures for the dications Sn2+, since many of these ions could potentially exist as strained bicyclic systems. In addition, MNDO appears to have difficulty handling long, partial SS σ bonds, as are found to occur in S82+. It may be for this reason that MNDO predicts, apparently incorrectly, that the open-chain isomers of Sn2+ are more stable than are any of the cyclic forms, at least for S52+ to S82+. With respect to neutral Sn molecules, however, the MNDO predictions appear more reliable than ab initio molecular orbital (MO) calculations using small basis sets without polarization functions and without configuration interaction (CI). However, MNDO apparently underestimates by about a factor of two the strength of the three-electron π bonds present in the terminal links of sulfur diradical chains.
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  • 54
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The Floating Point Systems, Inc. Model 164 Attached Processor (FPS-164) is a high-speed, pipelined, parallel processor designed for large-scale scientific computation. Benchmark studies of operations common in quantum chemistry codes are discussed and the performance of the FPS-164 is compared with other commonly available computers. A complete system of electronic structure codes has been implemented on the FPS-164 using the Fortran-77 cross-compiler and calls to optimized vector and matrix routines. The conversion of a generalized valence bond (GVB) code illustrates the strategy adopted to adapt Fortran codes to the FPS-164. A typical production example, a large scale (GVB) and configuration interaction calculation on the vinyl radical, shows a net throughput equivalent to nearly nine VAX 11/780 computers.
    Additional Material: 5 Ill.
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  • 55
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    Journal of Computational Chemistry 5 (1984), S. 104-112 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We discuss the implementation and computational efficiency of one approach to adjusting the Hill equation of adsorption to a set of empirical data, pointing out some aspects that seem to be valid in the general case. The approach consists basically of minimizing squares of deviations of the adsorbed amounts, which are numerically computed in terms of the empirical pressures and the parameters. Hill's equation is dealt with as a prototype of nonlinear equations seldom used by chemists because none of their variables can be set free.
    Additional Material: 4 Ill.
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  • 56
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    Journal of Computational Chemistry 5 (1984), S. 113-113 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
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  • 57
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    Journal of Computational Chemistry 5 (1984), S. 129-145 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We present an approach for deriving net atomic charges from ab initio quantum mechanical calculations using a least squares fit of the quantum mechanically calculated electrostatic potential to that of the partial charge model. Our computational approach is similar to those presented by Momany [J. Phys. Chem., 82, 592 (1978)], Smit, Derissen, and van Duijneveldt [Mol. Phys., 37, 521 (1979)], and Cox and Williams [J. Comput. Chem., 2, 304 (1981)], but differs in the approach to choosing the positions for evaluating the potential. In this article, we present applications to the molecules H2O, CH3OH, (CH3)2O, H2CO, NH3, (CH3O)2PO2-, deoxyribose, ribose, adenine, 9-CH3 adenine, thymine, 1-CH3 thymine, guanine, 9-CH3 guanine, cytosine, 1-CH3 cytosine, uracil, and 1-CH3 uracil. We also address the question of inclusion of “lone pairs,” their location and charge.
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  • 58
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A collection of programs which aid in the use of group theory has been developed for the Apple II. The programs automate much of the tedious algebra necessary to generate character tables and representation matrices from the properties of the operators chosen to generate the group. At the same time, the presentation of intermediate results provides a schematic guide to the procedures by which groups are constructed. The choice of generators is not limited to the reflections, rotations, and inversions, which are the familiar features of chemical group theory. Any generator representable as a permutation may be treated; thus general permutation groups and Longuet-Higgins groups may be studied. As an illustration we describe the states of beryllium borohydride, which require a form of Longuet-Higgins group theory.
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  • 59
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The geometries of several conformations of ethyl and isopropyl formate were optimized by the ab initio gradient method on the 4-21G level. The calculations are in agreemnt with the existence of two conformers of ethyl formate of nearly equal energy. The COCC torsional angle in one is anti (180°) and in the other is gauche (about 80°). The equilibrium configuration of the isopropyl group in the formate is found to be unsymmetrical, with a COCH torsional angle of about 40°. A second minimum of torsional energy, at COCH = 180°, is 1.2 kcal/mol less stable than the unsymmetrical form. The calculations demonstrate the tranferability of internal rotational-potential parameters and of conformationally dependent geometrical trends between ethyl and isopropyl formate. There is good agreement between the calculated results and empirical potential-energy functions and rotational constants determined from microwave spectroscopy.
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  • 60
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    Journal of Computational Chemistry 5 (1984), S. 200-206 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The conformational characteristics of allylamine were investigated by the ab initio STO-3G basis set. The results indicate that the molecule exists in a number of stable conformations through rotations about the CC—NH and CC—CN bonds. The TE (trans-CCNLP, LP representing lone-pair electrons, and eclipsed-CCCH) is the most stable, while TC (trans-CCNLP and cis-CCCN), GE (gauche-CCNLP and eclipsed-CCCH), G′C(gauche′-CCNLP and cis-CCCN), and G′E (gauche′-CCNLP and eclipsed-CCCH) conformations are less stable, respectively, by 0.41, 0.67, 0.92, and 1.14 kcal mol-1. These results are in general consistent with previous experimental results. Rationale for the conformational characteristics and order of stabilities are explored.
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  • 61
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    Journal of Computational Chemistry 5 (1984) 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
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  • 62
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    Journal of Computational Chemistry 5 (1984), S. 217-224 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The MINDO/3 calculations were performed on the potential energy profile involved in the equilibrium \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} {\rm crotonic acid \rightleftharpoons isocrotonic acid \rightleftharpoons but-3-enoic acid} \\ {\rm (III)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(II)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(I)} \\ {\rm } \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\to {\rm propene + CO}_{\rm 2} \\ \end{array} $$\end{document}Optimized structures of stable molecules and transition states have been determined; thermodynamic stabilities of pure acids and barriers indicated that the equilibrium can be set up from any acids. It was argued that direct decarboxylation is only conceivable from (I), since in this process a 1, 5-hydrogen shift is involved, whereas a higher barrier process of 1, 3-hydrogen shift is required in direct decarboxylations from other acids. Direct interconversion of (I) and (III) was found to be unfavorable due to a high barrier involved.
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  • 63
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    Journal of Computational Chemistry 5 (1984), S. 252-260 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Formulas are given for convergence-accelerated lattice sums over all intermolecular Coulomb, London, and repulsive interactions. Their implementation in the consistent force field is described. Optimum values of convergence constant and summation limit are found for r-12, r-9, and r-1 interaction terms. Energy minimization in all degrees of freedom, also intramolecular, for crystals of Ar, KCl, and C2H6 is reported.
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  • 64
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    Journal of Computational Chemistry 5 (1984), S. 263-271 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The effect of correlation energy on the relative stability of different structures and dissociation products of complex lithium beryllohydrides has been investigated. The adequacy of the method employed (third-order Möller-Plesset perturbation theory) and the basis set dependence have been assessed. Trends of the correlation energy according to the molecular structure have been discussed, and the validity of an additive scheme based on electron pair contributions has been tested.
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  • 65
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    Journal of Computational Chemistry 5 (1984), S. 326-335 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The tendency of C—O bond lengths to change as a function of the torsional angles at an acetal carbon has been included in a new version of the molecular mechanics program MM2(82), based on the observed behavior of molecules of this class as indicated by ab initio calculations and experimental structural data. The experimental geometries and energies are reasonably well reproduced.
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  • 66
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    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We have used energy minimization calculations to study a number of conformations of uncomplexed valinomycin. In certain cases, x-ray diffraction atomic coordinates were used directly as input coordinates, while in other cases, conformations were found by altering the x-ray coordinates prior to minimization. Five calculated conformations are reported along with their relative energies. The conformation found theoretically to be the most stable is in agreement with earlier, cruder calculations, but does not correspond to the predominant conformation observed in nonpolar solvents. A possible rationale is presented.
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  • 67
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    Journal of Computational Chemistry 5 (1984), S. 353-357 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The problem of determining the amount of reactant present in the steady state of a reaction-diffusion problem with pth order reaction kinetics and slab geometry can be achieved by solving the boundary value problem \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} u''(x) = \phi ^2 u^p (x),\,\,\,\,\,\,\,\,\,\,\,\,{\rm 0 〈 }x{\rm 〈 1} \\\\ u'(0) = 0{\rm }\,\,\,\,\,\,\,\,\,\,\,\,u(1) = 1 \\ \end{array} $$\end{document} where u is a normalized (dimensionless) concentration, and φ is the Thiele modulus. By considering the related nonlinear eigenvalue problem \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} y''(x) = \lambda y^p (x),\,\,\,\,\,\,\,\,\,\,\,\,{\rm 0 〈 }x{\rm 〈 1, }\,\,\,\,\,\,\,p{\rm 〈 0} \\\\ y'(0) = 0,{\rm }\,\,\,\,\,\,\,\,\,\,\,\,y(1) - y'(1) = 0 \\ \end{array} $$\end{document} and constructing a sequence of functions that converges monotonically to y(x), solutions of the original boundary value problem are obtained for the negative exponent case.
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  • 68
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    Journal of Computational Chemistry 5 (1984) 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
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  • 69
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    Journal of Computational Chemistry 5 (1984), S. 427-440 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The force constants and compliance constants of methyl, silyl, and germyl fluoride, chloride, bromide, and iodide have been calculated by the iterative consistency method. Using the force fields so obtained, centrifugal distortion constants, Coriolis coupling constants, and mean amplitudes of vibration have been computed and compared with experimental data, where available.
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  • 70
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    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The structures and conformational energies of several conformations of propanoic acid, 2-methylpropanoic acid, and butanoic acid were determined by geometrically unconstrained ab initio gradient geometry refinement on the 4-21G level. The O=C—C—C torsional potentials of propanoic acid and butanoic acid are found to be practically identical. There are energy minima at 0° and 120°, and maxima in the 60° region and at 180°. In 2-methylpropanoic acid there are energy minima at H—C—C=O dihedral angles of 0° and 120°, and maxima at 60° and 180°. The exact positions of the maxima and minima of the H—C—C=O torsional potential of 2-methylpropanoic acid are found to be predictable from propanoic acid rotational-potential parameters. Some conformationally dependent, local geometry trends are discussed.
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  • 71
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    Journal of Computational Chemistry 5 (1984), S. 457-465 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A Fortran-77 computer program has been written which calculates the rotation-torsion profile of a vibronic transition using an asymmetric top/free internal rotor Hamiltonian. The program is applicable to any molecule that is composed of a frame portion of C2v symmetry a free rotor portion of C3v symmetry. Rotation-torsion bands of A-, B-, and C-type contours may be calculated within an assumed Boltzmann distribution of rotation-torsion level populations or within a specified non-Boltzmann distribution of torsional level populations.
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  • 72
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    Journal of Computational Chemistry 5 (1984), S. 500-505 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The organization of a computer code to compute transition moments between states described in different orbital basis sets (a nonorthogonal transition moment) is described. The code is organized to minimize redundant work and allow efficient threshold checking. Three sample calculations are presented.
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  • 73
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    Journal of Computational Chemistry 5 (1984), S. 523-527 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A numerical procedure is described and tested for the determination of solvent sites in a crystal hydrate from computer simulation results. The method does not require the computation of density distributions.
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  • 74
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: In order to provide additional data for the relative lengths of methyl-C—H bond distances in acetyl derivatives, which are difficult to determine accurately by the conventional tools of structural chemistry, the geometries of CH3COH, CH3COF, CH3COCH3, CH3COOH, and CH3CONH2 were determined by ab initio SCF gradient optimization at the 5-31G** level and compared with previous 4-21G results. For acetaldehyde 6-311G4* calculations were also performed and the correlated methyl-C—H stretching potential energy functions were determined. It is found that the calculated differences between the in-plane and out-of-plane methyl-C—H bonds are practically independent of the computational scheme. The calculated results are in contrast to relative bond lengths obtained by some vibrational overtone spectroscopic studies, but are in perfect agreement with C—H bond length differences determined from isolated C—H stretching frequencies of partially deuterated compounds. The reliability of the latter, and other spectroscopic data concerning the assignment of the methyl-C—H vibrations are critically analyzed. On the basis of the available evidence we conclude: (1) the methyl groups of the CH3C(=O)X systems here discussed contain one strong (in-plane) and two weak (out-of-plane) C—H bonds; (2) intensities of C—H local mode spectra do not provide a reliable basis for assignment to individual bonds.
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  • 75
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    Journal of Computational Chemistry 5 (1984), S. 555-561 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A generalization of the quantum chemical definition of valence of atoms in molecules is suggested. Valence is considered as expectation value of diatomic parts of density operators. It appears as a sum of contributions from occupied orbitals of all atomic pairs that contain the reference atom. This definition is applicable on self-consistent-field (SCF) and configuration interaction (CI) level in any atomic orbitals (AO) basis. Its usefulness is demonstrated in an application to special molecules. Photoelectron spectroscopy and reactivity is discussed in this context.
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  • 76
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    Journal of Computational Chemistry 5 (1984), S. 299-306 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Molecular mechanical calculations for hetero-substituted hydrocarbons present certain difficulties that are not encountered in dealing with hydrocarbons. Ways are proposed to overcome such difficulties, sometimes by two-step or iterative computation. The following topics are considered: fitting the force field by using data from studies in solution; ways to estimate atomic charges or, alternatively, bond moments; ways to account for field effects upon atomic charges and bond moments.
    Additional Material: 6 Ill.
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  • 77
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: It is shown that a Lagrange multiplier method to constrain one or several internal coordinates, or averages and combinations of these, is easily implemented in a molecular mechanics computer program that uses Newton-Raphson (NR) minimization. Results are given for constraints on nonbonded distances and torsion angles. When a potential energy surface is to be explored, it is much better to constrain the average of three torsion angles around a bond than to constrain a single torsion angle. Certain conversions can only be achieved when averages of torsion angles around different bonds are constrained. Combinations of constraints have been applied to evaluate differences between calculated and observed geometries and to obtain transition states for relatively large molecules from results for smaller molecules at relatively low costs. The efficieny of the combination of the Lagrange multiplier method and NR minimization in terms of computing time can be rated as good.
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  • 78
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    Journal of Computational Chemistry 5 (1984), S. 343-348 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Theoretical calculations by the combined empirical force-field (EFF)-extended Hückel molecular orbital (EHMO) approach confirm that octalene and benzo-|c|-octalene present π-bond fixation with a common single bond between the cyclooctatetraene and cyclooctatriene fragments, whereas the structure of dibenzo-|c, j|-octalene is characterized by a central double bond. The dynamic behavior of these compounds is discussed and the interconversion energy barriers are calculated; the inversion of the cyclooctatriene ring is faster than that of the cyclooctatetraene ring in octalene, but it is slower in benzo-|c|-octalene.
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  • 79
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    Journal of Computational Chemistry 5 (1984), S. 349-352 
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    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Formulas fully exploiting the periodicity symmetry of the electron density of polymers are deduced. They are shown to lead to efficient algorithms for the evaluation of Coulomb and exchange interactions in those systems.
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  • 80
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    Journal of Computational Chemistry 5 (1984), S. 363-373 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Optimized monopole expansions for the subunits of the nucleic acids are developed by a reparametrizatio of the Hückel-Del Re procedure designed to reproduce closely the electrostatic properties obtained with precise overlap multipole expansions. It is shown that satisfactory values of both potential and field may be obtained for different DNA conformations and for a transfer RNA. The charge redistribution occuring between the subunits upon forming the nucleic acids is also investigated by ab initio calculations and accounted for in developing the new parametrization.
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  • 81
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    Journal of Computational Chemistry 5 (1984), S. 381-386 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The nitrogen protonation energies of the imino bases HN=CHR, where R is H, CH3, NH2, OH, and F, have been evaluated to determine the dependence of absolute and relative protonation energies on geometry, basis set, and correlation effects. Reliable absolute protonation energies require a basis set larger than a split-valence plus polarization basis, the inclusion of correlation, and optimized geometries of at least Hartree-Fock 4-31G quality. Consistent relative protonation energies can be obtained at the Hartree-Fock level with smaller basis sets. Extending the split-valence basis set by the addition of polarization functions on all atoms decreases the computed absolute Hartree-Fock nitrogen protonation energies of the imino bases HN=CHR except when R is F, but increases the oxygen protonation energies of the carbonyl bases O=CHR.
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  • 82
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    Journal of Computational Chemistry 5 (1984), S. 395-410 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The geometry and energy of 2-aza-1,3-butadiene and 2,3-diaza-1,3-butadiene have been calculated using the 6-31G* basis set as a function of the CNCC and CNNC dihedral angles, respectively. With the 2-aza derivative potential minima are located at 0° (trans) and at about 130° for a gauche structure approximately 9.5 kJ mol-1 less stable than the trans. Potential maxima are at about 75° giving a gauche barrier height of approximately 19 kJ mol-1 relative to the trans structure, and at 180° (cis) giving a barrier height of approximately 14.5 kJ mol-1 relative to the 130° gauche structure. With the 2,3-diaza derivative the gauche barrier has disappeared and there are a series of gauche structures in the region 70°-100° of almost equal energy 12.5-15 kJ mol-1 less stable than the trans. In addition the cis barrier is much greater, nearly 70 kJ mol-1 relative to the trans structure. Inclusion of electron correlation, accounting for about 50% of the correlation energy, produces no significant changes in the shape of the potential energy curves. There are systematic and progressive changes in almost all the geometrical parameters as the =CH— groups in butadiene are replaced by =N—. The outward tilt and compression within the methylene groups show adverse steric interactions to be operative in the cis structures. The values of Vnn indicate that gauche structures of both the 2-aza and the 2,3-diaza derivatives near the cis structure are more compact (as with butadiene), and gauche structures of the 2-aza derivative near the trans structure are less compact (as with butadiene). Originating in the changes in bond lengths and bond angles, rotation-independent nuclear-nuclear interactions again play an important role.
    Additional Material: 7 Ill.
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  • 83
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    Journal of Computational Chemistry 5 (1984), S. 441-450 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A number of force fields of the molecular mechanics type have been tested for their ability to represent as an energy minimum, the observed crystal structure for three cyclic hexapeptides, cyclo-(-Ala-Ala-Gly-Gly-Ala-Gly-), cyclo-(-Ala-Ala-Gly-Gly-Ala-Gly-), and cyclo-(-D-Ala-D-Ala-Gly-Gly-Gly-Gly-). The most effective force field tested was that recently proposed by Kollman and co-workers, notwithstanding its use of “united” atoms for CH, CH2, and CH3 groups. Fields proposed by Levitt, and adaptations of that of Scheraga and co-workers, were also effective. Force fields in which hydrogens bonded to electronegative atoms were not specified explicitly were less accurate in representation.
    Additional Material: 4 Tab.
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  • 84
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    Journal of Computational Chemistry 5 (1984), S. 466-470 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Structures and relative energies were obtained for the hydrogen bonded dimers of formamide and formamidic acid using the 3-21G basis set. A double proton transfer transition state is claimed to link these two dimers. While the structure of the transition state was intermediate between those of the two dimers, the energy was only 7.6 kJ/mol greater than the less stable formamidic acid dimer. The activation energy from the formamide dimer side of the reaction was found to be 125 kJ/mol of dimer. A similar transition state was found for the amidine dimer system. The activation energy for this model reaction was found to be 66.9 kJ/mol of dimer.
    Additional Material: 2 Ill.
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  • 85
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    Journal of Computational Chemistry 5 (1984), S. 486-499 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A set of procedures and guidelines are presented for the estimation of bond length, bond angle, and torsional potential constants for molecular mechanics force fields. The force field constants are ultimately derived by “subtracting” nonbonded molecular mechanics energies from corresponding molecular orbital energies using a model compound containing the chemical structure to be parameterized. Case study examples of bond length, bond angle, and torsional rotation force field parameterizations are presented. A general discussion of molecular mechanics force field parameterization strategy is included for reference and completeness. Finally, a curve-fitting program to generate force field parameters from raw data is given in Appendix I.
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  • 86
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    Journal of Computational Chemistry 5 (1984) 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
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  • 87
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    Journal of Computational Chemistry 5 (1984), S. 528-534 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Potential energy surface for methyl fluoride dimer has been studied theoretically with ab initio molecular orbital method, using a 4-31G basis set. Dimer dissociation energies, Mulliken electronic populations, and dipole moments were obtained.
    Additional Material: 6 Ill.
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  • 88
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    Journal of Computational Chemistry 5 (1984), S. 562-570 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A previously published scheme of estimating atomic charges in haloalkanes is extended to include olefines, alcohols amines, acids, ethers, and amides. In the conjugated systems the effects of mesomeric transfer of charge are explicitly included. Generally good agreement with the observed dipole moments of these compounds and their substituted derivatives is found. The atomic charges so obtained are compared with those of other semiempirical and quantum-mechanical calculations for the amide group. The charges so obtained fall within the range of values obtained by these other schemes, supporting the general validity of this approach.
    Additional Material: 7 Tab.
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  • 89
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    Journal of Computational Chemistry 5 (1984), S. 576-580 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Accurate vibration-rotation eigenvalues EvJ are sought for very high levels (up to dissociation) of a diatomic potential. The method used is the recent “eigenvalue equation” method [Kobeissi et al., J. Comput. Chem., 4, 218 (1983)] which dissociates the determination of the eigenvalue from that of the eigenfunction. A new mathematical formulation for any numerical potential is presented, which reduces the problem to the use of a single recurrent formula. A numerical application to the model potential used by Cashion [J. Chem. Phys., 39, 1872 (1963)], up to v = 23, gives results equal to the exact eigenvalues to approximately 10-14 cm-1. Another application to the model potential used by Johnson [J. Chem. Phys., 67, 4086 (1977)], up to v = 60, gives similar results.
    Additional Material: 2 Tab.
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  • 90
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    Journal of Computational Chemistry 5 (1984), S. 535-547 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: An ab initio self-consistent-field (SCF) algorithm taking into account all the features of the one-dimensional translational periodicity and the helical symmetry is presented. This algorithm includes the long-range correction to the Coulomb potential and is designed to calculate the band structure of periodic one-dimensional polymers (planar or helical). Its efficiency in terms of computing time and numerical accuracy is tested via applications on a (LiH)n chain, polyethylene, and four conformers of polypropylene.
    Additional Material: 5 Ill.
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  • 91
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    Journal of Computational Chemistry 5 (1984), S. 1-10 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The geometry of the ground states of the isomers and transition state for the systems HCN ⇌ HNC and BCN ⇌ BNC have been investigated using a wide variety of basis sets, both at the self-consistent-field (SCF) level and including correlation at the second-, and third-order Møller-Plesset (MP2 and MP3) levels. The barrier to isomerization and the isomerization energy were shown to be strongly dependent on the basis set and method, particularly for the BCN system.
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  • 92
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    Journal of Computational Chemistry 5 (1984), S. 19-23 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The structure of an isolated, infinite polyoxymethylene chain has been investigated with the aid of the ab initio crystal orbital method applying a basis set of double-zeta quality. Restricting the primitive unit cell to a single CH2O group, conformational potential curves as a function of the torsional angle have been evaluated. Only a single minimum closely corresponding to an all-gauche structure was detected. The all-trans conformation is a maximum on the energy curve for simultaneous rotation around C—O single bonds. Detailed geometry optimization in the vicinity of the all-gauche conformation led to the following structure: rCO = rOC = 1.425 Å, rCH = 1.072 Å, ∠HCH = 111.7°, ∠OCO = 110.9°, ∠COC = 115.1°, and τOCOC = 70.75°. The computed torsional angle τOCOC lies midway between the hexagonal (78.2°) and the orthorhombic (63.5°) modification of solid polyoxymethylene.
    Additional Material: 3 Ill.
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  • 93
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    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Extension of the inhomogeneous continuum solvent model to prolate spheroidal cavity systems in the context of Kirkwood-Westheimer substituent-reactivity theory is described. Reasonable effects attributable to electrical saturation and electrostriction, which are modeled by relatively simple spatial dielectric functions outside the solute-solvent boundary, may be demonstrated. It is also shown that choices of proper (i.e., nonaveraged) location of the interacting sites and magnitude of substituent dipole moments are comparably important to the quality of theoretical prediction.
    Additional Material: 6 Ill.
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  • 94
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    Journal of Computational Chemistry 5 (1984), S. 72-83 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A simple computational scheme for estimating the electrostatic potential about molecular models of moderate size is given. The large amount of calculations required for the evaluation of the hypersurface lends itself to treatment by high speed, unconventional computing machines. The essence of these calculations lies in Coulombic interactions that are computed between hypothetical proton test probes positioned in a gridded region surrounding the model and the partial electrostatic charges (CNDO/2) of each atom in the model. A specific scientific application is discussed which involves the recognition of amino acids and nucleotide bases. Three different evaluations of the potential hypersurface within the context of this approach were made. The first was performed on a VAX 11/780 which is a general purpose machine widely used in the scientific community; the second was performed using a pipelined Vector Processor, the FPS AP-120B; and the third by a processor array, the ILLIAC-IV. A comparison of the architectures and processing speeds of each class of machines is made. The computing power observed is consistent with the design and purpose of each machine. Also discussed are methods for displaying the vast amount of data that result from such calculations. It is determined that computer graphics offers an effective means for extracting information from large amounts of data. Finally, the scientific value of the calculations are briefly discussed. If caution is applied to interpreting the results, then the electrostatic potential (EP) mappings can be useful in identifying sites of potential chemical interactions.
    Additional Material: 5 Ill.
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  • 95
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    Journal of Computational Chemistry 5 (1984) 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
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  • 96
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The geometries of several conformations of propanal and butanal have been refined by geometrically unconstrained ab initio gradient relaxation on the 4-21G level. Both compounds possess energy minima at O—C—C—C torsional angles of 0° and in the 120° region, and energy maxima in the 70° region and at 180°. The structure of the aldehyde functional group is found to be relatively invariant both when different systems or when different conformations of the same system are compared. Conformationally dependent geometrical trends in propanal and butanal are discussed and found to be subtle yet noticeable.
    Additional Material: 6 Ill.
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  • 97
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    Journal of Computational Chemistry 5 (1984), S. 146-161 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Compact, contracted Gaussian basis sets for halogen atoms are generated and tested in ab initio molecular calculations. These basis sets have similar structure to that of Huzinaga and co-workers' (HTS) sets; however, they give both better atomic total energies and better properties of atomic valence orbitals. These sets, after splitting of valence orbitals and augmenting with polarization functions, provide molecular results that agree well with those given by extended calculations. Basis set superposition error (BSSE) is calculated using the counterpoise method. BSSE has only slight influence on calculated equilibrium geometry, shape of potential curve, and electric properties (dipole and quadrupole moments) of molecules. However, atomization energies may be significantly changed by the BSSE.
    Additional Material: 1 Ill.
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  • 98
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    Journal of Computational Chemistry 5 (1984), S. 186-189 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A computational procedure, developed from the power series method, is used to investigate oscillating systems. In addition to its great accuracy and reduced computer time, the method is very easily programmable since the algorithm is provided by the reaction mechanism itself.
    Additional Material: 2 Ill.
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  • 99
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    Journal of Computational Chemistry 5 (1984), S. 190-196 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab initio self-consistent-field molecular orbital calculations have been carried out for the CnH2n (n = 3 to 6) cycloalkanes and various conformers of their protonated forms. The calculated protonation energies for the sequence of conformers of the protonated forms follow the experimentally observed trend. Correlations between optimum C—C—C bond angles at the protonation site and the calculated protonation energies have been observed, and these correlations may be of some use in estimating protonation energy-bond angle relations in other (strained) cyclic compounds when the central carbon atom of a C—C—C moiety is protonated.
    Additional Material: 4 Ill.
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  • 100
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    Journal of Computational Chemistry 5 (1984), S. 237-240 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The activation energy and optimized transition-state geometry for the abstraction of a hydrogen atom from methane by methyl radical have been calculated by the semiempirical methods MINDO/3 and MNDO. These results are compared with other semiempirical and ab initio results. The MINDO/3 method, based upon accuracy of the computed energy of activation, appears to be the computational method of greatest reliability. A method of locating the transition state on semiempirical surfaces is demonstrated.
    Additional Material: 5 Tab.
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