bluuebunny/crossref_metadata_2025 huggingface dataset:
Untersuchungen an Siliciumphosphaten
Authors: Makart H.
Published: December 2004

Durch Synthesen mit Kieselgel und H3PO4 bei verschiedenen Temperaturen, bzw. mit Kieselgel und P2O5, wurden Silicophosphorsäure H2Si(PO4)2, eine Verbindung 3 SiO2, 2P2O5 und vier polymorphe Modifikationen von SiO2, P2O5, welche als Formen I‐IV bezeichnet wurden, erhalten.
über Struktur und Aktivität der den H2O2‐Zerfall katalysierenden Cu2+‐Komplexe VII
Authors: Sigel H.
Published: December 2004

It has been stated in a preceding paper [3] that only parts of a ligand coordinated to a metal ion can be oxidized by H2O2 (= peroxidative activity). Considering the reversal of this statement to be true, it is shown by means of the peroxidative activity of the Cu2+‐complexes of ATP, ITP, CTP, UTP, and TTP that in these complexes the heteroaromatic groups contribute to the coordination of Cu2+ ion. By analogy with the Cu2+‐ATP‐complex, where a macrocyclic phosphate‐metal‐adenine chelate is formed [4], and based on his experimental results, the author considers the existence of such a macrocyclic chelate in the copper complexes of ITP, GTP, CTP, UTP, and TTP as established. The coordination sites of the heteroaromatic groups in these complexes are discussed.
Untersuchung reversibler Photoprozesse durch Blitzlichtphotolyse III. Photochromie des 1, 3, 6′,8′‐Tetramethyl‐dehydrodianthrons
Authors: Huber J. R. , Wild U. , Günthard Hs. H.
Published: December 2004

The kinetic decay processes of photochromism of 1,3,6′,8′‐tetramethyl‐dianthrone (TMD) are investigated by means of flash photolysis in the solvents cyclohexane and triacetine, as well as in polymethyl‐methacrylate matrices. It is shown that in solution two distinct photochromic states exist which are both fully populated within 5 μs of exitation. The relative population of the two photochromic states is solvent and viscosity dependent. The green photochromic form can also be produced in polymethylmethacrylate matrices. Quenching experiments indicate that both generation and thermal decay kinetics are not influenced by the presence of molecular oxygen. Contrary to prevailing views, the authors conclude that both photochromic states are not triplet states of TMD but probably conformers of the ground state.
Recherches sur les arǒmes 14ecommunication [1] Sur 1′arǒme de café, II Pyrazines et pyridines
Authors: Goldman I. M. , Seibl J. , Flament I. , Gautschi F. , Winter M. , Willhalm B. , Stoll M.
Published: December 2004

Pyrazines and pyridines occurring in a coffee concentrate are analyzed by two procedures. 24 compounds have been identified and the presence of some 10 more is revealed. The syntheses, mass and infrared spectral data of reference compounds are given.
Zur kenntnis der ätherischen öle 6. Mitteilung [1] die thermische cyclisation des (−)‐(r)‐Linalools. Die struktur der Plinole und einiger derivate mit Iridan‐Gerüst [2]
Authors: Stirickler H. , Ohloff G. , Sz. Kováts E.
Published: December 2004

On heating linalool, all the four possible diastereomeric plinols are formed by way of an intramolecular Alder “ene”‐synthesis. The knowledge of their absolute configuration, shown to be 2A‐2D, allows a discussion of the stereochemical course of this reaction.
Magnetische Kernresonanz‐Untersuchungen über die Struktur der Komplexe aus Nitroaromaten mit aromatischen aminen 10. Mitteilung über nucleophile aromatische Substitutionsreaktionen [1]
Authors: Caveng P. , Zollinger H.
Published: December 2004

1. NMR. and visible spectra of the addition products of N,2,4,6‐tetranitro‐N‐methyl‐aniline, 2,4,6‐trinitrochlorobenzene, and 2,4‐dinitro‐6‐cyano‐chlorobenzene with aromatic amines (1‐naphthylamine, N‐mono‐ and ‐di‐methyl‐1‐naphthylamine, 5‐aminotetralin, N‐methylaniline) demonstrate that electron donator‐acceptor complexes (π‐complexes) are formed.
Beiträge zur Chemie der Si‐N‐Bindung, X [1] Oligo‐[1,3‐diaza‐2.sila‐cyclopentane]
Authors: Fink Walter
Published: December 2004

Aus Dimethyldichlorsilan und Äthylendiamin werden endständig‐chlorfunktionelle Oligo‐[1,3‐diaza‐2‐sila‐cyclopentane] dargestellt,magnified imagein denen sich das Halogen durch Butyl‐, Phenyl‐, Diäthylamino‐ oder Triorganosiloxy‐Reste ersetzen lässt.
Die Strukturen der mittleren Ringverbindungen. XII. Kristallstruktur der 1,1,5,5‐Tetramethylcyclodecan‐8‐carbonsäure
Authors: Dunitz J. D. , Eser H.
Published: December 2004

Crystals of 1,1,5,5‐tetramethylcyclodecane‐8‐carboxylic acid are monoclinic, a = 9.22 Å, b = 14.81 Å, c = 11.58 Å, β = 111° 0′, space group P21/c with 4 molecules in the unit cell. The structure has been solved by direct methods and refined by full‐matrix least‐squares analysis of three‐dimensional intensitiy data. The conformation of the ring differs from the previously observed cyclodecane conformation, but the detailed results are abnormal in a number of ways (extremely short CC bond lengths, wide CCC bond angles, large temperature factors). The possibility is discussed that the crystal structure is disordered.
Der Mechanismus der Hydratation von Magnesiumoxid mit Wasserdampf
Authors: Feitknecht W. , Braun H.
Published: December 2004

The hydration of different forms of magnesium oxide by water vapour was studied at room temperature using gravimetric, X‐ray and electron microscopic methods. It takes place in four steps; formation of a layer of chemi‐ and physisorbed water, transition of magnesium and hydroxide ions in the layer of physisorbed water, nucleation of the hydroxide and growth of the hydroxide crystals.
Die Synthese von Acetylen‐carbonyl‐Verbindungen durch Fragmentierung von α, β‐Epoxy‐ketonen mit p‐Toluolsulfonylhydrazin. Vorläufige Mitteilung
Authors: Schreiber J. , Felix Dorothee , Eschenmoser A. , Winter M. , Gautschi F. , Schulte‐Elte K. H. , Sundt E. , Ohloff G. , Kalovoda J. , Kaufmann H. , Wieland P. , Anner G.
Published: December 2004

More than twenty examples illustrate the recently developed oxidoketone‐alkynone‐fragmentation, whereby α,β‐epoxy‐ketones are cleaved under mild conditions with p‐toluenesulfonyl‐hydrazine to give acetylenic ketones or aldehydes.
Über Pterinchemie 23. Mitteilung [1]. Radikalbildung während der Oxydation von Tetrahydrofolsäure und 5,6,7,8‐Tetrahydropterin
Authors: Bobst A.
Published: December 2004

EPR. investigations show the existence of one‐electron oxidation of 5,6,7,8‐tetrahydropterine and tetrahydrofolic acid resulting in unstable cationic radicals of red color which are trapped at liquid nitrogen temperature.
Komplexone XLII. Die Untersuchung der 1:1:‐Komplexe von einigen drei‐und vierwertigen Metall‐Ionen mit Polyaminocarboxylaten mittels Redoxmessungen
Authors: Bottari E. , Anderegg G.
Published: December 2004

The formation of complexes of GaIII, InIII, BiIII, ScIII, ZrIV, and ThIV with polyaminocarboxylate ions was investigated using potentiometric measurements with the redox couples Fe3+/Fe2+ and Tl3+/Tl+. Some data concerning the formation of related hydroxo and hydrogen complexes are reported.
Die Kristallstruktur des l, 6‐8, 13‐Bis‐oxido‐[14]‐annulens
Authors: Ganis Paolo , Dunitz J. D.
Published: December 2004

Crystals of 1,6‐8, 13‐bis‐oxido‐[14]‐annulene are monoclinic, a = 9,29, b = 9,74, c = 11,46 Å, β = 90,0°, space group P 21/c, with 4 molecules in the unit cell. The structure has been solved by direct methods and refined by full‐matrix least‐squares analysis of three‐dimensional intensity data. The cis‐configuration of the two oxygen bridges is confirmed, and the observed molecular parameters are in full accord with the aromatic properties of the molecule.
Thermische Umwandlung von Phenyl‐penta‐2,4‐dienyläthern in 4‐[Penta‐2,4‐dienyl]‐phenole als Beispiel für [5,5]‐sigmatropische Umlagerungen. Vorläufige Mitteilung
Authors: Fráter Gy. , Schmid H.
Published: December 2004

The reaction between phenol and trans penta‐2,4‐dienyl chloride gave trans penta‐2,4‐dienyl Phenyl ether (I), whereas with a mixture of sorbyl chloride and 1‐methylpenta‐2,4‐dienyl chloride, pure trans, trans hexa‐2,4‐dienyl phenyl ether (IV) and trans 1‐methylpenta‐2,4‐dienyl phenyl ether (V) were obtained. The ether I gave, on heating in dilute solution at 185°, 4‐(penta‐2,4‐dienyl)‐phenol (III) as the main product, and also some 2‐(2‐vinylallyl)‐phenol (II). The ether IV provided, on heating at 165°, in addition to the ortho CLAISEN rearrangement product VI, mainly a mixture consisting of 94% 4‐(1‐methylpenta‐2,4‐dienyl)‐phenol (VIII) and only 6% 4‐(hexa‐2,4‐dineyl)‐phenol(IX). The latter product (IX) was the only para isomer produced on heating ether V, but in addition 22% of the ortho rearrangement product VII was formed.

The migrations I → III, IV → VIII, and V → IX, proceeding through a ten membered transition state, are the first [5,5] sigmatropic rearrangements described.
Komplexe von Enniatinen und anderen Antibiotica mit Alkalimetall‐Ionen
Authors: Wipf H.‐K. , Pioda Lavinia A. R. , Štefanac Z. , Simon W.
Published: December 2004

Crystalline 1: 1‐complexes of enniatins with potassium salts are described. Complex formation constants of different antibiotics with sodium and potassium are given.
Der Abbau des Insektizides GS 13005 in der Ratte. Strukturaufklärung der wichtigsten Metabolite [1]
Authors: Esser H. O. , Mücke W. , Alt K. O.
Published: December 2004

The structures of the essential metabolites which are excreted by the rat after oral application of GS 13005 (O,O‐dimethyl‐S‐[(2‐methoxy‐1,3,4‐thiadiazole‐5(4H)‐one‐4‐yl)‐methyl] dithiophosphate) have been elucidated. The product of final oxidation, CO2, was found to be the main metabolite (up to 36% of the dose applied). Among the degradation products excreted in the urine (up to 45% of the dose applied) the two most important were isolated. They are 4‐methylsulfinylmethyl and 4‐methylsulfonylmethyl derivatives respectively of the intact 2‐methoxy‐1,3,4‐thiadiazole‐5‐one heterocycle (metabolites III and II, in amounts of 20–25% and 5–7% of the dose applied, respectively). These metabolites originate by methylation and subsequent oxidation from the mercaptomethyl derivative liberated after hydrolysis of the PS bond of the dithiophosphoric acid ester.
Pulsradiolyse organischer Halogenverbindungen I. Nachweis kurzlebiger Charge‐Transfer Komplexe mit Chloratomen
Authors: Bühler Rolf E.
Published: December 2004

In a solution of benzene in carbon tetrachloride a transient absorption in the visible part of the spectrum could be detected. It appears within less than 0.3 μs after the irradiation by a high‐energy electron pulse, and it can be shown to be due to the charge‐transfer complex between the chlorine atoms as electron acceptors and benzene molecules as electron donors. A variety of aromatic hydrocarbons also yield similar absorption bands in the visible. They show a linear correlation between the absorption energy and the ionisation potential of the aromatic molecules, which is typical for charge‐transfer complexes. A minimum value for the equilibrium constant of complex formation is given. The equilibrium is almost fully shifted to the complex side. An estimated G value for the charge‐transfer complex indicates that the complex is actually part of a main reaction in the radiation‐induced mechanism. The decay of the charge‐transfer complex is mostly pseudo‐first order with a half life of a few microseconds.
Kupferkomplexe von Bisamiden, IV UV.‐Banden binuclearer Koordinationsverbindungen ohne Cu‐Cu‐Bindung
Authors: Zuberbühler A. , Kaden Th.
Published: December 2004

Cupric copper and N,N′‐Bis‐(2‐dimethylaminoethyl)‐oxamid form in aqueous solution six complexes, three of them being binuclear. Potentiometric and spectrophotometric data were used to obtain stability constants and concentration of each complex, and to calculate their electronic absorption spectra. The binuclear compounds show strong absorption bands in the near UV., in analogy to the quite differently structured dimeric copper acetate. It is proposed that all these bands near to 370 nm are of charge transfer type.
Struktur der makrocyclischen Alkaloide Oncinotin und Iso‐oncinotin. 129. (vorläufige) Mitteilung über Alkaloide
Authors: Badawi M. M. , Guggisberg A. , van den Broek P. , Hesse M. , Schmid H.
Published: December 2004

Two new macrocyclic alkaloids oncinotine (1) and isooncinotine (2) have been isolated from Oncinotis nitida BENTH. 1 can be converted into 2 by an amide exchange reaction. The spermidine residue was present in both bases. The structural elucidation was based mainly on (I) the determination of the functional groups, (II) degradation to compounds 12 and 13 and (III) mass spectrometric investigation of 1 and of the above mentioned degradation products.
SN‐2‐artige massenspektrometrische Fragmentierungen bei substituierten N‐Alkylpiperidinen. 10. Mitteilung über das massenspektrometrische Verhalten von Stickstoffverbindungen [1]
Authors: Sailer Kathi , Hesse M.
Published: December 2004

An SN2‐type fragmentation was observed on mass spectrometric analysis of N‐(ω‐X‐alkyl)‐2‐alkylpiperidines (X = NRCOR′, CONH2, COOR, NH2). The molecular ion after loss of the 2 alkyl substituent on the piperidine ring may eject the neutral piperideine on attack of the substituent X on the α‐carbon of the N‐substituted alkyl‐chain. Through this process a cyclic fragment ion is formed. The influence of its ring size and of the substituent X on the stability of this fragment was investigated. The SN2 reaction is favoured in the case of production of five‐ and six‐membered rings.
Etudes stéréochimiques VII Synthèses diéniques en série résinique; action des peroxoacides et des hydrures doubles
Authors: Gastambide Bernard , Langlois Nicole
Published: December 2004

Through a DIELS‐ALDER reaction between citraconic anhydride (1) and methyl resinates, the adducts 2a, b, c were obtained. The epoxide 6, derived from 2a, by acidic methanolysis gave 7 with retention of configuration. The structure of the latter compound was demonstrated by 7 → 8 → 9, the dilactone 9 being characterized by an electronic interaction and an «M coupling». Sodium borohydride reduced 2d and 2a, giving the diols 3d and 3a, respectively the cis‐configuration of which was chemically demonstrated.
Stoffwechselprodukte von Mikroorganismen 74. Mitteilung [1]. Synthese des Ferrichroms. 1. Teil: (S)‐α‐Amino‐δ‐nitr‐ovaleriansäure (δ‐Nitro‐L‐norvalin)
Authors: Maurer B. , Keller‐Schierlein W.
Published: December 2004

(S)‐α‐Amino‐δ‐nitropentanoic acid (δ‐nitro‐L‐norvaline), an intermediate of the total synthesis of ferrichrome, was synthesized starting from diethyl oxalate and γ‐butyrolactone.
Sur les carbonates basiques de fer (III): I. Carbonate basique de fer (III) amorphe
Authors: Dvořák V. , Feitknecht W. , Georǵes P.
Published: December 2004

The preparation of a non‐stoichiometric basic carbonate of iron (III) is described. The amounts of carbon dioxide and water can vary in large limits, depending on the way the samples are dried. The ratio of Fe2O3:CO2 in a fresh product is nearly one, but decomposition takes place already at room temperature and ambient humidity. When heated slowly, the carbon dioxide is given of in two clear steps, an intermediate product being formed at about 200°C. The basic iron (III) carbonate decomposes between 400° and 500°C to an α‐Fe2O3 with still a small amount of carbon dioxide. The infrared spectra show that in the freshly prepared products the greater part of the CO ions are linked by two oxygen atoms to two iron atoms, and a smaller part probably only by one oxygen to one iron atom. In the intermediate product, part of the CO2_3 ions are linked by two oxygen atoms to one iron atom, or a hydrogenocarbonate group may be formed. The X‐ray diagrams taken with Mo Kα rays show only two broad lines.
Sur les carbonates basiques de fer (III): II. Préparation, radiocristallographie et spectres IR. du (NH4)2Fe2(OH)4(CO3)2 · H2O
Authors: Dvořák V. , Feitknecht W.
Published: December 2004

The obtention of the crystalline basic carbonate of iron (III) and ammonium, (NH4)2Fe2(OH)4(CO3)2 · H2O, is described and its formula is established by chemical analysis and infrared spectroscopy. The powder X‐ray diagram could be indexed tetragonally leading to a body centred elementary cell with a = 12,04 ± 0,02 Å and c = 6,62 ± 0,01 Å.

The infrared spectra show that in the CO groups either one oxygen atom is linked to one iron atom or, rather, two oxygen atoms are linked to two iron atoms. The symmetry of the NH groups is lower than C3v. The OH‐groups are linked by hydrogen bonds of 2,75 Å. Two sorts of OH‐groups can be distinguished, with a radius of approximately 1,34 Å and 1, 48 Å, respectively. The iron atoms are octahedrally coordinated by oxygen atoms, but either the octahedra are deformed or the iron atoms are in part coordinated tetrahedrally.
Muscle regeneration, inflammation, and connective tissue expansion in canine inflammatory myopathy
Authors: Salvadori Claudia , Peters Iain R. , Day Michael J. , Engvall Eva , Shelton G. Diane
Published: December 2004

Inflammatory myopathies (IMs) are relatively common in dogs, and canine IMs have many similarities to human IMs. The aim of this work was to analyze aspects of the pathogenesis of canine IM with an ultimate goal of establishing canine IM as a model for human IM. Muscle biopsies from 16 dogs with a histological diagnosis of IM were analyzed to determine degree of muscle regeneration, presence of eosinophils, expression of selected cytokines and chemokines, and extent of fibrosis. Regeneration, as shown by staining for developmental myosin heavy chain, was more extensive than evidenced with hematoxylin–eosin staining in most cases of canine IM. Expression of mRNA encoding transforming growth factor‐beta (TGF‐β) and eotaxin 3 was upregulated in all cases evaluated. Eosinophils were abundant in most cases, and the connective tissue was variably expanded, as demonstrated by the distribution of the ubiquitous extracellular matrix proteins collagen VI and fibrillin. The extensive regeneration demonstrates that muscle may survive this adverse environment if inflammation and fibrosis can be stopped or reduced. Muscle Nerve, 2005
A semiempirical SCF–LCAO–MO treatment of some oxygen‐ and nitrogen‐containing heterocyclic molecules
Authors: Sallavanti Robert A. , Fitts Donald D.
Published: December 2004

The π‐electronic properties of furan, oxazole, benzofuran, benzoxazole, anthranil, and dibenzofuran are calculated by the semiempirical self‐consistent‐field molecular orbital method. A single set of parameters is found which satisfactorily reproduces the π → π* electronic transition energies and other π‐electronic properties.
Analytic techniques for the coupled multiconfiguration SCF perturbation theory
Authors: Jaszuński Michal , Sadlej Andrzej J.
Published: December 2004

The perturbation theory based on the paired excitation multiconfiguration self‐consistent field approach of Clementi and Veillard is considered. The coupled first‐order perturbed orbital equations are analysed and an appropriate computational scheme for their solution is discussed. The proposed computational scheme is analogous to the technique employed for the solution of the coupled Hartree–Fock equations in the one‐configuration approximation. However, because of the presence ofnondiagonal Lagrangian multipliers and the use of different one‐electron operators for different orbitals, the present scheme raises some new computational problems. In this context a new technique for the solution of the unperturbed multiconfiguration self‐consistent field equations is proposed. A simple illustration of the superiority of the multiconfiguration perturbation approach with respect to the ordinary coupled Hartree–Fock scheme is given. Also the validity of the variation formulation of the presented scheme and its relation to the finite‐field approach are discussed.
Calculation of intermolecular interactions within the PCILO framework using fixed wave‐functions
Authors: Lochmann R.
Published: December 2004

The PCILO method was used to calculate intermolecular interactions using fixed polarities. In this way our calculations are without any iteration cycle.

The investigated supermolecules involve London–van der Waals type, hydrogen bonding type, and charge transfer type interactions, respectively. Both stabilization energies and equilibrium distances are in good agreement with the calculated values using optimized wavefunctions.

Also the analysis of the individual contributions to the energy reflects well the mechanism of the intermolecular interactions.
Simplifications in the generation and transformation of two‐electron integrals in molecular calculations
Authors: Beebe Nelson H. F. , Linderberg Jan
Published: December 2004

Approximate numerical linear dependence among the columns of the two‐electron integral matrix and the positiveness of the Coulomb operator are exploited in order to reduce the number of integrals that need to be calculated when a numerical accuracy is given by the machine in use or by the choice of the investigator. Numerical results presented indicate that the method leads to an algorithm for carrying out the two‐electron integral four‐index transformation which in practice can be achieved in a small fraction (˜1/5–1/3) of the time required to generate the integrals by one of the fastest available Gaussian integral programs, Almlöf's MOLECULE. This effectively removes one of the major bottlenecks of computational quantum chemistry.
An algebraic approach to bound states of simple one‐electron systems
Authors: Čížek J. , Paldus J.
Published: December 2004

A very general realization of the so(2, 1) algebra, which easily follows from the basic commutation relations that are satisfied by any pair of mutually conjugate generalized coordinates and momenta, is constructed. Using special cases of this general realization, and closely following the well known derivation of the eigenvalue spectra of the angular‐momentum operators, based on the so(3) algebra, we derive the energy spectrum for the N‐dimensional isotropic harmonic oscillator, and for both the nonrelativistic and the relativistic N‐dimensional hydrogen atom. Special attention is given to a simple derivation of the form of these Hamiltonians in terms of the so(2, 1) algebra generators. In particular, the usually exploited tilting transformation is avoided, and the whole derivation is presented in an extremely simple and straightforward way. The present approach stresses the similarity and mutual relationship between the systems studied and, in addition to introducing some novel techniques and providing considerable insight into the overall structure of these problems, also has a definite pedagogical value.
Angular dependence of Gaussian‐Lobe orbitals. I. Analysis of standard p‐ and d‐orbitals
Authors: Le Rouzo H. , Silvi B.
Published: December 2004

Multipole expansions of Gaussian‐lobe atomic orbitals around their centers are theoretically investigated in order to study the exact angular dependence of such functions. Analytical expressions of the multipole coefficients are derived for standard lobe orbitals. It is shown that the average‐square values of multipole components are related to a unique orbital parameter λ. The numerical values of p‐ and d‐components are given for selected λ and the choice of this parameter is discussed on the basis of symmetry and computational arguments. The transferability of optimized atomic exponents from harmonic (or Cartesian) functions to lobe functions is established so that the possibility of applying the Gaussian‐lobe orbital approach in chemical studies is greatly extended.
Complex scaling transformations in stationary and scattering problems
Authors: Combes J. M.
Published: December 2004

We review the methods and some applications of complex scaling transformation as well as some goals that now seem accessible using this technique in atomic and molecular physics.
Ab initio molecular calculations with pseudopotentials: calculations of double‐zeta quality on BeH2, BH3, CH4, and C2H6
Authors: Gáspár R. , Gáspáar R.
Published: December 2004

A new form of pseudopotential for applicaiton in ab initio molecular calculations is described. A method for determining pseudopotential parameters is suggested and pseudopotential parameters of double‐zeta quality are presented for the first row atoms of the periodic table. The pseudopotential is especially well suited for incorporation into the floating‐spherical‐Gaussian‐orbital (FSGO) method, though it is not restricted to any particular method. Applications of the resulting pseudo‐FSGO method to BeH2, BH3, CH4, and C2H6 are presented.
Geometry of density matrices. III. Spin components
Authors: Harriman John E.
Published: December 2004

A definition is given for the spin‐tensorial components of a p‐electron density matrix for arbitrary p. Certain of these are defined to be standard components, and it is shown that all others can be obtained from them by linear combinations of permutations. When the density matrix is reduced, the standard components either map into standard components of the fewer‐electron density matrix or into the origin. One‐ and two‐electron density matrices are treated in greater detail. Reducing bases are given for the spaces in which the spatial coefficients of the spin components are elements. For spin eigenstates traces of all components are determined, and the π = 1 parts of all components are determined in terms of two independent components, which are themselves determined by the two‐electron charge density matrix. Geometric consequences are investigated.
Optical activity of nonrigid molecules
Authors: Philippot J. , Sengers I.
Published: December 2004

The Longuet‐Higgins group is used to obtain an alternative formulation of a criterion for optical activity of nonrigid molecules recently given by Frei and Günthard.
On the polarity of the amide group and its impact on dipeptide conformation
Authors: Prasad C. V. , Sundaram K.
Published: December 2004

Giving explicit consideration to the lone pairs of the carbonyl oxygen of the amide group it is found that the polarity of the amide group resides essentially in the lone pair. As a confirmation, the lone pairs of the ester group are also found to account for most of its polarity. This localization of amide dipole affects the dipeptide conformation map only in the unallowed regions of the map, but has significant impact on the dipole moment of the dipeptide in different conformations. The experimentally observed dipole moments of dipeptides in solution are in conformity with our assignment of polarity of the amide group.
Analytic perturbation theory and localization phenomena
Authors: Brändas E. J. , Obcemea C. H.
Published: December 2004

This paper attempts to apply the results of analytic perturbation theory to systems exhibiting some degree of randomness in their state variables. In particular, we focus on the localization problem in the Anderson model. It is shown that this approach proves the existence of bound states as a result of the statistical treatment of the Weinberg–van Winter–Hunziker irreducible N‐particle kernel. The analysis is extended beyond the one‐particle cluster approach and the occurrence of higher‐order clusters is discussed in relation to the diluteness criterion and the conditions set on the interaction potential V.
MCSCF optimization through combined use of natural orbitals and the brillouin–levy–berthier theorem
Authors: Ruedenberg K. , Cheung L. M. , Elbert S. T.
Published: December 2004

A novel approach is developed for optimizing molecular orbitals within the context of a multiconfiguration self‐consistent‐field problem. The MCSCF wave function is determined through a sequence of eigenvalue problems in the multiconfiguration space and the single‐excitation space. They are used to iteratively improve the natural orbitals, which in turn are related, by successively improved transformations, to the MCSCF orbitals. The mathematical problems arising out of this general concept are solved and the computational implementation is discussed. In many applications the method has proven itself as a powerful approach in forcing rapid convergence. Adaptation to spin and spatial symmetry is maintained throughout and the procedure is applicable to excited states as well as to ground states.
Electronic rearrangements during chemical reactions. II. Planar dissociation of ethylene
Authors: Cheung L. M. , Sundberg K. R. , Ruedenberg K.
Published: December 2004

The direct dissociation of ethylene into two methylenes is studied along the least motion reaction path by means of an ab initio multiconfiguration self‐consistent‐field (MCSCF) calculation. All eight configurations arising from those valence orbitals that form the CC bonds, seven of them singlet coupled and one triplet coupled, are taken into account. The HCH bond angle is optimized along the entire reaction path. Separate MCSCF optimizations are carried through for the lowest two states of 1Ag symmetry. The (1Agσ2π2) ethylene ground state dissociates into two (3B1σπ) ground‐state methylenes. The (1Agσ2π*2) excited state of ethylene dissociates into two (1A1σ2) excited methylenes. It is established that both these dissociations proceed without any barrier in the energy curve. In the ground state, where orbital symmetry is conserved, the π‐bond breaks before the σ‐bond, and the calculated heat of reaction agrees within 6 kcal/mol with the experimental value. In the excited state, where orbital symmetry is not conserved, the nonbonded repulsion between methylene σ2 lone pairs is found to blend into the antibonding character of the excited ethylene, yielding an energy curve that is everywhere repulsive. However, the variation of the HCH angle during the dissociation process is not simple, initially it expands and subsequently it contracts. Quantitative analytical approaches are developed which furnish conceptual interpretations of the orbital changes and configurational changes along the reaction path.
Energy of planar autoassociation of xanthine and spatial structure of poly(riboxanthylic acid)
Authors: Geller M. , Lesyng B. , Pohorille A.
Published: December 2004

First‐ and second‐order perturbation theory in a polarization approximation was employed to calculate interaction energies of planar xanthine–xanthine pairs in stable configurations. Electrostatic energy was obtained in the atomic‐dipole approximation. The results provided a basis for formulation of a four‐stranded model of poly(xanthylic acid) that allows two hydrogen bonds per base. The model accounts satisfactorily for the unusual thermal stability and the observed pH transition of the polymer. The latter is due to the gradual dissociation of the N3 protons accompanying by disrupture of the weak N3H ··· O6 hydrogen bonds. However, the structure is only moderately weakened since the configuration of the coplanar bases remains stabilized by four N1H ··· O2 hydrogen bonds.
Determination of potential‐energy surface of molecules in an applied field on the basis of virial relations
Authors: Rossikhin V. V. , Voronkov E. O. , Kruglyak Yu. A.
Published: December 2004

The quantum‐mechanical virial theorem (in diagonal and nondiagonal forms) for molecules in an external, weak, uniform electric field is used for obtaining the analytical expression of the potentialenergy surface in the Hartree–Fock–Roothaan one‐determinantal approximation. The polarizability tensor components of the H2O molecule are computed on this basis. The dependence of basing the atomic orbitals upon the intensity of the applied field lead to good coincidence of results with the data of near Hartree–Fock calculations.
Second‐order dispersion energy between interacting hydrogen pairs by using the Borel integral
Authors: Yousif F. N. , Shukla G. C.
Published: December 2004

The second‐order dispersion energy between interacting hydrogen pairs has been evaluated by the Borel‐integral method. The results are in complete harmony with those obtained by the method of Padé approximants.
Active‐site α‐helix in papain and the stability of the ion pair RS− ··· ImH+.Ab initio molecular orbital study
Authors: van Duijnen P. Th. , Thole B. Th. , Broer Ria , Nieuwpoort W. C.
Published: December 2004

Ab initio MO calculations, using both minimal (STO‐3G) and extended (Roos–Siegbahn) basis sets are reported for the systems methanethiol–imidazole, methanethiol–imidazole–formaldehyde, and methanethiol–imidazole–formamide, which, together with a point‐change representation of a long α‐helix, form models for the active site of papain. It is shown that the large electric field exerted by the helix in the active‐site region is responsible for the presence of the essential residues Cys 25 and His 159 in the form of an ion pair RS− ··· ImH+, which is crucial for a recently proposed mechanism for the catalytic action of the enzyme. Also, an explanation is given for the anomalies in measured pK values for these residues. Detailed studies on the (sub)systems show that minimal basis sets lack the flexibility necessary for describing the type of proton transfer involved. We conclude that α‐helices are essential parts of enzymes and that they play a significant role in the catalytic process.
Dynamic multipole polarizabilities of atomic systems
Authors: Easa S. I. , Shukla G. C.
Published: December 2004

Two previous schemes for the calculation of dynamic multipole polarizabilities of atomic systems, namely, a hydrodynamic analogy to quantum mechanics and a perturbation expansion of the energy in multipoles, follow also from the conventional time‐dependent perturbation scheme.
Possible generalization of the optimized diatomics‐in molecules theory: Further studies of the diatomic state mixing parameter adjustment
Authors: Zaitsevskii A. V. , Nemukhin A. V. , Stepanov N. F.
Published: December 2004

A generalization of optimized diatomics‐in‐molecules method that provides an accurate treatment of overlap integrals is presented. The possibilities of the method to reproduce potential surfaces of the 4B2, 2B2, and 2A1 states of the H3 molecule are investigated. It is shown that satisfactory results can be achieved only for a single state under consideration, but not for the three states simultaneously.
“Ring currents” static hypersusceptibilities
Authors: Gayoso J. , Maouche B. , Ouamerali O. , Baba‐Ahmed A.
Published: December 2004

The Hückel–London theory has been applied to the calculation of the “ring currents” octopole hypersusceptibilities of a series of conjugated compounds. Our calculations have been performed using fourth‐order Rayleigh–Schrödinger perturbation technique. This is believed to be the first calculation of this kind. It is found that the values of “ring currents” hypersusceptibilities of fulvene and azulene are larger, in absolute magnitude, than the values corresponding, respectively, to benzene and naphthalene. It is found that, in most cases, the “ring currents” hypersusceptibilities are diamagnetic (negative values) for aromatic molecules and paramagnetic (positive values) for pseudoaromatic or antiaromatic compounds.
Method for computing the characteristic polynomial
Authors: Mladenov Ivailo M. , Kotarov Marin D. , Vassileva‐Popova Julia G.
Published: December 2004

A new algorithm for calculating characteristic coefficients is proposed.
Chemical graph theory: Modeling the thermodynamic properties of molecules
Authors: Mekenyan O. , Bonchev D. , Trinajstić N.
Published: December 2004

Graph‐ and information‐theoretical indices were recently developed as quantitative structural characteristics of molecules. In this paper they are found to correlate well with a number of molecular properties of alkylbenzenes: heats of formation, combustion (both in liquid and gas phase) and vaporization, molecular volume, boiling point, and parachor. The topological information index and the number of carbon atoms are taken as variables. The correlation coefficient was found to be equal or close to 1. In three cases the mean relative error is less than 0.1%, in another three cases it is within the range 0.2–0.4%, and for boiling points only it is 1.25%. The proposed approach is compared with the additive scheme of Tatevskii.
Calculated optical spectrum of model oxyheme complex
Authors: Loew Gilda H. , Herman Zelek S. , Zerner Michael C.
Published: December 2004

The optical spectrum of a model oxyheme complex has been calculated using a new intermediate neglect of differential overlap (INDO‐SCF‐CI) method that allows for the inclusion of configuration interaction and transition metals. In addition to the porphyrin π→π* transitions common to all heme proteins, four weak x,y polarized transitions observed only in oxyheme complexes have been calculated and assigned to excitations involving the lowest‐empty highly delocalized (Oπ, dπ) orbital. Two broad z‐polarized bands observed in the single‐crystal polarized absorption spectra of oxymyoglobin and hemoglobin have also been calculated. Controversy exists over the assignment of these transitions and, in particular, over the extent of involvement of the oxygen ligand. Our calculations assign the weaker near‐IR visible band mainly to the d σ dπ→ dπ* excitations and the more intense UV band mainly to a2u → dσ* excitations. While significant participation (25%) of the highly delocalized (Oπ, dπ) virtual orbital is also found, these z‐polarized transitions need not be totally unique to oxyheme complexes, in keeping with experimental observation.
Weak interactions at the photoexcited states of partially oriented aromatic chromophores in man‐made bilayer membranes
Authors: Nagamura Toshihiko , Takayanagi Takashi , Matsuo Taku
Published: December 2004

Monoalkyl and dialkyl quarternary ammonium salt‐type cationic surfactants containing a phenoxy group as aromatic chromophores at different positions of alkyl chains were synthesized. Monoalkyl‐type surfactants formed micelles in aqueous solutions. The bilayer structure similar to that found in phospholipid liposomes was obtained in the aqueous dispersions of dialkyl‐type surfactants. The phenoxy groups were partially oriented and aligned in these molecular assemblies. The interactions of aligned phenoxy groups in micelles or bilayers resulted in luminescence with lower energy than that of the monomer fluorescence or in a radiationless deactivation of excited states. Such interactions could be effectively prevented in bilayer structures composed of surfactant molecules containing a “spacer chain” between aligned chromophores. Evidence was obtained supporting energy migrations between aligned chromophores that were separated by a dodecyl chain in the bilayer structure.
Physicochemical properties of SF 6847, a potent uncoupler of oxidative phosphorylation in mitochondria in relation to its activity
Authors: Yoshikawa Kenichi , Kumazawa Noriyuki , Terada Hiroshi , Akagi Kazuo
Published: December 2004

The steric and electronic structure of the most potent uncoupler of oxidative phosphorylation, SF 6847, was studied. From 1H NMR measurements, it was found that the benzylic protons meta to the hydroxyl group are equivalent in neutral form, and that these protons tend to become non‐equivalent on acid dissociation of the phenolic proton. The CNDO/2 calculation of the dimethyl derivative of SF 6847 showed that in the most stable conformation the angle of the malononitrile group with respect to the benzene ring is about 40° and that the planar form is quite unstable. Results on electronic absorption of SF 6847 in various media showed that the acid dissociation of its phenolic group is affected very much by small changes in the nature of the surrounding environment. It was also found that the calculated total energy differences between the anionic and neutral forms are correlated well with the uncoupling activities of 4‐substituted 2,6‐di‐tert‐butylphenol derivatives.
Scaled single‐zeta basis set for use with a silicon effective potential: Generalized valence bond description of disilane
Authors: Moskowitz Jules W. , Topiol Sid , Snyder Lawrence C. , Ratner Mark A.
Published: December 2004

A compact and efficient scaled single‐zeta basis set has been developed for use in conjunction with the coreless Hartree–Fock silicon effective potential. The scale factors were determined by minimizing the electronic energy of the disilane molecule. Based upon a generalized valence bond computation using this basis, we conclude that the classical concept of localized σ bonds is adequate to fully explain the electronic structure of disilane in analogy to the ethane molecule.
Optical oscillator strengths for isoelectronic ions of nitrogen
Authors: Ganas P. S.
Published: December 2004

An analytic atomic active electron model potential adjusted to experimental single‐particle energy levels is used to generate wave functions for the valence and excited states of O1+, F2+, Ne3+, Na4+, and Mg5+. Using these wave functions in conjunction with the Born approximation and the LS‐coupling scheme, we calculate optical oscillator strengths for excitations from the 1s22s22p3(4S3/2) ground state. The results are compared to experimental data and other calculations. Systematic trends along the isoelectronic sequence are discussed.
Calculation of the minimum energy conformation of acetylcholine using a global optimization technique
Authors: Rao Gita Subba , Tyagi R. S. , Mishra R. K.
Published: December 2004

The conformational energy of acetylcholine is minimized with respect to the distances between nonbonded atoms with the help of the Bremermann method of unconstrained global optimization. The set of distances for which the energy is the absolute minimum is then used to calculate the coordinates of all the atoms and hence the conformation of the molecule. The simplest type of potential function, namely the classical potential function is chosen for the calculation. The major advantages of this method are (i) that the starting point need not be close to the actual solution, (ii) that it gives the global minimum, irrespective of the starting point, (iii) that it is very general and can be used for any type of potential function, and (iv) that it does not require the computation of gradients. The results obtained are in very good agreement with those of other workers.
Ab initio valence bond calculations. XI. Pyridine: Ground and ionized states
Authors: Tantardini Gian Franco , Simonetta Massimo
Published: December 2004

The ab initio valence bond method has been used to study the ground and the lowest vertical valence ionized states of pyridine. On the basis of our calculations the first two ionization potentials are assigned to π and n electron removals, respectively. The final wave functions have been interpreted in terms of valence bond structures by means of an appropriate population analysis.
Morse matrix elements: An asymptotic expansion treatment
Authors: Chakraborty B. P.
Published: December 2004

An asymptotic expansion method has been used to calculate the Morse matrix elements for the vibration–rotation transition. A general expression has been derived for the quartic matrix elements, which can be reduced to the expressions for the cubic, quadratic, and linear matrix elements. The results agree extremely well with those given by the factorization method outlined by Badawi et al., and are similar to those given by Coquant et al., who used quite complicated and lengthy equations based on the Dunham potential. Earlier works to calculate the electronic transition probability parameters utilizing the above mentioned asymptotic expansion technique have also been extended and modified.
Application of the theory of symmetry of nonrigid molecules to the calculation of the conformational dependences of the torsional potential and dipole moment of acetone‐related molecules
Authors: Labbe A. Toro , Maruani J.
Published: December 2004

We have investigated the conformational dependences of the torsional potential and dipole moment of double‐rotor molecules related to acetone, using semiempirical and ab initio calculations and expressing the results in terms of limited Fourier‐series expansions. The use of the isodynamic operations of nonrigid molecules to obtain symmetry‐adapted quasianalytic forms for the various properties helps compute the representative surfaces with a minimum number of points. Potential surfaces have been calculated for planar ground‐state acetone (CNDO/2, STO/3G, and STO/4‐31G) and both pyramidal excited‐triplet acetone and ground‐state dimethylamine (CNDO/2). For groundstate acetone STO/4‐31G brings the results obtained with STO/3G closer to those from CNDO/2 and from experiment. The potential surface of excited‐triplet acetone appears intermediate between those of ground‐state acetone and dimethylamine. For dipole moments the convergence of the harmonic expansions of the vector components is slower than that of the torsional potential whereas that of the vector magnitude is faster.
Some properties of the Lagrange multiplier μ in density functional theory
Authors: Nguyen‐Dang T. T. , Bader R. F. W. , Essén H.
Published: December 2004

Some new properties of the Lagrange multiplier μ introduced through the normalization constraint on ρ in the variations of energy density functionals are determined. Through arguments concerning the homogeneity properties of these functionals with respect to μ, it is demonstrated that at the point of variation μ = μ0 = E0/N, where E0 is the ground state energy and N is the total particle number. It is also shown that the value of μ0 is independent of the normalization imposed on ρ. The interpretation of μ0 as a chemical potential is discussed in the light of these findings.
Large‐scale RPA calculations of chiroptical properties of organic molecules: Program RPAC
Authors: Bouman Thomas D. , Hansen Aage E. , Voigt Bjørn , Rettrup Sten
Published: December 2004

The computational considerations involved in calculating ordinary and rotatory intensities and electronic excitation energies in the random phase approximation (RPA) are examined. We employ a localized orbital formulation in order to analyze the results in terms of local and charge‐transfer excitations. Occupied orbitals are localized by the Foster–Boys procedure. The virtual space is transformed into a localized “valence” set that maximizes dipole strengths with the occupied counterparts, and a delocalized remainder. The two‐electron integral transformation is performed with an efficient algorithm, based on Diercksen's, that generates only the particle–hole‐type integrals required in the RPA. The lowest solutions of the RPA equations are obtained iteratively using a modification of the Davidson‐Liu simultaneous vector expansion method. This allows the inclusion of the entire set of particle–hole states supported by a basis set of up to 102 orbitals. Calculations at this level give better excitation energies and intensities than SDCI methods, at substantial savings in computational effort. Comparative timings, computed results and analysis in terms of localized orbitals are given for planar and distorted ethylene using extended atomic orbital bases including diffuse functions. The results for planar ethylene are in excellent agreement with experiment.
Culture and Welfare State Policies: Reflections on a Complex Interrelation
Authors: PFAU-EFFINGER BIRGIT
Published: December 2004

In comparative welfare state analyses, cross-national differences have often been explained both by the specific profiles of welfare state institutions and the constellations of social actors. However, the way in which cultural differences also contribute to the explanation is often ignored, or at least treated as a more marginal issue. The aim of this article is to reflect on the relationship between culture and welfare state policies, and consider how it might be analysed in a comparative perspective. A theoretical framework for analysis is introduced in which the relationship of culture and welfare state policies is conceptualised as a complex, multi-level relationship which is embedded in the specific context of a particular society and can develop in contradictory ways.