bluuebunny/crossref_metadata_2025 huggingface dataset:
Phosphinites of carbohydrates as chiral ligands for asymmetric synthesis catalysed by complexes. IV. Influence of the solvent and the structure of cationic 4,6‐0‐benzylidene‐2,3‐0‐bis(diphenylphosphino)‐D‐hexopyranoside‐rhodium(I) chelates on enantioselectivity in Hydrogenation of Dehydroamino Acid Derivatives
Authors: Selke Rüdiger
Published: January 2005

Cationic rhodium(I)‐chelates of 4,6‐benzylidene‐2,3‐0‐bis(diphenylphosphino)‐D‐hexopyranosides bearing axial 0‐functions, as for instance manno‐ 5 and galactopyranosides 4c, 4d or α‐D‐glycopyranosides, show lower enantioselectivity in the hydrogenation of dehydroamino acid derivatives than chelates of the all‐equatorial phenyl 4,6‐0‐(R)‐benzylidene‐2,3‐0‐bis(diphenylphosphino)‐β‐D‐glucopyranoside 3d (abbreviated Ph‐β‐glup). Complexes of the galactopyranosides 4c and 4d give an abnormal decrease of enantiomeric excess with the prochiral dehydroamino acid 1c in contrast to the analogous substrate ester 1d. In hydrogenations with [Rh(Ph‐β‐glup)(COD)] A as precatalyst various weak coordinating anions A⊖ do not produce differences in % ee, and the solvent effect remains low. However, an analogous chelate of the methyl α‐anomer bisphosphinite Me‐α‐glup 3a gives rise to inversion of the optical induction using benzene as solvent.
1,2,3‐Triazabutadiene XXI [1]. Zur Bestimmung des Oberflächenpotentials und des relativen pH‐Wertes in der Sternregion anionischer Mizellen unter Verwendung von 1‐(4′‐Chlorphenyl)‐3‐(3‐methylbenzthiazolinyliden‐(2))‐triazen als Sonde
Authors: Fanghänel E. , Ortmann W.
Published: January 2005

1,2,3‐Triazabutadienes. XXI. Determination of the Electrical Surface‐potential and of the Relative pH Value in the Stern Region of Anionic Micelles by using 1‐(4′‐Chlorphenyl)‐3‐(3‐methylbenzthiazolinyliden‐(2))‐triazene as Probe

The title triazene is insoluble in water but it can be solubilized in the Stern region of micelles. It is used as pH indicator for the Stern region of anionic micelles. The relative pKs‐values for the triazene are determined in anionic micellar solutions of different detergents. The electrical potential at the surface of the charged micelles is calculated using the value of SDS‐micelles for calibration. The dependence of the electrical potential and the pH value in the Stern region on the structure of the detergents is discussed.
Transformation von Uridin‐ zu Cytidinderivaten durch selektive Aminierung
Authors: Krug A. , Schmidt S. , Lekschas J. , Lemke K. , Cech D.
Published: January 2005

Transformation of Uridine Derivatives into Cytidines via Selective Amination

The synthesis of some 5‐fluorosubstituted cytidine 2 derivatives via amination of corresponding uridine derivatives 1 is described. 5‐Substituted 4‐tetrazolo pyrimidinone derivatives 5 are key intermediates in the procedure. The method used is extended to other fluorinated starting materials, e.g. fluorinated uridinedinueleotides 7 or 2′‐deoxy‐2′‐fluorouridine 9. The fluoro containing products are easily available by fluorination with elemental fluorine or hydrogene fluoride.
Pyryliumverbindungen. 44 [1]. 2‐(2‐Hydroxy‐3‐oxo‐cycloalk‐1‐enyl)‐2H‐thiopyrane aus 2,4,6‐Triaryl‐thiopyryliumsalzen und Cycloalkan‐1,2‐dionen
Authors: Zimmermann T. , Fischer G. W. , Olk B.
Published: January 2005

Pyrylium Compounds. 44. 2‐(2‐Hydroxy‐3‐oxo‐cycloalk‐1‐enyl)‐2H‐thiopyranes from 2,4,6‐Triarylthiopyrylium Salts and Cycloalkane‐1,2‐diones

2,4,6‐Triarylthiopyrylium salts 5 react with cyclopentane‐1,2‐dione (2a) or cyclo‐hexane‐1,2‐dione (2b) in the presence of an appropriate acid binding agent (e.g. sodium acetate, piperidine acetate, triethylamine/acetic acid, triethylamine) to give the hitherto unknown 2‐(2‐hydroxy‐3‐oxo‐cycloalk‐1‐enyl)‐2H‐thiopyranes 6. – The structure of the novel compounds was established by n.m.r., i.r. and u.v. spectroscopic methods.
Zur reversiblen Umwandlung von 3‐Diethylamino‐5‐phenyl‐1,2,4‐dithiazolium‐halometallaten in Metallchelate der 3‐(Thio)benzoyl(thio)harnstoffe
Authors: Hartung J. , Rosenbaum K. , Beyer L. , Losada J. , Fernandez V.
Published: January 2005

About the Reversible Conversion of 3‐Diethylamino‐5‐phenyl‐1,2,4‐dithiazoliumhalometallates into Metal Chelates of 3‐(Thio)benzoyl(thio)ureas

Redox reactions of 3‐diethylamino‐5‐phenyl‐1, 2,4‐dithiazolium halometallates 1a‐e and metal chelates (M = CuII (2 A), CoII (2 C), NiII (2 F)) of 3‐thiobenzoylthioureat was studied by cyclic voltammetry. 1 are converted by reduction into 2. The mechanism of the oxidation of 2 A, C, F into 1a, d, e is dependent on the central ion.

On formation of 1 a from copper(II) chelates of 3‐benzoylthiourea 3 A by means of thionylchloride as well as by electrochemical oxidation 3‐benzoylureas 4 A are formed as sideproducts.
Zur Stereochemie von N,N′‐Bis‐[3‐(o‐ethoxyphenoxy)‐2‐hydroxy‐propyl]‐ethylendiamin
Authors: Kristen H. , Wrubel F. , Widuwild H. , Lücke L.
Published: January 2005

Stereochemistry of N,N′‐Bis‐[3‐(o‐ethoxyphenoxy)‐2‐hydroxy‐propyl]‐ethylendiamine

N,N′‐Bis‐[3‐(o‐ethoxyphenoxy)‐2‐hydroxy‐propyl]‐ethylene diamine (5), synthesized from racemic 1,2‐anhydro‐3‐O‐(o‐ethoxyphenyl)‐glycerol (1) and ethylene diamine (2) or N,N′‐dibenzyl ethylene diamine (3) crystallized in two fractions with different melting points. Both of these analytically pure products gave identical two spot tl‐chromatograms on achiral phases. Attempts were made to resolve the mixtures which proved to consist of configurative but not constitutive isomers. Optically pure products were synthesized from chiral precursors.
Reactions of 2‐arylhydrazones of 1,2,3‐triketones with 1,2‐diaminoethane. I. Synthesis and spectral characterization of 6‐arylazo‐2,3‐dihydro‐1H‐1,4‐diazepines and 3,10‐diarylazo‐4,9‐dimethyl‐5,8‐diaza‐3,9‐dodecadiene‐2,11‐diones
Authors: Opozda Ewa , Śledziewska Ewa
Published: January 2005

Reactions of 3‐arylhydrazones of 2,3,4‐pentanetrione (1a–1e) and 2‐arylhydrazones of 1,3‐diphenyl‐1,2,3‐propanetrione (1f–1l) with 1,2‐diaminoethane have been studied. It was found, that 3‐arylhydrazones of 2,3,4‐pentanetrione react with 1,2‐diaminoethane with formation of 6‐arylazo‐2,3‐dihydro‐1,4‐diazepines (2a–2e) or the diarylazo derivatives of 4,9‐dimethyl‐5,8‐diaza‐3,9‐dodecadiene‐2,11‐dione (3a–3e). Analogous reactions of 2‐arylhydrazones of 1,3‐diphenyl‐1,2,3‐propanetrione yielded exclusively the derivatives of dihydrodiazepine. The structure of obtained products has been elucidated on the basis of i.r., m.s. and 1H‐n.m.r. spectra.
The Alkali Metal Reduction of Trimethoxybenzenes in hydrocarbon solvents
Authors: Dubis Alina T. , Morzycki Jacek W. , Poplawski Janusz
Published: January 2005

A series of trimethoxybenzenes was subjected to reduction in hydrocarbon solvents. 1,2,3‐Trimethoxybenzene (1) and 1,2,4‐trimethoxybenzene (2) underwent selective demethoxylation in high yields, whereas the 1,3,5‐substituted isomer 3 proved resistant to the reduction conditions. The reactions mechanism involves the fission of a methoxyl radical from an initial radical anion. The accompanying side‐reactions, i.e. demethylation and deoxygenation, may be suppressed by the addition of n‐butanol as a proton source.
Strukturelle Abwandlungen an N‐Acetylneuraminsäure. 22 [1]. Zur Umsetzung von Methyl‐5‐acetamido‐7,8‐anhydro‐4‐O‐t‐butyldimethylsilyl‐3,5‐didesoxy‐D‐glycero‐ und L‐glycero‐β‐D‐galakto‐nonulopyranosidonsäure‐methylester mit Bis‐imidazolylthiocarbonat
Authors: Zbiral E. , Brandstetter H. H.
Published: January 2005

Structural Variations on N‐Acetylneuraminic Acid. 22 On the Reaction of Methyl[5‐Acetamido‐7,8‐anhydro‐4‐O‐t‐butyldimethylsilyl‐3, 5‐dideoxy‐D‐glycero‐and‐L‐glycero‐β‐galacto‐2‐nonulopyranosid]onate with Diimidazolylthiocarbonate

The title compounds 1 and 3 are transformed with diimidazolylthiocarbonate into the cyclic 8(S),9(O)‐dithiocarbonatosialic acid derivatives 2 and 4 as well as into a mixture of the cyclic 8(S),9(O)‐monothiocarbonato derivatives 5a and 5b, which turned with acetanhydride pyridine to the corresponding 4‐O‐t‐butyldimethylsilyl‐7‐O‐acetyl‐ and 4,7‐di‐O‐acetyl derivatives 5c and 5d.
Neuartige Steroidale Orthoester durch intramolekulare Cyclisierung von Ethinylcarbinol‐Derivaten mittels Organylhypoioditen
Authors: Henkel T. , Beckert R. , Klemm D.
Published: January 2005

Novel Steroidal Orthoesters by Intramolecular Cyclisation of Ethynylcarbinol Derivatives with Organic Hypoiodites

The iodination of the 17β‐acetoxy‐17‐ethynylsteroid 2 using iodine/copper(II)‐acetate in combination with the nucleophiles acetic acid, water and methanol is reported. Examples for chemical modification of the products are described. A cyclisation occurs in the case of iodomethoxylation as a formal through‐space 1.4‐addition of the reagent forming a mixture of 4 isomer iodomethylen‐1,3‐dioxolanes. The configuration and ratio of the isomers as well as analytical data of this hitherto unknown dioxolane‐system are given.
Untersuchungen zu Mesityldimethylhalogensilanen als Schutzgruppenreagenzien für Alkohole
Authors: Weinzierl Uwe , Seidel Wolfgang
Published: January 2005

Investigation on Mesityldimethylhalosilanes as Protectiv Reagents for Alcohols

The use of mesityldimethylhalosilanes as protecting reagents for steroid alcohols was investigated. The resistance of the obtained silyl ethers was tested in various media. The reaction pathway of the acidic hydrolyses of the silyl ethers is explained.
Modelization by molecular mechanics (and X‐rays) of five‐membered heterocyclic nitramines
Authors: Delpeyroux D. , Blaive B. , Gallo R. , Graindorge H. , Lescop P.
Published: December 2004

Molecular Mechanics (MM) calculations and X‐ray structures are compared for 1,4‐dinitro tetraazabicyclo(3,3.0)octanedione [1,4‐dinitro glycoluryl = 1,4‐DINGU]; 1,3‐dinitro‐4,6‐diacetyl tetraazabicyclo(3.3.0)octanedione [1,3‐dinitro‐4,6‐diacetyl glycoluryl = 1,3‐DINDAGU]; and 2,5,7,9‐tetranitro tetraazabicyclo(3.4.0)non‐anone (K 56). The agreement between geometries obtained by MM and X‐ray is good. The structure and the conformational states of the three model molecules are discussed. 1.4‐DINGU and K 56 are more symmetrical by MM than by X‐ray; this is due (at least in part) to packing in the crystal lattice. The parameters to be used in MM calculations, for treating stretching, bending and eclipsing forces in nitramines are given.
The Gibbs Energy Minimization Approach in the estimation of detonation, explosion and work production parameters of confined charges
Authors: Rigas F. , Pitsinis N. , Tsimogianni P.
Published: December 2004

A method is suggested for the estimation of the physicochemical parameters associated with the entire phenomenon of detonation of explosive mixtures, exclusively containing the atomic species C,H,N,O, and expected to yield gaseous products. The equation of state applied for the products is a modified Abel equation. The calculation algorithm developed, constitutes the frame of construction of a computer program. The input required are the initial composition and apparent density of the explosive mixture and the final work production pressure. Sample applications for pure pentaerythrite tetranitrate detonation, TNT‐ammonium nitrate‐water slurries, and dry mixtures explosions are provided.
Synthesis, Properties and Performance of the High Explosive ANTA
Authors: Simpson R. L. , Pagoria P. F. , Mitchell A. R. , Coon C. L.
Published: December 2004

3‐Amino‐5nitro‐1,2,4‐triazole(ANTA) was prepared and evaluated in terms of insensitivity and performance. The material is very insensitive to impact and moderately so to thermal stimuli. Performance was found to be inferior to 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB). The best synthesis of ANTA is a three‐step route using commercially available 3,5‐diamino‐1,2,4‐triazole.
A variational approach to the solution of poisson's equation in prolate spheroidal coordinates
Authors: Csavinszky P.
Published: January 2005

The present paper considers a charge distribution with an axis of rotational symmetry and formulates a variational principle in prolate spheroidal coordinates by which an approximate solution to Poisson's equation may be obtained. The feasibility of the suggested approach is demonstrated by a simple example for which the exact solution is known.
Ab initio mo calculations on the chlorophyll–water system and estimation of the structure of the special pair
Authors: Kashiwagi Hiroshi , Hirota Fumihiko , Nagashima Umpei , Takada Toshikazu
Published: January 2005

Ab initio LCAO SCF MO calculations were carried out on the chlorophyll–water system, which is considered as a moiety of the so‐called special pair in the reaction center of photosynthesis. The ionization potential and electron affinity of the system were 6.16 and 0.30 eV from the ΔSCF calculations. By using the atom–atom potential method for describing intermolecular interactions, we estimate the structure of the pair to be very close to that proposed by Shipman and others. The two major contributions to interaction energy are due to hydrogen bonds with water molecules and dispersion between the two chlorophyll planes, respectively.
On the red shift of OH stretching region vibrations in ice and water
Authors: Kryachko Eugene S.
Published: January 2005

The nature of the red shift of frequencies of the fundamental modes, v1 and v3, in the OH stretching region of the vibrational spectrum of ice (and, possibly, in water) under H‐bonding formation is explained in the framework of the continuum approach for the one‐dimensional infinite chain of water molecules represented as dipolar and polarizable OH oscillators vibrating in the definite force field. The explicit expressions in the form of the generalized cnoidal nonlinear waves describing these fundamental modes and obtained as the solutions of the nonlinear Klein–Gordon equation of motion, and their red shifts that are consistent with experimental observations, are presented.
Quantitative measures of similarity between pharmacologically active compounds
Authors: Bowen‐Jenkins Philippa E. , Richards W. Graham
Published: January 2005

A theoretical measure of molecular similarity based on ab initio computations of electron density derived from molecular orbital wave functions is first applied to a model series (CH3CH2CH3, CH3OCH3, and CH3SCH3) and then to the rings in a series of prostaglandins and to some histamine H2 antagonists. Comparison in terms of valence electron density seems to be a good basis for structure‐activity studies.
Experimental and theoretical studies of small‐angle electron scattering by the water molecule
Authors: Takeuchi Munetaka , Nagashima Makoto , Tanaka Kiyoshi , Konaka Shigehiro , Kimura Masao
Published: January 2005

The total (elastic plus inelastic) intensities of 51 keV electrons scattered by water molecules have been measured over a range of 1 ≦ K = (4π/λ) sin(θ/2) ≦ 12 Å−1. A computer program, ELIC, has been written for calculating the total intensities of electrons scattered by free molecules. The intensities can be calculated with self‐consistent field and configuration interaction wavefunctions. The theoretical intensities based on a CI wavefunction are in good agreement with the observed intensities.
C. A. coulson and the surface energy of metals: The distribution of eigenvalues as a difficult problem in number theory
Authors: Čížek Jiří , Del Re Giuseppe
Published: January 2005

An article by Coulson on the relationhship of physics and mathematics has attracted our attention to problems already discussed by Titchmarsh, namely the distribution of quantum energy levels of a particle confined in a square or a cube with infinite potential‐energy walls. These problems are identical to some classical problems in the theory of lattice points, which belongs to number theory. They are seemingly simple, but in fact they are very difficult and not yet completely solved. We summarize the most relevant results from number theory. Whereas the beautiful theorems bearing directly on the error with respect to elementary estimates only provide indications concerning the order of that error; theorems concerning mean values can be used as a basis for a physicist's guess on its asymptotic mean value.

This paper has also been intended to contribute to bridging the gap between quantum mechanics and number theory.
Modified molecular charge similarity indices for choosing molecular analogues
Authors: Richard Ann M. , Rabinowitz James R.
Published: January 2005

Toward the goal of defining a molecular charge similarity idex that best quantifies the concept of molecular similarity as it relates to biological activity, we have evaluated a variety of definitions of the molecular charge distribution function, ρ, for use in the charge similarity index formalism. Spatially distributed nuclear charges are incorporated into electron distribution functions to approximately account for the screening of core electronic charge and to model the net effect of the total charge distribution in a manner that better reflects the inherent relation to the molecular electrostatic potential. The resulting charge similarity indices are evaluated based on their sensitivity to relative molecule displacement and their ability to meaningfully group or order a simple set of molecular structures: CH3CH2CH3, CH3OCH3, and CH3SCH3.
Fluorine peroxide (FOOF): A continuing problem for normally reliable theoretical methods
Authors: Clabo D. Allen , Schaefer Henry F.
Published: January 2005

The greatest single success of modern computational quantum chemistry has been its ability to correctly predict the geometrical structures of molecules. The FOOF molecule stands in contrast to the overwhelming mass of comparisons between theory and experiment. This research shows that configuration interaction (CI) methods including all single and double excitations (SD) fail to predict the correct FOOF structure, even when high‐quality basis sets are employed.
Generation of a full active configuration space basis in terms of symmetry‐ and spin‐adapted antisymmetrized orbital products
Authors: Lam Miu‐To Brenda , Elbert Stephen T. , Ruedenberg Klaus
Published: January 2005

A practical algorithm is described for generating a set of symmetry‐ and spin‐adapted antisymmetrized products of molecular orbitals (SAAPs) which form an orthogonal basis for a full active configuration space. The spin‐adaptation is completely general. The space‐symmetry adaptation is accomplished for the groups C∞v and D∞v.
Theoretical studies on conformational preferences of modified nucleic acid base N6‐(N‐glycylcarbonyl) adenine
Authors: Tewari Ravindra
Published: January 2005

Conformational preferences of modified nucleic acid base N6‐(N‐glycylcarbonyl) adenine, gc6Ade, have been investigated using the quantum chemical PCILO (Perturbative configuration interaction using localized orbitals) method. The multidimensional conformational space has been searched using selected grid points formed by combining various torsion angles that take favored values derived from energy variation with respect to each torsion angle individually. The theoretically predicted most stable, minimum energy conformation of the molecule is such that the substituent on N(6) spreads away from the imidazole moiety of the adenine ring, thus keeping distal orientation. The preferred molecular orientation is stabilized by an intramolecular hydrogen bond from N(11)H of the amino acid to N(1) of the adenine. The carboxylic group of the substituent is trurned away in relation to N(11)H…︁N(1) and is perpendicular to the plane through the rest of the molecule

The alternative stable conformation corresponding to an 0.8 kcal/mol higher energy has a coplanar carboxylic group turned towards the same side as N(11)H…︁N(1) and is exhibited in the crystal structure of the nucleoside derivative, gc6A. Energetically, the carboxyl group may change its orientation over a wide range, without much destabilization. This suggests probing by the carboxyl group of the molecular environment in the vicinity of the anticodon in tRNA.
Resonances in nuclear, atomic, and molecular physics—an introduction with some examples
Authors: Elander Nils
Published: January 2005

Examples from music and nuclear, as well as atomic and molecular, physics are given to introduce and illustrate the resonance concept. Some fundamental concepts of scattering theory such as the differential and the total cross section are presented. The concept of the collision complex is illustrated with a light particle scattering reaction in nuclear physics. The concept of channels is introduced, and this formalism (which is so far empirical in nature) is dressed in the language of quantum mechanics. Finally I show that our descriptions of phenomena in nuclear physics can also be used in atomic and molecular physics.
Intertwining methods in the theory of inverse scattering
Authors: Melin Anders
Published: January 2005

In this paper we make explicit constructions of a family Aθ of intertwining operators between the Schrödinger operator Hv = −Δ + v(x) and H0 = −Δ. The wave operators and the scattering matrix are expressed in terms of the Aθ, and some methods of inverse scattering are described.
Association of bound states of the coulomb potential with resonances of the coulomb potential perturbed by a barrier
Authors: Engelmann Alejandro R. , Natiello Mario A. , Höghede Mikael , Engdahl Erik , Brändas Erkki
Published: January 2005

In the present article we show how the bound states of the Coulomb potential may be associated with resonances that occur when this potential is perturbed by a barrier potential. The main idea is to trace the bound states on successive switching on of the barrier perturbation. It is found that those bound states that are localized inside the barrier are highly sensitive to variation with respect to the barrier height, whereas those that are localized outside are less sensitive. However, there are certain intervals for the barrier height when the role of being “a state localized inside the barrier” is shifted from one bound state to another. The result can be pictured as a “relay race,” where the “deliveries of the baton” are carried out over corresponding avoided crossings. The baton is ultimately handed over to a shape‐type resonance state.
Bond strength and bond angles for hybrid orbitals composed of arbitrary sets of orbital angular momentum quantum number
Authors: Zhan Chang‐Guo , (Liu Fan) Frank Liu , Hu Zhen‐Min
Published: January 2005

According to the formulas obtained in the preceding paper, it may be used for all types of the hybridization with any set of azimuthal quantum numbers l, l = 0 through l = 5, and a complete theoretical data of bond angles and bond strengths are shown in this paper.
Spin‐free quantum chemistry. XXIII. The generator‐state approach
Authors: Matsen F. A.
Published: January 2005

In the unitary‐group formulation of quantum chemistry, the spin‐projected, configuration‐state spaces of quantum chemistry are realized by the irreducible representation spaces (IRS) of the freeon unitary group U(n), where n is the number of freeon orbitals. The Pauli‐allowed IRS are labeled by the partitions [λ] = [2(N/2)−s, 12S], where N and S are the particle number and the spin, respectively. The generator‐state approach (GSA) to the unitary‐group formulation consists of (1) the construction of the overcomplete, nonorthonormal generator basis for each IRS; (2) the Lie‐algebraic computation of matrix elements over generator states; (3) the Moshinsky–Nagel construction of the complete, orthonormal Gel'fand basis in terms of the generator basis; and (4) the computation of matrix elements over Gel'fand states in terms of matrix elements over generator states.
Spin‐free quantum chemistry. XXIV. Freeon many‐body theory
Authors: Matsen F. A.
Published: January 2005

We present the freeon, singlet, unitary group formulation of many‐body theory as an alternative to the particle‐number‐conserving, spin‐projected, fermion, second‐quantized formulation. It is based on the generator‐state‐approach (GSA) developed in part 23 of this series. We develop C1, perturbation, coupled‐cluster, and random‐phase theories.
Point group symmetry adaptation in clifford algebra unitary group approach
Authors: Gao M. J. , Chen J. Q. , Paldus J.
Published: January 2005

The symmetry adaptation procedure of Chen et al. [Sciencia Sinica 23, 1116 (1980)], which can account for the invariance properties of the Hamiltonian with respect to any finite point group G, is both modified and adapted to the Clifford algebra unitary group approach (CAUGA). From orthogonal symmetry adapted Mo's, one first constructs a pure configuration many‐electron basis adapted to the chain U(ni) ⊃ G ⊃ G(s) in terms of the U(ni) Gel'fand–Tsetlin (GT) basis, where ni is the dimension of the irrep defining a given pure configuration, and G(s) designates the canonical chain supplying a unique labeling. The pure configuration basis is then coupled to the desired G‐adapted states using the point group Clebsch–Gordan coefficients and the U(n1) ⊂ U(n1 + n2) ⊂ …︁ ⊂ U(n) basis by using the permutation group outer‐product reduction coefficients. This basis can be expressed in terms of the U(n) GT basis by using the U(n) subduction coefficients (SAC'S). The SDC'S are particularly simple for the highest weight states (Hess's) of various subproblems, which can be in turn represented through the U(2n) two‐box Weyl tableaux of CAUGA. The non‐HWS's are obtained by applying the U(ni) lowering generators to the HWS's. In this way we can directly obtain the spin and point group adapted CAUGA basis. The procedure is illustrated on a nontrivial example.
More on basis set quality tests
Authors: Robertson Donald D. , Smith Vedene H. , Thakkar Ajit J.
Published: January 2005

The quality measure δ of Sordo and Pueyo is computed for 94 orbital basis sets for the atomic helium Hartree‐Fock problem and compared with various information theoretic quality measures reported previously by us for this data base. δ is in error often enough that it is unlikely to be a useful general purpose measure.
Some considerations on the sturmian approach to green's functions
Authors: Engelmann Alejandro R. , Natiello Mario A.
Published: January 2005

The Sturmian transformation is reviewed and some of its properties are discussed, in particular, its use in perturbative approaches, its connection with variational schemes, and its use for the study of resonances. One potential problem (Doolen) having no bound states is described exactly.
Rayleigh–Schrödinger perturbation expansions for a hydrogen atom in a polynomial perturbation
Authors: Vrscay Edward R.
Published: January 2005

Rayleigh–Schrouml;dinger (RS) perturbation expansions for the eigenvalues E(λ) of a hydrogen atom in the general polynomial perturbation V(r) = aλr + b>2r2, a, b > 0, are studied. When a2 = 2b, the ground state energy is exactly E(λ) = ‐(1/2) + (3/2)a>, i.e., the RS series is truncated. In the case a2 > 2b, the RS series is negative Stieltjes. In general, when λ < 0, a well of depth ω ≈ ‐a2/(4b2) (note the λ independence) is situated at rω = a/(2b|λ|). When a2 > 2b/N2, and interaction between this well and the hydrogenic state ψNLM(λ) is possible, thus creating a pair of asymptotically degenerate eigenstates separated by a “gap” δE(λ). The large order behavior of the RS coefficients E may be computed from the asymptotics of δE(λ), which is, in turn, related to the tunnelling integral. For excited states, stricter inequalities must be obeyed for Stieltjes behavior. The E(n)NLM may be calculated either numerically or in closed form via the “so(4, 2) Lie algebra technology” for such hydrogenic problems.
Some aspects of approach to equilibrium in classical and quantum systems
Authors: Kumičáak Juraj , Brändas Erkki
Published: January 2005

Investigations of general properties of time evolution of both classical and quantum systems show that the evolution (on a microscopic level) is reversible, and, if there is an approach to equilibrium, it exists only in the sense of weak convergence and necessarily in both directions of time. In this connection attempts to derive irreversibility and the approach to equilibrium in the sense of strong convergence and without any loss of information (using the so‐called Lyapunov converters) are discussed. After demonstrating their drawbacks, an alternative approach is proposed based on the spectral properties of the generator of the group. The relevant spectral criteria for the approach of both classical and quantum ensembles to equilibrium are given, and the decisive role of loss of information in obtaining stronger variants of convergence is emphasized. The asymmetry between initial and any other state —consisting of different levels of information needed to prepare the states—is proposed as an adequate explanation of irreversibility. The importance of the method of complex scaling in this context is discussed, and its application in proving some spectral properties in the quantal Hamiltonian formulation is stressed.
Spin‐Projected EHF equations
Authors: Pavlides P. , Sales K. D.
Published: January 2005

Extended Hartree‐Fock (EHF) equations are developed for the general open‐shell case using a modified pair‐orthogonality‐constrained variation (POCV) method. The EHF energy is expressed in terms of corresponding orbitals that are required to remain orthogonal and paired for all arbitrary infinitesimal variations.

The Euler equations for each set of orbitals are reduced to unique pseudosecular equations, the LCAO form of which may easily be derived. The Euler equations and the expressions obtained for the off‐diagonal elements of the ϵγδ (γ, δ = a or b) matrices for the closed‐shell case are identical to those obtained by Mayer, who used the generalized Brillouin theorem method. However, the present method yields equations for both closed‐ and open‐shell cases and for any spin state.
Analytical potential from ab initio calculations for the Fe+‐H2O and Feo‐H2O systems
Authors: González‐Lafont A. , Lluch J. M. , Oliva A. , Bertrán J.
Published: January 2005

Analytical intermolecular potentials for the Fe+−H2O and Feo−H2O systems have been determined from ab initio calculations. Interaction energies for a lot of points along the two potential energy surfaces were calculated using Huzinga's MINI−2 basis set. The results obtained were fitted to an analytical function containing 11 adjustable parameters that we have already used with success for the Fe2+−H2O system. The goodness of the generated intermolecular potentials is discussed.
Inclusion of relativistic effects into ZDO methods. II. Solavation of metal complexes
Authors: Boča Roman
Published: January 2005

The quasirelativistic CNDO/1 method has been in investigating the geometry, electronic structure, and redox stability of metal complexes. The systems of [Co(NH3)6]q and [MCl4]q, M being Ni, Pd, and Pt, have been studied. A modified Germer model of solvation has been implemented into the method. This yields reliable results on the redox stability of complexes in aqueous solutions. The calculated excitation energies resemble the electronic spectra of [MCl4]2− complexes.
New concepts in bonded functions theory II. Canonical set of high internal symmetry
Authors: Golebiewski A. , Broclawik E. , Witko M.
Published: January 2005

A new definition of a canonical set of bonded functions has been introduced. For a given configuration with r singly occupied orbitals and given multiplicity, the set exhibits symmetry properties of a group of order r. It simplifies the evaluation of the energy matrix H as well as the orthogonalization procedure.
A spin‐free form of valence bond theory
Authors: McWeeny Roy
Published: January 2005

Classical valence bond theory is recast in a spin‐free form which provides a practicable route to ab initio calculations of molecular electronic structure. The approach is simple and direct and requires only efficient algorithms for the generation and processing of permutations and the handling of Rumer diagrams: it makes modest demands on computing power and pilot calculations have indeed been performed entirely within the fast memory of a personal computer, which should be sufficient for dealing with systems possessing up to 10 electrons outside a closed shell. Simple applications confirm the conclusion of Cooper et al. [1] that, by using strongly overlapping orbitals, a small number of classical (nonpolar) structures can give results close to those obtained in a “full CI” calculation.
Theoretical studies on conformational preferences of model modified nucleic acid base N6‐(N‐alanylcarbonyl) adenine
Authors: Tewari Ravindra
Published: January 2005

Conformational preferences of model modified nucleic acid base N6‐(N‐alanylcarbonyl) adenine, ac6Ade, have been investigated using the quantum chemical PCILO (perturbative configuration interaction using localized orbitals) method. The multidimensional conformational space has been searched using selected grid points formed by combining the various torsion angles that take favored values derived from energy variation with respect to each torsion angle individually.

The preferred molecular structure is stabilized by an intramolecular hydrogen bond from N(11)H of the amino acid to N(1) of the adenine. The observed crystal structure conformations for the naturally occurring, anticodon adjacent, threonyl analogs, tc6Ade, correspond to the predicted most stable conformation for the model modified base ac6Ade. Three stable, low energy conformations differing in the orientations of the carboxyl group and the amino acid side chain are predicted within 1 kcal/mol of the most stable structure. The possible bifurcated hydrogen bonding of N(11)H with N(1) and either of the carboxyl oxygens is of minor significance.

The indicated orientational flexibility for the carboxyl group and the amino acid side chain may enable convenient probing of the molecular environment, in the vicinity of the anticodon in tRNA, by the amino acid substituent, with only modest changes in energy stabilization.
The role of hydrophobicity in the Ames test. The correlation of the mutagenicity of nitropolycyclic hydrocarbons with partition coefficients and molecular orbital indices
Authors: De Compadre Rosa L. Lopez , Shusterman Alan J. , Hansch Corwin
Published: January 2005

A set of 20 nitropolycyclic aromatic hydrocarbons, whose mutagenicity has been determined in the Ames test, has been studied using octanol‐water partition coefficients (P) as a measure of relative hydrophobicity and molecular orbital energies to account for variation in their electronic characteristics. A good structure‐activity relationship was found using log P and ϵLUMO. The latter were taken from the results of ab initio calculations performed by Maynard, Pedersen, Posner, and McKinney [7] and were also calculated by the MNDO method. The dependence of mutagenicity on hydrophobicity was found to be similar to that observed for triazenes [2]. ϵLUMO values calculated by MNDO and STO‐3G were found to be strongly correlated, and the role of hydrophobicity in correlating mutagenicity was not significantly affected by the molecular orbital model employed.
Shape wave in density functional theory
Authors: Tachibana Akitomo
Published: January 2005

The shape wave u(r) is defined in such a way that the square of its absolute value gives the shape of the electron charge density for a nonrelativistic many‐electron system: |u(r)|2 = ρ(r)/∫ρ(r) dr, where ρ(r) is the total electron charge density. The u(r) is treated as the probability amplitude for the shape of the electron charge density in the real three‐dimensional space. The secular equation of the u(r) is given as L(r)u(r) = λu(r), where L(r) and λ are a real Hermitean operator and the eigenvalue, respectively. This equation has the form of the spinless one‐particle Schrödinger equation. The potential is local and is a functional of ρ(r), and so we need a self‐consistent field procedure to solve it. For equilibrium state shape wave u = ueq, which is temperature‐dependent, and for stationary state shape wave u = u0, respectively, Leq(r)ueq(r) = λequeq(r) and L0(r)u0(r) = λ0u0(r). For one‐electron systems, the latter equation reduces to the Schrödinger equation for a stationary state, with the usual eigenvalue λ0 = E0. In general, λ is identified with the Gibbs chemical potential μG. Boundary conditions such as the cusp condition at a nucleus and exponential decay at an infinitely large distance from the nucleus are easily implemented. In case L(r) allows complex eigenfunctions, u(r) = A(r)eiS(r), the hydrodynamical potential appears in the secular equation for the real amplitude A(r). The real phase S(r) satisfies the equation of continuity. By introducing «apparatus» operators [16], the excited state shape wave is also obtained. Comparisons are made with a recent discussion of Levy, Perdew, and Sahni [3].
Usage de l'algèbre de lie SU(n) dans l'etude des systèmes quantiques a n etats. VII: Sur le “problème inverse”
Authors: Tillieu Jacques , Van Groenendael Augustin
Published: January 2005

Through a formalism developed in formr papers, some problems, set by the determination, from experimental data of the evolution equation of an n‐states quantum system are considered.
Application of the Mermin entropy principle to the “apparatus” density functional theory
Authors: Tachibana Akitomo
Published: January 2005

An “apparatus” operator approach is presented for the extension of the density functional theory of Hohenberg, Kohn, and Mermin. Using the Mermin entropy principle, a one‐to‐one correspondence is established between the density matrix for the system and the electron charge density for a finite‐temperature system in the presence of an apparatus. In the zero‐temperature limit in the absence of an apparatus, the Hohenberg–Kohn theory is recovered. The central aspect of this new density functional theory is that the principle of maximum entropy is applied to the system plus its surroundings under the additional constraint that the electron charge density is given. The system is treated as a subsystem of a composite system and is not necessarily in the equilibrium state as in the Mermin theory. As an example, it is shown how, in principle, excited states are encompassed by the theory.
Exact ground state for a Herndon–Simpson model via resonance–theoretic cluster expansion
Authors: Klein D. J. , Schmalz T. G.
Published: January 2005

The Herndon–Simpson model for a particular catacondensed polyphene chain is considered as a nontrivial many‐body Hamiltonian, defined on a space with a basis of orthonormal Kekulé structures. An Explicitly correlated cluster expanded resonance–theoretic wave function is described for this model, and its quality is judged by calculation of the standard deviation for the energy expectation. The quality is found to be high. Indeed, for a particular parameter ratio within the range of experimental interest, the wave function ansatz is found to be exact. This very accurate solution is then used to gauge the quality of the common ansatz with equally weighted Kekulé structures, and it is found to be reasonably good.
Conformational studies on L‐serine phosphate and hydrated L‐serine phosphate using ab initio SCF calculations
Authors: Lunell S. , Nakamura Y.
Published: January 2005

Ab initio MO‐LCAO‐SCF calculations using an STO‐3G basis set were performed to find the most stable conformations of L‐serine phosphate and hydrated L‐serine phosphate. The most favorable conformation of L‐serine phosphate is found to be one where the bond sequence OCCC is trans and POCC gauche, and a very short hydrogen bond is formed between an oxygen atom of the phosphate group and a hydrogen atom of the ammonium group.

For hydrated L‐serine phosphate, a bridge‐type hydration in which a water molecule links a phosphate oxygen and an ammonium hydrogen displays particularly low energy. In the four‐hydrated L‐serine phosphate anion, the most favorable conformation is such a bridged one having a rather extended configuration with regard to the bond sequences OCCC and POCC.
Time‐dependence of wave functions and the calculation of transition intensities
Authors: Sadlej Andrzej J.
Published: January 2005

The standard formalism of the perturbation theory for time‐dependent perturbations follows from the assumption that the exact solution of the unperturbed time‐independent problem is known. The consequences of this assumption are analyzed.

Particular attention is given to the methods used for the evaluation of transition intensities. It is shown that the traditional intensity formula in most cases violates the assumptions underlying its derivation. It is shown that for the given ansatz concerning the form of the approximate wave function, the transition intensities should be determined from the variation treatment of the corresponding time‐dependent problem. The wave functions of both states involved in the transition should be given the same amount of variation flexibility. This condition is satisfied if the transition intensity expression follows from the complete timedependent perturbation treatment of the perturbed system.
Density matrix approximation as a probe to the interaction range analysis of electronic structure
Authors: Nevalainen Vesa , Pakkanen Tapani A. , Lindblad Marina
Published: January 2005

An interaction range analysis of electronic structures has been developed with density matrix approximation techniques. A successive error analysis of electronic interaction of differing ranges reveals clear pattrns. Aromatic hydrocarbons and heterocycles are used as examples. The developed technique is proposed to be used as an illustrative tool for the description of delocalization and as a guide for studies where delocalized systems are modeled by small subsystems.
The Debye‐Waller factor: From villain to hero in protein crystallography
Authors: Frauenfelder Hans
Published: January 2005

A personal and partially anecdotal account is given of the role of the Debye–Waller factor in protein crystallography and protein dynamics.
A theoretical study of the diffuseness of the V(1B1u) state of planar ethylene
Authors: Lindh Roland , Roos Björn O.
Published: January 2005

The ground (N) state and the 1B1u(V) excited state of planar ethylene have been studied at the CPF and MR‐SDCI levels of theory, using an extended CGTO basis set of the ANO type. The investigation especially addresses the near‐degeneracy problem in the ground state and the coupling between the diffuse character of the π* orbital and the amount of correlation included in the wave function of the V state. The MR‐SDCI results yield a vertical excitation energy in the range 7.8–8.0 eV, whereas the CPF result is 7.9 eV. The best MR‐SDCI result for 〈1π*‖z2‖1π*〉 is 7.8, whereas CPF calculations based on MR‐SDCI INOS give the value 6.7. It is clear from the results that these numbers have not converged and that more extended calculations than was possible in the present work would yield an even more compact wave function.
Reaction ergodography for the additions of HLi and its dimer to acetylene
Authors: Zhao Cheng‐Da , Chen Bin , Huang Jing‐An
Published: January 2005

The ab initio calculation has been performed with the addition pathways of HLi and its dimer to acetylene at the RHF/3‐21G basis set. It shows that the reaction mechanisms of these two reactions are rather similar. In either of two reaction pathways, there is a meta‐stable molecular complex near the isolated reactant state. This kind of addition can be treated approximately as the unimolecular reaction in which the molecular complex rearranges into the product. We have estimated the activation entropies and the statistical A factors of these two reactions by the use of RRKM theory. Frontier molecular orbital analysis of these two transition states reveals their HOMOS to be formed from both HOMO‐LUMO and HOMO‐HOMO interactions.
Some properties of the bivariational Hartree–Fock scheme for complex symmetric many‐particle operators
Authors: Löwdin Per‐Olov , Froelich Piotr , Mishra Manoj
Published: January 2005

The bivariational Hartree–Fock scheme for a general many‐body operator T is discussed with particular reference to the complex symmetric case: T† = T*. It shown that, even in the case when the complex symmetric operator T is real and hence also self‐adjoint, the complex symmetric Hartree–Fock scheme does not reduce to the conventional real form, unless one introduces the constraint that the N‐dimensional space spanned by the Hartree–Fock functions ϕ should be stable under complex conjugation, so that ϕ* = ϕα. If one omits this constraint, one gets a complex symmetric formulation of the Hartree–Fock scheme for a real N‐electron Hamiltonian having the properties H = H* = H†, in which the effective Hamiltonian Heff (1) may have complex eigenvalues εk. By using the method of complex scaling, it is indicated that these complex eigenvalues—at least for certain systems—may be related to the existence of so‐called physical resonance states, and a simple example is given. Full details will be given elsewhere.
Pseudopotential investigation of some alkali metal molecules
Authors: Tamássy‐Lentei I. , Derecskei‐Kovács Á.
Published: January 2005

The effect of electron correlation on the results of pseudopotential calculations was examined using a simple analytical semiempirical pseudopotential and a correlated floating‐type one‐center wave function. Investigations were performed for the XH alkali metal hydride molecules (X  Na, K, Rb, Cs). The inclusion of the electron correlation in the ground state proved important for the calculation of the dissociation and ionization energies, but it is less significant for the determination of the equilibrium nuclear distances. The ground state potential energy curves are also determined.
Computational chemical studies of chiral stationary‐phase models: The nature of the Pi interaction in complexes of methyl N‐(2‐naphthyl) alaninate with N‐(3,5‐dinitrobenzoyl)leucine n‐propylamide
Authors: Sabio Michael , Topiol Sid
Published: January 2005

The pi interaction in complexes of (S)‐methyl N‐(2‐naphthyl)alaninate with (S)‐ and (R)‐N‐(3,5‐dinitrobenzoyl)leucine n‐propylamide was investigated with Hartree–Fock and second‐order Møller–Plesset perturbation theory calculations using the STO‐3G basis set. For each complex, the geometry of the model of the pi interaction (i.e., naphthalene and 1,3‐dinitrobenzene) was derived directly from the complex geometry which was relaxed by the semiempirical quantum‐mechanical AM1 method. At the level of treatment used herein, our results are in agreement with our earlier AM1 interaction energy calculations in which the pi interaction, one of the three primary interactions proposed in models of the aforementioned complexes, is attractive and of equal strength (ca. 0.8 kcal/mol) in both complexes.
The many‐body expansion of the potential energy function for elemental clusters
Authors: Murrell J. N.
Published: January 2005

The many‐body expansion of the potential energy function of elemental clusters is examined in general terms in regard to its convergence for microclusters and the bulk phase. The systems Ben and Lin are examined in detail. For Li it is clear that the many‐body expansion has no low‐order convergence, but it is shown that a potential of the form

gives good binding energies for Lin (3<n⩽9) and also a good value for the heat of atomization of the bcc crystal.
Pairing theorem of graph eigenvalues: Its new proof and a generalization
Authors: Shen Mingzuo
Published: January 2005

Each undirected graph has its own adjacency matrix, which is real and symmetric. The negative of the adjacency matrix, also real and symmetric, is a well‐defined mathematically elementary concept. By this negative adjacency matrix, the negative of a graph can be defined. Then an orthogonal transformation can be readily found that transforms a negative of an alternant graph to that alternant graph: (−G) → G. Since the procedure does not involve the edge weights, the pairing theorem holds true for all edge‐weighted alternant graphs, including the usual “standard” graphs.