bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interaction of tylophorinidine with lysozyme
Authors: Gurnani S. , Datta G. , Mulchandani N. B. , Sen G. , Mehta S. K. , Sengupta S. 
Published: December 2004

AbstractThe interaction of tylophorinidine (TPD) with lysozyme—a model protein—with biological activity, was investigated by determining its fluorescence and by assessing its activity under various conditions. The results indicated that TPD associated with lysozyme at pH 9.2 efficiently with an association constant Ka of 3.3 X 104 M–1 at 26°C. Ka increased with the increasing temperature in the range 26 to 55°C; the calculated enthalpy change ΔH was found to be 2.3 kcal/mol. Under the same conditions as above TPD also associated with the free amino acid tryptophan with a Ka of 1.7 X 104 M–1 indicating half the efficiency of its association with protein lysozyme. TPD associated lysozyme was less active than the uncomplexed enzyme in the above temperature range although beyond 45°C the inhibition was more significant. The results imply that TPD binds lysozyme outside the cleft region in the temperature range studied here. However, with increasing temperature the cleft region is gradually widened and/or the whole molecule is expanded such that the accommodation of whole or part of the TPD molecule is facilitated leading to the blockage of lytic activity.
Ab initio molecular orbital calculation of fe‐porphine with a double zeta basis set
Authors: Kashiwagi Hiroshi , Obara Shigeru 
Published: December 2004

AbstractAn ab initio LCAO SCF MO calculation was performed on planar Fe‐porphine with a double zeta basis set consisting of 300 CGTO's. SCF wave functions of several states of Fe‐porphine and its cation were obtained. The net charge of Fe is in the range of 1.39 to 1.53. The highest occupied orbital is ascertained to be a pure porphine π‐MO, 1a1u. The calculated ionization potentials of the two highest occupied orbitals, 1a1u and 5a2u are 5.98 and 6.43 eV, respectively. They are in good agreement with experiments. The role of the porphine macrocycle on the oxidation of Fe is discussed in terms of gross atomic populations and with contour maps of the density difference.
Methods of composite molecular wave functions. I. Variational principle and multiconfiguration SCF theory
Authors: Matsuoka Osamu 
Published: December 2004

AbstractThe Silverstone–Stuebing variational principle for the discontinuous wave functions of one‐electron systems is generalized for many‐electron systems. The variational functional of energy takes real or complex value. The condition that it is real is given. Using the generalized variational principle, a multiconfiguration SCF theory for the composite molecular wave function is formulated. According to the theory, we may divide the whole space into space‐filling cells, solve the SCF equations in each cell and build up the wave functions of the system by gathering the wave functions obtained in the cells. For use in the basis‐set expansion method, the SCF equations are rewritten as matrix forms in which only one‐ and two‐center integrals appear if an expansion center is located in each cell.
Monte‐Carlo simulation of water solvent with biomolecules: Serines with reaction‐field correction
Authors: Romano Silvano 
Published: December 2004

AbstractAlong the lines of previous work [S. Romano and E. Clementi, Gazz. Chim. Ital. 108, 319 (1978); Int. J. Quantum Chem. 14, 839 (1978); 17, 1007 (1980)], we carried out Monte Carlo simulation on serine–water clusters (the neutral molecule and two conformers of the zwitterion) surrounded by an appropriate dielectric continuum simulating the bulk solvent. Results for clusters in vacuo and in the dielectric continuum were compared; similarities and differences could be qualitatively interpreted as produced by competition among different factors.
A hybrid technique of orthonormality constrained orbital optimization in SCF calculations
Authors: PrasadBhattacharyya Sankar , Mukherjee Debashis 
Published: December 2004

AbstractA recently proposed orthonormality constrained orbital optimization technique is operationally modified further by coupling it to a gradient biased method, namely the steepest descent procedure of McWeeny. The hybrid technique developed in this way is shown to have better convergence properties in closed and unrestricted open‐shell calculations. The technique can be adapted to MCSCF procedures as well. The important role played by "orbital symmetries" in the operation of the method is analysed. Similarities and differences of the present method with the orthogonal gradient method are pointed out. Possible avenues of circumventing convergence difficulty that one may encounter in pathological cases, particularly in ab initio calculations involving extended basis set, are suggested.
Structure and spin‐purity conditions for reduced density matrices of arbitrary order
Authors: Luzanov A. V. , Whyman G. E. 
Published: December 2004

AbstractFor arbitrary k, the separation of spin variables is performed in the reduced density matrix of the kth order (RDM‐k) on the basis of the Fock coordinate function method. The independent spatial components of RDM‐k are analyzed. For RDM‐k of the total spin eigenstate, their number is proved never to exceed its spin multiplicity 2s + 1. Integral and other nontrivial interrelations between spatial components are established which turn out to be the necessary and sufficient conditions of spin purity of a wavefunction corresponding to a given RDM‐k. It is shown that the r‐rank k‐particle spin distribution matrix F, defined as a spatial coefficient at the spin‐tensorial operator of rank r in the RDM‐k expansion, can be obtained by reduction of the (k + r)‐particle charge density matrix F. In particular, all spatial components of RDM‐2 are explicitly expressed in terms of the four‐electron charge density matrix only. This allows us to purpose some approximative formulas for the McWeeny‐Mizuno spin–orbit and spin–spin coupling functions in the case of the weak spin contamination.
Partitioning technique, perturbation theory, and rational approximations
Authors: Löwdin Per‐Olov 
Published: December 2004

AbstractInstead of the Schródinger equation ℋ︁Ψ = EΨ subject to the boundary condition 〈φ|Ψ〉 = 1, where φ is a normalized reference function in the Hilbert space, one studies the inhomogeneous equation (ℋ︁ − ℰ)Ψℰ = aφ, where ℰ is a complex variable, with the same boundary condition, which gives a = 〈φ|ℋ︁|Ψℰ〉 − ℰ = ℰ1 − ℰ. Introducing the projector P = 1 − |φ〉〈φ| for the complement to O = |φ〉〈φ|, one finds easily the explicit solution Ψℰ = (1 − Pℋ︁/ℰ)−1φ = (1 + Tℰℋ︁)φ, where Tℰ = (ℰ − Pℋ︁)−1P = P(ℰ − Pℋ︁P)−1P is the reduced resolvent associated with the auxiliary Hamiltonian H̄ = Pℋ︁P. The existence of these operators is discussed. It is shown that, if the parameter ℰ is real in the “discrete part” of the spectrum to ℋ︁, then ℰ and ℰ1 = 〈φ|ℋ︁|Ψℰ〉 = 〈φ|ℋ︁ + ℋ︁Tℰℋ︁|Φ〉 ≡f(ℰ) bracket a true eigenvalue E satisfying the relation E = f(E). The Newton‐Raphson solution to the equation F(ℰ) = ℰ − f(ℰ) = 0 is related to the variation principle. Putting ℋ︁ = ℋ︁0 + V and expanding the inverse (ℰ − Pℋ︁0 − PV)−1 in terms of powers of V or (V − α), one gets various expansions relating to finite‐order perturbation theory. Exact expressions for the ordinary wave and reaction operators are obtained. If A is an arbitrary nonsingular operator and h = {h1,h2,…,hn} is a linearly independent set, the inner projection Án = |h〉 〈h|A−1|h〉−1〈h| is a “rational approximation” to the operator A which converges toward A when n→∞ and the set h becomes complete. If A is positive (or has a finite negative part) the convergence is from below. Applying this principle to the partitioning technique, one gets rational perturbation approximations instead of the standard power series, similar to the Padé approximants but derived in a different way with the remainder term under control. The method has been used to calculate lower bounds to eigenvalues.
Estimating tunneling phenomena
Authors: Harrell Evans M. 
Published: December 2004

AbstractSeveral tunneling phenomena are surveyed. A unified, rigorous treatment of them can be based on a simple technique of integration by parts coupled with growth estimates of eigenfunctions, using, for example, WKB approximations. In particular, the analysis of Harrell and Simon of the resonance widths in the hydrogen Stark effect can be simplified.
Towards a molecular theory of phase transitions in fatty acid monolayers
Authors: Dunne Lawrence J. , Combs Leon 
Published: December 2004

AbstractA molecular theory of phase transitions in fatty acid monolayers at the air/water interface is proposed based on rotational ordering of molecules about their longitudinal axes. The first order statistical mechanical lattice model of Bell, Mingins, and Taylor (BMT) which is an equilibrium diluted Ising model is used to describe the monolayer behavior of some simple aliphatic carboxylic acids. The interaction energy parameters in the BMT model are adjusted to give reasonable agreement with the experimentally observed chain length dependence, and the energies thus obtained are compared with those calculated for interacting aliphatic carboxylic acid dimers by the technique of perturbative configuration interaction using localized orbitals (PCILO). It is concluded that intermolecular rotational ordering due to the anisotropy of the intermolecular potential plays a significant role in simple fatty acid monolayer phase behavior. A possible experimental test of the model is briefly described.
Electronic structure of beryllium
Authors: Oriade Joseph 
Published: December 2004

AbstractThe electronic energy bands in beryllium have been recalculated. The earlier work of Terrell [1] was found to contain a systematic error in the form of overlapping muffin tins. The new band structures give a density of states with the Fermi surface lying in the hole like portion, consistent with Hall measurements. All existing calculations misplaced the Fermi surface. As a further check on the new bands, the Hall coefficient AH was calculated. We obtained AH = (7.6 ± 0.8) × 10−24 cgs units for the easy axis or c direction, in excellent agreement with the experimental value of AH = 8.56 × 1024 cgs units.
Structural factors affecting Aryl Hydrocarbon Hydroxylase induction by Dibenzo‐p‐dioxins and Dibenzofurans
Authors: Cheney B. Vernon 
Published: December 2004

AbstractQuantitative structure‐activity relationships have been developed to rationalize the experimental data obtained with a series of dibenzo‐p‐dioxins and dibenzofurans in the assays for receptor binding and aryl hydrocarbon hydroxylase (AHH) induction. Lateral substituents (in positions 2, 3, 7, and 8 of the tricyclic system) do not affect receptor binding and AHH induction in the same manner. Various hypotheses are suggested to explain this finding. Of special interest is the possibility that the lateral substituents are directly involved in the mechanism which transforms the receptor to the active state. The implications of this possibility are considered with regard to the design of an antidote for poisoning caused by the chlorinated congeners which occur as contaminants in certain commercial products.
Ab initio calculations on sulfur‐containing compounds. I. Uniform quality basis sets for sulfur: Total energies and geometries of H2S
Authors: Poirier R. A. , Daudel R. , Mezey P. G. , Csizmadia I. G. 
Published: December 2004

AbstractUniform quality basis sets (UQ‐NG; N=3, 4, 5), with s = p and s ≠ p, and a 6‐31 G* basis set have been optimized for the sulfur atom. These uniform quality basis sets in their uncontracted and contracted forms were used, together with other basis sets reported in the literature (a total of 40 basis sets), to study their accuracy in predicting the bond length and bond angle of H2S.
Interpretation of the antitumour activity of some diacridines
Authors: Abdul‐Ahad P. G. , Webb G. A. 
Published: December 2004

AbstractRelationships are formulated in an attempt to explain the variation in the antitumour activity and toxicity of a series of diacridines. Three types of conformation are considered, these being relevant to the three types of double intercalation of DNA. The CNDO/2 method, with the incorporation of symmetry adapted orbitals, is used to obtain electron reactivity indices. Significant correlations are presented between the biological activities and the electronic and steric indices employed.
Molecular orbital study on the active center of lactate dehydrogenase
Authors: Krechl Jiří , Kuthan Josef 
Published: December 2004

AbstractIn the active site of lactate dehydrogenase important roles are given to aminoacids His195 and Arg171. The coenzyme nicotinamide adenine dinucleotide (NAD) is required in oxidized form (NAD+) for the enzymatic oxidation of the substrate L‐lactate. Molecular orbital methods CNDO/2, INDO, and EHT were applied to the study of the model of active center of lactate dehydrogenase. An energetically preferred arrangement of the models of His195, Arg171, NAD+, and lactate was found. Possible biochemical aspects of these arrangements are discussed.
Theoretical study of the interaction of nonactin with Na+, K+, and NH
Authors: Gresh Nohad , Pullman Alberte 
Published: December 2004

AbstractIn an attempt to account for the preferential binding to nonactin of K+ relative to Na+, theoretical computations are performed using the intermolecular interaction energies of the ionophore with the two cations. Both K+ and Na+ liganding conformations are considered, and an evaluation is made of the intramolecular energy expenditure caused by the reduction of the size of the cavity. The energy balance for the complexation of the two cations computed by taking into account the cation–ionophore interactions, the interactions between the liganding groups, as well as the desolvation enthalpies of the cations in methanol, favors K+ over Na+ by 4 to 5 kcal/mol, in fair agreement with the difference in the measured enthalpies of binding. The binding of NH to nonactin is also investigated.
Angular integrations in m‐dimensional spaces and hyperspherical harmonics
Authors: Avery John , Wen Zhen‐Yi 
Published: December 2004

AbstractA general formula for angular integrations in many‐dimensional spaces (derived in a previous paper) is applied to several problems connected with solution of the Schrödinger equation for many‐particle systems. Matrix elements of the Hamiltonian are derived for cases where the potential can be expressed in terms of functions of the generalized radius multiplied by polynomials in the m coordinates. The theory of hyperspherical harmonics is reviewed, and a sum rule is derived relating the sum over all the harmonics belonging to a particular eigenvalue of angular momentum to the Gegenbauer polynomial corresponding to that eigenvalue. A formula is derived for projecting out the component of an arbitrary function corresponding to a particular eigenvalue of generalized angular momentum, and the formula is applied to polynomials in the m coordinates. An expansion is derived for expressing a many‐dimensional plane wave in terms of hyperspherical harmonics and functions which might be called “hyperspherical Bessel functions.” It is shown how this expansion may be used to calculate many‐dimensional Fourier transforms. A formula is derived expressing the effect of a group‐theoretical projection operator acting on a many‐dimensional plane wave. Finally, the techniques mentioned above are used to expand the Coulomb potential of a many‐particle system in terms of Gegenbauer polynomials.
Matrix element factorization in the unitary group approach for configuration interaction calculations
Authors: Payne Philip W. 
Published: December 2004

AbstractTechniques of diagrammatic spin algebra are employed to derive segment factorization formulas for spin‐adapted matrix elements of one‐ and two‐electron excitation operators. The spin‐adapted basis is formed by the Yamanouchi–;Kotani geneological coupling method, and therefore constitutes an irreducible basis of the unitary group U(N), as prescribed by Gel'fand and Tsetlin. Several features distinguish this paper from similar work that has recently been published. First, intermediate steps in the derivation of each segment factor are fully documented. Comprehensive tables list the spin diagrams and phases that contribute to the possible segment factors. Second, a special effort has been made to distinguish between those parts of a segment factor that can be ascribed to a spin diagram and those parts which arise from the orbitals. The results of this paper should thus be useful for those who wish to extend diagrammatic spin algebra to evaluation of matrix elements for states built from nonorthogonal orbitals. Third, a novel graphical method has been introduced to keep track of phase changes that are induced by line up permutations of creation and annihilation operators. This technique may be useful for extension of our analysis to higher excitations. The necessary concepts of second quantization and diagrammatic spin algebra are developed in situ, so the present derivation should be accessible to those who have little prior knowledge of such methods.
Classical limit of quantum mechanics in the large
Authors: Thomas L. H. 
Published: December 2004

AbstractHilbert space may be regarded as a convenient standard approximation by interpolation and extrapolation to a unitary space, in general decomposable into a sum of semisimple spaces. In the limit we expect a particle theory expanded in powers of h according to the number of interacting particles. In the classical limit h tending to zero, phase space, with equations of motion reducible to Hamiltonian form, replaces Hilbert space. The modification of states by observing them is taken care of by considering probability distributions of petty ensembles. If the equations for any single observer can be made autonomous by replacing empirical time by universal time with an arrow we have a causal system. We then obtain the relation between probability and negentropy required for the second law of thermodynamics. An approximate Newtonian theory provides proximate particles with internal and external variables and admits the Poincaré group. For the internal variables we have approximately the Breit interaction. For the external variables we have equivalence for observers of the homogeneous Lorentz group of relativity. We introduce grand ensembles of ultimate particles, and nebulae as proximate particles in the large. We assume the Einstein principle of equivalence for the ten parameter set of observers suggested by relativity and suppose the second law of thermodynamics holds for each observer. The Einstein law of gravitation follows in classical theory to the order of the reciprocal of the large constant, in general with positive natural curvature as well as that corresponding to mass. Replacing particle interactions by fields we include them in classical theory.
Stability of chemical species
Authors: Leroy G. 
Published: December 2004

AbstractIn the framework of our theoretical approach of the structure and reactivity of chemical intermediates we have been led to reexamine the concept of stability which is widely used by the experimentalists often without specifying its true meaning. In this work we propose a more general definition of the concept of stabilization energy, namely,

where ΔHa is the heat of atomization of the species under consideration and the EAB's are standard bond energy terms derived from the heats of atomization of reference compounds. Using experimental heats of formation or semiempirical ones deduced from theoretical heats of reaction of appropriate isodesmic processes, we have calculated the stabilization energies of various types of chemical species: saturated, unsaturated and conjugated molecules, free radicals, carbocations, and carbanions. The results obtained can be rationalized in terms of steric hindrance, angular strain, polar interactions, electron delocalization, and substituent effects. Moreover, we have shown that heats of hydrogenation and bond dissociation energies do not provide accurate information on the thermodynamic stabilization of unsaturated compounds and free radicals, respectively. Among other applications the concept of stabilization energy allowed us to propose a detailed classification of free radicals and to rationalize their reactivity. Considering the particular case of radical recombination reactions we have been able to deduce interesting equations showing the relations between the concept of stabilization energy and other quantities commonly used in chemical physics, namely, the bond cleavage enthalpy [BDE(CC) if one considers alkane thermolysis], the thermodynamic stability measured by the free enthalpy change of a given reaction, and the kinetic stabilization related to the activation energy of a chosen chemical process

This analysis allowed us to give a new interpretation of the adjectives transient, persistent, and stable introduced by Griller and Ingold and to show that the persistence of a radical may be due to other factors than steric ones. In conclusion, the concept of stabilization energy appears to be a good tool for rationalizing the static and dynamic properties of chemical species.
Exponential factor optimization in characteristic function method for electrically charged particles
Authors: Demiralp Metin 
Published: December 2004

AbstractIn this work, the simplest basis function on hyperspherical coordinates with an optimization parameter is used to construct the characteristic function for a system of electrically charged particles. The first three coefficients of the serial expansion of the characteristic function in powers of eigenvalue parameter are evaluated in terms of well‐known functions. The construction of a Padé table for this expansion with the aid of these coefficients, a theoretical discussion, the optimization of the exponential parameter, evaluation of ground state energies for certain systems, and finally comparison of accuracy increments due to optimization for several systems complete the work.
Improved SCF interaction energy decomposition scheme corrected for basis set superposition effect
Authors: Sokalski W. A. , Roszak S. , Hariharan P. C. , Kaufman Joyce J. 
Published: December 2004

AbstractA modified scheme for SCF interaction energy decomposition has been proposed where the nonphysical basis set superposition error (BSSE) has been corrected by means of the counterpoise method. A new procedure to separate the exchange and induction energy terms free of nonphysical BSSE has been tested in the case of the H2O dimer. The first order BSSE appears to be non‐negligible for strong hydrogen bonded complexes. In addition the scheme allows separation of the long‐controversial charge‐transfer contribution within the induction term, which has been considerably overestimated in previous studies.
Electronic structure and luminescent properties of Cu+ and Ag+ impurity centers in NaCl
Authors: Pedrini C. , Chermette H. 
Published: December 2004

AbstractFluorescence studies of Cu+ and Ag+ impurity centers embedded in NaCl are reported. The multiple scattering Xα method is used to describe the electronic structure of these ions in NaCl matrix. It is shown that taking into account the external lattice potential is necessary to obtain good results which can be compared to experiment. This has been done through the computation of an embedded NaCl cluster potential. Moreover, in NaCl:Ag+, it is also necessary to include relativistic corrections in order to obtain a reliable energy diagram. This is easily done by use of the Wood Hamiltonian, which allows the self‐consistent inclusion of Darwin and mass–velocity terms in MS Xα codes. A good quantitative agreement with experiment is finally obtained for the optical excitations and the emission mechanism of the luminescent centers. The metal–chlorine distance is predicted slightly larger than the NaCl bulk value and the harmonic force constant of the a1g vibrational breathing deformation of the cluster is calculated and found in good agreement within experiment. For the first time the Stoke shift of such systems is evaluated.