bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bioactive phenolic derivatives from Acaena splendens methanol extract
Authors: Backhouse N. , Delporte C. , Negrete R. , Feliciano S. A. San , López‐Pérez J. L. 
Published: October 2002

AbstractAcaena splendens H. et A. has been used in Chilean folk medicine for the treatment of fever and inflammation. A description of the in vivo reduction of bacterial pyrogen‐induced fever in rabbits and carrageenan‐induced paw oedema in guinea pigs is presented. The methanol extract named ME‐1, obtained after succesive extractions with petroleum ether and dichloromethane, showed a strong antipyretic action (45.7% of effect), though the antiinflammatory activity was only observed after submitting this extract to column fractionation, giving a crude mixture of flavonoids named C4 with both activities (55.7% and 98.9% of antiinflammatory and antipyretic effect respectively at a dose of 600 mg/kg). The bioassay‐guided fractionation by column chromatography afforded the active fraction, which contained (‐,‐)‐epicatechin, tiliroside, 7‐O‐acetyl‐3‐O‐β‐D‐glucosyl‐kaempferol and 7‐β‐D‐glucosyloxy‐5‐hydroxy‐chromone. Copyright © 2002 John Wiley & Sons, Ltd.
Thomas–Fermi theory revisited
Authors: Nesbet R. K. 
Published: October 2002

AbstractAn exact Thomas–Fermi theory requires the existence of a Fréchet functional derivative of the Hohenberg–Kohn universal functional. Although, as recently shown, such a functional derivative cannot exist in quantum theory for more than two electrons, functional derivatives of the more general type defined by Gâteaux do exist. When the theory is reformulated in terms of Gâteaux derivatives, for noninteracting electrons, it is equivalent to the Schrödinger theory. For interacting electrons, it defines a generalized orbital‐functional theory. The reformulated theory incorporates Fermi–Dirac statistics for electrons and deals correctly with atomic shell structure. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 90: 262–265, 2002
On canonical perturbation theory in classical mechanics
Authors: Fernández Francisco M. 
Published: October 2002

AbstractWe develop canonical perturbation theory for classical mechanics by means of the Lie method in a simple way that does not require the use of complex variables to solve the perturbation equations. In order to illustrate the approach we apply it to anharmonic oscillators. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Model study of the impact of orbital choice on the accuracy of coupled‐cluster energies. IV. Single‐reference‐state methods in applications to excited states*
Authors: Jankowski K. , Rubiniec K. 
Published: October 2002

AbstractModel studies of the impact of the choice of the molecular orbital sets defining the reference determinant on the results of single‐reference‐state coupled‐cluster (SR–CC) methods for excited states of a predominately closed‐shell structure were performed for the first time. We have used the H4 model, which offers an easy way of representing any set of symmetry‐adapted orbitals as well as the possibility of varying the degree of quasi‐degeneracy of the states considered. The CCD, CCSD, and CCSDT methods (D, S, T denote that doubly‐, singly‐, triply‐excited configurations, respectively, are accounted for) are applied in calculations for several excited states disclosing rather strong quasi‐degeneracy. Orbital sets representing multiple solutions to the restricted Hartree–Fock (RHF) equations and nonstandard orbitals defined by nodes of a two‐dimensional orbital grid have been used to define the reference determinant. Attention is paid to documenting and discussing similarities and differences for excited states and the ground state in the characteristic of SR–CC approaches. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Comparison of lithium and hydrogen bonds in (X···Li···X)− and (X···H···X)− (XF, Cl and Br) complexes: Topological analysis of electron localization function
Authors: Berski Sławomir , Latajka Zdzisław 
Published: October 2002

AbstractThe topological analysis of the electron localization function (ELF) is used to elucidate the nature of the hydrogen and lithium bonds in the (X···Y···X)− (XF, Cl, Br; YH, Li) complexes. The lithium bond that exhibits an electrostatic nature is characterized by a constant mean electron population of the lithium core basin C(Li) equal to 2.03e. The values of the ELF within Li···X regions are smaller than 0.5 corresponding to a totally delocalized electron density. For the X···H hydrogen bonds a covalent nature is found with an essential electron pairing, as implied by values of ELF in the H···X regions larger than 0.5. The mean electron population of the V(H) basin depends on electronegativity of a halogen atom, and it ranges from 0.17e for (F···H···F)− to 2.11e for (Br···H···Br)−. The polarization of halogen anions X− by lithium or hydrogen cations results in an anisotropy of the nonbonding electron density, which is reflected by two valence attractors V1(Xi=1,2) and V2(Xi=1,2) found inside and outside a complex, respectively. The analysis of the H···Br hydrogen bond reveals essential differences as compared with the H···X (XF and Cl) hydrogen bonds. The topology of nonbonding electrons of Br yields only one valence, monosynaptic basin V(Bri=1,2). Furthermore, similarity of the H···Br hydrogen bonds to a bond in an isolated HBr molecule is noted. The increased Pauli repulsion between the V(H) and V1(Xi=1,2) basins in the (X···H···X)− complexes leads to a larger electron delocalization of V1(Xi=1,2) as compared with the (X···Li···X)− systems. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Matrix isolation and DFT studies of nitrous acid complexes with nitrogen dioxide
Authors: Olbert‐Majkut Adriana , Mielke Zofia , Wieczorek Robert , Latajka Zdzisław 
Published: October 2002

AbstractComplexes between trans or cis isomers of nitrous acid and nitrogen dioxide have been isolated in argon matrices and studied using Fourier transform infrared (FTIR) spectroscopy and density functional theory (DFT) calculation at B3LYP level with the 6‐311++G(2d,2p) basis set. Six perturbed vibrations of trans‐HONO and three perturbed vibrations of cis‐HONO isomers were identified for the trans and cis‐HONO complexes, respectively. The perturbed asymmetric stretching vibration of NO2 molecule was also identified for the two complexes. The experimental spectra suggest and the theoretical calculations confirm that there is double interaction in the two complexes. The OH group of HONO molecule serves as a proton donor to an oxygen atom of NO2, and in addition to hydrogen bonding there is an electrostatic attraction between an oxygen atom of OH and nitrogen atom of NO2 molecules. Calculated counterpoise corrected interaction energy is equal to −1.19 and −1.10 kcal/mol for NO2…cis‐HONO and NO2…trans‐HONO complexes, respectively. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
DFT calculations and parameterization of the approximate valence bond method to describe the phosphoryl transfer reaction in a model system
Authors: Ginalski Krzysztof , Grochowski Pawel , Lesyng Bogdan , Shugar David 
Published: October 2002

AbstractDensity functional theory (DFT) calculations have been performed at the B3LYP/6‐31G+(d,p) level for a model phosphodiester system to describe a transphosphorylation reaction that mimics the phosphoryl transfer process in serine/threonine protein kinases. The DFT energy and electrostatic potential data have been used to extend the parameterization of the approximate valence bond (AVB) method. AVB mimics well the DFT results and is planned for use as a fast potential energy generator to simulate phosphoryl transfer processes in protein kinases using the quantum classic molecular dynamics approach. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Dipole moments calculations of transition metal mononitrides: ScN, TiN, VN, and CrN: Limits of the CCSD(T) method
Authors: Jansík Branislav , Kellö Vladimír , Urban Miroslav 
Published: October 2002

AbstractCoupled‐cluster calculations of selected molecular properties of ScN, TiN, VN, and CrN in their ground states are presented. It is shown that the single determinant reference Restricted Open Shell Hartree‐Fock Coupled Clusters Singles Doubles noniterative Triples (ROHF‐CCSD(T)) method provides reasonably accurate bond distances, harmonic frequencies, and most dipole moments of these molecules but fails to predict sufficiently accurate dipole moment of CrN. The reason for the low accuracy in obtaining the dipole moment of CrN is analyzed and is attributed to the presence of the series of large single excitation CC amplitudes. This affects the correct response of the molecular CC wavefunction to the external field. Quasirelativistic effects are considered using the Mass‐velocity‐Darwin correction. Changes of dipole moments due to relativity are stressed, and trends throughout the series of molecules are analyzed using their bonding characteristics. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Hopping conductivity in nucleotide base stacks*
Authors: Ladik J. , Ye Y.‐J. 
Published: October 2002

AbstractThe frequency‐dependent complex hopping conductivities of single nucleotide base stacks and base pair stacks were calculated on the following basis: (1) The determination of the density of states of these disordered systems with the help of the matrix block negative counting method. (2) Using the inverse iteration technique, the Anderson localization of the one‐electron functions belonging to the physically interesting levels were computed. (3) With the help of the latter quantities the hopping frequencies corresponding to the relative motion of the base pairs with respect to each other (acoustic phonons) were determined. (4) Finally, using a random‐walk theory the frequency‐dependent complex conductivities [σ(ω)] were computed. The |σ(ω)|−ω curves show a saturation at ω≈1010 s−1. The |σ(ω)|'s have the values in the base pairs case (taking into account the role of the sugar–phosphate backbone, basis set, and correlation effects) are a few times 1 Ω−1 cm−1 for ω>1010 s−1. This room temperature result is in excellent agreement with the energy loss (in a resonant cavity) experiment on lambda phage deoxyribonucleic acid (DNA) of Gruner and co‐workers. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Models for low‐temperature helium dimers and trimers
Authors: Lohr Lawrence L. , Blinder S. M. 
Published: October 2002

AbstractWe have shown that a simple model based on pairwise deltafunction potentials can, with an appropriate choice of parameters, represent the general behavior of ultra‐low temperature helium dimers and trimers, including all possible isotopomers. The species 4He2, 4He3, and 4He23He are stable, with binding energies of approximately 1.3, 100, and 10 mK, respectively. An Efimov state for 4He23He is also predicted, bound by 2.4 mK. The remaining dimers and trimers, 4He 3He, 3He2, 4He 3He2, and 3He3, are evidently unstable. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Theoretical modeling of infrared spectra of salicylaldehyde and its deuterated derivatives*
Authors: Boczar Marek , Wójcik Marek J. , Szczeponek Krzysztof , Jamróz Dorota , Ikeda Susumu 
Published: October 2002

AbstractTheoretical simulation of the νs stretching band is presented for salicyladehyde and its deuterated derivatives taking into account an adiabatic coupling between the high‐frequency O–H(D) stretching and the low‐frequency intramolecular OO stretching modes, linear and quadratic distortions of the potential energy for the low‐frequency vibration in the excited state of the O–H(D) stretching vibration, and resonance interaction between the O–H and the C–H stretching vibrations in the aldehyde group. The experimental infrared and Raman spectra of the liquid salicylaldehyde have been recorded. The geometry and experimental frequencies are compared with the results of our HF/6‐31++G**, MP2/6‐31++G**, and Becke3LYP/6‐31++G** calculations. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
SU(3)×𝒮20 algebras for uniform spin‐1 ensembles on [2H12C]20, or [14N]20, dodecahedrane‐type lattices and analogous isotopomeric [M2012C40] met‐carb subensembles: M‐based cardinalities and completeness of 𝒮20 spin irreps, via hierarchical {𝒞λ⊢(n=20):(M)} designs of polyhedral combinatorics*
Authors: Temme F. P. 
Published: October 2002

AbstractThe M‐based hierarchy cardinalities of spin irreps for \documentclass{article}\pagestyle{empty}\begin{document}$[A]_{20}^{(I_{i}=1)}$\end{document} uniform nuclear magnetic resonance (NMR) /isotopomer spin ensembles are derived. Such ideas define the completeness of the number‐partition‐based (intermediate) combinatorial designs (on M) themselves inherent in specific λ⊢n digit assembly combinatorial properties. Illustrative M‐subspatial irrep subsets are derived via Schur decompositions from symbolic algorithms (Sagan, B. E. Symmetric Group: Representations, C‐Algorithms, Symmetric Functions; Wadsworth: Belmont, CA, 1991; SYMMETRICA package, as per Kerber, A.; Kohnert, A.; Lascoux, A. Symbolic Comput 1992, 14, 195). The results are discussed in the context of the independant cardinality of underlying system scalar invariants (SI) corresponding to the democratic auxiliary labels (Chem Phys 1998, 238, 245; J Math Chem in press), or projective recoupling, of 20‐fold dual tensorial sets. Landau‐like 𝒮n‐maps for fundamental terms plus statistical weighted subsidary maps yield the independent ∣SI∣s (see Europhys Lett in press). Geometric aspects of the dual group mappings imply that eventually large cage NMR ensembles must be governed by a local, rather than a global, symmetry, with the former related to established spectral deceptive NMR. This suggests a further role for dynamical networks in NMR, beyond that given by K. Balasubramanian (J Chem Phys 1983, 78, 6369) as implied by D. Watts (Small Worlds; Princeton Univ. Press: Princeton, NJ, 1999). © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Brueckner orbitals and density‐functional theory
Authors: Lindgren Ingvar , Salomonson Sten 
Published: October 2002

AbstractBy means of many‐body perturbation theory (MBPT) it is shown that minimizing the energy expectation value of a closed‐shell system in a certain order of the perturbation expansion by varying the partitioning of the Hamiltonian leads to a zeroth‐order function, which—as the order of perturbation increases and provided the expansion converges properly—approaches a determinant of Brueckner orbitals. It is also shown that the energy eigenvalues of the Brueckner orbitals represent the corresponding ionization energies of the system, including orbital‐relaxation and correlation effects to all orders of perturbation theory. This is a generalization of the Koopmans theorem in Hartree–Fock theory. The MBPT treatment is used for a discussion of the density‐functional theory, and a new model is proposed—referred to as the Brueckner–Kohn–Sham scheme—where also the electron correlation is included in the functional. This leads to a nonlocal exchange‐correlation potential, quite similar to that of Brueckner orbitals (BO), implying that the orbitals of the new scheme are essentially BO. Arguments are given that also the orbitals of other schemes with a purely local potential, such as the standard Kohn–Sham (KS) scheme, would be close to BO. This has been conjectured by Heßelmann and Jansen ( J Chem Phys 2000, 112, 6949), and the present work gives more direct evidence of that. This might explain the recent observations that the KS orbitals and energy eigenvalues do have more physical significance than was originally anticipated. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Coupled‐perturbed Hartree–Fock treatment of infinite periodic systems: Application to static polarizabilities and hyperpolarizabilities of polydiacetylene, polybutatriene, and interacting pairs of polyacetylene chains
Authors: Kirtman Bernard , Champagne Benoît , Gu Feng Long , Bishop David M. 
Published: October 2002

AbstractStatic longitudinal polarizabilities (α) and second hyperpolarizabilities (γ) are determined for three quasi‐one‐dimensional polymeric systems using a new crystal orbital coupled‐perturbed Hartree–Fock method. Calculations of α and γ for polydiacetylene and polybutatriene at two different geometries are analyzed in terms of the alternation of bond lengths along the carbon backbone. For the third polymer, polyacetylene, the treatment is applied to a pair of chains in the two different configurations that occur in a stretched fiber. The results are in marked contrast to those previously obtained for short and medium‐sized oligomers. In order to relate the pair interaction effect between infinite chains to the bulk susceptibility of the natural fiber additional finite oligomer calculations are carried out. This allows us to discuss the role of finite chain length distribution, many‐body interchain interactions, and electron correlation. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Data mining, ab initio, and molecular mechanics study on conformation of phenylalanine and its interaction with neighboring backbone amide groups in proteins
Authors: Duan Guilin , Smith Vedene H. , Weaver Donald F. 
Published: October 2002

AbstractData mining results for 1029 X‐ray protein structures demonstrate that there are, on average, more than nine phenylalanine residues in a typical protein structure. Moreover, the conformations of these phenylalanine residues are not arbitrary but fall into four regular types. These four phenylalanine conformational types can be related to the interaction between the phenylalanine's phenyl group and its neighboring backbone amide groups. They are designated as “Aphe,” “Cphe,” “ACphe,” and “NACphe,” respectively, depending on the presence and absence of such phenyl–amide interactions. It is shown that 96.2% of the phenylalanine residues occurring in proteins fall into the first three types, which involve one or two types of these interactions. The side chain and associated backbone fragment of each phenylalanine type have characteristic conformational regularities. The interaction potential energy surfaces of these interactions were exhaustively and systematically evaluated by means of the validated CHARMm force field. We show that this force field produces interaction energies comparable to BSSE‐corrected values calculated using MP2/6‐311G(2d,2p) and MP2/6‐31+G(2d,p). The phenyl–amide interactions occurring in proteins have configurations corresponding to a stabilization energy of up to 11 kJ/mol in vacuum. None occur that would correspond to a phenyl–amide repulsion. We conclude that the phenyl–amide interaction is one of the factors responsible for the conformational regularity of the phenyalanine in proteins and that it is of significance due to its strength and common occurrence. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
The Löwdin challenge: Origin of the n+ℓ, n (Madelung) rule for filling the orbital configurations of the periodic table
Authors: Allen Leland C. , Knight Eugene T. 
Published: October 2002

AbstractThe periodic table may be viewed as an s‐block and p‐block framework internally perturbed by d and f electrons. A perturbation operator is devised to search the table for small energy changes and to locate the d‐ and f‐blocks. The unusually large s/d and s/f radial extent ratios are discussed and related to the unexpected order of ns and (n−1)d occupancy and to the charge transfer from s to d orbitals that occurs in transition metal complexes. The orbitals and their properties, obtained from Desclaux's 1973 Fock–Dirac neutral atom calculations for Z=1–118, are employed to verify our analysis. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Redox chemistry of organoselenium compounds: Ab initio and density functional theory calculations on model systems for transition states and intermediates of the redox cycle of selenoenzymes
Authors: Benkova Zuzana , Kóňa Juraj , Gann Gudrun , Fabian Walter M. F. 
Published: October 2002

AbstractAb initio [Hartree–Fock (HF)] and density functional theory (B3LYP) ECP calculations on intermediates and transition states of the reduction of phenylseleninic acid with hydrogen sulfide and of seleninic acid with benzenethiol as models for the species involved in the redox cycle of selenoenzymes are presented. Selenenyl sulfide is found to be the final product of the reduction reaction with sulfides. Further reduction to the selenol requires surmounting a substantial barrier (∼50 kcal mol−1). The final step of the redox cycle—oxidation of the selenol by hydrogen peroxide—is strongly exothermic. In case of the unsubstituted derivative H2Se three mechanisms for this oxidation are found [concerted and stepwise 1,2‐hydrogen and oxygen shift (TS6A, TS6B, resp.) and a four‐membered transition state TS6C]. For the oxidation of phenylselenol only TS6A and TS6B are obtained. For nearly all calculated structures the HF wave functions show a triplet instability. In contrast, at the B3LYP level only TS6C has a significant triplet instability. On the basis of QCISD(T)//QCISD results a mechanism involving TS6C seems highly unlikely. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Relativistic dynamics of positronium atom in uniform magnetic field*
Authors: Datta Sambhu N. , Misra Anirban 
Published: October 2002

AbstractThe relativistic dynamics of the positronium atom in a uniform external magnetic field is investigated in this work. Following our previous work on a general system of two spin‐½ particles, here too we choose three distinct forms of interaction, viz., the Bethe–Salpeter interaction, the Breit interaction, and the projected Breit interaction. We also include the interaction of the anomalous magnetic moment with the external magnetic field. As the system is overall electrically neutral, the center‐of‐mass motion can be completely separated out. The residual Hamiltonian operator describes only the relative movement. This operator can be brought into a form where the one‐particle part is exactly separable into positive and negative energy states and is diagonal. However, as a marked departure from our previous methodology, the separation of the odd terms from the transformed interaction operator up to order α2, where α is the fine‐structure constant, is accomplished here by a somewhat different procedure so as to avoid those unitary transformation operators which contain the mass difference (m1−m2) in the denominators of their arguments. Because of the nature of the one‐particle operators, the odd terms of order α2 are completely removed in the present treatment. Also, no unphysical term of order α2 results from the use of the Breit interaction. The effect of the virtual electron–positron pair, which appears at second order in the fine‐structure constant, is also incorporated in the Hamiltonian. Again, the reduction of the order‐α2 pair term to a previously known simpler form is exactly achieved here. Thus we obtain three different versions of the relativistic Hamiltonian operator for a positronium atom in a uniform magnetic field, with the electrodynamical interactions taken into account through order α2. All three lead to the same energy for the same spinor wave function under the so‐called uU separation. These operators are now used to calculate the conventional nonrelativistic limit, and the same limiting operator is obtained in every case. For zero magnetic field, the Hamiltonian reduced to the nonrelativistic limit is found to be identical with the standard nonrelativistic Hamiltonian known for the positronium atom. We also obtain the nonrelativistic limit Hamiltonian for the positronum atom in the high‐field case, where the ratio of the applied magnetic field and the velocity of light B/c, or, more precisely, the Larmor frequency ωL=eB/2mc, is of the order of one atomic unit. Finally, in the Appendices, we discuss the nature of the eigenfunctions and indicate how one can calculate these functions correctly through the zeroth order in the fine‐structure constants and find the eigenvalues correct through the second order. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002