bluuebunny/crossref_metadata_2025_split huggingface dataset:
An investigation on the reaction mechanism of the F2+Cl2→2ClF using the B3LYP method
Authors: Wang Zun Yao , Gong Xue Dong , Li Jin Shan , Xiao He Ming 
Published: August 2002

AbstractThe reaction mechanism of F2+Cl2→2ClF has been investigated with the density functional theory at the B3LYP/6‐311G* level. Six transition states have been found for the three possible reaction paths and verified by the normal mode vibrational and IRC analyses. Ab initio MP2/6‐311G* geometry optimizations and CCSD(T)/6‐311G(2df)//MP2/6‐311G* single‐point energy calculations have been performed for comparison. It is found that when the F2 (or Cl2) molecule decomposes into atoms first and then the F (or Cl) atom reacts with the molecule Cl2 (or F2) nearly along the molecular axis, the energy barrier is very low. The calculated energy barrier of F attacking Cl2 is zero and that of Cl attacking F2 is only 15.57 kJ⋅mol−1 at the B3LYP level. However, the calculated dissociation energies of F2 and Cl2 are as high as 145.40 and 192.48 kJ⋅mol−1, respectively. When the reaction proceeds through a bimolecular reaction mechanism, two four‐center transition states are obtained and the lower energy barrier is 218.69 kJ⋅mol−1. Therefore, the title reaction F2+Cl2→2ClF is most probably initiated from the atomization of the F2 molecule and terminated by the reaction of F attacking Cl2 nearly along the ClCl bond. MP2 calculations lead to the same conclusion, but the geometry of TS and the energy barrier are somewhat different. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002
Polarizability and chemical hardness—A combined study of wave function and density functional theory approach
Authors: Kolandaivel P. , Mahalingam T. , Sugandhi K. 
Published: August 2002

AbstractA flexible model for generating the molecular wave function and electron density for diatomic molecules is developed employing the quadratic anharmonic oscillator and Morse potential. The chemical hardness, Fukui function, and polarizability were calculated using the electron density of the molecules, and the values are found to be reasonably good. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Statistical mechanics of energy transfer in gas–surface scattering: A dynamical Lie algebraic approach
Authors: Guan Daren , Yi Xizhang , Meng Qingtian , Zheng Yujun , Wu Jianzhong , Sun Jiazhong 
Published: August 2002

AbstractThe dynamical Lie algebraic (DLA) method is used to describe statistical mechanics of energy transfer in rotationally inelastic molecule–surface scattering. Statistical average values of an observable for the scattering system are calculated in terms of density operator formalism in statistical mechanics. Employing a cubic expansion procedure of molecule–surface interaction potential leads to generation of a dynamical Lie algebra. Thus these statistical average values as a function of the group parameters can be obtained analytically in this formulation. The group parameters can be found from solving a set of coupled nonlinear differential equations. The DLA method, which has no need for determination of transition probabilities in advance as made routinely in the calculation, offers an efficient alternative to the method for computing the statistical average values. This method is much less computationally intensive because most of calculations can be analytically carried out. The average final rotational energies and their dependence on the main dynamic variables and the average interaction potential are presented for the rotationally inelastic scattering of NO molecules from a flat, static Ag(111) surface. Direct comparison is made between the predictions of this model calculation and experiment. The model reproduces well the degree of rotational excitation and correlation between the average final translational and the average rotational energies. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Energy profiles for the rate‐limiting stage of the serine protease prototype reaction
Authors: Nemukhin Alexander V. , Topol Igor A. , Burt Stanley K. 
Published: August 2002

AbstractThe energy profiles of reaction, modeling the rate‐limiting stage of serine protease catalyzed transformations, have been computed by quantum chemistry methods. The model includes fragments of the residues of the catalytic triad (serine, histidine, and aspartic acid), two water molecules as an oxyanion hole, represented by effective fragment potentials, and a formamide molecule as a substrate. Geometry optimizations have been performed along the reaction coordinate, chosen as the distance between oxygen of serine and carbon of substrate, by using the Hartree–Fock method. The density functional theory B3LYP/6‐31+G(d,p) calculations have been employed to recalculate energies along the reaction path in the gas phase and in the dielectric environment. The computed barrier heights are fairly consistent with the data cited in the literature. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 88: 34–40, 2002
Can cooperativity in hydrophobic association be reproduced correctly by implicit solvation models?*
Authors: Czaplewski Cezary , Ripoll Daniel R. , Liwo Adam , Rodziewicz‐Motowidło Sylwia , Wawak Ryszard J. , Scheraga Harold A. 
Published: August 2002

AbstractThe potential of mean force (PMF) of the hydrophobic association of pairs and triplets of nonpolar solute molecules with various sizes and strengths of van der Waals interactions has been studied by means of umbrella‐sampling molecular‐dynamic simulations combined with the weighted‐histogram analysis method. The TIP3P water model was used in these computations. It was found that the distance dependence of the PMF, including the three‐body (cooperative) contribution, is described qualitatively correctly by the variation of either the molecular surface area or the excluded solvation‐shell molecular volume with the distance between the solute molecules, while the solvent‐accessible surface and the hydration‐shell models, which are commonly used in mean‐field solvation approaches, give an incorrect distance dependence and the wrong sign of the cooperative contribution. The cooperative contribution to the PMF increases the strength of hydrophobic interactions and increases with the size of the solute. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 88: 41–55, 2002
A protoporphyrin IX‐based model for cytochrome P‐450 iron‐binding inhibitors: SAM1 calculations of structure and complexation enthalpy*
Authors: Pudzianowski Andrew T. 
Published: August 2002

AbstractA methyl diester protoporphyrin IX complex with ferric ion in a low‐spin doublet state and with ethyl sulfide as a constant axial ligand, is proposed as a model system for examining cytochrome P‐450 Fe‐binding inhibitors, e.g., imidazoles and pyridines, which can coordinate as a second axial ligand. The SAM1 semiempirical method was used to calculate optimized structures and complexation enthalpies for a variety of organic ligands, as well as for the resting state aquo complex, under the assumption that such inhibitors are stronger Fe ligands than a water molecule in the enzyme's resting state and thereby block the P‐450 catalytic cycle. The SAM1 structures agree qualitatively with X‐ray structures of P‐450cam with bound ligands, and are in reasonable agreement regarding details such as Fe‐ligand bond lengths. The enthalpy results and structures provide insights into how the inhibitory potency of imidazoles is decreased by substituents around the divalent nitrogen. In particular, a substituted imidazole may still intrinsically be able to bind to the resting state iron but with a lowered binding energy, so that it is thermodynamically unable to displace the bound water molecule. Qualitative predictions based on SAM1 binding enthalpies are in accord with experimental structural and inhibitory data. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 88: 147–153, 2002
Effect of the orbitals of the bridging group on magnetic coupling
Authors: Hu Haiquan , Chen Zhida 
Published: August 2002

AbstractWith an AXB centrosymmetrical model system, the qualitative relationship was demonstrated among the coupling constant and the fourth power of S13, which is the overlap integral between the orbitals of the bridging group and the symmetrical combination of the singly occupied orbitals of magnetic centers in the local ligand field. By using density functional theory and the broken symmetry approach HHeH, [HFH]− and OTi2Cl4 systems were calculated to inspect the above conclusion. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 88: 275–279, 2002
Improved generator coordinate Hartree–Fock method applied to generate Gaussian basis sets for the isoelectronic series of the atoms He to Ne
Authors: Canal Neto A. , Jorge F. E. , De Castro M. 
Published: August 2002

AbstractWe have generated Gaussian basis sets (GBSs) for the neutral and the first 20 cations members of the isoelectronic series of each ground state atom from He to Ne with the improved generator coordinate Hartree–Fock (IGCHF) method. For all atomic species studied here, our total energy errors are smaller than those calculated by the original GCHF method using GBSs of the same sizes. The largest difference between our total energy results and those computed with a numerical Hartree–Fock approach is equal to 215 μhartree for Co17+. We also compare the ionization potentials obtained with the IGCHF with the corresponding experimental values. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 88: 252–262, 2002
Time‐dependent Fourier grid Hamiltonian method for studying the curve crossing dynamics: Dynamics of predissociation of NaI
Authors: Kumar Modal Chandan , Bhattacharyya S. P. 
Published: August 2002

AbstractA time‐dependent Fourier route is proposed to study quantum dynamics in the presence of curve crossing. The method is tested on a model problem and is then used to study the predissociation dynamics of NaI by a femtosecond laser pulse. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Effect of trimethylsilyl substitution on the structure and properties of phthalocyanine: A density functional theory study
Authors: Dong Gong Xue , Ming Xiao He , Gao Pin , Tian He 
Published: August 2002

AbstractThe geometries of four isomers of the trimethylsilyl substituted phthalocyanine (Pc)—I, II, III, and IV—have been optimized at the B3LYP/3‐21G level of density functional theory. Normal‐mode vibrational analyses have been performed and their standard thermodynamic functions, molar fractions, and electronic absorption spectra calculated. Single‐point energies have been calculated at the B3LYP/6‐311G* level for all isomers to evaluate the heats of formation from an isodesmic reaction. It is found that substitution has little influence on the geometry and electronic structures of the Pc framework. The corresponding geometric parameters in various isomers are close. According to the B3LYP/6‐311G*//B3LYP/3‐21G results, substitution at the peripheral position of the isoindole with an inner hydrogen is most favorable. The energies increase in the order of IV < II < III < I, and the energy difference between IV and I is 5.75 kJ/mol. The molar fractions of IV, II, III, and I are 0.80, 0.17, 0.02, and 0.02 and the heats of formation are 2009.96, 2010.10, 2015.85, and 2016.52 kJ/mol, respectively. This indicates that nonperipheral substituted Pcs have higher energy and little production because they are not stable under the considered conditions. The electronic spectra of the substituted Pcs calculated using the ZINDO method have two strong Q absorption bands around 700 nm and one B band around 300 nm that are slightly shifted compared with those in Pc. The ratios of the oscillator strength of the B band to the Q bands are much lowered by trimethylsilyl substitution. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Gyroscopic tensor ab initio calculation of the molecular crystals: (Mo6X14)2−Y−(TTF+)3 (X=Br, Cl and Y=Br, Cl, I)
Authors: Dhouib A. , Essalah K. , Tangour B. , Abderraba M. 
Published: August 2002

AbstractThe aim of this study is the determination of the g tensor of the tetrathiafulvalene (TTF) molecule involved in chlorine and bromine radical–ion salts. This work is based on ab initio calculations using several basis sets which enabled us to compare theoretical and experimental measurement data. The results show clearly the impact of the structural distortions on the g gyroscopic matrix elements and proves the important fact that even a small variation of the crystallographic parameters has major consequences on the physical–chemical properties. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002
Solution of the Kronig–Penney model using variational Monte Carlo
Authors: Alexander S. A. , Coldwell R. L. 
Published: August 2002

AbstractVariance minimization and Monte Carlo integration are used to evaluate the energy bands of an electron in the presence of a periodic array of one‐dimensional square wells separated by finite‐width barriers. Our results for the ground state, as well as the first and second excited states, are in excellent agreement with the exact analytic results for this model system. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
New time‐independent perturbation theory for the multireference problem
Authors: Chen Feiwu , Davidson E. R. , Iwata Suehiro 
Published: August 2002

AbstractA new time‐independent perturbation theory is developed for the multireference problem. In the derivation, neither perturbed wave function nor intermediate normalization condition is required. In the single‐reference case, the present approach gives the same perturbation expressions as Rayleigh–Schrödinger perturbation theory. In the multireference case, the perturbation expressions are derived with two kinds of partitions and can be applied to those cases with or without the definition of the zeroth Hamiltonian \documentclass{article}\pagestyle{empty}\begin{document}$\hat{H}_{0}$\end{document}. As the size of the reference space is decreased to 1, one multireference expansion returns to the single‐reference one with Epstein–Nesbet partition, while another is reduced to a new expansion. These two multireference perturbation expansions are further expressed with the eigenvectors of the Hamiltonian within the reference space for an efficient implementation. The correspondences between the single‐reference and multireference perturbation expansion are discussed. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Adsorption of water in mordenite—An ab initio study
Authors: Demuth Th. , Benco L. , Hafner J. , Toulhoat H. 
Published: August 2002

AbstractThe adsorption of water in mordenite has been investigated using density functional theory using gradient corrections to the exchange–correlation functional. In the neutral complex water is strongly physisorbed through two different hydrogen bonds, the stronger between the acid site and the water oxygen atom, the weaker between a hydrogen atom of the adsorbed molecule and a framework oxygen atom. Strong polarizations and structural distortions of both the acid site and the molecule have been observed. To elucidate the question if a chemisorbed complex (creation of a hydroxonium ion) is possible, ab initio molecular dynamics have been performed, indicating that a protonation of water occurs even for the low coverage of one water molecule per unit cell. However, this ionic configuration cannot be stabilized by the electrostatic field of the zeolite framework and is therefore not a minimum of the potential energy surface. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 84: 110–116, 2001
Explicitly correlated SCF study of small hydrides
Authors: Shillady Donald D. , Craig John , Rutan Sarah 
Published: August 2002

AbstractThe “soft Coulomb hole” method of Chakravorty and Clementi has been implemented in a Gaussian lobe‐orbital (GLO) program to include explicit electron–electron correlation in molecules according to a modified form of Coulomb's law in a program for workstations and personal computers (PCLOBE):
f(R12)=(1−exp (−w(R12)2))/R12,  w=scaling parameter.
Twice as many two‐electron integrals must be calculated compared to the usual Hartree–Fock–Roothaan algorithm, but this “correlated self‐consistent field (SCF)” method may be embedded within well‐known SCF computer codes and yields more than 90% of the correlation energy in run times less than twice that of the restricted Hartree–Fock (RHF) method. A two‐parameter model of correlation is calibrated on HF and LiH using the 6‐311G** basis as Gaussian lobe orbitals. The quantum Monte Carlo energies of LiH and HF were fitted to within 150 cal/mol, but the scaling model for first‐row atoms is less good for H2. This work shows promise as a fast way to modify the Hartree–Fock–Roothaan method for accuracy approaching quantum Monte Carlo methods. This proof‐of‐concept work offers extension to modeling solvation properties of water solutions in high‐pressure liquid chromatography (HPLC). © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Accuracy and precision of flowing afterglow mass spectrometry for the determination of the deuterium abundance in the headspace of aqueous liquids and exhaled breath water
Authors: Španel Patrik , Smith David 
Published: August 2002

AbstractWe have assessed the accuracy and precision of our flowing afterglow mass spectrometric method (FA‐MS) for absolute measurements of deuterium abundance in water using standardised tap water/D2O mixtures within the D/H range from 155 ppm (local tap water) to 1104 ppm, prepared by the gravimetric method. The results of this study show that a precision and accuracy of 1% can be achieved for the deuterium abundance in water samples. This is quite adequate for the main application, which is the rapid, non‐invasive measurement of total body water by deuterium analysis of breath water vapour using the D2O dilution method. Copyright © 2001 John Wiley & Sons, Ltd.
Comparison of electron capture dissociation and collisionally activated dissociation of polycations of peptide nucleic acids
Authors: Olsen Jesper V. , Haselmann Kim F. , Nielsen Michael L. , Budnik Bogdan A. , Nielsen Peter E. , Zubarev Roman A. 
Published: August 2002

AbstractElectron capture dissociation (ECD) in Fourier transform ion cyclotron resonance mass spectrometry coupled with electrospray ionization enhances the sequence elucidation of peptide nucleic acids compared with conventional low‐energy collisionally activated dissociation (CAD). Examples are shown where ECD produced complete or extensive sequence coverage in PNAs six to ten nucleobases long. However, facile base losses from the reduced species and low abundances of backbone ECD fragments presented a significant problem. This was rationalized through the lower degree of charge solvation on the backbone compared to polypeptides. Combination of both CAD and ECD data is advantageous, as these techniques produce cleavages at different sites. Copyright© 2001 John Wiley & Sons, Ltd.
Aldehyde analysis by high performance liquid chromatography/tandem mass spectrometry
Authors: O'Brien‐Coker Ivan C. , Perkins George , Mallet Anthony I. 
Published: August 2002

AbstractThis paper describes the development of a high performance liquid chromatography/tandem mass spectrometric (MS/MS) procedure for the specific qualitative and quantitative analysis of lipid aldehydes in biological matrices. A derivatisation method, which results in molecules that exhibit a common product ion on MS/MS, permits informative precursor ion scans, at high sensitivity. This has been applied to the examination of plasma in order to examine the production of aldehydes consequent on in vitro lipid oxidation. Quantitative analysis of target molecules using multiple reaction monitoring has been developed to permit quantitation in the same matrices. Copyright© 2001 John Wiley & Sons, Ltd.
Electrospray ionisation tandem mass spectrometry in the characterisation of isomeric benzofurocoumarins
Authors: Begala M. , Delogu G. , Maccioni E. , Podda G. , Tocco G. , Quezada E. , Uriarte E. , Fedrigo M. A. , Favretto D. , Traldi P. 
Published: August 2002

AbstractA set of aminoalkoxy‐substituted, differently annullated furocoumarins, differing in the position of the aminoalkoxy chain and in the unsaturation level of the fused ring, has been subjected to electron impact and electrospray ionisation (ESI) experiments. In order to achieve a distinct characterisation of isomeric compounds, which partially failed under electron impact conditions, collision‐induced dissociation experiments were performed on protonated molecules. The breakdown curves obtained by varying the tickle voltage on an ion trap ESI instrument led to the desired characterisation. Copyright © 2001 John Wiley & Sons, Ltd.
Development of a high‐pressure gradient pumping system for parallel liquid chromatography/mass spectrometry for the analysis of combinatorial libraries
Authors: Tolson David , Organ Andrew , Shah Ajit 
Published: August 2002

AbstractParallel liquid chromatography/mass spectrometer (LC/MS) systems such as the Micromass MUX™ have been commercially available for several years. Until recently, the LC pumping systems available have been a serious limitation to the more widespread adoption of such systems, particularly in good laboratory practice (GLP) environments. In this work, we compare the performance of the Jasco PAR‐1500 pumping system, which delivers an equal gradient flow to eight individual flow channels, to that of a conventional system, where the flow is split post pump. Both systems were coupled to a Micromass LCT™ liquid chromatography/electrospray ionisation time‐of‐flight (LC/ESI‐TOF) mass spectrometer equipped with a parallel MUX™ inlet system, used for the analysis of combinatorial libraries. In addition to flow stability, the Jasco system has resulted in a dramatic improvement in chromatographic performance. Copyright © 2001 John Wiley & Sons, Ltd.
Dynamically assisted gated trapping for Fourier transform ion cyclotron mass spectrometry
Authors: Gorshkov Michael V. , Masselon Christophe D. , Anderson Gordon A. , Udseth Harold R. , Smith Richard D. 
Published: August 2002

AbstractAn efficient approach for trapping ions and enhancing signal based on ‘adiabatic amplitude reduction’ for Fourier transform ion cyclotron resonance (FTICR) mass spectrometry is described and evaluated. This method is a modification to the widely used gated trapping technique in which the trapping potential is raised adiabatically rather than instantaneously (non‐adiabatically). Compared with non‐adiabatic gated trapping, the final amplitudes of ion axial oscillations and energies are lower in the proposed method. All performance aspects of the FTICR spectrum (e.g., peak intensities, mass resolution, and mass accuracy) improve significantly compared to the conventional gated trapping technique. Copyright © 2001 John Wiley & Sons, Ltd.