bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regularities in the bond dissociation enthalpies of molecules of types AB and BAB: Energetics of 10‐ and 16‐valence electron ions of groups 13, 15, and 16
Authors: Deakyne Carol A. , Li Le , Zheng Wencui , Xu Danyu , Liebman Joel F. 
Published: October 2003

AbstractFor the quantitative and qualitative understanding of molecular energetics, contemporary calorimetric and mass spectrometric measurement techniques and correspondingly high‐level quantum chemical calculational methodologies increasingly work in concert. For example, letting A and B be group 14 and 16 elements, respectively, for their 10‐valence electron AB and 16‐valence electron AB2 gas‐phase diatomic and triatomic species, the bond enthalpy ratio 〈D(AB2)〉/D(AB) has been shown to remarkably constant, namely, 0.77 ± 0.02. In the current study we discuss the corresponding bond enthalpy ratio for the valence isoelectronic cations and anions, e.g., for the carcinogen [NO]+, explosive precursor [NO2]+, and discrete (monomeric, i.e., nonsalt containing) anions [BO2]− and [AlO2]−. From a combination of results taken from archival literature measurements and new quantum chemical calculations reported in this article, again roughly constant ratios are found. Numerically, these ratios are 0.66 ± 0.03 and 0.86 ± 0.02 for cations and anions, respectively. That the ratios increase in the order cation < neutral < anion is also explained in our study. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Ab initio molecular dynamics with maximally localized Wannier functions
Authors: Sharma Manu , Wu Yudong , Car Roberto 
Published: October 2003

AbstractWe present a novel formulation of ab initio molecular dynamics that should be useful to simulate insulating systems. In this scheme maximally localized Wannier functions instead of delocalized Bloch states evolve on the fly during nuclear dynamics. Localized Wannier orbitals offer several advantages over orbitals that are delocalized in the entire simulation cell. In fact, at variance with the latter, they provide a picture of the electronic bonds consistent with simple chemical intuition. In addition, by taking advantage of their exponential localization it should be possible to develop ab initio molecular dynamics schemes having a computational cost that scales linearly rather than cubically with system size. We show that maximally localized Wannier functions can be calculated efficiently within Car–Parrinello dynamics and use water in gas and liquid phase as a test system to demonstrate our scheme and illustrate its usefulness. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Molecular structures, thermochemistry, and electron affinities for the dichlorine oxides: Cl2On/Cl2O (n = 1–4)
Authors: Li Qianshu , Lü Shunfeng , Xie Yaoming , Schleyer Paul V. R. , Schaefer Henry F. 
Published: October 2003

AbstractThe molecular structures, relative energies, vibrational frequencies, and electron affinities for the Cl2On/Cl2O (n = 1–4) systems have been investigated using hybrid Hartree–Fock/density functional theories (BHLYP and B3LYP) and pure density functional theories (BP86 and BLYP). The three different types of neutral/anion energy differences reported in this research are the adiabatic electron affinity (EAad), the vertical electron affinity (EAvret), and the vertical detachment energy (VDE). The basis set used in this work is of double‐ζ plus polarization quality with additional s‐ and p‐type diffuse functions, and it is denoted DZP++. The geometries are fully optimized by all four DFT methods. We have predicted a number of possible low‐lying local minima, including some that are unprecedented. Most strikingly, in several cases structures that have been observed in the laboratory turn out not to be lowest in energy for a particular chemical composition. Two structures are predicted with a formally seven‐coordinate chlorine atom. The global minima for the Cl2On/Cl2O (n = 1–4) systems are ClOCl (C2v), ClClO− (Cs), ClOOCl (C2), OOCl (C2v), ClOOOCl (C2/C1), ClO(O2)Cl− (Cs), trans‐ClO(O2)OCl (Ci), and trans‐ClO(O2)OCl− (Ci), respectively. The relative energies of the different minima are reported. Five of the 42 structures predicted here have been determined experimentally. Our theoretical geometries and vibrational frequencies are carefully compared with the limited available experimental results, and the BHLYP functional in general provides the best agreement. The ClClO− and ClClO ground states might be regarded as Cl− … ClO and Cl− … ClO2 complexes, respectively. The adiabatic electron affinities, obtained at the favored DZP++ BLYP level of theory, are 3.12 eV for Cl2O, 3.96 eV for Cl2O2, 3.66 eV for Cl2O3, and 4.15 eV for Cl2O4. The adiabatic EAs for the first three systems are similar to those of Br2On (3.14, 3.80, and 3.46 eV with BLYP for Br2On, n = 1–3), and this may reflect the geometric similarity between these bromine and chlorine species. But, EAad for Br2O4 (1.97 eV) is different from Cl2O4 because the neutral and anionic bromine species have different global minimum geometries from those for Cl2O4. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Determination of the crystalline structure of nonlinear molecules in a combined quantum chemical and classic lattice potential description
Authors: Ko Gwon Hee , Fink William H. 
Published: October 2003

AbstractThe general problem of the prediction of the crystal parameters and molecular structure of nonlinear molecules is taken up in a treatment that couples the molecular electronic structure determination to the surrounding crystalline lattice field. The molecular electronic structure method used may be at any level of sophistication, but we used the Hartree–Fock approximation in this application. A partial charge analysis of the molecular electronic structure is performed to establish the values of atom‐centered partial charges that interact via Coulomb's law, along with a Lennard–Jones potential between all atoms to establish a crystalline lattice field. The Lennard–Jones parameters are taken from the widely used AMBER force field. The lattice field terms are included in the molecular Hamiltonian and exert forces on the nuclei, leading to a somewhat different equilibrium structure than is obtained for the isolated molecule. The positions, orientations, and unit cell parameters are optimized for the lattice field, leading to a full determination of the crystal structure, including the space group. Results for sulfur dioxide, ammonia, and water are reported. In each case an equilibrium crystalline geometry faithfully reproducing the experimentally determined space group is obtained. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
From electrons to proteins and back again
Authors: Lesk Arthur M. 
Published: October 2003

AbstractThe study of protein structure is now a legitimate topic in physics as well as in biochemistry. General methods for comparing and classifying the topologies of protein folding patterns are useful in organizing the structures that are known and enumerating possible protein structural patterns that have not yet been observed. A tableau representation of protein structures, suitable for manipulation and searching by algorithms, is described and an application to searching the databanks of known structures for a set of combinations of substructures is reported. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Critical distance model for the energy of activation of the Bergman cyclization of enediynes
Authors: Gaffney Shannon M. , Capitani Joseph F. , Castaldo Lyana , Mitra Abhijit 
Published: October 2003

AbstractThe reaction profile of the Bergman cyclization of enediynes is written as a cubic polynomial expansion about the critical distance. Using the “simple sewing” approximation, a relationship is derived that expresses the energy of activation as a function of the critical distance, with the effect of other geometric and electronic factors accounted for in the expansion coefficients. A training set of 10 representative enediynes were selected and input parameters were calculated by density functional theory at the B3LYP/6‐311G* level of theory. All calculations were corrected for zero‐point energy. All singlet biradical calculations were also checked for wave function stability. Calibration curves were then constructed that correlate the activation energy of cyclization of the molecules in the test set with the critical distance parameter. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Ab initio MO study of the symmetrical and asymmetrical isomers of bridging alkynylaluminum and alkynylberyllium dimers
Authors: Seida Pamela R. , Bundens Jeanne W. , Francl Michelle M. 
Published: October 2003

AbstractThe structures of models for known alkynylaluminum‐ and alkynylberyllium‐bridged dimers were predicted using ab initio molecular orbital methods at the HF/6‐31G* level. In both cases, the preferred structure has the bridging alkynyl fragments tilted toward one metal center. Structural comparisons and fragment molecular orbital arguments were used to elucidate the electronic factors leading to the distortion. The essential bonding interaction that stabilizes these structures is π complexation of the alkynyl fragment to one of the metal centers. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Origin of the bathochromic shift in the early photointermediates of the rhodopsin visual cycle: A CASSCF/CASPT2 study
Authors: Schreiber Marko , Buss Volker 
Published: October 2003

AbstractCASSCF/CASPT2 calculations have been applied to study the excited‐state properties of the chromophore in rhodopsin and in the early photointermediate, photorhodopsin. For rhodopsin, the chromophore geometry was taken from an optimized X‐ray structure while for photorhodopsin the structure proposed by Bifone et al.J Phys Chem B 1997, 101, 2954 was employed. The experimentally observed bathochromic shift of 72 nm is faithfully reproduced by the calculation. Analysis of a model chromophore in which the transition between the geometries is performed stepwise reveals that this shift is predominantly caused by double bond torsion. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
First‐principles simulation of the UV absorption spectrum of ketene
Authors: Nooijen Marcel 
Published: October 2003

AbstractThe absorption spectrum of ketene (CH2CO) in the 145‐ to 220‐nm region is calculated completely from first principles and compared to a recent high‐resolution synchrotron radiation experiment J Chem Phys 2002, 117, 4306. The simulations are based on a vibronic model, which is extracted from routinely applicable coupled cluster calculations for electronically excited states. Nonadiabatic effects are assessed by a comparison of the vibronic model simulations with Franck–Condon calculations and are found to be important to understand various aspects of the absorption spectrum of ketene. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Synthesis, structure, and physical properties of a new phenalenyl‐based neutral radical crystal: Correlation between structure and transport properties in carbon‐based molecular conductors
Authors: Chi X. , Itkis M. E. , Tham F. S. , Oakley R. T. , Cordes A. W. , Haddon R. C. 
Published: October 2003

AbstractA new class of phenalenyl‐based neutral radical molecular conductors has recently been reported; a distinctive feature of these molecular solids is the absence of the well‐defined conducting pathway(s) that are characteristic of the organic charge‐transfer salts. These radicals do not stack in the solid state, and the requisite carbon–carbon contacts are all larger than the sum of the van der Waals distances. Magnetic susceptibility measurements show that these compounds usually exist as isolated free radicals with one spin per molecule (at least over some temperature range), apparently supporting the idea that there is little interaction between the molecules in the solid state. Nevertheless, these radicals show the highest conductivity (σRT = 0.05 S/cm) of any neutral organic solid and the conduction mechanism is at present unresolved. In this article we report a structurally related radical with a resistivity five orders of magnitude higher than that of the previously reported radicals. We analyze the crystallographic and electronic structure of this solid in detail and point out some of the challenges that remain in relating structure, magnetism, and conductivity in this new class of organic solids. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Dopamine responsiveness to drugs of abuse: A shell‐core investigation in the nucleus accumbens of the mouse
Authors: Zocchi Alessandro , Girlanda Elena , Varnier Giorgia , Sartori Ilaria , Zanetti Lara , Wildish Grant A. , Lennon Mark , Mugnaini Manolo , Heidbreder Christian A. 
Published: October 2003

AbstractThe existence of subterritories within the nucleus accumbens has now been widely supported by histochemical, neurochemical, electrophysiological, as well as morphological and ultrastructural studies and suggest specific afferent and efferent systems involved in different behavioral aspects. Microdialysis studies in the rat have consistently shown that most drugs of abuse increase extracellular dopamine levels preferentially in the shell subregion of the nucleus accumbens. The study of the relative roles of NAc subregions may considerably help our understanding of the neurobiological basis of drug addiction. Accordingly, the aim of the present work was to extend the outcome of rat studies to the mouse species. Five major drugs of abuse were systemically and acutely administered to mice with a microdialysis probe implanted in either the shell or the core. A statistical comparison was performed on data transformed as percentage values of baseline dopamine vs. logarithmic values with baseline dopamine as a covariate. Results show a significant increase in dopamine levels in both the shell and core subregions following cocaine, amphetamine, nicotine, ethanol, and morphine treatments. A difference between shell and core after cocaine, nicotine, and morphine was evident when data were analyzed as percent values of baseline. However, such a shell‐core dichotomy became no longer significant when ANOVA was applied on the statistically more appropriate logarithmic transformation of data with baseline as a covariate. The significant baseline differences among groups of mice (dopamine levels in the shell significantly lower compared with dopamine levels in the core) may have compromised, at least in part, the statistical procedure usually applied in microdialysis studies. These findings suggest that a careful evaluation of the data is required when subtle changes in extracellular levels of DA are measured. Synapse 50:293–302, 2003. © 2003 Wiley‐Liss, Inc.
Amygdaloid D1 receptors are not linked to stimulation of adenylate cyclase
Authors: Leonard Sarah K. , Anderson Carl M. , Lachowicz Jean E. , Schulz David W. , Kilts Clinton D. , Mailman Richard B. 
Published: October 2003

AbstractIn contrast to the classic signal transduction of D1 dopamine receptors in striatum or molecular expression systems, it has been reported that D1 receptor agonists do not stimulate adenylate cyclase in homogenates of microdissected nuclei of the amygdaloid complex. This article examines this phenomenon in detail to determine if lack of cAMP signaling in the amygdaloid complex is an experimental artifact, or an indication of a marked difference from the well‐studied basal ganglia terminal fields. Thus, whereas dopamine agonists failed to increase cAMP synthesis in the amygdala, forskolin, guanine nucleotides, or Mg2+ were able to stimulate adenylate cyclase activity in the same preparations. Under several different conditions, caudate preparations responded more robustly than amygdaloid preparations, while amygdala homogenates exhibited higher basal production of cAMP. Whereas the β‐adrenergic agonist isoproterenol was able to stimulate cAMP efflux in membranes from both the caudate and amygdala under a variety of tested conditions, neither dopamine nor fenoldopam (D1 agonist) could stimulate adenylate cyclase in the amygdala. Additionally, while manipulation of Ca2+ and calmodulin affected the differential actions of dopamine in the caudate, no change in these parameters restored sensitivity to dopamine in the amygdala. Together, these data challenge the commonly accepted notion that cAMP is a mandatory signaling pathway for D1 receptors. Because it is now proven that G protein‐coupled receptors can signal promiscuously, elucidation of the non‐cAMP‐dependent signaling mechanisms resulting from D1 activation is clearly critical in understanding how this important receptor functions in situ. Synapse 50:320–333, 2003. © 2003 Wiley‐Liss, Inc.
Direct activation by dopamine of recombinant human 5‐HT1A receptors: Comparison with human 5‐HT2C and 5‐HT3 receptors
Authors: Oz Murat , Zhang Li , Rotondo Alessandro , Sun Hui , Morales Marisela 
Published: October 2003

AbstractThe effects of dopamine (DA) on the function of human 5‐HT1A receptors expressed in Xenopus oocytes and CHO‐K1 cells were investigated. In addition, the effect of DA on the activation of three different types of human 5‐HT receptors (5‐HT1A, 5‐HT2C, and 5‐HT3) were studied comparatively in Xenopus oocyte expression system. Application of 5‐HT or DA in oocytes coexpressing 5‐HT1A receptors and G‐protein‐activated inwardly rectifying potassium channels (GIRK1) induced inward currents with respective EC50 values of 4.2 nM and 11.2 μM. Maximal responses induced by DA were 85 ± 4% of maximal 5‐HT currents and DA responses were blocked by the specific 5‐HT1A antagonist, WAY‐100635 (50 nM). In CHO‐K1 cells expressing 5‐HT1A receptors, 5‐HT and DA inhibited the specific binding of selective antagonist [3H]‐8‐OH‐DPAT with IC50 values of 10.2 nM and 1.4 μM, and both 5‐HT and DA inhibited the forskolin‐induced accumulation of cAMP. In oocytes expressing 5‐HT2C receptors, 5‐HT and DA induced inward currents with respective EC50 values of 6.2 nM and 67.7 μM. Magnitudes of maximal DA induced currents were 42 ± 3% of maximal 5‐HT responses and blocked by the 5‐HT2 antagonist, piperazine (1 μM). In oocytes expressing 5‐HT3 receptors, 5‐HT and DA induced fast inward currents with respective EC50 values of 2.1 μM and 266.3 μM. Maximal DA induced currents were 37 ± 3% of maximal 5‐HT responses and blocked the specific 5‐HT3 antagonist LY‐278584 (0.1 μM). Comparison of the potencies and efficacies of 5‐HT and DA indicated that the relative potency of DA increased in the order of 5‐HT3 > 5‐HT1A > 5‐HT2C, and relative efficacy increased in the order of 5‐HT1A > 5‐HT2C > 5‐HT3. These results suggest that although DA activates different subtypes of human 5‐HT receptors directly, the potency and efficacy of the binding site varies significantly among different receptors. Synapse 50:303–313, 2003. Published 2003 Wiley‐Liss, Inc.
Evaluation of a new norepinephrine transporter PET ligand in baboons, both in brain and peripheral organs
Authors: Ding Yu‐Shin , Lin Kuo‐Shyan , Garza Victor , Carter Pauline , Alexoff David , Logan Jean , Shea Colleen , Xu Youwen , King Payton 
Published: October 2003

AbstractReboxetine is a specific norepinephrine transporter (NET) inhibitor and has been marketed in several countries as a racemic mixture of the (R,R) and (S,S) enantiomers for the treatment of depression. Its methyl analog (methylreboxetine, MRB) has been shown to be more potent than reboxetine itself. We developed a nine‐step synthetic procedure to prepare the normethyl precursor, which was used to synthesize [11C]O‐methylreboxetine ([11C]MRB). We also developed a convenient resolution method using a chiral HPLC column to resolve the racemic precursor to obtain enantiomerically pure individual precursors that lead to the individual enantiomers (R,R)‐[11C]MRB and (S,S)‐[11C]MRB. Here we report an evaluation of the racemate and individual enantiomers of [11C]MRB as radioligands for PET imaging studies of NET systems in baboons both in brain and in peripheral organs. The relative regional distribution of the radioactivity after injection of [11C]MRB in baboon brain is consistent with the known distribution of NET. For a NET‐poor region such as striatum, there were no significant changes in the striatal uptakes with and without the nisoxetine pretreatment. In contrast, a significant blocking effect was observed in NET‐rich regions such as thalamus and cerebellum after injection of racemic [11C]MRB, with an even more dramatic effect after injection of (S,S)‐[11C]MRB. These results, along with the fact that there was no regional specificity and no blocking effect by nisoxetine for (R,R)‐[11C]MRB, suggest the enantioselectivity of MRB in vivo, consistent with previous in vitro and in vivo studies in rodents. PET studies of baboon torso revealed a blocking effect by desipramine only in the heart, a NET‐rich organ, after injection of (S,S)‐[11C]MRB, but not the (R,R)‐isomer. These studies demonstrate that the use of (S,S)‐[11C]MRB would allow a better understanding of the role that NET plays in living systems. Synapse 50:345–352, 2003. © 2003 Wiley‐Liss, Inc.
Discontinuous Galerkin methods
Authors: Cockburn B. 
Published: October 2003

AbstractThis paper is a short essay on discontinuous Galerkin methods intended for a very wide audience. We present the discontinuous Galerkin methods and describe and discuss their main features. Since the methods use completely discontinuous approximations, they produce mass matrices that are block‐diagonal. This renders the methods highly parallelizable when applied to hyperbolic problems. Another consequence of the use of discontinuous approximations is that these methods can easily handle irregular meshes with hanging nodes and approximations that have polynomials of different degrees in different elements. They are thus ideal for use with adaptive algorithms. Moreover, the methods are locally conservative (a property highly valued by the computational fluid dynamics community) and, in spite of providing discontinuous approximations, stable, and high‐order accurate. Even more, when applied to non‐linear hyperbolic problems, the discontinuous Galerkin methods are able to capture highly complex solutions presenting discontinuities with high resolution. In this paper, we concentrate on the exposition of the ideas behind the devising of these methods as well as on the mechanisms that allow them to perform so well in such a variety of problems.
Genetic diversity analysis of captive populations: The Vietnamese sika deer (Cervus nippon pseudaxis) in zoological parks
Authors: Thévenon Sophie , Bonnet Amélie , Claro Françoise , Maillard Jean‐Charles 
Published: October 2003

AbstractThe Vietnamese sika deer (Cervus nippon pseudaxis) is an endangered subspecies; it has disappeared in the wild, but is being bred in zoological parks. We studied the neutral genetic diversity and population structure of herds kept in different European zoos, using nine microsatellite loci. The goal was to evaluate the consequences of founding effects and breeding practices on the level and structure of genetic variability. The level of genetic diversity within the European zoos is not lower than that of the populations kept in Vietnamese farms. Strong differences among zoological parks and between the European group and the Vietnamese population were detected. This is probably due to founding effects, genetic drift, and possibly hybridization in both Europe and Vietnam. We expected to find a much lower level of genetic diversity in Europe. The current overall level of genetic diversity is probably due to the recent introduction of Cuc Phuong individuals, and to important differences among the populations of different zoological parks, which increase the total genetic variability. Although the current level of genetic variability is not particularly low, future levels are probably threatened by the current herd sizes and structure. Based on these results, management guidelines are proposed. Zoo Biol 22:465–475, 2003. © 2003 Wiley‐Liss, Inc.