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1.
The three-dimensional (3D) potential energy surface of the ground state of Li3 was determined by the multireference configuration interaction method. The vibrational motions and pseudorotation were investigated
by a 3D time-dependent wavepacket formalism. The analytical expression of the 3D surface is given and the results of vibrational
analyses at several critical points are presented. The low-lying excited states of Li3 were examined for the C
2
v
structure and the vertical and adiabatic excitation energies were calculated. The ground and singlet excited states of Li2 were calculated and their spectroscopic constants compare well with the experimental values. A 3D wavepacket calculation
was performed for simulations of the stimulated emission pumping spectrum in which the A state was taken as an intermediate.
The recurrences of the autocorrelation functions were characterized by classical trajectory calculations. The autocorrelation
functions obtained by wavepacket propagation are reproduced well by the accumulation of the classical trajectories in the
short-time region.
Received: 2 July 1998 / Accepted: 3 September 1998 / Published online: 8 February 1999 相似文献
2.
Michael Schaefer Christian Bartels Martin Karplus 《Theoretical chemistry accounts》1999,101(1-3):194-204
To compare different implicit solvent potentials, the folding thermodynamics of the helical peptide RN24 and the β-hairpin
peptide BH8 are studied by molecular dynamics simulation with adaptive umbrella sampling. As the potential energy functions,
the analytical continuum solvent (ACS) potential and three simplified variants, termed EPSR1, EPSR4, and EPSR10, are used. The ACS potential is a combination of the standard CHARMM force field for the internal energy (bonds, angles,
dihedrals) and the van der Waals energy with the analytical continuum electrostatic (ACE) potential and a non-polar solvation
potential. The EPSR potentials differ from the ACS potential by the use of Coulomb's law with a distance-dependent dielectric
function to calculate the electrostatic energy. With the ACS potential, quantitative agreement with experiment is obtained
for the helix propensity (RN24: 62% calculated vs 50–60% experiment) and the β-hairpin propensity (BH8: 33% calculated vs
19–37% experiment) of the peptides. During the simulations with the EPSR potentials, no significant formation of secondary
structure is observed. It is shown that the preference for coil conformations over conformations with secondary structure
by the EPSR potentials is due to an overestimation of the energy of salt bridge formation, independent of the magnitude of
the Coulomb energy relative to the other energy terms. Possible improvements of the distance-dependent dielectric functions
which may permit their application to the simulation of peptide folding, are discussed.
Received: 11 July 1998 / Accepted: 22 September 1998 / Published online: 17 December 1998 相似文献
3.
Kazunari Naka Hirofumi Sato Akihiro Morita Fumio Hirata Shigeki Kato 《Theoretical chemistry accounts》1999,102(1-6):165-169
The free-energy profile for the Menshutkin-type reaction NH3 + CH3Cl → NH3CH3
+ + Cl− in aqueous solution is studied using the RISM-SCF method. The effect of electron correlation on the free-energy profile is
estimated by the RISM-MP2 method at the HF optimized geometries along the reaction coordinate. Solvation was found to have
a large influence on the vibrational frequencies at the reactant, transition state and product; these vibrational frequencies
are utilized to calculate the zero-point energy correction of the free-energy profile. The computed barrier height and reaction
exothermicity are in reasonable agreement with those of experiment and previous calculations. The change of solvation structure
along the reaction path is represented by radial distribution functions between solute-solvent atomic sites. The mechanisms
of the reaction are discussed from the view points of solute electronic and solvation structures.
Received: 26 June 1998/Accepted: 28 August 1998 / Published online: 2 November 1998 相似文献
4.
Peter Botschwina 《Theoretical chemistry accounts》1998,99(6):426-428
On the basis of large-scale coupled cluster calculations including connectedz triple substitutions in a perturbative way,
the geometrical parameters of the D
3
h
saddle point of the Walden inversion reaction Cl− + CH3Cl′→ ClCH3 + Cl′− are predicted to be R
s
(C—Cl) = 2.301 ? and r
s
(C—H) = 1.069 ?. The barrier height with respect to the reactants is recommended to be 11.5 ± 1.0 kJ mol−1. Connected triple substitutions lower the barrier height by almost a factor of 2, but have very little influence on the geometric
structure of the saddle point.
Received: 26 June 1998 / Accepted: 15 July 1998 / Published online: 28 September 1998 相似文献
5.
Hisayoshi Kobayashi Katsumi Nakashiro Tomoatsu Iwakuwa 《Theoretical chemistry accounts》1999,102(1-6):237-243
The mechanism of ethylene epoxidation on Ag surfaces has been investigated using the density functional method and Ag
n
clusters (n = 3 to 10) modeling the Ag(111) surface. The adsorption energy of O2 to the Ag clusters was strongly dependent on the HOMO level of the cluster, and the clusters with higher HOMO levels afforded
larger O2 adsorption energies. The energetics was investigated for both the molecular and atomic oxygen epoxidation mechanisms. For
the atomic oxygen mechanism, epoxidation was found to proceed without an activation energy, whereas a small amount of activation
energy (about 5 kcal/mol) was calculated for the molecular oxygen mechanism.
Received: 2 July 1998 / Accepted: 9 September 1998 / Published online: 8 February 1999 相似文献
6.
Jing-yao Liu Ze-sheng Li Zhen-wen Dai Xu-ri Huang Chia-chung Sun 《Theoretical chemistry accounts》2002,108(3):179-186
The hydrogen-abstraction reaction C2H5F+O → C2H4F+OH has been studied by a dual-level direct dynamics method. For the reaction, three reaction channels, one for α-abstraction
and two for β-abstraction, have been identified. The potential-energy surface information is obtained at the MP2(full)/6-311G(d,p)
and PMP2(full)/6-311G(3df,3pd) (single-point) levels. By canonical variational transition-state theory, rate constants for
each reaction channel are calculated with a small-curvature tunneling correction. The total rate constant is calculated from
the sum of the individual rate constants and the temperature dependence of the branching ratios is obtained over a wide range
of temperatures from 300 to 5,000 K. The agreement of the rate constants with experiment is good in the experimental temperature
range from 1,000 to 1,250 K. The calculated results indicate that at low temperatures α-abstraction is most likely to be the
major reaction channel, while β-abstraction channels will significantly contribute to the whole reaction rate as the temperature
increases.
Received: 23 January 2002 / Accepted: 23 June 2002 / Published online: 20 September 2002 相似文献
7.
Roman G. Efremov Gérard Vergoten Alexander S. Arseniev 《Theoretical chemistry accounts》1999,101(1-3):73-76
We present a “hydrophobic template” method enabling recognition of α-helix bundles in membrane channels from sequence analysis.
Inspection of hydrophobic properties of pore-forming helices in proteins with known structure (A-B5 toxins) permits delineation of a common polarity motif: two hydrophobic surface stretches separated by polar areas. The bundles
are stabilized by nonpolar interhelical contacts. A number of transmembrane segments were checked for presence of this motif,
and it was detected for pore-forming helices of several ion transporters (segments M2 of acetylcholine and GABAA receptors, α5 peptide of δ-endotoxin), which reveal five α-helix bundle architecture. Applications of the method to modeling
of membrane channels are discussed.
Received: 24 April 1998 / Accepted: 3 September 1998 / Published online: 7 December 1998 相似文献
8.
Silvia Castrignanò Sheila J. Sadeghi Gianfranco Gilardi 《Analytical and bioanalytical chemistry》2010,398(3):1403-1409
Human flavin-containing monooxygenases are the second most important class of drug-metabolizing enzymes after cytochromes
P450. Here we report a simple but functional and stable enzyme-electrode system based on a glassy carbon (GC) electrode with
human flavin-containing monooxygenase isoform 3 (hFMO3) entrapped in a gel cross-linked with bovine serum albumin (BSA) by
glutaraldehyde. The enzymatic electrochemical responsiveness is characterised by using well-known substrates: trimethylamine
(TMA), ammonia (NH3), triethylamine (TEA), and benzydamine (BZD). The apparent Michaelis–Menten constant (K′M) and apparent maximum current (I′max) are calculated by fitting the current signal to the Michaelis–Menten equation for each substrate. The enzyme-electrode has
good characteristics: the calculated sensitivity was 40.9 ± 0.5 mA mol−1 L cm−2 for TMA, 43.3 ± 0.1 mA mol−1 L cm−2 for NH3, 45.2 ± 2.2 mA mol−1 L cm−2 for TEA, and 39.3 ± 0.6 mA mol−1 L cm−2 for BZD. The stability was constant for 3 days and the inter-electrode reproducibility was 12.5%. This is a novel electrochemical
tool that can be used to investigate new potential drugs against the catalytic activity of hFMO3. 相似文献
9.
Wenfang Zhang P. Schmidt-Zhang G. Kossmehl W. Plieth 《Journal of Solid State Electrochemistry》1999,3(3):135-140
Photocurrent and differential capacity measurements have been carried out at polybithienyl (PBT) and poly(3-butylthiophene)
(PBuT) films on platinum. The photocurrents are cathodic, similar to inorganic p-type semiconductors. The band gap energy
was determined from the photocurrent spectra (E
g=1.7 eV for PBT and E
g=1.9 eV for PBuT). The dependence of the differential capacity on the potential could be presented as Mott-Schottky plot,
at least in a limited potential region. The flatband potential was determined (E
fb= 0.67 V for PBT and E
fb=0.58 V for PBuT).
Received: 9 June 1998 / Accepted: 22 August 1998 相似文献
10.
Mirjana Mladenović Peter Botschwina Peter Sebald Stuart Carter 《Theoretical chemistry accounts》1998,100(1-4):134-146
The results of various ab initio calculations are reported for the electronic ground state of the acetylide anion. An “Eyring's
lake” in the T-shaped configuration is identified with six different methods (SCF, MP2, CCSD, CCSD-T, CCSD(T), and CEPA–1).
The equilibrium bond lengths of HCC− are estimated to be r
e
(CH)=1.0689(3) ? and R
e
(CC)=1.2464(2) ?, and the ground-state rotational constant is predicted to be B
0=41636(20)MHz. The large permanent dipole moment of μ0=−3.093D should facilitate detection of the anion by microwave spectroscopy. The band centers are predicted to be 3211.3cm−1(ν1), 511.1cm−1(ν2), and 1805.0cm−1(ν3). A large transition dipole moment of 0.477 D is calculated for the ν2 band. Rovibrational levels of HCC− up to approximately 20 000 cm−1 above equilibrium are calculated with DVR-DGB and FBR methods on the basis of a previous CEPA–1 potential energy surface.
Different energy patterns are found and discussed, for which anharmonic and Coriolis resonances are shown to play an important
role.
Received: 27 July 1998 Accepted: 12 August 1998 / Published online: 19 October 1998 相似文献
11.
A new method for the evaluation of one- and two-centre magnetic and electric multipole integrals for Slater-type functions
is presented. The method is strictly analytical in that no approximations of any kind are involved. Two simple functions,
ℐ1
aug and ℐ2
aug, are introduced, which employ only functions that are well known in electronic structure theory. With the use of augmentation
exponents these functions apply to multipole integrals as well as other one-electron integrals, such as nuclear attraction
integrals. The proposed method includes the analytic determination of derivatives of the integrals with respect to atomic
displacements. Some illustrative test calculations are presented and compared to results from the literature.
Received: 20 April 1998 / Accepted: 13 October 1998 / Published online: 1 February 1999 相似文献
12.
William T. G. Johnson David A. Hrovat Anne Skancke Weston Thatcher Borden 《Theoretical chemistry accounts》1999,102(1-6):207-225
Ab initio calculations on the lowest singlet and triplet states of 2,2-disilylcyclopentane-1,3-diyl find that the singlet
lies well below the triplet. The C
2 singlet diradical is calculated to be a minimum on the potential energy surface with an enthalpic barrier to ring closure
of ΔH
‡
298 = 13.5 kcal/mol at the CASPT2/6-31G* level of theory. The energy of the 1,3-divinyl-substituted singlet diradical is calculated
to be only 0.8 kcal/mol higher than that of 5,5-disilyl-1,3-divinylbicyclo[2.1.0]pentane at this level of theory, but the
transition state for their equilibration is computed to be 12.8 kcal/mol above the diradical in energy.
Received: 2 July 1998 / Accepted: 4 August 1998 / Published online: 16 November 1998 相似文献
13.
High-level ab initio electronic structure theories have been applied to investigate the detailed reaction mechanism of the
spin-forbidden reaction CH(2∏) + N2 → HCN + N(4S). The G2M(RCC) calculations provide accurate energies for the intermediates and transition states involved in the reaction,
whereas the B3LYP/6-311G(d,p) method overestimates the stability of some intermediates by as much as about 10 kcal/mol. A few new structures have been
found for both the doublet and quartet electronic states, which are mainly involved in the dative pathways. However, due to
the higher energies of these structures, the dominant mechanism remains the one involving the C
2 intersystem-crossing step. The C
2 minima on the seam of crossing (MSX) structures and the spin-orbit coupling between the doublet and quartet electronic states
are rather close to those found in previous studies. Vibrational frequencies orthogonal to the normal of the seam which have
been applied in a separate publication to calculate the rate of the CH(2∏) + N2 → HCN + N(4S) reaction with a newly proposed nonadiabatic transition-state theory for spin-forbidden reactions have been calculated at
the MSX from first principles.
Received: 23 June 1998 / Accepted: 21 September 1998 / Published online: 8 February 1999 相似文献
14.
Alain Cartier David Brown Bernard Maigret Sandrine Boschi-Muller Sophie Rahuel-Clermont Guy Branlant 《Theoretical chemistry accounts》1999,101(1-3):241-245
In the framework of a theoretical approach to the relationship between structure and reactivity of the catalytic centers
of enzymes, glyceraldehyde-3 phosphate dehydrogenase (GAPDH) has been chosen as a model enzyme. In GAPDH, the proximity of
His176 increases the reactivity of Cys149 at neutral pH; however, its presence alone is not sufficient to explain the reactivity of the catalytic Cys. In order to
determine which other interactions play an important role, a study of the geometric and electronic structure of the catalytic
site has been made using a hybrid quantum mechanics/molecular mechanics local self-consistent field method. This allows the
computation of the electronic properties of amino acid residues in subsystems influenced by other parts of the macromolecule.
The quantum subsystem was centered on the Cys149 residue of GAPDH. The structures of GAPDH taken from the crystallographic database did not include hydrogen atoms and these
had to be added taking into account the fact that, in the active site, His176 has three tautomeric forms: δ-His protonated, ε-His protonated and His+. The results presented here suggest that the most stable His…Cys system in GAPDH is a strongly hydrogen-bonded Cys149
−/His176
+ ion pair.
Received: 24 March 1998 / Accepted: 3 September 1998 / Published online: 23 November 1998 相似文献
15.
M. Micov L. Turi Nagy D. Tunega M. Liška P. Perichta 《Theoretical chemistry accounts》1998,99(6):378-383
A method of solvation energy computation is proposed for ions and molecules in the environment of an ionic melt, based on
the approximation of the ionic melt as an ideal conductor. The method is used to compute equilibrium constants of some equilibria
in cryolite melt. Theoretically obtained results predict that aluminium is bound in tetrafluorocomplexes AlF4
−.
Received: 16 March 1998 / Accepted: 19 June 1998 / Published online: 7 October 1998 相似文献
16.
Bing-Joe Hwang Yu-Chuan Liu Wen-Cheng Hsu 《Journal of Solid State Electrochemistry》1998,2(6):378-385
The influences of the reductant concentration of NaBH4 and the quantity of Pt loading on the active surface area and the sensitivity of the Pt/Nafion electrodes prepared by an
impregnation-reduction method in detecting oxygen were investigated in this study. The Pt/Nafion electrodes with a Pt loading
of 4.99 mg/cm2, obtained at 0.0107 M Pt(NH3)4Cl2 and 0.06 M NaBH4, show maximum sensitivities of 0.0528 A/ppm and 0.0538 A/ppm obtained in O2 concentration regions of 0–5000 and 5000–50 000 ppm, respectively. A sensing model was also proposed to illustrate the sensing
phenomenon.
Received: 21 January 1998 / Accepted: 10 March 1998 相似文献
17.
Vladislav V. Kharton Aleksey A. Yaremchenko Evgeny N. Naumovich 《Journal of Solid State Electrochemistry》1999,3(6):303-326
The review is devoted to the analysis of experimental results on electrochemical and physicochemical properties of the perovskite-related
oxide phases obtained at scientific centers of the former Soviet Union. The main attention is focused on oxides with high
electronic conductivity, which are potentially useful as electrodes for high-temperature electrochemical cells with oxygen-ion
conducting solid electrolytes and interconnectors of solid oxide fuel cells, and on mixed ionic-electronic conductors for
oxygen separation membranes. Along with perovskite-like solid solutions based on LnMO3−δ (Ln is a rare-earth element, M = Cr, Mn, Fe, Co, Ni) and SrCoO3−δ, properties of the oxide phases Ln2MO4±δ (M = Cu, Ni, Co) with the K2NiF4-type structure are briefly reviewed.
Received: 5 November 1998 / Accepted: 26 November 1998 相似文献
18.
Cheol Ho Choi Miklos Kertesz Sergey Dobrin Josef Michl 《Theoretical chemistry accounts》1999,102(1-6):196-206
s-trans, s-cis and gauche conformers of 1,3-butadiene have been studied using density functional theory and the coupled-cluster
method using double substitutions (CCD). Matrix isolation Raman and IR data for the minor conformer were obtained and are
used in combination with the theoretical results to resolve earlier ambiguities in vibrational assignments. Based on high-quality
Hessians, new harmonic stretching force constants are reported for the carbon backbone of s-trans-1,3-butadiene. For the minor conformer the best unscaled root mean square error of the calculated frequencies for the s-cis
and gauche geometries are 17.5 cm−1 and 7.4 cm−1, respectively, primarily due to a better agreement of the gauche results for the vibrations at 983 cm−1, 596 cm−1 and 470 cm−1 which depend strongly on the torsional angle. Although this points towards the gauche form rather than the s-cis form, the
calculated transition dipole moment directions at the CCD/6-311G(d,p) level confirm the earlier conclusion that the minor
conformer has C
2
v
symmetry in the matrix. It is concluded that either the better agreement between the frequencies calculated for the gauche
form and the observed values is coincidental, or that the molecule is indeed nonplanar in the matrix and tunnels very rapidly
between the two mirror-image forms (or its lowest vibrational level lies above the barrier).
Received: 1 July 1998 / Accepted: 26 October 1998 / Published online: 15 February 1999 相似文献
19.
The effects of the amino acid side chains of the binding pocket of bacteriorhodopsin (bR) and of a water molecule on the
structure of the retinal Schiff base have been studied using Becke3LYP/6-31G* level of density functional theory. A model
protonated Schiff base structure including six conjugated double bonds and methyl substituents was optimized in the presence
of several amino acid side chains and of a water molecule, separately. The Schiff base structure was also calculated in the
form of a neutral species. At each optimized complex geometry the atomic charges of the model Schiff base were calculated
using Mulliken population analysis. In agreement with previously proposed counterion(s) of the protonated retinal Schiff base
in bR, the results show that Asp85 and Asp212, which are present in the form of negatively charged groups, have significantly large effects on the structure and electronic
configuration of both unprotonated and protonated model Schiff bases. The presence of a water molecule in the vicinity of
the Schiff base demonstrates significant effects which are comparable to those of aspartate groups. Other side chains studied
did not show any significant effect in this direction. Apart from the aspartate groups and the water molecule, in none of
the other complexes studied are the atomic charges and the bond alternation of the model Schiff base significantly influenced
by the presence of the neighboring amino acids.
Received: 24 March 1998 / Accepted: 3 September 1998 / Published online: 10 December 1998 相似文献
20.
Gerald Löffler 《Theoretical chemistry accounts》1999,101(1-3):163-169
We performed a very long molecular dynamics simulation of a peptide in explicit water molecules and ions and averaged the
electrostatic potential caused by peptide, water and ions at eight points in the vicinity of the peptide. These electrostatic
potential values were directly compared to the potential calculated by solving the non-linear Poisson-Boltzmann equation for
the system, which describes the solvent using continuum electrostatics. We analyze the contribution of dielectric constant,
conformational flexibility and solvation effects on the electrostatic potential at these eight points.
Received: 24 April 1998 / Accepted: 4 August 1998 / Published online: 23 November 1998 相似文献