Potential energy curves for the X~1Σ_g~ , B~1△_g and B′~1Σ_g~ states of C_2 using MRCI and approximate CI methods

The potential energy curves for the X1Σ g , B1△g and B′1Σ g states of C2 have been studied by using MRC and approximate CI methods, and are benchmarked against the calculations of full configuration in teraction (FCI). The results obtained by MRCI method agree with the FCI very well, and even are accu rate enough to compare other approximate methods as benchmark, when the calculations of FCI ar not feasible. The approximate CI methods mentioned in this paper are reliable for treating chemica problems.     

Theoretical study on the reaction of NbS~+(~3∑~-,~1Γ) with CO

Two possible reactions ofNbS+ (<3∑-,1ΓF) with CO in the gas phase have been studied by using B3LYP and CCSD(T) methods:the O/S exchange reaction (NbS+?" CO→NbO+?"CS) and the S-transfer reaction (NbS+?"CO→Nb+?"COS). The two reactions have a one-step mechanism. The barriers of the O/S exchange reaction on the triplet and singlet surfaces are 51.2 and 52.4 kcal/mol,respectively, and the barriers of the S-transfer reaction are 58.3 and 78.0 kcal/mol, respectively. The results indicate that the S-transfer and the O/S exchange reaction of the 3∑- ground state of NbS+ are competing, but, for the S-transfer reaction, the 1Γ exited state is more reactive. The differences between the reactions of NbS+ (3∑-, 1F) and VS+ (3∑-, 1Γ) are discussed.     

Ab initio investigation on the structures and spectra of the firefly luciferin

The ground state (S0) geometry of the firefly luciferin (LH2) was optimized by both DFT B3LYP and CASSCF methods. The vertical excitation energies (Tv) of three low-lying states (S1, S2, and S3) were calculated by TD-DFT B3LYP//CASSCF method. The S1 geometry was optimized by CASSCF method. Its Tv and the transition energy (Te) were calculated by MS-CASPT2//CASSCF method. Both the TD-DFT and MS-CASPT2 calculated S1 state Tv values agree with the experimental one. The IPEA shift greatly affects the MS-CASPT2 calculated Tv values. Some important excited states of LH2 and oxyluciferin (oxyLH2) are charge-transfer states and have more than one dominant configuration, so for deeply researching the firefly bioluminescence, the multireference calculations are desired.     

Cosine Moments and Their Application to ∑ Relationships

Recent advances In the theory of ∑ relationships lead to the Investigation of moments needed to derive the relavant joint probability densities. These together with the linear theory of relationships, make possible the calcualtion of therelationships from ∑1 to ∑2 one by one. The superior performance ofour new ∑4 and ∑r relationships, for example, with respect to the older ∑1 and ∑3 formulas strongly suggests a deeper study of the pertinent moments. In this paper a new concept, the cosine moment, is introduced which, together with a certain integral theorem, permits the derivation of the relevant joint probability densities. These lead in turn to the derivation of all ∑ relationships valid for all the space groups.     

Theoretical study on the reaction of VS~ (~3∑~-,~1Γ)with CO

Two possible reaction mechanisms of VS~ (~3∑~-,~1Γ)with CO in the gas phase have been studied by using B3LYP/TZVP and CCSD(T)/6-311 G(3dr,3pd)methods:the O/S exchange reaction(VS~ CO→VO~ CS)and the S-transfer reaction (VS~ CO→V~ COS).The two reactions proceed via two-step and one-step mechanism,respectively.The barriers of the triplet and singlet PESs are 30.6 and 50.9 kcal/mol,respectively,for O/S exchange reaction and 7.3 and 50.2 kcal/mol,respectively, for the S-transfer reaction.The results indicate that the triplet ground state reaction is more favorable,and the S-transfer reaction is more favorable than the O/S exchange reaction,which is in good agreement with the experimental observation.     

Theoretical study on S_1(~1B_(3u)) state electronic structure and absorption spectrum of pyrazine

Making use of a set of quantum chemistry methods, the harmonic potential surfaces of the ground state (S0(1Ag)) and the first (S1(1B3u)) excited state of pyrazine are investigated, and the electronic structures of the two states are characterized. In the present study, the conventional quantum mechanical method, taking account of the Born-Oppenheimer adiabatic approximation, is adopted to simulate the absorp-tion spectrum of S1(1B3u) state of pyrazine. The assignment of main vibronic transitions is made for S1(1B3u) state. It is found that the spectral profile is mainly described by the Franck-Condon progression of totally symmetric mode ν6a. For the five totally symmetric modes, the present calculations show that the frequency differences between the ground and the S1(1B3u) state are small. Therefore the displaced harmonic oscillator approximation along with Franck-Condon transition is used to simulate S1(1B3u) absorption spectra. The distortion effect due to the so-called quadratic coupling is demonstrated to be unimportant for the absorption spectrum, except the coupling mode ν10a. The calculated S1(1B3u) ab-sorption spectrum is in reasonable agreement with the experimental spectra.     

Synthesis,Crystal Structure,Characterizationand Quantum Chemical Studies on 1N-Acetyl-3-（2,4-dichloro-5-fluorophenyl）-5-（p-methyl-phenyl）-2-pyrazoline

1N-Acetyl-3-（2,4-dichloro-5-fluoro-phenyl）-5-（p-methyl-phenyl）-2-pyrazoline has been synthesized and characterized by elemental analysis, IR, UV-Vis and X-ray single-crystal diffraction. Ab intio calculations have been carded out for the compound by using both B3LYP and HF methods at the 6-31G^＊ basis set. The calculated results show that the predicted geometry can well reproduce the structural parameters. The electronic absorption spectra calculated by B3LYP/6-31G^＊ method are approximate to the experiments and the Natural Bond Orbital （NBO） analyses suggest that the above electronic transitions are mainly assigned to n→π^＊ and π→π^＊ transitions. CIS-HF/6-31G^＊ method is not suitable to predict the electronic spectra for the title compound. The calculation of the second order optical nonlinearity was carded out, giving the value of molecular hyperpolarizability equal to 2.194^＋ 10^-30 esu. On the basis of vibrational analyses, the thermodynamic properties of the compound at different temperature have been calculated, revealing the correlation between C p, m^0, S m^0, H m^0 and temperature.     

Theoretical Study on the Inclusion Complex of β-Cyclodextrin and Nitrobenzene

Quantum chemical calculations were carried out to investigate the structures and properties for the inclusion complexes of nitrobenzene (NB) into β-cyclodextrin. Two low-energy conformations of β-cyclodextrin (A and B) in the gas phase were initially investigated by the PM3 and B3LYP/6-31+G(d,p) calculations, respectively. Three different orientations were considered in the inclusion process of A and B with NB to form 1:1 complexes. Potential energy scan by PM3 calculations indicated that the phenyl orientation Ab for conformation A and the equator orientation Bc for conformation B are more favorable in energy, respectively. We also considered the 2:1 inclusion complexes of host A or B with guest NB in the gas phase. PM3 calculation indicated that the host-guest interaction energies to form 1:1 complexes are more negative than those to form 2:1 NB/B complexes. Finally, we studied the solvent effect of NB/CD complex, and PM3 results show that the influence of water molecules on the inclusion process is very important. The driving forces for the inclusion process and the geometries of complexes were discussed in detail.     

Synthesis, Characterization, Spectroscopy and Study of Antimicrobial Properties of Two New Substituted Trichloroaluminate（Ⅲ） Complexes [AlCl3X]- （X = SCN-, CN-）

The synthesis and characterization of two new aluminate(Ⅲ) complexes with general formula K[AlCl3X] are reported. These compounds derived from aluminate trichloride and related salts. Potassium trichlorothiocyanoaluminate, PCTA, and potassium trichlorocyanatoalu-minate, PCCA, are two new ionic aluminate complexes. They can be easily synthesized in a nearly quantitative yield by using the direct reaction of AlCl3 and KX. The complexes were characterized by physico-chemical and spectroscopic methods. Theoretical calculations have been used for the extraction of structural and spectroscopic data of these new synthesized complexes. The antibacterial activities of such compounds were studied against the Staphylococcus aureus, Escherichia coli, Staphylococcus Epidermidis, Estreptococo B and Shigella.     

Ab initio VB Studies of the Ground and Low-lying Excited States of BeH and BH

A scheme has been proposed to classify valence bond(VB) wave functions for the calculations of ground and excited states,according to the symmetry properties of one-electron orbitals which are involved in the construction of VB wave functions.This scheme is illustrated by the examples of BeH and BH.Ab initio VB computations of these two test molecules in combination with the present classification scheme give reliable results.For example,calculation results show that the state C2∑ of BeH is stable,with the bonding energy 0.87 eV and bond length 0.238nm,which are in good agreement with those obtained by Gerratt et al.The bonding features of ground and low-lying excited states of BeH and BH are discussed.     

Theoretical study on the reaction of VS^＋（^3∑^-, 1^Г） with CO

Two possible reaction mechanisms of VS^＋（^3∑^-, 1^Г） with CO in the gas phase have been studied by using B3LYP/TZVP and CCSD（T）/6-311＋G （3df, 3pd） methods： the O/S exchange reaction （VS^＋＋CO→VO^＋＋CS） and the S-transfer reaction （VS^＋ ＋ CO → V^＋ ＋ COS）. The two reactions proceed via two-step and one-step mechanism, respectively. The barriers of the triplet and singlet PESs are 30.6 and 50.9 kcal/mol, respectively, for O/S exchange reaction and 7.3 and 50.2 kcal/mol, respectively, for the S-transfer reaction. The results indicate that the triplet ground state reaction is more favorable, and the S-transfer reaction is more favorable than the O/S exchange reaction, which is in good agreement with the experimental observation.     

Theoretical Study of the Low-Lying Excited States of Butoxy Radicals and Non-Radiative Decay Routes

The potential energy surfaces for the butoxy radical dissociation into R·＋O on the six low-lying electronic states have been determined with the combined CASSCF and MR-CI methods. The isomerization reactions between the different conformers of 1- and 2-butoxy radicals at the X and B states have been also investigated with the MP2, B3LYP, and CASSCF methods. The non-radiative decay mechanisms of butoxy radicals at the B state have been characterized with the computed potential energy surfaces and intersections. Supported by recent LIF experimental results, it was predicted that the t-butoxy radical would predissociate via the B/C intersection. As to 1- and 2-butoxy radicals, the relative energies of the transition states for the isomerization reactions between conformers at the B state are much lower than those of the B/C intersections, resulting in the predominance of the isomerization in the decay of the B state for 1- and 2-butoxy radicals.     

Rapid titrimetric and spectrophotometric assay methods for the determination of lamivudine in pharmaceuticals using iodate and two dyes

One titrimetric and two spectrophotometric methods, which are simple, sensitive and rapid, are described for the assay of lamivudine in bulk drug and in tablet dosage forms using potassium iodate and two dyes, methyl orange and indigocarmine, as reagents. In titrimetry, an aqueous solution of lamivudine is titrated directly with iodate in an acidic medium, and in the presence of an excess of bromide using methyl orange as an indicator. After the decoloration of the red color of methyl orange, the residual bromine is titrated iodometrically to a starch endpoint. Spectrophotometric methods involve the addition of a known excess of iodate in an acidic medium and in the presence of an excess of bromide followed by the determination of residual bromine by the reaction with a fixed amount of either methyl orange and measuring the absorbance at 520 nm (method A), or indigo carmine and measuring the absorbance at 610 nm (method B). In all methods, the amount of iodate which reacted corresponds to the amount of lamivudine content. The titrimetric method is applicable over the 1.5–8.0 mg range. The systems obey Beer’s law for 0.5–5.0 μg/mL (method A) and 1.25–12.5 μg/mL (method B). The calculated apparent molar absorptivity values are found to be 3.3 × 10⁴ and 9.3 × 10³ L mol⁻¹ cm⁻¹, for method A and method B, respectively, and the corresponding Sandell sensitivity values are 6.94 and 24.62 ng/cm². The limits of detection and quantification are also reported for both spectrophotometric methods. Intra-and interday precision and accuracy for the developed methods have been evaluated. The methods were successfully applied to the assay of lamivudine in tablet form and the results were compared with those of a reference method by applying the Student’s t-test and F-test. No interference was observed from common tablet adjuvants. The accuracy and reliability of the methods were further ascertained by recovery experiments using the standard addition technique. The text was submitted by the authors in English.     

PROBABILITY CORRELATION OF ∑_1 RELATION-SHIPS AND THEIR TABLES OF 230 SPACE GROUPS

In the present paper, using the structure factor algebra method, we discuss the correla-tion and the distinction between thte conventionally used ∑_1 relationships and the probabilityvalue of P_ (h_1) on the basis of the P_ (h_1) of Hauptman's ana Karle's ∑_1 relationship. Theintroduction of conception on equivalent point weight ω of h_1 and degeneracy ω_2 of h_2 makesthe probability P_ (h_1) expressed by ∑_1 relationships become more strict. There are a lot ofinterrelated ∑_1 relationships in all four high symmetry crystal systems. According to theresults of this paper, what we need is noly to retain a few independent ∑_1 relationships. Usingthe principle of linearization, we have completed the tables of the ∑_1 relationships for 156space groups which belong to tetragonal, trigonal, hexagonal and cubic crystal systems.Now, we present the concise and perfect tables of 230 space groups of which 74 wereaccomplished by Hasek.     

Theoretical study on the synthesis reaction mechanism of trichlorogermyl crylic acid

The synthesis reaction of trichlorogermyl crylic acid has been studied systematically by using quantum chemistry methods for the first time.Geometries of reactants,transition states,and products have been optimized,respectively at the B3LYP/6-311G（d,p） level.Vibrational frequencies,IR intensities and relative energies for various stationary points have been determined.The reaction pathways are identified by intrinsic reaction coordinate（IRC）calculations.Theoretical analysis provided conclusive evidence that the process is completed through five pathways of addition reaction of double bond,and the transition states are found to be four- membered ring compounds.Solvent effects are taken into account with the PCM model at the same level.This preliminary study shows that the complex formation is favored by the use of polar solvent.     

IR and Raman Vibrational Assignments for Metal-free Phthalocyanine from Density Functional B3LYP／6-31G（d） Method

Vibrational (IR and Raman) spectra for the metal-free phthalocyanine (H2Pc) have been comparatively investigated through experimental and theoretical methods. The frequencies and intensities were calculated at density functional B3LYP level using the 6-3 IG(d) basis set. The calculated vibrational frequencies were scaled by the factor 0.9613 and compared with the experimental result. In the IR spectrum, the characteristic IR band at 1008.cm^-1 is interpreted as C-N (pyrrole) in-plane bending vibration, in contrast with the traditional assigned N-H in-plane or out-of-plane bending vibration. The band at 874 cm^-1 is attributed to the isoindole deformation and aza vibration. In the Raman spectrum, the bands at 540, 566, 1310, 1340, 1425, 1448 and 1618 cm^-1 are also re-interpreted. Assignments of vibrational bands in the IR and Raman spectra are given based on density functional calculations for the first time. The present work provides valuable information to the traditional empirical assignment and will be helpful for further investigation of the vibration spectra of phthalocyanine analogues and their metal complexes.     

Structure and Properties of Semiconductor Microclusters GanPn（n=1-4）： A First Principle Study

The possible geometrical structures and relative stabilities of semiconductor microclusters Ga.P.(n=1-4) were studied by virtue of density functional calculations with generalized gradient approximation(B3LYP). For the most stable isomers of Ga,,P.(n=1-4) clusters, the electronic structure, vibrational properties. dipole moment, polarizability and ionization potential were analyzed by means of HF. MP2. CISD and B3L YP methods with different basis sets.     

Quantum Topological Studies on the Molecular Complexes-CO_2-NCH and CO_2-OH_2

Topological properties of charge distribution for the title complexes and their constituent are analyzed by using ab initio calculations at 3-21G basis set. The results obtained are compared with those originated from ab initio and energy decomposition method. It has been determined that the title molecular complexes are T-shaped. The characteristics of the bonds and the changes originated from the formation of the complexes are discussed.     

Electronic Structures and Spectra of the Bases and Base Pairs of Nucleic Acids

The present paper covers electronic structures and spectra of the bases and the base pairs of nucleic acids calculated by using the INDO/S method. For free bases we give the energy levels of ground states and transition energies of low-lying excited states and discuss the band characters. The results indicate that the calculated spectra are in good agreement with experimental values. On the other hand, our calculations for A-T and G-C pairs are very beneficial to understanding hydrogen bond properties of these pairs.     

MRCI及其近似方法下C2分子X1∑+g, B1△g和B'1∑+g态的势能曲线

运用MRCI及其近似方法计算得到C2分子X1∑+g,B1△+g,和B'1∑+g 3个电子态的势能曲线,并以FCI方法为基准,考察比较各种方法的优缺点.MRCI计算与FCI计算几乎不存在差别,在FCI计算不现实的情况下,MRCI计算足以作为基准考验其他计算方法.多种近似方法均能达到化学精度,并提出一个有效的选择参考组态的方法,提高MRCI计算效率的同时,保证计算的精确性.