H2FCS单分子分解反应的直接动力学研究

采用量子化学QCISD(T)/6-311++G(d,p)//B3LYP/6-311+G(d,p)方法研究了H2FCS单分子分解反应的微观动力学性质, 构建了反应势能剖面. 利用经典过渡态理论(TST)与变分过渡态理论(CVT)并结合小曲率隧道效应模型(SCT), 分别计算了在200～3000 K温度范围内的速率常数kTST、kCVT和kCVT/SCT. 计算结果表明, H2FCS可经过不同的反应通道生成10种小分子产物, 脱H反应和HF消去反应为标题反应的主反应通道, 其中HF消去反应产物HCS可由两条反应通道生成. 在200~3000 K温度区间内得到三条反应通道的表观反应速率常数三参数表达式分别为 , 和 . 速率常数计算结果显示, 量子力学隧道效应在低温区间对反应速率常数的影响显著, 而变分效应在计算温度范围内可以忽略.     

Fluorescence properties of trans-ethyl-p-(dimethylamino) cinnamate in presence of bile acid host

The knowledge of the formation of bile acid micellar aggregates is of great importance because of the biological significance of these compounds and their pharmacological applications. The intramolecular charge transfer (ICT) fluorescence property of trans-ethyl-p-(dimethylamino) cinnamate is used to study the micelles formed by aggregation of three most important bile acids, viz. cholic acid, deoxycholic acid and chenodeoxycholic acid by steady state and picosecond time-resolved fluorescence spectroscopy. The ICT fluorescence band intensity was found to increase with concomitant blue shift with the addition of bile acids. The blue shift in ICT fluorescence maxima as well as decrease in nonradiative decay constants in presence of bile acids indicate the passage of the probe towards the micro domains formed from the aggregated bile acids. Binding constant of the probe with micelles as well as critical micelle concentration and average polarity parameter of the micellar environments were obtained from the variation of fluorescence intensity on increasing concentration of bile acids in the medium.     

Chemical Bonding and Electronic Structure of 4d-Metal Monosulfides

Bond distances, vibrational frequencies, dissociation energies, electron affinities, ionization potentials and dipole moments of the title molecules in neutral and charged ions were studied by use of density functional method. Ground states for each molecule were assigned. The calculated bond distance decreases with the increasing of atomic number of 4d metals, reaches minimum at RhS, then increases. For cationic molecules, the calculated bond distance decreases to the minimum at MoS⁺, then increases. The calculated vibrational frequency decreases from YS(YS⁺) to PdS(PdS⁺) for both neutral and cationic molecules. The bond ionic character decreases from YS(YS⁺) to PdS(PdS⁺) for neutral and cationic molecules. The bonding patterns are discussed and compared with the available studies. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Influence of basic residues on dissociation kinetics and dynamics of singly protonated peptides: time‐resolved photodissociation study

Product ion yields in postsource decay and time‐resolved photodissociation at 193 and 266 nm were measured for some peptide ions with lysine ([KF₆ + H]⁺, [F₆K + H]⁺, and [F₃KF₃ + H]⁺) formed by matrix‐assisted laser desorption ionization. The critical energy (E₀) and entropy (ΔS^?) were determined by RRKM fitting of the data. The results were similar to those found previously for peptide ions with histidine. To summarize, the presence of a basic residue, histidine or lysine, inside a peptide ion retarded its dissociation by lowering ΔS^?. On the basis of highly negative ΔS^?, presence of intramolecular interaction involving a basic group in the transition structure was proposed. Copyright © 2009 John Wiley & Sons, Ltd.     

Role of hydrogen bonding on the spectroscopic properties of thiazolidinedione derivatives in homogeneous solvents

In this work, three newly synthesized derivatives of thiazolidinediones, with potential for application as drugs in pharmaceutical industry and free radical scavenging activity, have been taken up to investigate their behaviour in different homogeneous solvents. The purpose of this work is to study the solvation characteristics in ground and excited states of the derivatives by monitoring the absorbance and fluorescence band maxima. The steady state and time resolved fluorescence studies in protic and aprotic solvents have been rationalized on the basis of solute–solvent interaction and substituent effect on these photophysical processes have been analyzed. Substituents at different positions of the aryl moiety affect the hydrogen bond formation ability of the probes.     

P NMR study of the stoichiometry, stability and thermodynamics of complex formation between palladium(II) acetate and bis(diphenylphosphino)ferrocene

The complexation reaction between palladium (II) acetate, and 1,1′-bis(diphenylphosphino)ferrocene, DPPF, was investigated in two different deuterated solvents CDCl₃ and DMSO at various temperatures using ³¹P NMR spectroscopy. The exchange between free and complexed DPPF is slow on the NMR time scale and consequently, two ³¹P NMR signals were observed. At metal ion-to-ligand mole ratio larger than 1, only one ³¹P NMR signal was observed, indicating the formation of a 1:1 Pd²⁺–DPPF complex in solution. The formation constant of the resulting 1:1 complexes was determined from the integration of two ³¹P signals. The values of the thermodynamic parameters (ΔH, ΔS and ΔG₂₉₈) for complexation were determined from the temperature dependence of stability constants. It was found that, in both solvents, the resulting complex is mainly entirely enthalpy stabilized and the ΔH compensates the TΔS contribution.     

Determination of the formation constant for the inclusion complex between Lanthanide ions and Dansyl chloride derivative by fluorescence spectroscopy: Theoretical and experimental investigation

In this paper, a sensitive, easy, efficient, and suitable method for the calculation of K_f values of complexation between one derivative of Dansyl chloride [5-(dimethylamino) naphthalene-1-sulfonyl 4-phenylsemicarbazide] (DMNP) and Lanthanide(III) (Ln) ions is proposed, using both spectrofluorometric and spectrophotometric methods. Determination of K_f showed that DMNP was mostly selective towards the erbium (III) ion. The validity of the method was also confirmed calculating the Stern–Volmer fluorescence quenching constants (K_sv) that resulted in the same consequence, obtained by calculating the K_f of complexation values. In addition, the UV–vis spectroscopy was applied for the determination of K_f only for the Ln ions that had interactions with DMNP. Finally, the DFT studies were done on Er³⁺ and the DMNP complex for distinguishing the active sites and estimating the pair wise interaction energy. It can be concluded that this derivative of Dansyl chloride with inherent high fluorescence intensity is a suitable reagent for the selective determination of the Er³⁺ ion which can be used in constructing selective Er³⁺ sensors.     

Study of multiple binding constants of dexamethasone with human serum albumin by capillary electrophoresis–frontal analysis and multivariate regression

Studies into the interactions between drugs and human serum albumin (HSA) are extremely important for drug discovery, since HSA behaves as a carrier for external drugs and internal biological molecules. In this paper, to evaluate the pharmacokinetic and pharmacodynamic properties of dexamethasone (DXM), the interaction between DXM and HSA was studied by capillary electrophoresis–frontal analysis (CE-FA). According to the Klotz equation, four binding sites between DXM and HSA were obtained, and the average binding constant was 1.05 × 10³ M⁻¹. Furthermore, according to multiple equilibrium theory, based on the assumption that there are two types of binding site, the binding constant at one site was calculated to be 3.539 × 10³ M⁻¹, and the average of the other three was 1.234 × 10³ M⁻¹. In addition, to obtain the detailed binding information at each binding site, new equations were deduced by multivariate regression. The four binding constants of DXM and HSA were calculated to be 5.558 × 10¹ M⁻¹, 2.158 × 10⁴ M⁻¹, 7.312 × 10³ M⁻¹ and 2.043 × 10³ M⁻¹, respectively, which is helpful for detailed studies into the interactions between drugs and proteins with multiple binding sites. Figure Electropherograms of DXM sodium phosphate and HAS mixtures for different protein to drug concentration ratios, obtained by CE-FA     

Spectrophotometric study of interaction and solubilization of procaine hydrochloride in micellar systems

The interaction of Procaine hydrochloride (PC) with cationic, anionic and non-ionic surfactants; cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS) and triton X-100, were investigated. The effect of ionic and non-ionic micelles on solubilization of Procaine in aqueous micellar solution of SDS, CTAB and triton X-100 were studied at pH 6.8 and 29°C using absorption spectrophotometry. By using pseudo-phase model, the partition coefficient between the bulk water and micelles, K_x, was calculated. The results showed that the micelles of CTAB enhanced the solubility of Procaine higher than SDS micelles (K_x = 96 and 166 for SDS and CTAB micelles, respectively) but triton X-100 did not enhanced the solubility of drug because of weak interaction with Procaine. From the resulting binding constant for Procaine-ionic surfactants interactions (K_b = 175 and 128 for SDS and CTAB surfactants, respectively), it was concluded that both electrostatic and hydrophobic interactions affect the interaction of surfactants with cationic procaine. Electrostatic interactions have a great role in the binding and consequently distribution of Procaine in micelle/water phases. These interactions for anionic surfactant (SDS) are higher than for cationic surfactant (CTAB). Gibbs free energy of binding and distribution of procaine between the bulk water and studied surfactant micelles were calculated.