A Study on the Interaction of the DAS-K with Bovine Serum Albumin by On-line Ultrafiltration and Chemiluminescence

Potassium dehydroandrographolide succinate （DAS-K） has antibacterial and antiviral effects. It has been used widely for the treatment of virus pneumonia, malaria and respiratory infections. In this work, a novel flow-injection chemiluminescence （CL） method for the determination of DAS-K was proposed. The method is based on the reaction between DAS-K and hexacyanoferrate（III） in alkaline solution to give weak CL signal, which is enhanced by rhodamine B. The experimental conditions for the CL reaction were optimized and the possible reaction mechanism was discussed. Under the optimum conditions, the concentration of DAS-K is proportional to the CL intensity in the range of 0.1-80 μmol·L^-1 with a detection limit of 0.05 μmol·L^-1. The interaction of the DAS-K with bovine serum albumin by on-line ultrafiltration and flow-injection chemiluminescence was studied. The concentrations of unbound DAS-K from ultra filter tube were determined by the flow-injection CL method. The binding parameters were estimated by the Scatchard plot and Klotz plot. The proposed system proved that FIA-CL coupled with on-line ultrafiltration sampling was a fast and simple technique for the study of drug-protein interaction.     

A Comparison Study on the Interaction of Sunset Yellow and β-Carotene with Bovine Serum Albumin

在模拟生理pH条件（pH=7．4）下,采用多种光谱法研究日落黄和β-胡萝卜素与BSA的相互作用,并比较两者与BSA相互作用过程的差异性．通过荧光光谱法和紫外吸收光谱法确定了日落黄和β-胡萝卜素对牛血清白蛋白的荧光猝灭机制,采用Stern—Volmer、双对数方程和热力学公式求出相互作用的猝灭常数、结合常数配、结合位点数月和作用力类型．结果表明：日落黄和β-胡萝卜素对BSA的猝灭属于静态猝灭,两者与BSA的民都达到10^5L／mol,结合位点数均为1,日落黄与BSA的作用力以静电引力为主,而β-胡萝卜素则是通过氢键和范德华力与BSA作用．通过红外光谱法和圆二色谱法研究了二者对BSA构象的影响,结果表明,日落黄与BSA作用的过程中,会引起BSA二级结构的改变,而β-胡萝卜素则对BSA的构象基本不产生影响．     

Spectroscopic Studies on the Interaction of 2,4-Dichlorophenol with Bovine Serum Albumin

The interaction between 2,4-dichlorophenol (DCP) and bovine serum albumin (BSA) was investigated by fluorescence spectroscopy combined with UV-vis absorption and circular dichroism (CD) spectroscopy under simulative physiological conditions. The experiment results show that the fluorescence intensity of BSA is dramatically decreased owing to the formation of a DCP–BSA complex. The corresponding effective quenching constants (K _a) between DCP and BSA at four different temperatures (292, 298, 304 and 310 K) were determined to be 10.08×10⁴, 9.082×10⁴, 8.177×10⁴, and 7.260×10⁴ L?mol^?1, respectively. The thermodynamics parameters enthalpy change (ΔH) and entropy change (ΔS) were calculated to be ?13.64 kJ?mol^?1 and 49.08 J?mol^?1?K^?1, which suggested that hydrophobic interaction was the predominant intermolecular force. Site marker competitive experiments indicated that the binding of DCP to BSA primarily takes place in subdomain IIA. The binding distance (r) between DCP and the tryptophan residue of BSA ias 4.09 nm according to Förster’s theory of non-radioactive energy transfer. The conformational investigation demonstrated that the presence of DCP decreased the α-helical content of BSA and induced a slight unfolding of the polypeptides of protein, which confirmed the occurrence some micro environmental and conformational changes of BSA molecules.     

Interaction of Surface-active Fluorescence Probes with Bovine Serum Albumin

The binding between three surface-active substituted 3H-indole fluorescence probes and bovine serum albumin (BSA) in aqueous solution was studied using fluorescence quenching. The binding constants of 3H-indole molecules with BSA were obtained. According to the Foerster resonance energy transfer theory, the distances between 3H-indole molecules and tryptophan of BSA were calculated. The results show that the oligoethyloxyethylene chain of 3H-indole molecules is longer, the binding between them is stronger, the energy transfer efficiency is higher, and the distance between tryptophan and 3H-indole is nearer.     

Spectroscopic Study on the Interaction between Bovine Serum Albumin and Tween‐20

The interaction between nonionic surfactant Tween-20 and bovine serum albumin (BSA) is studied in Tris‐HCl buffer solution by spectroscopic methods. The intrinsic fluorescence of BSA is quenched by the addition of Tween‐20. The UV‐visible absorption spectra and the synchronous fluorescence spectra show that the addition of Tween‐20 changes the polarity of the environment around tryptophan (trp) residues of BSA. The fraction of trp residues on the surface of BSA with and without Tween- 20 is calculated via I^? quenching experiments.     

Conjugation of Chitooligosaccharide-5-fluorouracil with Bovine Serum Albumin

The interaction between chitooligosaccharide-5-fluorouracil (COS-5FU) and bovine serum albumin (BSA) was studied by fluorescence spectroscopy. It was found that an energy transfer between COS-5FU and BSA had been occurred. The binding constants were calculated, k298K=1.175×104 L·mol-1.Based on the mechanism of energy transfer of dipole-dipole interaction between the donor and acceptor, the distance between BSA and COS-5FU was determined.     

Density Functional Study on the Reaction Mechanism for the Reaction of Ni^＋ with Ethane

The mechanism of the reaction of Ni^ (^2D) with ethane in the gas-phase was studied by using density functional theory.Both the B3LYP and BLYP functionals with standard all-electron basis sets are used to give the detailed information of the potential energy surface (PES) of [Ni,C2,H6]^ . The mechanisms forming the products CH4 and H2 in the reaction of Ni^ with ethane are proposed.The reductive eliminations of CH4 and H2 are typical addition-elimination reactions.Each of the two reactions consists of two elementary steps:C-C or C-H bond activations to form inserted species followed by isomerizations to from product-like intermediate.The rate determining steps for the elimination reactions of forming CH4 and H2 are the isomerization of the inserted species rather than C-C or C-H bond activations .The elimination reaction of forming H2 was found to be thermodynamically favored compared to that of CH4.     

Study on the Interaction between CdSe Quantum Dots and Bovine Serum Albumin with Ultraviolet Visible Absorption Spectroscopy

QDs (also called semiconductor nanocrystallines) were attracted considerable attention in the past decade1, 2. They have been used as luminescent probes in biology, medicine and more recently in analytical chemistry3-5. The interaction between QDs and ino…     

Interaction of Curculigosides and Their ��-Cyclodextrin Complexes with Bovine Serum Albumin: A Fluorescence Spectroscopic Study

Curculigosides A and B, two of the phyto-constituents of the medicinal plant Curculigo orchioides gatern, were isolated. The binding properties of these curculigosides with ??-cyclodextrin, and their interaction with bovine serum albumin in free and ??-cyclodextrin-complexed forms, were studied using fluorescence spectroscopy. The stoichiometry and binding constants of these complexes together with their binding modes are reported. Both of the curculigoside?Ccyclodextrin complexes are found to bind more weakly to the bovine serum albumin molecule than their free forms. The difference in the binding strengths of curculigoside A and curculigoside B with cyclodextrin makes a difference in their binding with bovine serum albumin.     

Theoretical Study on the Mechanism of Sonogashira Coupling Reaction

The mechanism of palladium-catalyzed Sonogashira cross-coupling reaction has been studied theoretically by DFT （density functional theory） calculations. The model system studied consists of Pd（PH3）2 as the starting catalyst complex, phenyl bromide as the substrate and acetylene as the terminal alkyne, without regarding to the co-catalyst and base. Mechanistically and energetically plausible catalytic cycles for the cross-coupling have been identified. The DFT analysis shows that the catalytic cycle occurs in three stages： oxidative addition of phenyl bromide to the palladium center, alkynylation of palladium（Ⅱ） intermediate, and reductive elimination to phenylacetylene. In the oxidative addition, the neutral and anionic pathways have been investigated, which could both give rise to cis-configured palladium（Ⅱ） diphosphine intermediate. Starting from the palladium（Ⅱ） diphosphine intermediate, the only identifiable pathway in alkynylation involves the dissociation of Br group and the formation of square-planar palladium（Ⅱ） intermediate, in which the phenyl and alkynyl groups are oriented cis to each other. Due to the close proximity of phenyl and alkynyl groups, the reductive elimination of phenylacetylene proceeds smoothly.     

Studies on Thermodynamics Features of the Interaction between Imidacloprid and Bovine Serum Albumin

At different temperatures, the interactions between imidacloprid （IMI） and bovine serum albumin （BSA） were investigated with a fluorescence quenching spectrum, a synchronous fluorescence spectrum, a three-dimensional fluorescence spectrum and an ultraviolet-visible spectrum. The average values of bonding constants （KLB： 3.424 × 10^4 L,mol^-1）, thermodynamic parameters （△H： 5.188 kJ,mol^-1, △G^（○—）：-26.36 kJ,mol^-1, △S： 103.9 J,K^-1,mol^-1） and the numbers of bonding sites （n： 1.156） could be obtained through Stern-Volmer, Lineweaver-Burk and ther- modynamic equations. It was shown that the fluorescence of BSA could be quenched for its reactions with IMI to form a certain kind of new compound. The quenching belonged to a static fluorescence quenching, with a non-radiation energy transfer happening within a single molecule. The thermodynamic parameters agree with △H〉 0, △S〉0 and△G^（○-）〈0, suggesting that the binding power between IMI and BSA should be mainly a hydrophobic interaction.     

Study on the Interaction between Strychnine and Bovine Serum Albumin by Capillary Electrophoretic Frontal Analysis

Most drugs are usually bound to proteins such as serum albumin,α1-acid glycoprotein,lipoprotein,and other blood constituents.The plasma concentration of an unbound drug shows better correlation to the pharmaceutical activity1.It is therefore necessary to know the extent of drug-protein binding in order to adjust the optimal therapeutic dose of the drug.Strychnos nux-vomica L.(Loganiaceae)is an evergreen tree native to southeast Asia.Its dried seeds are used for treatment of nervous diseases…     

In Vitro Study of the Binding of Taxifolin to Bovine Serum Albumin and the Influence of Common Ions on the Binding

The interaction between taxifolin and bovine serum albumin (BSA), and the effects of some common ions on their interaction, were investigated by fluorescence and UV-visible absorption spectroscopy. The results indicate that taxifolin has a strong ability to quench the intrinsic fluorescence of BSA through a static quenching process. According to values of the thermodynamic parameters, the hydrophobic force plays a major role in the interaction. Based on Főster’s non-radiation theory, the energy transfer distances between BSA and taxifolin in the absence and presence of some common ions were obtained. The experimental results indicate that the transfer distances are almost unaffected by these ions. The conformation of BSA undergoes significant change from the formation of a taxifolin–BSA complex, which was studied by synchronous and three-dimensional fluorescence spectroscopy.     

Ab initio Mechanism Study on the Reaction of Chlorine Atom with Formic Acid

The potential energy surface(PES) for the reaction of Cl atom with HCOOH is predicted using ab initio molecular orbital calculation methods at UQCIDS(T,full)6-311 G(3df,2p)//UMP2(full)/6-311 G(d,P) level of theory with zero-point vibrational energy (ZPVE) correction.The calculated results show that the reaction mechanism of Cl atom with formic acid is a C-site hydrogen abstraction reaction from cis-HOC(H)O molecule by Cl atom with a 3.73kJ/mol reaction barrier height,leading to the formation of cis-HOCO radical which will reacts with Cl atom or other molecules in such a reaction system.Because the reaction barrier height of O-site hydrogen abstraction reaction from cis-HOC(H)O molecule by Cl atom which leads to the formation of HCO2 radical is 67.95kJ/mol,it is a secondary reaction channel in experiment,This is in good agreement with the prediction based on the previous experiments.     

Quantum Chemical Study on the Reaction Mechanism of OBrO Radical with OH Radical

The reaction mechanism of OBrO with OH has been studied using the B3LYP/6-311 G(d,p) and the high-level electron-correlation CCSD(T)/6-311 G(d,p) at single-point. The results show that the title reaction could probably proceed by four possible schemes, generating HOBr O2, HBr O3, BrO HO2 and HOBrO2 products, respectively. The main channel is the one to yield HOBr O2. The whole reaction involves the formation of three-membered, four-membered and five-membered rings, followed by the complicated processes of association,H-shift, Br-shift and dissociation. All routes are exothermic.     

Spectroscopic Study on Interaction of Lomefloxacin with Human Serum Albumin in the Presence of Copper Ion

The interaction of lomefloxacin （LMF） with human serum albumin （HSA） in the presence of copper ions in a physiological medium and its thermodynamic characteristics were investigated by multi-spectroscopy. The experimental results showed that both LMF and LMF-Cu^2＋ could quench the fluorescence of HSA with a static quenching mechanism, indicating that LMF or LMF-Cu^2＋ could react with HSA. The apparent binding constants/numbers of binding sites were estimated as 4.924± 105 Lomol 1/1.473 for LMF-HSA, 8.990± 104 L·mol^-1/1.785 for LMF- Cu^2＋-HSA, 1.10± 105 L·mol^-1/1.21 for LMF-Cu^2＋ and 7.30± 102 L·mol^-1/0.82 for HSA-Cu^2＋, respectively. AH and AS for LMF-HSA system were calculated to be --2.189 kJ·mol^-1 and 61.25 J·mol^-1·K^-1, while those for LMF-Cu^2＋-HSA system were -7.401 kJ·mol^-1 and 47.63 J·mol^-1·K^-1 Although the values of AH and AS in these two systems were different, the treads were similar, which indicated that electrostatic interactions in these two systems played a major role. According to Forster theory, the distances were given as 5.006 nm for HSA-LMF and 4.709 nm for HSA-LMF-Cu^2＋. Synchronous fluorescence and circular dichroism spectra confirmed further that the conformations of human serum albumin before and after interacting with LMF or LMF-Cu^2＋ were different. All the results revealed that copper ions promoted the interaction of lomefloxacin with human serum albumin.     

Theoretical Study on the Dark Oxidation Reaction Mechanism of Ethers

1 INTRODUCTION Ethers are a kind of organic compounds that are easily oxidized under the conditions of lacking light and any additional excitement. According to dif- ferent mechanisms, the oxidation reactions could be classified into two types: photooxidation reaction and dark oxidation reaction. The former is the reaction with excited state oxygen molecule (singlet state), while the latter is the reaction with ground state oxygen molecule (triple state) without illuminance or any exciter…     

Theoretical Study on the Reaction Mechanism of SiCl_4 with H in the Gas Phase

1 INTRODUCTION Semiconductor silicon materials are vital for mi- croelectronic and information industry. Silicon has many advantages, for example, rich resource, out- standing quality and sophisticated processing tech- nology. So it has been widely used in semiconduc- tor industry. One of the key techniques of mo- dern microelectronic industry is epitaxial growth of single crystal thin film on single crystal silicon and its ba- cking materials. In the chemical vapour deposition of Si, g…     

Investigation on the Interaction of Dy(Ш)/Rutin Complexes with Bovine Serum Albumin by Spectroscopic Methods

Journal of Solution Chemistry - The interaction between Dy(Ш)/Rutin complexes and bovine serum albumin (BSA) was studied by fluorescence, ultraviolet (UV) absorption, three-dimensional...     

Study on the Mechanism of the Rearrangement Reaction of 3-n-Butylphthalide by Deuterium-Labelling

InthePangetal.report[l],l-methyl-5-cchp'tetrahdronaPhthalenewasobtalnedfromthetreatInentof3-ntwlphthalideusingAlCl3ascatalStinCS2byaproposedl,4-hydridetransfrprocess.InordertoexPlorethemechasticdetallsofthereaction,wepreParedastableisotope-labelledcomPound--I',l'ch-dotero-3-n-butylphthalideasfollowstl,lall-deutero-ldiutanolwasobtalnedbyreduedonreachonofethy1butwatewithNaBD4andAJCl3indiglpoeI2],treatmentoftheproductwithphosphoroustribroITildetogive1,1-dideutero-lbromobutane,whichunderwe…