Binding Constants for Terbium(Ⅲ) with Chicken Apoovotransferrin

The binding of Tb 3+ to chicken apoovotransferrin was studied by monitoring the fluorescent intensity of Tb 3+ at 549 nm. The conditional equilibrium constants for the complexation of Tb 3+ by chicken apoovotransferrin in 0 1 mol/L hepes, at pH 7 4 and room temperature were measured. The successive macroscopic binding constants are lg K 1=9 08±0 12 and lg K 2=7 36±0 22. The molar fluorescence enhancement of Tb 3+ apoovotransferrin complex is (2 06±0 14)×10 4 mol -1 ·L. The fluorescence quenching experiment and the titration of N terminal monoferric ovotransferrin showed that Tb 3+ has a preference for being bound to the N terminal binding site of apoovotransferrin.

Binding of Pyrene to Different Molecular Weight Fractions of Dissolved Organic Matter:Effects of Chemical Composition and Steric Conformation

The binding constant（KDOM） of pyrene onto different molecular weight（Mw） fractions of a dissolved organic matter（DOM） extract from an estuarine sediment was measured via a fluorescence quenching method,and the possible binding mechanisms were discussed.The influence of water chemical parameters on pyrene binding was studied to elucidate the effects of DOM steric conformation.DOM fraction with larger M w（14000） showed a greater KDOM（2.02×10 5） than that with smaller Mw did,and the KDOMs were 1.16×105 and 1.13×105 for the fractions with M w of 1000―14000 and 1000,respectively.The K DOM s of different M w DOM fractions were correlated positively with the atomic ratio of C/H and absorbance at 280 nm;while a negative correlation existed between K DOM and（O＋C）/N（atomic ratio）,and K DOM and O-containing groups.These correlations indicate the positive influence of aromatic structure and the negative effect of polarity on DOM binding capacity.Infrared spectroscopy revealed that specific interactions existed between pyrene and the DOM fraction with larger M W besides hydrophobic partition,i.e.,NH-π interaction in DOM moiety（1000―14000） and π-π electron donor acceptor（EDA） forces in DOM moiety（14000）.KDOM varied in a complex pattern with increasing cation concentration and pH,which could be explained by the change in DOM steric conformation.Formed aggregates favored the lipophilic partition of pyrene.However,the accessibility to some interior binding sites became low when the aggregate was too large,leading to a reduced KDOM.

Effects of urea,metal ions and surfactants on the binding of baicalein with bovine serum albumin

The interaction of baicalein with bovine serum albumin（BSA） was investigated with the help of spectroscopic and molecular docking studies.The binding affinity of baicalein towards BSA was estimated to be in order of 10~5 M^（-1） from fluorescence quenching studies.Negative ΔH°（-5.66 ＋ 0.14 kJ/mol） and positive（ΔS°）（＋ 79.96 ＋ 0.65J/mol K） indicate the presence of electrostatic interactions along with the hydrophobic forces that result in a positive ΔS°.The hydrophobic association of baicalein with BSA diminishes in the presence of sodium dodecyl sulfate（SDS） due to probable hydrophobic association of baicalein with SDS,resulting in a negative ΔS°（-40.65 ＋ 0.87 J/mol K）.Matrix-assisted laser desorption ionization/time of flight（MALDI-TOF） experiments indicate a 1：1 complexation between baicalein and BSA.The unfolding and refolding phenomena of BSA were investigated in the absence and presence of baicalein using steady-state and fluorescence lifetime measurements.It was observed that the presence of urea ruptured the non-covalent interaction between baicalein and BSA.The presence of metal ions（Ag~＋,Mg^（2＋）,Ni^（2＋）,Mn^（2＋）,Co^（2＋） and Zn^（2＋）） increased the binding affinity of ligand towards BSA.The changes in conformational aspects of BSA after ligand binding were also investigated using circular dichroism（CD） and Fourier transform infrared（FT-IR） spectroscopic techniques.Site selectivity studies following molecular docking analyses indicated the binding of baicalein to site 1（subdomain MA） of BSA.

Investigation of the interaction between indigotin and two serum albumins by spectroscopic approaches

The binding characteristics of indigotin with human serum albumin （HSA） and bovine serum albumin （BSA） have been investigated by various spectroscopic techniques. Spectroscopic analysis revealed that the quenching mechanism between indigotin and HSA/BSA belonged to the static quenching. The displacement experiments suggested that indigotin primarily bound to tryptophan residues on proteins within site I. The thermodynamic parameters indicated that the binding of indigoti^HSA/BSA mainly depended on the hydrophobic interaction. The binding distance of indigotin to HSA/BSA was evaluated. The results by synchronous fluorescence, three- dimensional fluorescence, Fourier Transform Infrared spectroscopy （FT-IR） and circular dichroism （CD） spectra showed that the conformation of proteins altered in the presence of indigotin.

Investigation of the interaction of DNA and neutral red by fluorescence spectroscopic analysis

The binding characteristics of neutral red （NR） with DNA were investigated by fluorescence spectrometry. Chemometrics approach as singular value decomposition （SVD） was used to evaluate the number of spectral species in the drug-DNA binding process, and then the intrinsic binding constant of 1.6 × 10^4 in base pairs and the binding site number of 0.97 were obtained from the Scatchard plot.

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

The protein binding constant, binding sites of the Strychnos alkaloid-strychnine and bovine serum albumin （BSA） was determined by capillary electrophoretic frontal analysis （CE-FA） for the first time. The experiment was carried out in a polyacrylamide-coated fused silica capillary （48.4 cm×50 μm i.d., 38.1 cm effective length） with 20 mmol/L citrate/MES buffer （pH 6.0, ionic strength 0.17）. The applied voltage was 12 kV and detection wavelength was set at 257 nm. The plateau height of the peak was employed to determine the unbound concentration of drug in BSA equilibrated sample solution based on the external drug standard in the absence of protein. The present method provides a convenient, accurate technique for the early stage of drug screening.

A Novel Method for Studying the interaction of Macromolecule with Small Molecule by Means of Affinity Capillary Electrophoresis

A novel capillary electrophoresis method coupled with on-line microdialysis using an attachable electrode has been developed to study the interaction of macromolecule with small molecule. The binding constants of bovine serum album (BSA) with D,L-tryptophan (Trp), sulfamethoxazole (SMZ) with trypsin and chymotrypsin were determined. These values are 2.3 x 10(4)L/mol for BSA-L-Trp; 1.77 x 10(3) L/mol for BSA-D-Trp in pH 7.4, 50 mmol/ L phosphate; 1.4 x 10(4) L/mol for SMZ- trypsin and 6.0 x 10(3) L/mol for SMZ-chymotrypsin in pH 6.5, 25 mmol/L Tris buffer. The proposed method has merits of speed, low sample consumption and readily available to be performed in desired physiological conditions.

Study of interaction between metal ions and quercetin

A displacement test based on the interaction between the flavonoid quercetin and an excess of metal chloride allows the determination of the binding constant for the reaction between quercetin and Ca2+,Mg^2+and Ni^2+.The values obtained were 2.20±1.77×10^3 for Ca^2+,1.37±0.59×10^3 for Mg^2+and 7.03±1.04×10^4 for Ni^2+,and all interactions showed type 1:1 stoichiometry,as determined by titration and by the method of continuous variations(Job’s method).The complexion effect was observed qualitatively through a colorimetric change in the medium(yellow→neon yellow)and spectroscopically through a bathochromic shift in the absorption band of quercetin in the presence of metals.This investigation serves as a tool for the development and testing of materials capable of capturing toxic metal ions or favoring the absorption of beneficial ions(in relation to the human metabolism)through the construction of efficient bioorganic systems.The results reported herein allow understanding of this detection system,indicating the following ascending order of the binding constants(Mg^2+<Ca^2+<Al^3+<Ni^2+).

(E)-2-Benzylidenecycloalkanones XII.*Kinetic Measurement of Bovine and Human Serum Albumine Interaction with Selected Chalcones and Their Cyclic Chalcone Analogues by UV Spectrophotometry

UV-VIS spectroscopic investigations of interaction of bovine and human serum albumin with selected chalcones (1) and their cyclic chalcone analogues: (E)-2-(4’-X-benzylidene-1-tetralones (3), benzosuberones (4) with dimethylamino and methoxy substituents and (E)-2-(2’,4’-dimethox- ybenzylidene)-1-indanone (2) were performed in polar respiration medium. Absorption maxima of the tested compounds were investigated in the presence of bovine and human serum albumin at the 0, 10, 30 and 60 minute timepoints of the interaction. The absorbance of all studied compounds in the presence of proteins decreased after one hour of the reaction. Molecule 4a showed the strongest and fastest kinet initial interaction with both albumins.

Prevention of La^(3+) on DNA Damage Caused by Hg^(2+) from Fish Intestines

The aim of this study was to investigate the effects of rare earth elements （REEs） in preventing Hg^2＋ pollution, using fish intestinal DNA in vitro and study the mechanism of the interactions between Hg^2＋ , La^3＋ , the mixture of La^3＋ and Hg^2＋ and DNA by spectroscopy. The interactions between Hg^2＋ , La^3＋ , the mixture of La^3＋ and Hg^2＋ and DNA from fish intestine in vitro was investigate by using absorption spectrum and fluorescence emission spectrum. Ultraviolet absorption spectra indicated that the addition of Hg^2＋ , La^3＋ , and the mixture of La^3＋ and Hg^2＋ to DNA generated obvious hypochromic effect. Meanwhile, the 205.2 nm peak of DNA blue and the 258.2 nm peak of DNA red shifted. The hypochromic effect and peak shift was caused by these ions in an order of Hg^2＋ 〉 Hg^2＋ ＋ La^3＋ 〉 La^3＋ . The fluorescence emission spectra showed that as the addition of Hg^2＋ , La^3＋ , and the mixture of La^3＋ and Hg^2＋ , the emission peak at about 416.2 nm of DNA did not obviously change, but the fluorescence intensity reduced gradually with the order in treatment was Hg^2＋ 〉 Hg^2＋ 〉 La^3＋ 〉 La^3＋ . Hg^2＋ , La^3＋ , and the mixture of La^3＋ and Hg^2＋ had 1.12, 0.58, and 0.81 binding sites to DNA, the fluorescence quenching of DNA caused by them all attributed to static quenching. The binding constants KA of binding sites were 3.82×10^4 and 4.22×10^2 L·mol^-1 ; 2.50×10^4 and 2.95×10^3 L·mol^-1 ; 3.05×10^4 and 1.00×10^3 L·mol^-1. The results showed that La^3＋ could relieve destruction caused by Hg^2＋ on the DNA structure.

Synthesis, Crystal Structure and DNA Interaction Study of 3-(2-(3,5-Diphenyl-4,5-dihydropyrazol-1-yl)thiazol-4-yl)-2H-chromen-2-one

A new compound 3-（2-（3,5-diphenyl-4,5-dihydropyrazol-1-yl）thiazol-4-yl）-2Hchromen-2-one was synthesized by cyclocondensation of 3,5-diphenyl-4,5-dihydropyrazole-1-carbothioamide with 3-（2-bromoacetyl）-2H-chromen-2-one in ethanol at reflux for 2hrs. The compound was characterized by IR, 1H-NMR, 13C-NMR and single-crystal X-ray diffraction analysis. The newly synthesized compound（C27H19N3O2S） crystallizes in the triclinic system, space group P1 with a = 5.2476（6）, b = 18.289（2）, c = 23.115（3） , α = 93.546（7）, β = 94.715（6）, γ = 92.347（7）°, V = 2204.3（4）3, Z = 4, Mr = 449.51, crystal size = 0.38 mm × 0.22 mm × 0.16 mm,（I 2σ（I）） = 35317, 9736, 3785, Rint = 0.081,（Δρ）max = 0.19 and（Δρ）min = –0.24 e·-3. DNA interaction studies revealed that the target compound strongly interacts with DNA through an intercalation binding mode and the binding constant of the compound is 7.45 × 104 M-1.

Study on State of Terbium Ion in Liposome by One order Derivative Fluorescence Quenching Method

The state of Tb3+ is investigated in liposome. When the concentration of PC is below CMC (critical micell concentration), most of Tb3+ is associated with PC, the binding constant is about 3.35×103 L/mol. When the concentration of PC is beyond CMC, most of Tb3+ is dimerized, the dimerization constant is about 3.92×104L/mol. In PC?CH?H2O system, the binding constant of Tb3+?CH complex 2.93×104L/mol is obtained.

Determination of Curcumin on Functionalized Carbon Nano Tube Modified Electrode and Probing its Interaction with DNA and Copper Ion

Voltammetry measurements have been employed to investigate the redox behaviour of curcumin in aqueous media using functionalized carbon nanotube(FCNTs)modified glassy carbon electrode(GCE).The electro-catalytic properties of FCNTs modified electrode are superior in comparison to the conventional electrode in generating the electrochemical response from curcumin.The oxidation process of the curcumin over the modified substrate is found to be p H dependent and shows 2e^(-)and 2H^(+)proton transfer electrochemical process.The oxidation peak is obtained at 0.37 V and the peak current is found to be linear with the varying concentration of curcumin.The limit of detection(LOD)and the limit of quantification(LOQ)for the curcumin are obtained as 60 and 200 nmol/L,respectively using the FCNTs modified GCE.The enhanced electrochemical response from the FCNTs modified GCE has been utilized in the evaluation of the chemical and biochemical behaviour of curcumin in presence of transition metal ions(Cu^(2+))and ds DNA,and the observation has been supported by the spectrochemical characteristics of the interactions.

Biosorption of Cu（II） to extracellular polymeric substances （EPS） from Synechoeystis sp.： a fluorescence quenching study

Biosorption of extracellular polymeric substances （EPS） from Synechocystis sp. （cyanobacterium） with Cu（II） was investigated using fluorescence spectroscopy. Three fluorescence peaks were found in the excitation-emission matrix （EEM） fluorescence spectra of EPS. Fluorescence of peak A （Ex/Em = 275/452 nm） and peak C （Ex/Em= 350/452nm） were originated from humic-like substances and fluorescence of peak B （Ex/ Em= 275/338nm） was attributed to protein-like sub- stances. Fluorescence of peaks A, B, and C could be quenched by Cu（II）. The effective quenching constants （lg Ka） were 2.8-5.84 for peak A, 6.4-9.24 for peak B, and 3.48-6.68 for peak C, respectively. The values of lg Ka showed a decreasing trend with increasing temperature, indicating that the quenching processes were static in nature. The binding constants （lg Kb） followed the order of peak A 〉 peak B 〉 peak C, implying that the humic-like substances in EPS have greater Cu（II） binding capacity than the protein-like substances. The binding site number, n, in EPS-Cu（II） complexes for peaks A, B, and C was less than 1. This suggests the negative cooperativity between multiple binding sites and the presence of more than one Cu binding site.

Zn^(2+) Recognition by Two New Bipyridine Ligands

Two new hipyridine ligands with intramolecular charge transfer system. (ICT) transition as the lowest excited state were designed and synthesized. Upon addition of metal ions, particularly Zr2+, the absorption and emission spectra experience great changes. The binding constants towards Zn2+ are 1.27 x 10(5) L/mol and 1.66 x 10(5) L/mol for ligands 1 and 2, respectively. The strong binding affinity and high selectivity make them attractive for application as fluorescence sensors for Zn2+.

Synthesis, DNA and Photocleavage Studies of Ru（ll） Polypyridyl Complexes： [Ru（dppz）（pyz）4]（ClO4）2 and [Ru（dppz）（dmpyz）4]（ClO4）2 Complexes

In view of the growing interest for the synthesis of metal complexes and their interaction with DNA, we have synthesized and characterized two complexes containing ruthenium as metal center. The complexes are of the type [Ru（dppz）L4]（C104）2 where L are biologically important ligands such as pyrazole and dimethylpyrazole. The characterization of these complexes is done by 1 H NMR, 13C NMR, elemental analysis and mass spectroscopy. The interaction of these complexes with CT DNA was monitored and binding constants were determined using absorption and fluorescence spectroscopy. The mode of binding was found to be intercalative for both complexes and was determined using hydrodynamic viscosity studies. The complexes were further studied for photocleavage studies with supercoiled plasmid pBR322 DNA.