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describe the interaction of GlyGly with copper(II) ions and to gain knowledge of the mechanism of formation of a biologically relevant complex, calorimetric measurements were conducted. Isothermal titration calorimetry and potentiometric measurements were

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The interaction of myelin basic protein (MBP) from the bovine central nervous system with divalent nickel ion was studied by isothermal titration calorimetry at 37 and 47 °C in Tris buffer solution at pH = 7. The new solvation model was used to reproduce the heats of MBP + Ni2+ interaction over the whole Ni2+ concentrations. It was found that MBP has three identical and independent binding sites for Ni2+ ions. The intrinsic dissociation equilibrium constant and the molar enthalpy of binding are 89.953 μM, −14.403 kJ mol−1 and 106.978 μM, −14.026 kJ mol−1 at 37 and 47 °C, respectively. The binding parameters recovered from the new solvation model were correlated to the structural changes of MBP due to its interaction with nickel ion interaction. It was found that in the low and high concentrations of the nickel ions, the MBP structure was destabilized.

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Heat divided by ligand concentration vs. heat, similar to the Scatchard plot, was introduced to obtain the equilibrium constant (K) and the enthalpy of binding (DH) using isothermal titration calorimetry data. Values of K and DH obtained by this linear pseudo-Scatchard plot for a system with a set of independent binding sites (such as binding fluoride ions on urease and monosaccharide methyl a-D-mannopyranoside on concavalin A) were remarkably like that obtained from a normal fitting Wiseman method and other our technical methods. On applying this graphical method to study the binding of copper ion on myelin basic protein (MBP), a concave downward curve obtained was consistent with the positive cooperativity in the binding. A graphical fitting by simple method for determination of thermodynamic parameters was also introduced. This method is general, without any assumption and restriction made in previous method. This general method was applied to the product inhibition study of adenosine deaminase.

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The micellization characteristics of sodium n-dodecyl sulfate (SDS) have been investigated by microcalorimetric technique at conditions close to the physiological ones. The thermodynamics of micellization were studied at 20, 25, 30, 35 and 40 °C in 50 mM HEPES buffer, pH 7.4 and 160 mM NaCl using isothermal titration calorimetric (ITC) technique. The calorimeter can operate in a stepwise addition mode, providing an excellent method of determination of critical micelle concentration (CMC) and enthalpy of demicellization (and hence micellization). It can as well distinguish between aggregating and non-aggregating amphiphiles (solutes) in solution. The dilution enthalpy (∆H dil) was calculated and graphed versus concentration in order to determine the micellization enthalpy (∆H mic) and CMC. In addition to the CMC and ∆H mic, the effective micellar charge fraction (α) of the ionic surfactant micellization process can also be determined from ITC curves. The Gibbs free energy of the micellization (∆G mic), entropy of the micellization (∆S mic), and specific heat capacity of the micellization (∆C P,mic) process have been evaluated by the direct calorimetric method (mass-action model) as well as by the indirect method of van’t Hoff by processing the CMC and α results of microcalorimetry at different temperatures. The differences of the results obtained by these two procedures have been discussed. The presence of NaCl (160 mM) in the solutions decreased the CMC of SDS. The enthalpy changes associated with micelle dissociation were temperature-dependent, indicating the importance of hydrophobic interactions. The ∆G mic was found to be negative, implying, as expected, that micellization occurs spontaneously once the CMC has been reached. The values of ∆G mic were found to become more negative with increasing temperature and the ∆S mic was found to decrease with increasing temperature in both models.

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An isothermal titration calorimetry (ITC) method to measure the heat effects evolving from the binding between cation exchanger Amberlite IRP 69 and the cationic drug substances propranolol hydrochloride (PROP), metoprolol tartarate (METO), acebutolol hydrochloride (ACEB) and chlorpheniramine maleate (CPR) has been developed. The method gives repeatable results with an error about 5% for the beta-blockers PROP, METO and ACEB, and about 10% for the antihistamine CPR. The calculation of the thermodynamic parameters enthalpy change (ΔH bind) and Gibbs free energy change (ΔG bind) show significant differences between the different drug substances.

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An uptake or a release of heat accompanies practically all molecular binding interactions. Therefore isothermal titration microcalorimetry is universally applicable for the characterisation of such binding processes. Calorimetric analyses do not require marker molecules or intrinsic spectroscopic reporter groups, which can modify the analysed interactions. Furthermore, measurements are carried out in solution and the adsorption of reactants to a solid phase is thus avoided. At variance with most other analytical approaches, titration calorimetry determines simultaneously enthalpy and entropy contributions of the binding interactions, as well as the binding constant and stoichiometry. In our analyses of the interactions between monoclonal antibodies and candidate antigens for vaccines vs. malaria and malignant melanoma, isothermal titration calorimetry has turned out to be a very valuable technique. The obtained quantitative data on biomolecular interactions can substantially support the rational design of epitope-focused vaccines.

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The interaction of a flavonoid molecule (puerarin) with bovine serum albumin (BSA) was characterized by isothermal titration calorimetry (ITC), optical spectroscopic technique, and molecular modeling method under physiological conditions. The binding parameters for the reaction were calculated according to ITC experiments at different temperatures. The thermodynamic parameters, negative enthalpy changes (ΔH), and positive entropy (ΔS) indicated that the binding processes were entropically driven. The alterations of protein secondary structure in the presence of puerarin in aqueous solution were estimated by the evidences from FT-IR and CD spectroscopy with reductions of α-helices. On the basis of fluorescence resonance energy transfer (FRET) between excited tryptophan in BSA and BSA bound puerarin, the critical transfer distance and mean distance between tryptophan in BSA and puerarin were estimated.

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A simple method for determination of binding isotherm in the protein-ligand interaction was introduced using isothermal titration calorimetric data. This general method was applied to the study of the interaction of myelin basic protein (MBP) from bovine central nervous system with divalent copper ion at 27C in Tris buffer solution at pH=7.2. The binding isotherm for copper-MBP interaction is easily obtained by carrying out titration calorimetric experiment in two different concentrations of MBP. MBP has two binding sites for copper ion, which show positive cooperativity in its sites. The intrinsic association equilibrium constants are 0.083 and 1.740 ?M-1 in the first and second binding sites, respectively. Hence, occupation of the first site has produced an appreciable enhancement 21 of the binding affinity of the second site. The molar enthalpies of binding are -13.5 and -14.8 kJ mol-1 in the first and second binding sites, respectively.

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, J , Payehghdr , M . A thermodynamic study on the interaction of nikel with mylin basic protein by isothermal titration calorimetry . J Therm Anal Cal . 2010 ; 101 : 379 – 384 . 10.1007/s10973-009-0596-0 . 9

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Binding mechanisms of nano-baskets toward alkali metals

Isothermal titration calorimetric study

Journal of Thermal Analysis and Calorimetry
Authors: Bahram Mokhtari and Kobra Pourabdollah

Introduction Isothermal titration calorimetry (ITC) as an analytical tool directly determines the binding heat of two species [ 1 – 6 ] and are used to characterize the binding thermodynamics in the chemical and the biological

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