nan Riyazuddeen

Calorimetric and spectroscopic binding studies of amoxicillin with human serum albumin

Abstract Amoxicillin is a common antibiotic drug used for preventing bacterial colonization of urinary and skin infections. The binding of amoxicillin (AX) to human serum albumin (HSA) in sodium phosphate buffer solution at pH 7.4 has been investigated by UV–visible spectroscopy, fluorescence spectroscopy, Förster resonance energy transfer, isothermal titration calorimetry (ITC), circular dichroism (CD) and FTIR spectroscopy. The binding studies using ITC revealed that the interaction is entropy driven rather than enthalpy as the change in enthalpy (ΔH°) and change in entropy (TΔS°) both are positive, indicating the endothermic reaction with low affinity and hydrophobic interaction. UV–visible absorption spectra of HSA are increased upon addition of AX which shows complex formation of HSA–AX. The fluorescence spectra reveal that the AX has an ability to quench the intrinsic fluorescence of HSA tryptophan through a static quenching procedure. The molecular distance r between donor (HSA) and acceptor (AX) was estimated according to Förster theory of nonradiative energy transfer. The CD spectra showed that the α-helix of HSA increases with increasing the amount of AX. The thermal denaturation has been studied by far-UV CD, and it is found that HSA stability is decreased by the complex formation of HSA and AX. The remarkable change in amide I peak position in infrared spectrum after interaction with AX indicated that secondary structure of HSA has been changed.

Unraveling the thermodynamics, binding mechanism and conformational changes of HSA with chromolyn sodium: Multispecroscopy, isothermal titration calorimetry and molecular docking studies

Cromolyn sodium is an anti-allergic drug effective for treatment in asthma and allergic rhinitis. In this project, interaction of chromolyn sodium (CS) with human serum albumin (HSA) has been investigated by various techniques such as UV-vis, fluorescence, circular dichorism (CD), fourier transform infrared (FT-IR) spectroscopy, isothermal titration calorimetric (ITC) and molecular docking. The fluorescence quenching results revealed that there was static quenching mechanism in the interactions of CS with HSA. The binding constant (Kb), enthalpy change (ΔH°), entropy change (ΔS°) and Gibbs free energy change (ΔG°) were calculated. The negative values of TΔS° and ΔH° obtained from fluorescence spectroscopy and isothermal titration calorimetry, indicate that hydrogen bonding and van der Waals forces played major role in the binding process and the reaction is exothermic in nature. The binding constant (Kb) was found to be in the order of 104M-1 which depicts a good binding affinity of CS towards HSA. The conformational changes in the HSA due to interaction of CS were investigated from CD and FT-IR spectroscopy. The binding site of CS in HSA was sub-domain IIA as evident from site probing experiment and molecular docking studies.

A comprehensive calorimetric, spectroscopic, and molecular docking investigation to probe the interaction of colchicine with HEWL

Colchicine (Col), a naturally occurring alkaloid, has been used as an anti-inflammatory, anti-fibrotic, and anti-tumor drug. The present study reports in vitro interaction between Col and hen egg white lysozyme (HEWL) by spectroscopy, isothermal titration calorimetry (ITC), and molecular docking techniques. The fluorescence results indicated that Col quenches the intrinsic fluorescence of HEWL through static quenching mechanism which is also substantiated by UV–visible spectroscopy. The average distance (r) between donor (HEWL) and acceptor (Col) was evaluated by Förster’s resonance energy transfer theory. Thermodynamic parameters obtained from ITC suggested that hydrophobic interaction plays a major role in the complex formation, and it is an entropically driven process. Col altered the secondary structure of HEWL revealed by circular dichroism which is further corroborated by synchronous, 3D fluorescence and FTIR techniques. In addition, molecular docking was employed to find out binding site of Col on HEWL and amino acid residues involved in the binding process. This study is expected to provide insights into the type of interaction and binding mechanism of Col with HEWL.

Effects of concentration and temperature on molar volumes of L-serine, L-isoleucine, and L-glutamine in aqueous NaCl and NaNO3 solutions

Densities of L-serine, L-isoleucine, L-glutamine in 1.5 mol kg−1 aqueous NaCl, and NaNO3 solutions have been measured for several molal concentrations of amino acids at temperatures from 298.15 to 323.15 K. The partial molar volumes (ϕv0) of L-serine, L-isoleucine, and L-glutamine in 1.5 mol kg−1 aqueous NaCl/NaNO3 solutions have been computed using density data. The transfer partial molar volumes (Δtrϕv0) of L-serine, L-isoleucine, and L-glutamine from water to 1.5 mol kg−1 aqueous NaCl/1.5 mol kg−1 aqueous NaNO3 solutions have been determined at 298.15 K. The trends of variation of ϕv0 and Δtrϕv0 with change in temperature have been discussed in terms of ion-ion, ion-hydrophilic, and ion-hydrophobic interactions operative in solutions.

Erratum to: “Interactions in L-Phenylalanine/L-Leucine/L-Glutamic Acid/L-Proline + 2 M Aqueous NaCl/2 M NaNO3 Systems at Different Temperatures”

Density (ρ) and speed of sound (u) in 2 M aqueous NaCl and 2 M NaNO3 solutions of amino acids: L-phenylalanine, L-leucine, L-glutamic acid, and L-proline have been measured for several molal concentrations of amino acids at different temperatures. The ρ and u data have been used to calculate the values of isothermal compressibility and internal pressure at different temperatures. The trends of variations of κT and Pi with an increase in molal concentration of amino acid and temperature have been discussed in terms of solute-solvent and solute-solute interactions in the systems.