Research Article
Shilpa Sanwlani and Bohidar
Abstract
Specific hydration induced coil-globule transition in gelatin-B(GB) chain, a polypeptide, in ethanol, ethylene glycol and glycerol solutions (organo-solutions) was studied by Raman spectroscopy, viscosity and dynamic light scattering techniques to map its differential hydration behavior in mono, di and tri-ol solutions (alcohols are non-solvents for this polypeptide). The chain stiffness, determined from the hydrodynamic radius to radius of gyration ratio Rg/Rh, was estimated to be around 0.67 in water which was found to be dependent on the nature of alcohol and its concentration. This clearly attributed same random coil conformation to GB in all thesolutions at low alcohol concentration, but chain collapse to a near-globular shape (Rg/Rh=0.77) was observed when alcohol concentration was increased which was found to occur in glycerol at ≈ 60% (v/v), in ethylene glycol at ≈ 35% and in ethanol at ≈ 40% (v/v) concentrations consistence with the intrinsic viscosity data. The Huggins (KH) and Kraemer (KK) solute-solvent interaction parameter determined from the concentration dependence plot of relative viscosity revealed poorer interaction between GB and organo-solvents with increase in concentration of the organic phase. Differential chain hydration was evaluated from characteristic Raman active modes of water molecule. Three signatures Raman peaks were observed at 3200, 3310, and 3460 cm-1 specific to structured, partially structured and amorphous water respectively. The peak at 3310 cm-1 was observed to decrease with alcohol concentration while the peak at 3200 cm-1 was observed to increase indicating the increase in the water structure in all the solutions and depletion of water density near the first hydration sheath of the protein molecule which caused GB chain to collapse.