Nonmonotonic Hydration Behavior of Bovine Serum Albumin in Alcohol/Water Binary Mixtures: A Terahertz Spectroscopic Investigation

Abstract

We report the experimental observation of nonmonotonic changes in the collective hydration of bovine serum albumin (BSA) in the presence of alcohols of varying carbon-chain lengths, that is, ethanol, 2-propanol, and tert-butyl alcohol (TBA), by using terahertz (THz) time domain spectroscopy. We measured the THz absorption coefficient (α) of the protein solutions, and it was observed that α fluctuated periodically as a function of alcohol concentration at a fixed protein concentration. For a fixed alcohol concentration, an increase in the protein concentration resulted in nonmonotonic changes in α; thus, it first decreased rapidly and then increased, which was followed by a shallow decrease. An alcohol-induced α helix to random coil transition of the protein secondary structure was revealed by circular dichroism spectroscopy measurements, and the effect was most prominent in TBA. The anomalous change in the hydration was found to be a delicate balance between the various interactions present in the three-component system.

Anomalous Dynamics in tert-Butyl Alcohol–Water and Trimethylamine N-Oxide–Water Binary Mixtures: A Femtosecond Transient Absorption Study

“…72 The aggregation of TBA molecules at around X TBA = 0.10 is further supported by other groups. 19,73 Hence, our result is completely in line with the other reports. Therefore, the long-lifetime component of 15–50 ps is probably responsible for large TBA clusters.…”

“…Biswas and co-workers have shown the structural transition from the waterlike tetrahedral network to the zigzag alcohol-like structure at around X TBA = 0.10 in TBA–water binary mixtures. ,, It has been reported that with the increasing TBA concentration, aggregation tendency increases and reaches its maximum in the range of X TBA = 0.14–0.17 . The aggregation of TBA molecules at around X TBA = 0.10 is further supported by other groups. , Hence, our result is completely in line with the other reports. Therefore, the long-lifetime component of 15–50 ps is probably responsible for large TBA clusters.…”

Effect of Microheterogeneity of Different Aqueous Binary Mixtures on the Proton Transfer Dynamics of [2,2′-Bipyridyl]-3,3′-diol: A Femtosecond Fluorescence Upconversion Study

“…60 Very recently, Das et al have used terahertz (THz) time-domain spectroscopy to study nonmonotonic hydration behavior of bovine serum albumin in different alcohol–water binary mixtures. 61…”

“…Matsuura and co-workers have reported that a small amount of water enhances the self-association of alcohols . Very recently, Das et al have used terahertz (THz) time-domain spectroscopy to study nonmonotonic hydration behavior of bovine serum albumin in different alcohol–water binary mixtures …”

“…60 Very recently, Das et al have used terahertz (THz) time-domain spectroscopy to study nonmonotonic hydration behavior of bovine serum albumin in different alcohol−water binary mixtures. 61 Interestingly, the aqueous solution of TBA exhibits significant microheterogeneity and solute aggregation compared to the other homologous alcohols because of higher hydrophobicity at a low concentration range. 36,38,52 An isotopic substitution with the neutron diffraction technique provides a better understanding of TBA−water binary mixtures, and it interprets the dominance of the nonpolar alkyl group of TBA rather than that of the polar hydroxyl group in the formation of the intermolecular association.…”