Abstract-Nonlinear TeraHertz Transmission by Liquid Water at 1 THz

Fabio Novelli, Chun Yu Ma,Nidhi Adhlakha,Ellen M. Adams,Thorsten Ockelmann ,Debasish Das Mahanta,Paola Di Pietro, Andrea Perucchi, Martina Havenith

https://www.mdpi.com/2076-3417/10/15/5290

The solvation properties of liquid water originate from the transient network of hydrogen-bonded molecules. In order to probe the coupling between the different modes of this network, nonlinear terahertz (THz) spectroscopy techniques are required. Ideally, these techniques should use a minimal volume and capitalize on sensitive field-resolved detection. Here we performed open aperture z-scan transmission experiments on static liquid cells, and detect the THz fields with electro-optical techniques. We show that it is possible to quantify the nonlinear response of liquid water at ~1 THz even when large signals originate from the sample holder windows

Abstract-The Decisive Role of Hydrophobicity on the Effect of Alkylammonium Chlorides on Protein Stability: A Terahertz Spectroscopic Finding

Debasish Das Mahanta, Rajib Kumar Mitra, and Nirnay Samanta

http://pubs.acs.org/doi/abs/10.1021/acs.jpcb.7b04088?journalCode=jpcbfk

Many biologically important processes involve a subtle interplay between Columbic and hydrophobic interactions among molecular groups with water. A comprehensive understanding of such processes, specially while occurring simultaneously in the same molecule is of practical importance. In this contribution we report the ultrafast (sub-ps to ps) collective hydrogen bond dynamics of water in the extended hydration layers in a series of alkylammonium chloride salts using THz time domain spectroscopic (TTDS) technique (0.3-1.6 THz (10-55 cm-1)). We found the THz absorption coefficient (α) of the salt solutions systematically vary with the salt type. We obtain the hydrogen bond relaxation dynamics by fitting the frequency dependent dielectric constants in a multiple Debye dielectric relaxation model. We found these salts to transform from being a water ‘structure breaker’ to ‘structure maker’ with increasing carbon content. We also investigate their effect on a model protein ‘bovine serum albumin’ and found systematic trend towards disrupting the protein secondary structure. The associated changes in the protein hydration in presence of these salts have also been investigated using TTDS.

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

Dr. Dipak Kumar Das, Debasish Das Mahanta, Dr. Rajib Kumar Mitra

http://onlinelibrary.wiley.com/doi/10.1002/cphc.201601217/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.