Debasish Das Mahanta | The University of Texas at Austin (original) (raw)
Papers by Debasish Das Mahanta
The journal of physical chemistry. B, Apr 8, 2024
Chemical Science, 2023
Please note that technical editing may introduce minor changes to the text and/or graphics, which... more Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal's standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
Chemical Physics Letters, Nov 1, 2022
Journal of Molecular Liquids
Chemical Science
Based on THz-spectra we quantify hydrophilic solvation and correlate with mixing enthalpy.
Photo-induced excited-state proton transfer (ESPT) reactions are of central importance in many bi... more Photo-induced excited-state proton transfer (ESPT) reactions are of central importance in many biological and chemical processes. Based on the results of a joint study using optical pump THz probe (OPTP) spectroscopy and molecular dynamics simulations, we were able to elucidate the ultrafast changes in the solvation environment for three derivatives of pyranine: the photoacid HPTS, the methoxy derivative MPTS, and the photobase OPTS. Experimentally, we find damped oscillations in the THz signal at short times and our simulations enable their assignment to vibrational energy transfer beatings between the photoexcited chromophore and nearby solvent molecules. The simulations of HPTS reveal strikingly efficient sub-ps energy transfer into a particular solvent mode, that is active near 4 THz, and which can provide the requisite energy required for solvent reorganization promoting proton transfer. Similar oscillations are present in the THz signal for all three derivatives, however the s...
Glycerol is a major cryoprotective agent and is widely used to promote protein stabilization. Thr... more Glycerol is a major cryoprotective agent and is widely used to promote protein stabilization. Through a combined experimental and theoretical study, we show that global thermodynamic mixing properties of glycerol and water are dictated by local solvation motifs. We identify three water populations, i.e., bulk water, bound water H-bonded to hydrophilic groups of glycerol and wrap water hydrating hydrophobic moieties. Each population provides distinct spectroscopic fingerprints in the THz/FIR spectral range, which allow to quantify their respective abundance and their partial contributions to the mixing enthalpy. We uncover a 1:1 connection between the number of bound waters and the mixing enthalpy, as deduced from experiments as well as from simulations. The balance between local hydrophobic wrap and hydrophilic bound contributions at the molecular level dictates macroscopic thermodynamics of mixing. This offers opportunities to rationally design polyol water mixtures to optimize tec...
Physical Chemistry Chemical Physics
A new methodology to describe temporal heterogeneity in aqueous solutions through large amplitude... more A new methodology to describe temporal heterogeneity in aqueous solutions through large amplitude angular jump motions.
The Journal of Physical Chemistry B
Biological membranes are highly organized supramolecular assemblies of lipids and proteins. The m... more Biological membranes are highly organized supramolecular assemblies of lipids and proteins. The membrane interface separates the outer (bulk) aqueous phase from the hydrophobic membrane interior. In this work, we have explored the microstructure and collective dynamics of the membrane interfacial hydration shell in zwitterionic and negatively charged phospholipid membrane bilayers using terahertz time-domain spectroscopy. We show here that the relaxation time constants of the water hydrogen bond network exhibit a unique "rise and dip" pattern with increasing lipid concentration. More importantly, we observed a dependence of the critical lipid concentration corresponding to the inflection point on the charge of the lipid headgroup, thereby implicating membrane electrostatics as a major factor in the microstructure and dynamics of water at the membrane interface. These results constitute one of the first experimental evidences of the modulation of the dielectric relaxation response of membrane interfacial water by membrane lipid composition in a concentration-dependent manner. Lipid-stringent membrane hydration could be relevant in the broader context of lipid diversity observed in biological membranes and the role of negatively charged lipids in membrane protein structure and function.
The Journal of Physical Chemistry B
Many biologically important processes involve a subtle interplay between Columbic and hydrophobic... more 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 (subpicosecond to picosecond) 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 a systematic trend toward disrupting the protein secondary structure. The associated changes in the protein hydration in the presence of these salts have also been investigated using TTDS.
The Journal of chemical physics, Jan 28, 2017
A detailed understanding of hydration of amino acids, the building units of protein, is a key ste... more A detailed understanding of hydration of amino acids, the building units of protein, is a key step to realize the overall solvation processes in proteins. In the present contribution, we have made a combined GHz (0.2-50) to THz (0.3-2.0) experimental spectroscopic study to investigate the dynamics of water at room temperature in the presence of different amino acids (glycine, L-serine, L-lysine, L-tryptophan, L-arginine, and L-aspartic acid). The THz absorption coefficient, α(ν), of amino acids follows a trend defined by their solvent accessible surface area. The imaginary and real dielectric constants obtained in GHz and THz regions are fitted into multiple Debye model to obtain various relaxation times. The ∼100 ps time scale obtained in the GHz frequency region is attributed to the rotational motion of the amino acids. In the THz region, we obtain ∼8 ps and ∼200 fs time scales which are related to the cooperative dynamics of H-bond network and partial rotation or sudden jump of t...
Journal of Molecular Liquids, 2016
Abstract In this contribution we present experimental evidences of the ultrafast (sub-ps to ps) c... more Abstract In this contribution we present experimental evidences of the ultrafast (sub-ps to ps) collective hydrogen bond dynamics of water in the extended hydration layers of alkali metal chlorides by using THz time domain spectroscopy (TTDS) in the terahertz frequency region (0.3–2.1 THz; 10–70 cm− 1). The behaviour of the frequency dependent absorption coefficient (α), refractive index (n) and the dielectric relaxation response time (τ), obtained by fitting both real and imaginary parts of the permittivity (e) using a triple Debye relaxation model are studied. The timescales obtained for bulk water are of the order of ~ 9 ps, 200 fs and 80 fs. The relaxation time constant in the presence of the salt shows an accelerated reorientation dynamics of the water dipoles, which, in turn renders an indirect support for the ‘water structure breaking’ ability of monovalent ions, the effect being ion specific. We have also studied the effect of these ions on the secondary structure as well as hydration dynamics around a model protein bovine serum albumin (BSA). It is found that the structure and hydration of the protein as well as the salt hydration suffer negligible perturbation in the presence of the alkali metal chlorides.
2015 40th International Conference on Infrared, Millimeter, and Terahertz waves (IRMMW-THz), 2015
We have addressed a very fundamental question, whether urea and guanidinium chloride (GdmCl) act ... more We have addressed a very fundamental question, whether urea and guanidinium chloride (GdmCl) act as water `structure breakers'. Our study using THz time domain spectroscopy (TTDS) confirm that both these molecules perturb the extended solvation layer around themselves which supports the strongly debated “water structure breaker” notion of urea and GdmCl during their protein denaturation process[1,2].
Chemistry - An Asian Journal, 2014
We report the ultrafast collective hydrogen-bond dynamics of water in the extended hydration laye... more We report the ultrafast collective hydrogen-bond dynamics of water in the extended hydration layer of urea by using terahertz time-domain spectroscopy in the frequency region of 0.3-2.0 THz. The complex dielectric function has been fitted using a Debye relaxation model, and the timescales obtained are in the order of approximately 9 ps and 200 fs for bulk water; this exhibits a considerable acceleration beyond the 4 M urea concentration and indicates a possible disruption in the collective hydrogen-bonded water-network structure, which, in turn, provides an indirect support for the water "structure-breaking" ability of urea. With 5 M urea in the presence of different concentrations of trimethylamine-N-oxide (TMAO), it was found that these parameters essentially follow the trend observed for TMAO itself, which signifies that any possible disruption of the water structure by urea is outdone by the strong hydrogen-bonding ability of TMAO, which explains its ability to revive urea-denatured proteins to their respective native states.
Phys. Chem. Chem. Phys., 2014
The remarkable ability of guanidinium chloride (GdmCl) to denature proteins is a well studied yet... more The remarkable ability of guanidinium chloride (GdmCl) to denature proteins is a well studied yet controversial phenomenon; the exact molecular mechanism is still debatable, especially the role of hydration dynamics, which has been paid less attention. In the present contribution, we have addressed the issue of whether the collective hydrogen bond dynamics of water gets perturbed in the presence of GdmCl and its possible impact on the denaturation of a globular protein human serum albumin (HSA), using terahertz (THz) time domain spectroscopy (TTDS) in the frequency range of 0.3-2.0 THz. The collective hydrogen bond dynamics is determined by fitting the obtained complex dielectric response in a multiple Debye relaxation model. To compare the results, the studies were extended to two more salts: tetramethylguanidinium chloride (TMGdmCl) and sodium chloride (NaCl). It was concluded that the change in hydration dynamics plays a definite role in the protein denaturation process.
Biochimie, 2014
In the present study we have investigated the thermal stability of the globular transport protein... more In the present study we have investigated the thermal stability of the globular transport protein human serum albumin (HSA), in the presence of two small chain polyethylene glycols (namely PEG 200 and PEG 400). Both near- and far-UV circular dichroism (CD) study reveal that addition of PEG moderately increases the α-helical content of the protein without abruptly changing its tertiary structure. The hydration structure at the protein surface experiences a notable change at 30% PEG (v/v) concentration as evidenced from compressibility and dynamic light scattering (DLS) measurements. Thermal denaturation of HSA in the presence of PEG has been studied by CD and fluorescence spectroscopy using the intrinsic fluorophore tryptophan and it has been found that addition of PEG makes the protein more prone towards unfolding, which is in contrary to what has been observed in case of larger molecular weight polymers. The energetics of the thermal unfolding process has been obtained using differential scanning calorimetry (DSC) measurements. Our study concludes that both the indirect excluded volume principle as well as interaction of the polymer at the protein surface is responsible for the observed change of the unfolding process.
Applied Sciences
The solvation properties of liquid water originate from the transient network of hydrogen-bonded ... more 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.
The journal of physical chemistry. B, Apr 8, 2024
Chemical Science, 2023
Please note that technical editing may introduce minor changes to the text and/or graphics, which... more Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal's standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
Chemical Physics Letters, Nov 1, 2022
Journal of Molecular Liquids
Chemical Science
Based on THz-spectra we quantify hydrophilic solvation and correlate with mixing enthalpy.
Photo-induced excited-state proton transfer (ESPT) reactions are of central importance in many bi... more Photo-induced excited-state proton transfer (ESPT) reactions are of central importance in many biological and chemical processes. Based on the results of a joint study using optical pump THz probe (OPTP) spectroscopy and molecular dynamics simulations, we were able to elucidate the ultrafast changes in the solvation environment for three derivatives of pyranine: the photoacid HPTS, the methoxy derivative MPTS, and the photobase OPTS. Experimentally, we find damped oscillations in the THz signal at short times and our simulations enable their assignment to vibrational energy transfer beatings between the photoexcited chromophore and nearby solvent molecules. The simulations of HPTS reveal strikingly efficient sub-ps energy transfer into a particular solvent mode, that is active near 4 THz, and which can provide the requisite energy required for solvent reorganization promoting proton transfer. Similar oscillations are present in the THz signal for all three derivatives, however the s...
Glycerol is a major cryoprotective agent and is widely used to promote protein stabilization. Thr... more Glycerol is a major cryoprotective agent and is widely used to promote protein stabilization. Through a combined experimental and theoretical study, we show that global thermodynamic mixing properties of glycerol and water are dictated by local solvation motifs. We identify three water populations, i.e., bulk water, bound water H-bonded to hydrophilic groups of glycerol and wrap water hydrating hydrophobic moieties. Each population provides distinct spectroscopic fingerprints in the THz/FIR spectral range, which allow to quantify their respective abundance and their partial contributions to the mixing enthalpy. We uncover a 1:1 connection between the number of bound waters and the mixing enthalpy, as deduced from experiments as well as from simulations. The balance between local hydrophobic wrap and hydrophilic bound contributions at the molecular level dictates macroscopic thermodynamics of mixing. This offers opportunities to rationally design polyol water mixtures to optimize tec...
Physical Chemistry Chemical Physics
A new methodology to describe temporal heterogeneity in aqueous solutions through large amplitude... more A new methodology to describe temporal heterogeneity in aqueous solutions through large amplitude angular jump motions.
The Journal of Physical Chemistry B
Biological membranes are highly organized supramolecular assemblies of lipids and proteins. The m... more Biological membranes are highly organized supramolecular assemblies of lipids and proteins. The membrane interface separates the outer (bulk) aqueous phase from the hydrophobic membrane interior. In this work, we have explored the microstructure and collective dynamics of the membrane interfacial hydration shell in zwitterionic and negatively charged phospholipid membrane bilayers using terahertz time-domain spectroscopy. We show here that the relaxation time constants of the water hydrogen bond network exhibit a unique "rise and dip" pattern with increasing lipid concentration. More importantly, we observed a dependence of the critical lipid concentration corresponding to the inflection point on the charge of the lipid headgroup, thereby implicating membrane electrostatics as a major factor in the microstructure and dynamics of water at the membrane interface. These results constitute one of the first experimental evidences of the modulation of the dielectric relaxation response of membrane interfacial water by membrane lipid composition in a concentration-dependent manner. Lipid-stringent membrane hydration could be relevant in the broader context of lipid diversity observed in biological membranes and the role of negatively charged lipids in membrane protein structure and function.
The Journal of Physical Chemistry B
Many biologically important processes involve a subtle interplay between Columbic and hydrophobic... more 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 (subpicosecond to picosecond) 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 a systematic trend toward disrupting the protein secondary structure. The associated changes in the protein hydration in the presence of these salts have also been investigated using TTDS.
The Journal of chemical physics, Jan 28, 2017
A detailed understanding of hydration of amino acids, the building units of protein, is a key ste... more A detailed understanding of hydration of amino acids, the building units of protein, is a key step to realize the overall solvation processes in proteins. In the present contribution, we have made a combined GHz (0.2-50) to THz (0.3-2.0) experimental spectroscopic study to investigate the dynamics of water at room temperature in the presence of different amino acids (glycine, L-serine, L-lysine, L-tryptophan, L-arginine, and L-aspartic acid). The THz absorption coefficient, α(ν), of amino acids follows a trend defined by their solvent accessible surface area. The imaginary and real dielectric constants obtained in GHz and THz regions are fitted into multiple Debye model to obtain various relaxation times. The ∼100 ps time scale obtained in the GHz frequency region is attributed to the rotational motion of the amino acids. In the THz region, we obtain ∼8 ps and ∼200 fs time scales which are related to the cooperative dynamics of H-bond network and partial rotation or sudden jump of t...
Journal of Molecular Liquids, 2016
Abstract In this contribution we present experimental evidences of the ultrafast (sub-ps to ps) c... more Abstract In this contribution we present experimental evidences of the ultrafast (sub-ps to ps) collective hydrogen bond dynamics of water in the extended hydration layers of alkali metal chlorides by using THz time domain spectroscopy (TTDS) in the terahertz frequency region (0.3–2.1 THz; 10–70 cm− 1). The behaviour of the frequency dependent absorption coefficient (α), refractive index (n) and the dielectric relaxation response time (τ), obtained by fitting both real and imaginary parts of the permittivity (e) using a triple Debye relaxation model are studied. The timescales obtained for bulk water are of the order of ~ 9 ps, 200 fs and 80 fs. The relaxation time constant in the presence of the salt shows an accelerated reorientation dynamics of the water dipoles, which, in turn renders an indirect support for the ‘water structure breaking’ ability of monovalent ions, the effect being ion specific. We have also studied the effect of these ions on the secondary structure as well as hydration dynamics around a model protein bovine serum albumin (BSA). It is found that the structure and hydration of the protein as well as the salt hydration suffer negligible perturbation in the presence of the alkali metal chlorides.
2015 40th International Conference on Infrared, Millimeter, and Terahertz waves (IRMMW-THz), 2015
We have addressed a very fundamental question, whether urea and guanidinium chloride (GdmCl) act ... more We have addressed a very fundamental question, whether urea and guanidinium chloride (GdmCl) act as water `structure breakers'. Our study using THz time domain spectroscopy (TTDS) confirm that both these molecules perturb the extended solvation layer around themselves which supports the strongly debated “water structure breaker” notion of urea and GdmCl during their protein denaturation process[1,2].
Chemistry - An Asian Journal, 2014
We report the ultrafast collective hydrogen-bond dynamics of water in the extended hydration laye... more We report the ultrafast collective hydrogen-bond dynamics of water in the extended hydration layer of urea by using terahertz time-domain spectroscopy in the frequency region of 0.3-2.0 THz. The complex dielectric function has been fitted using a Debye relaxation model, and the timescales obtained are in the order of approximately 9 ps and 200 fs for bulk water; this exhibits a considerable acceleration beyond the 4 M urea concentration and indicates a possible disruption in the collective hydrogen-bonded water-network structure, which, in turn, provides an indirect support for the water "structure-breaking" ability of urea. With 5 M urea in the presence of different concentrations of trimethylamine-N-oxide (TMAO), it was found that these parameters essentially follow the trend observed for TMAO itself, which signifies that any possible disruption of the water structure by urea is outdone by the strong hydrogen-bonding ability of TMAO, which explains its ability to revive urea-denatured proteins to their respective native states.
Phys. Chem. Chem. Phys., 2014
The remarkable ability of guanidinium chloride (GdmCl) to denature proteins is a well studied yet... more The remarkable ability of guanidinium chloride (GdmCl) to denature proteins is a well studied yet controversial phenomenon; the exact molecular mechanism is still debatable, especially the role of hydration dynamics, which has been paid less attention. In the present contribution, we have addressed the issue of whether the collective hydrogen bond dynamics of water gets perturbed in the presence of GdmCl and its possible impact on the denaturation of a globular protein human serum albumin (HSA), using terahertz (THz) time domain spectroscopy (TTDS) in the frequency range of 0.3-2.0 THz. The collective hydrogen bond dynamics is determined by fitting the obtained complex dielectric response in a multiple Debye relaxation model. To compare the results, the studies were extended to two more salts: tetramethylguanidinium chloride (TMGdmCl) and sodium chloride (NaCl). It was concluded that the change in hydration dynamics plays a definite role in the protein denaturation process.
Biochimie, 2014
In the present study we have investigated the thermal stability of the globular transport protein... more In the present study we have investigated the thermal stability of the globular transport protein human serum albumin (HSA), in the presence of two small chain polyethylene glycols (namely PEG 200 and PEG 400). Both near- and far-UV circular dichroism (CD) study reveal that addition of PEG moderately increases the α-helical content of the protein without abruptly changing its tertiary structure. The hydration structure at the protein surface experiences a notable change at 30% PEG (v/v) concentration as evidenced from compressibility and dynamic light scattering (DLS) measurements. Thermal denaturation of HSA in the presence of PEG has been studied by CD and fluorescence spectroscopy using the intrinsic fluorophore tryptophan and it has been found that addition of PEG makes the protein more prone towards unfolding, which is in contrary to what has been observed in case of larger molecular weight polymers. The energetics of the thermal unfolding process has been obtained using differential scanning calorimetry (DSC) measurements. Our study concludes that both the indirect excluded volume principle as well as interaction of the polymer at the protein surface is responsible for the observed change of the unfolding process.
Applied Sciences
The solvation properties of liquid water originate from the transient network of hydrogen-bonded ... more 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.