Polymer and Biophysics Laboratory

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Polymer and Biophysics Laboratory

science, India
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Rawat K.,Polymer and Biophysics Laboratory | Rawat K.,Jawaharlal Nehru University | Pathak J.,Polymer and Biophysics Laboratory | Bohidar H.B.,Polymer and Biophysics Laboratory | Bohidar H.B.,Jawaharlal Nehru University
Soft Matter | Year: 2014

We present a systematic investigation of the effect of solvent hydrophobicity (alkyl chain length) on the gelation kinetics and the phase states of the polypeptide gelatin in imidazolium based ionic liquid (IL) solutions. We have observed that IL concentration and hydrophobicity had dramatic influences on the thermal and viscoelastic properties of gelatin ionogels. Gelation concentration cg was observed to increase from 1.75 to 2.75% (w/v) while the gelation temperature Tg was found to decrease from 32 to 26 °C with increase in 1-octyl-3-methyl imidazolium chloride [C8mim][Cl] (most hydrophobic) concentration as compared to the case of the least hydrophobic IL 1-ethyl-3-methyl imidazolium chloride [C2mim][Cl], where the corresponding changes were marginal. Gradual softening of the gel with increase in hydrophobicity and concentration of IL was clearly noticed. The viscosity of the gelling sol diverged as ηr ∼ ε-k1 and storage modulus of gel grew as G0 ∼ εt1 where ε1 = 1 - c/cg with the exponents having values k = 1.2-1.8 ± 0.08 and t = 1.2-1.6 ± 0.08, close to but not exactly the same as predicted by the percolation model: k = 0.7-1.3 and t = 1.9. Thus, the gelation kinetics involved in the growth of interconnected networks could be conceived to follow an anomalous percolation model. The temporal growth of self-assembled structures followed a power law dependence given by: ηr ∼ ε-α2 and Rh ∼ ε-β2 where, t > tg (α = 1-2.9 ± 0.08 and β = 1-2.7 ± 0.08). The low frequency storage modulus G0, gelation temperature Tg, gelation concentration cg and gelation time tg adequately defined the sol-gel phase diagram. Results clearly revealed that by adjusting the hydrophobic chain length and concentration of IL it was possible to customize both thermal and mechanical properties of these ionogels to match specific application requirements. © 2014 The Royal Society of Chemistry.


Rawat K.,Polymer and Biophysics Laboratory | Pathak J.,Polymer and Biophysics Laboratory | Bohidar H.B.,Polymer and Biophysics Laboratory | Bohidar H.B.,Jawaharlal Nehru University
Physical Chemistry Chemical Physics | Year: 2013

The effect of persistence length on the intermolecular binding of DNA (200 bp, persistence length lp = 50 nm, polyanion) with three proteins, gelatin B (GB) (lp = 2 nm, polyampholyte chain), bovine serum albumin (BSA) (lp = 7 nm, polyampholyte colloid), gelatin A (GA) (l p = 10 nm, polyampholyte chain), and a polysaccharide chitosan (lp = 17 nm, polycation), was investigated in aqueous and in 1-methyl-3-octyl imidazolium chloride ionic liquid ([C8mim][Cl]) solutions. In DNA-GB and DNA-BSA solutions complexation primarily arises from surface patch binding whereas DNA-chitosan and DNA-GA binding was predominantly governed by electrostatic forces. These occurred at well defined pH values: (i) at pH c associative interactions ensued and soluble complexes were formed, (ii) at pHΦ soluble complexes coalesced to give rise to liquid-liquid phase separation (coacervation) and (iii) at pHprep formation of large insoluble complexes drove the solution towards liquid-solid phase separation. A universal phase diagram encapsulating the aforesaid interactions can be made using the persistence length of polyion as an independent variable. DNA formed overcharged intermolecular complexes with all these polyions when the polyion concentration was more than the concentration required to produce charge neutralized complexes (disproportionate binding). In IL solutions maximum binding occurred when 0.075 < [IL] < 0.10% (w/v) and the effect of overcharging was substantially screened. The extent of overcharge was a monotonous increasing function of the polyion persistence length. Results clearly revealed that DNA-polyion binding was hierarchical in polyion concentration and persistence length. Overcharging of the DNA-polyion complex was found to be ubiquitous for the polyions used in the present study. © 2013 the Owner Societies.


Rawat K.,Polymer and Biophysics Laboratory | Bohidar H.B.,Polymer and Biophysics Laboratory | Bohidar H.B.,Jawaharlal Nehru University
International Journal of Biological Macromolecules | Year: 2015

At room temperature, ionic liquids (ILs) 1-alkyl-3-methyl imidazolium chloride (alkyl: ethyl, butyl, hexyl and octyl) are observed to exhibit aggregate dissociation behavior of native proteins. This is similar to the well known protein aggregation inhibitor and aggregate dissociation molecule heparin. Dynamic light scattering (DLS) experiments performed on three model proteins bovine serum albumin (BSA), β-lactoglobulin (β-Lg) and immunoglobulin (IgG) revealed that on addition of ILs the fractal aggregates of proteins (apparent maximum hydrodynamic radius Rmax and fractal dimension df=1.5±0.2) dissociated into oligomers (hydrodynamic radius Rh) following an exponential decay profile with time, Rh=Rmaxexp(-kat) The dissociation constant ka has been correlated to hydrophobicity index (H-index) of the protein concerned. Thus, if the combined contributions of dissociation constant and hydration effect on secondary structure are taken into account together, [C8mim][Cl] with BSA, [C2mim][Cl] with β-Lg and IgG, rank as the best aggregation reversal agent (ARA) amongst all other ionic liquid samples examined. The additional advantage of the used ILs over heparin is the release of mobile Cl- ions to the solution. This lead to the increased solution entropy, thereby, providing stability to the final dispersions. © 2014 Elsevier B.V.


PubMed | Polymer and Biophysics Laboratory
Type: Journal Article | Journal: Physical chemistry chemical physics : PCCP | Year: 2013

The effect of persistence length on the intermolecular binding of DNA (200 bp, persistence length l(p) = 50 nm, polyanion) with three proteins, gelatin B (GB) (l(p) = 2 nm, polyampholyte chain), bovine serum albumin (BSA) (l(p) = 7 nm, polyampholyte colloid), gelatin A (GA) (l(p) = 10 nm, polyampholyte chain), and a polysaccharide chitosan (l(p) = 17 nm, polycation), was investigated in aqueous and in 1-methyl-3-octyl imidazolium chloride ionic liquid ([C8mim][Cl]) solutions. In DNA-GB and DNA-BSA solutions complexation primarily arises from surface patch binding whereas DNA-chitosan and DNA-GA binding was predominantly governed by electrostatic forces. These occurred at well defined pH values: (i) at pHc associative interactions ensued and soluble complexes were formed, (ii) at pH soluble complexes coalesced to give rise to liquid-liquid phase separation (coacervation) and (iii) at pH(prep) formation of large insoluble complexes drove the solution towards liquid-solid phase separation. A universal phase diagram encapsulating the aforesaid interactions can be made using the persistence length of polyion as an independent variable. DNA formed overcharged intermolecular complexes with all these polyions when the polyion concentration was more than the concentration required to produce charge neutralized complexes (disproportionate binding). In IL solutions maximum binding occurred when 0.075 < [IL] < 0.10% (w/v) and the effect of overcharging was substantially screened. The extent of overcharge was a monotonous increasing function of the polyion persistence length. Results clearly revealed that DNA-polyion binding was hierarchical in polyion concentration and persistence length. Overcharging of the DNA-polyion complex was found to be ubiquitous for the polyions used in the present study.

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