Pannuru Venkatesu

University of Delhi, Old Delhi, NCT, India

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Publications (45)177.66 Total impact

  • Pannuru Venkatesu, Indrani Jha
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    ABSTRACT: The stupendous attention grabbed by ionic liquids (ILs) among various physical and chemical sciences has been attributed to their unique and designer nature. In the past few years, the role of ILs in protein folding/unfolding has been rapidly growing. In sight of the increasing importance of ILs, it is enviable to systematize the ion effects on protein properties such as structure stability, activity and enantioselectivity. Various studies available in the literature show ILs as a potential solvent media for many enzymatic reactions as well as in various protein folding/unfolding studies. Various reviews by many researchers focus on the synthesis, application and general properties of the ILs however, the review focussing the effect of various ILs on the activity, structure and stability of protein is still missing. Also, according to best of our knowledge there is no single review available throughout the literature which focuses the effect of same family of IL on different proteins. Therefore, the paramount need is to have a complete knowledge of the biomolecules particularly amino acids (AAs) and proteins in a particular IL family. The cynosure of the present perspective is to nose around the performance of a list of proteins and protein model compounds in presence of ammonium-based ILs. This perspective presents a survey of all the key developments from the available reports and also our past and present experience related to proteins and ammonium-based ILs. Additionally, we have tried to put the available information in chronological order in most of the cases. The use of ammonium family ILs as co- solvent for various proteins model compounds and proteins have been outlined. This perspective can act as barometer for reckoning the various advancements made in this field and also galvanize further cogitation of various untouched aspects of this research area.
    Physical Chemistry Chemical Physics 06/2015; DOI:10.1039/C5CP01735A · 4.20 Impact Factor
  • Indrani Jha, Awanish Kumar, Pannuru Venkatesu
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    ABSTRACT: Spectroscopic and Molecular Docking investigations were carried out to characterize the effect of imidazolium-based ionic liquids (ILs) with varying chain length of the cation on the thermal stability as well as spectroscopic behaviour of heme protein hemoglobin (Hb). The goal of this work is to investigate the role of concentration of ILs, the effect of alkyl chain length of the cation and the related Hofmeister series on the structure of Hb. To achieve this goal, a series of ILs possessing same Cl- anion and a set of cation [Cnmim]+ with increasing chain length such as 1-ethyl-3-methylimidazolium chloride ([Emim][Cl]), 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]), 1-hexyl-3-methylimidazolium chloride ([Hmim][Cl]) and 1-decyl-3-methylimidazolium chloride ([Dmim][Cl]) were used in this study. It was observed that the stability of the protein was concentration dependent as well as the hydrophobic interactions between [Cnmim]+ of ILs and the amino acid residues in the protein played major role in protein unfolding. As a consequence, the destabilization tendency of the ILs towards the Hb increases with increasing chain length of the cation of ILs. Additionally, the cations of the ILs obeyed the Hofmeister series when arranged in the order of providing stability to Hb structure.
    The Journal of Physical Chemistry B 06/2015; 119(26). DOI:10.1021/acs.jpcb.5b04660 · 3.30 Impact Factor
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    ABSTRACT: Here, circular dichroism (CD) spectroscopy, fluorescence spectroscopy, UV-Vis spectroscopy, SDS-PAGE, substrate SDS-PAGE, and molecular dynamics (MD) simulations techniques have been employed to understand the structural behavioral changes of trypsin (MW:19.72 kDa, source: digestive system of adult Indian major carp, catla C. catla) in the presence of various chemical environments. The stability of the trypsin can be increased by stabilizers, including trimethylamine N-oxide (TMAO), proline, and betaine, without affecting its native structure. Trypsin has shown the unusual high thermal stability in the presence of betaine. Further, these experimental results were confirmed by means of MD simulations. The present results explicitly elucidated that the behavior of co-solvent may vary depend upon the type of the protein.
    RSC Advances 05/2015; 5(54). DOI:10.1039/C5RA01302J · 3.84 Impact Factor
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    ABSTRACT: This review covers recent developments in the area of excess molar volumes for mixtures of {ILs (1) + H2O (2)} where ILs refers to ionic liquids involving cations: imidazolium, pyridinium, pyrrolidinium, piperidinium, morpholinium and ammonium groups; and anions: tetraborate, triflate, hydrogensulphate, methylsulphate, ethylsulphate, thiocyanate, dicyanamide, octanate, acetate, nitrate, chloride, bromide, and iodine. The excess molar volumes of aqueous ILs were found to cover a wide range of values for the different ILs (ranging from 1.7 cm(3) mol center dot 1 to 1.2 cm3 center dot mol(-1)). The excess molar volumes increased with increasing temperature for all systems studied in this review. The magnitude and in some cases the sign of the excess molar volumes for all the aqueous ILs mixtures, apart from the ammonium ILs, were very dependent on temperature. This was particularly important in the dilute IL concentration region. It was found that the sign and magnitude of the excess molar volumes of aqueous ILs (for ILs with hydrophobic cations), was more dependent on the nature of the anion than on the cation.
    The Journal of Chemical Thermodynamics 03/2015; 82:34-46. DOI:10.1016/j.jct.2014.10.003 · 2.42 Impact Factor
  • Varadhi Govinda, Pannuru Venkatesu
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    ABSTRACT: The solubility and stability of biomolecules may be influenced by the addition of cosolvents. Ionic liquids (ILs) have emerged as novel cosolvents for widespread applications in biotechnology and industrial processes. In the present study, we report the solubilities and apparent transfer free energy (ΔGtr′) values for zwitterions containing glycine peptides (GPs) such as glycine (Gly), diglycine (Gly2), triglycine (Gly3), tetraglycine (Gly4), and cyclicglycylglycine (c(GG)) from water to aqueous solutions of imidazolium-based ILs at 25 °C and atmospheric pressure. ILs used here have different anions such as chloride (Cl–), bromide(Br–), hydrogen sulfate (HSO4–), acetate (CH3COO–), and thiocyanate (SCN–) and a common 1-butyl-3-methylimidazolium cation [Bmim]+. The ΔGtr′ values of GPs from water to aqueous IL solutions have been obtained from the solubilities, which are determined from density (ρ) measurements as a function of IL concentration at 25 °C. Further, we have calculated the salting constant (k) from the Setschenow equation, and the values have been analyzed with salting-out/salting-in effects. The experimental ΔGtr′ data allowed the calculation of the transfer free energy contributions (Δgtr′)of the peptide backbone unit (−CH2C═ONH−) from water to aqueous ILs. The effects of anions of ILs on GPs have been analyzed through solubilities, stabilities, and ΔGtr′ values to obtain a usual understanding of the Hofmeister series. The results are discussed in terms of solute–solute and solute–solvent interactions in the aqueous IL solution.
    Industrial & Engineering Chemistry Research 12/2014; 53(50):141205090758007. DOI:10.1021/ie503736g · 2.24 Impact Factor
  • Awanish Kumar, Pannuru Venkatesu
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    ABSTRACT: To reveal the impact of ionic liquids (ILs) on the stability of proteins, a series of ILs possessing same 1-butyl-3-methylimidazolium cation [Bmim](+) with a set of Hofmeister anions such as SCN-, HSO4-, Cl-, Br-, CH3COO- and I- were used and their effects on the myoglobin (Mb) structure and stability were studied. For the sake of comparison and also to explore the extent of the stabilization behavior of ILs toward Mb stability, we have chosen a set of ionic salts (I-s) of a fixed sodium cation (Na+) with the same series of anions such as SCN-, SO4-2, Cl-, Br-, CH3COO- and I-. UV-vis, fluorescence and circular dichroism (CD) spectroscopic techniques were used in order to investigate the stability behavior of Mb in ionic species (I-s and ILs). The results reveal that both I-s and ILs had a negative influence on the stability of Mb. Apparently, the flexibility in the native structure of Mb gradually increases with the increase in the concentration of I-s and ILs at pH 7.0. Therefore, a sharp decrease in the transition temperature (T-m) of the native Mb is observed in the presence of I-s and ILs.
    PROCESS BIOCHEMISTRY 12/2014; 49(12). DOI:10.1016/j.procbio.2014.09.014 · 2.52 Impact Factor
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    Anjeeta Rani, Pannuru Venkatesu
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    ABSTRACT: In present study, an attempt is made to elucidate the effects of various naturally occurring osmolytes and denaturants on BM at pH 7.0. The effects of the varying concentrations of glycerol, sorbitol, sucrose, trehalose, urea and guanidinium chloride (GdnHCl) on structure, stability and activity of BM are explored by fluorescence spectroscopy, circular dichroism (CD), UV-vis spectroscopy and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Our experimental observations reveal that glycerol and sorbitol are acting as stabilizers at all concentrations while sucrose and trehalose are found to be destabilizers at lower concentrations, however, acted as stabilizers at higher concentrations. On the other hand, urea and GdnHCl are denaturants except at lower concentrations. There is a direct relationship between activity and conformational stability as the activity data are found to be in accordance with conformational stability parameters (ΔGu, Tm, ΔCp) and BM profile on SDS-PAGE. Copyright © 2014 Elsevier B.V. All rights reserved.
    International Journal of Biological Macromolecules 11/2014; 73. DOI:10.1016/j.ijbiomac.2014.10.068 · 3.10 Impact Factor
  • Pannuru Venkatesu, Awanish kumar, Anjeeta Rani
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    ABSTRACT: In this article, we have compared the anions of sodium salts (Is) and ionic liquids (ILs) with the stability and structure of α-chymotrypsin (CT), through fluorescence, thermal fluorescence analysis and circular dichroism (CD) spectroscopy. The experimental results revealed that the Hofmeister series of anions such as SCN‾, SO42ˉ, Cl‾, Br‾, CH3COO‾ and I‾ of Is destabilized the native structure of the CT. On the contrary, the anions such as CH3COO‾, Cl‾ and Br‾ of imidazolium-based IL with fixed cation such as 1-butyl-3-methylimidazolium, [Bmim]+ stabilized the native structure of the CT. The remaining anions of ILs such as SCN‾, HSO4‾, and I‾ acted as denaturing agents for the native structure of CT. Furthermore, molecular docking results show that the imidazolium-cation of the IL enters the sub-domains of the CT and interacts with the ionic residues of the CT, that is Ser217 close to Trp215. This interaction is in well agreement with the fluorescence quenching observed for CT in the presence of [Bmim]+. On the other hand, the destabilizing anion such as SO42ˉwas observed to be directly interacting with Ser195 in the active site of the CT. We have observed that the Hofmeister series effects of anions of either Is or ILs are entirely based on the interaction of the anions with its counterion, that is the cation, with solvent molecules, as well as with the protein surface. Evidently, these interactions vary with co-solvent system and the type of the protein. Hence, the stability of a biomolecule in the presence of the anions may or may not obey Hofmeister series.
    New Journal of Chemistry 11/2014; 39(2). DOI:10.1039/C4NJ01596G · 3.16 Impact Factor
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    Awanish Kumar, Pannuru Venkatesu, Mohamed Taha, Ming-Jer Lee
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    ABSTRACT: Amino acids (AAs) combine to form a three-dimensional protein structure and are of very much importance in understanding the biophysical properties of biomolecules. Basically, the nature and the arrangement of the AAs in a protein backbone is only responsible for the individual characteristics of the macromolecule. The AAs in a protein backbone are influenced by the solvent molecules hence, it is very important to have a clear idea on the solubility, stability, and thermodynamic properties of these AAs in various solvents and co-solvents. A basic level of quantifying protein-solvent interactions involve the use of transfer free energies, �ΔGtr from water to solvents. The values of �Gtr for side chains and peptide backbone quantify the thermodynamic consequences of solvating a protein species in a co-solvent solution relative to pure water. Based on the transfer model and experimental Δ�Gtr for these AAs, it has been proposed that these cosolvents exert their effect on protein stability primarily via the protein backbone. The Δ�Gtr of AAs from water to another solvent system will be either favorable or unfavorable. By definition, an unfavorable transfer free energy, Δ�Gtr > 0, means that the protein becomes solvophobic on transfer to a solvent, whereas a favorable transfer free energy, Δ�Gtr < 0, represents that the protein becomes solvophilic on transfer to a solvent. The sign and magnitude of the measured Δ�Gtr quantifies the protein response to changes in solvent quality. Therefore, this review will provide the basis of a universal mechanism for co-solvent-mediated (that includes the new novel biocompatible ionic liquids (ILs)) protein stabilization and destabilization as the protein backbone is shared by all proteins, regardless of side chain sequence.
    07/2014; 1(2):125-140 (16). DOI:10.2174/2212711901666131224222431
  • Awanish Kumar, Anjeeta Rani, Pannuru Venkatesu, Anil Kumar
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    ABSTRACT: Significant non-reversible two-state denaturation was observed for proteins such as myoglobin (Mb) and α-chymotrypsin (CT) with decreasing temperature in the presence of 1-butyl-3-methylimidazolium-based ([C4mim](+)X(-)) ionic liquids (ILs) with various anions (X(-)). Interestingly, for the first time, ILs having acetate and bromide anions were proven to counteract the cold-induced unfolding of proteins.
    Physical Chemistry Chemical Physics 06/2014; 16(30). DOI:10.1039/c4cp01001a · 4.20 Impact Factor
  • Pankaj Attri, Indrani Jha, Eun Ha Choi, Pannuru Venkatesu
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    ABSTRACT: Protein stability in ionic solution depends on the delicate balance between protein-ion and ion-ion interactions. To address the ion specific effects on the protein, we have examined the stability of myoglobin (Mb) in the presence of buffer and ammonium-based ionic liquids (ILs) (50% (v/v)). Here, fluorescence and circular dichroism (CD) spectroscopy experiments are used to study the influence of ILs on structure and stability of Mb. Our experimental results reveal that more viscous ILs (sulphate or phosphate ions) are stabilizers and therefore more biocompatible for Mb structure. Surprisingly, the less viscous ILs such as acetate anion based ILs are destabilizers for the native structure of Mb. Our results explicitly elucidate that anion variation has significant influence on Mb stability efficiency than cation variation. This study provides insight into anion effects on protein stability and explains that the intrasolvent interactions can be leveraged to enhance the stability.
    International Journal of Biological Macromolecules 05/2014; 69. DOI:10.1016/j.ijbiomac.2014.05.032 · 3.10 Impact Factor
  • Reddicherla Umapathia, Pankaj Attri, Pannuru Venkatesu
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    ABSTRACT: Experimental densities (ρ), ultrasonic sound velocities (u), viscosities () and refractive indices (nD) of binary mixtures of ammonium-based ionic liquids (ILs) such as diethylammonium acetate (DEAA) [(CH3CH2)2NH][CH3COO], triethylammonium acetate (TEAA) [(CH3CH2)3NH][CH3COO], diethylammonium hydrogen sulfate (DEAS) [(CH3CH2)2NH][HSO4], triethylammonium hydrogen sulfate (TEAS) [(CH3CH2)3NH][HSO4], trimethylammonium acetate (TMAA) [(CH3)3NH][CH3COO] and trimethylammonium hydrogen sulfate (TMAS) [(CH3)3NH][HSO4] with water are reported over the wide composition range at 25 0C under atmospheric pressure. The excess molar volumes (VE), deviation in isentropic compressibilities (Δs), deviation in viscosities (Δ) and deviation in refractive indices (ΔnD) are calculated from experimental values and are correlated by Redlich-Kister polynomial equations. The VE and Δs values for the aforesaid systems are negative over the entire composition range while the Δ and ΔnD values are positive under the same experimental conditions. The intermolecular interactions and structural effects were analyzed on the basis of measured and derived properties. A qualitative analysis of the results is discussed in terms of the ion-dipole, ion-pair interactions and hydrogen bonding between ILs and water. Furthermore, the hydrogen bonding features between ILs with water were analyzed by using a molecular modeling program with the help of HyperChem7.
    The Journal of Physical Chemistry B 05/2014; 118(22). DOI:10.1021/jp502400z · 3.30 Impact Factor
  • Indrani Jha, Pankaj Attri, Pannuru Venkatesu
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    ABSTRACT: The nature of solvent-biomolecule interactions is generally weak and non-specific. The addition of ionic liquids (ILs), which have emerged as a new class of solvents, strengthen the stability of some proteins whereas the same ILs weaken the stability of some other proteins. Although ILs are commonly used for the stabilization of biomolecules, the bimolecular interactions of their stabilization-destabilization is still an active subject of considerable interest and studies on this topic have been limited. To reveal the impact of ILs on the stability of proteins, a series of protic ILs possessing a tetra-alkyl ammonium cation [R4N](+) with a hydroxide [OH](-) anion were synthesized. In this study, we report the structural stability of heme proteins such as myoglobin (Mb) and hemoglobin (Hb) in a series of ammonium-based ILs such as tetramethyl ammonium hydroxide [(CH3)4N](+)[OH](-) (TMAH), tetraethyl ammonium hydroxide [(C2H5)4N](+)[OH](-) (TEAH), tetrapropyl ammonium hydroxide [(C3H7)4N](+)[OH](-) (TPAH) and tetrabutyl ammonium hydroxide [(C4H9)4N](+)[OH](-) (TBAH) by fluorescence and circular dichroism (CD) spectroscopic studies. Our experimental results reveal that less viscous ILs carrying smaller alkyl chain such as TMAH are strong destabilizers of the heme proteins as compared to the ILs carrying bulkier alkyl chains which are more viscous ILs, such as TBAH. Therefore, our results demonstrate that the addition of these ILs to the heme proteins decreases their thermal stability allowing the protein to be in an unfolded state at lower temperatures. Further, we describe the molecular-structural interaction of the heme proteins with the ILs (molecule like a ligand) by the PatchDocking method.
    Physical Chemistry Chemical Physics 02/2014; 16(12). DOI:10.1039/c3cp54398f · 4.20 Impact Factor
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    ABSTRACT: In this work, we have explored the thermophysical properties of tetraalkylammonium hydroxide ionic liquids (ILs) such as tetrapropylammonium hydroxide (TPAH) and tetrabutylammonium hydroxide (TBAH) with isomers of butanol (1-butanol, 2-butanol and 2-methyl-2-propanol) within the temperature range 293.15-313.15 K, with interval of 5 K and over the varied concentration range of ILs. The molecular interactions between ILs and butanol isomers are essential for understanding the function of ILs in related measures and excess functions are sensitive probe for the molecular interactions. Therefore, we calculated the excess molar volume (V(E) ) and the deviation in isentropic compressibility (Δκs ) using the experimental values such as densities (ρ) and ultrasonic sound velocities (u) that are measured over the whole compositions range at five different temperatures (293.15, 298.15, 303.15, 308.15 and 313.15 K) and atmospheric pressure. These excess functions were adequately correlated by using the Redlich-Kister polynomial equation. It was observed that for all studied systems, the V(E) and Δκs values are negative for the whole composition range at 293.15 K. And, the excess function follows the sequence: 2-butanol>1-butanol>2-methyl-2-propanol, which reveals that (primary or secondary or tertiary) position of hydroxyl group influence the magnitude of interactions with ILs. The negative values of excess functions are contributions from the ion-dipole interaction, hydrogen bonding and packing efficiency between the ILs and butanol isomers. Hence, the position of hydroxyl group plays an important role in the interactions with ILs. The hydrogen bonding features between ILs and alcohols were analysed using molecular modelling program by using HyperChem 7.
    PLoS ONE 01/2014; 9(1):e86530. DOI:10.1371/journal.pone.0086530 · 3.53 Impact Factor
  • Awanish Kumar, Pannuru Venkatesu
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    ABSTRACT: Fibril or aggregation formation in insulin (In) has been a subject of severe biomedical and biotechnological complications. The search for a novel solvent/co-solvent that can provide long term stabilization for In monomeric form has not been completed yet. In this quest, for the first time we have successfully explored the stability of the monomeric form of In in the presence of ammonium-based ionic liquids (ILs) [A. Kumar and P. Venkatesu, RSC Adv., 2013, 3, 362-367]. Further, in continuation, in this study, we have established the stability of In in the presence of imidazolium-based ILs with different anions. These anions represent the Hofmeister series of anions of ILs. In this regard, we have carried out UV-vis, fluorescence, circular dichroism spectral analysis and dynamic light scattering (DLS) measurements of In in various concentrations of these ILs. Our experimental findings reveal that Br− and Cl− ILs stabilized the native state while the rest of the ILs with anions such as SCN−, HSO4−, CH3COO− and I− were denaturants for the In. Further, the results show that IL-In interactions are difficult to classify on the basis of the Hofmeister series, as bromide containing ILs show more stabilizing properties on the In structure. The disulfide bonds were almost intact in the presence of Br− IL as compared to Cl− and the rest of the Hofmeister anions. On the other hand, a strongly hydrated kosmotropic anion like HSO4− interacts with the structure of In, leading it towards complete denaturation of the In structure. Additionally, all ILs failed to protect the native state of In with increasing temperature.
    RSC Advances 01/2014; 4(9):4487. DOI:10.1039/c3ra44477e · 3.84 Impact Factor
  • Awanish Kumar, Pannuru Venkatesu
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    ABSTRACT: Understanding the behavior of Hofmeister anions of ionic liquids (ILs) on protein stability helps to shed light on how the anions interact with proteins in aqueous solution and is a long standing object for chemistry and biochemistry. Ions effects play a major role in understanding the physicochemical and biological phenomenon that undertakes the protein folding/unfolding and refolding process. Despite the generality of these effects, our understanding of ions at the molecular-level is still limited. This review offers a tour through past successful investigations and presents a challenge in current research in the field to reassess the possibilities of ions and to apply new strategies. This review highlights on the stability behavior of the proteins and also comparisons of our past research work in the Hofmeister series of ILs. Furthermore, we specifically focus on the critical discussion on the recent findings with existing results and their implications, along with our understanding of the Hofmeister series of anions of ILs on biomolecular stability. A detailed examination of the difference between selective proteins can provide a better understanding of the molecular mechanism of protein folding/unfolding in the presence of the Hofmeister series of ions of ILs.
    International journal of biological macromolecules 11/2013; 63. DOI:10.1016/j.ijbiomac.2013.10.031 · 3.10 Impact Factor
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    ABSTRACT: In recent years, ionic liquids (ILs) represent a new class of biocompatible co-solvents for biomolecules. In this work, we report the apparent transfer free energies (ΔG'tr) for six amino acids (AA) from water to aqueous solutions of six ammonium based ILs (diethylammonium acetate (DEAA), diethylammonium sulfate (DEAS), triethyl ammonium acetate (TEAA), triethylammonium sulfate (TEAS), triethylammonium dihydrogen phosphate (TEAP), and trimethylammonium acetate (TMAA)) through solubility measurements, as a function of IL concentration at 298.15 K under atmospheric pressure. Salting-out effect was found for AA in aqueous IL solutions with increasing IL concentrations. In addition, we observed positive values of ΔG'tr for AA from water to ILs, indicating that the interactions between ILs and AA are unfavorable. From the obtained results, we found that the selected ammonium based ILs act as stabilizers for the structure of AA.
    Protein and Peptide Letters 07/2013; 21(1). DOI:10.2174/09298665113209990071 · 1.74 Impact Factor
  • Pankaj Attri, Pannuru Venkatesu
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    ABSTRACT: Ammonium based ionic liquids (ILs) are biocompatible co-solvents that stabilize the native state of proteins. Experimentally, we have explored the stability of α-chymotrypsin (CT) in the presence of nine ILs, i.e., diethylammonium acetate (DEAA), diethylammonium hydrogen sulfate (DEAS), diethylammonium dihydrogen phosphate (DEAP), triethylammonium acetate (TEAA), triethylammonium hydrogen sulfate (TEAS), triethylammonium dihydrogen phosphate (TEAP), trimethylammonium acetate (TMAA), trimethylammonium hydrogen sulfate (TMAS), trimethylammonium dihydrogen phosphate (TMAP). Thermodynamic folding properties such as transition temperature (Tm), Gibbs free energy change of unfolding (ΔGU), enthalpy change (ΔH) and heat capacity change (ΔCp) of CT in ILs are obtained by fluorescence spectra analysis. Fluorescence and circular dichroism (CD) spectroscopy experiments were performed to probe CT stabilization and structural changes in the presence of ILs. Our experimental results suggest that the ILs act as stabilizers for the CT structure and the stability of CT depends on the structural arrangement of the ions of ILs. Our experimental results reveal that ILs (DEAA, DEAS and DEAP) having more hydrophobic ammonium cations [DEA+] are weak stabilizers for CT, while trimethyl ammonium cations [TMA+] ILs having small alkyl chain length such as TMAA, TMAS and TMAP are strong stabilizers and therefore more biocompatible for the native structure of CT.
    PROCESS BIOCHEMISTRY 03/2013; 48(3):462–470. DOI:10.1016/j.procbio.2013.02.006 · 2.52 Impact Factor
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    ABSTRACT: In this article, we investigate the effect of guanidinium hydrochloride (GdnHCl) on the phase transition temperature of poly (N-isopropylacrylamide) (PNIPAM) in aqueous solution with the aid of fluorescence spectroscopy, viscosity (η), and dynamic light scattering (DLS) measurements. Temperature dependent fluorescence intensity measurements have been employed successfully to determine the conformational change of PNIPAM through evaluating the Gibbs free energy changes. Additionally, direct hydrogen bonding formation between GdnHCl and PNIPAM has been confirmed by Fourier transform infrared (FTIR) spectroscopy measurements at various concentrations of GdnHCl. The intermolecular interactions were also studied in terms of amide I band analysis, which reveals the interruption of hydrated coil conformation of PNIPAM. The degree of destabilization of PNIPAM progressively increases with increasing concentration of the denaturant.
    Polymer 01/2013; 54(2):791–797. DOI:10.1016/j.polymer.2012.12.032 · 3.77 Impact Factor
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    ABSTRACT: In this article, we have reported the solubilities, apparent transfer free energies (ΔG′tr) and UV-visible absorption measurements of glycine peptides (GPs), such as glycine (Gly), diglycine (Gly2), and cyclic glycylglycine (c(GG)) in aqueous ionic liquids (ILs), bearing sulfate and phosphate anions with ammonium cation, at T = 298.15 K. Values of solubility were obtained from density (ρ) measurements of GPs in water and in aqueous ILs. The ammonium ILs such as diethylammonium hydrogen sulfate (DEAS) [(CH3CH2)2NH][HSO4], triethylammonium hydrogen sulfate (TEAS) [(CH3CH2)3NH][HSO4], and triethylammonium dihydrogen phosphate (TEAP) [(CH3CH2)3NH][H2PO4] have been used in the present study. We observed the positive values of ΔG′tr for Gly, Gly2, and c(GG) from water to ILs. These results reveal that the unfavourable interactions are dominated between ILs and the GPs. This indicates that the ammonium based ILs stabilize the GP structure. Further, we have used the ΔG′tr results to evaluate the transfer free energies (Δg′tr) contribution of the peptide backbone unit, also known as glycyl residue, (–CH2CONH–) as function of ILs concentration. Our results suggest that all the investigated ammonium ILs are compatible with GPs and act as stabilizers for GPs structure through exclusion of ILs from GPs’ surface. Furthermore, UV-vis spectrophotometer measurements are used as evidence for the stability of GPs in aqueous ILs at T = 298.15 K.
    The Journal of Chemical Thermodynamics 01/2013; 56:21–31. DOI:10.1016/j.jct.2012.07.009 · 2.42 Impact Factor