Pannuru Venkatesu

University of Delhi, Old Delhi, NCT, India

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Publications (34)126.18 Total impact

  • 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; · 3.83 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;
  • 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; · 3.61 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; · 3.83 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. · 3.73 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.
    Current Biochemical Engineering. 01/2014; 1(2):125-140 (16).
  • 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; · 2.37 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; · 1.99 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.
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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.
  • Awanish Kumar, Pannuru Venkatesu
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    ABSTRACT: The self-aggregation and thermal instability of insulin (In) was considerably controlled in the presence of ammonium-based protic ionic liquids (PILs). The thermal stability of In in PILs was observed using fluorescence and absorption spectroscopy of the Tyr environment of the biomolecule. Additionally, from circular dichroism (CD) measurements, we observed the shift in the wavelength towards lower values in the presence of PILs, which indicates the formation of monomers of In, further evidently supported by dynamic light scattering (DLS) measurements. Surprisingly, it is the monomeric form of the In that exists in the active form. For the first time, ammonium-based PILs have been shown to be novel solvents for In, which prevent it from associating into an inactive form and also stabilizes In against thermal influence.
    RSC Advances 12/2012; 3(2):362-367. · 3.71 Impact Factor
  • Awanish Kumar, P. Madhusudhana Reddy, Pannuru Venkatesu
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    ABSTRACT: Interestingly, various behaviors of ionic liquids (ILs) having different cation chains with a common anion is observed in the coexistence curve of isobutyric acid–water (IBW). The critical region of IBW was found to increase in the presence of aliphatic chain 1-hexyl-3-methyl-imidazolium tetrafluoroborate [C6mim][BF4], (IL-1) whereas the critical region decreased in the presence of aromatic chain 1-benzyl-3-methylimidazolium tetrafluoroborate [Bnmim][BF4], (IL-2). Adding 0.5–2.0 mg ml−1 of IL-1 or IL-2 to IBW caused the critical temperature (Tc) to decrease by 0.553–2.898 K (for IL-1) and to increase by 0.502–1.664 K (for IL-2). The critical exponent (β) increases with increasing the IL concentrations, which are fully renormalized critical exponents. Further, our dynamic light scattering (DLS) results for the binary critical solution of IBW indicate that there exists a fluctuation in the local density that contributes significantly to the fluctuations in the scattered intensity at Tc. The variations in fluctuations are found to be pronounced in the presence of IL as an impurity. The reason for this behavior may be the formation of large water clusters with the neighboring molecules of ILs at Tc. This indicates that the IL entangles with the both coexisting phases, thereby, the IL strongly interacts with the neighboring solvent molecules. In addition, we report the fluorescence spectroscopy data for the critical mixture of IBW and its mixture with ILs as impurities using Nile Red as a fluorescent probe. Noticeable transitions of the two phases were detected at Tc through fluorescence technique. The observed variations in the fluorescence intensities with temperature predict unambiguously the formation of the solvation structure at Tc for the pure critical mixture as well as in presence of ILs.
    New Journal of Chemistry 10/2012; 36(11):2266-2279. · 2.97 Impact Factor
  • T Vasantha, Pankaj Attri, Pannuru Venkatesu, R S Rama Devi
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    ABSTRACT: Protein folding/unfolding is a fascinating study in the presence of cosolvents, which protect/disrupt the native structure of protein, respectively. The structure and stability of proteins and their functional groups may be modulated by the addition of cosolvents. Ionic liquids (ILs) are finding a vast array of applications as novel cosolvents for a wide variety of biochemical processes that include protein folding. Here, the systematic and quantitative apparent transfer free energies (ΔG'(tr)) of protein model compounds from water to ILs through solubility measurements as a function of IL concentration at 25 °C have been exploited to quantify and interpret biomolecular interactions between model compounds of glycine peptides (GPs) with ammonium based ILs. The investigated aqueous systems consist of zwitterionic glycine peptides: glycine (Gly), diglycine (Gly(2)), triglycine (Gly(3)), tetraglycine (Gly(4)), and cyclic glycylglycine (c(GG)) in the presence of six ILs such as diethylammonium acetate (DEAA), diethylammonium hydrogen sulfate (DEAS), triethylammonium acetate (TEAA), triethylammonium hydrogen sulfate (TEAS), triethylammonium dihydrogen phosphate (TEAP), and trimethylammonium acetate (TMAA). We have observed positive values of ΔG'(tr) for GPs from water to ILs, indicating that interactions between ILs and GPs are unfavorable, which leads to stabilization of the structure of model protein compounds. Moreover, our experimental data ΔG'(tr) is used to obtain transfer free energies (Δg'(tr)) of the peptide backbone unit (or glycyl unit) (-CH(2)C═ONH-), which is the most numerous group in globular proteins, from water to IL solutions. To obtain the mechanism events of the ILs' role in enhancing the stability of the model compounds, we have further obtained m-values for GPs from solubility limits. These results explicitly elucidate that all alkyl ammonium ILs act as stabilizers for model compounds through the exclusion of ILs from model compounds of proteins and also reflect the effect of alkyl chain on the stability of protein model compounds.
    The Journal of Physical Chemistry B 09/2012; 116(39):11968-78. · 3.61 Impact Factor
  • Awanish Kumar, P. Madhusudhana Reddy, Pannuru Venkatesu
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    ABSTRACT: Upper critical solution temperature (UCST)-type phase behavior was observed in the critical mixture of water (W) and hydrophobic ionic liquid, 1-hexyl-3-methylimidazolium tetrafluoroborate (IL), by refractive index and fluorescence measurements. The phase separation temperature depends on the composition of IL as well as water. Furthermore, for the first time, the behavior of high molecular weight polymer polyacrylic acid, PAA (Mw = 450000 g mol−1), as an impurity in the UCST mixture was investigated by simultaneous refractive index (n) measurements for both the coexisting phases of ILW. The refractive index in each phase of ILW as well as three different PAA concentrations (C = 0.5, 1.0, and 1.5 mg cm−3) in the near critical composition of ILW have been measured at temperatures below the system's upper critical point. We observed that the polymer significantly affected on the critical region of ILW. The phase-transition region of coexisting phases of ILW significantly shifts down with an increase in the concentrations of PAA. The Tc values decreases linearly from 58.256 (free of PAA) to 55.168 °C (PAA in ILW) with increasing PAA concentrations in ILW. This indicates that the polymer chain entangles with the coexisting phases, thereby the polymer monomers strongly interact with neighbor solvent particles. At temperatures T close enough to Tc, the critical exponent (β) values were obtained from the measured n values of both the coexisting liquid phases and was found to increase from 0.332 to 0.379, when the PAA concentration changes from 0.5 to 1.5 mg cm−3. The obtained 3D Ising values are modified in the presence of PAA and obviously belong to the renormalized class. These values are higher than that of 0.326 ± 0.002 of pure ILW, which is compatible with the 3D Ising value β = 0.325. In addition, we have performed the fluorescence measurement for the determination of Tc for ILW and in the presence of PAA as an impurity. The observed increase in the fluorescence intensities with temperature predicts unambiguously the formation of the solvation structure at Tc for the critical mixture in presence of the polymer.
    RSC Advances 07/2012; 2(17):6939-6947. · 3.71 Impact Factor
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    ABSTRACT: Trimethylamine N-oxide (TMAO) is a compatible or protective osmolyte that stabilizes the protein native structure through non-bonding mechanism between TMAO and hydration surface of protein. However, we have shown here first time the direct binding mechanism for naturally occurring osmolyte TMAO with hydration structure of poly(N-isopropylacrylamide) (PNIPAM), an isomer of polyleucine, and subsequent aggregation of PNIPAM. The influence of TMAO on lower critical solution temperature (LCST) of PNIPAM was investigated as a function of TMAO concentration at different temperatures by fluorescence spectroscopy, viscosity (η), multi angle dynamic light scattering, zeta potential, and Fourier transform infrared (FTIR) spectroscopy measurements. To address some of the basis for further analysis of FTIR spectra of PNIPAM, we have also measured FTIR spectra for the monomer of N-isopropylacrylamide (NIPAM) in deuterium oxide (D(2)O) as a function of TMAO concentration. Our experimental results purportedly elucidate that the LCST values decrease with increasing TMAO concentration, which is mainly contributing to the direct hydrogen bonding of TMAO with the water molecules that are bound to the amide (-CONH) functional groups of the PNIPAM. We believed that the present work may act as a ladder to reach the heights of understanding of molecular mechanism between TMAO and macromolecule.
    The Journal of Chemical Physics 06/2012; 136(23):234904. · 3.12 Impact Factor
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    ABSTRACT: Enzymes exhibit a substantial degree of structural variability in the folded state and they are very sensitive to environmental changes. In order to investigate the effect of environmental changes on enzymes, we have studied the effect of cold atmospheric pressure plasma jets (APPJ) on a-chymotrypsin (CT). The APPJ consists of microdischarges, which are ejected from porous alumina through a 1 mm hole, reaching the CT samples and resulting in changes in the CT conformation. Furthermore, to gain insight into the contribution of the co-solvents, such as osmolytes (1 M trimethylamine N-oxide (TMAO), 1 M proline, 1 M betaine, 1 M sorbitol and 1 M glycerol) and the denaturant (1 M urea), on CT against the APPJ action, we monitored the associated structural changes in a-chymotrypsin (CT) using circular dichroism (CD), fluorescence and NMR measurements. Contrasting results are obtained from experimental data in the case of TMAO and urea, which allow us to infer that TMAO is able to attenuate strongly the deleterious action of APPJ on CT. Furthermore, the deleterious action of urea is enhanced in the presence of APPJ. The alterations in the secondary structure of this b/b protein, as quantified by the CD spectra, show reasonable enhancement for the b-strands in the presence of osmolytes as compared to buffer, even after the treatment with APPJ.
    RSC Advances 05/2012; 2(2012, 2, 7146–7155):7146-7155. · 3.71 Impact Factor
  • Pankaj Attri, Pannuru Venkatesu
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    ABSTRACT: We report the synthesis of a series of ionic liquids (ILs) from various ions having different kosmotropicity including dihydrogen phosphate (H(2)PO(4)(-)), hydrogen sulfate (HSO(4)(-)) and acetate (CH(3)COO(-)) as anions and chaotropic cation such as trialkylammonium cation. To characterize the biomolecular interactions of ILs with protein, we have explored the stability of succinylated Con A (S Con A) in the presence of these aqueous ILs, which are varied combinations of kosmotropic anion with chaotropic cation such as triethylammonium dihydrogen phosphate [(CH(3)CH(2))(3)NH][H(2)PO(4)] (TEAP), trimethylammonium acetate [(CH(3))(3)NH][CH(3)COO] (TMAA), trimethylammonium dihydrogen phosphate [(CH(3))(3)NH][H(2)PO(4)] (TMAP) and trimethylammonium hydrogen sulfate [(CH(3))(3)NH][HSO(4)] (TMAS). Circular dichroism (CD) and fluorescence experiments have been used to characterize the stability of S Con A by ILs. Our data distinctly demonstrate that the long alkyl chain IL TEAP is a strong stabilizer for S Con A. Further, our experimental results reveal that TEAP is an effective refolding enhancer for S Con A from a thermally denatured protein structure.
    International journal of biological macromolecules 04/2012; 51(1-2):119-28. · 2.37 Impact Factor
  • Awanish Kumar, Pannuru Venkatesu
    Chemical Reviews 04/2012; 112(7):4283-307. · 41.30 Impact Factor
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    ABSTRACT: In order to study the wide scope of structural information of biomolecules in the presence of biocompatible cold atmospheric pressure plasma jets (CAPJ), we used circular dichroism (CD) and fluorescence experiments. Biomolecules are very sensitive and are highly complex systems, exhibit-ing a substantial degree of structural variability in their folded state. In the present investigation, we compared the compatiblity of α-chymotrypsin (CT) in the presence of biocompatible CAPJ. Using circular dichroism (CD) and fluorescence experiments, we describe the associated structural changes in CT after a 5 min treatment with CAPJ. The modifications in the secondary structure of this β/β protein were quantified by using the CD spectra. A reasonable decrease was observed for β-strands after treatment with CAPJ as compared to buffer, which contributes to its deterioration power. The implications of our results from studies delineating the effects of CAPJ on enzyme solutions are discussed.
    Journal- Korean Physical Society 04/2012; 60(6):959-964. · 0.51 Impact Factor
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    ABSTRACT: Mixing of ionic liquids (ILs) with molecular solvent can expand the range of structural properties and the scope of molecular interactions between the molecules of the solvents. Exploiting of these phenomena essentially require a basic fundamental understanding of mixing behavior of ILs with molecular solvents. In this context, a series of protic ILs possessing tetra-alkyl ammonium cation [R(4)N](+) with commonly used anion hydroxide [OH](-) were synthesized and characterized by temperature dependent thermophysical properties. The ILs [R(4)N](+)[OH](-) are varying only in the length of alkyl chain (R is methyl, ethyl, propyl, or butyl) of tetra-alkyl ammonium on the cationic part. The ILs used for the present study included tetramethyl ammonium hydroxide [(CH(3))(4)N](+)[OH](-) (TMAH), tetraethyl ammonium hydroxide [(C(2)H(5))(4)N](+)[OH](-) (TEAH), tetrapropyl ammonium hydroxide [(C(3)H(7))(4)N](+)[OH](-) (TPAH) and tetrabutyl ammonium hydroxide [(C(4)H(9))(4)N](+)[OH](-) (TBAH). The alkyl chain length effect has been analyzed by precise measurements such as densities (ρ), ultrasonic sound velocity (u), and viscosity (η) of these ILs with polar solvent, N-methyl-2-pyrrolidone (NMP), over the full composition range as a function of temperature. The excess molar volume (V(E)), the deviation in isentropic compressibility (Δκ(s)) and deviation in viscosity (Δη) were predicted using these properties as a function of the concentration of ILs. Redlich-Kister polynomial was used to correlate the results. A qualitative analysis of the results is discussed in terms of the ion-dipole, ion-pair interactions, and hydrogen bonding between ILs and NMP molecules. Later, the hydrogen bonding features between ILs and NMP were also analyzed using a molecular modeling program with the help of HyperChem 7.
    The Journal of Physical Chemistry B 03/2012; 116(15):4561-74. · 3.61 Impact Factor