Time filter

Source Type

Wedberg R.,Technical University of Denmark | Wedberg R.,Swedish Defence Research Agency | Abildskov J.,Technical University of Denmark | Peters G.H.,Technical University of Denmark | Peters G.H.,Center for Biomembrane Physics
Journal of Physical Chemistry B | Year: 2012

In nonaqueous enzymology, control of enzyme hydration is commonly approached by fixing the thermodynamic water activity of the medium. In this work, we present a strategy for evaluating the water activity in molecular dynamics simulations of proteins in water/organic solvent mixtures. The method relies on determining the water content of the bulk phase and uses a combination of Kirkwood-Buff theory and free energy calculations to determine corresponding activity coefficients. We apply the method in a molecular dynamics study of Candida antarctica lipase B in pure water and the organic solvents methanol, tert-butyl alcohol, methyl tert-butyl ether, and hexane, each mixture at five different water activities. It is shown that similar water activity yields similar enzyme hydration in the different solvents. However, both solvent and water activity are shown to have profound effects on enzyme structure and flexibility. © 2012 American Chemical Society.

Wang Y.,Technical University of Denmark | Teraoka I.,New York University | Hansen F.Y.,Technical University of Denmark | Peters G.H.,Technical University of Denmark | And 2 more authors.
Macromolecules | Year: 2011

We present a general method for calculating the mean span dimension of various branched and ringed polymers under the assumption of Gaussian chain statistics. The method allows a routine construction of an integral expression of the mean span dimension based on three base functions, determined for a connector, an arm and a loop, respectively. Applications of our method are shown to a variety of polymer architectures including star, two-branch-point, comb and various cyclic chains (eight-shaped, θ-shaped and several semicyclic chains). Comparing the mean span dimension with other commonly used molecular size parameters - the radius of gyration and the hydrodynamic radius, it is found that both the mean span dimension and the hydrodynamic radius shrink less than does the radius of gyration when comparing averaged sizes of a branched chain with its linear analogue. Finally, possible use of the mean span dimension in size exclusion chromatography (SEC) experiments is discussed. © 2010 American Chemical Society.

Kalugin O.N.,University of Kharkiv | Voroshylova I.V.,University of Kharkiv | Riabchunova A.V.,University of Kharkiv | Lukinova E.V.,University of Kharkiv | Chaban V.V.,Center for Biomembrane Physics
Electrochimica Acta | Year: 2013

Although a few groups have recently published transport properties for extensive sets of imidazoliumand pyridinium-based room-temperature ionic liquids (RTILs) and their solutions, there are still no prediction techniques for the conductivity maximum in these systems. We contribute to the discussion by reporting own conductometric data and establishing implicit empirical correlations between ionic structure, concentration and temperature. Our analysis is based on binary systems containing ionic (RTIL) and molecular (acetonitrile) co-solvent. The molar fraction of RTIL in each system ranges from 0 to 50% whereas temperature ranges from 278.15 to 328.15 K. Imidazolium-based RTILs are sampled by 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium and 1-hexyl-3- methylimidazolium tetrafluoroborates, 1-n-butyl-3- methylimidazolium trifluoromethanesulfonate, and 1-butyl-3-methylimidazolium bromide. 1-butyl-4-methylpyridinium tetrafluoroborate is employed to distinguish a role of aromatic ring. Ionic association in all RTIL-AN systems poorly correlates with the cation structure, although strongly depends on the anion size and structure. Cation and anion of RTILs form the 'contact ion pairs' (CIPs) where anion is coordinated by imidazole and pyridine rings. Notably, all binary systems exhibit conductivity maximum between χ(RTIL) = 10 and 20%. This maximum slightly shifts towards smaller χ(RTIL), as counterion gets larger. Smaller cations and anions lead to substantial conductivity growth. Conductivity maximum can be boosted and observed at larger χ(RTIL) even at insignificant temperature increase. Our observations provide novel insights into a complicated functional dependence of ionic conductivity versus ionic concentration and temperature. The results may be of extensive practical application, particularly for construction of high-performance electrolyte systems. © 2013 Elsevier Ltd. All rights reserved.

Fileti E.E.,Federal University of Sao Paulo | Chaban V.V.,Center for Biomembrane Physics
Journal of Physical Chemistry Letters | Year: 2014

Light fullerenes attract significant interest in pharmacy and medicine as drug vectors and antioxidants and to block AIDS virus enzyme. The progress of these applications is hindered by poor solubility of fullerenes in aqueous media. We propose a highly efficient hydrophilic system to disperse the C 60 fullerene based on the accurate atomistic-resolution computer simulations. The introduced system is based on 1-butyl-3-methylimidazolium tetrafluoroborate, [C4C1IM][BF4]-water mixtures. The first component is used to form a corona around C60 while exhibiting a significant miscibility with water. Structural and dynamical peculiarities of the C60-[C4C1IM][BF 4]-water mixtures are discussed. © 2014 American Chemical Society.

Samanta A.,Jadavpur University | Chattopadhyay D.,ICMR Virus Unit | Sinha C.,Jadavpur University | Jana A.D.,Jadavpur University | And 6 more authors.
Anti-Infective Agents | Year: 2012

We investigated the in vitro and in vivo antimicrobial potential of a selective serotonin reuptake inhibitor sertraline hydrochloride, against clinical isolates of bacteria and Candida species. Minimum Inhibitory Concentration of sertraline against 161 human isolates of 12 Gram negative and 5 Gram positive genera, Candida albicans ATCC10231 and Candida tropicalis ATCC13803 was determined by spot inoculation, broth and agar dilution methods along with its postantibiotic effect following a short drug exposure. The toxicity and protective efficacy was tested in vivo with a mousevirulent strain of Salmonella typhimurium NCTC74.The MIC was 20-200μg/ml for bacteria, and 200μg/ml for Candida. The growth inhibitory study with Bacillus subtilis UC564 and Shigella dysenteriae NCTC599/52 revealed that the drug is bacteriostatic at its MIC and cidal at higher concentrations. Study on its post-antibiotic effect following a short drug exposure revealed that Sertraline has a time- and dose-dependent effect. Treatment for 4h at concentrations below and equipotent to the minimal static concentration resulted in a lag of regrowth at 8-24h for Candida isolates. The in vivo study with Salmonella typhimurium in Swiss mice showed that the median lethal dose was 1.9 × 107 cfu and 50 LD50 was 0.95×109. Interestingly, the drug at a non-toxic single dose provides significant protection (P<0.001) to the mice challenged with S. typhimurium. Sertraline remarkably reduced the number of viable bacteria in organ homogenates and blood of the treated animals and demonstrate both in vitro and in vivo antibacterial potential at lower dose than its predesignated pharmacological activity. © 2012 Bentham Science Publishers.

Discover hidden collaborations