Center for Biomembrane Physics

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

Nitromethane (NM) is widely applied in chemical technology as a solvent for extraction, cleaning, and chemical synthesis. NM was considered safe for a long time, until a railroad tanker car exploded in 1958. We investigate the detonation kinetics and explosion reaction mechanisms in a variety of systems consisting of NM, molecular oxygen, and water vapor. Reactive molecular dynamics allows us to simulate reactions in time-domain, as they occur in real life. High polarity of the NM molecule is shown to play a key role, driving the first exothermic step of the reaction. Rapid temperature and pressure growth stimulate the subsequent reaction steps. Oxygen is important for faster oxidation, whereas its optimal concentration is in agreement with the proposed reaction mechanism. Addition of water (50 mol %) inhibits detonation; however, water does not prevent detonation entirely. The reported results provide important insights for improving applications of NM and preserving the safety of industrial processes. © 2014 American Chemical Society.


Chaban V.V.,University of Rochester | Chaban V.V.,Center for Biomembrane Physics | Prezhdo V.V.,Jan Kochanowski University | Prezhdo O.V.,University of Rochester
Journal of Physical Chemistry Letters | Year: 2013

Nonadiabatic molecular dynamics combined with time-domain density functional theory are used to study electron transfer (ET) from a CdSe quantum dot (QD) to the C60 fullerene, occurring in several types of hybrid organic/inorganic nanocomposites. By unveiling the time dependence of the ET process, we show that covalent bonding between the QD and C60 is particularly important to ensure ultrafast transmission of the excited electron from the QD photon-harvester to the C60 electron acceptor. Despite the close proximity of the donor and acceptor species provided by direct van der Waals contact, it leads to a notably weaker QD-C60 interaction than a lengthy molecular bridge. We show that the ET rate in a nonbonded mixture of QDs and C60 can be enhanced by doping. The photoinduced ET is promoted primarily by mid-and low-frequency vibrations. The study establishes the basic design principles for enhancing photoinduced charge separation in nanoscale light harvesting materials. © 2012 American Chemical Society.


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

Atomistic molecular dynamics simulations were employed to investigate the solvation properties of the fullerene C60 in binary water/dimethyl sulfoxide (DMSO) mixtures. Structural analysis indicates a preferential solvation with the predominance of DMSO molecules in the first solvation shell for the solutions with low concentrations of DMSO. PMF calculations indicate a maximization of the hydrophobic interaction at low concentrations of DMSO. The contact minima indicate a tendency of aggregation of these nanostructures in water/DMSO mixtures and in the both pure solvents. The free energy of solvation suggests that the hydrophobicity of the fullerene increases monotonically with the increase of DMSO concentration. This result is incompatible with the polarity of DMSO, since it was expected that increasing the concentration of DMSO entailed an increase of C60 solubility. © 2014 American Chemical Society.


PubMed | University of Southern California, Center for Biomembrane Physics and University of Sao Paulo
Type: Journal Article | Journal: The journal of physical chemistry letters | Year: 2015

Nitromethane (NM) is widely applied in chemical technology as a solvent for extraction, cleaning, and chemical synthesis. NM was considered safe for a long time, until a railroad tanker car exploded in 1958. We investigate the detonation kinetics and explosion reaction mechanisms in a variety of systems consisting of NM, molecular oxygen, and water vapor. Reactive molecular dynamics allows us to simulate reactions in time-domain, as they occur in real life. High polarity of the NM molecule is shown to play a key role, driving the first exothermic step of the reaction. Rapid temperature and pressure growth stimulate the subsequent reaction steps. Oxygen is important for faster oxidation, whereas its optimal concentration is in agreement with the proposed reaction mechanism. Addition of water (50 mol %) inhibits detonation; however, water does not prevent detonation entirely. The reported results provide important insights for improving applications of NM and preserving the safety of industrial processes.


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.


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.


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.


Voroshylova I.V.,University of Kharkiv | Voroshylova I.V.,University of Porto | Smaga S.R.,University of Kharkiv | Lukinova E.V.,University of Kharkiv | And 2 more authors.
Journal of Molecular Liquids | Year: 2015

A detailed investigation of the dilute solutions of several imidazolium-based ([BMIM][Br], [EMIM][BF4], [BMIM][BF4], [HexMIM][BF4], [BMIM][Tf]) and pyridinium-based ([BMP][BF4]) ionic liquids, and two tetraalkylammonium salts (Bu4NBr and Bu4NBPh4) in methanol was carried out between 278.15 and 328.15 K. The limiting molar and ionic association constants were derived using the Lee-Wheaton equation. The limiting molar conductivity for room-temperature ionic liquids with common anion ([BF4]-) is found to obey the Stokes' law: Λ0 increases as the cation size decreases. Ionic association in all studied systems does not show definite correlation with cation structure, while it strongly depends on anion size and structure. Ion association constants are discussed and the role of non-Coulombic forces is demonstrated with the help of short-range square-mound potential. Performed data analysis indicates the formation of contact ion pair of similar structure in studied solutions of ionic liquids, with anion coordinated by imidazole or pyridine ring. The formation of H-bonding between bromide-anion and hydroxy-group of methanol was observed. © 2014 Elsevier B.V. All rights reserved.


Fileti E.E.,Federal University of São 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.


Dreier J.,Center for Biomembrane Physics | Brewer J.,University of Southern Denmark | Simonsen A.C.,Center for Biomembrane Physics
Langmuir | Year: 2014

The tilted gel phase of lipid bilayers can display in-plane orientational texture due to long-range alignment of the molecular director. We explore systematic variations of texture defects in a series of binary phospholipid membranes. Using polarized two-photon fluorescence microscopy, the texture pattern of single domains is revealed. The appearance of a central vortex-type defect in each domain correlates with a particular range of hydrophobic mismatch values h > 1 nm at the domain border while domains with h < 1 nm correlate with uniformly aligned texture. The central vortex defect is characterized by a defect angle, indicating its bend or splay nature. Using image analysis, we measure the defect angle and find that it has primarily bend character for small mismatch values (h ≈ 1 nm) and primarily splay nature for larger values of h. For domains containing a vortex, the domain shape is decoupled from the texture while for uniformly textured domains there is a preferred texture orientation of ≈45° along the domain border. The results establish a foundation for understanding texture phenomena in compositionally complex membranes. © 2014 American Chemical Society.

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