Search results for "Hydrophobic effect"

1984

Alkaline hydrolyses of anionic phenyl esters such as 4-acetoxy-3-nitrobenzoic acid and 4-butyryloxy-3-nitrobenzoic acid were examined in the presence of cationic and polymeric liposomes, liposomes of low molecular weight compounds, and micelles. All the additives accelerate the reaction due to the hydrophobic interaction between substrates and additives and the electrostatic interaction both between substrates and additives and between OH− and additives. In the Arrhenius plots of the reactions catalyzed by the liposomes, discontinuous regions were observed due to the phase transition of liposomes from the gel state to the liquid crystal state. Activation parameters ΔH≠, ΔS≠ and ΔV≠ for thes…

Size Exclusion Chromatography of Proteins on Improved Bonded Silica Columns

1985

Publisher Summary This chapter discusses the size exclusion chromatography (SEC) of proteins on improved bonded silica columns. Over the past few years, the use of high performance liquid chromatography (HPLC) has been extended to protein chemistry as a powerful separation and isolation technique. A spectrum of variants providing high resolution potential—ion exchange, reversed phase, hydrophobic interaction, affinity, and size exclusion—is available. Of these, SEC is the simplest with respect to method development and equipment design: proteins are separated according to their size in a short and predictable time span under isocratic conditions. The SEC columns are packed with micro-partic…

Molecular surface area and hydrophobic effect.

1992

Influence of End Groups on the Stimulus-Responsive Behavior of Poly[oligo(ethylene glycol) methacrylate] in Water

2010

The influence of the chemical structure of both end groups onto the lower critical solution temperature (LCST) of poly[oligo(ethylene glycol) monomethyl ether methacrylate] (POEGMA) in water was systematically investigated. POEGMA of Mn = 3550 g/mol and Mw/Mn = 1.14 prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization was equipped with two different functional end groups in a one-step postpolymerization reaction combining activated esters, functional amines, and functional methane thiosulfonates. As end groups, n-propyl, n-hexadecyl, di(n-octadecyl), poly(ethylene glycol)-550 (PEG), 1H,1H-perfluorononyl, azobenzene, and trimethylethylammonium groups were system…

Transfers of small analytes in a multiphasic stirred fruit yoghurt model

2007

International audience; The transfer of small analytes in a multiphasic stirred fruit yoghurt model, made of a pectin gel aimed to mimic fruit pieces and of a dairy gel done with milk acidified by glucono-δ-lactone hydrolysis, have been studied. The concentration gradients between the pectin gel and the dairy gel were the driving force for the migration of small analytes (i.e. water, protons and colorants). Water migrated from the dairy to the pectin gel, causing modifications in the water content of both gels and an equilibration of their water activity at 0.938±0.003. Inversely, protons migrated from the pectin to the dairy gel. These changes in composition of both gels being likely to ha…

Effects of electric charges on hydrophobic forces. II.

2000

We study by molecular-dynamics simulations the effect of electric charges of either sign on hydrophobic interactions and on the dynamics of hydration water, using explicit water and very simplified solutes. Results show that the presence of a charged solute can disrupt the "hydrophobic contact bond" between two apolar solutes nearby, by forcing them towards a different configuration. As a consequence of different structural changes of the solvent caused by charges of opposite sign, the effect is markedly charge-sign-dependent. Analogous weaker effects appear to be induced by the presence of one additional apolar element. The dynamics of hydration water around each solute is also seen to be …

B-DNA Structure and Stability as Function of Nucleic Acid Composition. Dispersion-Corrected DFT Study of Dinucleoside-Monophosphate Single and Double…

2013

actions of the sugar-phosphate skeleton with water; (6) hydrophobic interactions of the DNA cylindrical core, made up by the hydrogen-bonded and stacked nitrogen bases, with the water solvent. Recently, there has been increasing effort in developing and applying quantum chemical methods able to reproduce the structure of native B-DNA and to correctly describe the energy involved in the intrastrand and interstrand noncovalent interactions between the nucleotide monomers. This topic has been approached by both wave function methods and density functional theory. [2] Water solvent and sodium counterions also play an important role in the formation and relative stabilization of the double-helic…

Solution properties of polyelectrolytes XII. Semi-quantitative approach to mixed electrostatic and hydrophobic polymer-gel interactions

1996

Abstract Aqueous size-exclusion chromatography of polyanions, where secondary effects affect the total separation mechanism, was investigated. For elution of polyelectrolytes on inorganic silica-based supports, the electrostatic polymer-gel repulsive interactions were evaluated through the values for a hypothetical repulsion layer, X e , according to the model developed by other workers. Using a similar procedure, the existence of an effective barrier defined as X e − X h is proposed for those systems in which electrostatic repulsion and hydrophobic interactions take place simultaneously as secondary mechanisms. X h can be viewed as a measure of the “enlargement” of the geometrical pore rad…

Quantitation of hydrophobicity in micellar liquid chromatography

1999

Abstract Micellar liquid chromatography (MLC) is shown to be a promising technique for measuring the hydrophobicity of solutes. The presence of micelles has a profound effect on the chromatographic characteristics of reversed-phase columns. The linear relationships between the logarithm, log k , of the retention factor and such diverse properties as the number of carbon atoms in homologous series, octanol–water partition coefficients and solvatochromic parameters, which are observed in conventional reversed-phase liquid chromatography (RPLC), are not usually valid in MLC. For series of compounds exhibiting a wide range of hydrophobicity, k itself is linearly related to these properties. The…

Thermal induced conformational changes involved in the aggregation pathways of beta-lactoglobulin.

2004

Aggregation of proteins appears to be associated most often with conformational and structural changes that lead to exposure of some apolar residues. Depending on the native structure of the protein in exam, aggregation is a process that involves different mechanisms, whose time of occurrence and interplay can depend upon temperature. To single out information about the multistages of the aggregation pathway, here we investigate the thermally induced conformational and structural changes of the beta-lactoglobulin (BLG). The experimental approach consists in studying steady-state fluorescence spectra of intrinsic chromophores, two tryptophans, and Anylino-Naphthalene-Sulfonate dye (ANS) mole…