Influence Of Cosolutes Research Articles

The influence of co-solutes on tribology of agar fluid gels

The effects of glucose and glycerol on the lubrication properties of agar fluid gels have been studied using soft tribology. A novel approach using the sediment and supernatant of centrifuged fluid gels has allowed investigation of the distinct contributions of both the gelled particulate phase and the continuous phase on fluid gel tribology. The friction coefficient of both the particulate phase and fluid gels was significantly lower than that of the continuous phase across the three lubrication regimes. This indicates that particle entrainment occurs at all entrainment speeds, enhancing lubrication by prevention of surface contact.Softer fluid gel particles produced with intermediate levels of glycerol (up to 30%) show increased friction as would be expected for an increased contact area between the tribological surfaces. At high levels of glycerol, the friction does not increase. It is proposed that soft particles are produced but the increasing friction is overcome with the increased lubrication from the more highly viscous continuous phase. In contrast, the presence of intermediate levels of glucose (up to 30%) increases the friction of the aqueous continuous phase but does not affect the particle properties. Texture analysis, rheology and light scattering techniques were used to elucidate the structural changes of the fluid gels induced by the addition of co-solutes and the influence this has upon lubrication.

Competitive sorption between 17α-ethinyl estradiol and bisphenol A/4-n-nonylphenol by soils

The sorption of 17α-ethinyl estradiol (EE2), bisphenol A (BPA), and 4-n-nonylphenol (NP) in single systems and the sorption of EE2 with different initial aqueous concentrations of BPA or NP were examined using three soils. Results showed that all sorption isotherms were nonlinear and fit the Freundlich model. The degree of nonlinearity was in the order BPA (0.537–0.686) > EE2 (0.705–0.858) > NP (0.875–0.0.951) in single systems. The isotherm linearity index of EE2 sorption calculated by the Freundlich model for Loam, Silt Loam and Silt increased from 0.758, 0.705 and 0.858, to 0.889, 0.910 and 0.969, respectively, when BPA concentration increased from 0 to 1000 μg/L, but the effect of NP was comparably minimal. Additionally, EE2 significantly suppressed the sorption of BPA, but insignificantly suppressed that of NP. These findings can be attributed to the difference of sorption affinity of EE2, NP and BPA on the hard carbon (e.g., black carbon) of soil organic matter that dominated the sorption in the low equilibrium aqueous concentration range of endocrine-disrupting chemicals (EDCs). Competitive sorption among EDCs presents new challenges for predicting the transport and fate of EDCs under the influence of co-solutes.

DNA Conformational Effects on the Interaction of Netropsin with A-tract Sequences

The influence of cosolutes and DNA sequence on the interaction of netropsin with three duplexes has been studied by isothermal titration calorimetry. In buffer, netropsin forms two complexes with a net stoichiometry of 1:1 in the minor groove of the oligonucleotide (GCGCGAATTCGCGC)2. One complex has a weaker affinity and is more enthalpically favored relative to the other one, consistent with previous studies [Freyer, M. W., et al. (2006) Biophys. Chem. 126, 186-196]. With the cosolutes betaine and 2-methyl-2,4-pentanediol, the enthalpy and heat capacity changes indicate that the complex with weaker affinity is disfavored relative to the complex with higher affinity. With (CGCGCAATTGCGCG)2, netropsin has one binding mode in buffer, and complex formation is not influenced by the cosolutes. The similarities of the enthalpy and heat capacity changes suggest that netropsin interacts similarly with these two oligonucleotides in the presence of cosolutes. The oligonucleotide (GCGCAAATTTGCGC)2 also forms two complexes with netropsin, and the complex with weaker affinity is again disfavored by the cosolutes. Thus, the interaction of netropsin with these A/T binding sites is influenced both by the bases adjacent to the binding site and by cosolutes. We suggest that these two factors influence the conformation of the minor-groove binding site of DNA.

Influence of Cosolutes on Phase Behavior and Viscosity of a Nonionic Cellulose Ether. The Effect of Hydrophobic Modification

The phase behavior and viscosity of aqueous solutions of two nonionic polymers, ethyl(hydroxyethyl)cellulose (EHEC) and the hydrophobically modified analogue (HM-EHEC), have been studied as a function of added cosolutes, ranging from alcohols with different chain lengths to salts with different anions and to substances usually referred to as denaturants. The change in phase behavior on addition of a cosolute is dominated by the general structure of the polymer chain and is negligibly influenced by the hydrophobic tails of HM-EHEC, as they are present in such a low number. Therefore, the cosolute induced changes in phase behavior are akin for the two polymers. However, the situation is different for added cosolutes which have a particularly strong affinity for the hydrophobic moieties of HM-EHEC and at a closer inspection differences in phase behavior between the two polymers can be seen on addition of long-chained alcohols. On the other hand, changes in viscosity on addition of cosolutes are generally much more pronounced for HM-EHEC as rheology probes network formation and association resulting from small changes in the interaction energy between the polymer chains. The observations, both phase behavior and viscosity, can be qualitatively understood in terms of the distribution of cosolute between bulk solution and polymer surface. As an example, addition of NaCl or a long-chained alcohol increases the viscosity more for HM-EHEC than for EHEC, while an addition of NaSCN or a short-chained alcohol rather decreases the viscosity, again more pronounced for HM-EHEC.

Diels–Alder reaction of fumaronitrile and cyclopentadiene in water: the influence of cosolutes

Rates of reaction are reported for the title compounds in aqueous solution. The influence of added salts on the rate of reaction is recorded: alkali-metal salts advance the rate, while tetraethylammonium chloride retards it. Sodium dodecyl sulphate and cetyltrimethylammonium bromide also retard the reaction, while the effect of cyclodextrins depends on their cavity size. The explanation of these phenomena in terms of the hydrophobic effect is considered and extended by measurement of ΔH‡ and ΔS‡ parameters for the reaction.

Influence of cosolutes upon the conformation of carbohydrates in aqueous solutions. Part III. Effect of inorganic ions upon the binding of iodine by starch and derivatives of amylose

For solutions of starch, diethylaminoethylamylose, amylose sulphate, and carboxymethylamylose in aqueous inorganic acids or salts at 20°, plots of the optical density at 680 nm against the concentration of added potassium tri-iodide (KI3) showed maxima whose values were highly dependent upon the concentration and identity of the ions present. The absorption spectra in the different media were also different, and similar changes in the absorption spectra could not be brought about by varying the concentration of I3– in the system.With polyvinyl alcohol, there was no tendency to develop different maxima in different media, and the absorption spectrum was independent of the medium. It thus appeared that the acids and salts were bringing about a conformational change in the glucans, leading to an increase or decrease in the number of sites that were able to bind I3– strongly.By working with a very large excess of I3–, it was possible to avoid complications arising from the competitive binding of species other than I3–, or salt effects upon the activity coefficient of I3–, and to study the effect of different media upon the conformational change alone. These media included aqueous sulphuric, phosphoric, hydrochloric, and hydrobromic acids, alkali-metal halides, and various other salts of lithium, sodium, and potassium.The effect of the acids and salts upon the maximal optical density at 680 nm could not be correlated with their effect upon the volume of gels prepared by cross-linking starch with epichlorohydrin, or with their salting-out parameters for non-polar compounds. This was interpreted as evidence that the conformational changes were not primarily associated with changes in the stability of intramolecular hydrogen bonding, or of hydrophobic interactions.On the other hand, there was a close correlation between the maximal optical density in the four acids named above, and their previously demonstrated capacity to change the magnitude of the anomeric effect in the methyl glucopyranosides and in cellobiose and maltose. With an apparent exception that was noted for fluorides, the effect of all the other salts upon the optical density correlated well with their expected capacity to modify the magnitude of the anomeric effect, based upon the idea that the ring and glycoside-oxygen atoms are selectively desolvated by salts whose anion is the stronger electrostrictor, and solvated by salts whose cation is the stronger electrostrictor.It was therefore concluded that the conformational changes were mainly due to changes in the magnitude of the exo-anomeric effect, which would be expected to modify the relative stabilities of the rotamers generated about the C(1)–O(1) bonds, and, hence, the ease with which the linear segments of the glucan chains are able to take up the helical, V-conformation in solution. It is pointed out that similar changes can be expected in any flexible molecule, whose net dipole moment in different conformational states can be expected to vary.

Influence of cosolutes upon the conformation of carbohydrates in aqueous solutions. II. Demonstration of the anomeric effect in cellobiose and maltose, and proposal of a mechanism for the influence of inorganic ions upon its magnitude.

Influence of cosolutes upon the conformation of carbohydrates in aqueous solutions. II. Demonstration of the anomeric effect in cellobiose and maltose, and proposal of a mechanism for the influence of inorganic ions upon its magnitude.

Influence of cosolutes upon the conformation of carbohydrates in aqueous solutions. I. Dependence upon the anion of the relative rates of hydrolysis of the anomeric methyl glucopyranosides in aqueous mineral acids.

Influence of cosolutes upon the conformation of carbohydrates in aqueous solutions. I. Dependence upon the anion of the relative rates of hydrolysis of the anomeric methyl glucopyranosides in aqueous mineral acids.