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 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An assay was developed for K+ in aqueous solution at neutral pH. The method was based on the change in optical absorbance of the hydrophobic indicator 7-(n-decyl)-2-methyl-4-(3',5'-dichlorophen-4'-one)indonaphthl++ +-1-ol (MEDPIN) in phospholipid vesicles. Formation of a ternary complex between a valinomycin-K+ pair and the anionic form of MEDPIN in the bilayer resulted in an absorption band at 584 nm. K+ concentration was determined by monitoring the MEDPIN absorbance at 584 nm and MEDPIN quenching of lissamine rhodamine B sulfonylphosphatidylethanolamine (L-RhB-PE) fluorescence by an energy-transfer mechanism. Both the fluorescence intensity and lifetime of L-RhB-PE decreased by more than 25% upon addition of 50 mM K+. Kinetic studies using stopped-flow photometry showed a single-exponential reaction of MEDPIN and valinomycin in vesicles with aqueous K+ (maximum rate 1.7 s-1) that was dependent upon [valinomycin] and [K+]. The lipid surface charge was shown to influence the ratio of anionic to neutral MEDPIN at constant pH, and to alter the sensitivity of MEDPIN absorbance to aqueous [K+]. A 1:20 neutral/negative lipid mole ratio was optimal for K+ detection at pH 7.4. Spectroscopic and kinetic data suggest that the optical response of MEDPIN to K+ involves the formation of a ternary complex between K+, valinomycin and MEDPIN.
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PMID:Optical measurement of aqueous potassium concentration by a hydrophobic indicator in lipid vesicles. 280 47

The kinetics of Na+ and K+ transport across the membrane of large unilamellar vesicles (LUV) were determined at two pH's when transport was induced by (221)C10-cryptand (diaza-1,10-decyl-5-pentaoxa-4,7,13,16,21-bicyclo [8.8.5.] tricosane) at various temperatures, and by nonactin at 25 degrees C and (222)C10-cryptand at 20 and 25 degrees C. The rate of Na+ and K+ transport by (221)C10 saturated with the cation and carrier concentrations. Transport was noncooperative and exhibited selectivity for Na+ with respect to K+. The apparent affinity of (221)C10 for Na+ was higher and less pH-dependent than that for K+, and seven times higher than the affinity for Na+ of nonactin. Its enthalpy was higher than that of (222)C10 for K+ ions (20.5 vs. 1.7 kcal . mole-1). The efficiency of (221)C10 transport of Na+ was pH- and carrier concentration-dependent, and was similar to that of nonactin; its activation energy was similar to that for (222)C10 transport of K+ (35.5 and 29.7 kcal . mole-1, respectively). The reaction orders in cation n(S) and in carrier m(M), respectively, increased and decreased as the temperature rose, and were both independent of carrier or cation concentrations; in most cases, they varied slightly with the pH. n(S) varied with the cation at pH 8.7 and with the carrier for Na+ transport only, while m(M) always depended on the type of cation and carrier. Results are discussed in terms of the structural, physico-chemical and electrical characteristics of carriers and complexes.
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PMID:Efficiency, Na+/K+ selectivity and temperature dependence of ion transport through lipid membranes by (221)C10-cryptand, an ionizable mobile carrier. 344 19

The absorbance maximum, lambda max, of a local anesthetic, benzyl alcohol, is shifted to longer wavelengths when solvent polarity is decreased. The shift was approximately a linear function of the dielectric constant of the solvent. This transition in electronic spectra according to the microenvironmental polarity is used to analyze benzyl alcohol binding to surfactant micelles. A facile method is devised to estimate the micelle/water partition coefficient from the dependence of lambda max of benzyl alcohol on surfactant concentrations. The effective dielectric constants of the sodium decyl sulfate, dodecyl sulfate and tetradecyl sulfate micelles were 29, 31 and 33, respectively. The partition coefficient of benzyl alcohol between the micelles and the aqueous phase was 417, 610 and 1089, respectively, in the mole fraction unit. The pressure dependence of the partition coefficient was estimated from the depression of the critical micelle concentration of sodium dodecyl sulfate by benzyl alcohol under high pressure up to 200 MPa. High pressure squeezed out benzyl alcohol molecules from the micelle until about 120 MPa, then started to squeeze in when the pressure was further increased. The volume change of benzyl alcohol by transfer from the aqueous to the micellar phase was calculated from the pressure dependence of the partition coefficient. The volume change, estimated from the thermodynamic argument, was 3.5 +/- 1.1 cm3.mol-1 at 298.15 K, which was in reasonable agreement with the partial molal volume change determined directly from the solution density measurements, 3.1 +/- 0.2 cm3.mol-1. Benzyl alcohol apparently solvates into the micelles close to surface without losing contact with the aqueous phase.
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PMID:Benzyl alcohol penetration into micelles, dielectric constant of the binding site, partition coefficient and high-pressure squeeze-out. 648 18

A new series of N-alkylated uric acids (2,6,8-purinetrione) and 5,6-diaminouracils (5,6-diamino-2,4-pyrimidinedione) were synthesized, and their activities against free radicals were evaluated. Long-chain derivatives of both series exhibited a large inhibitory activity against oxygen radical induced lipid peroxidation in bovine heart mitochondria (IC50 lower than 1 microM), compared to the reference antioxidants trolox C or alpha-tocopherol. This activity appeared related to (i) the ability of these compounds to reduce the stable radical 1,1-diphenyl-2-picrylhydrazyl and (ii) their lipophilicity estimated by log P determination. In order to study the scavenging mechanisms of diaminouracils and urate derivatives against lipid radicals, they were also tested against the azo-initiated peroxidation of either methyl linoleate in organic solvents or a liposomal suspension of dilinoleoylphosphatidylcholine. Urate derivatives reacted moderately with lipid radicals and were slowly consumed, significantly affecting the propagation of the peroxidation. Diaminouracils strongly reduced the propagation rate. They were quickly consumed and were able to deactivate about 1 mol of lipid radical per mole of compound in organic solvent. Dodecyl urates and decyl- and dodecyldiaminouracils were chosen for further in vitro investigation and in vivo evaluation.
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PMID:Long-chain-substituted uric acid and 5,6-diaminouracil derivatives as novel agents against free radical processes: synthesis and in vitro activity. 849 14

The thermodynamic relations were developed for examining the miscibility of surfactants in the adsorbed film from the viewpoints of the thermodynamic quantities of adsorption such as Gibbs free energy, entropy, volume, enthalpy, and energy. The deviation from the additivity relation, the straight line connecting the thermodynamic quantities of the respective pure surfactants as a function of the composition of the adsorbed film, was proved to yield the corresponding excess quantities of adsorption. The criterion of the ideal mixing was offered and summarized with respect to the composition of adsorbed film, the mean area occupied by surfactants, and the thermodynamic quantities of adsorption. The resulting equations were applied to the simple nonionic surfactants mixture of decyl methyl sulfoxide (DeMS) and octyl methyl sulfoxide (OMS). The surface tension of the aqueous solution was measured as a function of not only the total molality and mole fraction of surfactants but also temperature under atmospheric pressure. Copyright 1999 Academic Press.
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PMID:The Excess Thermodynamic Quantities of Adsorption of a Binary Nonionic Surfactant Mixture. 1044 19

The surface tension of an aqueous solution of decyltrimethylammonium decyl sulfate (DeTADeS) was measured as a function of temperature T at various molalities &mcirc; under atmospheric pressure. DeTADeS has been found to form equilibrium multilamellar vesicles (MLV) spontaneously. The surface density, the entropies of adsorption, and the entropy of vesicle formation are evaluated. The mechanism of formation of equilibrium vesicles is investigated from the standpoint of thermodynamics and from the comparison of the results with those of the micelle-forming systems. From the relatively small change of the surface density Gamma;(H) on T at a given &mcirc;, the adsorbed film is implied to be tightly packed due to the strong electrostatic attraction between the polar headgroups. The energy change associated with adsorption from the vesicular state per mole of surfactant Delta(V)(H)u is positive in the entire temperature range; thus, the curved bilayer in MLV is energetically more favorable than the planar adsorbed film. From the negative values of the entropy of vesicle formation Delta(W)(V)s, it is concluded that vesicle formation is driven by enthalpy whereas micelle formation is mostly entropy driven. Copyright 2001 Academic Press.
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PMID:Thermodynamic Study on Vesicle Formation and Adsorption of Decyltrimethylammonium Decyl Sulfate. 1139 72

By means of surface tension measurement (Wilhelmy method), micellization and adsorbed film formation were investigated for three combinations of mixed surfactant systems, all of which are used for solubilizing membrane proteins: a typical zwitterionic surfactant, CHAPS (a derivative of cholic acid) with n-alkyl (octyl, nonyl and decyl)-N-glucamides, MEGA-n (n=8, 9, 10). The data based on plotting of surface tension (gamma) versus logarithmic total molarity (or molality) (Ct or Mt) as a function of mole fraction of surfactant 2 (2 corresponds to MEGA-n's) enabled us to determine critical micellization concentration (CMC), minimum surface tension at CMC (gammaCMC), surface excess (Gamma(t)), mean molecular surface area (Am), the minimum Gibbs energy (Gmin(S)) of adsorbed film of both single and mixed surfactant systems and partial molecular area (PMA) in addition to parameters such as pC20 and CMC/C20 being related to synergism accompanied by blending (mixing) in regard to surface activity as well as micelle forming ability. On the basis of the regular solution theory, the relations of compositions of singly dispersed phase (X2), micellar phase (Y2) and adsorbed film (Z2) were estimated, and then the interaction parameters in micelles (omegaR) and in the adsorbed film phase (omegaA) were also calculated. From both the CMC-X2 and CMC-Y2 curves, it was found for all the combinations to show synergistically enhanced ability of mixed micelle formation as well as surface tension reduction. The resultant synergism coming from blending CHAPS with MEGA-n's was discussed in comparison with different combinations of various types of surfactants including membrane proteins solubilizers.
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PMID:Blending effects on adsorption and micellization of different membrane protein solubilizers: a thermodynamic study on three mixed systems of CHAPS with MEGA-8, -9 and -10 in pH 7.2 phosphate buffer solution. 1614

The surface tension of aqueous solutions of a sodium chloride (NaCl)-decyl methyl sulfoxide (DeMS) mixture was measured as a function of the total molality of the mixture and the mole fraction of DeMS in the mixture at 298.15 K under atmospheric pressure. The total surface density of the mixture and the mole fraction of DeMS in the adsorbed film and micelle were numerically evaluated by applying the thermodynamic treatment of surfactant mixture to the NaCl-DeMS mixture. Miscibility of NaCl and DeMS in the adsorbed film and micelle was clarified by use of the phase diagram of adsorption and micelle formation. Positive adsorption of NaCl was observed in the presence of DeMS and attributed to attractive interaction between the polar head group of DeMS molecule and Na+ or Cl- ions in the adsorbed film and micelle. The results were compared with those of NaCl-octyl methyl sulfoxide and NaCl-decyldimethylphosphine oxide mixtures to elucidate the structure effect of nonionic surfactant on the miscibility.
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PMID:Miscibility of sodium chloride and decyl methyl sulfoxide in the adsorbed film and micelle. 1625 87

Surfactant self-diffusion coefficients have been measured on a binary system of 1-O-beta-3,7-dimethyloctyl-D-maltopyranoside (beta-Mal(2)(Ger))/water and a mixed surfactant system of beta-Mal(2)(Ger)/1-O-beta-3,7-dimethyloctyl-D-glucopyranoside (beta-Glc(Ger))/water at 25 degrees C. For comparison, measurements have also been made on 1-O-beta-decyl-D-maltopyranoside (beta-Mal(2)C(10))/water and beta-Mal(2)C(10)/1-O-beta-decyl-D-glucopyranoside (beta-GlcC(10))/water. The hydrodynamic radius of beta-Mal(2)(Ger) micelles obtained from the micellar diffusion coefficient is around 3 nm and nearly equal to that of beta-GlcC(10) micelles within experimental error. In the mixed surfactant systems, the hydrodynamic radii for both systems increase with increasing X(G) (the mole fraction of beta-Glc(Ger) or beta-GlcC(10) in the total mixed solute) above X(G) congruent with 0.4 when the total surfactant concentration is kept constant at 2 wt%. The R(H) of beta-Glc(Ger)/Mal(2)(Ger) micelles increases more rapidly than beta-GlcC(10)/beta-Mal(2)C(10) micelles, and then phase separation occurs at X(G) congruent with 0.65. On the other hand, the R(H) of beta-GlcC(10)/beta-Mal(2)C(10) micelles continues to increase until the phase separation occurs at X(G) congruent with 0.92. Measurements have also been performed as a function of total surfactant concentration at constant X(G) (=0.6). The CMC of the beta-Glc(Ger)/Mal(2)(Ger) system is larger than that of the beta-GlcC(10)/beta-Mal(2)C(10) system as expected from the results of the pure surfactant systems published previously. The R(H) increases with increasing total surfactant concentration for both systems. At higher concentrations, the R(H) of beta-Glc(Ger)/Mal(2)(Ger) micelles increases more rapidly than beta-GlcC(10)/beta-Mal(2)C(10) micelles. These results can be explained by the fact that the geranyl and decyl chains have the same volume but different chain lengths.
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PMID:Micelle structures in aqueous solutions of glucose-based surfactants having an isoprenoid-type hydrophobic chain. 1754 33

A series of newly designed ascorbic acid based room temperature ionic liquids were successfully used to prepare quasi-spherical and anisotropic gold nanostructures in an aqueous medium at ambient temperature. The synthesis of these room temperature ionic liquids involves, first, the preparation of a 1-alkyl (such as methyl, ethyl, butyl, hexyl, octyl, and decyl) derivative of 3-methylimidazolium hydroxide followed by the neutralization of the derivatised product with ascorbic acid. These ionic liquids show significantly better thermal stability and their glass transition temperature (Tg) decreases with increasing alkyl chain length. The ascorbate counter anion of these ionic liquids acts as a reducing agent for HAuCl4 to produce metallic gold and the alkylated imidazolium counter cation acts as a capping/shape-directing agent. It has been found that the nature of the ionic liquids and the mole ratio of ionic liquid to HAuCl4 has a significant effect on the morphology of the formed gold nanostructures. If an equimolar mixture of ionic liquid and HAuCl4 is used, predominantly anisotropic gold nanostructures are formed and by varying the alkyl chain length attached to imidazolium cation of the ionic liquids, various particle morphologies can formed, such as quasispherical, raspberry-like, flakes or dendritic. A probable formation mechanism for such anisotropic gold nanostructures has been proposed, which is based on the results of some control experiments.
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PMID:Novel ascorbic acid based ionic liquids for the in situ synthesis of quasi-spherical and anisotropic gold nanostructures in aqueous medium. 1847 Aug 52


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