Testing the Gouy-Chapman theory by means of surface tension measurements for SDS-NaCl-H2O mixtures

Surface tension isotherms were measured for sodium dodecyl sulfate (SDS) at different concentrations of added salt (NaCl). The free energy of the surfactant monolayer was assessed by invoking the Gouy-Chapman theory for the charged head groups, the hydrophobic (Tanford) free energy of transfer of the hydrocarbon chain, and the hydrocarbon chain configurational free energy according to Gruen's calculations and finally macroscopic contact terms. In particular, the effect of an increased salt concentration in bulk was examined. Theoretical predictions compare well with the experimental findings, and good agreement was found with respect to both the variation of free energy of the monolayer and the surface pressure behavior. Thus, at least for a liquid-expanded monolayer of SDS, the Gouy-Chapman model yields a satisfactory account of the electrostatic contribution to the thermodynamic properties at different salt concentrations of NaCl.     

Highly hydrated cations: deficiency, mobility, and coordination of water in crystalline nonahydrated scandium(III), yttrium(III), and lanthanoid(III) trifluoromethanesulfonates

Trivalent lanthanide-like metal ions coordinate nine water oxygen atoms, which form a tricapped trigonal prism in a large number of crystalline hydrates. Water deficiency, randomly distributed over the capping positions, was found for the smallest metal ions in the isomorphous nonahydrated trifluoromethanesulfonates, [M(H2O)n](CF3SO3)3, in which M = Sc(III), Lu(III), Yb(III), Tm(III) or Er(III). The hydration number n increases (n = 8.0(1), 8.4(1), 8.7(1), 8.8(1) and 8.96(5), respectively) with increasing ionic size. Deuterium (2H) solid-state NMR spectroscopy revealed fast positional exchange between the coordinated capping and prism water molecules; this exchange started at temperatures higher than about 280 K for lutetium(III) and below 268 K for scandium(III). Similar positional exchange for the fully nonahydrated yttrium(III) and lanthanum(III) compounds started at higher temperatures, over about 330 and 360 K, respectively. An exchange mechanism is proposed that can exchange equatorial and capping water molecules within the restrictions of the crystal lattice, even for fully hydrated lanthanoid(III) ions. Phase transitions occurred for all the water-deficient compounds at approximately 185 K. The hydrated scandium(III) trifluoromethanesulfonate transforms reversibly (DeltaH degrees = -0.80(1) kJ mol(-1) on cooling) to a trigonal unit cell that is almost nine times larger, with the scandium ion surrounded by seven fully occupied and two partly occupied oxygen atom positions in a distorted capped trigonal prism. The hydrogen bonding to the trifluoromethanesulfonate anions stabilises the trigonal prism of water ligands, even for the crowded hydration sphere of the smallest metal ions in the series. Implications for the Lewis acid catalytic activity of the hydrated scandium(III) and lanthanoid(III) trifluoromethanesulfonates for organic syntheses performed in aqueous media are discussed.     

Noncollinear magnetization density in VAu4

The spin and orbital magnetic moments of VAu₄ have been calculated using a first principles method that allows for noncollinear magnetic ordering. The large spin–orbit coupling of the Au atom is argued to induce large noncollinear components of the magnetization density as well as a parallel coupling between spin and orbital moments of the V atom, in contrast to expectations from Hund's third rule. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Determination of vanilmandelic acid in urine by coupled-column liquid chromatography combining affinity to boronate and separation by anion exchange

An automated liquid chromatographic method for assaying vanilmandelic acid in urine is described. Vanilmandelic acid and potential interfering substances, such as catechol compounds and their metabolites, have been tested for affinity to boronic acid-substituted silica at various pH values. Vanilmandelic acid and the internal standard, isovanilmandelic acid, were bound to the boronate matrix at an acidic pH, whereas for instance catecholamines were unretained and passed through the column. The alpha-hydroxycarboxylic acids were then desorbed by another mobile phase (pH 6.0) and transferred to an anion exchanger for chromatography and electrochemical detection. A relative standard deviation of 2.8% was obtained for the analysis of human urine samples containing 6.6 microM vanilmandelic acid.     

Pyrosequencing trade mark technology at elevated temperature

To date, the Pyrosequencing trade mark technology has been performed at 28 degrees C due to the low thermostability of the firefly luciferase. In this study, firefly luciferase was stabilized in the presence of glycine betaine, allowing DNA sequencing at 37 degrees C. By increasing the temperature to 37 degrees C, false signals due to primer-dimers and loop-structures were decreased significantly. In addition, a combination of (i) replacing the natural dGTP with 7'deaza-dGTP in the polymerase chain reaction (PCR), (ii) 1.6 M glycine betaine, and (iii) an increase of the temperature to 37 degrees C enabled us to sequence a DNA template with the initial sequence 3'-ATGGCCCGGGGGGGAGCTCCA em leader 5'. Furthermore, we describe a method to analyze if a primer forms a primer-dimer with extendable 3'-ends.     

Photoreaction of skin-sensitizing trimethyl psoralen with lipid membrane models

The concerted photoreaction between trimethyl psoralen (TMP) and isomeric model compounds of oleic acid methyl ester (OAME) and eadilic acid methyl ester (EAME) are explored using density functional theory. The S(1) surfaces all reveal large barriers (25-31 kcal/mol) to reach the decay channels, whereas the S(2) surfaces differ considerably between the furan and pyrone side adducts. For the pyrone side adducts, a small barrier to reach the intersection between the S(1) and S(2) states is found, followed by a small second barrier on the S(1) surface to the low-lying decay channel. For the furan-side adducts, no such intersection between S(1) and S(2) is seen, which thus prevents these products from being formed in high yields. The photoinduced cycloaddition is more favorable between OAME and the pyrone side double bond of TMP than for any of the other systems, which agrees with the experimental findings that this is formed in the highest yield. The computed UV absorption spectra of TMP and the TMP(pyrone)-OAME cycloadduct agree well with the experimental spectra.     

Production of succinate from glucose, cellobiose, and various cellulosic materials by the ruminai anaerobic bacteriaFibrobacter succinogenes andRuminococcus flavefaciens

The production of organic acids by two anaerobic ruminal bacteria,Fibrobacter succinogenes S85 andRuminococcus flavefaciens FD-1, was compared with glucose, cellobiose, microcrystalline cellulose, Walseth cellulose (acid swollen cellulose), pulped paper, and steam-exploded yellow poplar as substrates. The major end product produced byF. succinogenes from each of these substrates was succinate (69.5–83%), the principal secondary product was acetate (16–30.5%). Maximum succinate productivity ranged from 14.1 mg/L · h for steam-exploded yellow Poplar to 59.7 mg/L · h for pulped paper. ForR. flavefaciens, the major end product from cellobiose, microcrystalline cellulose, and acid-swollen Walseth cellulose was acetate (39–46%), pulped paper and steam-exploded yellow poplar yielded succinate (42–54%) as the major product. Maximum succinate productivity byR. flavefaciens ranged from 9.21 mg/L · h for cellobiose to 43.1 mg/L · h for pulped paper. In general, much less succinate was produced at a lower maximum productivity byR. flavefaciens than byF. succinogenes under similar fermentation conditions. The maximum succinate productivities by these two organisms are comparable to the previously reported value of 59 mg/L · h forAnderobiospirillum succiniciproducens grown on glucose and corn steep liquor.     

The effects of nonlocal gradient corrections in density functional calculations of hydrocarbon radical hyperfine structures

Ground-state equilibrium geometries and hyperfine structures of a number of organic neutral and charged radical compounds are computed using the linear combination of Gaussian-type orbitals–density functional theory method. In addition to the local spin-density approximation, we also use two different nonlocal (gradient corrected) schemes for the calculations of the exchange and correlation potentials. The different functional forms are found to generate slightly different total and unpaired spin-density distributions in the molecules, and as a result, the computed isotropic hyperfine coupling constants vary markedly. The smallest variations are found for the hydrogens, where the results are generally in satisfactory agreement with experiment. For the carbon atoms, however, large differences in isotropic coupling constants are observed. The anisotropic hyperfine structures are generally very well described at all levels of theory. © John Wiley & Sons, Inc.     

Practical synthesis of unsymmetrical ureas from isopropenyl carbamates

A very convenient method for the synthesis of unsymmetrical ureas is described, based on isopropenyl carbamates. The synthetic efficiency of traditional methods for urea formation, such as use of phosgene or alkyl and aryl carbamates, is limited by the formation of symmetrical urea side products or reaction reversibility. Isopropenyl carbamates react with amines cleanly and irreversibly and give unsymmetrical ureas in high yield and purity. This method is ideal for the rapid synthesis of compound libraries.