- Enantioselective stereoinversion of sec-alkyl sulfates by an alkylsulfatase from Rhodococcus ruber DSM 44541
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Enantioselective biohydrolysis of sec-alkyl sulfate esters using a bacterial alkylsulfatase from Rhodococcus ruber DSM 44541 proceeded in a stereoselective fashion though inversion of configuration. Thus, from racemic substrates, the corresponding (R)-enantiomers were hydrolyzed selectively to furnish the corresponding sec-alcohol and non-reacted sulfate ester, both of (S)-configuration, which represents a homochiral product mixture. The enantioselectivities were found to depend on the substrate structure and were optimal for sec-sulfate esters in the ω-1 position (up to E=21). Since the enzyme was inactive on prim-sulfate esters, it can be classified as a sec-alkylsulfatase [EC 3.1.6.X].
- Pogorevc, Mateja,Faber, Kurt
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p. 1435 - 1441
(2007/10/03)
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- The association of an ionic surfactants with β-cyclodextrin. An isothermal titration calorimeter study
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The association of a series of anionic surfactants (CnH2n+1SO4Na, n = 6, 8, 10, 12, 14) with β-cyclodextrin was studied by means of the isothermal titration calorimeter (i.t.c.) at T = 298.15 K. For these types of inclusion complexes, the results agreed well with a 1:1 association mode. Apparent values for the association constants, and changes in the standard molar Gibbs energies, enthalpies, and entropies were derived for the association process. The results indicated that the association of surfactants with β-cyclodextrin is characterized by both favourable enthalpy and favourable entropy changes. The results also demonstrated that the longer the alkyl chain of the anionic surfactant, the greater the association constant with β-cyclodextrin.
- Eli, Wumanjiang,Chen, Wenhai,Xue, Qunji
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p. 1283 - 1296
(2007/10/03)
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- Influence of Chain Length on the Sphere-to-Rod Transition in Alkyl Sulfate Micelles
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Using Quasielastic light scattering spectroscopy (QLS) we have deduced the mean hydrodynamic radius (Rh) of alkyl sulfate micelles as functions of chain length (number of carbons nc = 8-16), temperature (0-85 deg C), detergent concentration (0.01-4g/dL), and NaCl concentration (0.1-2 M).In the region of low chain length (nc h values (extrapolated to the cmc) increase approximately linearly with the chain length.These results combained with Huisman's aggregation numbers (nw(cmc)) are consistent with a micellar shape that is close to spherical (axial ratio less than 2).Under conditions of high NaCl concentrations of high NaCl concentration the micelles exhibit a temperature-dependent growth from small spherical aggregates into long spherocylindrical micelles at concentrations above the cmc.With increasing chain length the temperature dependence of Rh becomes stronger and the NaCl and detergent concentrations needed for micellar growth become smaller.Light scattering intensity measurements confirm a rodlike growth for these micelles at all chain lengths.From these Rh measurements, values of the thermodynamic parameter K governing the sphere-to-rod transition are determined by using an extension of our previous thermodynamic model (Missel et al., J.Phys.Chem., 84, 1044 (1980)).A quantitative analysis of the dependence of K on chain length, temperature, and NaCl concentration provides new insights into energetic factors which govern the structure and growth of micelles.
- Missel, Paul J.,Mazer, Norman A.,Benedek, George B.,Carey, Martin C.
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p. 1264 - 1277
(2007/10/02)
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