Chiral electrokinetic chromatography using dipeptide polymeric surfactants: present state of the art

Polymeric amino acid based surfactants have been recently employed as pseudostationary phases in capillary electrophoresis. These phases are effective for chiral separation of analytes in different charge states and hydrophobicities. This review paper focuses on polymeric dipeptide surfactants. The benefits of dipeptide over single amino acid micelle polymers are shown. Some aspects of dipeptide surfactants that are presented here includes the amino acid order, effect of number and position of chiral centers, and steric factors on enantiomeric separation of chiral compounds in different charge states. In addition, the preferential site of interaction of the chiral analyte using diastereomers of polymeric dipeptide surfactants is discussed.     

Determination of carbaryl as its primary metabolite, 1-naphthol, by reversed-phase high-performance liquid chromatography with fluorometric detection

Carbaryl and its hydrolysis product, 1-naphthol, are determined simultaneously, and in a mixture of other pesticides, by reversed-phase high-performance liquid chromatography (HPLC). Fluorometric detection affords a higher degree of selectivity than absorbance detection, while providing detection limits of 1.0 ng ml(-1) and 1.4 mg ml(-1) for 1-naphthol and carbaryl, respectively. The described method requires no enrichment of samples and includes a simple hydrolysis step. Additionally, enhancement of fluorescence detection signal intensity is explored through HPLC solvent composition effects as well as through formation of cyclodextrin inclusion complexes. The method described in this report is a selective and fast alternative to the currently accepted U.S. Environmental Protection Agency (EPA) method of detection carbaryl in ground water.     

Proton inventory studies of alpha-thrombin-catalyzed reactions of substrates with selected P and P' sites

Deuterium kinetic solvent isotope effects for the human alpha-thrombin-catalyzed hydrolysis of (1) substrates with selected P(1)-P(3) sites, Z-Pro-Arg-7-amido-4-methylcoumarin (7-AMC), N-t-Boc-Val-Pro-Arg-7-AMC, Bz-Phe-Val-Arg-4-nitroanilide (pNA), and H-D-Phe-L-Pip-Arg-pNA, are (DOD)k(cat) = (2.8-3.3) +/- 0.1 and (DOD)(k(cat)/K(m)) = (0.8-2.1) +/- 0.1 and (2) internally fluorescence-quenched substrates (a) (AB)Val-Phe-Pro-Arg-Ser-Phe-Arg-Leu-Lys(DNP)-Asp-OH, an optimal sequence, and (b) (AB)Val-Ser-Pro-Arg-Ser-Phe-Gln-Lys(DNP)-Asp-OH, recognition sequence for factor VIII, are (DOD)k(cat) = 2.2 +/- 0.2 and (DOD)(k(cat)/K(m)) = (0.8-0.9) +/- 0.1, at the pL (L = H, D) maximum, 8.4-9.0, and (25.0-26.0) +/- 0.1 degrees C. The most plausible models fitting the partial isotope effect (proton inventory) data have been selected on the basis of lowest values of the reduced chi squared and consistency of fractionation factors at all substrate concentrations, assuming rate-determining acylation. The data for Z-Pro-Arg-7-AMC are consistent with a single-proton bridge at the transition state phi(TS) = 0.39 +/- 0.05 and components for solvent reorganization phi(S) = 0.8 +/- 0.1 and phi(S) = 1.22 for k(cat) and k(cat)/K(m), respectively. The data for tripeptide amides fit bowl-shaped curves; an example is N-t-Boc-Val-Pro-Arg-7-AMC: phi(TS)(1) = phi(TS)(2) = 0.57 +/- 0.01 and phi(S) = 1 for k(cat) and 1.6 +/- 0.1 for k(cat)/K(m). Proton inventories for the nonapeptide (2b) are linear. The data for k(cat) for H-D-Phe-L-Pip-Arg-pNA and the decapeptide (2a) are most consistent with two identical fractionation factors for catalytic proton bridging, phi(TS)(1) = phi(TS)(2) = 0.68 +/- 0.02 and a large inverse component (phi(S) = 3.1 +/- 0.5) for the latter, indicative of substantial solvent reorganization upon leaving group departure. Proton inventory curves for k(cat)/K(m) for nearly all substrates are dome-shaped with an inverse isotope effect component (phi(S) = 1.2-2.4) originating from solvent reorganization during association of thrombin with substrate. These large contributions from medium effects are in full accord with the conformational adjustments required for the fulfillment of the dual, hemostatic and thrombolytic, functions of thrombin.     

Oscillatory persistent currents in self-assembled quantum rings

We report the direct measurement of the persistent current carried by a single electron by means of magnetization experiments on self-assembled InAs/GaAs quantum rings. We measured the first Aharonov-Bohm oscillation at a field of 14 T, in perfect agreement with our model based on the structural properties determined by cross-sectional scanning tunneling microscopy measurements. The observed oscillation magnitude of the magnetic moment per electron is remarkably large for the topology of our nanostructures, which are singly connected and exhibit a pronounced shape asymmetry.     

Detection of NMR signals with a radio-frequency atomic magnetometer

We demonstrate detection of proton NMR signals with a radio-frequency (rf) atomic magnetometer tuned to the NMR frequency of 62 kHz. High-frequency operation of the atomic magnetometer makes it relatively insensitive to ambient magnetic field noise. We obtain magnetic field sensitivity of 7 fT/Hz1/2 using only a thin aluminum shield. We also derive an expression for the fundamental sensitivity limit of a surface inductive pick-up coil as a function of frequency and find that an atomic rf magnetometer is intrinsically more sensitive than a coil of comparable size for frequencies below about 50 MHz.     

Reversed-phase high-performance liquid chromatography method for the determination of prolactin in bacterial extracts and in its purified form

Reversed-phase high-performance liquid chromatography methodology for the determination of human prolactin (hPRL) in bacterial periplasmic space or in purified preparations has been developed. The technique, based on the high hydrophobicity of the hPRL molecule, allows its separation from the bulk of bacterial proteins. The precision for periplasmic shock fluid analysis was characterized by relative standard variations of 3-7% for intra-day and of 3-25% for inter-day determinations. Accuracy, evaluated by recovery tests, was of the order of 90%, a calibration curve being constructed with the use of a lyophilized osmotic shock fluid extract, which provided a stable, readily prepared internal reference. Sensitivity was of the order of 0.5 microg of hPRL. The methodology developed also provided a tool for comparing the hydrophobicity of glycosylated and non-glycosylated prolactin molecules obtained from several different species and of different preparations of native or biosynthetic human prolactin.     

Applications of inverse gas chromatography in the study of liquid crystalline stationary phases

We describe measurements on a number of low-molar-mass and polymeric liquid crystals that contain the same mesogenic groups. Transition temperatures for the mesophases have been measured and the supercooled region of hexyloxycyanobiphenyl studied, revealing some differences from the stable mesophase. Activity coefficients and interaction parameters for a range of probes have been measured and allow us to determine the nature and origin of the thermodynamic interactions in the systems. A discussion of how this fundamental information can be used in designing more efficient stationary phases for analytical gas chromatography is also presented.     

Separation and preconcentration in a batch mode of Cd(II), Cr(III, VI), Cu(II), Mn(II, VII) and Pb(II) by solid-phase extraction by using of silica modified with N-propylsalicylaldimine

The complexes formed between IE11 and Cd(II), Cr(III), Cu(II), Mn(II) and Pb(II) were identified and confirmed by IR, UV and pH-metric titration. The uptake behavior of porous silica modified with N-propylsalicylaldimine (IE11) and these metal ions were studied. Log k(d) was found to be within the range 2.19-5.16 depending on pH and time of stirring. IE11 was used in the separation and preconcentration of Cd(II), Cr(III, VI), Cu(II), Mn(II, VII) and Pb(II) from some natural water samples. Data were compared with those obtained by the solvent extraction method APDC/MIBK. The proposed methodology allows to verify an improvement in the water quality of Nile River probably attributed to high to moderate floods in the last few years. The method was found to be accurate and not subject to random error, i.e. precise.