Differentiation of sulfate and phosphate by H/D exchange mass spectrometry: application to isoflavone

Often phosphorylation or sulfation is an important step which occurs in the signal transduction and cascade of metabolic pathways. Some natural products and metabolites contain one or more sulfate or phosphate groups. Isoflavone sulfate has been identified from high-resolution mass spectrometry (HRMS) and enzymatic digestion by sulfatase. We previously reported the new water-soluble isoflavone analogs, daidzein 7-O-phosphate and genistein 7-O-phosphate, which were surprisingly hydrolyzed by sulfatase. In this previous study, we could not determine the phosphate from the results of HRMS and enzymatic digestion, that is, HRMS and enzymatic digestion did not provide clear evidence. In this case, we drew conclusions from NMR analysis. HRMS has been ineffective with a regular fast atom bombardment (FAB) mass spectrometer to distinguish between phosphate and sulfate since the mass difference is only 0.009 mass units. There was, however, no conventional method of microanalysis to distinguish phosphate from sulfate owing to the same nominal mass. It is still very difficult to determine by negative FABMS [--O--P(==O)(OH)(2)] = 80 and [--O--S(==O)(2)OH] = 80. In this paper, we report a method to distinguish between these groups by using a popular low-resolution mass instrument; thus, phosphate and sulfate were measured by H/D exchange mass spectrometry at the picomole level to differentiate [--O--P(==O)(OD)(2)] = 82 and [--O--S(==O)(2)OD] = 81, respectively. This method is applicable not only to the isoflavone, but also to other phospho and sulfo compounds.     

Effect of fluorine substituents on the properties of nylon copolymers

Nylon 610/65F and nylon 610/65 copolymers were prepared by melt polycondensation from the diethylester of sebacic acid (10) and hexafluoroglutaric acid (5F) or glutaric acid (5) with hexamethylene diamine (6). Reduced specific viscosities of nylon 610/65F were lower than those of nylon 610/65. The crystallinity measured by WAXS and the melting point measured by DTA were depressed by the copolymerization. The melting point depression of nylon 610/65F was much larger than that of nylon 610/65. The thermal decomposition temperature measured by TG was also depressed significantly for nylon 610/65F. The residue at 600°C was increased by the fluorine substitution. The copolymers with higher fluorine content became flame retardant. The solubility was appreciably affected by the fluorine substitution. The contact angle for nylon 610/65F varied in a complicated manner with increasing 65F content and tended to be higher than the corresponding nylon 610/65.     

An elementary proof of the existence of uncountably many nonclosed isometry-invariant geodesics

An isometry A on a Riemannian manifold M will be called of compact type if the subgroup generated by A is relatively compact in the isometry group of M. A geodesic : RM is called invariant under the isometry A if there exists a nonzero constant b such that A(t)=(t+b) for any real t. We prove that if A is an isometry of compact type on a connected Riemannian manifold, and if A has a nonclosed invariant geodesic, then A has uncountably many invariant geodesics.     

Adsorption and order formation of colloidal nanoparticles on a substrate: a Brownian dynamics study

Adsorption process and order formation of electrostatically stabilized colloidal particles with a radius of 50 nm onto a planar surface with countercharge are examined. We perform Brownian dynamics simulations with a new three-dimensional cell model, in which the particle-particle and particle-substrate interactions are modeled based on the DLVO theory. The simulations yield the following results: (1) a larger bulk concentration would be required for larger kappaa to reach order formation to compensate for the decrease in the bulk potential; (2) the phase transition from a disordered to an ordered structure of the adsorbed particles on the substrate is considered to be of the Kirkwood-Alder type of transition through the examination of the two-dimensional pressure of the adsorbed particles; (3) the adsorbed particles are found to form a hexagonally ordered array, only if what we call "one-directional average force" acting on an adsorbed particle exceeds a critical value, which is independent of the ionic strength, or the interaction potentials. The critical value of the one-directional average force is interpreted as the force needed to keep an ordered structure by localizing adsorbed particles at fixed positions. In addition, the critical force is used to develop a new model to estimate the surface coverage at the order-disorder transition and it is demonstrated that the new model gives better estimation than other models previously reported.     

Alcohol-FET sensor based on a complex cell membrane enzyme system

An alcohol -FET sensor was developed by use of a complex enzyme system in a cell membrane and an ion-sensitive field effect transistor (ISFET). The cell membrane of Gluconobacter suboxydans IFO 12528, which converts ethanol to acetic acid, was immobilized on the gate of an ISFET with calcium alginate gel coated with nitrocellulose. This ISFET (1), a reference ISFET without the cell membrane (ISFET 2) and an Ag/AgCl reference electrode were placed in 5 mM Trismalate buffer (pH 5.5, 25°C), and the differential output between ISFETS 1 and 2 was measured. The output of the sensor was stabilized by adding pyrroloquinoline quinone. The response time was ca. 10 min., and there was a linear relationship between the differential output voltage and the ethanol concentration up to 20 mg l^?1. The output of the sensor was stable for 40 h below 30°C. The sensor responded to ethanol, propan- 1-ol and butan- 1-ol, but not to methanol, propan-2-ol and butan-2-ol. The sensor was used to determine blood ethanol.     

Liquid-phase microextraction of tributyltin and triphenyltin coupled with gas chromatography-tandem mass spectrometry. Comparison between 4-fluorophenyl and ethyl derivatizations

This paper describes the liquid-phase microextraction (LPME) of tributyltin (TBT) and triphenyltin coupled with gas chromatography-tandem mass spectrometry. The 4-fluorophenylation and ethylation reactions were used for the derivatization of the organotins. For the two derivatizations, the LPME parameters such as organic solvent, stirring rate, temperature, extraction time and the other additional conditions were examined. Using pure water, the calibration curves, method detection limits (MDLs) and reproducibilities (RSDs) of the two derivatizations were compared under the respective optimized procedures. The 4-fluorophenyl derivatization, which showed a lower MDL (0.36 ng/l) and better reproducibility (RSD = 11% at 10 ng/l) for TBT, was applied to the analysis of seawater. The TBT was detected in the range from 1.1 to 2.0 ng/l in the seawater samples collected in Osaka Bay.     

Radical polymerization behavior of N,N-disubstituted acrylamide: Absolute rate constants for polymerization and copolymerization of N-acryloylpiperidine

The absolute rate constants of propagation (k_p) and of termination (k_t) of N-acryloylpiperidine (NAPi) were determined by the rotating sector method in bulk; k_p = 273 and k_t = 1.79 × 10⁷ L/mol s at 30°C. It was noted that k_p for NAPi was 100 times smaller than that for N,N-dimethylacrylamide (DMAcAm). The absolute rate constants of cross-propagations for copolymerizations with common monomers were evaluated by combination of the k_p value and the monomer reactivity ratios. Quantitative comparison of the rate constants with those of DMAcAm and poly(DMAcAm) radical shows that NAPi is as reactive as DMAcAm and the smaller k_p value for NAPi is ascribable to much the lower reactivity of the poly(NAPi) radical. The large difference in reactivity of the polymer radicals is discussed in relation to the steric factor of the piperadino and the dimethylamino groups which seems to affect the capability of the carboxamide group to stabilize the polymer radical.     

Solvent extraction of microgram amounts of magnesium with 8-quinolinol and tetrabutyl-ammonium iodide followed by spectrophotometry with chlorophosphonazo-III

A rapid and sensitive solvent-extraction procedure for the separation of magnesium is reported. Microgram (0.1–10) amounts of magnesium are extracted with a chloroform solution of 8-quinolinol and tetrabutylammonium iodide in the presence of tartrate and phosphate. Magnesium is then back-extracted into an aqueous buffer solution (pH 7.3; tetrabutylammonium hydroxide—boric acid) and determined spectrophotometrically using chlorophosphonazo-III. Up to 500 mg of sulphate, phosphate or cyanide, 200 mg of chloride, 20 mg of aluminum, barium or silicate, and 2 mg of calcium can be tolerated.     

Application of the TORO technique of 1H NMR to the structural analysis of cyclic peptide isomers having a slightly distorted symmetry from C2

The extended TORO technique was applied to the structural analysis of endo-D-Tyr-gramicidin S, cyclo(-Val-Orn-Leu-D-Phe-D-Tyr-Pro-Val-Orn-Leu-D-Phe-Pro-), which has a slightly distorted symmetry from C2, by the insertion of D-Tyr and equivalent alpha-proton chemical shifts in the 1H NMR spectrum. All NMR signals of the two dominant isomers of this antibiotic with trans-trans prolines were determined by using the extended TORO technique with TOCSY and ROESY spectra. This technique is generally applicable for distinguishing overlapped signals of alpha- and amide protons from the main chains of peptides.