Manganese detection in marine sediments: anodic vs. cathodic stripping voltammetry

Three different electroanalytical techniques for the detection of manganese in marine sediments are evaluated. The anodic stripping voltammetry of manganese at an in situ bismuth-film-modified boron-doped diamond electrode and cathodic stripping voltammetry at a carbon paste electrode are shown to lack the required sensitivity and reproducibility whereas cathodic stripping voltammetry at a bare boron-doped diamond electrode is shown to be reliable and selective with a limit of detection, from applying a 60 s accumulation period of 7.4 × 10⁻⁷ M and a sensitivity of 0.24 A M⁻¹. The method was used to evaluate the manganese content of marine sediments taken from Šibenik, Croatia.     

Perylene-based profluorescent nitroxides for the rapid monitoring of polyester degradation upon weathering: An assessment

A profluorescent nitroxide possessing an isoindoline nitroxide moiety linked to a perylene fluorophore was developed to monitor radical mediated degradation of melamine-formaldehyde crosslinked polyester coil coatings in an industry standard accelerated weathering tester. Trapping of polyester-derived radicals (most likely C-radicals) that are generated during polymer degradation leads to fluorescent closed-shell alkoxy amines, which was used to obtain time-dependent degradation profiles to assess the relative stability of different polyesters towards weathering. The nitroxide probe couples excellent thermal stability and satisfactory photostability with high sensitivity and enables detection of free radical damage in polyesters under conditions that mimic exposure to the environment on a time scale of hours rather than months or years required by other testing methods. There are indications that the profluorescent nitroxide undergoes partial photo-degradation in the absence of polymer-derived radicals. Unexpectedly, it was also found that UV-induced fragmentation of the NO–C bond in closed-shell alkoxy amines leads to regeneration of the profluorescent nitroxide and the respective C-radical. The maximum fluorescence intensity that could be achieved with a given probe concentration is therefore not only determined by the amount of polyester radicals formed during accelerated weathering, but also by the light-driven side reactions of the profluorescent nitroxide and the corresponding alkoxy amine radical trapping products. Studies to determine the optimum probe concentration in the polymer matrix revealed that aggregation and re-absorption effects lowered the fluorescence intensity at higher concentrations of the profluorescent nitroxide, but too low probe concentrations, where these effects would be avoided, were not sufficient to trap the amount of polyester radicals formed upon weathering. The optimized experimental conditions were used to assess the impact of temperature and UV irradiance on polymer degradation during accelerated weathering.     

p-aminophenyl phosphate: an improved substrate for electrochemical enzyme immnoassay

An alternative substrate is described for enzyme immunosaasay with electrochemical detection. Alkaline phosphatase (EC.3.1.3.1) activity is determined by using p-aminophenyl phosphate as the enzyme substrate. Enzyme-generated p-aminophenol is detected amperometrically at a glassy carbon electrody by liquid chromatography with electrochemical detection. The oxidation potential obtained for the detectionof p-aminophenol is lower than that for phenol, the previously used substrate product. The detection limit for p-aminophenol is 0.20pmol. A detection limit of 30 pg ml^-1 for digoxin and a 5-min incubationtime for the enzyme reaction were obtained with the new system.     

Improved RP‐HPLC method for determination of bovine lactoferrin and its proteolytic degradation in simulated gastrointestinal fluids

The objective of this study was to qualitatively and quantitatively evaluate bovine lactoferrin (bLf) and its stability using a rapid RP‐HPLC method. bLf could be rapidly detected within 20 min and quantitated at levels down to 5 µg/mL, and the equation of linearity was y = 86.10x + 178.31 with the correlation coefficient (r²) 0.9997. Quantitative data obtained in the present study proved the improved RP‐HPLC method to be a sensitive and accurate analytical tool for bLf determination. The proteolytic cleavage of bLf in simulated human gastrointestinal fluids was further analyzed by RP‐HPLC, and found to follow pseudo‐first‐order kinetics. The typical equation obtained by pepsin was log₁₀ [A_t]/[A₀] = ?0.03x (r² = 0.85), and log₁₀ [A_t]/[A₀] = ?0.01x (r² = 0.81) for trypsin and chymotrypsin combination. Pepsinolysis of bLf in simulated gastric fluid was relatively fast with the half‐life t_1/2 23.1 min. The digestion of bLf in simulated intestinal fluid was slower with about a 3‐fold increase in half‐life (69.3 min). After the complete proteolysis of bLf, small cleaved peptide fragments were fully separated and identified by RP‐HPLC. The proteolytic study indicated that this validated RP‐HPLC was able to evaluate bLf stability though monitoring the derivatization products. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis of Quadruply Carbon-13 Labeled Tetramethyltetrathiaful Valene

A short synthesis of tetramethyltetrathiafulvalene quadruply labeled with carbon-13 is described.     

N-Acetylneuraminic Acid: Neoglycoproteins and Pseudopolysaccharides

Abstract

A simplified procedure for the synthesis of acetochloroneuraminic acid is described starting from the methyl ester. N-acetyl neuraminic acid α-allyl glycoside was prepared in high yield using silver salicylate as catalyst. Reductive ozonolysis of the allyl group, followed by direct reductive ami nation to protein carriers, gave immunogenic neoglycoproteins. Copolymerization of the α-allyl glycoside with acrylamide produced a water-soluble pseudopolysaccharide useful for the EL ISA technique.     

STUDIES OF HETEROCYCLIC COMPOUNDS: VI1 THE MASS SPECTRA OF SOME 2-THIOPHENEMERCURIC DERIVATIVES

Abstract

The mass spectra of some 2-thiophenemercuric derivatives are determined and the fragmentation interpretations are based on mechanistic analogy and supported in some cases by metastable peaks and low energy mass spectra. They all fragment ultimately to the 2-thienyl cation formed either through a two-step process, by cleavage of Hg[sbnd]X bond to give the 2-thienylmercuric cation, followed by extrusion of mercury, or by a one-step process through cleavage of carbon-mercury bond. Their base peaks being the C₃H₃ ⁺ion (m/e 39).