Chromatographic determination of the mycotoxin patulin in fruit and fruit juices

Patulin is a mycotoxin produced by several fungal species of the genera Penicillium and Aspergillus, but principally by Penicillium expansum on fruit such as apples. The occurrence of patulin as a natural contaminant of apple juice is a worldwide problem and international recommendations and regulations have been made for maximum levels permitted in consumer products. This paper reviews currently available analytical methods for its determination in fruit and fruit juices. Of these, HPLC with ultraviolet or, preferably, photodiode array detection is most widely used, although GC and TLC methods have also been described.     

Carbon nanohorns grown from ruthenium nanoparticles

A nanoscale ruthenium/gold bimetallic cluster of clusters has been used as a molecular precursor to produce pure ruthenium nanoparticles (seeds) as catalysts for the growth of carbon nanohorns (CNHs).     

Moisture induced solid phase degradation of l-ascorbic acid part 2, separation and characterization of the major degradation products

The influence of moisture in the presence and absence of air on the solid state degradation of l-ascorbic acid has been investigated previously [1]. Reaction kinetics were studied using tristimulus colorimetry and a quantitative high performance liquid chromatographic assay for both total l-ascorbic acid and dehydroascorbic acid. The degradation gave rise to a discolouration of the samples, the most severely degraded samples were almost black in appearance although over 68% w/w of the l-ascorbic acid remained. The samples were analyzed for the presence of carbonyl compounds, furan related compounds, compounds responsible for the discolouration and evolution of carbon dioxide. No 2,4-dinitrophenylhydrazine (2,4-DNP) derivatives of carbonyl compounds or furan related compounds were detected by HPLC. An HPLC screening procedure was developed which was used to monitor for compounds responsible for the discolouration, at least eight unknown compounds were resolved and a relative response factor of 5.47 was assigned to them with respect to l-ascorbic acid at 280 nm. One mole of carbon dioxide was evolved per mole of l-ascorbic acid. This paper describes the investigation into the identity of the degradation products.     

Moisture induced solid phase degradation of l-ascorbic acid Part 1: a kinetic study using tristimulus colorimetry and a quantitative HPLC assay

l-Ascorbic acid was found to degrade in the solid phase with discoloration under the influence of moisture in proportion to the moisture content. This degradation pattern was different to that in solution and followed zero order kinetics. The exclusion of air reduced the rate of reaction suggesting the degradation may proceed via an oxidative route but no evidence was found for the presence of dehydroascorbic acid. A method was developed for the determination of dehydroascorbic acid using an automated precolumn reduction reaction with dl-dithiothreitol. The degradation was found to be zero order and activation energy was been measured at 37.57 kJ mol(-1) by high performance liquid chromotography (HPLC) assay and 33.30 kJ mol(-1) by tristimulus colorimetry, resulting in a 12.8% difference between the two methods. Tristimulus colorimetry was more sensitive to the onset of degradation than HPLC assay, but it is non-specific. The purpose of this study was to obtain kinetic data on the rate of degradation of l-ascorbic acid alone under the influence of moisture and air and to identify whether tristimulus colorimetry could be used as a rapid and non-destructive means of monitoring for the degradation of l-ascorbic acid in the solid phase. Further studies to determine the degradation pathway and to identify the degradation products are to be reported in subsequent papers.     

Infrared spectra of metal anthranilates

The infrared spectra of the sodium salts and the Mn(II), Co(II), Ni(II), Cu(II) and Zn(Il) chelates of anthranilic acid and 5-methyl-, 5-chloro-, 5-bromo-and 5-iodo-anthranilic acid are discussed. ¹⁵N-Labelling of sodium anthranilate and the complexes of anthranilic acid provides assignments of the ligand vibrations involving the amino group. The metal-ligand stretching frequencies (vM-N and vM-O) are assigned by observing the effects on the spectra caused by ¹⁵N-labelling, metal ion substitution and ligand substitution. The vCu-O bands are split by tetragonal distortion in the Cu(II) complex which involves elongation of the axial Cu~O bonds. The metal ion dependence of vM-N and vM-O parallels the Irving-Williams stability sequence. The ligand substituents shift vM-O in accordance with their inductive effects while vM-N exhibits a substituent dependence which is roughly the opposite of that shown by vM-O.     

Use of U-shaped donor-bridge-acceptor molecules to study electron tunneling through nonbonded contacts

A systematic determination of electronic coupling matrix elements in U-shaped molecules is demonstrated. The unique architecture of these systems allows for the determination of the electronic coupling through a pendant molecular moiety that resides between the donor and acceptor groups; this moiety quantifies the efficiency of electron tunneling through nonbonded contacts. Experimental electron-transfer rate constants and reaction free energies are used to calibrate a molecular-based model that describes the solvation energy. This approach makes it possible to experimentally determine electronic couplings and compare them with computational values.