Atmospheric pressure chemical ionization Fourier transform ion cyclotron resonance mass spectrometry for complex thiophenic mixture analysis.

RATIONALE: Polycyclic aromatic sulfur heterocycles (PASHs) are detrimental species for refining processes in petroleum industry. Current mass spectrometric methods that determine their composition are often preceded by derivatization and dopant addition approaches. Different ionization methods have different impact on the molecular assignment of complex PASHs. The analysis of such species under atmospheric pressure chemical ionization (APCI) is still considered limited due to uncontrolled ion generation with low- and high-mass PASHs. METHODS: The ionization behavior of a model mixture of five selected PASH standards was investigated using an APCI source with nitrogen as the reagent gas. A complex thiophenic fraction was separated from a vacuum gas oil (VGO) and injected using the same method. The samples were analyzed using Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS). RESULTS: PASH model analytes were successfully ionized and mainly [M + H](+) ions were produced. The same ionization pattern was observed for the real thiophenic sample. It was found that S1 class species were the major sulfur-containing species found in the VGO sample. These species indicated the presence of alkylated benzothiophenic (BT), dibenzothiophenic (DBT) and benzonaphthothiophenic (BNT) series that were detected by APCI-FTICR MS. CONCLUSIONS: This study provides an established APCI-FTICR MS method for the analysis of complex PASHs. PASHs were detected without using any derivatization and without fragmentation. The method can be used for the analysis of S-containing crude oil samples.

High molecular weight non-polar hydrocarbons as pure model substances and in motor oil samples can be ionized without fragmentation by atmospheric pressure chemical ionization mass spectrometry.

RATIONALE: High molecular weight non-polar hydrocarbons are still difficult to detect by mass spectrometry. Although several studies have targeted this problem, lack of good self-ionization has limited the ability of mass spectrometry to examine these hydrocarbons. Failure to control ion generation in the atmospheric pressure chemical ionization (APCI) source hampers the detection of intact stable gas-phase ions of non-polar hydrocarbon in mass spectrometry. METHODS: Seventeen non-volatile non-polar hydrocarbons, reported to be difficult to ionize, were examined by an optimized APCI methodology using nitrogen as the reagent gas. RESULTS: All these analytes were successfully ionized as abundant and intact stable [M-H](+) ions without the use of any derivatization or adduct chemistry and without significant fragmentation. Application of the method to real-life hydrocarbon mixtures like light shredder waste and car motor oil was demonstrated. CONCLUSIONS: Despite numerous reports to the contrary, it is possible to ionize high molecular weight non-polar hydrocarbons by APCI, omitting the use of additives. This finding represents a significant step towards extending the applicability of mass spectrometry to non-polar hydrocarbon analyses in crude oil, petrochemical products, waste or food.

Synthesis of novel enantiomerically pure tetra-carbohydrazide cyclophane macrocycles.

A total of twelve novel enantiomerically pure tetra-carbohydrazide cyclophane macrocycles have been synthesised in quantitative yields by reacting chiral (4R,5R)- and (4S,5S)-1,3-dioxolane-4,5-dicarbohydrazides with aromatic bis-aldehydes in a [2 + 2]-cyclocondensation reaction. The compounds show a dynamic behaviour in solution, which has been rationalized in terms of an unprecedented conformational interconversion between two conformers one stabilised by intramolecular hydrogen bonding and π-π stacking interactions.

Hill coefficients of dietary polyphenolic enzyme inhibitiors: can beneficial health effects of dietary polyphenols be explained by allosteric enzyme denaturing?

Inspired by a recent article by Prinz, suggesting that Hill coefficients, obtained from four parameter logistic fits to dose-response curves, represent a parameter allowing distinction between a general allosteric denaturing process and real single site enzyme inhibition, Hill coefficients of a number of selected dietary polyphenol enzyme inhibitions were compiled from the available literature. From available literature data, it is apparent that the majority of polyphenol enzyme interactions reported lead to enzyme inhibition via allosteric denaturing rather than single site inhibition as judged by their reported Hill coefficients. The results of these searches are presented and their implications discussed leading to the suggestion of a novel hypothesis for polyphenol biological activity termed the insect swarm hypothesis.