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Acetonitrile as a solvent used in liquid chromatography/mass spectrometry (LC/MS) of peptides and proteins is a relatively toxic solvent (LD50 oral; rat; 2,460 mg/kg) compared to alternatives like methanol (LD50 oral; rat; 5,628 mg/kg) and acetone (LD50 oral; rat; 5,800 mg/kg). Strategies to minimize its consumption in LC are either to reduce the inner diameter of the column or replace acetonitrile with a suitable alternative. Methanol is often recommended to replace acetonitrile in peptide analysis. In this study however, the main focus lies on another alternative solvent for LC/MS of peptides; acetone. A number of model proteins were tryptically digested and the peptide solutions were analyzed on a linear trap quadrupole (LTQ) mass spectrometer. The performances of acetonitrile, methanol and acetone were compared according to the quality of the chromatograms obtained and identification of the peptides using the BioWorks software developed by Thermo Scientific. In accordance to the elutropic series, acetone was found to significantly reduce the retention times of peptides separated by C18 column material with regard to acetonitrile while methanol led to increased retention times. Acetone was the superior solvent to methanol for most of the tested model proteins reaching similar sequence coverage and numbers of identified peptides as acetonitrile. We therefore propose acetone as an alternative to acetonitrile in LC/MS of peptides., (Copyright 2009 John Wiley & Sons, Ltd.)

The electrochemical initiated heterocoupling of 3-methylcatechol and n-hexylamine was investigated. The oxidation of 3-methylcatechol was performed in an electrochemical flow cell with glassy carbon as the working electrode. As a result, the two-electron, two-proton oxidised chinone intermediate undergoes a C-N coupling reaction in the presence of an amine (Michael addition). This mono coupling product can undergo a second two-electron, two-proton oxidation depending on acidic or basic conditions and substrate ratios. This flow cell was coupled on-line with electrospray ionisation mass spectrometry to identify the possible coupling products. Higher substrate concentrations were performed off-line as first scale-up experiments in a two-step procedure. [ABSTRACT FROM AUTHOR]

Flavonols, a class of flavonoids, are jointly responsible for antioxidant activities as free radical acceptors in flowers, fruits and vegetables. Due to their electroactive behaviour, the oxidation of chrysin, flavonol, kaempferol, morin, quercetin and myricetin in methanol was performed in an electrochemical flow cell with glassy carbon as the working electrode. This flow cell was coupled online with electrospray ionisation mass spectrometry to identify the possible oxidation products. Based on these experiments, it was concluded that when certain structural requirement are present, the initial electrode reaction of flavonols involves an electron delivery electrochemical step followed by a chemical step via methanol addition. The redox activity of the selected species explains the number of observed multiple methoxylation. Moreover, we identified a second two-electron, two-proton oxidation of the formed oxidation products of quercetin and myricetin for the first time. [ABSTRACT FROM AUTHOR]