Biological sulphur-containing compounds – Analytical challenges

Abstract

This review covers analytical methods applied to the determination of none volatile sulphur-containing biological compounds. The classes of S-compounds include amino acids, proteins, lipids, carbohydrates and sulphur-containing metabolites. Techniques covered include element specific detectors as well as molecular specific detectors from X-ray absorption near-edge structure (XANES) to elemental and molecular mass spectrometers. The major techniques used are inductively coupled plasma mass spectrometry (ICP-MS) and high-resolution electrospray mass spectrometry (ESI-MS) in their various forms. Both techniques either individually or combined require the sample to be present in liquid form and therefore involve sample preparation usually extraction and depending on sample and molecular class studied potentially also derivatisation in addition to generally requiring chromatographic separation. Over recent years, detection limits achieved by elemental methods and computational methods to extract signals of sulphur-containing compounds out of the mass of data produced by molecular high-resolution mass spectrometers made significant gains. Still the determination of sulphur-containing compounds is challenging, but nowadays the methods have been developed well enough to allow application to real samples for absolute quantification of biomolecules such as proteins or lipids.In this review, we try to show where in our opinion the challenges in the determination of sulphur-containing biological compounds are from the point of view of an elemental analytical chemist. Part one of the review consists of a short description of sulphur-containing compounds as examples of the wide variety encountered in living cells. Part two covers analytical techniques and analytical challenges when analysing sulphur-containing compounds. Due to the wide variety and the use of different analytical methods, we do not cover volatile sulphur-containing compounds and their detection and quantification methods. Classes of sulphur-containing compoundsThis part gives a short summary of sulphur-containing compounds present in biological matrices in addition to the ubiquitous sulphate ions. The major principal structures in which sulphur can occur in nature are summarised in Table 1. Sulphur is essential to life in all its forms. It is involved in its variable molecular species in among others all major redoxprocesses, synthesis of proteins, carbohydrates, secondary metabolites (Figure 1) with bacteria forming the basis of the biological sulphur cycle. Amino acids, peptides and proteinsThe main sulphur-containing amino acids methionine and cysteine are present in most proteins [1]. Methionine itself is essential for human beings, whereas cysteine can be synthesised in a five-step process from methionine. Cysteine is redox active and often binds thiophilic metal-ions in the catalytic centre of proteins. It is also often involved in stabilising the three-dimensional structure of proteins by formation of disulphide bridges [2]. Oxidation of cysteine can le...

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A Simple and Sensitive Inhibitory Kinetic Method for the Carbocisteine Determination

“…In this regard, several kinetic studies on the exchange of integrated cyanide with ligand variants containing -O, -P, -S, and -N donor atoms from [Ru(CN)6] 4were examined by numerous authors [18][19]. Numerous reports are available for the micro-level determination of sulfur-containing drugs and molecules in biological samples and pharmaceutical preparations [20][21][22][23]. The determination methods includes potentiometry [24], NMR-spectrometry [25], colorimetry [20], chromatography [26][27][28], flow injection analysis [29], fluorimetry [30], voltammetry [31] and spectrophotometry [32,33].…”