A Simple and Specific Colorimetric Determination of Cysteine with p-Dimethylaminocinnamaldehyde

Abstract

Summary:A simple and specific assay was developed for the determination of cysteine. Cysteine was reacted with /7-dimethylaminöcinnamaldehyde in methanol at 60 °C for 2 h in the presence of sulphuric acid äs a catalyst. Absorbance was ineasured at 587 nm; the chromogen was stable at 60 °C for at least 5 h. The colour reactiqn was specific for cysteine, and was negative for other amino acids but positive for cysteamine. The absorbance followed Beer's law in the ränge from 0.825 to 413« 1/1, and the apparent molar lineic absorbance was calculated to be 5000 m 2 · mol" 1 . This procedure is applicable to the determination of cysteine and cystine in amino acid mixtures and in plasma, since cystine can be quantitatively reduced to cysteine with dithiothreitol under alkaline conditions. Recovery of cysteine and cystine from human plasma was 98.5 to 103% and 94.2 to 102%, respectively. Einfache und spezifische kolorimetrische Bestimmung von Cystein mit p-Dimethylaminocinnamaldehyd Zusammenfassung

Determination of cysteine in pharmaceuticals via liquid chromatography with postcolumn derivatization

“…The important role that thiol compounds in general and cysteine in particular play in pharmaceutical formulations places a premium on an analytical methodology that is highly sensitive and selective for this species. While many methods have been reported for the determination of cysteine, including ion exchange chromatography (1)(2)(3)(4); spectophotometry (5)(6)(7)(8)(9)(10)(11); gas (12)(13)(14), thin-layer (15,16), and high-performance liquid chromatographies (17)(18)(19)(20)(21)(22)(23)(24)(25)(26); polarography (11); and fluorometry (27)(28)(29); these methodologies generally suffer from sensitivity, specificity, or productivity limitations. Specificity is particularly critical in most pharmaceutical applications, where the formulations may include a large number (and quantity) of structurally similar species, their degradation products, and matrix components (pH buffers, preservatives).…”

Fluorescent Indicators for Disease Biomarkers

“…2.5) at 60 0 C in methanol, in presence of catalytic amounts of sulfuric acid. 32 The absorption max of reaction product was observed at 587 nm. This method has been widely used as the detection method for free cysteine in solutions and TLC tests.…”

Selective fluorescence detection of cysteine and N-terminal cysteine peptide residues

“…1 Aldehyde-functionalized fluorophores and chromophores can be used for highly selective detection of homocysteine (Hcy) and/or cysteine (Cys) over all other sulfhydryls due to characteristic thiazinane or thiazolidine formation, respectively. 2 Moreover, selectivity for Cys 3 has been directly achieved at room temperature via visible detection using α,β-unsaturated aldehydes initially in 2005. 4 Unlike our previous work in which the response toward thiols resulted in fluorescence quenching, we report herein a new fluorogenic fluorescein derivative ( 1 ) exhibiting a combination of covalent and non-covalent interactions between the fluorophore and bound analyte which generates a turn-on response.…”