Spectrophotometric determination of some sulphur compounds and tryptophan with brucine and sodium metaperiodate

Abstract

Brucine (2,3-dimethoxystrychnidin-lO-one) under acidic conditions has been reported to be an effective reagent for the spectrophotometric determination of NO3-, NO2-and Ce4+. 1.2 Subsequent investigations have shown that in combination with potassium persulphate, it can also be used for the spectrophotometric determination of halides3 and c y ~t e i n e . ~ Potassium persulphate was found to be a specific reagent for cysteine, as other thiols tested and amino acids (thioglycollic acid, S-methylcysteine, N-acetylcysteine, cystine, homocystine and glutathione) did not interfere. However, the stability of the blue species formed and the precision and accuracy of this method was not good.Sodium metaperiodate (104-) is an efficient oxidant for converting methyl-substituted o-dihydric phenols into o-qui-nones5 and is also a colour stabiliser.6 This investigation was concerned with the development of a spectrophotometric method for the routine determination of thiols and biologically active amino acids (thioglycollic acid, P-mercaptoethanol, P-mercaptopropionic acid, thiosalicylic acid, cystamine hydrochloride, 2-aminothiophenol, 4-aminothiophenol, cysteine , cystine , tryptophan, glutathione and penicillamine) using brucine -104-. The purple colour (hmax, 500-510 nm) developed was stable for 10 h and hence was suitable for routine work with good precision and accuracy. Experimental ApparatusAbsorbance measurements were carried out with a Systronics Model 105 (MKl) spectrophotometer using 1-cm glass cells.

Electroanalytical exploitation of quinone–thiol interactions: application to the selective determination of cysteine

“…The aim of this paper was to report on the application of electrochemical techniques, principally square wave voltammetry, to the reaction of quinones with thiols as a method of quantifying the latter. The addition of thiols to quinone moieties is well established, forming the basis of numerous spectroscopic [39][40][41][42] and pre-column chromatographic derivatisation protocols. 43,44 The basic reaction pathway exploited in the proposed protocol is shown in Scheme 1 with the foundations of the approach relying on the ability of the electrochemical technique primarily to differentiate between the unreacted quinone (I) and the consequent quinone-thiol adduct (II and III).…”

An electrochemical platform for acetylcholinesterase activity assay and inhibitors screening based on Michael addition reaction between thiocholine and catechol-terminated SAMs

“…The platform has proven to have potential applications in the ultrasensitive analysis of metal ions. 16 The metabolic mechanism of catechol-containing compounds in biological systems, 17,18 which involves their oxidation to the corresponding o-quinones and subsequent nucleophilic addition reaction with thiols, 19 has been investigated in studies of catechol estrogens, [20][21][22] catecholamines, 23 p-cresol (4-methylphenol), 24 chlorogenic acid 25 and dopamine. 26 The same mechanism forms the basis of the thiol-catechol reactions in this work.…”

Ultraviolet and light absorption spectrometry

“…p-Chloranil has been used to determine primary and secondary amines based on the formation of a colored monoamine-quinone (458). Methods utilizing periodate oxidation followed by addition of m-phenylenediamine (387) and dimethyl-m-phenylenediamine (386) for phenols and brucine (504) for tryptophan and thiols have been published. The red (500-520 nm) antipyrine dye formed by alkaline oxidation with potassium ferricyanide in the presence of 4-aminoantipyrine has been used for the determination of 8-hydroxyquinoline and its 5-chloro-7-iodo-, 5,7-diiodo-, and 8-hydroxy-7-iodo-5-sulfonic acid derivatives (34) and of terbutaline sulfate, amoxycillin, isoxsuprine hydrochloride, and salbutamol in pharmaceutical preparations (420).…”