Cysteine solution preparation

Use free cysteine rather than the hydrochloride salt. Cysteine solutions will oxidize readily and should be freshly prepared daily. 

Test Solution Prepare a solution from the enzyme preparation so that 2 mL of the final dilution will give a AA in the Procedure between 0.2 and 0.5. Weigh the sample accurately, transfer it quantitatively to a glass mortar, and triturate with Phosphate-Cysteine-EDTA Buffer Solution. Transfer the mixture quantitatively into a volumetric flask of appropriate size, dilute to volume with Phosphate-Cysteine-EDTA Buffer Solution, and mix. 

The exchange of labelled sulphur can be promoted by enzyme catalysts, instead of heating. Bird egg yolk and the cysteine desulphydrase that it contains catalyse the exchange of sulphur-35 from Na2 S to L-cysteine, L-cystine and L-cysteic acid. In a typical experiment, 150 ml of a buffer solution containing 2 millimoles of cysteine-HCl, 2 millimoles of Naa S and 500 mg of cysteine desulphydrase preparation is incubated at 38°C for 15 h. A mixture of 74-4% cystine- S and 25-3% cysteine- S is obtained. L-Cystine- S is subsequently reduced electrolytically to cysteine- S. The total yield of L-cysteine- S obtained by isotope exchange is 70%. 

An interesting crop of papers dealing with polysulphides contains a variety of preparative procedures. Treatment of C HaSH with A A -thiobisphthalimide gives the trisulphide C HaSaC Hg, and a selenium analogue (H02CCMe2S>2Se has been prepared from the thiol and selenous or selenic acid. Cysteine trisulphide is a minor product of the radiolysis of cysteine solutions at pH 5.3. The use... 

Permanent coloration can also be achieved by exposing hair to certain metals copper, silver, and especially lead salts. Preparations containing aqueous solutions of lead acetate may include a source of sulfur, usually thiosulfate, which may react with cystine in the hair to produce some cysteine or may react directiy with the metal ion to form dark metallic sulfides. Preparations of this type, which darken hair gradually, are not universally considered safe. 

Thiazolidines have been prepared from /3-aminothiols—for example, cysteine—to protect the —SH and — NH groups during syntheses of peptides, including glu-tathione. Thiazolidines are oxidized to symmetrical disulfides with iodine they do not react with thiocyanogen in a neutral solution. 

Reactions between A -(l-chloroalkyl)pyridinium chlorides 33 and amino acids in organic solvents have a low synthetic value because of the low solubility of the amine partner. A special protocol has been designed and tested in order to circumvent this drawback. Soon after the preparation of the salt, an aqueous solution of the amino acid was introduced in the reaction medium and the two-phase system obtained was heated under reflux for several hours. However, this was not too successful because sulfur dioxide, evolved during the preparation of the salt, was converted into sulfite that acted as an 5-nucleophile. As a result, A -(l-sulfonatoalkyl)pyridinium betaines such as 53 were obtained (Section IV,B,3) (97BSB383). To avoid the formation of such betaines, the salts 33 were isolated and reacted with an aqueous solution of L-cysteine (80) to afford thiazolidine-4-carboxylic acids hydrochlorides 81 (60-80% yields). 

Prepare a set of standards by dissolving cysteine in 0.1M sodium phosphate, pH 8.0, at an initial concentration of 2mM (3.5mg/ml) and serially diluting this solution (1 1) with reaction buffer down to at least 0.125 mM. This will produce five solutions of cysteine for generating a standard curve. If a more dilute concentration range is required, continue to serially dilute until a set of standards in the desired range is obtained. 

The Au-NPs were electrodeposited on the carbon fiber microelectrodes from 0.5 M H2S04 solution containing l.OmM Na AuCl4] by applying a potential step from 1.1 V to 0V for 30 s. Cysteine-modified Au-NPs-electrodeposited CFMEs were prepared by... 

Chen and coworkers were the first to describe the electrochemical behavior of PB NPs [41]. They prepared solutions of PB NPs by reaction of Fe(III) with Fe(CN)6 in the presence of H2O2, giving 30-50-nm diameter NPs. These were then immobilized at cysteine-modified Au electrodes with pendant amine groups by prolonged (10 h) exposure of the modified electrode to a solution of the NPs. This produced a monolayer of immobilized NPs that was subsequently examined using cyclic voltammetry. Interestingly, they observed two redox processes near 0.25 V vs. 

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