L-cysteine In Solution Research Articles

Speciation of arsenic by hydride generation–atomic absorption spectrometry (HG–AAS) in hydrochloric acid reaction medium

The effects on the absorbance signals obtained using HG–AAS of variations in concentrations of the reaction medium (hydrochloric acid), the reducing agent [sodium tetrahydroborate(III); NaBH 4], the pre-reducing agent ( l-cysteine), and the contact time (between l-cysteine and arsenic-containing solutions) for the arsines generated from solutions of arsenite, arsenate, monomethylarsonic acid (MMA), and dimethylarsenic acid (DMA), have been investigated to find a method for analysis of the four arsenic species in environmental samples. Signals were found to be greatly enhanced in low acid concentration in both the absence (0.03–0.60 M HCl) and the presence of l–cysteine (0.001–0.03 M HCl), however with l-cysteine present, higher signals were obtained. Total arsenic content and speciation of DMA, As(III), MMA, and As(V) in mixtures containing the four arsenic species, as well as some environmental samples have been obtained using the following conditions: (i) total arsenic: 0.01 M acid, 2% NaBH 4, 5% l-cysteine, and contact time<10 min; (ii) DMA: 1.0 M acid, 0.3–0.6% NaBH 4, 4.0% l-cysteine, and contact time <5 min; (iii) As(III): 4–6 M acid and 0.05% NaBH 4 in the absence of l-cysteine; (iv) MMA: 4.0 M acid, 0.03% NaBH 4, 0.4% l-cysteine, and contact time of 30 min; (v) As(V): by difference. Detection limits (ppb) for analysis of total arsenic, DMA, As(III), and MMA were found to be 1.1 ( n=7), 0.5 ( n=5), 0.6 ( n=7), and 1.8 ( n=4), respectively. Good percentage recoveries (102–114%) of added spikes were obtained for all analyses.

L-Cysteine determination using a polyphenol oxidase-based inhibition flow injection procedure

The use of crude extract of sweet potato root ( Ipomoea batatas L. Lam.) as a source of polyphenol oxidase (PPO; tyrosinase; EC 1.14.18.1) for the determination of L-cysteine in pharmaceutical products is reported. This enzyme catalyses the oxidation of catechol to o-quinone with a strong absorption at 410 nm. When L-cysteine solution is inserted into the flow injection (FI) system, its inhibitory effect on the PPO activity was proportional to the L-cysteine concentration. The analytical curve of absorbance versus concentration of L-cysteine obtained was A = 0.851 − 963.16[ L-cysteine]; r = 0.9987 in the L-cysteine concentration range from 6.0 × 10 −5 to 8.0 × 10 −4 mol l −1 with a detection limit of 4.4 × 10 −6 mol l −1. Recovery of L-cysteine from three samples ranged from 98.8 to 101.4% and the relative standard deviations (Sr) were less than 1.2% for solutions containing 2.0 × 10 −4 and 4.0 × 10 −4 mol l −1 of L-cysteine ( n = 10) with stable baselines. The throughput was 26 determinations per hour and the results obtained for L-cysteine by the proposed FI procedure were in good agreement with those obtained using a pharmacopeial procedure and within an acceptable range of error.

Effects of L-cysteine and N-acetyl-L-cysteine on 4-hydroxy-2, 5-dimethyl-3(2H)-furanone (furaneol), 5-(hydroxymethyl)furfural, and 5-methylfurfural formation and browning in buffer solutions containing either rhamnose or glucose and arginine.

Solutions of L-cysteine (Cys) and N-acetyl-L-cysteine (AcCys), containing glucose or rhamnose, with or without arginine, were buffered to pH 3, 5, and 7 and incubated at 70 degrees C for 48 h. Cys and AcCys inhibited the formation of (hydroxymethyl)furfural (HMF) from glucose and methylfurfural (MF) from rhamnose under acidic conditions. AcCys inhibited the accumulation of 4-hydroxy-2, 5-dimethyl- 3(2H)-furanone (DMHF, Furaneol) from rhamnose, but Cys, under our experimental conditions, enhanced Furaneol accumulation from rhamnose. Cys and AcCys reacted directly with Furaneol but not with HMF or MF. Both Cys and AcCys inhibited nonenzymatic browning at pH 7. At pH 3, however, Cys reacted with both glucose and rhamnose to produce unidentified compounds that increased the visible absorbency.

The optimum relative centrifugal force and centrifugation time for improved sensitivity of smear and culture for detection of Mycobacterium tuberculosis from sputum

Direct microscopy is the only available method for diagnosis of tuberculosis in most centres in developing countries. Methods to improve the sensitivity of direct smear are an urgent requirement. Sputum specimens artificially seeded with known concentrations of Mycobacterium tuberculosis were liquefied and decontaminated with sodium hydroxide-sodium citrate- N-acetyl- l-cysteine solutions. They were subjected to different centrifugation forces and centrifugation times after which the centrifuged deposits were examined by smear and culture. Statistical analysis of results was carried out using EpiInfo version 6.0. The optimum relative centrifugal force (RCF) and centrifugation time combination was 4000 g for 15 min. The sensitivity of detection at an RCF of 4000 g for 15 min was 5000 organisms/mL and 500 organisms/mL for smear and culture, respectively. When results of 163 clinical samples were analysed after centrifugation at 4000 g for 15 min sensitivity of the direct smear improved from 63% to 92% ( P < 0·05) and negative predictive value from 30·5% to 45% ( P < 0·05) when culture was considered the ‘gold standard’. With the concentrated smear there was a reduction in specificity from 82% to 60% ( P > 0·05). As most laboratories are equipped with a simple centrifuge, smear sensitivity can be improved with this simple modification. The other advantage is that the same centrifuged deposit can be cultured, in contrast to when sodium hypochlorite is used for liquefaction.

Interference of copper and nickel on electrochemical hydride generation

Interferences by copper and nickel on electrochemical hydride generation of stibine, arsine and hydrogen selenide were examined using flow injection sample introduction. Direct interference or memory interference by either metal was found to be severe when using lead, pyrolytic graphite or vitreous carbon as a cathode. With a lead cathode, corresponding signal recoveries (%) for AsH3, SbH3, and SeH2 were, 20, 20 and 60 in the presence of 20, 10 and 40 µg ml–1 of NiII, respectively, and 30 and 50 for AsH3, and SbH3 in the presence of 120 and 7.5 µg ml–1 of CuII, respectively. Although nickel presented less interference on arsine production with a platinum cathode [no interference from 600 µg ml–1 NiII], arsine production efficiency is too low to be analytically useful with this material (<8%). An increase in acidity of the catholyte solution and use of thiourea or L-cysteine resulted in no alleviation of interference from copper on stibine production [50% suppression due to 7.5 µg ml–1 CuII]. A discussion is presented outlining the potential remedial action which can be undertaken to minimize or eliminate such interferences.

Acoustic absorption in L-cysteine solutions at physiological pH and temperature measured using a novel technique

Absorption of ultrasound in L-cysteine has been measured at 37 °C for the pH range 6.8–8.0 for 0.2 and 0.5 mol dm–3 solutions. A new pulse-transmission technique has been used which produces continuous absorption spectra for the range 2–50 MHz, enabling accurate determination of relaxation frequency (f0) within this range. The variation of f0 with concentration and pH is explained in terms of a mechanism involving both intra- and inter-molecular proton transfer. For the first time, values have been determined for the volume change of the intramolecular proton-transfer reaction and for a number of the individual ionization rate constants for cysteine.

Isolation and identification of volatile chemicals formed in aqueous L-cysteine solution with a UV light.

Thirty-six volatile compounds were positively identified in the dichloromethane extract of an aqueous solution of L-cysteine that was irradiated with UV light at 253.7 nm for 24 hr. The irradiated solution was colorless but has a cooked meat-like flavor. The compounds identified were thiophenes, pyrazines, thiazoles, thiazolines, thiazolidines, and polymethylene sulfides. 2-Methylthiazole was found in the largest quantity, approximately 40% of the extract. Proposed photochemical reactions of cysteine included Strecker degradation, isomerization, dimerization, and homolytic fission of C-C, C-S, or S-H bonding.

The Nature and Action of Host Signals

It is clear that excystations in vitro of the coccidia so far examined involves two steps, in the first of which CO2 is important, and the second, in which an external source of chymotrypsin and surface-active agents are required. However, the details of the mechanism of excystment are not clear. We do not know how the presence of CO2 changes the permeability of the oocyst wall. We do not know whether CO2 does anything to the sporozoite or sporocyst; the circumstance that mechanically-released sporocysts readily excyst under appropriate conditions without the necessity for high concentrations of, or perhaps any, CO2 suggests it does not. Circumstantial evidence suggests that the substrate in which chymotrypsin acts is the Stieda body, but whether the enzyme has other roles we do not know. Similarly, the role of bile is ill-defined, although it does seem that the induction of activity is important--but how is this brought about? The techniques available to excyst oocysts are, for many species, very efficient. If CO2 is, as it seems to be, a fundamental stimulus, then efficiency might be enhanced if more attention was given, not so much to increasing the time of exposure and amount of CO2 in the gas phase, but rather to the pH of the medium, which is rarely stated or apparently, controlled. The pH determines the proportion of the different carbonate species in solution, which may be of greater significance than the partial pressure of CO2 in the gas phase (see also Section V A). Although high numbers of excysted sporocysts can be obtained with a particular technique, this does not necessarily mean that all the signals supplied by the host are reproduced in vitro. Jackson (1962) found it necessary to wash oocysts in water or dilute buffers between the primary phase and the secondary phase, a step which implies a deficiency in the methods he used. Commonly, oocysts are exposed to a strong solution of L-cysteine. Does this reflect a general deficiency in the technique, or a counterpart of strongly reducing conditions in ruminant and non-ruminant alike? It seems that we have only a very general outline of excystment, and that we do not understand the details. Yet the problem seems to have been put aside; the most recent relevant reference we have found is dated 1983.

The partial molar enthalpies in aqueous solution of some amino acids with polar and non-polar side chains

The enthalpies of dilution of aqueous solutions of L-alanine, L-arginine, L-cysteine, glycine, L-serine, and L-valine have been measured by flow calorimetry, and used to calculate the partial molar enthalpies of the solution components. Partial molar entropies of water in the solutions were calculated using literature data for the activity of H 2O in the solutions. The partial molar enthalpies of H 2O in the solutions of amino acids with non-polar side chains were negative but in the solutions of amino acids with polar side chains and in glycine solutions they were positive.

Studies on the Photolysis of L-Cysteine and L-Cystine

In the presence and absende of riboflavin, the aqueous solutions of l-cysteine and l-cystine were exposed to sunlight. The solutions in the presence of riboflavin developed the typical flavor of cooked rice. Hydrogen sulfide, ammonia, carbon dioxide and acetaldeohyde were found from the solutions that formed the flavor.The component responsible for the flavor was not a single one but consisted of three compounds, such as hydrogen sulfide, ammonia and acetaldehyde. An aqueous solution of the mixture containing these three compounds developed organoleptically the typical flavor of cooked rice. These compounds were also present in the vapor of cooked rice.

The β-structure of poly- S-carbobenzoxymethyl- l-cysteine in solution

Poly-S-carbobenzoxymethyl-L-cysteine has been shown from a study of polarized infrared spectra to exist in oriented films in the cross-β-conformation with an anti-parallel arrangement of polypeptide chains. Solutions of the polymer in chloroform-dichloroacetic acid mixtures were investigated by measurements of optical rotatory dispersion, viscosity and infrared spectra; their properties suddenly changed at solvent compositions near 2% dichloroacetic acid content. The polymer was found to assume the random coil form at higher diehloroacetic acid contents but to associate into the intermolecular β-conformation at lower dichloroacetic acid contents. At the solvent composition where the transition between random coil and β-form occurred, the β-form was partly converted into the random coil as the temperature was raised or the polymer concentration was diluted. The rotatory dispersion of the β-form of the polymer is characterized by a large positive a0 value but a small b0 value.