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Introduction The aim of this work is to study the thermal behavior in the medium–high temperature range of the sulfur containing amino acid l -cysteine and its corresponding dimer l -cystine, which is composed of two l

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Gold nanoparticles (AuNPs) and l-cysteine (l-cys), in order, as first and second layer were coated on the surface of a commercial thin-layer chromatography (TLC) plate. This assemble has been used as a new substrate for direct resolution of propranolol enantiomers based on the ordinary TLC technique. The effect of concentrations of the involved chemicals, time periods of the required processes, pH of the sample solutions, as well as the effects of different coating protocols on the resolution of the enantiomers, were investigated in order to find the optimized separation conditions. The results showed that 10.0 mM copper(II) acetate, in 70% ethanol-water adjusted at pH = 6.3, was suitable for being used as the mobile phase. The AuNPs with the average size of 15 nm and l-cys solution with a concentration of 10.0 mM and pH = 8.1 had been chosen for impregnating TLC plates.

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Abstract  

Heat capacity C p(T) of the orthorhombic polymorph of L-cysteine was measured in the temperature range 6–300 K by adiabatic calorimetry; thermodynamic functions were calculated based on these measurements. At 298.15 K the values of heat capacity, C p; entropy, S m 0(T)-S m 0(0); difference in the enthalpy, H m 0(T)-H m 0(0), are equal, respectively, to 144.6±0.3 J K−1 mol−1, 169.0±0.4 J K−1 mol−1 and 24960±50 J mol−1. An anomaly of heat capacity near 70 K was registered as a small, 3–5% height, diffuse ‘jump’ accompanied by the substantial increase in the thermal relaxation time. The shape of the anomaly is sensitive to thermal pre-history of the sample.

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JPC - Journal of Planar Chromatography - Modern TLC
Authors: Agnieszka Godziek, Anna Maciejowska, Ewa Talik, Mieczysław Sajewicz, and Teresa Kowalska

Spontaneous oscillatory chiral conversion and condensation of low-molecular-weight chiral carboxylic acids have been investigated by our research group for almost 10 years now. However, dynamics of these oscillatory processes substantially differ from one compound to another, moreover, spontaneous chiral conversion and condensation of sulfur-containing amino acids have not been investigated so far. To this effect, we present in this paper the results of our current investigations on spontaneous oscillatory chiral conversion and condensation of l-cysteine (l-Cys), a biologically important sulfur-containing semiessential amino acid. In our thin-layer chromatographic experiments, we employ the Mn(II) and Zn(II) cations to facilitate the enantioseparation of l-Cys from the spontaneously formed d-Cys, to prevent chiral conversion of the L form, and to highlight rapid consumption of Cys in the course of condensation. Spontaneous peptidization of Cys is confirmed with use of thin-layer chromatography-mass spectrometry (TLC-MS). Additionally, we emphasize the oscillatory nature of the investigated process with use of high-performance liquid chromatography-evaporative light scattering detection (HPLC-ELSD) and provide a complementary insight in the chemical structure of the spontaneously formed Cys-derived oligopeptides with use of HPLC-MS.

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Abstract  

Liquid-liquid distribution method has been applied for the determination of the composition and stability constants of mercury species with L-cysteine /H2L/. In the pH range 2–8, mercury /II/ forms a complex Hg/HL/2 with very high stability constant /lg 2 = 40.0/, whereas methylmercury and phenylmercury form complexes CH3HgHL /lg 1 = 15.56/ and C6H5HgHL /lg 1 = 16.5/. At pH13, anionic complexes HgL 2 2– /lg 2 = 42.7/, CH3HgL /lg 1 = 16.58/ and lg 1 = 17.7 are formed.

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Abstract  

Thermal neutron irradiation experiments performed with cellulose-based l-cysteine-treated and untreated Hg standards showed Hg losses of 59–81% for untreated standards but only about a 0.2% loss for treated standards. These results and others for multielement standards showed that Hg loss is highly dependent on total mass and placement of materials in the irradiation vessel and that distribution of volatilized Hg was fairly uniform throughout the sample-containing region of the vessel. Polyethylene trapped volatile Hg much more efficiently than cellulose and a multielement standard containing inorganic Se selectively trapped Hg lost from a co-irradiated multielement standard containing Hg.

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Abstract  

The sulphur-containing proteinaceous amino acids l-cysteine, l-cystine and l-methionine were irradiated in the solid state to a dose of 3.2 MGy. This dose corresponds to that delivered by radionuclide decay in a timescale of 1.05 × 109 years to the organic matter buried at a depth >20 m in comets and asteroids. The purity of the sulphur-containing amino acids was studied by differential scanning calorimetry (DSC) before and after the solid state radiolysis and the preservation of the chirality after the radiolysis was studied by chirooptical methods (optical rotatory dispersion, ORD) and by FT-IR spectroscopy. Although the high radiation dose of 3.2 MGy delivered, all the amino acids studied show a high radiation resistance. The best radiation resistance was offered by l-cysteine. The radiolysis of l-cysteine leads to the formation of l-cystine. The radiation resistance of l-methionine is not at the level of l-cysteine but also l-methionine is able to survive the dose of 3.2 MGy. Furthermore in all cases examined the preservation of chirality after radiolysis was clearly observed by the ORD spectroscopy although a certain level of radioracemization was measured in all cases. The radioracemization is minimal in the case of l-cysteine and is more pronounced in the case of l-methionine. In conclusion, the study shows that the sulphur-containing amino acids can survive for 1.05 × 109 years and, after extrapolation of the data, even to the age of the Solar System i.e. to 4.6 × 109 years.

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Abstract  

The volatilization losses of mercury before, during and after neutron irradiation were studied. To minimize the losses, respectively, were added to the standards, thiourea, L-cysteine, thioacetamide and ammonium sulfide. It was possible to minimize the losses by preserving the standard at −20°C after irradiation. No loss was seen in the biological materials after irradiation.

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Abstract  

In order to investigate the utility of selected thiols as scavengers of MIC, we first assessed the chemical stability of SMG, AMCC and SMC by measuring their rates of reaction in vitro with thiophan. The inital rates of carbamoylation of thiorphan (0.5 mM) by the above conjugates (0.5 mM) in aqueous buffer at pH 7.4 and 37°C were 2.51, 0.76 and 8.47 mol L–1 min–1, respectively, indicating that the mercapturate AMCC was the most stable of the three MIC conjugates.In light of these results, studies were conducted to examine the effect of pretreatment withN-acetyl-l-cysteine (l-NAC; 500 mg kg–1, i.p.) on the urinary elimination of AMCC in rats dosed with MIC (15 mg kg–1, i.p.). In separate experiments, groups of rats were pretreated with eitherN-acetyl-d-cysteine (d-NAC) orN-trideuteroacetyl-l-cysteine (d3-l-NAC) in order to explore the mechanism by which MIC undergoes conjugation to AMCCin vivo. The results indicated that exogenous NAC effectively enhances the urinary excretion of MIC in the form of AMCC, and that it does so largely by direct conjugation with the isocyanate, rather thanvia biosynthesis to GSH.

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Summary

The enantiomers of serine have been separated after pre-column derivatization with ortho-phthaldialdehyde (OPA) and N-tert-butyloxycarbonyl-l-cysteine (Boc). Analysis of the enantiomers of amino acids after pre-column derivatization with OPA-Boc has been reported in the literature but no critical evaluation has been carried out. In this study, decomposition of the diastereomers, effect of the sample pH, and amount of derivatization agent were studied; the half life of the decomposition was also determined. The method was used for analysis of D and l-serine from three different areas of rat brain (the striatum, prefrontal cortex, and cerebellum).

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