L-cysteine Complex Research Articles

Structural Characterization of Toxicologically Relevant Cd2+-L-Cysteine Complexes.

The exposure of humans to Cd exerts adverse human health effects at low chronic exposure doses, but the underlying biomolecular mechanisms are incompletely understood. To gain insight into the toxicologically relevant chemistry of Cd2+ in the bloodstream, we employed an anion-exchange HPLC coupled to a flame atomic absorption spectrometer (FAAS) using a mobile phase of 100 mM NaCl with 5 mM Tris-buffer (pH 7.4) to resemble protein-free blood plasma. The injection of Cd2+ onto this HPLC-FAAS system was associated with the elution of a Cd peak that corresponded to [CdCl3]-/[CdCl4]2- complexes. The addition of 0.1-10 mM L-cysteine (Cys) to the mobile phase significantly affected the retention behavior of Cd2+, which was rationalized by the on-column formation of mixed CdCysxCly complexes. From a toxicological point of view, the results obtained with 0.1 and 0.2 mM Cys were the most relevant because they resembled plasma concentrations. The corresponding Cd-containing (~30 μM) fractions were analyzed by X-ray absorption spectroscopy and revealed an increased sulfur coordination to Cd2+ when the Cys concentration was increased from 0.1 to 0.2 mM. The putative formation of these toxicologically relevant Cd species in blood plasma was implicated in the Cd uptake into target organs and underscores the notion that a better understanding of the metabolism of Cd in the bloodstream is critical to causally link human exposure with organ-based toxicological effects.

Novel copper complexes-polyurethane composites that mimics anti-inflammatory response

Copper is a trace element of biological significance that can form complexes with several thiol containing compounds which can be used as filler in biomedical polyurethanes. In this work, segmented polyurethanes (SPUs) were synthesized with thiol containing compounds as chain extenders including d-penicillamine (DP), l-penicillamine (LP), l-cysteine (LC) and reduced glutathione (GR). Then, the synthesized polyurethane was filled with copper chelates based on the same chain extenders. Evidence of free thiol containing chain extender in polyurethane was not observed by FTIR and Raman but EDX provided evidence of sulfur in the unfilled polyurethane and copper and sulfur in their composite. DSC and DRX showed the semi-crystalline nature of the polyurethanes which provided good mechanical properties, especially to those prepared with DP. The Tg of the PCL determined by DMA shifted toward higher temperatures by the addition of copper complexes while TGA studies showed that the thermal degradation was slightly improved when LCCu and GRCu complex were added. Macrophage viability was observed in all composition studied after longer times of extraction (72 h) and dilutions (1:2 to 1:32) but remarkably high in those prepared with LCCu and GRCu. The anti-inflammatory response was proved in LC and GR copper complex filled polyurethanes as IL-4 and IL-10 increased with time while IL-1β and TNF-α were reduced.

Complexation Equilibria and Determination of Stability Constants of Some Divalent Metal Ion Complexes of L-Cysteine and Diphenylamine in Aqueous Media

<i>Background. </i>Metal complexes of biologically active ligands had considerable interests. L-cysteinate residue, L-Cys, is a biologically abundant and important versatile binding site of proteins. Diphenylamine, DPA, is an important aromatic amine containing two phenyl groups. Complexation equilibria of the divalent metal ions, Ca²⁺ and Zn²⁺ with the bio- relevant α-amino acid, L-cysteine and the nitrogen-containing diphenylamine ligand were investigated by means of the potentiometric technique at 25.0 ± 0.1°C and constant ionic strength of 0.200 ± 0.001 mol·dm^-3 NaNO₃. <i>Objective.</i> The stability constants and standard free energy changes of the α-amino acid, L-cysteine and diphenylamine complex species were determined at 0.200 ± 0.001 mol·dm^-3ionic strength. <i>Methods.</i> The formation of the different 1:1 and 1:2 binary complexes and 1:1:1 ternary complexes were inferred from the potentiometric titrations. <i>Results.</i> The concentration distribution of L-cysteine species formed in solution was evaluated. The dissociation constants of the α-amino acid and diphenylamine were determined at different ionic strength. The stability constants of these binary and ternary systems were calculated. The values of ∆ log₁₀ K, percent relative stabilization, %R.S. and log₁₀ X for the ternary systems were evaluated and discussed. <i>Concussion.</i> The ternary complex formation occurred in a stepwise manner with L-cysteine acting as the primary ligand. The obtained values of ∆ G⁰ indicated that Complex formation reactions are spontaneous. Also, for all systems studied, the ternary complexes formed are more thermodynamically stable than the binary complexes.

Non inflammatory properties of ex situ thiol-based copper chelates

Copper complexes were synthesized via thiol complexation with either d or l-penicillamine (DP and LP), l-cysteine (LC) and reduced glutathione (GR) by solution-precipitation method. Complex formation was demonstrated by thiol disappearance by FTIR and Raman. DP, LC and GR complexes were crystalline as shown by XRD, but LC and GR complexes exhibited higher decomposition temperatures as shown by TGA. DP and LP copper complexes were cytotoxic to macrophages in the 800 to 1600 µM range but not for LC and only at 1600 µM for GR complexes. The later complexes slightly suppressed IL-1β, IL-6 and TNF-α production while enhancing IL-4 and IL-10 expression. These results suggest that LC and GR based copper complexes can be promising fillers or coatings for biomedical applications.

L-cysteine complex of palladium onto mesoporous channels of MCM-41 as reusable, homoselective and organic–inorganic hybrid nanocatalyst for the synthesis of tetrazoles

In this study, ordered structure with a hexagonal arrangement MCM-41 was synthesized and functionalized with L-cysteine group and further palladium particles has been supported on its surface (L-cysteine-Pd@MCM-41). The prepared catalyst is well characterized by various techniques such as low-angle X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption–desorption measurement isotherms, energy-dispersive X-ray spectroscopy (EDS), X-ray Mapping (WDX), scanning electron microscopy (SEM) and inductively coupled plasma (ICP) techniques. The collected data from all techniques provided evidence that palladium complex was immobilized onto MCM-41 pores. The obtained nanocatalyst demonstrated excellent activity as a new heterogeneous catalyst for the homoselective synthesis of 5-substituted 1H-tetrazole derivatives. This method has the advantages of simple methodology, eco-friendly and simplicity in the separation of catalyst, shorter reaction times, and high yields of the product. Finally, easy catalyst recovery was achieved and the catalyst could be recycled for six times without a significant decrease in activity and selectivity.

Synthesis of hemicellulose/deep eutectic solvent based carbon quantum dots for ultrasensitive detection of Ag+ and L-cysteine with “off-on” pattern

The hypersensitive detection of metal ions and amino acid becomes more important for environmental and human physical conditions monitor but remains still a great challenge. In this work, we have reported a green and straight forward procedure (solvothermal treatment) for the synthesis of N-doped hemicellulose-based carbon quantum dots (N-H-CQDs) used as an “off-on” fluorescence sensor for ultrasensitive detecting Ag+ ion and L-Cysteine (L-Cys). During this process, hemicellulose used as carbon source and nitrogen-rich deep eutectic solvent (DES) of choline chloride/urea acted as both solvent and doping agent. The prepared N-H-CQDs displayed narrow diameter ranging from 2 to 8 nm with relatively higher quantum yield (QY) of 23.45%. This probe was able to selectively detect Ag+ ion on account of the formation of N-H-CQDs- Ag+ complex and possessed extremely low detection limit of 21 nM. Additionally, the fluorescence of N-H-CQDs-Ag+ complex was restored by the addition of L-Cysteine as Ag+ ion would assemble a more stable Ag+-L-Cysteine complex through Ag+-thiol bonds. Accordingly, the N-H-CQDs-Ag+ solution behaved as secondary fluorescent probe to detect L-Cys in the dynamic range of 0–100 μM with a LOD of 242 nM. The prepared N-H-CQDs are promising probes for hypersensitive detection of Ag+ and L-Cys.

Electrochemical selective detection of carnitine enantiomers coupling copper ion dependent DNAzyme with DNA assistant hybridization chain reaction

An electrochemical method for carnitine enantiomers recognition is proposed employing Cu (II)-l-cysteine complexes and signal amplification strategies based on DNAzyme and DNA assistant hybridization chain reaction (HCR). The reported method combined Cu (II)-amino acids complexes with DNAzyme and proposed a smart and efficient electrochemical method to recognize chiral molecules through the difference between homochiral interaction and heterochiral interaction. Moreover, further employment of hairpin DNA assistant HCR greatly enhanced the detecting signal, realizing the selective recognition of carnitine enantiomers in low concentrations. This study creatively provides a general sensing method for sensitive chiral molecules recognition without large-scale precision instruments.

Vanadium as a chemoprotectant: effect of vanadium(III)-L-cysteine complex against cyclophosphamide-induced hepatotoxicity and genotoxicity in Swiss albino mice.

Vanadium is an essential micronutrient for living systems and has antioxidant and genoprotective property. In the present study, the protective role of an organovanadium compound vanadium(III)-L-cysteine (VC-III) was evaluated against hepatotoxicity and genotoxicity induced by cyclophosphamide (CP) (25 mg/kg b.w., i.p.) in Swiss albino mice. Treatment with VC-III (1 mg/kg b.w., p.o.) mitigated CP-induced hepatic injury as indicated by reduction in activities of alanine transaminase, aspartate transaminase, alkaline phosphatase by 1.57-, 1.58- and 1.32-fold in concomitant treatment schedule and by 1.83-, 1.77- and 1.45-fold in pretreatment schedule, respectively, and confirmed by histopathological evidences. Parallel to these changes, VC-III ameliorated CP-induced oxidative stress in liver by 1.46-, 1.26-, 1.32- and 1.42-fold in concomitant treatment group and by 1.95-, 1.40-, 1.46- and 1.73-fold in pretreatment group at the level of H2O2, superoxide, nitric oxide and lipid peroxidation, respectively. VC-III also enhanced activities of antioxidant enzymes such as superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase and glutathione (reduced) level in mice liver by 1.46-, 1.37-, 1.29-, 1.44- and 1.45-fold in concomitant treatment schedule and by 1.64-, 1.65-, 1.42-, 1.49- and 1.57-fold in pretreatment schedule, respectively. In addition, the organovanadium compound could efficiently attenuate CP-induced chromosomal aberrations, DNA fragmentation and apoptosis in bone marrow cells and DNA damage in lymphocytes by 1.49-, 1.43-, 1.48- and 1.59-fold in concomitant treatment group and by 1.76-, 1.92-, 1.99- and 2.15-fold in pretreatment group, respectively. Thus, the present study showed that VC-III could exert protection against CP-induced hepatotoxicity and genotoxicity.

Hydrogen-Bonded Interactions in the Systems L-Cysteine - H2SeO3 and L-Cysteine -H2SeO4

Using the density functional theory method at the B3LYP/6-31G(d,p) level of theory, the formation of hydrogen-bonded complexes of L-cysteine with selenious and selenic acids has been studied. In both cases of selenium-containing acids, the complexes occur preferably by cysteine carboxylic group, therewith the enthalpy of formation values consist from –19 to –21 kcal/mol, and free energy from –6 to –9 kcal/mol. Probably, the initial act of interaction in the system hydroxyl-containing selenium compound - a-amino acid, proceeding with mutual orientation of the reactants molecules and intermolecular hydrogen bonds formation, serves as a prerequisite for the thiol group capability of participating in the subsequent stages (including more completed transformations) of biologically important reactions.

Mercury Extraction from Contaminated Soils by l-Cysteine: Species Dependency and Transformation Processes

A new approach in soil remediation washing techniques is the use of l-cysteine based on the formation of organic complexes. In this study, the applicability of l-cysteine for the mobilisation of different mercury species from contaminated soils was evaluated. Soils were treated with l-cysteine solutions with S–Hg molar ratios of 1, 2, 10, 20, 100 and 200. In 24 h batch experiments, leachates with water could mobilise 1% of Hg. The addition of l-cysteine led to an increase of Hg mobilisation of 42% for soils with inorganically bound Hg. In column experiments, the maximum Hg removal rate was 75%. For soils with organically bound Hg or HgS, only 1–5% of Hg was mobilised. Thus, the extraction of Hg from soils with l-cysteine is highly dependent on the Hg-binding form. Hg speciation analyses of leachates indicate that Hg–l-cysteine complexes are labile complexes which can be easily transformed. Soil samples speciation analysis revealed that reduction to elemental mercury takes place at low S–Hg ratios (1 to 10), assumingly by microbial activity. At higher S–Hg ratios of 10 and 100, precipitation of stable Hg–S complexes could be observed. These species transformation processes are limitations for considering l-cysteine leaching as a remediation strategy.

Interaction of L-cysteine with selenious and selenic acids: A study by the density functional theory method

Using the density functional theory method at the B3LYP/6-31G(d,p) theory level, the formation of hydrogen bonded complexes of L-cysteine with selenious and selenic acids is studied. In both cases, complexes formed through the carboxyl group of cysteine mostly arise, their enthalpy of formation being of -19kcal/mol to -21 kcal/mol and the free energy of -6kcal/mol to -9kcal/mol. The primary act of interaction in the system of hydroxyl-containing selenium compound — α-aminoacid, including the mutual orientation of reactant molecules and the formation of intermolecular hydrogen bonds is likely to a serve as prerequisite for the thiol group to be able to participate in the next stages (including deeper chemical transformations) of biologically significant reactions.

Anion-Exchange Chromatographic Separation of Hg for Isotope Ratio Measurements by Multicollector ICPMS

A procedure is described for precise Hg isotope ratio measurements by solution nebulization multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). Hg was released from geological samples using aqua regia extraction and then separated from other matrix elements with the aid of anion-exchange chromatography using strongly basic Dowex 1-X8 anion-exchange resin. Performance of the chromatographic procedure was evaluated using various types of replacement anions for elution of mercury, including l-cysteine, thiourea, NO3-, and SO42-. A solution of 0.15% l-cysteine in 0.06 M HCl was found to be the most convenient eluent for subsequent MC-ICPMS measurements. The optimized procedure provides separation of Hg from virtually all concomitant matrix elements while maintaining quantitative (>95%) recovery. In addition, band displacement chromatographic experiments were conducted to assess whether the anion-exchange purification can produce Hg isotope fractionation artifacts. No isotope fractionation between the Hg(II)-l-cysteine complex in aqueous solution and Hg ions in the anion-exchange resin was observed. Hg isotope ratio measurements were performed using the bracketing standards approach and on-line correction for instrumental mass discrimination using Tl spiking and normalization to the 205Tl/203Tl ratio. The absence of spectral interference during Hg isotope ratio measurements was verified using a three-isotope plot. Uncertainties of Hg isotope ratio measurements for replication of the entire procedure, expressed as two standard deviations, are better than +/-0.08 per thousand/amu. The described procedure facilitates study of variations in the isotopic composition of Hg in nature.

Dual-cloud point extraction as a preconcentration and clean-up technique for capillary electrophoresis speciation analysis of mercury

A novel dual-cloud point extraction (dCPE) technique is proposed in this paper for the sample pretreatment of capillary electrophoresis (CE) speciation analysis of mercury. In dCPE, cloud point was carried out twice in a sample pretreatment. First, four mercury species, methylmercury (MeHg), ethylmercury (EtHg), phenylmercury (PhHg), and inorganic mercury (Hg(II)) formed hydrophobic complexes with 1-(2-pyridylazo)-2-naphthol (PAN). After heating and centrifuging, the complexes were extracted into the formed Triton X-114 surfactant-rich phase. Instead of the direct injection or analysis, the surfactant-rich phase containing the four Hg species was treated with 150 μL 0.1% (m/v) l-cysteine aqueous solution. The four Hg species were then transferred back into aqueous phase by forming hydrophilic Hg– l-cysteine complexes. After dCPE, the aqueous phase containing the Hg– l-cysteine complexes was subjected into electrophoretic capillary for mercury speciation analysis. Because the concentration of Triton X-114 in the extract after dCPE was only around critical micelle concentration, the adsorption of surfactant on the capillary wall and its possible influence on the sample injection and separation in traditional CPE were eliminated. Plus, the hydrophobic interfering species were removed thoroughly by using dCPE resulted in significant improvement in analysis selectivity. Using 10 mL sample, 17, 15, 45, and 52 of preconcentration factors for EtHg, MeHg, PhHg, and Hg(II) were obtained. With CE separation and on-line UV detection, the detection limits were 45.2, 47.5, 4.1, and 10.0 μg L −1 (as Hg) for EtHg, MeHg, PhHg, and Hg(II), respectively. As an analysis method, the present dCPE–CE with UV detection obtained similar detection limits as of some CE–inductively coupled plasma mass spectrometry (ICPMS) hyphenation technique, but with simple instrumental setup and obviously low costs. Its utilization for Hg speciation was validated by the analysis of the spiked natural water and tilapia muscle samples.

Preparation, Characterization, and Antioxidative Effects of Oligomeric Proanthocyanidin−l-Cysteine Complexes

Controlled acid-catalyzed degradation of proanthocyanidin polymers in grape seeds together with L-cysteine led to oligomeric proanthocyanidin-L-cysteine complexes along with monomeric flavan-3-ol derivatives being isolated, and their structures were confirmed on the basis of spectroscopic data and by chemical means. In addition, comparative studies on the antioxidative and survival effects of oligomeric proanthocyanidin-L-cysteine complexes and proanthocyanidin polymers were performed. The oligomeric proanthocyanidin-L-cysteine complexes showed higher bioavailability and antioxidant capacity and enhanced survival time in the animal test groups. In addition, it is suggested that the oligomeric complexes may help to prevent oxidative stress and may reduce free radical production.

Complexes of diphenylarsinic acid and phenylarsonic acid with thiols: a 1H and 13C NMR study

The high toxicity of diphenylarsinic acid, found in ground water and well water as a probable consequence of the inappropriate disposal of warfare agents, prompted us to study the reaction, monitored by 1H and 13C NMR spectroscopy, of the compound and its monophenyl analogue, phenylarsonic acid, with cellular thiols as represented, in particular, by glutathione. Glutathione reduced the phenylarsenic acids to trivalent forms and complexed them: diphenylarsinic acid to a monoglutathione adduct and phenylarsonic acid to a diglutathione adduct. The complexes were characterized by 1H and 13C NMR spectroscopy and mass spectrometry. The NMR spectra showed the diastereotopic nature of the two phenyl groups in the diphenylarsinic acid-glutathione compound, and of the two glutathione residues in the phenylarsonic acid-diglutathione complex. The stereochemistry of thiol compounds of phenylarsonic acid was further explored by 1H and 13C NMR spectroscopy of the L-cysteine complex. The diphenylarsinic acid-glutathione complex was stable below pH 12 but at higher pH the complex dissociated into diphenylarsinous acid and reduced glutathione. The released diphenylarsinous acid then oxidized to diphenylarsinic acid with a half-life of about 7 h at pH 13 and at room temperature.

Vanadium(III) complexes with l-cysteine – stability, speciation and the effect on actin in hepatoma Morris 5123 cells

The complexation processes of vanadium(III) with l-cysteinate and s-methyl- l-cysteinate ligands have been studied in aqueous solutions in the pH range 2–7 by the pH–potentiometric, UV–Vis absorption and CD spectroscopy methods. The equilibria model of complex formation, evaluated by SUPERQUAD program, so as careful inspection of spectroscopic data have allowed to determine the speciation and the coordination mode of vanadium(III) ion in the major species present in aqueous solutions. Relatively stable ML 2 species of vanadium(III)– l-cysteinate system exists in aqueous solutions above pH 5. It was deduced from spectral data that the coordination sphere of vanadium(III) ion in V(Cys) 2 is completed by oxygen, nitrogen and sulfur atoms of two l-cysteinate ligands. Solution of vanadium(III) with l-cysteine (pH ∼ 7, L/ M = 20) was administrated to the culture medium of hepatoma Morris 5123 growing cells. Cytotoxic effect of this solution towards tumor cells was observed. The viability of these cells depended on the complex concentration. It was reduced by 70% at 100 μM of the vanadium species concentration in the culture medium. The death of cancer cells seems to be induced on apoptotic route. The statistically significant increase of total actin level and filamentous to monomeric actin ratios ( F/ G) were found in the cytoplasm of cells exposed to the vanadium(III)– l-cysteine complex. It was accompanied by the rearrangement of actin cytoskeleton architecture. These factors are important for migration and metastasis formation of the cancer cells.

Transport of a neurotoxicant by molecular mimicry: the methylmercury-L-cysteine complex is a substrate for human L-type large neutral amino acid transporter (LAT) 1 and LAT2.

Methylmercury (MeHg) readily crosses cell membrane barriers to reach its target tissue, the brain. Although it is generally assumed that this rapid transport is due to simple diffusion, recent studies have demonstrated that MeHg is transported as a hydrophilic complex, and possibly as an L-cysteine complex on the ubiquitous L-type large neutral amino acid transporters (LATs). To test this hypothesis, studies were carried out in Xenopus laevis oocytes expressing two of the major L-type carriers in humans, LAT1-4F2 heavy chain (4F2hc) and LAT2-4F2hc. Oocytes expressing LAT1-4F2hc or LAT2-4F2hc demonstrated enhanced uptake of [(14)C]MeHg when administered as the L-cysteine or D,L-homocysteine complexes, but not when administered as the D-cysteine, N -acetyl-L-cysteine, penicillamine or GSH complexes. Kinetic analysis of transport indicated that the apparent affinities ( K (m)) of MeHg-L-cysteine uptake by LAT1 and LAT2 (98+/-8 and 64+/-8 microM respectively) were comparable with those for methionine (99+/-9 and 161+/-11 microM), whereas the V (max) values were higher for MeHg-L-cysteine, indicating that it may be a better substrate than the endogenous amino acid. Uptake and efflux of [(3)H]methionine and [(14)C]MeHg-L-cysteine were trans -stimulated by leucine and phenylalanine, but not by glutamate, indicating that MeHg-L-cysteine is both a cis - and trans -substrate. In addition, [(3)H]methionine efflux was trans -stimulated by leucine and phenylalanine even in the presence of an inwardly directed methionine gradient, demonstrating concentrative transport by both LAT1 and LAT2. The present results describe a major molecular mechanism by which MeHg is transported across cell membranes and indicate that metal complexes may form a novel class of substrates for amino acid carriers. These transport proteins may therefore participate in metal ion homoeostasis and toxicity.

γ-Glutamyl Transpeptidase and [formula omitted]-Cysteine Regulate Methylmercury Uptake by HepG2 Cells, a Human Hepatoma Cell Line

Mechanisms of methylmercury (MeHg) and inorganic mercury (Hg) uptake were examined in HepG2 cells, a human hepatoma-derived cell line. MeHg uptake was faster when it was present as the l-cysteine complex, as compared to the glutathione (GSH), CysGly, γ-GluCys, d-cysteine, N-acetylcysteine, l-penicillamine, or albumin complexes. Uptake of MeHg-l-cysteine was independent of Na+, stereoselective, and was inhibited by the amino acid transport system l substrates l-leucine, l-valine, and l-phenylalanine (5 mM). Moreover, [3H]l-leucine uptake was inhibited by MeHg-l-cysteine, suggesting that MeHg-l-cysteine is transported into HepG2 cells by an l-type amino acid carrier. Uptake of MeHg as the GSH complex (MeHg-SG) was dependent on the extracellular GSH concentration, and was diminished when cellular γ-glutamyl transpeptidase activity was inhibited. Inorganic mercury uptake was slower than that of MeHg, but was also sensitive to the type of thiol ligand present. These findings demonstrate that mercury uptake by HepG2 cells is dependent on the chemical structure of the mercury compound, the thiol ligand, and the activity of γ-glutamyl transpeptidase. γ-Glutamyl transpeptidase appears to play a key role in the disposition of MeHg-SG by facilitating the formation of MeHg-l-cysteine, which is readily transported into the cells on an amino acid-type carrier.

Flow-injection hydride generation atomic absorption spectrometric study of the automated on-line pre-reduction of arsenate, methylarsonate and dimethylarsinate and high-performance liquid chromatographic separation of their l-cysteine complexes

An automated on-line pre-reduction of arsenate, monomethylarsonate (MMA) and dimethylarsinate (DMA) using flow injection hydride generation atomic absorption spectrometry (FI-HGAAS) is feasible. The kinetics of pre-reduction and complexation depend strongly on the concentration of l-cysteine and on the temperature in the following increasing order: inorganic As(V)<DMA<MMA. Arsenate is pre-reduced/complexed within less than 50 s at 70–100°C compared to 1 h at room temperature, while MMA and DMA require 1.5–2 min at 70–100°C and up to 1–2 h at room temperature. The characteristic masses and concentrations for 100 μl injections are 0.01 ng and 0.1 μg l −1 in integrated absorbance and 0.2 ng and 2 μg l −1 in peak height measurements, and the limits of detection are ca. 0.5 ng and 5 μg l −1, respectively. In a high-performance liquid chromatography (HPLC)–HGAAS system, the l-cysteine complexes of inorganic As(III), MMA and DMA are best separated within 7 min by HPLC on a strongly acidic cation exchange column such as Spherisorb S SCX 120×4 mm (5 μm) with a mobile phase containing 12 mmol l −1 phosphate buffer (KH 2PO 4/H 3PO 4)–2.5 mmol l −1 l-cysteine, pH 3.3–3.5. Upon dilution to l-cysteine levels below 10 mmol l −1, which are compatible with HPLC separations, the DMA–cysteine complex is unstable on storage. No baseline separations are possible with anion exchange and reverse phase C 18 HPLC columns. The limits of detection with 50 μl injections in peak area mode are ca. 0.5 ng and 10 μg l −1, respectively.

Boron complexes of L-cysteine

The synthesis of diphenyl[(R)- thiazolidine-4-carboxylato-O,N ] boron 4 , 9- borabicyclo[3.3.1]non-9-yl[(R)- thiazolidine-4-carboxylato-O,N ] boron 9 , 9- borabicyclo[3.3.1]non-9-yl[S-methyl-(R)- cysteinato-O,N ] boron 10 , and 9- borabicyclo[3.3.1]non-9-yl[S-trityl-(R)- cysteinato-O,N ] boron 11 with potential application in Boron Neutron Capture Therapy is reported. The preparation of two derivatives of 2-oxo-propanoic acid, diphenyl[2-benzylimino-2-oxopropanoato-O,N] boron 6 and dicyclohexyl[2-imino-2-oxopropanoato-O,N ] boron 8 is described. Compound 6 represents the first example of a monocyclic unsaturated oxazaborolidine-5-one whose crystal structure has been determined.