Anodic stripping voltammetry in the complexation study of the peptide Lys-Cys-Thr-Cys-Cys-Ala [56–61] MT I and cadmium: application in determination of the complexing capacity and stability constant

Fully automated two-step assay for detection of metallothionein through magnetic isolation using functionalized γ-Fe2O3 particles

Metallothioneins (MTs) are involved in heavy metal detoxification in a wide range of living organisms. Currently, it is well known that MTs play substantial role in many pathophysiological processes, including carcinogenesis, and they can serve as diagnostic biomarkers. In order to increase the applicability of MT in cancer diagnostics, an easy-to-use and rapid method for its detection is required. Hence, the aim of this study was to develop a fully automated and high-throughput assay for the estimation of MT levels. Here, we report the optimal conditions for the isolation of MTs from rabbit liver and their characterization using MALDI-TOF MS. In addition, we described a two-step assay, which started with an isolation of the protein using functionalized paramagnetic particles and finished with their electrochemical analysis. The designed easy-to-use, cost-effective, error-free and fully automated procedure for the isolation of MT coupled with a simple analytical detection method can provide a prototype for the construction of a diagnostic instrument, which would be appropriate for the monitoring of carcinogenesis or MT-related chemoresistance of tumors.

Interactions of helquats with chiral acidic aromatic analytes investigated by partial-filling affinity capillary electrophoresis

Noncovalent molecular interactions between helquats, a new class of dicationic helical extended diquats, and several chiral acidic aromatic drugs and catalysts have been investigated using partial-filling affinity capillary electrophoresis (PF-ACE). Helquats dissolved at 1mM concentration in the aqueous background electrolyte (40mM Tris, 20mM acetic acid, pH 8.1) were introduced as ligand zones of variable length (0-130mm) into the hydroxypropylcellulose coated fused silica capillary whereas 0.1mM solutions of negatively charged chiral drugs or catalysts (warfarin, ibuprofen, mandelic acid, etodolac, binaphthyl phosphate and 11 other acidic aromatic compounds) were applied as a short analyte zone at the injection capillary end. After application of electric field, analyte and ligand migrated against each other and in case of their interactions, migration time of the analyte was increasing with increasing length of the ligand zone. From the tested compounds, only isomers of those exhibiting helical chirality and/or possessing conjugated aromatic systems were enantioselectively separated through their differential interactions with helquats. Some compounds with conjugated aromatic groups interacted with helquats moderately strongly but non-enantiospecifically. Small compounds with single benzene ring exhibited no or very weak non-enantiospecific interactions. PF-ACE method allowed to determine binding constants of the analyte-helquat complexes from the changes of migration times of the analytes. Binding constants of the weakest complexes of the analytes with helquats were less than 50L/mol, whereas binding constants of the strongest complexes were in the range 1 000-1 400L/mol.

Structural effects and nanoparticle size are essential for quantum dots-metallothionein complex formation

Interaction between semiconductor nanocrystals, cadmium telluride quantum dots (CdTe QDs) capped with mercaptosuccinic acid (MSA) and metallothionein (MT) was investigated. MSA-capped CdTe QDs were synthesized in aqueous solution. Mixture of MT and MSA-capped CdTe QDs has been investigated by various analytical methods as follows: tris-tricine gel electrophoresis, fluorescence evaluation and electrochemical detection of catalysed hydrogen evolution. The obtained results demonstrate that MSA-capped CdTe QDs and MT do not create firmly bound stabile complex. However, weak electrostatic interactions contribute to the interaction of MT with MSA-capped CdTeQDs. It can be concluded that QDs size influences the QDs and MT interaction. The smallest QDs had the highest affinity to MT and vice versa.

Cadmium availability to freshwater mussel (Unio tumidus) in the presence of organic matter and UV radiation

The influence of ultraviolet radiation (UV) on cadmium availability to freshwater mussel (Unio tumidus) in the presence of organic matter was investigated. Water solutions containing 1000, 500, and 250 microg x L(-1) of cadmium and 28.8 mg x L(-1) of total organic carbon (TOC) were exposed to ecologically relevant biologically effective UV-A and UV-B irradiances of 1.73 x 10(-6) W x cm(-2) and 1.50 x 10(-5) W x cm(-2) respectively for 12 h. The availability of cadmium was measured directly as Cd concentration in gills, mantle, digestive gland and foot, and indirectly as its impact on the content of essential cations. The concentration of cadmium ions, soluble forms of cadmium, pH and conductivity in UV irradiated solutions were also measured. UV exposures resulted in a decrease of the TOC to 25.9 mg x L(-1), followed by a decrease in the total concentration of Cd soluble forms, increase in the concentration of cadmium bound to particulate matter, and increase in the concentration of free cadmium ions in comparison to non-irradiated mixtures. Mussels from mixtures exposed to UV accumulated more cadmium than specimens from non-irradiated mixtures. This was confirmed by the fluctuations of essential cations, i.e. decreases in the contents of Zn, Ca, Fe and increase of the Cu content. Na/K molar ratios in gills were negatively correlated with cadmium content, while a positive trend occurred in other organs. We suggest that in UV-exposed water more ionic forms of cadmium occur. On the other hand more cadmium is also bound to particulate matter. Our research indicate that the increase of cadmium accumulation in mussels grown in humic acid solutions exposed to UV were most probably related to the increase in the concentration of cadmium bound to particulate matter.

Determination of major and trace elements in human scalp hair by pressurized-liquid extraction with acetic acid and inductively coupled plasma–optical-emission spectrometry

An analytical method has been developed for determination of major (Ca, K, Mg, and Na) and trace elements (As, Cd, Co, Li, Ni, and Sr) in human scalp hair. The proposed method includes a novel, simple, rapid, highly efficient, and automated metal-leaching procedure, by pressurized-liquid extraction (PLE), combined with a rapid simultaneous detection system-inductively coupled plasma-optical-emission spectrometry (ICP-OES). PLE is one of the most promising recently introduced sample-preparation techniques, with the advantages of reducing solvent consumption and enabling automated sample handling. The operating conditions for PLE, including concentration of the extraction solvent, extraction temperature, static time, number of extraction steps, pressure, mean particle size, diatomaceous earth (DE) mass/sample mass ratio, and flush volume were studied using an experimental design (Plackett-Burman design, PBD). The optimum conditions were use of 0.75 mol L-1 acetic acid as extracting solution and powdered hair samples thoroughly mixed with DE, as a dispersing agent, at a DE mass/sample mass ratio of 4. Extraction was performed at room temperature and an extraction pressure of 140 atm for 5 min in one extraction step. The flush volume was fixed at 60%. The PLE-assisted multi-element leaching proposed is complete after 7 min (5 min static time plus 1 min purge time plus 1 min end relief time). Under the optimised conditions the figures of merit, for example limits of detection and quantification, repeatability of the over-all procedure, and accuracy, were evaluated. Analysis of GBW-07601 (human hair) certified reference material revealed accuracy was good for the target elements. The optimised method was finally applied to several human scalp-hair samples.

Influence of dissolved organic carbon content on modelling natural organic matter acid-base properties

Natural organic matter (NOM) behaviour towards proton is an important parameter to understand NOM fate in the environment. Moreover, it is necessary to determine NOM acid-base properties before investigating trace metals complexation by natural organic matter. This work focuses on the possibility to determine these acid-base properties by accurate and simple titrations, even at low organic matter concentrations. So, the experiments were conducted on concentrated and diluted solutions of extracted humic and fulvic acid from Laurentian River, on concentrated and diluted model solutions of well-known simple molecules (acetic and phenolic acids), and on natural samples from the Seine river (France) which are not pre-concentrated. Titration experiments were modelled by a 6 acidic-sites discrete model, except for the model solutions. The modelling software used, called PROSECE (Programme d'Optimisation et de SpEciation Chimique dans l'Environnement), has been developed in our laboratory, is based on the mass balance equilibrium resolution. The results obtained on extracted organic matter and model solutions point out a threshold value for a confident determination of the studied organic matter acid-base properties. They also show an aberrant decreasing carboxylic/phenolic ratio with increasing sample dilution. This shift is neither due to any conformational effect, since it is also observed on model solutions, nor to ionic strength variations which is controlled during all experiments. On the other hand, it could be the result of an electrode troubleshooting occurring at basic pH values, which effect is amplified at low total concentration of acidic sites. So, in our conditions, the limit for a correct modelling of NOM acid-base properties is defined as 0.04 meq of total analysed acidic sites concentration. As for the analysed natural samples, due to their high acidic sites content, it is possible to model their behaviour despite the low organic carbon concentration.

Voltammetry assisted by multivariate analysis as a tool for speciation of metallothioneins: competitive complexation of alpha- and beta-metallothionein domains with cadmium and zinc

Multivariate Curve Resolution by Alternating Least Squares (MCR-ALS) is applied to voltammetric data obtained in the study of competitive complexation of Zn(II) and Cd(II) by alpha- and beta-domains of metallothionein (MT). The application of MCR-ALS allows the estimation of both the voltammograms and the concentration profiles associated with each electrochemical process. The complexity of the voltammograms obtained in titrations of the alpha- or beta-domains of MT with Cd(II) and later Zn(II) (or vice versa) prevents their direct interpretation using traditional electrochemical methods. But when MCR-ALS is applied, voltammograms can be interpreted rather satisfactorily in both qualitative and quantitative terms. MCR-ALS showed the formation of Cd2Znbeta dom and Cd3Znalpha dom complexes when both metals were competitively added. A method based on the combined use of voltammetry and some chemometric techniques is proposed. It can be useful for the metal speciation of environmentally relevant natural ligands.