Evaluation of the association of mercury(II) with some dicysteinyl tripeptides

Synthesis, fluorescence and theoretical insights into a novel FRET-based dansyl-rhodamine sensor for the in vitro detection of toxic bioaccumulated Hg(II) ions

This work describes the successful design and synthesis of a new fluorescence resonance energy transfer (FRET)-based sensor, denoted as RD1. This sensor incorporates a robust dual-fluorophore design, which combines a rhodamine and a dansyl derivative, functionalized with a thiosemicarbazide group that acts as Hg(II) specific recognition site. A synthetic pathway was developed that allowed the efficient synthesis of RD1 with a remarkable overall yield of 44% over four steps, through microwave-assisted protocols. The influence of ethyl, benzyl and phenyl substituents of isothiocyanate in the preparation of the thiosemicarbazide moiety was studied, revealing a crucial dependence of the nature of the isothiocyanate in the formation of the recognition site. Owing to its characteristic ratiometric detection, RD1 exhibited remarkable robustness to external parameters such as pH and solvent composition. The sensor demonstrated a hybrid two-stage response to Hg(II), with an initial quenching of fluorescence followed by an enhancement of emission through a FRET mechanism, both stages being corroborated by DFT (density functional theory) calculations. In vitro studies demonstrated that RD1 presents excellent cytocompatibility and capacity to permeate cellular membranes and be effectively internalized by L929 cell line. Importantly, RD1 retained its sensory ability in a complex cellular environment, affirming its efficacy as a fluorescent sensor for the in vitro detection of bioaccumulated mercury species. These results suggest the potential of RD1 for the detection of toxic bioaccumulated mercury species, aiding in environmental and biomedical research.

Novel Insights into Hg0 Oxidation in Rice Leaf: Catalase Functions and Transcriptome Responses

Rice leaves can assimilate atmospheric mercury (Hg0), which is accumulated by grains and causes health risks to rice consumers. However, the molecular mechanisms underlying Hg0 assimilation in rice leaves remain poorly understood. Here, we investigated catalase's (CAT) function in Hg0 oxidation within rice leaves, as well as the Hg speciation and transcriptomic profiles of rice leaves exposed to Hg0. The inactivation of catalase reduced Hg0 oxidation by 91% in the leaf homogenate and the Hg0 oxidation rate increased along with CAT activity, showing the CAT's function in Hg0 oxidation. Hg0 was converted to Hg(cysteine)2 complexes in the leaf. Transcriptomic results revealed that the expression levels of both OsCATA and OsCATB (catalase-encoding genes) increased with Hg concentration, suggesting the involvement of catalase-related molecular network in Hg0 oxidation. Upstream transcription factors, including NAC (NAM-no apical meristem, ATAF-Arabidopsis transcription activation factor, and CUC-cup-shaped cotyledon), and ethylene-responsive transcription factor, are likely involved in catalase expression. Genes related to cysteine metabolism and amino acid transport appeared to regulate Hg accumulation. Our findings demonstrate the important function of catalase in Hg0 oxidation within rice and are fundamental for developing genetically modified rice cultivars to minimize human Hg exposure health risks.

Comparative Analysis of the Effects of Olive Oil Hydroxytyrosol and Its 5-S-Lipoyl Conjugate in Protecting Human Erythrocytes from Mercury Toxicity

Oxidative stress is one of the underlying mechanisms of the toxic effects exerted by mercury (Hg) on human health. Several antioxidant compounds, including the olive oil phenol hydroxytyrosol (HT), were investigated for their protective action. Recently, we have reported that 5-S-lipoylhydroxytyrosol (Lipo-HT) has shown increased antioxidant activities compared to HT and exerted potent protective effects against reactive oxygen species (ROS) generation and oxidative damage in human hepatocellular carcinoma HepG2 cell lines. In this study, the effects of Lipo-HT and HT on oxidative alterations of human erythrocytes induced by exposure to 40 μM HgCl₂ were comparatively evaluated. When administered to the cells, Lipo-HT (5–20 μM) proved nontoxic and it decreased the Hg-induced generation of ROS, the hemolysis, and the depletion of intracellular GSH levels. At all tested concentrations, Lipo-HT exhibited higher ability to counteract Hg-induced cytotoxicity compared to HT. Model studies indicated the formation of a mercury complex at the SH group of Lipo-HT followed by a redox reaction that would spare intracellular GSH. Thus, the enhanced erythrocyte protective action of Lipo-HT from Hg-induced damage with respect to HT is likely due to an effective chelating and reducing ability toward mercury ions. These findings encourage the use of Lipo-HT in nutraceutical strategies to contrast heavy metal toxicity in humans.

Fluorescence probe for mercury(ii) based on the aqueous synthesis of CdTe quantum dots stabilized with 2-mercaptoethanesulfonate

A new capping ligand, 2-mercaptoethanesulfonate (MES), for CdTe quantum dots passivation provide high selectivity and sensitivity in Hg(ii) determination.

A Study of the Complexation of Mercury(II) with Dicysteinyl Tetrapeptides by Electrospray Ionization Mass Spectrometry

In this study we evaluated a method for the characterization of complexes, formed in different relative ratios of mercury(II) to dicysteinyl tetrapeptide, by electrospray ionization orbitrap mass spectrometry. This strategy is based on previous successful characterization of mercury-dicysteinyl complexes involving tripeptides by utilizing mass spectrometry among other techniques. Mercury(II) chloride and a dicysteinyl tetrapeptide were incubated in a degassed buffered medium at varying stoichiometric ratios. The complexes formed were subsequently analyzed on an electrospray mass spectrometer consisting of a hybrid linear ion- and orbi- trap mass analyzer. The electrospray ionization mass spectrometry (ESI-MS) spectra were acquired in the positive mode and the observed peaks were then analyzed for distinct mercury isotopic distribution patterns and associated monoisotopic peak. This work demonstrates that an accurate stoichiometry of mercury and peptide in the complexes formed under specified electrospray ionization conditions can be determined by using high resolution ESI MS based on distinct mercury isotopic distribution patterns.

Heavy metal complexation of thiol-containing peptides from soy glycinin hydrolysates

Many thiol-containing molecules show heavy metal complexation ability and are used as antidotes. In this study, the potential function associated with thiol-containing peptides (TCPs) from soy protein hydrolysates as natural detoxicants for heavy metals is reported. TCPs enriched by Thiopropyl-Sepharose 6B covalent chromatography had different molecular weight distributions as well as different numbers of proton dissociable groups, depending on the proteases and degree of hydrolysis. The major contribution of sulfhydryl groups was confirmed by the largest pH decrease between 8.0 and 8.5 of the pH titration curves. The complexation of TCPs with heavy metalswas evaluated by stability constants (β_n) of TCP-metal complexes whose stoichiometry was found to be 1:1 (ML) and 1:2 (ML₂). TCPs from degree of hydrolysis of 25% hydrolysates gave high affinities towards Hg²⁺, Cd²⁺, and Pb²⁺ (giving similar or even bigger lgβ values than that of glutathione). A significantly positive correlation was found between the logarithm of stability constants for ML₂ (lgβ₂) and the sulfhydryl group content. Molecular weight distribution of TCPs affected the complexation with Pb²⁺ notably more than Hg²⁺ and Cd²⁺. These results suggest that soy TCPs have the potential to be used in the formulation of functional foods to counteract heavy metal accumulation in humans.

New insights into coenzyme A interaction with mercury ions provided by mass spectrometric and circular dichroism spectroscopic approaches

The interaction of coenzyme A (CoA) with mercury ions was investigated using electrospray ionization mass spectrometry and circular dichroism spectroscopy. Our results indicated a 1:1 stoichiometric CoA-Hg complex at physiological pH. Furthermore, the CoA conformation considerably changed in the presence of mercury ions. In addition, a by-product of the reaction, thiocoenzyme A, was identified using mass spectrometry.

Synthesis and ESI mass spectrometric analysis of the association of mercury(II) with multi-cysteinyl peptides

In order to gain more insight into the associations of mercury(II) with cysteinyl peptides, we investigated the effect of increasing cysteinyl residues on complex type formations. Three series of di-, tri-, and tetra-cysteinyl peptides, D[CGD]nCG (CP 2A, CP 3A, and CP 4A), E[CEG]nCG (CP 2B, CP 3B, and CP 4B) and E[CDG]nCG (CP 2C, CP 3C, and CP 4C), where n=1, 2, or 3, were prepared by microwave-assisted solid phase peptide synthesis. Complexes formed in different relative ratios of mercury(II) to cysteinyl peptides were characterized by electrospray orbitrap mass spectrometry utilizing complex specific mercury isotopic patterns. In equimolar mercury(II) to peptide ratio, all three series of di-, tri-, and tetra-cysteinyl peptides form predominantly the 1:1Hg(peptide) complex type, indicating that the intervening amino acid residues do not elicit preferential complex type formation. However, in non-equivalent mercury(II) to peptide ratio, the number of cysteinyl residues has a significant effect on the Hg:peptide stoichiometry in the complex formed. For example, in four times excess peptide, the 1:2Hg(peptide)2 and 1:1Hg(peptide) complexes are formed for di-cysteinyl peptides but not for the tri- and tetra-cysteinyl peptides. In contrast, the 2:1Hg2(peptide) and 1:1Hg(peptide) complexes are formed for the tri- and tetra-cysteinyl peptides. In excess mercury(II), CP 4C formed exclusively the 2:1Hg2(peptide) complex. The exact number of deprotonations observed for each complex could be derived from its signature mercury isotope pattern and monoisotopic peak mass. These multi-cysteinyl peptides present an attractive option for mercury chelation or environmental heavy metal remediation.