Natural amino acids as potential chelators for soil remediation.

The soils contaminated by toxic metals are often remediated using EDTA and similar non-biodegradable chelators. Most chelators are in fact synthetic amino acid derivatives, whereas natural proteinogenic amino acids (PAAs) have not been systematically explored as remediation agents, despite their well-known metal chelating abilities and environmental benefits. Our study represents a comprehensive research exploring 16 structurally and functionally different PAAs as potential remediating agents, applied to 3 different heavy metal-contaminated samples. The study was mostly focused on extracting Cd, Cu, Ni, and Zn. The reaction parameters were screened and optimized. It was found that the efficiencies of extracting Cu, Ni, and Zn by Threonine, Aspartic acid and Histidine were comparable to those by EDTA, whereas non-polar side chain-containing PAAs demonstrated consistently lower PTM extraction rates compared to other PAAs. The sulfur-containing Cysteine appeared to be efficient to extract Cd (to some extent), Ni and Zn, but not Cu, due to chemical reasons. The structure-functional correlations were identified, described, and found to be independent on the specific samples. Possible molecular mechanisms of metal extraction from soils by PAAs are discussed. In contrast to EDTA, the soil-essential elements are almost not extracted by PAAs. This important feature of the PAAs, along with their availability, observed selectivity, competitive efficiency, non-toxicity and even fertilizing properties, make them particularly soil-friendly, and thus, potentially applicable chelators in certain remediation processes.

New insights into chelator recycling by a chelating resin: From molecular mechanisms to applicability.

As part of the project of developing a "green" and highly feasible soil remediation process, recycling an eco-friendly chelating agent, glycine, using Chelex-100 chelating resin, was studied. Two model complexes, copper and nickel glycinates, were tested under various conditions, including equivalent viscosity but different temperature conditions. Two similar complexes demonstrated very different reactivity towards Chelex-100. An in-depth study led to the discovery of unusual metal-dependent mechanisms of the complex-to-resin metal transfer. Particularly, nickel transfer proceeds via a dissociative mechanism, whereas copper transfer does not require pre-dissociation of the complexes, and proceeds via the associative ligand-exchange mechanism. Both processes result in the recovery of the used chelator. The glycine solution was applied on the spiked soil, then recovered on Chelex-100 resin and successfully reused, thus demonstrating a proof of the concept. These findings contribute to the science, strategies, and methodology of both water purification and chelator recycling fields.

Garlic allicin as a potential agent for controlling oral pathogens.

Garlic has been used medicinally throughout human history. Allicin is considered the most therapeutic constituent of garlic. This study tested the antimicrobial activity of garlic allicin on oral pathogens associated with dental caries and periodontitis. Allicin was found effective against all the tested bacteria. The broth dilution method revealed that planktonic growth of the cariogenic, gram-positive species Streptococcus mutans, S. sobrinus, and Actinomyces oris was inhibited by an allicin concentration of 600 µg/mL or higher. Planktonic growth of the tested gram-negative periopathogenic species Aggregatibacter actinomycetemcomitans and Fusobacterium nucleatum was inhibited by a minimum allicin concentration of 300 µg/mL. Porphyromonas gingivalis, an anaerobic, gram-negative pathogen and the bacterium most associated with chronic periodontitis, demonstrated the lowest sensitivity to allicin (2,400 µg/mL). Gel zymography and the synthetic chromogenic substrate N(α)-benzoyl-L-arginine 4-nitroanilide hydrochloride demonstrated that allicin inhibits the proteases of P. gingivalis, including the arginine and lysine gingipains known as major virulence factors of this organism. A gingipain-inactivated mutant demonstrated high sensitivity to allicin (<300 µg/mL), revealing that gingipains confer resistance to allicin. Live/dead staining followed by analysis with confocal laser scanning microscopy revealed that allicin was bactericidal to S. mutans grown in mature biofilms. However, this bactericidal effect was reduced as biofilm depth increased. In conclusion, these results support the traditional medicinal use of garlic and suggest the use of allicin for alleviating dental diseases.

Allicin purified from fresh garlic cloves induces apoptosis in colon cancer cells via Nrf2.

Allicin (diallyl thiosulfinate) is the best-known biologically active component in freshly crushed garlic extract. We developed a novel, simple method to isolate active allicin, which yielded a stable compound in aqueous solution amenable for use in in vitro and in vivo studies. We focused on the in vitro effects of allicin on cell proliferation of colon cancer cell lines HCT-116, LS174T, HT-29, and Caco-2 and assessed the underlying mechanisms. This allicin preparation exerted a time- and dose-dependent cytostatic effect on these cells at concentrations ranging from 6.2 to 310 µM. Treatment with allicin resulted in HCT-116 apoptotic cell death as demonstrated by enhanced hypodiploid DNA content, decreased levels of B-cell non-Hodgkin lymphoma-2 (Bcl-2), increased levels of bax and increased capability of releasing cytochrome c from mitochondria to the cytosol. Allicin also induced translocation of NF-E2-related factor-2 (Nrf2) to the nuclei of HCT-116 cells. Luciferase reporter gene assay showed that allicin induces Nrf2-mediated luciferase transactivation activity. SiRNA knock down of Nrf2 significantly affected the capacity of allicin to inhibit HCT-116 proliferation. These results suggest that Nrf2 mediates the allicin-induced apoptotic death of colon cancer cells.