Synthesis, characterisation and catalytic activity of 4, 5-imidazoledicarboxylate ligated Co(II) and Cd(II) metal-organic coordination complexes

Mitigating the toxicity of reactive oxygen species induced by cadmium via restoring citrate valve and improving the stability of enzyme structure in rice

The mechanism of reactive oxygen species (ROS) burst in rice cells induced by cadmium (Cd) stress remains poorly understood. The present study shows that the burst of superoxide anions (O₂^·-) and hydrogen peroxide (H₂O₂) in roots and shoots led by Cd stress was attributed to the disturbance of citrate (CA) valve and the damage of antioxidant enzyme structure in the rice seedlings. Cd accumulation in cells altered the molecular structure of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) through attacking glutamate (Glu) and other residues, leading to the significant reduction of their activities in clearing O₂^·- and decomposing H₂O₂. Citrate supplementation obviously increased the activity of antioxidant enzymes and decreased ∼20-30% of O₂^·- and H₂O₂ contents in roots and shoots. Meanwhile, the synthesis of metabolites/ligands such as CA, α-ketoglutarate (α-KG) and Glu as well as the activities of related enzymes in CA valve were remarkably improved. The activities of antioxidant enzymes were protected by CA through forming stable hydrogen-bonds between CA and antioxidant enzymes, and forming the stable chelates between ligands and Cd. These findings indicate that exogenous CA mitigated the toxicity of ROS under Cd stress by the ways of restoring CA valve function to reduce the production of ROS, and improving the stability of enzyme structure to enhance antioxidant enzymes activity.

Rice organs concentrate cadmium by chelation of amino acids containing dicarboxyl groups and enhance risks to human and environmental health in Cd-contaminated areas

When rice plants grown in paddy fields with Cd content of 0.3-1.5 mg kg^-1, Cd quantities in roots and straws were 2-7 times higher than that in topsoil. Return of these vegetative organs to topsoil aggravated the ecological risk of Cd pollution. Cd content in rice grains was 0.1-1.3 mg kg^-1, and hazard quotients for local consumers by intake of these rice were 0.7-8.8. Planting low-Cd-accumulating (LCA) cultivar reduced hazard quotients for consumers by intake of rice, but had similar ecological risks as high-accumulating (HCA) cultivars. LCA cultivar had lower Cd content in grains as well as higher efficiency of altering Cd into insoluble forms in flag leaves and upmost nodes than HCA cultivars. Insoluble Cd content in nodes was linearly increased with soil Cd content, companied by significant decline of 4 amino acids with dicarboxyl groups. Glu or Asp can form a cyclic complex with Cd by two O atoms from α-COO- and side chain-COO-. These results indicate that roots and straws have high potential to concentrate Cd by forming complexes between amino acids and Cd ions, and Cd-enriched straw return to topsoil may aggravate the ecological risk of Cd contamination.

A Review on Metal-Organic Frameworks as Congenial Heterogeneous Catalysts for Potential Organic Transformations

Metal-organic frameworks (MOFs) have emerged as versatile candidates of interest in heterogeneous catalysis. Recent research and developments with MOFs positively endorse their role as catalysts in generating invaluable organic compounds. To harness the full potential of MOFs in value-added organic transformation, a comprehensive look at how these materials are likely to involve in the catalytic processes is essential. Mainstays of MOFs such as metal nodes, linkers, encapsulation materials, and enveloped structures tend to produce capable catalytic active sites that offer solutions to reduce human efforts in developing new organic reactions. The main advantages of choosing MOFs as reusable catalysts are the flexible and robust skeleton, regular porosity, high pore volume, and accessible synthesis accompanied with cost-effectiveness. As hosts for active metals, sole MOFs, modified MOFs, and MOFs have made remarkable advances as solid catalysts. The extensive exploration of the MOFs possibly led to their fast adoption in fabricating new biological molecules such as pyridines, quinolines, quinazolinones, imines, and their derivatives. This review covers the varied MOFs and their catalytic properties in facilitating the selective formation of the product organic moieties and interprets MOF’s property responsible for their elegant performance.

Nanoporous bimetallic metal-organic framework (FeCo-BDC) as a novel catalyst for efficient removal of organic contaminants

In this work, we report on the synthesis and characterization of nanoporous bimetallic metal-organic frameworks (FeCo-BDC). Effects of synthesis time and temperature on the structures, morphology, and catalytic performance of FeCo-BDC were investigated. Scanning Electron Microscopy (SEM), Transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) were used to reveal the morphological and textural characteristics. The crystal structure and chemical composition of FeCo-BDC were determined by means of X-ray powder diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Photoelectron Spectroscopy (XPS), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) measurements. Interestingly, FeCo-BDC grew into the same crystal structure with different morphology in the temperature of 110-150 °C with 12-48 h. The heterogeneous catalytic activity of FeCo-BDC was tested to activate peroxydisulfate (PDS) and peroxymonosulfate (PMS) for removal of methylene blue (MB). The results found that FeCo-BDC synthesized at 150 °C with 24 h exhibited the best catalytic performance for PMS and obtained 100% of MB removal within 15 min. The abundant unsaturated metal active sites of Fe(II) and Co(II) in the skeleton of FeCo-BDC made a great contribution to the generation of sulfate () and hydroxyl radicals (OH), which resulted in the excellent performance for MB degradation.

Modeling Solid State Stability for Speciation: A Ten-Year Long Study

Speciation studies are based on fundamental models that relate the properties of biomimetic coordination compounds to the stability of the complexes. In addition to the classic approach based on solution studies, solid state properties have been recently proposed as supporting tools to understand the bioavailability of the involved metal. A ten-year long systematic study of several different complexes of imidazole substituted ligands with transition metal ions led our group to the definition of a model based on experimental evidences. This model revealed to be a useful tool to predict the stability of such coordination complexes and is based on the induced behavior under thermal stress. Several different solid state complexes were characterized by Thermally Induced Evolved Gas Analysis by Mass Spectrometry (TI-EGA-MS). This hyphenated technique provides fundamental information to determine the solid state properties and to create a model that relates stability to coordination. In this research, the model resulting from our ten-year long systematic study of complexes of transition metal ions with imidazole substituted ligands is described. In view of a systematic addition of information, new complexes of Cu(II), Zn(II), or Cd(II) with 2-propyl-4,5-imidazoledicarboxylic acid were precipitated, characterized, and studied by means of Thermally Induced Evolved Gas Analysis performed by mass spectrometry (TI-EGA-MS). The hyphenated approach was applied to enrich the information related to thermally induced steps, to confirm the supposed decomposition mechanism, and to determine the thermal stability of the studied complexes. Results, again, allowed supporting the theory that only two main characteristic and common thermally induced decomposition behaviors join the imidazole substituted complexes studied by our group. These two behaviors could be considered as typical trends and the model allowed to predict coordination behavior and to provide speciation information.