Autometallographic Localization of Heavy Metals in Resin Sections, Cryosections and Isolated Cells of the Mussel Mytilus galloprovincialis (L.)

In the present study, autometallography (AMG) has been performed on resin-embedded tissue sections, cryosections, as well as on isolated cells from the digestive gland, the gills and the haemolymph of mussels (Mytilus galloprovincialis) collected from the field. The AMG reaction was more intense in cryosections and isolated cells compared to resin sections. This intense AMG reaction found in cryosections and in isolated cells and the time effectiveness of the procedures enhances their use in a variety of studies, such as biomonitoring, even if small amount of metals are to be detected. In addition, the preparation of isolated cells does not require specific instruments or qualified personnel and, thus, the use of isolated cells is encouraging for AMG applications, although further laboratory investigation is required. On the other hand, the use of resin-embedded tissue sections for AMG applications, even though it is complicated and time consuming, leads to a high preservation of structural morphology and allows the exact localization of metals in discrete cellular compartments.     

Microbial leaching of metals from solid industrial wastes

Biotechnological applications for metal recovery have played a greater role in recovery of valuable metals from low grade sulfide minerals from the beginning of the middle era till the end of the twentieth century. With depletion of ore/minerals and implementation of stricter environmental rules, microbiological applications for metal recovery have been shifted towards solid industrial wastes. Due to certain restrictions in conventional processes, use of microbes has garnered increased attention. The process is environmentally-friendly, economical and cost-effective. The major microorganisms in recovery of heavy metals are acidophiles that thrive at acidic pH ranging from 2.0–4.0. These microbes aid in dissolving metals by secreting inorganic and organic acids into aqueous media. Some of the well-known acidophilic bacteria such as Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans and Sulfolobus spp. are well-studied for bioleaching activity, whereas, fungal species like Penicillium spp. and Aspergillus niger have been thoroughly studied for the same process. This mini-review focuses on the acidophilic microbial diversity and application of those microorganisms toward solid industrial wastes.     

Rational Design of Graphene‐Supported Single Atom Catalysts for Hydrogen Evolution Reaction

The proper choice of nonprecious transition metals as single atom catalysts (SACs) remains unclear for designing highly efficient electrocatalysts for hydrogen evolution reaction (HER). Herein, reported is an activity correlation with catalysts, electronic structure, in order to clarify the origin of reactivity for a series of transition metals supported on nitrogen‐doped graphene as SACs for HER by a combination of density functional theory calculations and electrochemical measurements. Only few of the transition metals (e.g., Co, Cr, Fe, Rh, and V) as SACs show good catalytic activity toward HER as their Gibbs free energies are varied between the range of –0.20 to 0.30 eV but among which Co‐SAC exhibits the highest electrochemical activity at 0.13 eV. Electronic structure studies show that the energy states of active valence d_z² orbitals and their resulting antibonding state determine the catalytic activity for HER. The fact that the antibonding state orbital is neither completely empty nor fully filled in the case of Co‐SAC is the main reason for its ideal hydrogen adsorption energy. Moreover, the electrochemical measurement shows that Co‐SAC exhibits a superior hydrogen evolution activity over Ni‐SAC and W‐SAC, confirming the theoretical calculation. This systematic study gives a fundamental understanding about the design of highly efficient SACs for HER.     

Oxygen Reduction Reactions on Single‐ or Few‐Atom Discrete Active Sites for Heterogeneous Catalysis

The oxygen reduction reaction (ORR) is of great importance in energy‐converting processes such as fuel cells and in metal–air batteries and is vital to facilitate the transition toward a nonfossil dependent society. The ORR has been associated with expensive noble metal catalysts that facilitate the O₂ adsorption, dissociation, and subsequent electron transfer. Single‐ or few‐atom motifs based on earth‐abundant transition metals, such as Fe, Co, and Mo, combined with nonmetallic elements, such as P, S, and N, embedded in a carbon‐based matrix represent one of the most promising alternatives. Often these are referred to as single atom catalysts; however, the coordination number of the metal atom as well as the type and nearest neighbor configuration has a strong influence on the function of the active sites, and a more adequate term to describe them is metal‐coordinated motifs. Despite intense research, their function and catalytic mechanism still puzzle researchers. They are not molecular systems with discrete energy states; neither can they fully be described by theories that are adapted for heterogeneous bulk catalysts. Here, recent results on single‐ and few‐atom electrocatalyst motifs are reviewed with an emphasis on reports discussing the function and the mechanism of the active sites.     

Designer metalloenzymes for synthetic biology: Enzyme hybrids for catalysis

Combining organometallics and biology has generated broad interest from scientists working on applications from in situ drug release to biocatalysis. Engineered enzymes and biohybrid catalysts (also referred to as artificial enzymes) have introduced a wide range of abiotic chemistry into biocatalysis. Predominantly, this work has concentrated on using these catalysts for single step in vitro reactions. However, the promise of using these hybrid catalysts in vivo and combining them with synthetic biology and metabolic engineering is vast. This report will briefly review recent advances in artificial metalloenzyme design, followed by summarising recent studies that have looked at the use of these hybrid catalysts in vivo and in enzymatic cascades, therefore exploring their potential for synthetic biology.     

综述与专论: 贵金属和碳纳米酶分子机制的理论研究

2007年四氧化三铁类过氧化物酶活性的发现催生了纳米酶这一新兴多学科交叉研究方向,多种基于金属、金属氧化物和碳纳米材料的纳米酶被发现,并在环境,食品安全,化工,生物医学等领域获得应用。相应的,纳米酶催化分子机制的理论研究也取得了进展。本文将回顾化学催化的基本原理,重点总结贵金属和碳纳米酶分子机制的理论研究进展。     

Single Atoms and Clusters Based Nanomaterials for Hydrogen Evolution,Oxygen Evolution Reactions,and Full Water Splitting

The sustainable and scalable production of hydrogen through hydrogen evolution reaction (HER) and oxygen through oxygen evolution reaction (OER) in water splitting demands efficient and robust electrocatalysts. Currently, state‐of‐the‐art electrocatalysts of Pt and IrO₂/RuO₂ exhibit the benchmark catalytic activity toward HER and OER, respectively. However, expanding their practical application is hindered by their exorbitant price and scarcity. Therefore, the development of alternative effective electrocatalysts for water splitting is crucial. In the last few decades, substantial effort has been devoted to the development of alternative HER/OER and water splitting catalysts based on various transition metals (including Fe, Co, Ni, Mo, and atomic Pt) which show promising catalytic activities and durability. In this review, after a brief introduction and basic mechanism of HER/OER, the authors systematically discuss the recent progress in design, synthesis, and application of single atom and cluster‐based HER/OER and water splitting catalysts. Moreover, the crucial factors that can tune the activity of catalysts toward HER/OER and water splitting such as morphology, crystal defects, hybridization of metals with nonmetals, heteroatom doping, alloying, and formation of metals inside graphitic layered materials are discussed. Finally, the existing challenges and future perspectives for improving the performance of electrocatalysts for water splitting are addressed.     

Synergetic effects of Ca2+ and Cu2+ on phase transition in phosphatidylserine membranes

In complexes of divalent metals with large exchange rate constant (K_H2O) of the coordinated H₂O, such as Ca²⁺ and Cu²⁺, the cubic structure in the ligand field is usually unstable and conformation changes are easily induced. We observed the molecular motion of phosphatidylserine (PS) in an amphipathic solvent (water / methanol / chloroform) by ¹H-NMR and ESR using Ca²⁺ and / or Cu²⁺, which has a similar K_H2O to that of Ca²⁺. We found that Ca²⁺ did not hinder the molecular movements of PS. However, Cu²⁺ reduced the movements of both headgroups and the double bonds in the fatty acids of PS. By addition of both Ca²⁺ and Cu²⁺, phase transition to a soft solid phase in the PS membrane was observed at room temperature. The results indicate that the headgroups are clustered in two-dimensional network with each ligand field displaced from the aqueous phase to the water / oil interface. The structure changes of the polar headgroups after the binding of divalent cations are considered to trigger the phase transition of this acidic phospholipid membrane.     

Dioximes: Synthesis and biomedical applications

The selective properties of dioxime compounds were discovered and outlined in the beginning of 20th century by Tschugaeff [L.Z. Tschugaeff, Z. Anorg. Allgem. Chem. 46 (1905) 144]. Dioximes have special properties as analytical reagents for transition metals. Dioximes complexation properties with metals were carried out by many investigations and these complexations showed a wide range of applications such as antimicrobial and theranostic agents. This review will provide general synthetic methods of oximes especially dioximes and brief overview on the applications of dioximes (applications of their metal complexes).     

The saga of IMAC and MIT

Immobilized Metal-ion Affinity Chromatography, IMAC, has been gaining in popularity as the purification technique of choice for proteins and peptides. IMAC of proteins on transition metals (Co, Ni, Cu, Zn) can be rationalized in terms of the coordination of histidine residues. Brief accounts of the principles of IMAC, its anticipated development and plausible applications are presented. Metal Ion Transfer, MIT, may offer an efficient means to deplete a metal ion from a metalloprotein or, conversely, to charge its apo form with a metal.     

The emerging age of cell-free synthetic biology

The engineering of and mastery over biological parts has catalyzed the emergence of synthetic biology. This field has grown exponentially in the past decade. As increasingly more applications of synthetic biology are pursued, more challenges are encountered, such as delivering genetic material into cells and optimizing genetic circuits in vivo. An in vitro or cell-free approach to synthetic biology simplifies and avoids many of the pitfalls of in vivo synthetic biology. In this review, we describe some of the innate features that make cell-free systems compelling platforms for synthetic biology and discuss emerging improvements of cell-free technologies. We also select and highlight recent and emerging applications of cell-free synthetic biology.     

Prion Protein Does Not Confer Resistance to Hippocampus-Derived Zpl Cells against the Toxic Effects of Cu2+, Mn2+, Zn2+ and Co2+ Not Supporting a General Protective Role for PrP in Transition Metal Induced Toxicity

The interactions of transition metals with the prion protein (PrP) are well-documented and characterized, however, there is no consensus on their role in either the physiology of PrP or PrP-related neurodegenerative disorders. PrP has been reported to protect cells from the toxic stimuli of metals. By employing a cell viability assay, we examined the effects of various concentrations of Cu²⁺, Zn²⁺, Mn²⁺, and Co²⁺ on Zpl (Prnp ^-/-) and ZW (Prnp ^+/+) hippocampus-derived mouse neuronal cells. Prnp ^-/- Zpl cells were more sensitive to all four metals than PrP-expressing Zw cells. However, when we introduced PrP or only the empty vector into Zpl cells, we could not discern any protective effect associated with the presence of PrP. This observation was further corroborated when assessing the toxic effect of metals by propidium-iodide staining and fluorescence activated cell sorting analysis. Thus, our results on this mouse cell culture model do not seem to support a strong protective role for PrP against transition metal toxicity and also emphasize the necessity of extreme care when comparing cells derived from PrP knock-out and wild type mice.     

Developments in Bioremediation of Soils and Sediments Polluted with Metals and Radionuclides: 2. Field Research on Bioremediation of Metals and Radionuclides

Bioremediation of metals and radionuclides has had many field tests, demonstrations, and full-scale implementations in recent years. Field research in this area has occurred for many different metals and radionuclides using a wide array of strategies. These strategies can be generally characterized in six major categories: biotransformation, bioaccumulation/bisorption, biodegradation of chelators, volatilization, treatment trains, and natural attenuation. For all field applications there are a number of critical biogeochemical issues that most be addressed for the successful field application. Monitoring and characterization parameters that are enabling to bioremediation of metals and radionuclides are presented here. For each of the strategies a case study is presented to demonstrate a field application that uses this strategy.     

Factors inducing transition from growth to dormancy in rhizobacteria Azospirillum brasilense

The factors suppressing division of the cells of the rhizobacterium Azospirillum brasilense and inducing their transition to a dormant state were analyzed. These included the presence of hexylresorcinol or heavy metals (Cu and Co) in the medium, oxygen stress, and transfer of the cells into the physiological saline or phosphate buffer solution. The results were used to develop a protocol for obtaining of nonculturable cells of A. brasilense Sp245, a natural symbiont of wheat. The cells lost their ability to grow on synthetic agar medium, but could revert to growth when incubated in freshly prepared liquid medium. Needle-shaped crystals differing from struvite, which has been previously reported for this strain, were found in the dormant culture of A. brasilense Sp245.     

Artificial mussels as indicators of metal pollution in freshwater systems: A field evaluation in the Koekemoer Spruit,South Africa

There has been a recent increase in water quality problems in South Africa. The monitoring of water resources is important for the continued management of water resources. The use of artificial mussels (AMs) as passive sampling devices in the monitoring of metals within a freshwater system was evaluated in a recent field study. Correlation testing was conducted between the AMs and Melanoides tuberculata for As, Cd, Cr, Co, Cu, Pb, Mn, Ni, U, V and Zn. It was found that a positive significant correlation exists between AMs and M. tuberculata with regards to As, U, and Co accumulations. The trend of metal accumulation between AMs and M. tuberculata were found to be similar for all of the metals tested. Site 2 which is located close to a gold mine, was found to have the highest metal concentrations in this study. This study confirms the hypothesis that AMs can be used as a useful tool for monitoring metals in freshwater.     

Hydrogen gas accelerates thermal inactivation ofClostridium botulinum 113B spores

Summary Heat inactivation ofClostridium botulinum spores was accelerated in atmospheres containing hydrogen gas. Hydrogen gas also moderately increased the thermal destruction ofBacillus spores. Hydrogen gas may react with components inC. botulinum spores such as transition metals producing hydrogen ions or hydrides, which destroy essential spore components. Thermal processing in modified atmospheres may have applications in food processing and in sterilization of medical supplies.     

Transition metal homeostasis: from yeast to human disease

Transition metal ions are essential nutrients to all forms of life. Iron, copper, zinc, manganese, cobalt and nickel all have unique chemical and physical properties that make them attractive molecules for use in biological systems. Many of these same properties that allow these metals to provide essential biochemical activities and structural motifs to a multitude of proteins including enzymes and other cellular constituents also lead to a potential for cytotoxicity. Organisms have been required to evolve a number of systems for the efficient uptake, intracellular transport, protein loading and storage of metal ions to ensure that the needs of the cells can be met while minimizing the associated toxic effects. Disruptions in the cellular systems for handling transition metals are observed as a number of diseases ranging from hemochromatosis and anemias to neurodegenerative disorders including Alzheimer??s and Parkinson??s disease. The yeast Saccharomyces cerevisiae has proved useful as a model organism for the investigation of these processes and many of the genes and biological systems that function in yeast metal homeostasis are conserved throughout eukaryotes to humans. This review focuses on the biological roles of iron, copper, zinc, manganese, nickel and cobalt, the homeostatic mechanisms that function in S. cerevisiae and the human diseases in which these metals have been implicated.     

X-ray microanalysis of unfixed chromatin in dinoflagellate cells prepared by a monolayer cryotechnique

The fine structural appearance and elemental composition of unfixed chromatin is described for cells of the dinoflagellate Prorocentru micans prepared by a freeze-drying technique. This involves rapid freezing, cryo-dehydration and resin infiltration of a monolayer of cells dispersed over a resin base.The fine structure of the nucleus appears quite different from chemically fixed and dehydrated cells. In stained sections, the chromosomes are seen as pale areas containing diffuse chromatin, and are surrounded by electron-dense nucleoplasm which has a reticulate substructure.X-ray microanalysis reveals the presence of high levels of chromatin-associated Ca and transition metals Fe, Ni, Cu and Zn, in accordance with previous observations on chemically processed cells. Calculation of elemental mass fractions by on-line computer demonstrates an overall ratio of one divalent cation per two phosphorus groups (or per two nucleotides). This ratio is similar to that obtained previously for chemically fixed chromatin, and shows that the precise overall association of metals is not primarily determined by the process of fixation.     

Biosorption of toxic metals from aqueous solutions by bacteria strains isolated from metal-polluted soils

The use of biological materials for effective removal and recovery of heavy metals from contaminated wastewaters has emerged as a potential alternative method to conventional treatment techniques. The aim of this paper was the laboratory study of biosorption of toxic metals from aqueous solution by the application of microorganisms (Bacillus laterosporus or Bacillus licheniformis), isolated from polluted (metal-laden) soil. Microorganisms have a high surface area-to-volume ratio, because of their small size and therefore, they can provide a large contact interface, which would interact with metals from the surrounding environment. Microbial metal accumulation has received much attention during recent years, due to the potential use of microorganisms for treatment of metal-polluted water or wastewater streams. Two toxic metals were selected as typical examples: a cation (cadmium) and an oxyanion (hexavalent chromium, and promising results were obtained, under optimized conditions.     

Metal and metalloid containing natural products and a brief overview of their applications in biology,biotechnology and biomedicine

Bioinorganic natural product chemistry is a relatively unexplored but rapidly developing field with enormous potential for applications in biology, biotechnology (especially in regards to nanomaterial development, synthesis and environmental cleanup) and biomedicine. In this review the occurrence of metals and metalloids in natural products and their synthetic derivatives are reviewed. A broad overview of the area is provided followed by a discussion on the more common metals and metalloids found in natural sources, and an overview of the requirements for future research. Special attention is given to metal hyperaccumulating plants and their use in chemical synthesis and bioremediation, as well as the potential uses of metals and metalloids as therapeutic agents. The potential future applications and development in the field are also discussed.