Spectroscopic and computational investigations of organometallic complexation of group 12 transition metals by methanobactins from Methylocystis sp. SB2.

Methanotrophic bacteria catalyze the aerobic oxidation of methane to methanol using Cu-containing enzymes, thereby exerting a modulating influence on the global methane cycle. To facilitate the acquisition of Cu ions, some methanotrophic bacteria secrete small modified peptides known as "methanobactins," which strongly bind Cu and function as an extracellular Cu recruitment relay, analogous to siderophores and Fe. In addition to Cu, methanobactins form complexes with other late transition metals, including the Group 12 transition metals Zn, Cd, and Hg, although the interplay among solution-phase configurations, metal interactions, and the spectroscopic signatures of methanobactin-metal complexes remains ambiguous. In this study, the complexation of Zn, Cd, and Hg by methanobactin from Methylocystis sp. strain SB2 was studied using a combination of absorbance, fluorescence, extended x-ray absorption fine structure (EXAFS) spectroscopy, and time-dependent density functional theory (TD-DFT) calculations. We report changes in sample absorbance and fluorescence spectral dynamics, which occur on a wide range of experimental timescales and characterize a clear stoichiometric complexation dependence. Mercury L3-edge EXAFS and TD-DFT calculations suggest a linear model for HgS coordination, and TD-DFT suggests a tetrahedral model for Zn2+ and Cd2+. We observed an enhancement in the fluorescence of methanobactin upon interaction with transition metals and propose a mechanism of complexation-hindered isomerization drawing inspiration from the wild-type Green Fluorescent Protein active site. Collectively, our results represent the first combined computational and experimental spectroscopy study of methanobactins and shed new light on molecular interactions and dynamics that characterize complexes of methanobactins with Group 12 transition metals.

A magneto-fluorescence bacteria assay strategy based on dual colour sulfide fluorescent nanoparticles with high near-IR conversion efficiency.

Anti-Stokes fluorescence induced by near-IR (NIR) radiation is particularly advantageous for the bioassay of complex samples, but most of the commonly used NIR-induced fluorescence nanomaterials such as up-conversion nanoparticles (UCNPs) do not exhibit satisfactory fluorescence intensity and work against achieving a highly sensitive bioassay. In this study, we a construct sensitive and specific bacteria biosensor based on the NIR-stimulated CaS: Eu, Sm, Mn and SrS: Ce, Sm, Mn nanoparticles. The fluorescent nanoparticles are conjugated with bacteria recognition fragments. In addition, the independent emission bands of these two types of fluorescent nanoparticles make it possible to detect and quantify Gram-positive strain and Gram-negative strain, simultaneously. Intense fluorescence and magnetic enrichment of magneto-fluorescence systems enable bacteria discrimination with the naked eye and improve sensitivity in trace bacteria detection (<20 CFU mL-1). The linear relationship between the fluorescence intensity and bacterial concentration is established with a detection range of 25-106 CFU mL-1. Furthermore, this NIR-excited assay strategy demonstrates better anti-interference capability than UV/visible-excited assay methods, showing high potential and practical value for medical diagnostics and bacteria monitoring.

Fluorescent metal-based complexes as cancer probes.

The ability to track drugs inside of cells and tumours has been highly valuable in cancer research and diagnosis. Metal complexes add attractive features to fluorescent drugs, such as targeting and specificity, solubility and uptake or photophysical properties. This review focuses on the latest fluorescent metal-based complexes, their cellular targets, photophysical properties and possible anticancer effects.

Construction of novel Z-scheme Ag/ZnFe2O4/Ag/BiTa1-xVxO4 system with enhanced electron transfer capacity for visible light photocatalytic degradation of sulfanilamide.

A novel Z-scheme system, Ag/ZnFe2O4/Ag/BiTa1-xVxO4 with enhanced electron transfer capacity was constructed for degrading sulfanilamide (SAM) using solar light. The photocatalytic activity of Ag/ZnFe2O4/Ag/BiTa1-xVxO4 was investigated. The effects of the mass ratio (ZnFe2O4:BiTaO4), doped V dose, Ag wt.% content, and irradiation time on the catalytic performance were evaluated. The reasonable mechanism of Ag/ZnFe2O4/Ag/BiTa1-xVxO4 solar photocatalytic degradation was also presented. These results reveal Ag/ZnFe2O4/Ag/BiTa1-xVxO4 possesses enhanced photocatalytic performance. The loaded Ag as electron mediator increases the electron transfer rate. Particularly, the doped V and the Fe ions from ZnFe2O4 form a powerful electron driving force, which enhances the electron transfer capacity. Ag/ZnFe2O4/Ag/BiTa1-xVxO4 shows optimal photocatalytic performance at 2.0 wt.% Ag and 0.5% doped V dose (ZnFe2O4:BiTaO4 = 1.0:0.5). Also, Ag/ZnFe2O4/Ag/BiTa1-xVxO4 exhibits high stability and repeatability in photocatalytic degradation. Several active species (•OH, •O2-, and h+) are produced in the Z-scheme photodegradation of SAM. These results on the enhanced photocatalytic activity of Ag/ZnFe2O4/Ag/BiTa1-xVxO4 are ascribed to synergistic photocatalytic effects of ZnFe2O4 and BiTa1-xVxO4 mediated through Ag and driven by doped V and Fe ions. Therefore, the Z-scheme Ag/ZnFe2O4/Ag/BiTa1-xVxO4 photocatalytic technology proves to be promising for the solar photocatalytic treatment of antibiotics under solar light.

DNA Origami Nanophotonics and Plasmonics at Interfaces.

DNA nanotechnology provides a versatile toolbox for creating custom and accurate shapes that can serve as versatile templates for nanopatterning. These DNA templates can be used as molecular-scale precision tools in, for example, biosensing, nanometrology, and super-resolution imaging, and biocompatible scaffolds for arranging other nano-objects, for example, for drug delivery applications and molecular electronics. Recently, increasing attention has been paid to their potent use in nanophotonics since these modular templates allow a wide range of plasmonic and photonic ensembles ranging from DNA-directed nanoparticle and fluorophore arrays to entirely metallic nanostructures. This Feature Article focuses on the DNA-origami-based nanophotonics and plasmonics-especially on the methods that take advantage of various substrates and interfaces for the foreseen applications.

Coupled electrokinetics-adsorption technique for simultaneous removal of heavy metals and organics from saline-sodic soil.

In situ remediation technologies for contaminated soils are faced with significant technical challenges when the contaminated soil has low permeability. Popular traditional technologies are rendered ineffective due to the difficulty encountered in accessing the contaminants as well as when employed in settings where the soil contains mixed contaminants such as petroleum hydrocarbons, heavy metals, and polar organics. In this study, an integrated in situ remediation technique that couples electrokinetics with adsorption, using locally produced granular activated carbon from date palm pits in the treatment zones that are installed directly to bracket the contaminated soils at bench-scale, is investigated. Natural saline-sodic soil, spiked with contaminant mixture (kerosene, phenol, Cr, Cd, Cu, Zn, Pb, and Hg), was used in this study to investigate the efficiency of contaminant removal. For the 21-day period of continuous electrokinetics-adsorption experimental run, efficiency for the removal of Zn, Pb, Cu, Cd, Cr, Hg, phenol, and kerosene was found to reach 26.8, 55.8, 41.0, 34.4, 75.9, 92.49, 100.0, and 49.8%, respectively. The results obtained suggest that integrating adsorption into electrokinetic technology is a promising solution for removal of contaminant mixture from saline-sodic soils.

Heavy metallic oxide nanoparticles for enhanced sensitivity in semiconducting polymer x-ray detectors.

Semiconducting polymers have previously been used as the transduction material in x-ray dosimeters, but these devices have a rather low detection sensitivity because of the low x-ray attenuation efficiency of the organic active layer. Here, we demonstrate a way to overcome this limitation through the introduction of high density nanoparticles having a high atomic number (Z) to increase the x-ray attenuation. Specifically, bismuth oxide (Bi(2)O(3)) nanoparticles (Z = 83 for Bi) are added to a poly(triarylamine) (PTAA) semiconducting polymer in the active layer of an x-ray detector. Scanning electron microscopy (SEM) reveals that the Bi(2)O(3) nanoparticles are reasonably distributed in the PTAA active layer. The reverse bias dc current-voltage characteristics for PTAA-Bi(2)O(3) diodes (with indium tin oxide (ITO) and Al contacts) have similar leakage currents to ITO/PTAA/Al diodes. Upon irradiation with 17.5 keV x-ray beams, a PTAA device containing 60 wt% Bi(2)O(3) nanoparticles demonstrates a sensitivity increase of approximately 2.5 times compared to the plain PTAA sensor. These results indicate that the addition of high-Z nanoparticles improves the performance of the dosimeters by increasing the x-ray stopping power of the active volume of the diode. Because the Bi(2)O(3) has a high density, it can be used very efficiently, achieving a high weight fraction with a low volume fraction of nanoparticles. The mechanical flexibility of the polymer is not sacrificed when the inorganic nanoparticles are incorporated.

Characterization and detoxification of a mature landfill leachate using a combined coagulation-flocculation/photo Fenton treatment.

The aim of the present work was to characterize and treat a mature landfill leachate using a coagulation/flocculation process followed by a photo-Fenton oxidation treatment. The leachate was obtained from a landfill in Tetlama, Morelos (Mexico) during the drought season and was characterized in terms of its major pollutants. Considerable levels of chemical oxygen demand (COD), total carbon (TC) and NH4+ were identified, as well as high concentrations of Hg, Pb, and As. Other heavy metals such as Ni, Co, Zn, Cd, and Mn were detected at trace levels. The lethal concentration (LC50) of the leachate, evaluated on Artemia salina, was 12,161±11 mg/L of COD, demonstrating an antagonistic interaction among the leachate's components. The treatment of this effluent consisted of a coagulation-flocculation process using an optimal dose of FeCl3 · 6H2O of 300 mg/L. The supernatant was treated using a photo-Fenton process mediated with FeCl2 · 4H2O and H2O2 in a compound parabolic concentrator (CPC) photo-reactor operating in batch mode using an R ratio (R=[H2O2]/[Fe2+]) of 114. The global removal efficiencies after treatment were 56% for the COD, 95% for TC, and 64% for NH4+. The removal efficiencies for As, Hg, and Pb were 46%, 9%, and 85%, respectively.

Acumulación de mercurio (Hg) por caña flecha (Gynerium sagittatum) (Aubl) Beauv. in vitro / Accumulation of mercury (Hg) by arrow cane (Gynerium sagittatum) (Aubl) Beauv. in vitro

En este estudio se evaluó, in vitro, la capacidad de acumulación de mercurio (Hg) que pueda poseer la caña flecha (Gynerium sagittatum) (Aubl) Beauv. como una alternativa viable de ser implementada para la rehabilitación de suelos contaminados. Este estudio fue realizado en el laboratorio de Biotecnología Vegetal de la Universidad de Sucre (9º18’ N, 75º23’ O). Se usó un diseño experimental de bloques al azar, un análisis de varianza para comparación de medias, una prueba de Tukey (p≤0,05) para la establecer las diferencias significativas entre los tratamientos, pruebas de normalidad (Kolmogorov-Smirnov) y test de homogeneidad de varianza de Bartlett. Los análisis de mercurio se realizaron en un espectrofotómetro de absorción atómica Thermo Electron S4, provisto de una celda con ventanas de cuarzo, por el método de espectroscopia de absorción atómica con vapor frío. Los resultados muestran que la parte de la planta que presenta mayor acumulación es la raíz con 55,98 µg g-1 HgT, seguida de los tallos-hojas con 14,84 µg g-1 HgT, valores relacionados con el grado de concentración del metal en el medio de cultivo. Además, la acumulación de mercurio en raíces y tallos aumentó con el tiempo. En conclusión, in vitro esta planta acumula Hg debido a las altas concentraciones en sus tejidos sin afectar la viabilidad de las plantas.

In this in vitro study was evaluated the potential for accumulation of mercury (Hg) that can hold the cane arrow (Gynerium sagittatum) (Aubl) Beauv. as a viable alternative to be implemented for the rehabilitation of contaminated soils. This study was conducted at the Plant Biotechnology Laboratory, University of Sucre (9º 18' N, 75° 23' W). An experimental design was randomized block, an analysis of variance to compare means, Tukey test (p ≤ 0.05) to establish significant differences between the treatments, tests of normality (Kolmogorov-Smirnov) and homogeneity test Bartlett variance. The mercury analyses were performed on atomic absorption spectrophotometer Thermo Electron S4, a cell equipped with quartz windows, by the method of atomic absorption spectrometry with cold steam. The results show that the plant part that presents the greatest accumulation is the root with 55.98 mg g-1 HgT, followed by the stems, leaves 14.84 g g-1 HgT and these values ​​are related to the degree of metal concentration in the culture medium. Furthermore, the accumulation of mercury in roots and stems increased with time. In conclusion, in vitro this plant accumulates due to the high Hg concentrations in their tissues without affecting the viability of plants.

An elastically compressible phantom material with mechanical and x-ray attenuation properties equivalent to breast tissue.

We have developed a novel phantom material: a solution of polyvinyl alcohol (PVAL) in ethanol and water, freeze-thawed to produce a solid yet elastically compressible gel. The x-ray attenuation and mechanical properties of these gels are compared with published measurements of breast tissue. Gels with PVAL concentrations from 5 to 20% w/v were produced. The linear x-ray attenuation coefficients of these gels range from 0.76 to 0.86 cm(-1) at 17.5 keV, increasing with PVAL concentration. These values are very similar to the published values of breast tissue at this energy, 0.8-0.9 cm(-1). Under compression cancerous breast tissue is approximately ten times stiffer than healthy breast tissue. The Young's moduli of the gels increase with PVAL concentration. Varying the PVAL concentration from 7.5 to 20% w/v produces gels with Young's moduli from 20 to 220 kPa at 15% strain. These values are characteristic of normal and cancerous breast tissue, respectively.

Energy spectrum based calculation of the half and the tenth value layers for brachytherapy sources using a semiempirical parametrized mass attenuation coefficient formulism.

As different types of radionuclides (e.g., 131Cs source) are introduced for clinical use in brachytherapy, the question is raised regarding whether a relatively simple method exists for the derivation of values of the half value layer (HVL) or the tenth value layer (TVL). For the radionuclide that has been clinically used for years, such as 125I and 103Pd, the sources have been manufactured and marketed by several vendors with different designs and structures. Because of the nature of emission of low energy photons for these radionuclides, energy spectra of the sources are very dependent on their individual designs. Though values of the HVL or the TVL in certain commonly used shielding materials are relatively small for these low energy photon emitting sources, the question remains how the variations in energy spectra affect the HVL (or TVL) values and whether these values can be calculated with a relatively simple method. A more fundamental question is whether a method can be established to derive the HVL (TVL) values for any brachytherapy sources and for different materials in a relatively straightforward fashion. This study was undertaken to answer these questions. Based on energy spectra, a well established semiempirical mass attenuation coefficient computing scheme was utilized to derive the HVL (TVL) values of different materials for different types of brachytherapy sources. The method presented in this study may be useful to estimate HVL (TVL) values of different materials for brachytherapy sources of different designs and containing different radionuclides.

Photochromism of novel metal coordination polymers with 1,2-Bis(2'-methyl-5'-(carboxylic acid)-3'-thienyl)perfluorocyclopentene in the crystalline phase.

Three new metal complexes with 1,2-bis(2'-methyl-5'-(carboxylic acid)-3'-thienyl)perfluorocyclopentene (BM-5-CATP) were synthesized and characterized by X-ray diffraction analysis. BM-5-CATP serves as a bis-monodentate ligand that bridges metal centers to generate three 1D polymers. The two thienyl rings in the three complexes adopt antiparallel fashions, and the distances of 3.39, 3.53, and 3.57 A between the two reactive carbons are short enough to allow photocyclizations to occur in the crystalline phase. [Co(BM-5-CATP)(py)2(MeOH)2] (1) displayed effective photoisomerization in the crystalline phase. Interestingly, solvated 1 underwent a solid-state conversion upon heating to generate, through the release of the coordinated MeOH and rearrangement of the coordination geometry, the desolvated form (1a), while maintaining reversible photochromism. The removal of the solvent led to obvious changes in physical properties such as color and magnetic properties. The ESR spectra of 1 and 1a changed reversibly upon photoexcitation, indicating changes in coordination geometry accompanied by photoreaction. The magnetic susceptibilities of 1 and 1a showed no obvious changes, suggesting that the cobalt-cobalt interaction through the long bridging BM-5-CATP is less effective. Both [Cu(BM-5-CATP)(py)3](EtOH)(py)1.8 (2) and [Zn(BM-5-CATP)(phen)(H2O)] (3) exhibited reversible photoreactions in the crystalline phase. However, 3 did not show remarkable spectral changes because of steric hindrance from the coordinated bulky phenanthroline and the intramolecular H bonds.

A rapid fractionation method for heavy metals in soil by continuous-flow sequential extraction assisted by focused microwaves.

A microwave-assisted continuous-flow sequential extraction system was developed for rapid fractionation analysis of heavy metals in soil. Insertion of pressure-adjusted air between the extractants provided stable flows of the extractants without mutual mixing and back-pressure influence of a column packed with soil, thereby facilitating reliable continuous-flow extractions. In addition, use of pure water as a pumping solvent removed metal contamination because of direct contact between corrosive extractants and the pump containing metallic materials. Focused microwave irradiation to the soil accelerated the selective extractions of the acid-soluble and reducible fractions of heavy metals in soil in the first and second steps of the sequential extraction conditions, as defined by the Commission of the European Bureau of Reference (BCR). The microwave-assisted continuous-flow extraction provided high correlations in amounts of six heavy metals except Zn in the first step and Cu in the second step extracted from a reference sludge soil, BCR CRM 483, with a conventional batchwise extraction proposed by BCR; continuous-flow extraction assisted by conductive heating provided lower correlations for all the six metals. The proposed method drastically reduced the time required for the sequence extraction to ca. 65 min without losing accuracy and precision of the fractionation analysis of heavy metals in soil, whereas the BCR batchwise method requires ca. 33 h.

Microwave-assisted one-step synthesis of polyacrylamide-metal (M = Ag, Pt, Cu) nanocomposites in ethylene glycol.

Polyacrylamide-metal (M = Pt, Ag, Cu) nanocomposites with metal nanoparticles homogeneously dispersed in the polymer matrix have been successfully prepared with the corresponding metal salt and acrylamide monomer in ethylene glycol by microwave heating. This method is based on the single-step simultaneous formation of metal nanoparticles and polymerization of the acrylamide monomer, leading to a homogeneous distribution of metal nanoparticles in the polyacrylamide matrix. Ethylene glycol acts as both a reducing reagent and a solvent, thus no additional reductant is needed. Another advantage is that no initiator for AM polymerization and no surfactant for stabilization of metal nanoparticles are necessary. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), ultraviolet visible (UV-vis) absorption spectra, and thermogravimetric (TG) and differential scanning calorimetric analysis (DSC).

Towards the enhancement of the photon/neutron discrimination of C6D6 detectors in the range from 1 to 10 MeV using liquid scintillator materials doped with high-Z elements.

The study on the behaviour of deuterated benzene detectors in the energy range from 1 to 10 MeV has been carried out. It is shown that the photon-to-neutron discrimination, attained with standard detectors, can be improved by doping the C6D6 liquid scintillator with high-Z elements. The motivation for doping the organic scintillator stems from the fact that they should increase the gamma detection efficiencies with no significant changes in the abilities to detect neutrons. The results obtained using the MCNP and EGS4 codes show that increasing the fraction of high-Z elements: (a) the energy deposited in the medium by photons increases, (b) the energy deposited by neutrons decreases and (c) the rate of detection of photon/neutron is enhanced. Owing to their low sensitivity to neutrons and the enhanced gamma detection efficiency, these detectors could be ideally used to carry out studies in mixed neutron-photon fields in the energy range considered and to assess the gamma backgrounds in noisy neutron environments.