Ionothermal Synthesis of Cadmium Coordination Polymers: Ionic Liquid Effects on the Synthesis, Structural, and Thermal Characterization.

Ionothermal synthesis is a little used method for the preparation of coordination polymers. By this method, two cadmium compounds were synthesized, 1, with formula Cd3(ox)F2(Ina)2 (Ina = isonicotinate) and 2, Cd(NO3)2(4,4'-Bpy) (4,4'-Bpy = 4,4'-Bipyridine). The modification of the reaction conditions has allowed to obtain 2 as a pure phase. The structure of both compounds was determined by a single-crystal X-ray diffraction. Compound 1 is isostructural to the previously reported Cd2Zn(ox)(OH)2(Ina)2. It crystallizes in the monoclinic space group P21/n and present a three-dimensional (3D) network, built-up from [Cd3(ox)F2]n2n+ layers, linked by isonicotinate ligands. Crystals of 2 are formed by twins of two components which are rotated ca. 180° to each other. This compound crystallizes in the triclinic P-1 space group and its structure can be describe as a two-dimensional (2D) 4 connected 'sql' net. The layers are composed by [Cd(NO3)2]n chains linked through 4,4'-Bpy ligands, and are pillared along the [011] direction. The thermal decomposition of 2 was studied by thermogravimetric and thermodiffractiometric techniques. The compound decomposes gradually starting from 160 °C, and due to heating, the structure suffers slight reversible changes in the bond distances and angles.

Key challenges for nanotechnology: Standardization of ecotoxicity testing.

Nanotechnology is expected to contribute to the protection of the environment, but many uncertainties exist regarding the environmental and human implications of manufactured nanomaterials (MNMs). Contradictory results have been reported for their ecotoxicity to aquatic organisms, which constitute one of the most important pathways for their entrance and transfer throughout the food web. The present review is focused on the international strategies that are laying the foundations of the ecotoxicological assessment of MNMs. Specific advice is provided on the preparation of MNM dispersions in the culture media of the organisms, which is considered a key factor to overcome the limitations in the standardization of the test methodologies.

Coordination and crystallization molecules: their interactions affecting the dimensionality of metalloporphyrinic SCFs.

Synthetic metalloporphyrin complexes are often used as analogues of natural systems, and they can be used for the preparation of new Solid Coordination Frameworks (SCFs). In this work, a series of six metalloporphyrinic compounds constructed from different meso substituted metalloporphyrins (phenyl, carboxyphenyl and sulfonatophenyl) have been structurally characterized by means of single crystal X-ray diffraction, IR spectroscopy and elemental analysis. The compounds were classified considering the dimensionality of the crystal array, referred just to coordination bonds, into 0D, 1D and 2D compounds. This way, the structural features and relationships of those crystal structures were analyzed, in order to extract conclusions not only about the dimensionality of the networks but also about possible applications of the as-obtained compounds, focusing the interest on the interactions of coordination and crystallization molecules. These interactions provide the coordination bonds and the cohesion forces which produce SCFs with different dimensionalities.

Superprotonic Conductivity in a Metalloporphyrin-Based SMOF (Supramolecular Metal-Organic Framework).

Metal-organic frameworks and supramolecular metal-organic frameworks (SMOFs) exhibit great potential for a broad range of applications taking advantage of the high surface area and pore sizes and tunable chemistry. In particular, metalloporphyrin-based MOFs and SMOFs are becoming of great importance in many fields due to the bioessential functions of these macrocycles that are being mimicked. On the other hand, during the last years, proton-conducting materials have aroused much interest, and those presenting high conductivity values are potential candidates to play a key role in some solid-state electrochemical devices such as batteries and fuel cells. In this way, using metalloporphyrins as building units we have obtained a new crystalline material with formula [H(bipy)]2[(MnTPPS)(H2O)2]·2bipy·14H2O, where bipy is 4,4'-bipyidine and TPPS4- is the meso-tetra(4-sulfonatephenyl) porphyrin. The crystal structure shows a zig-zag water chain along the [100] direction located between the sulfonate groups of the porphyrin. Taking into account those structural features, the compound was tested for proton conduction by complex electrochemical impedance spectroscopy (EIS). The as-obtained conductivity is 1 × 10-2 S·cm-1 at 40 °C and 98% relative humidity, which is a remarkably high value.

Fe-TPP coordination network with metalloporphyrinic neutral radicals and face-to-face and edge-to-face π-π stacking.

Compound ([FeTPPbipy](•))n (TPP = meso-tetraphenylporphyrin and bipy = 4,4'-bipyridine) is the first example of a Fe-TPP-bipy coordination network, and it consists of 1D polymers packed through face-to-face and edge-to-face π-π interactions. The compound has been investigated by means of X-ray diffraction, IR, Mössbauer, UV-visible, and EPR spectroscopies, thermogravimetry, magnetic susceptibility measurements, and quantum-mechanical density functional theory (DFT) and time-dependent DFT calculations. The chemical formula for this compound can be confusing because it is compatible with Fe(II) and TPP(2-) anions. However, the spectroscopic and magnetic properties of this compound are consistent with the presence of low-spin Fe(III) ions and [FeTPPbipy](•) neutral radicals. These radicals are proposed to be formed by the reduction of metalloporphyrin, and the quantum-mechanical calculations are consistent with the fact that the acquired electrons are located on the phenyl groups of TPP.

High-Performance Room Temperature Lithium-Ion Battery Solid Polymer Electrolytes Based on Poly(vinylidene fluoride-co-hexafluoropropylene) Combining Ionic Liquid and Zeolite.

The demand for more efficient energy storage devices has led to the exponential growth of lithium-ion batteries. To overcome the limitations of these systems in terms of safety and to reduce environmental impact, solid-state technology emerges as a suitable approach. This work reports on a three-component solid polymer electrolyte system based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), the ionic liquid 1-butyl-3-methylimidazolium thiocyanate ([BMIM][SCN]), and clinoptilolite zeolite (CPT). The influences of the preparation method and of the dopants on the electrolyte stability, ionic conductivity, and battery performance were studied. The developed electrolytes show an improved room temperature ionic conductivity (1.9 × 10-4 S cm-1), thermal stability (up to 300 °C), and mechanical stability. The corresponding batteries exhibit an outstanding room temperature performance of 160.3 mAh g-1 at a C/15-rate, with a capacity retention of 76% after 50 cycles. These results represent a step forward in a promising technology aiming the widespread implementation of solid-state batteries.

Structural characterization and mechanical performance of calcium phosphate scaffolds and natural bones: a comparative study.

PURPOSE: The knowledge of the mechanical response of bones and their substitutes is pertinent to numerous medical problems. Understanding the effects of mechanical influence on the body is the first step toward developing innovative treatment and rehabilitation concepts for orthopedic disorders. METHODS: This was a comparative study of 5 synthetic scaffolds based on porous calcium phosphates and natural bones, with regard to their microstructural, chemical, and mechanical characterizations. The structural and chemical characterizations of the scaffolds were examined by means of X-ray diffraction, scanning electron microscopy, and X-ray spectroscopy analysis. The mechanical characterization of bones and bone graft biomaterials was carried out through compression tests using samples with noncomplex geometry. RESULTS: Analysis of the chemical composition, surface features, porosity, and compressive strength indicates that hydroxyapatite-based materials and trabecular bone have similar properties.

Encapsulation of ß-alanine model amino-acid in zirconium(IV) metal organic frameworks: Defect engineering to improve host guest interactions.

Metal-Organic Frameworks (MOFs) are porous coordination networks assembled through metal complexes with organic linkers. Due to their chemical versatility, these materials are being investigated for various applications including gas storage and separation, biomedicine and catalysis. The aim of this work is the encapsulation of the model ß-alanine amino-acid in the nanostructured zirconium-based MOF (UiO-66) which contains the ligand H2BDC (1,4-benzenedicaboxylic acid). Additionally, ligand functionalization (by using H2doBDC (2,5-dihydroxy-1,4-benzenedicarboxylic acid) and defect engineering have been carried out to produce UiO-66 derivatives, in order to modify the host-guest interactions, and hence study their influence on the ß-alanine loading capacity and release kinetics. The as-obtained materials have been characterized by X-ray diffraction (XRD), X-ray thermo diffraction (TDX), infrared (IR) spectroscopy, thermogravimetric analysis-differential scanning calorimetry (TG-DSC) and elemental analysis (EA). Morphology of nanoscale MOFs has been explored by transition electron microscopy (TEM). Adsorption isotherms have been constructed, and the concentration of ß-alanine in the post-adsorption solution (supernatant) has been quantified by high performance liquid chromatography coupled with mass spectroscopy (HPLC-MS) and EA. Adsorption capacity values indicate that the presence of hydroxyl groups at the organic linker H2doBDC enhances the host-guess affinity between the framework and the adsorbate ß-alanine. The influence of defect engineering, on the adsorption however, is not that obvious. On the other hand, desorption experiments show similar behaviour for H2doBDC-based derivatives. An adsorption mechanism has been proposed consisting of a combination of host-guest interaction at low concentrations, and covalent anchoring/ligand displacement by ß-alanine at the inorganic clusters.

Double role of metalloporphyrins in catalytic bioinspired supramolecular metal-organic frameworks (SMOFs).

Heterogeneous catalysts are of great interest in many industrial processes for environmental reasons and, during recent years, a great effort has been devoted to obtain metal-organic frameworks (MOFs) with improved catalytic behaviour. Few supramolecular metal-organic frameworks (SMOFs) are stable under ambient conditions and those with anchored catalysts exhibit favourable properties. However, this paper presents an innovative approach that consists of using metal nodes as both structural synthons and catalysts. Regarding the latter, metalloporphyrins are suitable candidates to play both roles simultaneously. In fact, there are a number of papers that report coordination compounds based on metalloporphyrins exhibiting these features. Thus, the aim of this bioinspired work was to obtain stable SMOFs (at room temperature) based on metallo-porphyrins and explore their catalytic activity. This work reports the environmentally friendly microwave-assisted synthesis and characterization of the compound [H(bipy)]2[(MnTPPS)(H2O)2]·2bipy·14H2O (TPPS = meso-tetra-phenyl-porphine-4,4',4'',4'''-tetra-sulfonic acid and bipy = 4,4'-bi-pyridine). This compound is the first example of an MnTPPS-based SMOF, as far as we are aware, and has been structurally and thermally characterized through single-crystal X-ray diffraction, IR spectroscopy, thermogravimetry and transmission electron microscopy. Additionally, this work explores not only the catalytic activity of this compound but also of the compounds µ-O-[FeTCPP]2·16DMF and [CoTPPS0.5(bipy)(H2O)2]·6H2O. The structural features of these supra-molecular materials, with accessible networks and high thermal stability, are responsible for their excellent behaviour as heterogeneous catalysts for different oxidation, condensation (aldol and Knoevenagel) and one-pot cascade reactions.

Towards the standardization of nanoecotoxicity testing: Natural organic matter 'camouflages' the adverse effects of TiO2 and CeO2 nanoparticles on green microalgae.

In the last few years, the emission of CeO2 and TiO2 nanoparticles (NPs) into the environment has been raising concerns about their potential adverse effects on wildlife and human health. Aquatic organisms constitute one of the most important pathways for the entrance of these NPs and transfer throughout the food web, but divergences exist in the experimental data published on their aquatic toxicity. The pressing need for standardization of methods to analyze their ecotoxicity requires aquatic media representing realistic environmental conditions. The present study aimed to determine the usefulness of Suwannee River natural organic matter (SR-NOM) in the assessment of the agglomeration kinetics and ecotoxicity of CeO2 and TiO2 NPs towards green microalgae Pseudokirchneriella subcapitata. SR-NOM alleviated the adverse effects of NPs on algal growth, completely in the case of TiO2 NPs and partially in the case of CeO2 NPs, suggesting a 'camouflage' of toxicity. This behavior has been observed also for other algal species and types of natural organic matter in the literature. Furthermore, SR-NOM markedly increased the stability of the NPs in algal medium, which led to a better reproducibility of the toxicity test results, and provided an electrophoretic mobility similar to that previously reported in various river and groundwaters. Thus, SR-NOM can be a representative sample of what is found in many different ecosystems, and the observed 'camouflage' of the effects of CeO2 and TiO2 NPs on algal cells might be considered as a natural interaction occurring in their standardized ecotoxicological assessment.

Colloidal stability and ecotoxicity of multiwalled carbon nanotubes: Influence of select organic matters.

In the last few years, the release of multiwalled carbon nanotubes (MWCNTs) into the environment has raised serious concerns regarding their fate and potential impacts. Aquatic organisms constitute an important pathway for their entrance and transfer throughout the food web, and the current demand for standardization of methodologies to analyze the interactions of MWCNTs with them requires aquatic media that represent natural systems. However, the inherent hydrophobicity of MWCNTs and the substances present in natural waters may greatly affect their stability and bioavailability. The present study analyzes the influence of the most referenced synthetic and natural organic matters (Sigma-Aldrich humic acid and Suwannee River natural organic matter) in the agglomeration kinetics and ecotoxicity of MWCNTs, with the aim of determining their suitability to fulfill the current standardization requirements. Natural organic matter provides increased colloidal stability to the MWCNTs' dispersions, which results in higher adverse effects on the key invertebrate organism Daphnia magna. Furthermore, the results obtained with this type of organic matter allow for observation of the important role of the outer diameter and content impurities of MWCNTs in their stability and ecotoxicity on daphnids. Sigma-Aldrich humic acid appeared to alter the response of the organisms to carbon nanotubes compared with that observed in the presence of natural organic matter.

Ecotoxicity of multiwalled carbon nanotubes: standardization of the dispersion methods and concentration measurements.

There are currently a variety of applications for multiwalled carbon nanotubes (MWCNTs), but considerable concerns exist regarding their release into the environment. Their potential accumulation by aquatic organisms could lead to transfer throughout food chains. Considering the divergences in experimental data published on the ecotoxicity of carbon nanotubes, further research is required. The dispersion of MWCNTs in aqueous culturing media of organisms as well as the determination of concentrations are relevant aspects to obtain accurate ecotoxicity results. Ultraviolet-visible spectroscopy is one of the most reported techniques to analyze concentration quickly and economically, but the methodologies to prepare dispersions and selecting the wavelengths for ultraviolet-visible measurements have not yet been clearly defined. The present study demonstrates that dispersion procedures influence absorbance, and an approach to determine the most appropriate measurement wavelength is proposed. Ecotoxicity tests with MWCNTs were performed on Vibrio fischeri bacteria, and divergences in the results were observed with respect to those previously reported. The present study contributes to the attempt to overcome the lack of standardization in the environmental assessment of MWCNTs.

Development of Ti-C-N coatings with improved tribological behavior and antibacterial properties.

In artificial metallic joint implants, the failure is provoked by two effects in most of the cases: mass loss and wear debris removed due to tribological-corrosive effects on the implant alloy, and infections due to the presence of bacteria. In this work, several Ti-C-N corrosion and wear protective coatings were developed by Physical Vapour Deposition technology, and deposited on Ti6Al4V alloy. In order to provide the implant antibacterial properties, an additional silver top coating has been deposited. Tribological behavior was characterized through tribocorrosion and fretting tests. On the other hand, wettability tests were performed to study the grade of hydrophilicity/hydrophobia. Additionally, antibacterial properties were evaluated by means of bacterial adhesion tests. As a result of these characterization studies, the coating with the best performance was selected. The as-coated material includes excellent protection against tribocorrosion and fretting effects (in relation to the uncoated one) and the silver layer has been confirmed to exhibit antibacterial properties.

Heterogeneous catalytic properties of unprecedented µ-O-[FeTCPP]2 dimers (H2TCPP = meso-tetra(4-carboxyphenyl)porphyrin): an unusual superhyperfine EPR structure.

During the past few years, a great deal of effort has been devoted to the anchoring of catalysts into solid coordination networks in order to achieve heterogeneous catalysts. In this sense, an innovative approach consists in using the coordination-network synthons both as structural units and as catalysts. Regarding the latter, metalloporphyrins are suitable candidates for synthons. In fact, a few studies report on coordination compounds based on metalloporphyrins exhibiting these features. On the other hand, highly distorted di-iron oxo dimers containing electron withdrawing groups rank amongst the most effective catalyst models. Thus, the aim of this work was to obtain coordination networks based on iron porphyrins exhibiting those characteristics. In this way, this work reports on the synthesis and characterisation of the µ-O-[FeTCPP]2·16DMF compound (H2TCPP = meso-tetra(4-carboxyphenyl)porphyrin, DMF = N,N-dimethylformamide). This compound is the first example of a µ-oxo dimer with TCPP. The inter-dimer connections give rise to a laminar structure. The structural, spectroscopic and magnetic properties of this compound are consistent with the presence of high-spin Fe(III) ions, exhibiting a strong antiferromagnetic coupling in the µ-oxo dimer (J = -132 cm(-1)). An unusual superhyperfine structure has been observed in EPR that is related to the high accessible volume of the compound. The structural features of the dimers and the accessible network are responsible for the excellent behaviour of the compound as a heterogeneous catalyst for different oxidations of alcohols. Therefore, this compound is one of the very few examples of metalloporphyrins where structural units act as catalysts.