Solvent-dependent modulation of metal–metal electronic interactions in a dinuclear cyanoruthenate complex: a detailed electrochemical, spectroscopic and computational study

The dinuclear complex [{Ru(CN)4}2(μ-bppz)]4− shows a strongly solvent-dependent metal–metal electronic interaction which allows the mixed-valence state to be switched from class 2 to class 3 by changing solvent from water to CH2Cl2. In CH2Cl2 the separation between the successive Ru(II)/Ru(III) redox couples is 350 mVand the IVCT band (from the UV/Vis/NIR spectroelectrochemistry) is characteristic of a borderline class II/III or class III mixed valence state. In water, the redox separation is only 110 mVand the much broader IVCT transition is characteristic of a class II mixed-valence state. This is consistent with the observation that raising and lowering the energy of the d(π) orbitals in CH2Cl2 or water, respectively, will decrease or increase the energy gap to the LUMO of the bppz bridging ligand, which provides the delocalisation pathway via electron-transfer. IR spectroelectrochemistry could only be carried out successfully in CH2Cl2 and revealed class III mixed-valence behaviour on the fast IR timescale. In contrast to this, time-resolved IR spectroscopy showed that the MLCTexcited state, which is formulated as RuIII(bppz˙−)RuII and can therefore be considered as a mixed-valence Ru(II)/Ru(III) complex with an intermediate bridging radical anion ligand, is localised on the IR timescale with spectroscopically distinct Ru(II) and Ru(III) termini. This is because the necessary electron-transfer via the bppz ligand is more difficult because of the additional electron on bppz˙− which raises the orbital through which electron exchange occurs in energy. DFT calculations reproduce the electronic spectra of the complex in all three Ru(II)/Ru(II), Ru(II)/Ru(III) and Ru(III)/Ru(III) calculations in both water and CH2Cl2 well as long as an explicit allowance is made for the presence of water molecules hydrogen-bonded to the cyanides in the model used. They also reproduce the excited-state IR spectra of both [Ru(CN)4(μ-bppz)]2– and [{Ru(CN)4}2(μ-bppz)]4− very well in both solvents. The reorganization of the water solvent shell indicates a possible dynamical reason for the longer life time of the triplet state in water compared to CH2Cl2.

Review of R&D progress and practical application of the solar photovoltaic/thermal (PV/T) technologies

In this paper, the global market potential of solar thermal, photovoltaic (PV) and combined photovoltaic/thermal (PV/T) technologies in current time and near future was discussed. The concept of the PV/T and the theory behind the PV/T operation were briefly introduced, and standards for evaluating technical, economic and environmental performance of the PV/T systems were addressed. A comprehensive literature review into R&D works and practical application of the PV/T technology was illustrated and the review results were critically analysed in terms of PV/T type and research methodology used. The major features, current status, research focuses and existing difficulties/barriers related to the various types of PV/T were identified. The research methods, including theoretical analyses and computer simulation, experimental and combined experimental/theoretical investigation, demonstration and feasibility study, as well as economic and environmental analyses, applied into the PV/T technology were individually discussed, and the achievement and problems remaining in each research method category were described. Finally, opportunities for further work to carry on PV/T study were identified. The review research indicated that air/water-based PV/T systems are the commonly used technologies but their thermal removal effectiveness is lower. Refrigerant/heat-pipe-based PV/Ts, although still in research/laboratory stage, could achieve much higher solar conversion efficiencies over the air/water-based systems. However, these systems were found a few technical challenges in practice which require further resolutions. The review research suggested that further works could be undertaken to (1) develop new feasible, economic and energy efficient PV/T systems; (2) optimise the structural/geometrical configurations of the existing PV/T systems; (3) study long term dynamic performance of the PV/T systems; (4) demonstrate the PV/T systems in real buildings and conduct the feasibility study; and (5) carry on advanced economic and environmental analyses. This review research helps finding the questions remaining in PV/T technology, identify new research topics/directions to further improve the performance of the PV/T, remove the barriers in PV/T practical application, establish the standards/regulations related to PV/T design and installation, and promote its market penetration throughout the world.

Optimizing the methods of synthesis for barium hexagonal ferrite: an experimental and theoretical study

M-type barium hexaferrite (BaM) is a hard ferrite, crystallizing in space group P6(3)/mmc possessing a hexagonal magneto-plumbite structure, which consists of alternate hexagonal and spinel blocks. The structure of BaM is thus related to those of garnet and spinel ferrite. However the material has proved difficult to synthesize. By taking into account the presence of the spinel block in barium hexagonal ferrite, highly efficient new synthetic methods were devised with routes significantly different from existing ones. These successful variations in synthetic methods have been derived by taking into account a detailed investigation of the structural features of barium hexagonal ferrite and the least change principle whereby configuration changes are kept to a minimum. Thus considering the relevant mechanisms has helped to improve the synthesis efficiencies for both hydrothermal and co-precipitation methods by choosing conditions that invoke the formation of the cubic block or the less stable Fe3O4. The role played by BaFe2O4 in the synthesis is also discussed. The distribution of iron from reactants or intermediates among different sites was also successfully explained. The proposed mechanisms are based on the principle that the cubic block must be self-assembled to form the final product. Thus, it is believed that these formulated mechanisms should be helpful in designing experiments to obtain a deeper understanding of the synthesis process and to investigate the substitution of magnetic ions with doping ions.

Host–guest supramolecular interactions in the coordination compounds of 4,4′-azobis(pyridine) with MnX2(X = NCS–, NCNCN–, and PF6–): structural analyses and theoretical study

Three new Mn(II) coordination compounds {[Mn(NCNCN)2(azpy)]·0.5azpy}n (1), {[Mn(NCS)2(azpy)(CH3OH)2]·azpy}n (2), and [Mn(azpy)2(H2O)4][Mn(azpy)(H2O)5]·4PF6·H2O·5.5azpy (3) (where azpy = 4,4'-azobis-(pyridine)) have been synthesized by self-assembly of the primary ligands, dicyanamide, thiocyanate, and hexafluorophosphate, respectively, together with azpy as the secondary spacer. All three complexes were characterized by elemental analyses, IR spectroscopy, thermal analyses, and single crystal X-ray crystallography. The structural analyses reveal that complex 1 forms a two-dimensional (2D) grid sheet motif These sheets assemble to form a microporous framework that incorporates coordination-free azpy by host-guest pi center dot center dot center dot pi. and C-H center dot center dot center dot N hydrogen bonding interactions. Complex 2 features azpy bridged one-dimensional (ID) chains of centrosymmetric [Mn(NCS)(2)(CH3OH)(2)} units which form a 2D porous sheet via a CH3 center dot center dot center dot pi supramolecular interaction. A guest azpy molecule is incorporated within the pores by strong H-bonding interactions. Complex 3 affords a 0-D motif with two monomeric Mn(II) units in the asymmetric unit. There exist pi center dot center dot center dot pi, anion center dot center dot center dot pi, and strong hydrogen bonding interactions between the azpy, water, and the anions. Density functional theory (DFT) calculations, at the M06/6-31+G* level of theory, are used to characterize a great variety of interactions that explicitly show the importance of host-guest supramolecular interactions for the stabilization of coordination compounds and creation of the fascinating three-dimensional (3D) architecture of the title compounds.

A new tetranuclear copper(II) complex with oximate bridges: structure, magnetic properties and DFT study

A new tetranuclear complex, [Cu4L4](ClO4)4·2H2O (1), has been synthesized from the self-assembly of copper(II) perchlorate and the tridentate Schiff base ligand (2E,3E)-3-(2-aminopropylimino) butan-2-one oxime (HL). Single-crystal X-ray diffraction studies reveal that complex 1 consists of a Cu4(NO)4 core where the four copper(II) centers having square pyramidal environment are arranged in a distorted tetrahedral geometry. They are linked together by a rare bridging mode (μ3-η1,η2,η1) of oximato ligands. Analysis of magnetic susceptibility data indicates moderate antiferromagnetic (J1 = −48 cm−1, J2 = −40 cm−1 and J3 = −52 cm−1) exchange interaction through σ-superexchange pathways (in-plane bridging) of the oxime group. Theoretical calculations based on DFT technique have been used to obtain the energy states of different spin configurations and estimate the coupling constants and to understand the exact magnetic exchange pathways.

Is optical imaging spectroscopy a viable measurement technique for the investigation of the negative BOLD phenomenon? A concurrent optical imaging spectroscopy and fMRI study at high field (7T)

Traditionally functional magnetic resonance imaging (fMRI) has been used to map activity in the human brain by measuring increases in the Blood Oxygenation Level Dependent (BOLD) signal. Often accompanying positive BOLD fMRI signal changes are sustained negative signal changes. Previous studies investigating the neurovascular coupling mechanisms of the negative BOLD phenomenon have used concurrent 2D-optical imaging spectroscopy (2D-OIS) and electrophysiology (Boorman et al., 2010). These experiments suggested that the negative BOLD signal in response to whisker stimulation was a result of an increase in deoxy-haemoglobin and reduced multi-unit activity in the deep cortical layers. However, Boorman et al. (2010) did not measure the BOLD and haemodynamic response concurrently and so could not quantitatively compare either the spatial maps or the 2D-OIS and fMRI time series directly. Furthermore their study utilised a homogeneous tissue model in which is predominantly sensitive to haemodynamic changes in more superficial layers. Here we test whether the 2D-OIS technique is appropriate for studies of negative BOLD. We used concurrent fMRI with 2D-OIS techniques for the investigation of the haemodynamics underlying the negative BOLD at 7 Tesla. We investigated whether optical methods could be used to accurately map and measure the negative BOLD phenomenon by using 2D-OIS haemodynamic data to derive predictions from a biophysical model of BOLD signal changes. We showed that despite the deep cortical origin of the negative BOLD response, if an appropriate heterogeneous tissue model is used in the spectroscopic analysis then 2D-OIS can be used to investigate the negative BOLD phenomenon.

Patterning and detailed study of human hNT astrocytes on parylene-C/silicon dioxide substrates to the single cell level

It is estimated that the adult human brain contains 100 billion neurons with 5–10 times as many astrocytes. Although it has been generally considered that the astrocyte is a simple supportive cell to the neuron, recent research has revealed new functionality of the astrocyte in the form of information transfer to neurons of the brain. In our previous work we developed a protocol to pattern the hNT neuron (derived from the human teratocarcinoma cell line (hNT)) on parylene-C/SiO2 substrates. In this work, we report how we have managed to pattern hNT astrocytes, on parylene-C/SiO2 substrates to single cell resolution. This article disseminates the nanofabrication and cell culturing steps necessary for the patterning of such cells. In addition, it reports the necessary strip lengths and strip width dimensions of parylene-C that encourage high degrees of cellular coverage and single cell isolation for this cell type. The significance in patterning the hNT astrocyte on silicon chip is that it will help enable single cell and network studies into the undiscovered functionality of this interesting cell, thus, contributing to closer pathological studies of the human brain.

Dimer formation by symbiotic donor–acceptor interaction between two molecules of a specially designed dioxomolybdenum(VI) complex containing both donor and acceptor centers – A structural, spectroscopic and DFT study

This work presents a model study for the formation of a dimeric dioxomolybdenum(VI) complex [MoO2L]2, generated by simultaneous satisfaction of acceptor and donor character existing in the corresponding monomeric Mo(VI) complex MoO2L. This mononuclear complex is specially designed to contain a coordinatively unsaturated Mo(VI) acceptor centre and a free donor group, (e.g. –NH2 group) strategically placed in the ligand skeleton [H2L = 2-hydroxyacetophenonehydrazone of 2-aminobenzoylhydrazine]. Apart from the dimer [MoO2L]2, complexes of the type MoO2L·B (where B = CH3OH, γ-picoline and imidazole) are also reported. All the complexes are characterized by elemental analysis, spectroscopic (UV–Vis, IR, 1H NMR) techniques and cyclic voltammetry. Single crystal X-ray structures of [MoO2L]2 (1), MoO2L·CH3OH (2), and MoO2L.(γ-pic) (3) have been determined and discussed. DFT calculation on these complexes corroborates experimental data and provides clue for the facile formation of this type of dimer not reported previously. The process of dimer formation may also be viewed as an interaction between two molecules of a specially designed complex acting as a monodentate ligand. This work is expected to open up a new field of design and synthesis of dimeric complexes through the process of symbiotic donor–acceptor (acid–base) interaction between two molecules of a specially designed monomer.

Multistep π dimerization of tetrakis(n-decyl)heptathienoacene radical cations: a combined experimental and theoretical study

Radical cations of a heptathienoacene a,b-substituted with four n-decyl side groups (D4T7C+) form exceptionally stable p-dimer dications already at ambient temperature (Chem. Comm. 2011, 47, 12622). This extraordinary p-dimerization process is investigated here with a focus on the ultimate[D4T7C+]2 p-dimer dication and yet-unreported transitoryspecies formed during and after the oxidation. To this end, we use a joint experimental and theoretical approach that combines cyclic voltammetry, in situ spectrochemistry and spectroelectrochemistry, EPR spectroscopy, and DFT calculations. The impact of temperature, thienoacene concentration, and the nature and concentration of counteranions on the p-dimerization process is also investigated in detail. Two different transitory species were detected in the course of the one-electron oxidation: 1) a different transient conformation of the ultimate [D4T7C+]2 p-dimer dications, the stability of which is strongly affected by the applied experimental conditions, and 2) intermediate [D4T7]2C+ p-dimer radical cations formed prior to the fully oxidized [D4T7]2C+ p-dimer dications. Thus, this comprehensive work demonstrates the formation of peculiar supramolecular species of heptathienoacene radical cations, the stability, nature, and structure of which have been successfully analyzed. We therefore believe that this study leads to a deeper fundamental understanding of the mechanism of dimer formation between conjugated aromatic systems.

Thiocyanate complexes of uranium in multiple oxidation states: a combined structural, magnetic, spectroscopic, spectroelectrochemical, and theoretical study

A comprehensive study of the complexes A4[U(NCS)8] (A = Cs, Et4N, nBu4N) and A3[UO2(NCS)5] (A = Cs, Et4N) is described, with the crystal structures of [nBu4N]4[U(NCS)8]·2MeCN and Cs3[UO2(NCS)5]·O0.5 reported. The magnetic properties of square antiprismatic Cs4[U(NCS)8] and cubic [Et4N]4[U(NCS)8] have been probed by SQUID magnetometry. The geometry has an important impact on the low-temperature magnetic moments: at 2 K, μeff = 1.21 μB and 0.53 μB, respectively. Electronic absorption and photoluminescence spectra of the uranium(IV) compounds have been measured. The redox chemistry of [Et4N]4[U(NCS)8] has been explored using IR and UV–vis spectroelectrochemical methods. Reversible 1-electron oxidation of one of the coordinated thiocyanate ligands occurs at +0.22 V vs Fc/Fc+, followed by an irreversible oxidation to form dithiocyanogen (NCS)2 which upon back reduction regenerates thiocyanate anions coordinating to UO22+. NBO calculations agree with the experimental spectra, suggesting that the initial electron loss of [U(NCS)8]4– is delocalized over all NCS– ligands. Reduction of the uranyl(VI) complex [Et4N]3[UO2(NCS)5] to uranyl(V) is accompanied by immediate disproportionation and has only been studied by DFT methods. The bonding in [An(NCS)8]4– (An = Th, U) and [UO2(NCS)5]3– has been explored by a combination of DFT and QTAIM analysis, and the U–N bonds are predominantly ionic, with the uranyl(V) species more ionic that the uranyl(VI) ion. Additionally, the U(IV)–NCS ion is more ionic than what was found for U(IV)–Cl complexes.

Effect of impurities in biodiesel-derived waste glycerol on the performance and feasibility of biotechnological processes

The rapid development of biodiesel production technology has led to the generation of tremendous quantities of glycerol wastes, as the main by-product of the process. Stoichiometrically, it has been calculated that for every 100 kg of biodiesel, 10 kg of glycerol are produced. Based on the technology imposed by various biodiesel plants, glycerol wastes may contain numerous kinds of impurities such as methanol, salts, soaps, heavy metals and residual fatty acids. This fact often renders biodiesel-derived glycerol unprofitable for further purification. Therefore, the utilization of crude glycerol though biotechnological means represents a promising alternative for the effective management of this industrial waste. This review summarizes the effect of various impurities-contaminants that are found in biodiesel-derived crude glycerol upon its conversion by microbial strains in biotechnological processes. Insights are given concerning the technologies that are currently applied in biodiesel production, with emphasis to the impurities that are added in the composition of crude glycerol, through each step of the production process. Moreover, extensive discussion is made in relation with the impact of the nature of impurities upon the performances of prokaryotic and eukaryotic microorganisms, during crude glycerol bioconversions into a variety of high added-value metabolic products. Finally, aspects concerning ways of crude glycerol treatment for the removal of inhibitory contaminants as reported in the literature are given and comprehensively discussed

The Bone Formation Capabilities of the Anorganic Bone Matrix-Synthetic Cell-Binding Peptide 15 Grafts in an Animal Periodontal Model: A Histologic and Histomorphometric Study in Dogs

Background: The aim of this study is to verify the regenerative potential of particulate anorganic bone matrix synthetic peptide-15 (ABM-P-15) in class III furcation defects associated or not with expanded polytetrafluoroethylene membranes. Methods: Class III furcation defects were produced in the mandibular premolars (P2, P3, and P4) of six dogs and filled with impression material. The membranes and the bone grafts were inserted into P3 and P4, which were randomized to form the test and control groups, respectively; P2 was the negative control group. The animals were sacrificed 3 months post-treatment. Results: Histologically, the complete closure of class III furcation defects was not observed in any of the groups. Partial periodontal regeneration with similar morphologic characteristics among the groups was observed, however, through the formation of new cementum, periodontal ligament, and bone above the notch. Histologic analysis showed granules from the bone graft surrounded by immature bone matrix and encircled by newly formed tissue in the test group. The new bone formation area found in the negative control group was 2.28 +/- 2.49 mm(2) and in the test group it was 6.52 +/- 5.69 mm(2), which showed statistically significant differences for these groups considering this parameter (Friedman test P <0.05). There was no statistically significant difference among the negative control, control, and test groups for the other parameters. Conclusions: The regenerative potential of ABM-P-15 was demonstrated through new bone formation circumscribing and above the graft particles. The new bone also was accompanied by the formation of new cementum and periodontal ligament fibers. J Periodontol 2010;81:594-603.