Carboxylate coordination chemistry of a mononuclear Ni(II) center in a hydrophobic or hydrogen bond donor secondary environment: relevance to acireductone dioxygenase

A series of Ni(II) carboxylate complexes, supported by a chelate ligand having either secondary hydrophobic phenyl groups (6-Ph2TPA, N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine) or hydrogen bond donors (bnpapa, N,N-bis((6-neopentylamino-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine), have been prepared and characterized. X-ray crystallographic studies of [(6-Ph2TPA)Ni(O2C(CH2)2SCH3)]ClO4.CH2Cl2 (4.CH2Cl2) and [(6-Ph2TPA)Ni(O2CCH2SCH3)]ClO(4).1.5CH2Cl2 (5.1.5CH2Cl2) revealed that each complex contains a distorted octahedral Ni(II) center and a bidentate carboxylate ligand. A previously described benzoate complex ([(6-Ph2TPA)Ni(O2CPh)]ClO4 (3)) has similar structural characteristics. Recrystallization of dry powdered samples of 3, 4.0.5CH2Cl2, and 5 from wet organic solvents yielded a second series of crystalline Ni(II) carboxylate complexes having a coordinated monodentate carboxylate ligand ([(6-Ph2TPA)Ni(H2O)(O2CPh)]ClO4 (6), [(6-Ph2TPA)Ni(H2O)(O2C(CH2)2SCH3)]ClO4.0.2CH2Cl2 (7.0.2CH2Cl2), [(6-Ph2TPA)Ni(H2O)(O2CCH2SCH3)]ClO4 (8)) which is stabilized by a hydrogen-bonding interaction with a Ni(II)-bound water molecule. In the cationic portions of 7.0.2CH2Cl2 and 8, weak CH/pi interactions are also present between the methylene units of the carboxylate ligands and the phenyl appendages of the 6-Ph2TPA ligands. A formate complex of the formulation [(6-Ph2TPA)Ni(H2O)(O2CH)]ClO4 (9) was isolated and characterized. The mononuclear Ni(II) carboxylate complexes [(bnpapa)Ni(O2CPh)]ClO4 (10), [(bnpapa)Ni(O2C(CH2)2SCH3)]ClO4 (11), [(bnpapa)Ni(O2CCH2SCH3)]ClO4 (12), and [(bnpapa)Ni(O2CH)]ClO4 (13) were isolated and characterized. Two crystalline solvate forms of 10 (10.CH3CN and 10.CH2Cl2) were examined by X-ray crystallography. In both, the distorted octahedral Ni(II) center is ligated by a bidentate benzoate ligand, one Ni(II)-bound oxygen atom of which accepts two hydrogen bonds from the supporting bnpapa chelate ligand. Spectroscopic studies of 10(-13) suggest that all contain a bidentate carboxylate ligand, even after exposure to water. The combined results of this work enable the formulation of a proposed pathway for carboxylate product release from the active site Ni(II) center in acireductone dioxygenase.     

Conformations in dioctyl substituted polyfluorene: a combined theoretical and experimental Raman scattering study

The structural properties of polyfluorenes (PF) are extremely sensitive to the choice of functionalizing side chains. Dioctyl substituted PF (PF8) adopts metastable structures that depend upon the thermal history and choice of solvents used in film forming conditions. We present a detailed study of the changes in the backbone and side chain morphology in PF8, induced by the various crystallographic phases, using Raman scattering techniques. The vibrational frequencies and intensities of fluorene oligomers are calculated using hybrid density-functional theory with a 3-21G(*) basis set. The alkyl side chains are modeled as limiting conformations: all anti, anti-gauche-gauche, and end gauche representations. The calculated vibrational spectra of single chain oligomers in conjunction with our experimental results demonstrate the beta phase, which is known to originate in regions of enhanced chain planarity as a direct consequence of the alkyl side chain conformation.     

Surface/interface phenomena in nano‐multilayer coating under severing tribological conditions

An extensive study of surface/interface phenomena during wear of an adaptive TiAlCrSiYN/TiAlCrN nano‐multilayer coating deposited using physical vapor deposition was undertaken under increasingly severe tribological conditions associated with dry end milling of H13 hardened tool steel. The results of FEM modeling on the temperature/stress distribution at different cutting speeds outline actual cutting conditions on the both rake and flank frictional surfaces of the coated tool. Studies of the surface/interface phenomena were made by means of SEM/high‐resolution transmission electron microscopy/XPS analyses. Results demonstrate that intensifying tribological conditions facilitates improved wear performance of the adaptive coating layer. In extreme tribological conditions of ultra‐performance machining (cutting speed of 500 m/min), the self‐organization process establishes entirely through the formation of a nano‐scale layer of dynamically re‐generating tribo‐ceramic films. The formation of these surface nano‐films results in exceptionally efficient protection of the underlying coating layers. In response to the extreme external environment, the coating layer remained almost undamaged during a long run, demonstrating the capacity to efficiently replenish necessary tribo‐ceramic films. In this way, interconnection of various surface and undersurface processes is established in the hierarchically structured tribo‐films/coating layer. This integral performance is responsible for exceptional wear resistance under intensifying and extreme tribological conditions. Copyright © 2016 John Wiley & Sons, Ltd.     

Electrochemical deposition of cadmium selenide films and their properties: a review

This review gives brief information of experimental conditions employed by different researchers for deposition of cadmium selenide (CdSe) thin films. For the films synthesized at room temperature, films should be annealed and etched to increase the solar cell efficiency. A photoelectrochemical study revealed that values of fill factor and efficiency of CdSe thin films deposited on fluorine-doped tin oxide-coated glass substrates exhibited maximum value compared to the film deposited on titanium and stainless steel substrates. This review will be helpful to researchers entering in field to understand basics about the electrodeposition of CdSe and its development towards next-generation photovoltaics.     

On Mann iteration in Hilbert spaces

Let K$K$ be a compact convex subset of a real Hilbert space H$H$; T:K→K$T:K\to K$ a hemicontractive map. Let {_αn}$\left\{{\alpha }_n\right\}$ be a real sequence in [0,1] satisfying appropriate conditions; then for arbitrary _x0∈K$x_0\in K$, the sequence {_xn}$\left\{x_n\right\}$ defined iteratively by _xn=_αnxn−1+(1−_αn)T_xn$x_n={\alpha }_n{x}_{n-1}+(1-{\alpha }_n)T{x}_n$, n≥1$n\ge 1$ converges strongly to a fixed point of T$T$.     

Autoacetylation induced specific structural changes in histone acetyltransferase domain of p300: probed by surface enhanced Raman spectroscopy

Reversible acetylation of histone and non-histone proteins plays an important role in the regulation of gene expression and cellular homeostasis. A balance between acetylation and deacetylation of these proteins are maintained by histone acetyltransferases (HATs) and histone deacetylases (HDACs). Among different HATs, p300/CBP is the most widely studied chromatin modifying enzymes. p300 is involved in several physiological processes like cell growth, regulation of gene expression, development, and tumor suppressor, and therefore its dysfunction causes different diseases. The autoacetylation of p300 is one of the key regulators of its catalytic activity. Mechanistically, autoacetylation induced structural changes in the p300 HAT domain acts as a master switch. In this report, we have shown that the natural HAT inhibitor garcinol could potently inhibit the autoacetylation activity. Furthermore, for the first time, we demonstrate that indeed autoacetylation induces structural changes in p300 HAT domain, as probed by surface-enhanced Raman scattering. Presumably, SERS will be a very useful tool to find out the structural changes in the other self-modifying enzymes like kinases and methyltransferases.     

Effect of copolymer architecture on the micellization and gelation of aqueous solutions of copolymers of ethylene oxide and styrene oxide

The micellar properties and solubilization capacity of poorly water soluble drugs of several micellar and gel solutions of diblock and triblock copolymers of styrene oxide/ethylene oxide have been measured and compared with block copolymers of butylene oxide/ethylene oxide, showing that the solubilization capacity of the styrene oxide block is approximately four times that of a butylenes oxide block for dilute solutions. To continue establishing the correlation between micellar characteristics and solubilization capacity, we have found it interesting to compare the micellar and gelation properties of the diblock and triblock copolymers PSO10PEO135 and PEO69PSO8PEO69 (subindexes are the number-average block lengths), with different architecture but similar average block lengths. Surface tension measurements allowed the determination of the critical micelle concentrations at several temperatures and, so, to calculate standard enthalpies of micellization. Static and dynamic light scattering data permitted us to determine micellar parameters and to obtain qualitatively the extent of hydration of the copolymer micelle. A tube inversion method was used to define the mobile-immobile (soft-hard gel) phase boundary. To refine the phase diagram and observe the existence of additional phases, rheological measurements were done. The results are in good agreement with previous values published for PSOnPEOm and PEOmPSOnPEOm copolymers.     

Intramolecular azide trapping of the Nazarov intermediate: formation of peroxy-bridged indolizidinones via a deep-seated rearrangement and aerobic oxidation

Cross-conjugated dienones with pendent azide side chains undergo interrupted Nazarov trapping, leading to peroxy-bridged indolizidinones in good yields. This process is proposed to involve skeletal rearrangement of the initial trapping product, with loss of dinitrogen, to give an intermediate 1,4-betaine, which then undergoes reaction with atmospheric oxygen. The endoperoxide products can be reduced under catalytic hydrogenation conditions to furnish alpha-hydroxylactams. [reaction: see text].     

Single-crystal to single-crystal phase transitions of bis(N-phenylisonicotinamide)silver(I) nitrate reveal cooperativity properties in porous molecular materials

Two single-crystal to single-crystal phase transitions in trans-[Ag(NPI)(2)](NO(3)).2CH(3)OH (), (NPI = N-phenylisonicotinamide) were characterized with X-ray crystallography; the first transition is reversible and arises from a desolvation transition induced by vacuum and generated ; the second transition was induced by heat at 140 degrees C and generated .     

In vitro pharmacological screening of three newly synthesised pyrimidine derivatives

The antibacterial and antifungal activities of three new pyrimidine derivatives, namely, 2,6-bis(4,6-dimethylpyrimidin-2-ylthio)benzene-1,4-diol (1),3,5-bis(4,6-dimethylpyrimidin-2-ylthio)-2-methylbenzene-1,4-diol (2) and 3,5-bis(4,6-dimethylpyrimidin-2-ylthio)-2-methoxybenzene-1,4-diol (3), synthesised by electrochemical method are presented here. The compounds were screened for their activities against Gram-positive and Gram-negative bacteria, Bacillus subtilis, Staphylococcusaureus, Escherichia coli and a pathogenic fungus Aspergillus niger. The results show that these compounds have significant activity against these bacteria and fungus. The minimum inhibitory concentration of compound 1 was determined as 62.5 μg/mL against B. subtilis, 125 μg/mL against E. coli and 250 μg/mL against S. aureus establishing its promising activities higher than susceptible ranges.