Importance of halogen···halogen contacts for the structural and magnetic properties of CuX2(pyrazine-N,N′-dioxide)(H2O)2 (X = Cl and Br)

The structural and magnetic properties of the newly crystallized CuX(2)(pyzO)(H(2)O)(2) (X = Cl, Br; pyzO = pyrazine-N,N'-dioxide) coordination polymers are reported. These isostructural compounds crystallize in the monoclinic space group C2/c with, at 150 K, a = 17.0515(7) ?, b = 5.5560(2) ?, c = 10.4254(5) ?, β = 115.400(2)°, and V = 892.21(7) ?(3) for X = Cl and a = 17.3457(8) ?, b = 5.6766(3) ?, c = 10.6979(5) ?, β = 115.593(2)°, and V = 950.01(8) ?(3) for X = Br. Their crystal structure is characterized by one-dimensional chains of Cu(2+) ions linked through bidentate pyzO ligands. These chains are joined together through OH···O hydrogen bonds between the water ligands and pyzO oxygen atoms and Cu-X···X-Cu contacts. Bulk magnetic susceptibility measurements at ambient pressure show a broad maximum at 7 (Cl) and 28 K (Br) that is indicative of short-range magnetic correlations. The dominant spin exchange is the Cu-X···X-Cu supersuperexchange because the magnetic orbital of the Cu(2+) ion is contained in the CuX(2)(H(2)O)(2) plane and the X···X contact distances are short. The magnetic data were fitted to a Heisenberg 1D uniform antiferromagnetic chain model with J(1D)/k(B) = -11.1(1) (Cl) and -45.9(1) K (Br). Magnetization saturates at fields of 16.1(3) (Cl) and 66.7(5) T (Br), from which J(1D) is determined to be -11.5(2) (Cl) and -46.4(5) K (Br). For the Br analog the pressure dependence of the magnetic susceptibility indicates a gradual increase in the magnitude of J(1D)/k(B) up to -51.2 K at 0.84 GPa, suggesting a shortening of the Br···Br contact distance under pressure. At higher pressure X-ray powder diffraction data indicates a structural phase transition at ～3.5 GPa. Muon-spin relaxation measurements indicate that CuCl(2)(pyzO)(H(2)O)(2) is magnetically ordered with T(N) = 1.06(1) K, while the signature for long-range magnetic order in CuBr(2)(pyzO)(H(2)O)(2) was much less definitive down to 0.26 K. The results for the CuX(2)(pyzO)(H(2)O)(2) complexes are compared to the related CuX(2)(pyrazine) materials.     

Selective G-quadruplex DNA stabilizing agents based on bisquinolinium and bispyridinium derivatives of 1,8-naphthyridine

Various biologically relevant G-quadruplex DNA structures offer a platform for therapeutic intervention for altering the gene expression or by halting the function of proteins associated with telomeres. One of the prominent strategies to explore the therapeutic potential of quadruplex DNA structures is by stabilizing them with small molecule ligands. Here we report the synthesis of bisquinolinium and bispyridinium derivatives of 1,8-naphthyridine and their interaction with human telomeric DNA and promoter G-quadruplex forming DNAs. The interactions of ligands with quadruplex forming DNAs were studied by various biophysical, biochemical, and computational methods. Results indicated that bisquinolinium ligands bind tightly and selectively to quadruplex DNAs at low ligand concentration (～0.2-0.4 μM). Furthermore, thermal melting studies revealed that ligands imparted higher stabilization for quadruplex DNA (an increase in the T(m) of up to 21 °C for human telomeric G-quadruplex DNA and >25 °C for promoter G-quadruplex DNAs) than duplex DNA (ΔT(m) ≤ 1.6 °C). Molecular dynamics simulations revealed that the end-stacking binding mode was favored for ligands with low binding free energy. Taken together, the results indicate that the naphthyridine-based ligands with quinolinium and pyridinium side chains form a promising class of quadruplex DNA stabilizing agents having high selectivity for quadruplex DNA structures over duplex DNA structures.     

Tannase Production by Penicillium purpurogenum PAF6 in Solid State Fermentation of Tannin-Rich Plant Residues Following OVAT and RSM

Tannase production by newly isolated Penicillium purpurogenum PAF6 was investigated by ??one variable at a time?? (OVAT) approach followed by response surface methodology (RSM). Tannin-rich plant residues were used as supporting solid substrate and sole carbon source and, among them, tamarind seed was found to be the most favorable substrate than haritaki, pomegranate, tea leaf waste and arjun fruit. Physicochemical parameters were initially optimized using OVAT methodology and some important factors like incubation time, incubation temperature, substrate:moisture ratio as well as carbon, nitrogen and phosphate concentrations were verified with Box?CBehken design of response surface methodology. Phosphate source, nitrogen source and temperature were found as the most favorable variables in the maximization of production. Tannase production was enhanced from 1.536 U/g to 5.784 U/g using tamarind seed OVAT optimization and further enhancement up to 6.15 U/g following RSM. An overall 3.76- and 4.0-fold increases in tannase production were achieved in OVAT and RSM, respectively.     

Ytterbium-sensitized thulium-doped fiber laser with a single-mode output operating at 1900-nm region

A single-mode laser is demonstrated using a newly developed double-clad thulium-ytterbium-doped fiber (TYDF) in a linear cavity formed by two fiber Bragg gratings (FBGs). The YTF used is drawn from a D-shape preform fabricated using the modified chemical vapor deposition and solution doping technique. The laser is operated at 1 901.6 nm via the transition of thulium ions from 3F4 to 3H6 with the assistance of ytterbium to thulium ion energy transfer. The efficiencies of the laser are 0.71% and 0.75% at 927- and 905-nm multimode pumping, respectively. The thresholds of the launched pump power for 927- and 905-nm pumping are 1 314 and 1 458 mW, respectively. A 7-mW output is obtained at a 905-nm pump power of 2 400 mW.     

Assessing the roles of the constituents of ionic liquids in dynamic solvation: Comparison of an ionic liquid in micellar and bulk form

Dynamic solvation of the dye, coumarin 153, is compared in an ionic liquid that forms micelles in water against the bulk solvent. This provides the unprecedented opportunity of investigating the behavior of the ionic liquid in two globally different configurations. It is proposed that the imidazolium moiety is in both cases responsible for the majority of the solvation, which manifests itself in the first 100 ps. Exploiting the use of ionic liquids capable of accommodating specific structures thus provides a deeper insight into how solutes interact with these fascinating and interesting solvents (at least those that are imidazolium based) that are gaining ever increasing interest in the scientific community.     

Synthesis, structure, and electrochemical properties of a family of 2-(arylazo)phenolate complexes of ruthenium with unusual C-C coupling and N=N cleavage

Reaction of 2-(4'-R-phenylazo)-4-methylphenols (R = OCH3, CH3, H, Cl, and NO2) with [Ru(dmso)(4)Cl2]affords a family of five ruthenium(III) complexes, containing a 2-(arylazo)phenolate ligand forming a six-membered chelate ring and a tetradentate ligand formed from two 2-(arylazo)phenols via an unusual C-C coupling linking the two ortho carbons of the phenyl rings in the arylazo fragment. A similar reaction with 2-(2'-methylphenylazo)-4-methylphenol with [Ru(dmso)(4)Cl2] has afforded a similar complex, in which one 2-(2'-methylphenylazo)-4-methylphenolate ligand is coordinated forming a six-membered chelate ring, and the other two ligands have undergone the C-C coupling reaction, and the coupled species is coordinated as a tetradentate ligand forming a five-membered N,O-chelate ring, a nine-membered N,N-chelate ring, and another five-membered chelate ring. Reaction of 2-(2',6'-dimethylphenylazo)-4-methylphenol with [Ru(dmso)(4)Cl2] has afforded a complex in which two 2-(2',6'-dimethylphenylazo)-4-methylphenols are coordinated as bidentate N,O-donors forming five- and six-membered chelate rings, while the third one has undergone cleavage across the N=N bond, and the phenolate fragment, thus generated, remains coordinated to the metal center in the iminosemiquinonate form. Structures of four selected complexes have been determined by X-ray crystallography. The first six complexes are one-electron paramagnetic and show rhombic ESR spectra. The last complex is diamagnetic and shows characteristic 1H NMR signals. All the complexes show intense charge-transfer transitions in the visible region and a Ru(III)-Ru(IV) oxidation on the positive side of SCE and a Ru(III)-Ru(II) reduction on the negative side.     

Experimental and theoretical investigations of solvation dynamics of ionic fluids: appropriateness of dielectric theory and the role of DC conductivity

An analysis is provided of the subnanosecond dynamic solvation of ionic liquids in particular and ionic solutions in general. It is our hypothesis that solvation relaxation in ionic fluids, in the nonglassy and nonsupercooled regimes, can be understood rather simply in terms of the dielectric spectra of the solvent. This idea is suggested by the comparison of imidazolium ionic liquids with their pure organic counterpart, butylimidazole (J. Phys. Chem. B 2004, 108, 10245-10255). It is borne out by a calculation of the solvation correlation time from frequency dependent dielectric data for the ionic liquid, ethylammonium nitrate, and for the electrolyte solution of methanol and sodium perchlorate. Very good agreement is obtained between these theoretically calculated solvation relaxation functions and those obtained from fluorescence upconversion spectroscopy. Our comparisons suggest that translational motion of ions may not be the predominant factor in short-time solvation of ionic fluids and that many tools and ideas about solvation dynamics in polar solvents can be adapted to ionic fluids.     

Bulk Viscous Bianchi-III Models with Time Dependent G and?Λ

Bulk Viscous anisotropic Bianchi-III cosmological models are investigated with time dependent gravitational and cosmological constants in the framework of Einstein’s general relativity. In order to get some useful information about the time varying nature of G and Λ, we have assumed an exponentially decaying rest energy density of the universe. The extracted Newtonian gravitational constant G varies with time but its time varying nature depends on bulk viscosity and the anisotropic nature of the model. The cosmological constant Λ is found to decrease with time to a small but positive value for the models.     

Imidazole‐Based Small Molecules that Promote Neurogenesis in Pluripotent Cells

Reported herein are two imidazole‐based small molecules, termed neurodazine (Nz) and neurodazole (Nzl), which induce neuronal differentiation of pluripotent P19 cells. Their ability to induce neurogenesis of P19 cells is comparable to that of retinoic acid. However, Nz and Nzl were found to be more selective neurogenesis inducers than retinoic acid owing to their unique ability to suppress astrocyte differentiation of P19 cells. Our results also show that Nz and Nzl promote production of physiologically active neurons because P19‐cell‐derived neurons induced by these substances have functional glutamate responsiveness. The present study suggests that Nz and Nzl could serve as important chemical tools to induce formation of specific populations of neuronal cell types from pluripotent cells.