Synthesis and characterization of {Ni(NO)}10 and {Co(NO)2}10 complexes supported by thiolate ligands

Nitric oxide is an important molecule in biology and modulates a variety of physiological and pathophysiological processes. Some of its regulatory functions are exerted through interactions with redox-active elements, including iron, nickel, cobalt, and sulfur. Metalloenzymes containing [ nFe- nS] ( n = 2 or 4) clusters can be activated or inactivated by reaction with NO, affording dinitrosyl iron complexes. Studies of the NO chemistry of small-molecule iron thiolate complexes have provided insight into these biological processes and suggested probable intermediates. To explore this chemistry from a different perspective, we prepared nickel and cobalt thiolate complexes and investigated their reactions with NO and related compounds. We report here the first examples of anionic complexes containing {Ni(NO)} (10) and {Co(NO) 2} (10) units, the reactivity of which suggests possible intermediates in the interconversion of iron thiolate nitrosyl compounds. Our results demonstrate new chemistry involving NO and simple complexes of nickel and cobalt supported by thiolates, which have been known for more than 30 years. The use of mass balance methodology was key to their discovery. Among the novel complexes reported are (Et 4N) 2[Ni(NO)(SPh) 3] ( 2), from (Et 4N) 2[Ni(SPh) 4] ( 1) and NO, (Et 4N) 2[Ni 2(NO) 2(mu-SPh) 2(SPh) 2] ( 3), from 1 and NO (+) or 2 and Me 3O (+), (Et 4N)[Co(NO) 2(SPh) 2] ( 5), from (Et 4N) 2[Co(SPh) 4] ( 4) and NO, and [Co 3(NO) 6(mu-SPh) 3] ( 6), from 5 and Me 3O (+). In the syntheses of 2 and 5, NO could be replaced by the convenient solid Ph 3CSNO.     

Photosensitizer in a molecular bowl and its effect on the DNA-binding and -cleavage activity of 3d-metal scorpionates

Ternary 3d -metal complexes [M(Tp (Ph))(B)](ClO 4) ( 1- 8), where M is Co(II), Ni(II), Cu(II) and Zn(II), Tp (Ph) is anionic tris(3-phenylpyrazolyl)borate, and B is N,N-donor heterocyclic base, namely, 1,10-phenanthroline (phen, 1- 4) and dipyrido[3,2- d:2',3'- f]quinoxaline (dpq, 5- 8), were prepared from a reaction of the perchlorate salt of the metal with KTp (Ph) and B in CH 2Cl 2. The complexes were characterized by various physicochemical methods. 4- 6 and 8 were structurally characterized by single-crystal X-ray crystallography. The crystal structures of the complexes show the presence of discrete cationic complexes having a square-pyramidal (4 + 1) coordination geometry in which two nitrogen atoms of the phenanthroline base (B) and two nitrogen atoms of the Tp (Ph) ligand occupy the basal plane and one nitrogen of the Tp (Ph) ligand binds at the axial site. The phenyl groups of the Tp (Ph) form a bowl-shaped structure that essentially encloses the {M(phen/dpq)} moiety. DNA-binding studies were carried out using various spectral techniques and from viscosity measurements. The complexes show moderate binding propensity to calf thymus DNA at the minor groove, giving binding constant values ( K b) of approximately 10 (4) M (-1). The complexes exhibit poor DNA-cleavage activity in the dark in the presence of 3-mercaptopropionic acid (MPA) or hydrogen peroxide (H 2O 2). The photoinduced DNA-cleavage activity of the complexes was investigated using UV-A radiation of 365 nm and visible light of two different wavelengths with a tunable multicolor Ar-Kr mixed gas ion laser source. The dpq complexes show efficient photoinduced DNA-cleavage activity via a metal-assisted photoexcitation process involving the formation of singlet oxygen as the cleavage active species in a type-II pathway. The paramagnetic d (7)-Co(II)-dpq and d (9)-Cu(II)-dpq complexes exhibit efficient DNA-cleavage activity in visible light. The paramagnetic d (8)-Ni(II)-dpq complex displays only minor DNA-cleavage activity in visible light. Diamagnetic d (10)-Zn(II)-dpq complex shows only UV-A light-induced DNA cleavage but no apparent DNA-cleavage activity in visible light. Steric protection of the photoactive quinoxaline moiety of the dpq ligand inside the hydrophobic {M(Tp (Ph))} molecular bowl has a positive effect on the photoinduced DNA-cleavage activity.     

Particle production, back reaction and singularity avoidance

We consider particle production in Robertson-Walker spacetime as particle-antiparticle rotation. We thereby obtain a scale factor that guarantees particle production. We then study quantum field effects in spatially flat homogeneous and isotropic spacetime with energy density of created particles and one loop quantum correction as back reaction. In the numerical solution initial values are determined from particle production simulated scale factor and obtain the evolution of the universe both at early and late times having a bounce.     

Electrons, phonons and superconductivity in C16 structured Zr2Fe

Inelastic neutron scattering and low-temperature specific heat measurements are reported for a polycrystalline sample of Zr₂Fe. Lattice dynamical calculation of the phonon spectrum, along with first-principles LMTO electronic structure calculations have been used for deriving the specific heat parameters, the electron–phonon coupling constant and the superconducting transition temperature. The results are in fair agreement with the experimental data.     

High density,high performance optical data storage via volume holography: Viability at last?

The long held promise of using volume holography to deliver high performance optical storage is reviewed. The problems, which limited the development for many years, are accessed. Finally, we describe a series of innovations, which may make the technology viable at last.     

Deformation and microhardness studies on natural apophyllite crystals

Microhardness testing of three different planes of natural apophyllite crystals is reported. Variation of Vicker's microhardness value H_v with applied load ranging from 10–100 g indicates two distinct regions. In the low load region (10–70 g) H_v increases with load till it attains maximum value and then decreases thereafter. This variation is explained qualitatively in terms of depth of penetration of the indentor. Variation of orientation of the indentor w.r.t. each of the (100) and (111) planes indicates microhardness anisotropy.     

Characteristics of electrical properties of wide temperature range TGB phases in liquid crystal dimers

4-n-decyloxy-4′-(cholesteryloxycarbonyl-1-butyloxy) chalcone and its two successive homologous are optically active dimeric compound derived from cholesterol. They possess wide temperature ranges of two twist grain boundary (TGB) phases namely TGBA and TGBC*. Comprehensive dielectric studies have been carried out for these compounds in the frequency range of 1 Hz to 10 MHz for different conditions of molecular anchoring. Various electrical parameter viz. dielectric permittivity, dielectric anisotropy, dc conductivity, and activation energy have been determined for these two TGB phases. Weak relaxation processes have been detected under planar anchoring of molecules in the TGBA and TGBC* phases presumably due to amplitude (soft mode) and phase (Goldstone mode) fluctuations.     

The first ionic liquid-promoted three-component coupling strategy for an expeditious synthesis of β-nitrocarbonitriles/thiocyanates

A novel and convenient three-component coupling reaction of nitromethane, aromatic aldehydes and trimethylsilyl cyanide (TMSCN) or ammonium thiocyanate has been developed for an expeditious synthesis of β-nitrocarbonitriles or β-nitrothiocyanates, respectively, via C-C and C-S bond-forming reactions. The synthetic protocol strategically involves a one-pot sequential Henry reaction and a Michael addition efficiently promoted by the same ionic liquid [bmim]OH. The main advantages of the present approach include the use of inexpensive simple substrates and an ionic liquid as an efficient reaction promoter for the mild synthesis in a one-pot procedure.