ESR studies on calcite encrustation on Fili neotectonic fault, Greece

Electron spin resonance (ESR) study was done on calcite encrustation on Fili neotectonic fault surface, Greece. Normally such calcite encrustations on fault surfaces are not observed. Significantly, the ESR study has detected the presence of nitrate NO₃²⁻ radical in this calcite encrustation, havingg _⊥=2.0063±0.0001 and hyperfine coupling constantA _⊥=3.44 mT, the second such detection of nitrate NO₃²⁻ radical following a sample from Scott Glacier, Antarctica. From isochronal thermal annealing measurement the NO₃²⁻ radical was found to be quite stable, only fully annealed at 475°C. This study also shows that the ESR, as a tool, can be suitably applied to date the age of formation of the calcite encrustation with SO₃⁻ as an ESR dating signal by additive γ-ray irradiation. A preliminary estimation indicates the age of formation of calcite precipitation at Fili fault, Greece to be about 5600 years.     

Experimental characterization of hexatic smectic phases through electro-optic studies and dielectric relaxation spectroscopy

The electro-optic and complex dielectric behaviour of an antiferroelectric liquid crystal 4-(1-methylheptyloxycarbonyl)phenyl 4'-(n-butanoyloxyprop-1-oxy)biphenyl-4-carboxylate, having chiral SmC_A* and hexatic smectic phases, have been investigated. Complex dielectric permittivities were measured as a function of frequency, d.c. bias field and temperature. Spontaneous polarization was measured by the current reversal technique; tilt angle was measured under a polarizing microscope using a low frequency electric field. The electro-optic properties and dielectric behaviour of the material are compared with results obtained by DSC and polarizing optical microscopy. Dielectric relaxation processes in SmC_A* and hexatic smectic phases were determined. The dielectric strength at the SmC_A* to hexatic smectic phase transition is discussed in terms of coupling between the long range bond orientational order and smectic C director. It seems from the results of spontaneous polarization and dielectric relaxation spectroscopy that the material might possess an additional phase between the SmC_A* and hexatic smectic I* phases.     

Dielectric spectroscopy of a smectic liquid crystal

Complex dielectric spectroscopy (frequency range 5 Hz-13 MHz) has been used to analyse the frequency, temperature and bias-field dependences of the molecular dynamics of a very high-spontaneous-polarization ferroelectric liquid crystalline material exhibiting SmA, SmC* and unknown SmX smectic phases. Different smectic phase transition temperatures have been observed from the study of the temperature dependence of the dielectric strength and the relaxation frequency. The phase transition temperatures (crystalline to isotropic phases) have also been described very accurately from the temperature-dependent symmetric and asymmetric shape parameters of the relaxation function and also the dc conductivity. In a planar aligned cell, two symmetric modes (Goldstone mode and domain mode) have been observed in both the SmX and SmC* phases. One asymmetric mode (X-mode) observed in the SmC* and SmA phases could be related to the interaction of dipoles of the ferroelectric liquid crystals being affected by the surface of the cell. The soft mode, which usually appears very close to the SmC*-SmA phase transition was not observed until the bias field was applied. The second order nature of the SmC*-SmA phase transition was revealed.     

Electrocatalytic Proton Reduction by a Cobalt Complex Containing a Proton-Responsive Bis(alkylimdazole)methane Ligand: Involvement of a C−H Bond in H2 Formation

Homogeneous electrocatalytic proton reduction is reported using cobalt complex [ 1 ](BF₄)₂. This complex comprises two bis(1-methyl-4,5-diphenyl-1H-imidazol-2-yl)methane (HBMIM ) ligands that contain an acidic methylene moiety in their backbone. Upon reduction of [ 1 ](BF₄)₂ by either electrochemical or chemical means, one of its HBMIM ligands undergoes deprotonation under the formation of dihydrogen. Addition of a mild proton source (acetic acid) to deprotonated complex [ 2 ](BF₄) regenerates protonated complex [ 1 ](BF₄)₂. In presence of acetic acid in acetonitrile solvent [ 1 ](BF₄)₂ shows electrocatalytic proton reduction with a k_obs of ≈200 s⁻¹ at an overpotential of 590 mV. Mechanistic investigations supported by DFT (BP86) suggest that dihydrogen formation takes place in an intramolecular fashion through the participation of a methylene C−H bond of the HBMIM ligand and a Co^II−H bond through formal heterolytic splitting of the latter. These findings are of interest to the development of responsive ligands for molecular (base)metal (electro)catalysis.     

Electronic phase separation in transition metal oxide systems

Electronic phase separation is increasingly getting recognized as a phenomenon of importance in understanding the magnetic and electron transport properties of transition metal oxides. The phenomenon dominates the rare-earth manganates of the formula Ln(1-x)A(x)MnO(3)(Ln = rare earth and A = alkaline earth) which exhibit ferromagnetism and metallicity as well as charge-ordering, depending on the composition, size of A-site cations and external factors such as magnetic and electric fields. We discuss typical phase separation scenarios in the manganates, with particular reference to Pr(1-x)Ca(x)MnO(3)(x= 0.3-0.4), (La(1-x)Ln(x))(0.7)Ca(0.3)MnO(3)(Ln = Pr, Nd, Gd and Y) and Nd(0.5)Sr(0.5)MnO(3). Besides discussing the magnetic and electron transport properties, we discuss electric field effects. Rare-earth cobaltates of the type Pr(0.7)Ca(0.3)CoO(3) and Gd(0.5)Ba(0.5)CoO(3) also exhibit interesting magnetic and electron transport properties which can be understood in terms of phase separation.     

Synthesis of 5-ethynylorotic acid

Condensation of 2,4-dimethoxy-5-iodo-6-carbomethoxypyrimidine ( 10 ) with copper (I) 3-tetrahydropyranyloxyprop-1-ynide ( 4 ) afforded 2,4-dimethoxy-5-(3′-tetrahydropyranyloxyprop-1′-yn)-6-carbomethoxypyrimidine ( 11 ), which was hydrolyzed to produce 2,4-dimethoxy-5-(3′-hydroxyprop-1′-yn)-6-carbomethoxypyrimidine ( 12 ). Oxidation of 12 with dimethyl sulfoxide-oxalyl chloride reagent gave the acetylenic aldehyde ( 13 ), which on treatment with sodium methoxide in dry tetrahydrofuran yielded 2,4-dimethoxy-5-ethynyl-6-carbomethoxypyrimidine ( 14 ). The trimethylsilyl derivative ( 15 ) was deprotected by sequential treatment with iodotrimethylsilane and aqueous sodium hydroxide, leading to the formation of 5-ethynylorotic acid ( 1 ).     

Structural models of the bimetallic subunit at the A-cluster of acetyl coenzyme a synthase/CO dehydrogenase: binuclear sulfur-bridged Ni-Cu and Ni-Ni complexes and their reactions with CO

The Ni(II)-dicarboxamido-dithiolato complexes (Et4N)2[Ni(NpPepS)] (1) and (Et4N)2[Ni(PhPepS)] (2) were used as Nid metallosynthons in the construction of higher nuclearity dinuclear Ni-Cu and Ni-Ni species to model the bimetallic Mp-Nid site of the A-cluster of acetyl coenzyme A synthase/CO dehydrogenase (ACS/CODH). Reaction of 1 with [Cu(neo)Cl] and [Ni(terpy)Cl2] in MeCN affords the dinuclear complexes (Et4N)[Cu(neo)Ni(NpPepS)] (3) and [Ni(terpy)Ni(NpPepS)] (4), respectively. Reaction of 2 with [Ni(dppe)Cl2] in MeCN yields [Ni(dppe)Ni(PhPepS)] (6). The Ni-Cu complex 3 exhibits no redox chemistry at the Nid site and no reaction with CO. In contrast, the Nip sites in 4 and 6 are readily reduced (characterized by their Ni(I) EPR spectra) and bind CO, exhibiting nuco bands at 2044 and 1997 cm-1, respectively, indicating terminal CO binding. The present Ni-Ni systems replicate the structural and chemical properties of the A-cluster site in ACS/CODH and support the presence of Ni at Mp in the catalytically active enzyme.     

A new route to obtain shape-controlled gold nanoparticles from Au(III)-beta-diketonates

Ligands with a beta-diketone skeleton have been employed for the first time as reductant to produce ligand stabilized gold nanoparticles of different shapes from aqueous HAuCl(4) solution. Evolution of stable gold nanoparticles follows first order (k approximately equal to 10(-2) min(-1)) kinetics with respect to Au(0) concentration. Growth of particles of different shapes (spherical or triangular or hexagonal) goes hand in hand under the influence of different beta-diketones, which have excellent capping and reducing properties. Chlorine insertion was observed to take place in the beta-diketone skeleton.