Spectroscopic,Voltammetric and Coordination Studies on Novel Schiff Base Ligand Derived from Fluorenone with Phenyl Thiosemicarbazide. III

Some new transition metal complexes of the Schiff base ligand (FPTH) formed by condensation of fluorenone with 4-phenylthiosemicarbazide were prepared. Isolation of the solid metal (II) complexes depends on the metal salt used, pH and the reaction conditions. Characterization of these complexes has been made by elemental analyses, molar conductivities, NMR (¹H, ¹³C), magnetic susceptibility, vissible studies and IR spectra. From EPR studies; symmetry and bonding character for paramagnetic copper(II) complex were determined. The polarographic and cyclic voltammetric curves of the Schiff base (FPTH) were recorded in Britton-Robinson buffer series of pH 3–10. The DC polarograms and the cyclic voltammograms exhibited a single 4-electron irreversible diffusion-controled reduction step represented the saturation of C=N and C=S electroactive centers. The corrosion inhibition of aluminium in HCl using FPTH is studied. The antimicrobial activity of ligand and its metal complexes has also been demonstrated.     

Adsorption and desorption characteristics of 3-dimensional networks of fused graphene

Here we explore the exceptional structural characteristics of a set of graphene-related materials prepared by a wet chemical approach. We present a comprehensive study of the effects of morphology, sonication, temperature, probe species, and stacking behaviour on the measurement of graphene surface area. Nitrogen gas was used in the solid state gas adsorption measurements and methylene blue dye for adsorption measurements on aqueous dispersions of graphene. The surface area values obtained are among the highest reported for synthetic graphenes: 1700 m² g^? 1 in aqueous dispersions and 612 m² g^? 1 in the solid state. Microscopy revealed the graphene used in the study was present in large part as free sheets and electron diffraction confirmed the successful synthesis of high quality graphene with a regular C–C bond length of 1.41 ± 0.02 Å.     

Ac conductivity study of lithium and potassium diphosphate LiK3P2O7 using impedance spectroscopy

In this work, a LiK₃P₂O₇ ceramic material was prepared by the solid-state reaction method and identified by X-ray diffractometry. The dielectric properties, impedance characteristics, and modulus were studied over a range of frequency (200 Hz to 5 MHz) and temperature (615–708 K). The frequency and temperature dependence of dielectric permittivity, dielectric loss, and electric modulus is studied. The frequency analysis of modulus properties showed a distribution of relaxation times. Conductivity plots against frequency at a higher frequency suggested the response obeying the universal power law. The temperature behavior of the frequency exponents shows that the correlated barrier hopping CBH model is well adapted to this material. The activation energy associated with the impedance relaxation and the electric modulus spectra is close to the activation energy for dc conductivity indicating the similar nature of relaxation and conductivity. Thermodynamic parameters such as free energy of activation, enthalpy, and entropy have been calculated.     

Strong Interplay between the Electron Spin Lifetime in Chemically Synthesized Graphene Multilayers and Surface‐Bound Oxygen

The electron spin lifetime in an assembly of chemically synthesized graphene sheets was found to be extremely sensitive to oxygen. Introducing small concentrations of physisorbed O₂ onto the graphene surface reduced the exceptionally long 140 ns electron spin lifetime by an order of magnitude. This effect was completely reversible: Removing the O₂ by using a dynamic vacuum restored the spin lifetime. The presence of covalently bound oxygen also decreased the electron spin lifetime in graphene, although to a far lesser extent compared to physisorbed O₂. The conduction electrons in graphene were found to play a significant role by counter‐balancing the spin depolarization caused by oxygen molecules. Our results highlight the importance of chemical environment control and device packing in practical graphene‐based spintronic applications.     

Indium- or Zinc-Mediated One-Pot Synthesis of Homoallylamines, beta-Amino Esters, and beta-Amino Nitriles

Homoallylamines, beta-amino esters, and beta-amino nitriles were obtained in a one-pot synthesis directly from an aldehyde and a secondary amine such as dibenzylamine or diallylamine. Their condensation with titanium(IV) isopropoxide generates an intermediate aminoalkoxy titanium complex. Further reaction in THF with nucleophilic organometallic species, generated in situ from indium or zinc and a reactive halide (allyl bromide, alkyl bromo- or iodoacetate, iodoacetonitrile), furnished the corresponding amines.     

Likonides A and B: new ansa farnesyl quinols from the marine sponge Hyatella sp

[structure: see text] Two novel ansa farnesyl quinols, designated likonides A and B, were isolated together with avarone from the Kenyan sponge Hyatella sp. The compounds are of a unique ansa structure. The structures and stereochemistry of the compounds were elucidated by interpretation of MS, two-dimensional NMR, and CD experiments.     

(Bio)sensors based on manganese dioxide-modified carbon substrates: retrospections, further improvements and applications

An overview is presented which summarizes our accomplishment in the development of sensors and biosensors based on heterogenous carbon electrodes modified with manganese dioxide. Brief account of each sensor and biosensor has been given and example of real sample applications provided where appropriate.     

Initial excited-state structural dynamics of 2'-deoxyguanosine determined via UV resonance Raman spectroscopy

The resonance Raman spectra of 2'-deoxyguanosine, a DNA nucleoside, were measured in aqueous solution at wavelengths throughout its 260 nm absorption band. Self-consistent analysis of the resulting resonance Raman excitation profiles and absorption spectrum using a time-dependent wave packet formalism with two electronic states yielded the initial excited-state structural dynamics in both states. The vibrational modes containing the N(7)═C(8) stretching and C(8)-H bending internal coordinates were found to exhibit significant initial structural dynamics upon photoexcitation to either state and are coincident with the photochemical reaction coordinate involving the formation of the 2'-deoxyguanosine cation radical.     

Effect of exchange of terminal substituents on the mesophase behaviour of some azo/ester compounds

Six homologous series of 4-(4′-alkoxy phenylazo) phenyl 4″-substituted benzoates (In_a-f) were prepared in which, within each homologous series, the length of the terminal alkoxy chain varies between 6, 8, 10, and 12 carbons, while the other terminal substituent, X, is a polar group that alternatively changed from CH₃O, CH₃, H, Br, NO₂ and CN. Compounds prepared were characterised by spectroscopic methods, and their mesophase behaviour investigated by differential scanning calorimetry (DSC) and polarised optical microscopy (POM). The results were discussed in terms of mesomeric and polarisability effects. In each group of compounds, bearing the same alkoxy substituent, the nematic-to-isotropic transition temperatures (T_C) were successfully correlated with the polarisability anisotropy of bonds to the substituent X. A comparative study was made between the investigated compounds and their previously prepared isomers, namely, 4-(4′-substituted phenylazo) phenyl 4″-alkoxybenzoates (IIn_a-f) in which the two terminal (alkoxy- and X) groups are exchanged.