Synthesis,crystal structures and luminescent properties of phenylmercury(II) complexes with thiohydrazone ligands having weak Hg····π and Hg····Hg interactions

The Reaction of phenylmercury(II) acetate with salicylaldehyde morpholine N-thiohydrazone (H₂smth) and 2-hydroxyacetophenone morpholine N-thiohydrazone (H₂apmth) in dry ethanol under gentle refluxing condition form light yellow complexes [PhHg(Hsmth)] (1) and [PhHg(Hapmth)] (2) involving formation of Hg-S bond from the thiol form of the ligands after deprotonation of the SH proton. The structures of the complexes as determined by X-ray crystallography shows that the complex (1) has a distorted T-shaped geometry while the complex (2) adopts familiar linear coordination geometry. Complex (2) has two independent molecules comprising the asymmetric unit. Both the complexes form two-dimensional supramolecular assemblies due to a combination of weak intermolecular Hg····π and Hg····Hg interactions. The Hg····π and Hg····Hg distances are 3.937 and 4.0216(10) Å, respectively, possibly indicating weak mercuriophilic interactions. The luminescent properties of the complexes in solution and in the solid state at room temperature are also described.     

Controlling the optical bistability and multistability in a two-level pumped-probe system

We study the behavior of the optical bistability (OB) and multistability (OM) in a two-level pumped-probe atomic system by means of a unidirectional ring cavity. We show that the optical bistability in a two-level atomic system can be controlled by adjusting the intensity of the pump field and the detuning between two fields. We find that applying the pumping field decreases the threshold of the optical bistability.     

Synthesis,characterization and impedance spectroscopy of the new material [(CH3) (C6H5) 3P] 2CoBr4: a member of the A2BX4 family

The crystal structure of bis‐(methyltriphenylphosphonium) tetrabromocobaltate (II), [(C₁₉H₁₈P)₂ CoBr₄] is determined: M_r = 933.203, monoclinic, P2₁, a = 9. 6977 (3) Å, b = 12.5547 (4)Å, c = 16.4503 (6)Å, β = 105.603 (2)°, V = 1929.04 (11)ų, Z = 2, D_x = 1.607 Mg m^‐3, T = 298 K. Differential thermal analysis at high temperatures shows three endothermic peaks characterizing four phases, with onset temperatures at T₁= 313±2 K, T₂ = 320±4 K and T₃= 360±1 K. The structural instability detected via the temperature dependence of permittivity at T₁ is ascribed to order‐disorder transition associated with cation dipole reorientation. Permittivity and ac conductivity studies as a function of temperature (295 K‐375 K) and frequency (0.11 kHz < f <100 kHz) are presented. The results indicate the importance of the cation size and shape on the phase transitions in the system. Bulk conductivity behavior is thermally activated. The associated activation energies are in the range 2.9 to 1.0 eV depending on the temperature regime. Two contributions to the ac conductivity, one dominating at low temperatures and high frequencies which are characterized by superlinear frequency exponent and the second dominates at high temperatures characterized by a sublinear frequency exponent. The behavior is interpreted in terms of the jump relaxation model. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A facile synthesis of stable phosphorus ylides derived from 3,6‐dibromocarbazole and kinetic investigation of the reactions by UV spectrophotometry technique

Stable crystalline phosphorus ylides were obtained in excellent yields from the 1:1:1 addition reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, in the presence of NH‐acid, such as 3,6‐dibromocarbazole. These stable ylides exist in solution as a mixture of two geometrical isomers as a result of restricted rotation around the carbon–carbon partial double bond, resulting from the conjugation of the ylide moiety with the adjacent carbonyl group. To determine the kinetic parameters of the reactions, they were monitored by UV spectrophotometry. The second‐order fits were drawn, and the values of the second‐order rate constant (k₂) were calculated using standard equations within the program. At the temperature range studied, the dependence of the second‐order rate constant (ln k₂) on reciprocal temperature was in a good agreement with the Arrhenius equation. This provided the relevant plots to calculate the activation energy of all reactions. Furthermore, useful information was obtained from studies of the effect of solvent, structure of reactants (different alkyl groups within the dialkyl acetylenedicarboxylates), and also the concentration of reactants on the rate of reactions. The proposed mechanism was confirmed according to the obtained results and a steady‐state approximation and the first step (k₂) of reaction was recognized as a rate‐determining step on the basis of the experimental data. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:723–732, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20501     

Addressing difficulties in using XRD intensity for structural study of thin films

The problem of structure investigation of thin films using laboratory XRD diffraction intensities was discussed as a matter of debate. Is the variation in relative intensities of the diffraction patterns due to crystallographic preferred orientation, lattice defects or both? The answer to this question shows a discrepancy in the literatures. The present work is an attempt to propose a possible approach to judge the most probable answer. Thin films of SnO₂ were prepared by spray pyrolysis technique using solution of different SnCl₂ concentrations (molarity); at fixed substrate temperature and deposition time. The theoretically calculated integrated intensities together with the experimentally obtained and calculated XRD data (relative intensities, texture coefficients and profile analysis) were considered together in order to get the proper picture of the structure characteristics of the prepared films. The complete picture can be assembled by integration and correlation of all the crystallographic information that are extracted from the diffraction pattern including not only the observed intensities but also the size/strain analysis and lattice parameters. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Charge Transport through Self‐Assembled Monolayers of Monoterpenoids

The nature of the processes at the origin of life that selected specific classes of molecules for broad incorporation into cells is controversial. Among those classes selected were polyisoprenoids and their derivatives. This paper tests the hypothesis that polyisoprenoids were early contributors to membranes in part because they (or their derivatives) could facilitate charge transport by quantum tunneling. It measures charge transport across self‐assembled monolayers (SAMs) of carboxyl‐terminated monoterpenoids (O₂C(C₉HX)) and alkanoates (O₂C(C₇HX)) with different degrees of unsaturation, supported on silver (Ag^TS) bottom electrodes, with Ga₂O₃/EGaIn top electrodes. Measurements of current density of SAMs of linear length‐matched hydrocarbons—both saturated and unsaturated—show that completely unsaturated molecules transport charge faster than those that are completely saturated by approximately a factor of ten. This increase in relative rates of charge transport correlates with the number of carbon–carbon double bonds, but not with the extent of conjugation. These results suggest that polyisoprenoids—even fully unsaturated—are not sufficiently good tunneling conductors for their conductivity to have favored them as building blocks in the prebiotic world.     

Kinetics and related studies of the formation of 2,3‐dihydroquinazolin‐4(1H)‐ones in the presence of different benzaldehyde derivatives

The kinetics and activation parameters for the reaction between 2‐amino‐benzamide and some benzaldehyde derivatives in the presence of formic acid have been reported and discussed. A linear plot of lnk vs l/T showed that the reactions obey the Arrhenius equation. Both the Arrhenius and the Eyring equations were used to calculate the activation energy. The effect of nitro groups was studied on different positions of benzaldehyde. For all substituents, the reactions followed second‐order kinetics, and the partial orders of reactions were recognized with respect to each reactant. Comparisons between the magnitudes of ΔH^? and TΔS^?showed that the reactions were enthalpy controlled. The validity of the isokinetic relationship and the compensation effect was tested, and the isokinetic temperature (β) was obtained. A linear enthalpy‐entropy plot (ΔH^?versusΔS^?) showed that the compensation effect is established, and this process occurs via a same mechanism across a series of reactions. From the Van't Hoff and Exner's plots, the isokinetic temperature was obtained.     

Postsphaleron baryogenesis

We present a new mechanism for generating the baryon asymmetry of the Universe directly in the decay of a singlet scalar field S(r) with a weak scale mass and a high dimensional baryon number-violating coupling. Unlike most currently popular models, this mechanism, which becomes effective after the electroweak phase transition, does not rely on the sphalerons for inducing a nonzero baryon number. CP asymmetry in S(r) decay arises through loop diagrams involving the exchange of W+/- gauge bosons and is suppressed by light quark masses, leading naturally to a value of eta(B) approximately 10(-10). The simplest realization of this idea which uses a six quark DeltaB=2 operator predicts colored scalars accessible to the CERN Large Hadron Collider and neutron-antineutron oscillation within reach of the next-generation experiments.     

Electrospun electroactive nanofibers of gelatin‐oligoaniline/Poly (vinyl alcohol) templates for architecting of cardiac tissue with on‐demand drug release

In this study, grafted gelatin with oligoaniline (GelOA) was synthesized and then mixed with Poly (vinyl alcohol) (PVA). Several scaffolds with different ratio of PVA/GelOA were electrospun to fabricate electroactive scaffolds. GelOA was characterized using Fourier‐transform infrared spectroscopy (FTIR); moreover, nanofiber properties were evaluated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscope (SEM) analyses. Nanofibers diameter was decreased with aniline oligomer increment form 300 to 150 nm because of the hydrophobic nature of the aniline oligomer. Aniline oligomer electroactivity was studied using cyclic voltammetry, which exhibited two redox peaks at 0.4 and 0.6. Moreover, aniline oligomer enhancement resulted in melting point increasing from 220°C to 230°C because of the crystallinity increment. To assess the biocompatibility of nanofibers, cell viability and cell adhesion were tracked using mesenchymal stem cell (MSCs). It was revealed that the presence of aniline oligomer leads to enhancing the conductivity, thermal properties and lowering the degradation rate and drug release. Among of different scaffolds, sample with high content of GelOA shows better behavior in physical and biological properties. Accumulative drug releases under applied electrical field at 40 minutes showed that the drug release for stimulated condition is about 33% more than the unapplied electrical field one.     

N-Propylsulfamic acid supported onto magnetic Fe3O4 nanoparticles (MNPs-PSA) as a green and reusable heterogeneous nanocatalyst for the chemoselective preparation and deprotection of acylals

Research on Chemical Intermediates - N-propylsulfamic acid supported onto magnetic Fe3O4 nanoparticles (MNPs-PSA) was simply synthesized and used as a highly efficient, environmentally friendly,...