Synthesis of multi‐substituted dibenzo[b,d]furan

The synthesis of multi‐substituted dibenzo[b,d]furan derivatives 7a‐b and 11a‐b from readily available starting materials is described. These compounds are important intermediates for synthesis of molecules having wide therapeutic applications.     

Achiral bent-core salicylaldimine compounds exhibiting dark conglomerate and B2 mesophases: effect of linkage groups and lateral substituents

Four new series of achiral bent-core compounds and two biphenyl derivatives of them have been synthesised and their mesomorphic properties are studied. These mesogens are salicylaldimine derivatives, designed with an aim to study the effect of salicylaldimine group and lateral substituents, viz., ?F and ?Cl at different locations of the molecular structure, on the mesomorphic properties. The newly synthesised compounds are characterised using organic spectroscopy and elemental analysis (EA). The liquid crystalline properties of these compounds are studied using polarising optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical studies. They are found to exhibit dark conglomerate (DC) and B₂ mesophases. The DC phases are of sponge and HNC type, and the B₂ is SmC_aP_A in nature. The compounds, wherein the salicylaldimine group is present at the centre of the bent-core, mainly exhibit DC mesophases and when this group is present in one of the wings of the bent-core molecule, the compounds tend to show only a B₂ mesophase, irrespective of the nature of lateral substituents. Many of the DC liquid crystals synthesised here retained the chirality even in their crystalline states which are confirmed by the circular dichroism spectroscopic studies.     

Palladium based heterogeneous catalyst by evaporation-induced self-assembly: use of biopolymer as a surface functionalizing and reducing agent

Palladium-based composites are widely used as a heterogeneous catalyst in carbon–carbon coupling reactions and in catalytic converters used in the car industry. In this work, we demonstrate a simple, green and scalable synthesis procedure to obtain palladium (Pd) based heterogeneous catalyst. Surface functionalized silica microparticles were obtained in one-step by spray-drying a colloidal suspension of silica nanoparticles and gum arabic, an environmental-friendly biopolymer. Subsequently, palladium nanoparticles were reduced and attached to the substrate by gum arabic. The as-synthesized composite was characterized by field-emission scanning electron microscopy (FESEM), energy-dispersive x-ray spectroscopy (EDS), x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), small angle x-ray scattering (SAXS), and high-resolution transmission electron microscopy (HR-TEM). The Pd@SiO₂ composite was used as a catalyst in the reduction reaction of 4-nitrophenol by sodium borohydride. The catalyst showed good recycling properties. The present environmental-friendly approach for fabrication of Pd-based heterogeneous catalyst circumvents various complex chemical steps involved in conventional chemical methods and could be generalized for the production of ceramic or magnetite-based Pd composites.     

A simplified eigenvector-following technique for locating transition points in an energy landscape

We derive an eigenvector-following technique for locating transition points in an N-dimensional energy landscape. A separate Lagrange multiplier is used for each eigendirection to provide maximum flexibility in determining step sizes. In contrast to previous techniques based on a similar approach, we provide a simple algorithm for choosing specific values of these Lagrange multipliers. We demonstrate the robustness of the algorithm using two-dimensional Cerjan-Miller and Adams landscapes. The technique has also been applied to the S(12) molecular cluster.     

Dynamic microscopic basis for IBM-2: A new approach

A dynamic approach, based on deformed Hartree-Fock solution of a nucleus, is suggested for obtaining correlated identical nucleon pair wave function for neutrons and protons. Expressions for single pair energies and two pair interaction matrix elements amongst the neutron and proton pairs in the microscopic fermion basis are presented. These matrix elements define the IBM-2 Hamiltonian through Marumori mapping. The entire procedure is illustrated by obtaining the IBM-2 spectra of²⁰Ne,⁴⁴Ti,⁶⁰Zn and⁹⁴Mo and comparing them with shell model (SM) and/or experimental results. The Yrast levels given by our calculations match well with those of the SM and the experimental results for all the four nuclei, while the non-Yrast levels do not barring the case of⁹⁴Mo. This is due to the loss of isospin symmetry for light nuclei in IBM-2. These results are discussed in detail.     

Revealing the Nano‐Level Molecular Packing in Chitosan–NiO Nanocomposite by Using Positron Annihilation Spectroscopy and Small‐Angle X‐ray Scattering

Chitosan–NiO nanocomposite (CNC) is shown to be a potential dielectric material with promising properties. CNCs containing NiO nanoparticles (0.2, 0.6, 1, 2, 5 wt %) are prepared through chemical methods. The inclusion of NiO nanoparticles in the chitosan matrix is confirmed by scanning electron microscopy (SEM) and X‐ray diffraction. The morphology of the NiO nanoparticles and the nanocomposites is investigated by transmission electron microscopy and SEM, respectively. Positron annihilation lifetime spectroscopy (PALS) and the coincidence Doppler broadening (CDB) technique are used to quantify the free volume and molecular packing in the nanocomposites. The triplet‐state positronium lifetime and the corresponding intensity show the changes in nanohole size, density, and size distribution as a function of NiO loading. Small‐angle X‐ray scattering indicates that the NiO aggregates are identical in all the CNCs. The momentum density distribution obtained from CDB measurements excludes the possibility of a contribution of vacant spaces (pores) available in NiO aggregates to the free volume of nanocomposites upon determination by using PALS. The results show systematic variation in free‐volume properties and nano‐level molecular packing as a function of NiO loading, which is presumed to play a vital role in determining the various properties of the nanocomposites.     

The origin of DC electrical conduction and dielectric relaxation in pristine and doped poly(3‐hexylthiophene) films

We present here the evidence for the origin of dc electrical conduction and dielectric relaxation in pristine and doped poly(3‐hexylthiophene) (P3HT) films. P3HT has been synthesized and purified to obtain pristine P3HT polymer films. P3HT films are chemically doped to make conducting P3HT films with different conductivity level. Temperature (77–350 K) dependent dc conductivity (σ_dc) and dielectric constant (ε′(ω)) measurements on pristine and doped P3HT films have been conducted to evaluate dc and ac electrical conduction parameters. The relaxation frequency (f_R) and static dielectric constant (ε₀) have been estimated from dielectric constant measurements. A correlation between dc electrical conduction and dielectric relaxation data indicates that both dc and ac electrical conductions originate from the same hopping process in this system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1047–1053, 2010     

A convenient one-pot synthesis of trisubstituted 1,3,5-triazines through intermediary amidinothioureas

A thiophile-promoted one-pot synthesis of trisubstituted 1,3,5-triazines starting from isothiocyanates, N,N-diethylamidines, and carbamidines has been studied. The reaction proceeds through the formation of intermediary amidinothioureas, which react with carbamidines in the presence of mercury(II) chloride to generate the desired 1,3,5-triazines in good to moderate yields (40-70%).     

Regioselective aminoethylation of 1,4-benzodiazepin-2-one under conventional heating and microwave irradiation

The regioselective aminoethylation of 1,4-benzodiazepin-2-one 1 can be carried out using classical heating or microwave irradiation as the source of energy to furnish either N-1 or N-4 aminoethylated products 2a-d and 3a-d, respectively. The regioselectivity observed has been rationalized using computational studies and has been traced to the disparity of the rate-determining steps along the N-1 product (N-1 PR) and N-4 product (N-4 PR) formation pathways.     

Effects of axial coordination on the Ru-Ru single bond in diruthenium paddlewheel complexes

The 1,8-naphthyridine-based (NP-based) ligands with furyl, thiazolyl, pyridyl, and pyrrolyl attachments at the 2-position have been synthesized. Reactions of 3-MeNP (3-methyl-1,8-naphthyridine), fuNP (2-(2-furyl)-1,8-naphthyridine), tzNP (2-(2-thiazolyl)-1,8-naphthyridine), pyNP (2-(2-pyridyl)-1,8-naphthyridine), and prNP(-1) (2-(2-pyrrolyl)-1,8-naphthyridine) with [Ru2(CO)4(CH3CN)6]2+ lead to [Ru2(3-MeNP)2(CO)4(OTf)2] (1), [Ru2(fuNP)2(CO)4]2[BF4]2 (2), [Ru2(tzNP)2(CO)4][ClO4]2 (3), [Ru2(pyNP)2(CO)4][OTf]2 (4), and [Ru2(prNP)2(CO)4] (5). The molecular structures of complexes 1-5 have been established by X-ray crystallographic studies. The modulation of the Ru-Ru single-bond distances with axial donors triflates, furyls, thiazolyls, pyridyls, and pyrrolyls has been examined. A small and gradual increase in the Ru-Ru distance is measured with various donors of increasing strengths. The shortest Ru-Ru distance of 2.6071(9) angstroms is observed for the axially coordinated triflates in complex 1, and the longest Ru-Ru distance of 2.6969(10) angstroms is measured for axial pyrrolyls in complex 5. The Ru-Ru distances in complexes 3 (2.6734(7) angstroms) and 4 (2.6792(9) angstroms), having thiazolyls and pyridyls at axial sites respectively, are similar. The Ru-Ru distance for axial furyls in complex 2 (2.6261(9) angstroms) is significantly shorter than the corresponding distances in 3, 4, and 5. DFT calculations provide insight into the interaction of the Ru-Ru sigma orbital with axial donors. The Ru-Ru sigma orbital is elevated to a higher energy because of the interaction with axial lone pairs. The degree of destabilization depends on the nature of axial ligands: the stronger the ligand, higher the elevation of Ru-Ru orbital. The lengthening of Ru-Ru distances with respect to the axial donors in compounds 1-5 follows along the direction pyrrolyl > pyridyl approximately thiazolyl > furyl > triflate, and the trend correlates well with the computed destabilization of the Ru-Ru sigma orbitals.