Optical and X-ray studies of a four component cyano liquid crystal mixture: Comparison of properties with that of a similar mixture

Optical and X-ray studies have been conducted on a four component liquid crystal mixture (code name 2013) with cyano–end groups in all the four components and a lateral substitution of fluorine atom in one of them. The variations in the optical birefringence with temperature, have been investigated and the thermal dependence of polarisability anisotropy and orientational order parameter have been evaluated. X-ray studies have been conducted to determine the effective molecular characteristics such as apparent molecular length and inter molecular distance and their variations with temperature. From nature of molecular alignment as envisaged from X-ray photographs the order parameter variation with temperature has been determined and compared with macroscopic order parameter variation as determined from birefringence studies. The results have been compared with these obtained for another structurally similar four-component liquid crystal mixture (code name 2014) with isothiocyanato end group in place of cyano.     

Aqueous medium effects on multi-component reactions

The effect of aqueous media on many organic reactions has been studied, and often those reactions exhibiting pressure acceleration are also accelerated in water. Because some specific examples of the Ugi and Passerini reactions that are inefficient under conventional conditions have been accelerated by pressure, we examined Ugi and Passerini reactions in aqueous solutions, where significant increases in efficiency were observed. These effects were correlated to the cohesive energy density of aqueous solutions.     

Dielectric relaxation phenomena of rigid polar liquid molecules under giga hertz electric field

The dielectric relaxation phenomena of rigid polar liquid molecules chloral and ethyltrichloroacetate (j) in benzene, n-hexane and n-heptane (i) under 4.2, 9.8 and 24.6 GHz electric fields at 30°C are studied to show the possible existence of double relaxation times τ ₂ and τ ₁ for rotations of the whole and the flexible parts of molecules. The probability of showing double relaxation is more in aliphatic solvents indicating their nonrigidity. The symmetric and asymmetric distribution parameters γ and δ are obtained from X _ij ^′ /X _0ij and X _ij ^″ /X _0ij and w _j →0 where X _ij ^′ and X _ij ^″ are real and imaginary parts of the complex orientational susceptibility X _i ^* and X _0ij is the low frequency susceptibility which is real. X _ij ’s are involved with the measured dielectric relative permittivities ε _ij ^′ , ε _in ^″ , ε _0ij and ε _∞ij of solutions. The theoretical weighted contributions c ₁ and c ₂ towards dielectric dispersions by Fröhlich’s method are compared with the experimental ones obtained from the graphical variation of X _ij ^′ /X _0ij and X _ij ^″ /X _0ij with weight fractions w _j ’s at w _j → 0. The measured dipole moments μ ₂ and μ ₁ of the whole and the flexible part of a polar molecule in terms of the linear coefficients β’s of X _ij ^′ ’s with w _j ’s and the estimated τ ₂ and τ ₁ reveal their associations with aliphatic solvents. The theoretical dipole moments μ _theo’s from the available bond angles and bond moments of the substituent polar groups of the molecules with the estimated μ’s suggest the mesomeric, inductive and electromeric effects in them under GHz electric field.     

Multicomponent reactions are accelerated in water

Two multicomponent reactions, the Ugi and Passerini reactions, are accelerated by the use of aqueous solutions. The rate enhancements compared to those by organic solvents can approach 300-fold. Reactions performed in water offer another advantage that products are often insoluble, permitting direct isolation by precipitation. The methods were applied to the preparation of three small combinatorial libraries.     

Scale invariance and superfluid turbulence

We construct a Schroedinger field theory invariant under local spatial scaling. It is shown to provide an effective theory of superfluid turbulence by deriving, analytically, the observed Kolmogorov 5/3 law and to lead to a Biot–Savart interaction between the observed filament excitations of the system as well.     

Postsynthetic Exterior Decoration of an Organic Cage by Copper(I)‐Catalysed A3‐Coupling and Detection of Nitroaromatics

A new synthetic protocol based on one‐pot, copper(I)‐catalysed multicomponent reaction of formaldehyde, secondary amine and terminal alkyne has been employed to postsynthetically modify a self‐assembled nanoscopic organic cage. By employing this synthetic strategy, three new cages appended with phenyl‐, xylyl‐ and naphthyl‐acetylene moieties have been synthesised. The resulting modified cages were characterised by using a range of spectroscopic techniques. The synthesised cages were fluorescent and thus one of them was tested to explore the potential use of such compounds as chemosensors for the detection of nitroaromatics. Experimental findings suggest a high selective quenching of initial fluorescence intensity in the presence of nitroaromatic compounds. Furthermore, it has been observed that among the various nitroaromatics tested, nitrophenolic compounds have better quenching ability.     

Efforts toward the total synthesis of a jatrophane diterpene

A significant effort toward the model study of jatrophane skeleton has been made. To synthesize an important synthon, Horner–Emmons–Wadsworth olefination was attempted.     

Synthesis of the Upstream Terminal Disaccharide of the O-Antigenic Polysaccharide of Vibrio cholerae O37

The terminal disaccharide of the O-antigenic polysaccharide of Vibrio cholerae O37, 4-O-methyl-α-D-QuiNAc-(1→4)-α-d-QuiNAc, was synthesized as methyl glycoside involving glycosylation between glycosyl donor ethyl 2-azido-3-O-benzyl-2,6-dideoxy-4-O-methyl-6-iodo-1-thio-α-d-glucopyranoside and glycosyl acceptor methyl 2-azido-3-O-benzyl-2,6-dideoxy-6-iodo-α-d-glucopyranoside. Dehalogenation, global deprotection, and reduction of the azide to amine were effected in one step by catalytic hydrogenation. It was followed by selective N-acetylation to give the desired deprotected disaccharide.     

Desynchronization bifurcation of coupled nonlinear dynamical systems

We analyze the desynchronization bifurcation in the coupled Ro?ssler oscillators. After the bifurcation the coupled oscillators move away from each other with a square root dependence on the parameter. We define system transverse Lyapunov exponents (STLE), and in the desynchronized state one is positive while the other is negative. We give a simple model of coupled integrable systems with quadratic nonlinearity that shows a similar phenomenon. We conclude that desynchronization is a pitchfork bifurcation of the transverse manifold. Cubic nonlinearity also shows the bifurcation, but in this case the STLEs are both negative.     

Intrinsically Low Thermal Conductivity and High Carrier Mobility in Dual Topological Quantum Material,n‐Type BiTe

A challenge in thermoelectrics is to achieve intrinsically low thermal conductivity in crystalline solids while maintaining a high carrier mobility (μ). Topological quantum materials, such as the topological insulator (TI) or topological crystalline insulator (TCI) can exhibit high μ. Weak topological insulators (WTI) are of interest because of their layered hetero‐structural nature which has a low lattice thermal conductivity (κ_lat). BiTe, a unique member of the (Bi₂)_m(Bi₂Te₃)_n homologous series (m:n=1:2), has both the quantum states, TCI and WTI, which is distinct from the conventional strong TI, Bi₂Te₃ (where m:n=0:1). Herein, we report intrinsically low κ_lat of 0.47–0.8 W m^?1 K^?1 in the 300–650 K range in BiTe resulting from low energy optical phonon branches which originate primarily from the localized vibrations of Bi bilayer. It has high μ≈516 cm² V^?1 s^?1 and 707 cm² V^?1 s^?1 along parallel and perpendicular to the spark plasma sintering (SPS) directions, respectively, at room temperature.