Diversity-oriented synthetic approach to naturally abundant S-amino acid based benzannulated enantiomerically pure medium ring heterocyclic scaffolds employing inter- and intramolecular mitsunobu reactions

The diversity-oriented organic synthesis of enantiomerically pure benzannulated oxazepine, diazepine, thiazepine, oxazocine, and diazocine scaffolds is described from easily accessible naturally occurring S-amino acids as chiral synthons. Inter- and intramolecular Mitsunobu reactions for the formation of carbon-nitrogen, carbon-oxygen, and carbon-sulfur bonds have been used as key transformations to construct these biologically important privileged heterocycles. This is the first example where the Mitsunobu approach has been utilized for the construction of S-amino acid based seven- and eight-membered ring systems.     

Metal-binding effects of sirtuin inhibitor sirtinol

Sirtinol, a Schiff base derived from 2-hydroxy-1-naphthaldehyde, is an inhibitor of sirtuin proteins, a family of deacetylases active in gene regulation and relevant to the study of cancer growth. The formation of copper(II) and zinc(II) complexes of sirtinol is investigated by spectroscopic and structural methods. The molecular structure of this protein inhibitor allows for coordination of first-row transition metals in both tridentate and bidentate fashion. In addition, assays in cultured breast cancer cells reveal that Cu^II(sirtinol?H)₂ and previously reported Fe^III(sirtinol?H)(NO₃)₂ present enhanced cytotoxicity when compared to the free ligand, and that the ferric complex causes an increase in intracellular oxidative stress. Transition metal coordination in the biological milieu could therefore contribute additional effects to the biological profile of sirtinol.     

Kinetic Analysis and Optimization for the Catalytic Esterification Step of PPT Polymerization

Summary: A well‐validated kinetic scheme has been studied for PPT, poly(propylene terephthalate) polymerization process in batch and semi‐batch mode with tetrabutoxytitanium (TBOT), a proven catalyst. Optimization study and analysis for PPT are rare, as the industrial relevance of PPT just became vibrant due to the commercial availability of one of its monomers in industrial scale in the recent past. Correctness of the analysis is checked by a new approach and parameters for the model are estimated from available experimental data. Solubility of terephthalic acid (TPA) is less in reaction medium and this effect is also considered along with the reaction scheme. Several simulations have been performed to see various process dynamics and this ultimately helps in formulating optimization problems. Using recently developed and well tested real‐coded non‐dominated sorting genetic algorithm‐II, a state‐of‐the art evolutionary optimization algorithm, a couple of three objective optimization problems have been solved and corresponding Pareto sets are presented. Results show remarkably promising aspects of productivity enhancement with an improvement in product quality. Sensitivity analysis for relatively uncertain solubility parameter is also performed to estimate its effect over the proposed optimal solutions.

Multiobjective Pareto front for 3 objectives: degree of polymerization, time and (bTPA + bPG).     

Synthesis of new fluorinated 4H-1,4-benzothiazines as possible anticancer agents

A single-step synthesis for ring-fluorinated 4H-1,4-benzothiazines is reported by the condensation and oxidative cyclization of β-diketones with 2-amino-5-fluorobenzenethiol. The reaction is believed to proceed via an enaminoketone system.     

The oblique chiral nematic phase in calamitic bimesogens

ABSTRACT

The discovery of the oblique chiral (or, the twist-bend, N_TB) nematic phase predicted for bent-core mesogens has engendered much interest due to its unique structure and physical properties, and the possibility of use in the next generation of fast electro-optic technology. Bimesogenic calamitic as well as bent-core mesogens are found to form the N_TB phase. Here, we report direct measurements of the temperature dependence of the conical tilt and the evidence of volcano-like orientational distribution of molecules in the N_TB phase. Optical and x-ray scattering investigations of two single-component calamitic bimesogens and their mixtures show that, while the Maier–Saupe orientational distribution function (ODF) is valid for the higher temperature nematic phase, a generalised expansion in terms of even Legendre functions is needed for the N_TB phase. Temperature dependence of the ODFs and the order parameters 〈P₂(cosβ)〉, 〈P₄(cosβ)〉, and 〈P₆(cosβ)〉 has been measured in both phases. The parameters 〈P₂(cosβ)〉 and 〈P₄(cosβ)〉 increase/decrease in the N/N_TB phase with decreasing temperature, while 〈P₆(cosβ)〉 remains vanishingly small for all samples. The value of 〈P₄(cosβ)〉 becomes negative in the N_TB phase confirming a conical distribution of molecules as they follow a helical trajectory keeping the local director tilted at an angle α wrt the macroscopic director. The heliconical tilt calculated from ODFs, exhibits a power law behaviour with temperature, vanishing at the transition to the N phase.     

Effect of nanoclay and barium sulfate nanoparticles on the thermal and morphological properties of polyvinylidene fluoride nanocomposites

The thermal, morphological and optical studies of BaSO₄ and MMT (nanoclay) embedded in PVDF were investigated. Nanocomposites samples of PVDF–BaSO₄–MMT were prepared by varying the loadings (1–4 mass%) in case of BaSO₄ and MMT nanomaterials, respectively. Polyvinylidene fluoride–barium sulfate-montmorillonite (PVDF–BaSO₄–MMT) nanocomposites were prepared by solvent-mixing technique. Nanoparticles were synthesized by in situ deposition technique with the help of nonionic polymeric surfactant, and the particle size of nanoparticles was recognized by scanning electron microscopy (SEM) analysis which confirms that the particle has diameter of 80–90 nm. As prepared, nanocomposites films (thickness, 25 μm) were characterized by Fourier transform infrared microscopy (FTIR), SEM and electron diffraction spectroscopy (EDS). FTIR shows that all the chemical constituents were present in the nanocomposites, whereas SEM analysis suggested that the nanofillers dispersed well in polymer matrix and EDS showed the elemental composition of nanocomposite samples. Thermal properties of nanocomposites were studied by using TG/DTA/DTG. TG/DTA studies showed decomposition temperature of pure PVDF is 473.5 °C. The decomposition temperature (T _d) of nanocomposites was increased by 93 °C in case of nanocomposites with addition of both BaSO₄ and MMT nanomaterials. The difference in the thermal degradation temperature was found to be 1.2% higher in case of addition of BaSO₄ nanoparticle as compared to nanoclay. The obtained transparent nanocomposite films were characterized by using UV–Vis spectrophotometer which shows that transparencies of nanocomposites are maintained in visible region, the intensity of absorption band in UV region is increased with the addition of BaSO₄ nanoparticles, while in case of addition of nanoclay the UV region does not show drastic changes. Addition of both nanoparticle and nanoclay shows higher absorption in comparison with the individual samples. But further, doubling the amount of nanoparticle and nanoclay shows decrease in UV absorption. Overall, the results of thermal studies show that the incorporation of BaSO₄ and MMT could significantly improve the thermal properties of nanocomposites.     

Isochronicity and limit cycle oscillation in chemical systems

Chemical oscillation is an interesting nonlinear dynamical phenomenon which arises due to complex stability condition of the steady state of a reaction far away from equilibrium which is usually characterised by a periodic attractor or a limit cycle around an interior stationary point. In this context Lienard equation is specifically used in the study of nonlinear dynamical properties of an open system which can be utilized to obtain the condition of limit cycle. In conjunction with the property of limit cycle oscillation, here we have shown the condition for isochronicity for different chemical oscillators with the help of renormalisation group method with multiple time scale analysis from a Lienard system. When two variable open system of equations are transformed into a Lienard system of equation the condition for limit cycle and isochronicity can be stated in a unified way. For any such nonlinear oscillator we have shown the route of a dynamical transformation of a limit cycle oscillation to a periodic orbit of centre type depending on the parameters of the system.     

Spatial dependency of the groundwater uranium in the alluvial soil region of Gunnaur,India

Journal of Radioanalytical and Nuclear Chemistry - GIS based groundwater uranium and other physico-chemical parameters pH, electrical conductivity, oxidation reduction potential, temperature,...     

Advancing MXene Electrocatalysts for Energy Conversion Reactions: Surface,Stoichiometry, and Stability

MXenes, due to their tailorable chemistry and favourable physical properties, have great promise in electrocatalytic energy conversion reactions. To exploit fully their enormous potential, further advances specific to electrocatalysis revolving around their performance, stability, compositional discovery and synthesis are required. The most recent advances in these aspects are discussed in detail: surface functional and stoichiometric modifications which can improve performance, Pourbaix stability related to their electrocatalytic operating conditions, density functional theory and advances in machine learning for their discovery, and prospects in large scale synthesis and solution processing techniques to produce membrane electrode assemblies and integrated electrodes. This Review provides a perspective that is complemented by new density functional theory calculations which show how these recent advances in MXene material design are paving the way for effective electrocatalysts required for the transition to integrated renewable energy systems.