Synthesis,characterization, and solution behavior of well-defined double hydrophilic linear amphiphilic poly (N-isopropylacrylamide)-b-poly (ε-caprolactone)-b-poly (N-isopropylacrylamide) triblock copolymers

Well-defined linear dihydrophilic amphiphilic ABA-type triblock copolymers of ε-caprolactone (CL) and N-isopropylacrylamide (NIPAAm) have successfully been synthesized with a high yield by combining the ring opening polymerization (ROP) and xanthate-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization methods. The resulted block copolymer shows the formation of micelles in water as supported by light scattering. The critical micelle concentration (cmc) value of the micelle increases with the increase in the chain length of the poly (N-isopropylacrylamide) (PNIPAAm) block. Cloud point of the block copolymers decreases with the decrease in the PNIPAAm chain length. The TGA analysis shows a one-step degradation and a lower thermal stability of the triblock copolymer than the PNIPAAm. The DSC analysis of the triblock copolymer shows the lowering of glass transition temperature (T _g), and melting temperature (T _m) peaks possibly due to the partial miscibility of the poly (ε-caprolactone) (PCL) block with the amorphous PNIPAAm block through the interaction of ester groups of PCL with the amide groups of PNIPAAm. The XRD pattern of the triblock copolymer shows a broad peak due to the suppression of the crystallization of PCL block owing to the mixing of PNIPAAm block with the PCL block.     

C60‐Mediated Molecular Shape Sorting: Separation and Purification of Geometrical Isomers

A supramolecular crystallization‐based approach has been developed for the shape‐dependent separation of geometrical isomers under near‐ambient conditions. Difficulties to separate such isomers arise because of their very similar physical properties. The present approach relies on the ability of C₆₀ to preferentially form solvate crystals with molecules of a specific geometry. Subsequently, these molecules are released upon mild heating to regenerate pure C₆₀. By taking isomers of xylene and trimethylbenzene (TMB) as examples, we show that one of the isomers can be extracted from the rest with very high purity. To separate TMB isomers, a new C₆₀–1,3,5‐TMB solvate was developed, which led to the isolation of isomer purities greater than 99.6 %. Versatility, a low operating temperature of approximately 100 °C, a separation efficiency of more than 10 weight % of C₆₀ per cycle, and reagent recyclability makes this a promising molecular shape‐sorting approach.     

Super reduced Fe4S4 cluster of Balch's dithiolene series

A super reduced Fe(4)S(4) cluster with a sulfur based radical, [NBu(4)](4)[Fe(3)(III)Fe(II)(μ(3)-S)(4)(mnt)(3)(6-)(mnt)(1-)˙](4-)˙, (1) (mnt, maleonitrile dithiolate) which evolves H(2)S gas on treatment with acid under ambient conditions has been synthesized and structurally characterized. The Fe-S distances in 1 are in the range 2.246-2.383 ?, in stark contrast to that of the known n = -2 member of the series based on the [Fe(4)(μ(3)-S)(4)(S(2)C(2)R(2))(4)](n) unit (R = CF(3), Ph) with Fe-S bond lengths of 2.149-2.186 ?. The EPR of 1 displays very weak signals at g, 4.03 and 2.38 along with a strong S-based radical EPR signal at g, 2.003 associated with five structured components tentatively assigned to hyperfine interaction arising out of the naturally abundant (57)Fe with = 88 G. The EPR profile resembles the reduced Fe-S cluster of CO inhibited Clostridium pasteurianum W5 hydrogenase or the Fe(4)S(4) centers of wild-type enzyme, IspH treated with HMBPP or IPP.     

A Zwitterionic Tetrastanna(II) Cyclic Crown

A 12-membered zwitterionic tetrastanna(II) cycle 1 having a crown ether-like topology has been isolated from the deprotonation of 1,1′-methylenediimidazole ( B ) with two equivalents of Sn[N(SiMe₃)₂]₂ ( A ). The solid-state structure and NMR analysis confirms the tetrastanna(II) cycle 1 to be comprised of two stannate(II) and two stannyliumylidene ion pairs in alternating positions of the heterocycle. Computational analysis shows greater nucleophilicity at the proximally located stannate(II) centers. Nonetheless, the tetrastanna(II) cycle 1 remains poorly reactive due to engagement of Sn^II lone pair electrons in intramolecular donor-acceptor interactions. Simple deprotonation reaction between Sn[N(SiMe₃)₂]₂ ( A ) and N-(diisopropylphenyl)imidazole ( C ) in equimolar ratio has led to a stannylene 2 , involving the formation of a Sn−C covalent bond with the anionic imidazol-2-yl carbon center along with the release of NH(SiMe₃)₂. Compound 2 exists as a dimer, where the unsubstituted ring nitrogen atom coordinated intermolecularly to the other stannylene center.     

Thermoelectricity in a Quasiperiodic Lattice Beyond Nearest-Neighbor Electron Hopping

A new route to obtain a large figure of merit (>1) is reported, for the first time, by considering a one-dimensional quasiperiodic lattice where an electron can hop beyond usual nearest-neighbor sites. A finite positional correlation is imposed among the constituent lattice sites, following the well-known Aubry-André-Harper (AAH) form. In the presence of second-neighbor hopping, the AAH lattice exhibits energy dependent mobility edge which plays the central role for efficient energy conversion. Employing a tight-binding framework, all the thermoelectric quantities are computed based on the standard nonequilibrium Green's function formalism. The analysis can be utilized to investigate thermoelectric phenomena in similar kinds of other aperiodic systems possessing higher order electron hopping.