Effect of hydrogen-bonded supramolecular assembling on liquid crystal properties of imidazole-containing azomethines and their chelates with copper(II)

A series of imidazole-containing rod-like Schiff's bases and their ionic copper(II) chelates with various lengths of the terminal alkyl chain containing 6, 8, 10, 12, 14 and 16 carbon atoms have been synthesised. The synthesised compounds were characterised by elemental analyses, ¹H NMR, IR and UV–vis and mass spectroscopies. Thermotropic smectic C mesophases in the ligands and smectic A mesophases in the copper(II) complexes were identified using POM, DSC and small-angle XRD scattering methods. X-ray diffraction patterns of the prepared imidazole imines indicate to supramolecular self-assembled structures in the liquid crystal state, which are formed by means of intermolecular hydrogen bonds. It was established that both liquid crystal arrangement and supramolecular assemblies in ligands disappeared near 190°C, mainly regardless of the lengths of the terminal alkyl chains. Contrary, assembling of the copper(II) complexes into supramolecular bilayers occurs near 200°C, which causes their transition to a smectic A mesophase.     

Phase transition behavior of a poly(oxyethylene-b-butylene adipate) ionomer with shape memory properties

A series of biodegradable poly(oxyethylene-b-butylene adipate) ionomers (POBAi) were prepared by two-step in situ polymerization using adipic acid, 1,4-butanediol and mixed monomers of bis(poly(oxyethylene)) sulfonated dimethyl fumarate. The chemical composition of these POBAi was ascertained by ¹H NMR spectroscopy. The objective of this study was to investigate the shape memory effect of POBAi containing ionomer compared to non ionic POBA. It was observed that POBA5.0i showed a good shape memory effect than that of POBA 2.5 mol% or none of ionic group due to much physical cross-linking point by rich ionic group. Stress-induced phase transition was investigated during the shape deformation and recovery process using a wide-angle X-ray diffractometer (WAXD). The POBA crystal phase transition from β- to α-form was observed in all POBA samples by either thermal treatment or physical drawing. The α-form crystal did not recover to the initial β-form during the recovery process because the monoclinic α-form crystal is structurally more stable than the orthorhombic β-form crystal.     

The role of electronic coupling in linear porphyrin arrays probed by single-molecule fluorescence spectroscopy

Single-molecule photophysical properties of two families of linear porphyrin arrays have been investigated by single-molecule fluorescence detection techniques. Butadiyne-linked arrays (Z(N)B) with extensive π-conjugation perform as photostable one-quantum systems. This demonstration has been suggested by the long-lasting initial emissive state and subsequent discrete one-step photobleaching in the fluorescence intensity trajectories (FITs). As in the behavior of a one-quantum system, Z(N)B shows anti-bunching data in the coincidence measurements. On the other hand, in directly-linked arrays (Z(N)) with strong dipole coupling, each porphyrin moiety keeps individual character in photobleaching dynamics. The stepwise photobleachings in the FITs account for this explanation. Most of the FITs of Z(N) do not carry momentary cessation of fluorescence emission, which has been explained by the strongly bound electron-hole pair of Frenkel exciton that suppresses charge transfer between the molecule and surrounding polymers. These results give insight into the influences of interchromophorinc interactions between porphyrin moieties in the multiporphyrin arrays on their fluorescence dynamics at the single-molecule level.     

Kinetic separation of propene and propane in metal-organic frameworks: controlling diffusion rates in plate-shaped crystals via tuning of pore apertures and crystallite aspect ratios

A series of isostructural, noncatenated, zinc-pillared-paddlewheel metal-organic framework materials has been synthesized from 1,2,4,5-tetrakis(carboxyphenyl)benzene and trans-1,2-dipyridylethene struts. Substantial kinetic selectivity in the adsorption of propene over propane can be observed, depending on the pore apertures and the rectangular-plate morphology of the crystals.     

Spin-orbit effects on structures of closed-shell polyatomic molecules containing heavy atoms calculated by two-component Hartree–Fock method

We have implemented geometry optimization using an analytic gradient to a two-component Kramers' restricted Hartree–Fock (KRHF) method for polyatomic molecules with closed-shell configurations. The KRHF method is a Hartree–Fock method based on relativistic effective core potentials with effective spin-orbit operators. The derivatives of spin-orbit integrals are obtained by numerical differentiation. Geometries for the various forms of polyatomic hydrides containing row 6 p-block elements are optimized with and without spin-orbit interactions. The structural changes due to spin-orbit interactions are small, but show definite trends, which correlate well with the p_1/2 spinor population. Atomization energies are reduced significantly by incorporating spin-orbit interactions for all molecules considered. The KRHF calculations of several methylhalides demonstrate that the spinor energies from the KRHF method can be useful for the interpretation of experimental photoelectron spectra of molecules exhibiting spin-orbit splittings. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1526–1533, 1998     

Kramers' unrestricted Hartree–Fock and second-order Møller–Plesset perturbation methods using relativistic effective core potentials with spin–orbit operators: Test calculations for HI and CH3I

The Kramers' restricted Hartree–Fock (KRHF) and second-order Møller–Plesset perturbation (KRMP2) methods using relativistic effective core potentials (RECP) with spin–orbit operators and two-component spinors are extended to the unrestricted forms, KUHF and KUMP2. As in the conventional unrestricted methods, the KUHF and KUMP2 methods are capable of qualitatively describing the bond breaking for a single bond. As a result, it is possible to estimate spin–orbit effects along the dissociation curve at the HF and MP2 levels of theory as is demonstrated by the test calculations on the ground states of HI and CH₃I. Since the energy lowering due to spin–orbit interactions is larger for the I atom than for the closed-shell molecules, dissociation energies are reduced and bond lengths are slightly elongated by the inclusion of the spin–orbit interactions. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66 : 91–98, 1998     

Simultaneous Quantification of Organic Acids in Tamarillo (Solanum betaceum) and Untargeted Chemotyping Using Methyl Chloroformate Derivatisation and GC-MS

Sixteen organic acids were quantified in peel and pulp of Amber, Laird’s Large and Mulligan cultivars of tamarillo using GC-MS. Fourteen of these compounds had not previously been quantified in tamarillo. An untargeted metabolomics approach was used in parallel to identify and quantify 64 more metabolites relative to the internal standard, indicating abundances of glutamic acid, pro-line, aspartic acid and γ-aminobutyric acid as well as lower concentrations of several other essential fatty acids and amino acids. The main findings were that total organic acid concentration was significantly higher (p < 0.05) in pulp than in peel, with the highest concentration seen in Mulligan pulp (219.7 mg/g DW). Remarkably, after citric acid, the potent bactericide itaconic acid was the second most abundant organic acid. At least 95% of organic acids in tamarillo were one of these two acids, as well as cis-aconitic, malic and 4-toluic acids. Differences between cultivar chemotypes were as substantial as differences between tissues. These results suggest that the bitter flavour of the peel does not result from organic acids. The combination of targeted and untargeted metabolomics techniques for simultaneous qualitative and quantitative investigation of nutrients and flavours is efficient and informative.     

Cytotoxic dammarane glycosides from processed ginseng

Steaming ginseng at high temperature increased its cytotoxicity to SK-Hep-1 hepatoma cancer cells. HPLC separation and fractionation followed by MTT assay revealed that ginsenosides Rg3, Rg5, Rk1, Rs5, and Rs4 are the active principles. Their 50% growth inhibition concentration (GI50) values were 41, 11, 13, 37, and 13 microM, respectively. Cisplatin had a GI50 of 84 microM in the same assay conditions.