In situ Raman and UV-vis spectroscopic studies of polypyrrole and poly(pyrrole-2,6-dimethyl-β-cyclodextrin)

Polypyrrole (PPy) and poly(pyrrole-2,6-dimethyl-β-cyclodextrin) [P(Py-β-DMCD)] films prepared by potential cycling in aqueous acidic solutions on indium tin oxide (ITO)-coated glass and gold electrodes were studied by in situ UV-vis and Raman spectroscopy. Characteristic UV-vis and Raman bands were identified and their dependencies on the electrode potential have been discussed. Spectroelectrochemical results reveal differences both in the position of the spectral bands and their potential dependence for PPy and P(Py-β-DMCD) films indicating interactions between polymer chains and CDs during electropolymerization process. The films were also characterized by cyclic voltammetry and FT-IR spectroscopy.     

Secondary Metabolites from the Fruiting Bodies of Coriolopsis aspera in Vietnam and their Bioactivities

Chemistry of Natural Compounds -     

Anticyanobacterial phenolic constituents from the aerial parts of Eupatorium fortunei Turcz

Four thymol derivatives and two phenolic compounds were isolated from the aerial parts of Eupatorium fortunei. The new structures were elucidated to be 7,8,9-trihydroxythymol (1), and 8,10-didehydro-7,9-dihydroxythymol (2) by means of MS and NMR analysis. The known compounds were identified as 8,9,10-trihydroxythymol (3), 10-acetoxy-8,9-dihydroxythymol (4), o-coumaric acid (5) and 4-(2-hydroxyethyl)benzaldehyde (6). Compound 3 showed strongest inhibitory effect on the growth of Microcystis aeruginosa in comparison with CuSO₄.     

Fabrication of Nano Flower‐shaped Platinum on Glassy Carbon Electrode as a Sensitive Sensor for Lead Electrochemical Analysis

Platinum nanoflowers modified glassy carbon electrodes (PtNFs/GCE) was fabricated simply for lead determination in water samples. The modified electrodes were prepared by electrodeposition in hexachloroplatinic acid solution at constant potential. The influence of deposition time and potential on surface morphology, chemical composition, electrochemical properties of electrode were investigated. At ?0.2 V of potential and 150 s of deposition duration, platinum developed as nanoflower shape and scattered densely all over the glassy carbon surface, producing the largest electrochemically active surface areas. The highest differential pulse stripping voltammetry (DPSV) signal of lead was obtained by using the prepared electrode. Under optimized experimental condition of electrolyte, accumulation potential and time, the peak current was found to be linear proportion to lead concentration in range of 1 to 100 μg L^?1 (slope=0.371) with a limit of detection of 0.398 μg L^?1. The method has good repeatability and reproducibility with relative standard deviations of 1.47 % and 4.83 %, respectively. The modified PtNFs/GCE also demonstrated an excellent long‐term stability with only 9 % decrease in Pb peak current over 30 days. Moreover, the performance of the modified PtNFs/GCE in determination of Pb(II) in two industrial wastewaters was good agreement with data obtained by a graphite furnace atomic absorption spectrometry (GFAAS) method.     

Photoelectron spectroscopy and theoretical studies of UF5(-) and UF6(-)

The UF(5)(-) and UF(6)(-) anions are produced using electrospray ionization and investigated by photoelectron spectroscopy and relativistic quantum chemistry. An extensive vibrational progression is observed in the spectra of UF(5)(-), indicating significant geometry changes between the anion and neutral ground state. Franck-Condon factor simulations of the observed vibrational progression yield an adiabatic electron detachment energy of 3.82 ± 0.05 eV for UF(5)(-). Relativistic quantum calculations using density functional and ab initio theories are performed on UF(5)(-) and UF(6)(-) and their neutrals. The ground states of UF(5)(-) and UF(5) are found to have C(4v) symmetry, but with a large U-F bond length change. The ground state of UF(5)(-) is a triplet state ((3)B(2)) with the two 5f electrons occupying a 5f(z3)-based 8a(1) highest occupied molecular orbital (HOMO) and the 5f(xyz)-based 2b(2) HOMO-1 orbital. The detachment cross section from the 5f(xyz) orbital is observed to be extremely small and the detachment transition from the 2b(2) orbital is more than ten times weaker than that from the 8a(1) orbital at the photon energies available. The UF(6)(-) anion is found to be octahedral, similar to neutral UF(6) with the extra electron occupying the 5f(xyz)-based a(2u) orbital. Surprisingly, no photoelectron spectrum could be observed for UF(6)(-) due to the extremely low detachment cross section from the 5f(xyz)-based HOMO of UF(6)(-).     

Functional group effects on metal-organic framework topology

Functionalization of the ligand 1,3,5-tris(4-carboxyphenyl)benzene (H(3)BTB) has been realized with methoxy (H(3)BTB-[OMe](3)) and hydroxy (H(3)BTB-[OH](3)) groups. Combining H(3)BTB-[OMe](3) and Zn(ii) results in the formation of the first isostructural, functionalized analogue of MOF-177 (MOF-177-OMe), while the combination of H(3)BTB-[OH](3) and Zn(ii) generates a rare, interpenetrated pcu-e framework.     

Photocrosslinking of functionalized rubber. II. Photoinitiated cationic polymerization of epoxidized liquid natural rubber

Low molecular weight epoxidized natural rubber has been crosslinked within seconds by UV irradiation in the presence of a triarylsulfonium salt. The photoinitiated cationic ring-opening polymerization was studied quantitatively by infrared spectroscopy and shown to proceed with surprisingly long kinetic chains in such solid medium. The high conversion (60%) needed for complete insolubilization, together with the presence of tetrahydrofuran structures, argue in favor of an intramolecular polymerization process involving neighboring epoxy groups. The photoinitiator concentration has a strong influence on the rate and extent of the reaction, as well as on the depth of cure profile. Because of an efficient dark process, close to 100% conversion was reached upon storage of the irradiated elastomer at ambient, with a concomitant increase of the gel fraction and the polymer hardness. The grafting of pendent acrylate groups onto the polymer chain leads to a three-fold decrease of the initial rate of polymerization of the epoxide. The photocuring of natural rubber bearing both epoxy and acrylate groups generates a dual polymer network which combines the properties of the two moieties. © 1995 John Wiley & Sons, Inc.