Time-resolved C2 swan emission from short-pulse UV fragmentation of CO: evidence for two C2 formation mechanisms

We have studied C₂ Swan (d³Π → a³ Π_u) emission resulting from multiphoton UV excitation of CO. Population of d³Π proceeds through distinct early and late processes, the former giving rise only to normal Swan emission. The late process is responsible for v = 6 enhancement (high-pressure bands), and it dominates time-averaged emission in an bands for ? 10 Torr of CO.     

A (bpy)2Ru-coordinated dehydro[12]annulene with exotopically fused diimine binding sites

Synthesis and electronic properties of a dinuclear (bpy)(2)Ru(II) polypyridyl complex are described in which the bridging ligand consists of two dipyridophenazines fused to a formally antiaromatic dehydro[12]annulene and where the electronic and electrochemical properties of the complex are markedly influenced by the cyclic all-carbon core.     

15N-Traceruntersuchungen zum Mechanismus der N2O-Bildung in Böden

Nitrous oxide is a potential environmental hazard responsible for the green house effect and the destruction of the ozone layer in the lower stratosphere. Biological denitrification under anaerobic conditions in soils results in the formation of both N₂O and N₂, whereby highly nitrogen-fertilized agricultural soils contribute to a considerable extent of the N₂O emission. Latest results in the literature indicate that nitrous oxide can also be formed as a byproduct of the microbial nitrification. This is of importance for soils in central Germany because of the non-existence of typical denitrification conditions in a semiaride climate.

This study was conducted to measure the path of N₂O formation in Haplic Phaeozen: using [¹⁵N] ammonium and [¹⁵N] nitrat and a GC-MS aided incubation system. The kinetic isotope method was used to evaluate the experimental data. The results are:

- Under anaerobic conditions (～ 90% of the water holding capacity = WHC) N₂O originates mainly from the nitrate pool by denitrification.

- As expected, the N₂O formation is low under aerobic conditions (～ 80% WHC) but the gas originates directly from the ammonium and not from the nitrate pool, probably as a byproduct of the nitrification process.     

Self Organization and Redox Behavior of Poly(vinylferrocene)-block-Poly(isobutylene)-block-Poly(vinylferrocene) Triblock Copolymer †

Self organization and redox behavior of a ferrocene containing triblock copolymer, poly(vinylferrocene)-block-poly(isobutylene)-block-poly(vinylferrocene), with narrow molecular weight distribution in solutions and in thin films were investigated. Dynamic light scattering studies of the block copolymer in dilute solutions indicated that the polymer chains aggregated at relatively low concentrations. The aggregations of polymer chains were observed in toluene, as well as in tetrahydrofuran at concentrations as low as 0.014 mg/mL and 0.0045 mg/mL, respectively. Thin films of the copolymer showed reversible single electron redox behavior, similar to that of ferrocene. Morphology and micro-phase separation of the copolymer was analyzed by transmission electron microscopy.     

Polyisobutylene-Based Thermoplastic Elastomers. I. Synthesis and Characterization of Polystyrene-Polyisobutylene-Polystyrene Triblock Copolymers

Abstract

Polystyrene-polyisobutylene-polystyrene triblock copolymer thermoplastic elastomers have been synthesized by living carbocationic sequential copolymerization using the tert-butyl dicumyl chloride/TiCl₄/methylcyclohexane:methyl chloride (60:40 v:v)/ ?80°C system in the presence of the proton trap 2,6-di-tert-butylpyridine. Structure-property relationships have been examined by varying the M_n of the PIB middle block (39,000 to 156,000) and that of the PSt end-segment (1,000 to 19,000). The tensile strength is controlled by the molecular weight of the PSt segment and independent of the PIB middle block length in the studied range. Phase separation starts when the M_n of the PSt segment reaches ～ 5,000, and it is complete when the M_n reaches ～ 15,000. These triblocks exhibited 23-25 MPa tensile strength, similar to that of styrenic thermoplastic elastomers obtained by anionic polymerization.     

Poly(vinyl alcohol)-based Amphiphilic Copolymer Aggregates as Drug Carrying Nanoparticles

A series of amphiphilic polyisobutylene-block-poly(vinyl alcohol) (PIB-b-PVA) copolymers of constant PIB and varying PVA block length was synthesized by living carbocationic polymerization and their solution behavior was studied. The synthesis involved the preparation of polyisobutylene-b-poly(tert.-butyl vinyl ether) followed by hydrolysis with hydrogen bromide. The copolymers were characterized by gel permeation chromatography, ¹H-NMR, and MALDI-TOF MS methods. The micellization behavior of the copolymers was investigated in aqueous media by direct dissolution and dialysis using static and dynamic light scattering. The critical micelle concentration, micelle size, aggregation number, and micelle shape were determined. The ability of the aggregates as drug carrying nanodevices was also investigated by doping them with indomethacin. UV-Vis measurements showed that the solubility of indomethacine increased significantly. Our findings suggest that the solubility is largely dependent upon the block segment ratios.