Structural tuning of ligand-based two-electron intervalence charge transfer

The lowest-energy optical transition of two-electron-oxidized porphyrinogens [L(Delta)M] is a ligand-based charge transfer. The color of the intermediary, two-electron mixed-valent oxidation state shifts from vermilion (lambdamax = 480 nm) to yellow (lambdamax = 270 nm) upon increasing the ionic radius of the central metal dication from Mg2+ to Zn2+ and Ca2+. Structural, spectroscopic, and computational studies establish that the relative energies of the highest occupied and lowest unoccupied orbitals, between which the intervalence charge-transfer optical transition occurs, are modulated by the molecular dipole moment, which in turn depends on the only structural variable among the [L(Delta)M] compounds, the position of M2+ relative to the dianionic dipyrrole unit.     

Characterization of polyalkylvinyl ether phases by solid-state and suspended-state nuclear magnetic resonance investigations

Pure organic polyalkylvinyl ether phases were synthesized by suspension polymerization using different ratios and compositions of n-butylvinyl ether (C₄VE) and n-octadecylvinyl ether (C₁₈VE) with triethylene glycol divinyl ether or divinylbenzene as crosslinkers, respectively. These phases were investigated by means of solid-state ¹³C cross-polarization magic angle spinning nuclear magnetic resonance (NMR) spectroscopy and ¹H high-resolution magic angle spinning (HR MAS) NMR spectroscopy in suspended-state. A comparison of these two methods showed the substantial advantages of ¹H HR MAS NMR measurements. Structure elucidation was achieved using a 2D H,H-COSY NMR experiment performed under MAS conditions enabling full peak assignment of the ¹H NMR spectra of these phases. The dynamic behavior of the polyalkylvinyl ether phases was determined by employing temperature-dependent measurements of spin–lattice relaxation times (T₁) as well as accumulation of a 2D wide line separation NMR spectrum.     

Infrared laser specific reactions of boranes. Conversion of diborane to icosaborane(16), B20H16

Monochromatic low power radiation of a CO₂ laser (1.5 W) initiates in diborane B₂H₆ a chain reaction in the course of which icosaborane(16) B₂₀H₁₆ is formed as the main product. This reaction is accompanied by visible luminescence.     

Metrische Teilebenen hyperbolischer projektiv-metrischer Ebenen

Ohne Zusammenfassung     

Higher-Order Temporal and Spatial Plasma Wave Echoes

The collisionsless Boltzmann equation is solved in two ways by the method of characteristics. The solution is used for an exact treatment of higher-order temporal and spatial plasma wave echoes in the absence of steady external fields. The second-order spatial echo is treated separately and analyzed numerically.     

Self-immobilization of poly(methyloctylsiloxane) on high-performance liquid chromatographic silica

Poly(methyloctylsiloxane) (PMOS) was deposited on HPLC silica by a solvent evaporation procedure and this material was then extracted, using a good solvent for the PMOS, after different time periods, to remove unretained liquid polymer. Solvent extraction data reveal changes which occur at ambient temperature as a function of the time interval between particle loading and extraction. The quantity of PMOS remaining on the silica after extraction, as determined by elemental analysis for carbon, is attributed to strongly adsorbed polymer. This phenomenon is termed self-immobilization. Solid-state 29Si NMR spectra indicate the formation of a silicon species with a different chemical shift than the original PMOS. These new signals are attributed to a combination of different adsorbed and chemically bonded groups.     

Synthesis of aminosaccharide‐derived polymers with urea,urethane, and amide linkages

The synthesis of novel polyurethanes and polyureas based on modified glycosylamines and glucosamines has been successfully accomplished by catalytic polymerizations. Several modified glucosamine monomers were synthesized to study their reactivities during these polymerization reactions. It was found that the anomeric hydroxyl groups are more reactive than the amino groups. The resulting polymers were characterized by NMR and IR spectroscopy, elementary analysis, viscosimetry, and gel permeation chromatography. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2332–2341, 2001