Halogenation of Lewis acid/base stabilised phosphanylboranes

The reaction pattern of the Lewis-acid/base stabilised phosphanylborane [(CO)₅W(H₂PBH₂ · NMe₃)] (1) with elemental halogens is comprehensively studied. The reaction with iodine and bromine leads to a selective halogenation at the tungstencarbonyl moiety under formation of [WX₂(CO)₄(H₂PBH₂ · NMe₃)] (X = I (2), Br (3)). Whereas 2 is a stable product the brominated compound 3 dimerises easily to [WBr₂(CO)₃(H₂PBH₂ · NMe₃)]₂ (4) under lost of CO. The CO elimination reaction of 3 is extensively studied. If 3 is reacted with [Et₄N][Br] the ionic compound [Et₄N][WBr₃(CO)₃(H₂PBH₂ · NMe₃)] (5) is formed. Otherwise, if 3 is combined with the donor ligand [H₂PBH₂ · NMe₃], the complex [WBr₂(CO)₃(H₂PBH₂ · NMe₃)₂] (6) is obtained. Compounds 2–6 are comprehensively characterised by X-ray diffraction analysis, NMR, and IR spectroscopy.     

Substituent effects on the basicity of 3,7-diazabicyclo[3.3.1]nonanes

Basicity constants for a series of 3,7-diazabicyclo[3.3.1]nonane derivatives in acetonitrile with a variation over 13 orders of magnitude have been determined using a spectrophotometric titration technique. An excellent correlation between basicity and calculated proton affinities obtained at PCM-B3LYP/6-31+G(d)//B3LYP/6-31G(d) level was found. The results are discussed in terms of substituent effects and compared to (15)N NMR chemical shifts.     

Kinetic control of the supramolecular chirality of porphyrin J-aggregates

The aggregation of achiral sulfonatophenyl- and phenyl-meso-substituted diprotonated porphyrins to chiral J-aggregates is a hierarchical noncovalent polymerization process preceded by a critical nucleation stage. This allows significant enantiomeric excesses by the formation of a few primary nuclei and the control of their growth by the effect that flows (imperfect mixing) have on the secondary nucleation of the J-aggregate particles. In addition, the results strongly suggest that when only one species of aggregate predominates, the CD signals of the three excitonic bands in the visible region (around 420, 490, and 700 nm) show the same sign. Thus, differences on their relative sign would be due to the presence of different species.     

High Pressure Induced Coil-Globule Transitions of Smart Polymers

Summary: In current work time-resolved optical spectroscopy (TROS) has been used to study coil-globule transitions monitored by the local segmental dynamics of anthracene labeled poly (N-isopropymethacrylamide), PNIPMAM as a function of pressure (0.1 MPa–200 MPa) over a temperature range of 283 K to 333 K. The positions of temperature-induced transition were observed to be independent on molecular weight of polymer at low pressures. The positions of pressure-induced transition were observed to be dependent on molecular weight of polymer at temperatures below LCST at atmospheric pressure. Double globule-coil-globule transition was observed to occur with pressure increasing at temperatures nearly above LCST. All these results along with values of intrinsic viscosity evaluated from values of correlation times measured for globules formed at different pressure/temperature conditions suggest the different mechanisms of compactisation governed by pressure and temperature and, correspondently, the different types of final structures. At low pressures with temperature increasing the compact, well-packed globules are forming via initial interactions between neighboring parts of polymer chain and further collapse. Relatively loosened particles are forming with pressurizing at low temperatures. Interaction between remote along the chain units takes part from the first stage of globule formation. And finally, rather solvated and irregularly twisted particles are forming at high pressure and high temperatures, i.e. at conditions, when both processes are involved.     

Filmbildung aus Emulsionen,II

Ohne ZusammenfassungMitteilung Nr. 50.     

Funktionentheorie und Randwertproblem der Diracschen Differentialgleichungen

Ohne Zusammenfassung     

Beiträge zur allgemeinen Kolloidchemie. II

Ohne Zusammenfassung