A ROLE FOR STEROLS IN THE PORPHYRIN MEDIATED PHOTOSENSITIZATION OF YEAST

The yeast Saccharomyces cerevisiae was used as a model system to determine the role of sterols in the porphyrin mediated photosensitization of yeast. A sterol auxotroph, RD5-R, was grown on sterols with different levels of unsaturation and assayed for photosensitivity in the presence of either protoporphyrin IX or hematoporphyrin (both at 100 micrograms/ml). Cells grown on the completely saturated sterol (stanol), cholestanol, were substantially more resistant to the photosensizing effects of the porphyrin. We hypothesize that this resistance arises from the inability of the porphyrin to mediate the oxidation of the membrane sterol. Our results indicate that photodegradation of the native yeast sterol, ergosterol, can account for substantial losses of cell viability.     

In Situ Quenching Methods Toward exo-Olefin-Terminated Polyisobutylene

exo-Olefin-terminated polyisobutylene was obtained directly from living isobutylene polymerizations by addition of a quenching compound to the living chain ends. Three broad classes of compounds were evaluated including hindered bases such as hindered pyridines and piperidines, N-hydro-2,5-disubstitutedpyrroles, and sulfides, ethers, and silylethers. The proposed mechanism of quenching unique to each class was discussed, with supporting kinetic, spectroscopic, and structure-based evidence presented. Hindered bases were proposed to operate by E2 elimination reaction of free base at the carbenium ion. N-Hydro-2,5-disubstitutedpyrroles were proposed to form the η⁵-2,5-disubstitutedpyrrolyltrichloro-titanium(IV) coordination complex, which serves as the true quencher. Sulfides, ethers, and silylethers were proposed to operate by first converting the PIB chain ends quantitatively to the onium adduct, which is then decomposed to form exo-olefin PIB. Sulfides and ethers were the best performing quenchers of all the types studied, particularly bulky ones such di-tert-butylsulfide and diisopropyl ether.     

Intermediates in associative phosphine substitution reactions of (η5-C5H5)W(CO)2(NO)

The reaction of (η⁵-C₅H₅)W(CO)₂(NO), 6W, with P(CH₃)₃ proceeds rapidly at 25°C to give (η⁵-C₅H₅)W(CO)(NO)[P(CH₃)₃], 7W. The rate of formation of 7W was found to be 4.48 × 10^?2M^?1 [6W] [P(CH₃)₃] at 25.0°c in THF. In neat P(CH₃)₃ at ?23°C, 6W is converted to (η¹-C₅H₅)W(CO)₂(NO)[P(CH₃)₃]₂, 8W. In dilute solution, 8W decomposes to initially give a 2:1 mixture of 6W and 7W. The mixture is then converted to 7W. The reaction of (η⁵-C₅H₅)Mo(CO)(NO), 6Mo, with P(CH₃)₃ is 6.1 times faster than that of the tungsten analog.     

The energy-critical quantum harmonic oscillator

We consider the energy critical nonlinear Schrödinger equation in dimensions 3 and above with a harmonic oscillator potential. In the defocusing situation, we prove global wellposedness for all initial data in the energy space Σ. This extends a result of Killip-Visan-Zhang, who treated the radial case. For the focusing nonlinearity, we obtain wellposedness for data in Σ satisfying an analogue of the usual size restriction in terms of the ground state W. We implement the concentration compactness variant of the induction on energy paradigm and, in particular, develop profile decompositions adapted to the harmonic oscillator.