THE PREPARATION AND STABILITY OF COLLOIDAL METAL DISPERSIONS PREPARED BY A TWO-PHASE NON-AQUEOUS ROUTE

Stable suspensions of small metal Au, Ru, PI, Pd, Rh, Co and Nl particles dispersed in n-heptane and n-dodecane have been prepared using a novel two-phase system, Involving the formation of the particles In a methanolic phase and subsequent phase transfer of the panicles to the alkane medium. The dispersions consisted of small particles having diameters In the range of 8-30 nm (the gold sols were very polydlsperse having average diameters of ca.34 nm). The phase transfer of the particles and their subsequent colloid stability were effected by the presence of dissolved dispersant in the hydrocarbon phase (either Oloa 1200 or Hypermer LP 8). In the case of Oloa 1200, a widely-used polylsobutylene succinimide automotive engine dispersant, It Is proposed that the amlne groups adsorb strongly to the acidic surface o1 the particles, and the 70-carbon polyisobutylene chains extend Into the hydrocarbon medium sufficiently to maintain the separation of adjacent particles by steric and possibly also by electrical repulsion.     

X-RAY SENSITIVITY OF PHOTOSYNTHETIC AND REPRODUCTIVE SYSTEMS IN CHLORELLA

Abstract— Some effects of X rays on the green alga Chlorella pyrenoidosa have been investigated by measurements of survival and oxygen-evolving capability. Photosynthetic oxygen evolution at light saturation and endogenous respiration showed the same radiation sensitivity, and these two processes were about 40 times more resistant to X-ray-induced inactivation than survival. Responses of cells receiving doses in excess of 200krad are in agreement with the existence of two photosystems, photoreaction II being apparently more sensitive to X rays than photoreaction I.     

Liposome fluidization and melting point depression by pressurized CO2 determined by fluorescence anisotropy

The influence of CO2 on the bilayer fluidity of liposomes, which are representative of model cellular membranes, was examined for the first time at the elevated pressures (up to 13.9 MPa) associated with CO2-based processing of liposomes and microbial sterilization. Fluidization and melting point depression of aqueous dipalmitoylphosphatidylcholine (DPPC) liposomes by pressurized CO2 (present as an excess phase) were studied by steady-state fluorescence anisotropy using the membrane probe 1,6-diphenyl-1,3,5-hexatriene (DPH). Isothermal experiments revealed reversible, pressure-dependent fluidization of DPPC bilayers at temperatures corresponding to near-gel (295 K) and fluid (333 K) phases at atmospheric pressure, where the gel-to-fluid phase transition (Tm) occurs at approximately 315 K. Isobaric measurements (PCO2 =1.8, 7.0, and 13.9 MPa) of DPH anisotropy demonstrate substantial melting point depression (DeltaTm = -4.8 to -18.5 K) and a large broadening of the gel-fluid phase transition region, which were interpreted using conventional theories of melting point depression. Liposome fluidity is influenced by CO2 accumulation in the hydrocarbon core and polar headgroup region, as well as the formation of carbonic acid and/or the presence of buffering species under elevated CO2 pressure.