Cyanobacterial blooms: carbon and nitrogen limitation have opposite effects on the buoyancy of oscillatoria

Gas vacuolation in Oscillatoria rubescens decreased with increased nitrogen limitation and increased with transitions from nitrogen to inorganic carbon limitation. Gas vacuoles consist of protein vesicles that can accumulate in carbon- limited but not in unenriched nitrogen-limited cells. Nitrogen limitation is a factor in the formation of deep population maxima; carbon limitation can promote surface blooms.     

Silicon-mediated organic synthesis

Organic chemists have used the chemical properties of tetracovalent silicon in a remarkable variety of new synthetic transformations. In carbon-functional silanes, exceptional stabilization is provided to a carbocation center in the beta position when the carbon-silicon bond lies in plane. This phenomenon directs electrophilic attack to the silicon-substituted carbon in aryl-, vinyl-, and alkynylsilanes and to carbon-3 in allylsilanes. For different reasons, silicon also stabilizes a carbon-metal bond in the alpha position. Consequently, access to many silicon-containing organometallics is readily available. The exceptional strength of silicon-oxygen and silicon-fluorine bonds is yet another factor that controls the chemical reactivity of silicon reagents. In recent developments, preparative chemists have taken advantage of these properties in imaginative and useful ways.     

The other frontiers of science

Frontiers of science are usually considered as those areas where the boundares of human knowledge are being pushed most vigorousl into the unknown. These are the intemal frontiers. But no less important are the external frontiers. Those bordering on the federal govermment, on education, on private industry and on intemational affairs and the developing world are among the most critical and demanding. Some of the outstanding problems facing science, and scientists in these extemal interactions, are discussed within the context of our changing national and international priorities.