mg, 0.2 mmol) was dissolved in refluxing 1-pentanol (15 ml). Zinc acetate dihydrate (50 mg, excess) was added and reflux continued for 30 minutes. The solvent was removed under reduced pressure and the residue chromatographed on silica gel (eluent: petroleum ether (b.p. 40-60 ºC)-THF 1:1). The green fraction was separated and an oily blue material was precipitated from THF-MeOH (190 mg, 74 %). m.p.

Nanosized insoluble metal sulfate aggregates, predominantly CaSO4, have been prepared in a variety of water-in-oil (w/o) microemulsions stabilized by either nonionic or ionic surfactants. Particles were visualized by transmission electron microscopy (TEM) and the identities of the aggregates confirmed by energy-dispersive X-ray analysis (EDXA). BaSO4 prepared in n-heptane microemulsions stabilized by the sodium salt of Aerosol-OT (AOT) appeared as slightly irregular aggregates, 8−50 nm in diameter. In contrast, BaSO4 in n-heptane microemulsions stabilized by ammonium diethylhexyl phosphate (NH4DEHP) existed in the form of submicron-sized “flocs” comprising nanospheres 5−7 nm in diameter. BaSO4 synthesis in cyclohexane microemulsions stabilized by tetraethylene glycol monododecyl ether (C12E4), produced discrete essentially monodisperse nanospheres 8−10 nm in diameter. A wider variety of morphologies were encountered in the synthesis of CaSO4 which produced nanospheres, ellipsoids, rods, nanohairs, nanowires, and nanobundles. The greatest structural diversity was obtained in systems stabilized by C12E4 where product morphology was sensitive to the mole ratio of water to surfactant (ω0) in the reaction medium, the overall water content, surfactant concentration, reactant concentration, and incubation time. The growth of CaSO4 nanowires was monitored as a function of time and was fastest at high overall reactant concentrations. Nanowires and nanobundles were often observed to span completely the individual sections of the copper grid used in TEM measurements, indicating lateral growth potential on the order of hundreds of microns. In contrast, CaSO4 formed in microemulsion systems stabilized by AOT in dodecane yielded only nanospheres whose size was largely independent of composition and reaction conditions.

~~ ~Klebsiella pneumoniae overcomes cadmium toxicity through the biotransformation ' of cadmium ions into photoactive, nanometre-sized CdS particles deposited on the cell surface. The kinetics of particle formation during batch culture growth was monitored by electron microscopy (EM), energy-dispersive X-ray analysis and electronic absorption spectroscopy (EAS). During the deceleration phase of bacterial growth, the presence of CdS particles on the outer cell wall of K. pneumoniae ( 2 5 nm in diameter) was detected by EM. The size of these electron-dense particles continued to increase throughout the stationary phase of growth, with some of the particles reaching a diameter >200 nm. The formation of the extracellular CdS particles contributed to around 3 4 O / 0 of the total cell biomass. EAS undertaken on these extracellular ' bio-CdS ' particles suggested that the large 'superparticles ' observed by EM, e.g. 200 nm, were aggregates of smaller particles termed 'Q-particles', -4 nm in diameter. Metal sulfide particles were not formed in batch cultures of K. pneumoniae grown in the presence of lead, zinc, mercury, copper or silver ions. Growth in the presence of lead ions resulted in the formation of extracellular electron-dense particles containing lead but not sulfide or phosphate. lntracellular phosphorus-containing electron-opaque particles were formed during growth in the presence of copper and mercury. lntracellular electrondense particles were formed in the presence of zinc ions but these did not contain phosphorus. From these results it was thought that metal sulfide formation in K. pneumoniae showed some cadmium-specif icity. When cadmium and zinc ions were both added to the growth medium, metal sulfide particles were formed that were predominantly composed of cadmium, e.g. 486% cadmium and 0*04% zinc. Similarly, when cadmium and lead ions were both present during growth only CdS particles formed. In both cases analysis of the cells by EAS confirmed the presence of CdS only. These observations suggest that the mechanism of CdS formation is unlikely to occur simply through a cadmium-induced release of hydrogen sulfide by the cells into the external environment. If hydrogen sulfide production was the mechanism of sulfide formation then metal sulfide particles containing lead and zinc ions in addition to cadmium ions should have been produced.

No abstract

Klebsiella aerogenes forms electron-dense particles on the cell surface in response to the presence of cadmium ions in the growth medium. These particles ranged from 20 to 200 nm in size, and quantitative energy dispersive X-ray analysis established that they comprise cadmium and sulfur in a 1:1 ratio. This observation leads to the conclusion that the particles are cadmium sulfide crystallites. A combination of atomic absorption spectroscopy, inductively coupled plasma mass spectrometry, and acid-labile sulfide analysis revealed that the total intracellular and bound extracellular cadmium:sulfur ratio is also 1:1, which suggests tha the bulk of the cadmium is fixed as extracellular cadmium sulfide. The tolerance of K. aerogenes to cadmium ions and the formation of the cadmium sulfide crystallites were dependent on the buffer composition of the growth medium. The addition of cadmium ions to phosphate-buffered media resulted in cadmium phosphate precipitates that remove the potentially toxic cadmium ions from the growth medium. Electron-dense particles formed on the surfaces of bacteria grown under these conditions were a combination of cadmium sulfide and cadmium phosphates. The specific bacterial growth rate in the exponential phase of batch cultures was not affected by up to 2mM cadmium in Tricine-buffered medium, but formation of cadmium sulfide crystallites was maximal during the stationary phase of batch culture. Cadmium tolerance was much lower (10 to 150 microM) in growth media buffered with Tris, Bistris propane, Bes, Tes, or Hepes. These results illustrate the importance of considering medium composition when comparing levels of bacterial cadmium tolerance.