We report on the cooperative photoluminescence (PL) properties of closely packed CdSe nanocrystal thin films and propose a model to elucidate the nonlinear PL behavior. The PL exhibits an initial decay and a subsequent enhancement under continuous excitation, which are attributed to the photodarkening and the effects of photooxidation (neutralization and suppression of the photoionization rate). The PL enhancement correlates with the degree of oxidation. X-ray photoelectron spectroscopy (XPS) confirms that photooxidation of nanocrystals proceeds as a function of time.

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The esterase catalyzes the stereoselective hydrolysis of methyl DL-beta-acetylthioisobutyrate (DL-ester) to give D-beta-acetylthioisobutyric acid (DAT). To use the enzyme for DAT production, the esterase gene of Pseudomonas putida was cloned and expressed in E. coli. The recombinant E. coli containing the esterase gene produced a large amount of the enzyme in an active form. This strain could be used for the asymmetric synthesis of DAT.