what is precursors of vitamin A

化工类专业英语求大神翻译
organic solvents, precursors of block and graft copolymers,
template cores, or emulsion phases, thus avoiding the compli-
cated preparation schemes typically used for making hollow
nanospheres, and decreasing their potential toxicity so that
they may be used as drug carriers. We started with polymer±
monomer complexes formed between a biopolymer with ami-
no groups and an organic monomer with a carboxylic group.
Depending on the concentration of the two precursors in
aqueous solution, such polymer±monomer complexes can
form micelles through electrostatic interactions. Then, hollow
polymeric nanospheres could be obtained by polymerizing the
monomers inside the micelles.

英语翻译
请帮忙翻译这段文字,precursors in a high-temperature coordinating solution made of TOP/ Tapa mixed with additional amine terminated ligands,followed by overcoating the native core with a thick layer of ZnS (consisting of 5-7 monolayers),also carried out in a high-temperature coordinating mixture; ZnS overcoating is usually carried out at temperatures lower than those used during CdSe nanocrystal growth to avoid compromising the integrity of the native cores.Robust nanocrystals with narrow size distribution,symmetric photoemission spectra (fwhm of 30-40 nm),and high photoluminescence quantum yields (QY) are prepared using this synthetic approach.Three QD samples having PI.emission maxima at 510,530,and 555 nm were synthesized and used in this study.The resulting CdSe-ZnS core-shell QDs were rendered water soluble by replacing the native TOP/Tapa organic capping shell with bidentate dihydrolipoic acid (DHLA,a dithiol-alkyl-COOH) ligands,as described previously." This provided aggregate-free water-soluble QD prepara?tions with good quantum yields and which were exceptionally stable in basic pH buffer.DHLA-capped CdSe-ZnS QD samples 1O-40 ,uM) stable over a period of 1 year have been routinely prepared in our laboratory.The DHLA-capped nanocrystals have a homogeneous density of charge due to deprotonation of the carboxylic acid end groups.The relatively long term stability is presumably due to the strong bidentate interactions of the DHLA ligands with the ZnS surface via their dithiol polar heads in comparison,for example,with monothiol terminated caps."
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