PubMed · 14198448
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G LEVY, W TANSKI. 1964. PRECISION APPARATUS FOR DISSOLUTION RATE DETERMINATIONS.. https://doi.org/10.1002/jps.2600530624
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A novel poly(DL-lactic acid) (PLA) derivative with a diethoxy propanol ester at the end, named PLA-acetal, was synthesized by ring opening polymerization using DL-lactide and 3,3-diethoxy propanol. PLA-acetal was hydrolyzed to a PLA derivative with a formyl group, named PLA-aldehyde, by acid treatment. Reductive amination between PLA-aldehyde and methoxypolyethylene glycol amine (MeO-PEG(N)) gave the block copolymer (PLA-(MeO-PEG(N))). Nanoparticles were prepared by emulsification-solvent evaporation or solvent diffusion using PLA-(MeO-PEG(N)) or a conventional methoxypolyethylene glycol-PLA block copolymer, PLA-(MeO-PEG(O)). PLA-(MeO-PEG(N)) nanoparticles had a particle size of 60-340 nm, dependent on the preparative procedure, while PLA-(MeO-PEG(O)) nanoparticles prepared by solvent diffusion showed a particle size of 60 nm. The PLA-(MeO-PEG) nanoparticles with a smaller PEG introduction degree exhibited a more negative zeta potential. 1,1'-Dioctadecyl-3,3,3',3'-tetramethylindodicarbocyanine perchlorate (DiD) could be incorporated efficiently in PLA-(MeO-PEG(N)) nanoparticles. It is suggested that PLA-aldehyde should be useful as a functional intermediate for derivatization of PLA, and PLA-(MeO-PEG(N)) can be used for the preparation of PEG-coated PLA nanoparticles.
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A convergent approach has been developed for the preparation of nonsymmetric tertiary arylureas possessing two or three urea linkages. This approach has been used for the preparation of ureas possessing 1-naphthylenyl and 4-nitrophenyl end groups separated by either one or two phenylene diamine bridging units. These ureas were constructed as prototypes for donor-bridge-acceptor systems based on tertiary arylurea architecture. AM1 calculations indicate a preference of these arylureas for folded, protophane structures in which the aryl groups are loosely pi-stacked. Analysis of the (1)H NMR chemical shifts supports the assignment of folded structures in solution. The absorption and luminescence spectra of tertiary ureas possessing 1-naphthylenyl and/or 4-nitrophenyl are reported. The absence of fluorescence and appearance of structured phosphorescence at 77 K are attributed to nitrophenyl-localized lowest energy singlet and triplet states. Localization of excitation on the acceptor chromophore precludes investigation of charge transfer in these systems.