2-Nitrobenzyl Borate Based Photolabile Linker for Breakable Polymer Vesicles.

Fluorescent photolabile groups undergoing convenient synthesis and fast cleavage are being explored because of their increasing utility in both synthetic and biological chemistry. Herein, a model photosensitive poly(ethylene glycol)-lipid of NP-B-PEG with a 2-nitrobenzyl 2-pyridinylmethyl borate hydrophobic tail is synthesized. The H-1[-NMR and absorption spectra analysis of NP-B-PEG upon 365 nm irradiation in water supports a rapid photocleavage of nitrobenzyl borate with the concomitant hydrolysis of 2-pyridinylmethyl borate. It is also shown that the borate tail hydrolyzes slowly in water. Fortunately, when the polymer aqueous solution is loaded with the hydrophobic doxorubicin (DOX), the borate hydrolysis can be much retarded. The phototriggered experiment shows a two-stage DOX release: first, the slow leakage as a result of the photocleavage of 2-nitrobenzyl borate before the vesicle disintegration; second, the quick DOX precipitation from the disintegrated vesicles induced by the speeding up hydrolysis of 2-pyridinylmethyl borate.