Light-Sensitive Polymeric Nanoparticles Based on Photo-Cleavable Chromophores by Daniel Klinger

Author:Daniel Klinger
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Irradiation of either the CL-4B (see Sect. 5.1.1.1) or the CL-5B crosslinker with UV light of the wavelengths λ = 315–390 nm resulted in every case in a red shift of the absorption maxima to λ max = 385 nm. These light-induced changes of the absorption spectra point towards successful photo-reactions. However, the formation of possible side products absorbing light in the same spectral region could not be excluded. In the case of CL-4B, no further changes in the absorption spectra were detected after an irradiation time of 5 min indicating no further conversion of the photo-reaction. In comparison, more than 10 min of irradiation were necessary to complete the light-induced cleavage of the CL-5B molecule. Comparing the molecular structure of CL-4B to CL-5B, it becomes obvious that for the same molar concentration in THF, in the latter case two chromophores per molecule have to be cleaved. As a result, the required irradiation time is increased.

In order to perform a quantitative time-dependent degradation analysis of the crosslinkers, HPLC measurements were conducted to examine the composition of the reaction mixtures at various irradiation times. The kinetics of the photolysis of the photo-labile molecules was therefore investigated by monitoring the rate of disappearance of the starting compounds during irradiation. Kinetic plots of −ln [CL]t/[CL]0 versus time show all excellent linearity, indicating the expected first order kinetic with respect to the chromophore concentration (see Fig. 5.36b). Figure 5.36 presents an example of the time-dependent HPLC elution curves of the photo-reaction of CL-B and the kinetic plots for the calculation of the rate constants for both crosslinkers. The obtained half-life times and rate constants are listed in Fig. 5.36b.

Fig. 5.36Kinetic investigations on the photolytic crosslinker degradation: a irradiation time-dependent HPLC measurements of CL-5B; b kinetic plots of −ln [CL]t/[CL]0 versus irradiation time for CL-4B and CL-5B, respective rate constants and half times. Adapted with permission from [38]. Copyright 2011 American Chemical Society

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