Photolytic Control and Infrared Probing of Amide I Mode in the Dipeptide Backbone-Caged with the 4,5-Dimethoxy-2-nitrobenzyl Group
journal contributionposted on 21.02.2008 by Hanju Rhee, Jang-Soo Lee, Jihae Lee, Cheonik Joo, Hogyu Han, Minhaeng Cho
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Alanine dipeptide analog 1 backbone-caged with a photolabile linker, 4,5-dimethoxy-2-nitrobenzyl (DmNb), was synthesized. UV-pulse-induced photochemical reaction of 1 was monitored by Fourier transform IR absorption spectroscopy under a steady-state condition or in a fast-scan mode. Upon photolysis of 1, the amide I band is changed from a doublet to a singlet with concomitant line shape changes of several IR bands. The change of the amide I band is directly associated with the photocleavage of the covalent N−C bond connecting the backbone amide of 2 to DmNb. Therefore, IR spectroscopy is useful for directly probing the photocleavage of backbone-caged peptide 1 and the concurrent release of native peptide 2. In contrast, UV−vis spectroscopy probing the irradiation-induced structural change of the 2-nitrobenzyl moiety itself may not provide a clue directly relevant to the photocleavage of such N−C bond. Time-resolved IR spectra recorded in a fast-scan mode after pulsed UV irradiation of 1 reveal that such photocleavage occurs at least faster than a few seconds of our instrumental time resolution.