Forest S E, Simon J D
Department of Chemistry, Duke University, Durham, NC 27708, USA.
Photochem Photobiol. 1998 Sep;68(3):296-8.
Photoacoustic calorimetry is used to examine the energy dissipation in melanin under physiological conditions (pH 7.2) following irradiation by UV and visible (VIS) light. Four different excitation wavelengths were examined: 264 nm, representative of UVC radiation, 351 nm and 400 nm (UVA-I radiation) and 527 nm, representative of VIS radiation. Following absorption at 527 nm, essentially all of the photon energy is released nonradiatively on a sub-nanosecond of excitation. Similar results are observed at 400 nm. At 351 nm, most of the energy was released as heat; a small amount of energy was retained (5 +/- 5%). When melanin is excited at 264 nm, 29 +/- 7% of the photon energy is retained by the molecule for a time period longer than a few hundred nanoseconds. These results show that a long-lived excited state or reactive intermediate is generated upon UV irradiation, whereas all of the excitation energy is dissipated nonradiatively in the visible portion of the spectrum. These results establish that the photochemistry of melanin is wavelength dependent.
光声量热法用于研究在生理条件（pH 7.2）下，紫外线（UV）和可见光（VIS）照射后黑色素中的能量耗散情况。研究了四种不同的激发波长：代表UVC辐射的264 nm、351 nm和400 nm（UVA-I辐射）以及代表VIS辐射的527 nm。在527 nm处吸收后，基本上所有的光子能量在亚纳秒激发时以非辐射方式释放。在400 nm处观察到类似结果。在351 nm处，大部分能量以热的形式释放；少量能量被保留（5±5%）。当黑色素在264 nm处被激发时，29±7%的光子能量被分子保留超过几百纳秒的时间。这些结果表明，紫外线照射会产生长寿命的激发态或反应中间体，而在光谱的可见光部分，所有激发能量均以非辐射方式耗散。这些结果证实黑色素的光化学作用与波长有关。
