Acta Chimica Sinica ›› 2013, Vol. 71 ›› Issue (02): 169-172.

Communications

### 向光素LOV1-C57S固态Photo-CIDNP效应的磁场依赖性

1. a 国防科技大学理学院化学与生物学系 长沙 410073;
b 莱顿大学化学院 莱顿 2300RA 荷兰;
c 莱比锡大学分析化学系 莱比锡 04103 德国
• 投稿日期:2012-12-23 发布日期:2013-01-17
• 通讯作者: 王孝杰, 誉宫 E-mail:yj605@126.com; joerg.matysik@uni-leipzig.de
• 基金资助:

项目受荷兰科学研究组织(NOW) (ALW open competitie, 818.02.019; Middelgroot 700.57.107)资助.

### Magnetic Field Dependence of the Solid-State Photo-CIDNP Effect Observed in Phototropin LOV1-C57S

Wang Xiaojiea, Smitha Surendran Thamarathb,c, Jörg Matysikb,c

1. a Department of Chemistry and Biology, College of Science, National University of Defense Technology, Changsha 410073;
b Leiden Institute of Chemistry, Einsteinweg 55, Leiden, 2300RA The Netherlands;
c Institut f黵 Analytische Chemie, Universität Leipzig, Linnéstr. 3, 04103 Leipzig, Germany
• Received:2012-12-23 Published:2013-01-17
• Supported by:

Project supported by the Netherlands Organization for Scientific Research (NOW) through a Middelgroot grant (ALW open competitie, 818.02.019; Middelgroot 700.57.107).

Here we present the magnetic field dependence of the solid-state Photo-CIDNP effect observed in phototropin LOV1-C57S using 13C magic-angle spinning (MAS) NMR spectroscopy. Both dark and light spectra were measured at 4.7 T (i.e., 200 MHz 1H frequency) using a spinning frequency of 8 kHz. An Avance 200 MHz spectrometer equipped with 4-mm MAS probe (Bruker, Karlsruhe, Germany) was used for the 13C MAS NMR experiments. The sample was packed into a 4-mm sapphire rotor and inserted into the MAS probe. For a homogeneous sample distribution against the rotor wall, the sample was frozen at a very low spinning frequency of 500 Hz. Freezing was monitored on the proton tuning channel as a shift of ca. 0.1 MHz. The variable temperature unit on the spectrometer was set to 235 K. The spinning frequency was increased to 8 kHz after the sample is completely frozen. This frequency and set temperature were used for all 13C MAS NMR measurements. A simple Hahn-echo pulse sequence with two-pulse phase modulation proton-decoupling was used. Continuous illumination was supplied by a 1 kW xenon lamp. The cycle delay was 2 s, and the measurement time was about 12 h. In the spectrum obtained in the dark, standard broad protein responses appear. Under illumination, several strong additional light-induced signals appeared. In contrast to the entirely emissive (negative) peaks in the photo-CIDNP MAS NMR spectra observed at 2.3 T (i.e., 100 MHz 1H frequency), the first observation of this effect in a nonphotosynthetic system, the light induced 13C NMR peaks at 4.7 T show mixed absorptive/emissive enhancement pattern. This pattern is reminiscent of the spectra observed by liquid state photo-CIDNP of a LOV2 sample. The observed solid-state photo-CIDNP effect is strongly magnetic field dependent, and this field-dependence is well distinguished for the various nuclei. This large difference in magnetic field dependence reflects the large variety of hyperfine factors found in this comparable small-sized and asymmetric radical pair.

Key words: photo-CIDNP, MAS, NMR, phototropin, LOV