Wansheng Zong,Lixin Wang,Qing Guo,Juan Li,Wenbo Wu,Yingliang Liu,Shengang Xu,Shaokui Cao
A hyper-structured molecule (HSM) CRA-DR1 and a model molecule Ph-DR1 for photorefractive (PR) application under non-electric field were designed and synthesized via highly reactive “click” reaction between alkynyl derivatives of calix [4]resorcinarene (CRA) or resorcinol and an azide derivative of disperse red 1 (DR1) in satisfactory yields. XRD pattern and UV–Vis absorption spectra indicated that the CRA-DR1 with three-dimensional (3D) CRA core could effectively decrease the aggregation, packing and crystallization of the nonlinear optical (NLO) chromophores . AFM images showed a smooth and pinhole-free morphology of the CRA-DR1 film. Two-beam coupling (TBC) experiment was used to test the photorefractive performance in optically transparent films of Ph-DR1 and CRA-DR1 doped with [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) as a photosensitizer and N -ethyl-carbazole (ECz) as a plasticizer . Without poling and without external electric filed, the coupling gain coefficient obtained in the CRA-DR1-based composite is 147.4 cm −1 , which is higher than that of Ph-DR1-based composite (132.6 cm −1 ) owing to its asymmetrical 3D CRA core. Coupled with its convenient synthesis and commercial DR1, CRA-DR1 could serve as a good candidate for PR application.
Yun-Bin Han,Liu-Qing Chen,Zhuo Li,Yu-Meng Tan,Yan Feng,Guang-Yu Yang
Endoglycoceramidases (EGCases) specifically hydrolyze the glycosidic linkage between the oligosaccharide and the ceramide moieties of various glycosphingolipids, and they have received substantial attention in the emerging field of glycosphingolipidology. However, the mechanism regulating the strict substrate specificity of these GH5 glycosidases has not been identified. In this study, we report a novel EGCase I from Rhodococcus equi 103S (103S_EGCase I) with remarkably broad substrate specificity. Based on phylogenetic analyses, the enzyme may represent a new subfamily of GH5 glycosidases. The X-ray crystal structures of 103S_EGCase I alone and in complex with its substrates monosialodihexosylganglioside (GM3) and monosialotetrahexosylganglioside (GM1) enabled us to identify several structural features that may account for its broad specificity. Compared with EGCase II from Rhodococcus sp. M-777 (M777_EGCase II), which possesses strict substrate specificity, 103S_EGCase I possesses a longer α7-helix and a shorter loop 4, which forms a larger substrate-binding pocket that could accommodate more extended oligosaccharides. In addition, loop 2 and loop 8 of the enzyme adopt a more open conformation, which also enlarges the oligosaccharide-binding cavity. Based on this knowledge, a rationally designed experiment was performed to examine the substrate specificity of EGCase II. The truncation of loop 4 in M777_EGCase II increased its activity toward GM1 (163%). Remarkably, the S63G mutant of M777_EGCase II showed a broader substrate spectra and significantly increased activity toward bulky substrates (up to >1370-fold for fucosyl-GM1). Collectively, the results presented here reveal the exquisite substrate recognition mechanism of EGCases and provide an opportunity for further engineering of these enzymes.
危险品化学品经营许可证（带存储）