Wei Jiao

Visible-Light-Responsive beta-Rhombohedral Boron Photocatalysts

Photocatalytic solar-energy conversion has been attracting worldwide attention owing to its great significance in the provision of renewable energy and protection of the environment. As important as the tailoring of well-known photocatalysts, such as TiO2, for high photocatalytic efficiency [4–7] is the investigation of unknown semiconductor photocatalysts. So far, hundreds of photocatalysts have been examined, most of which have been compounds. Recently, elemental semiconductors (Si, Se, P, S) have emerged as an attractive class of photocatalysts owing to their visible-light response and suitable band edges for targeted photocatalysis reactions. It is logical to also anticipate the use of elemental boron in photocatalysis because of its semiconducting properties. When we investigated b-rhombohedral boron crystals with and without an amorphous oxide layer on their surface, we discovered that the crystals were indeed photocatalytically active under visible light, and that the existence of a surface amorphous oxide layer substantially impaired their photocatalytic activity. The findings in this study may open a door to the development boron-based photocatalysts. Boron has aroused wide interest owing to its fascinating properties (light weight, high strength, high hardness, high melting point, high chemical resistance, typical semiconductivity, and superconductivity at high pressure), although a pure phase was not obtained until 1909. It has at least 17 polymorphs (or more precisely, boron-rich compounds) as a result of electron-deficient bonding. All polymorphs contain B12 icosahedral clusters as a basic building block (see the inset in Figure 1a). Among these polymorphs, a-tetragonal, a-rhombohedral, b-tetragonal, and b-rhombohedral boron are the four main forms under ambient conditions. Experimentally, b-rhombohedral boron is the most thermodynamically stable form, although its superior stability was not supported by theoretical investigations until 2007. This long-term discrepancy stems from the difference between the idealized structural model of 105 boron atoms (B105) that is used to describe the b-rhombohedral form and the real structure, which contains partially occupied sites. As a consequence, the theoretically predicted metallic property does not agree with the experimentally derived p-type semiconducting behavior of b-rhombohedral boron with a proposed bandgap of 1.5–1.6 eV. Improved crystallographic studies and optimized theoretical structure models have reduced the gap between experiment and theory to some extent and provided a strong background for the further investigation of structure–property relationships and the exploration of new uses for b-rhombohedral boron. The bandgap of 1.5–1.6 eV indicates that b-rhombohedral boron should respond to visible light over a wide range of wavelengths. It was also found in quasi-four-electrode measurements that b-rhombohedral boron exhibited strong photoconductivity under illumination by a halogen lamp or argonion laser (at 488 nm). Encouraged by these favorable properties, we investigated the photocatalytic activity of two kinds of commercially available b-rhombohedral boron crystals (sub-micrometer-sized and micrometer-sized) by structural characterization, measurement of their optical properties, and theoretical calculation of their electronic structures. Figure 1a shows the X-ray diffraction (XRD) pattern of sub-micrometer-sized boron powder. All diffraction peaks can be assigned to b-rhombohedral boron (JCPDS: 11-0618; space group: R 3m (166); a= 10.952 , c= 23.824 ). Besides the sharp peaks, there are several diffuse peaks in the background, which indicate the existence of amorphous Figure 1. Structure characterization: a) XRD pattern of sub-micrometer-sized b-rhombohedral boron. b) High-resolution TEM image recorded at the edge of a sub-micrometer-sized b-rhombohedral boron particle. The inset in (a) shows the structure of an icosahedral B12 cluster.

Enantiodifferentiating photoisomerization of cyclooctene included and sensitized by aroyl-beta-cyclodextrins: A critical enantioselectivity control by substituents

A series of 6-O-benzoyl-beta-cyclodextrins (CDs) with methyl, methoxy, methoxycarbonyl, and bromo substituent(s) at the ortho-, meta-, and/or para-position(s) were synthesized as chiral sensitizing hosts for the use in supramolecular enantiodifferentiating photoisomerization of (Z)-cyclooctene (1Z) to its chiral (E)-isomer (1E). The complex stability constants (K(S)) of the modified beta-CDs with 1Z in aqueous methanol solutions were highly sensitive to the substituent(s) introduced to the benzoate moiety, and the log K(S) values decreased linearly with slightly different slopes with increasing methanol content. The enantiomeric excess (ee) of 1E obtained upon photosensitization with these hosts was a critical function of the size and position of the substituent, varying from almost zero to 46% ee. This indicates that even an apparently small structural difference between methyl and methoxy can critically affect the enantiodifferentiating photoisomerization of a guest included in the chiral cavity, probably through manipulation of both the orientation of ground-state 1Z and the subsequent rotational relaxation of excited 1Z inside the chiral cavity.

Lathyrane diterpenes from Euphorbia lathyris as modulators of multidrug resistance and their crystal structures

Two lathyrane diterpenes (1-2) together with previous ones (3-6) were isolated from Euphorbia lathyris. The structures of 1 and 2 were established on the basis of extensive spectroscopic methods, including two-dimensional NMR techniques. Stereo configuration and conformation of 1 and 2 were analyzed by X-ray diffraction for the first time. The configuration of the unique isolathyrol diterpene 2 from the seeds of E. Lathyris, was rectified from S * to R * at C-5. All compounds were examined as modulators of multidrug resistance on MCF-7/ADM cell lines in vitro. Their structure-activity relationship was discussed from aspect of different skeletons. A class of potential P-gp inhibitors with five different types (jokinol, isolathyrol, epoxylathyrol, 7-hydroxylathyrol, lathyrol) was discovered.

Synthesis of mesoporous single crystal rutile TiO2 with improved photocatalytic and photoelectrochemical activities

Mesoporous single crystal rutile TiO2 with clear facets was prepared by a seeded template method. As a result of unique microstructure, the resulting TiO2 exhibits remarkably improved photocatalytic and photoelectrochemical activities in hydrogen or oxygen evolution.

Supramolecular enantiodifferentiating photoisomerization of cyclooctene with modified β-cyclodextrins: critical control by a host structure

Enantiodifferentiating photoisomerization of (Z)-cyclooctene included and sensitized by m-methoxybenzoyl-beta-cyclodextrin gave chiral (E)-isomers in up to 46% enantiomeric excess, which is the highest value ever reported for supramolecular photochirogenesis with analogous hosts, thus demonstrating the crucial role of the sensitizer-spacer moiety in supramolecular photochirogenic systems.

Lathyrol Diterpenes as Modulators of P-Glycoprotein Dependent Multidrug Resistance: Structure–Activity Relationship Studies on Euphorbia Factor L3 Derivatives

Five series of 37 new acylate and epoxide derivatives (3-39) of Euphorbia factor L3, a lathyrol diterpene isolated from Euphorbia lathyris, were designed by modifying the hydroxyl moiety of C-3, C-5, or C-15. Chemoreversal effects of the acylates on multidrug resistance (MDR) were evaluated in breast cancer multidrug-resistant MCF-7/ADR cells that overexpress P-glycoprotein (P-gp). Eight derivatives exhibited greater chemoreversal ability than verapamil (VRP) against adriamycin (ADR) resistance. Compounds 19 and 25 exhibited 4.8 and 4.0 times, respectively, more effective reversal ability than VRP against ADR resistance. To determine the key characteristics of Euphorbia factor L3 derivatives that contribute to MDR reversal, we conducted a structure-activity relationship study of these compounds. The simulation studies indicated different possible mechanisms and revealed the important influence of hydrophobic interactions and hydrogen bonds in the flexible cavity of P-gp.

Euphorbia factor L8: a diterpenoid from the seeds of Euphorbia lathyris

The title compound [systematic name: (2S*,3S*,4R*,5R*,9S*,11S*,15R*)-5,15-diacetoxy-3-nicotinoyloxy-14-oxolathyra-6(17),12(E)-diene], C30H37NO7, was isolated from the seeds of Euphorbia lathyris. The tricyclic diterpenoid molecule contains an 11-membered ring, a five-membered ring exhibiting an envelope conformation and a three-membered ring. The 11-membered ring is cis-fused with the three-membered ring and trans-fused with the five-membered ring.