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The facile electron-hole pair recombination in earth-abundant transition-metal oxides is a major limitation for the development of highly efficient hydrogen evolution photocatalysts. In this work, the thickness of a layered β-CoOOH semiconductor that contains metal/hydroxy groups was reduced to obtain an atomically thin, two-dimensional nanostructure. Analysis by ultrafast transient absorption spectroscopy revealed that electron-hole recombination is almost suppressed in the as-prepared 1.3 nm thick β-CoOOH nanosheet, which leads to prominent electron-hole separation efficiencies of 60-90 % upon irradiation at 350-450 nm, which are ten times higher than those of the bulk counterpart. X-ray absorption spectroscopy and first-principles calculations demonstrate that [HO-CoO6-x] species on the nanosheet surface promote H(+) adsorption and H2 desorption. An aqueous suspension of the β-CoOOH nanosheets exhibited a high hydrogen production rate of 160 μmol g(-1) h(-1) even when the system was operated for hundreds of hours.

Protein splicing is a unique post-translational process in which an intein excises itself from a precursor with the concomitant ligation of flanking sequences. The binding of zinc to intein inhibits protein splicing reversibly and EDTA relieves the inhibition. Copper was found to inhibit protein trans splicing; however, the recovery of intein splicing required both EDTA and TCEP, suggesting a different inhibition mechanism for copper compared to zinc. In this work, we have investigated the binding properties and inhibition effects of copper ions on the RecA intein from Mycobacterium tuberculosis. Both Cu(+) and Cu(2+) exhibited high binding affinity to inteins, while different binding sites were identified. Cu(2+) coordinates to Cys1, the key residue involved in the mechanism of protein splicing, however, Cu(+) does not coordinate to cysteine. An in vitro inhibition assay indicated that monovalent Cu(+) demonstrates reversible inhibition to protein splicing, and the inhibitory efficiency is comparable to Zn(2+). Redox reaction between Cu(2+) and cysteine in inteins were observed and the rate constants were determined. The results suggested a dual role for Cu(2+) in the inhibition of intein splicing: strong coordination of Cu(2+) to key residues (including Cys1) in the intein, and subsequent oxidation of Cys1, the residue required for the N-->S acyl shift step in protein splicing. A kinetic study suggested that the coordination could be the major cause of inhibition effect of Cu(2+) initially, whereas the redox reaction could play an additional role in inhibition at a later stage.

Purpose: Sample radiation damage is one of the main drawbacks limiting applications of the x-ray phase-contrast imaging method. Recently, for x-ray grating-based phase contrast imaging, the reverse projection (RP) method has been proposed by Zhu et al. [Proc. Natl. Acad. Sci. U.S.A. 107, 13576-13581 (2010)]. Compared to the conventional phase stepping technique, the RP method allows a strong reduction of the exposure time and minimization of the errors induced by mechanical vibrations. However, so far, it has only been considered for parallel beam illumination, typical of a synchrotron radiation source. In this paper, a generalization of the RP method from parallel beam geometry to fan beam geometry was presented and discussed. Methods: Within parallel beam geometry, the RP method utilizes the conjugate characteristic between reverse projection images. Nevertheless, this characteristic is not directly satisfied for fan beam geometry. In this study, a phantom composed of known materials was constructed and the projection images of the phantom were calculated in a fan beam geometry. By considering single ray, the conjugate images of the projection images were derived from the projection dataset. After that, using the modified RP method the authors retrieved phase and absorption information from paired images. Results: Extracted phase and absorption information of the phantom were in good agreement with theoretical values. Additionally, the slice reconstruction was performed and the results turned out to be in the authors' expectation. Conclusions: Theoretical calculations and numerical simulations confirm both feasibility and validity of the RP method under fan beam illumination. Because this method is simple, fast, and releases a relatively low dose, the authors believe that this research is very useful for the x-ray phase contrast imaging applications in clinical diagnosis, bioresearch, and industrial nondestructive testing. (C) 2013 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.4791672]