Stepwise reduction of graphene oxide and studies on defect-controlled physical properties.

Graphene oxide (GO) is a monolayer of oxidized graphene which is a convenient and potential candidate in a wide range of fields of applications like electronics, photonics, optoelectronics, energy storage, catalysis, chemical sensors, and many others. GO is often composed of various oxygen-containing groups such as hydroxyl, carboxyl, and epoxy. One appealing method for achieving graphene-like behavior with sp2 hybridized carbon is the reduction of GO i.e. formation of reduced graphene oxide (RGO). A stepwise reduction GO to form a family of RGO, containing various quantities of oxygen-related defects was carried out. Herein, the defects related chemical and physical properties of GO and the RGO family were studied and reported in an effort to understand how the properties of RGO vary with the reduction rate. Although there are several reports on various features and applications of GO and RGO but a systematic investigation of the variation of the physical and chemical properties in RGO with the varying quantities of oxygeneous defects is imperative for the engineered physical properties in achieving the desired field of applications. We have attempted to look at the role of sp2 and sp3 carbon fractions, which are present in RGO-based systems, and how they affect the electrical, optoelectronic, and adsorption characteristics.

Cytochrome c(552) from Thermus thermophilus engineered for facile substitution of prosthetic group.

The facile replacement of heme c in cytochromes c with non-natural prosthetic groups has been difficult to achieve due to two thioether linkages between cysteine residues and the heme. Fee et al. demonstrated that cytochrome c(552) from Thermus thermophilus, overproduced in the cytosol of E. coli, has a covalent linkage cleavable by heat between the heme and Cys11, as well as possessing the thioether linkage with Cys14 [Fee, J. A. (2004) Biochemistry 43, 12162-12176]. Prompted by this result, we prepared a C14A mutant, anticipating that the heme species in the mutant was bound to the polypeptide solely through the thermally cleavable linkage; therefore, the removal of the heme would be feasible after heating the protein. Contrary to this expectation, C14A immediately after purification (as-purified C14A) possessed no covalent linkage. An attempt to extract the heme using a conventional acid-butanone method was unsuccessful due to rapid linkage formation between the heme and polypeptide. Spectroscopic analyses suggested that the as-purified C14A possessed a heme b derivative where one of two peripheral vinyl groups had been replaced with a group containing a reactive carbonyl. A reaction of the as-purified C14A with [BH(3)CN](-) blocked the linkage formation on the carbonyl group, allowing a quantitative yield of heme-free apo-C14A. Reconstitution of apo-C14A was achieved with ferric and ferrous heme b and zinc protoporphyrin. All reconstituted C14As showed spontaneous covalent linkage formation. We propose that C14A is a potential source for the facile production of an artificial cytochrome c, containing a non-natural prosthetic group.