Critical Assessment of the Important Residues Involved in the Dimerization and Catalysis of MERS Coronavirus Main Protease.

BACKGROUND: A highly pathogenic human coronavirus (CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), has emerged in Jeddah and other places in Saudi Arabia, and has quickly spread to European and Asian countries since September 2012. Up to the 1st October 2015 it has infected at least 1593 people with a global fatality rate of about 35%. Studies to understand the virus are necessary and urgent. In the present study, MERS-CoV main protease (Mpro) is expressed; the dimerization of the protein and its relationship to catalysis are investigated. METHODS AND RESULTS: The crystal structure of MERS-CoV Mpro indicates that it shares a similar scaffold to that of other coronaviral Mpro and consists of chymotrypsin-like domains I and II and a helical domain III of five helices. Analytical ultracentrifugation analysis demonstrated that MERS-CoV Mpro undergoes a monomer to dimer conversion in the presence of a peptide substrate. Glu169 is a key residue and plays a dual role in both dimerization and catalysis. The mutagenesis of other residues found on the dimerization interface indicate that dimerization of MERS-CoV Mpro is required for its catalytic activity. One mutation, M298R, resulted in a stable dimer with a higher level of proteolytic activity than the wild-type enzyme. CONCLUSIONS: MERS-CoV Mpro shows substrate-induced dimerization and potent proteolytic activity. A critical assessment of the residues important to these processes provides insights into the correlation between dimerization and catalysis within the coronaviral Mpro family.

A Self-Aligned High-Mobility Graphene Transistor: Decoupling the Channel with Fluorographene to Reduce Scattering.

The conduction channel of a graphene field-effect transistor (FET) is decoupled from the parasitic charge impurities of the underlying substrate. Fluorographene as a passivation layer is fabricated between the oxide substrate and channel, and a self-aligned gate-terminated FET is also fabricated. This approach significantly reduces the scattering and, as a result, the mobility increases ten fold.

Liquid Crystalline Esters of Dibenzophenazines.

A series of esters of 2,3,6,7-tetrakis(hexyloxy)dibenzo[a,c]phenazine-11-carboxylic acid was prepared in order to probe the effects of the ester groups on the liquid crystalline behavior. These compounds exhibit columnar hexagonal phases over broad temperature ranges. Variations in chain length, branching, terminal groups, and the presence of cyclic groups were found to modify transition temperatures without substantially destabilizing the mesophase range.

Fluorinated graphene as high performance dielectric materials and the applications for graphene nanoelectronics.

There is broad interest in surface functionalization of 2D materials and its related applications. In this work, we present a novel graphene layer transistor fabricated by introducing fluorinated graphene (fluorographene), one of the thinnest 2D insulator, as the gate dielectric material. For the first time, the dielectric properties of fluorographene, including its dielectric constant, frequency dispersion, breakdown electric field and thermal stability, were comprehensively investigated. We found that fluorographene with extremely thin thickness (5 nm) can sustain high resistance at temperature up to 400 °C. The measured breakdown electric field is higher than 10 MV cm(-1), which is the heightest value for dielectric materials in this thickness. Moreover, a proof-of-concept methodology, one-step fluorination of 10-layered graphene, is readily to obtain the fluorographene/graphene heterostructures, where the top-gated transistor based on this structure exhibits an average carrier mobility above 760 cm(2)/Vs, higher than that obtained when SiO2 and GO were used as gate dielectric materials. The demonstrated fluorographene shows excellent dielectric properties with fast and scalable processing, providing a universal applications for the integration of versatile nano-electronic devices.

One-step formation of a single atomic-layer transistor by the selective fluorination of a graphene film.

In this study, the scalable and one-step fabrication of single atomic-layer transistors is demonstrated by the selective fluorination of graphene using a low-damage CF4 plasma treatment, where the generated F-radicals preferentially fluorinated the graphene at low temperature (<200 °C) while defect formation was suppressed by screening out the effect of ion damage. The chemical structure of the C-F bonds is well correlated with their optical and electrical properties in fluorinated graphene, as determined by X-ray photoelectron spectroscopy, Raman spectroscopy, and optical and electrical characterizations. The electrical conductivity of the resultant fluorinated graphene (F-graphene) was demonstrated to be in the range between 1.6 kΩ/sq and 1 MΩ/sq by adjusting the stoichiometric ratio of C/F in the range between 27.4 and 5.6, respectively. Moreover, a unique heterojunction structure of semi-metal/semiconductor/insulator can be directly formed in a single layer of graphene using a one-step fluorination process by introducing a Au thin-film as a buffer layer. With this heterojunction structure, it would be possible to fabricate transistors in a single graphene film via a one-step fluorination process, in which pristine graphene, partial F-graphene, and highly F-graphene serve as the source/drain contacts, the channel, and the channel isolation in a transistor, respectively. The demonstrated graphene transistor exhibits an on-off ratio above 10, which is 3-fold higher than that of devices made from pristine graphene. This efficient transistor fabrication method produces electrical heterojunctions of graphene over a large area and with selective patterning, providing the potential for the integration of electronics down to the single atomic-layer scale.