A cylindrical piece of Au/graphene hydrogel, 1.08 cm in diameter and 1.28 cm in height, has been synthesized through the self-assembly of Au/graphene sheets under hydrothermal conditions for the first time. The hydrogel, containing 2.26 wt% Au, 6.94 wt% graphene, and 90.8 wt% water, exhibited excellent catalytic performance towards the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), which is about 90 times larger than previously reported values for spongy Au nanoparticles and 14 times more than the highest value among the polymer supported Au nanoparticle catalysts. The high catalytic activity arises from the synergistic effect of graphene: (1) the high adsorption ability of graphene towards 4-NP, providing a high concentration of 4-NP near to the Au nanoparticles on graphene; and (2) electron transfer from graphene to Au nanoparticles, facilitating the uptake of electrons by 4-NP molecules.

Primary and secondary kinetic and equilibrium isotope effects are calculated with density-functional methods for the in-line dianionic methanolysis of the native (unsubstituted) and thio-substituted cyclic phosphates. These reactions represent reverse reaction models for RNA transesterification under alkaline conditions. The effect of solvent is treated with explicit (single and double) water molecules and self-consistently with an implicit (continuum) solvation model. Singly substituted reactions at the nonbridging O(P1) position and bridging O(2)('), O(3)('), and O(5)(') positions and a doubly substituted reaction at the O(P1) and O(P2) positions were considered. Aqueous free energy barriers are calculated, and the structures and bond orders of the rate-controlling transition states are characterized. The results are consistent with available experimental data and provide useful information for the interpretation of measured isotope and thio effects used to probe mechanism in phosphoryl transfer reactions catalyzed by enzymes and ribozymes.

No abstract