Highly Efficient and Durable Electrocatalysis by a Molecular Catalyst with Long Alkoxyl Chains Immobilized on a Carbon Electrode for Water Oxidation.

A dinuclear Ru complex, proximal,proximal-[Ru2L(C8Otpy)2(OH)(OH2)]3+ (C8Otpy = 4'-octyloxy-2,2'; 6',2″-terpyridine) (1) with long alkoxyl chains, was synthesized to be immobilized on a carbon paper (CP) electrode via hydrophobic interactions between the long alkoxyl chains and the CP surface. The 1/CP electrode demonstrated efficient electrocatalytic water oxidation with a low overpotential (ηonset) of 0.26 V (based on the onset potential for water oxidation) in an aqueous medium at pH 7.0, which is compared advantageously with those of hitherto-reported molecular anodes for water oxidation. The active species of RuIIIRuIII(µ-OO) with a µ-OO bridge was involved in water oxidation at 0.95 V versus Ag/AgCl. As the applied potential increased to 1.40 V, water oxidation was promoted by participation of the more active species of RuIIIRuIV(µ-OO), and very durable electrocatalysis was gained for more than 35 h without elution of 1 into the electrolyte solution. The introduced long alkoxyl chains act as a dual role of the linker of 1 on the CP surface and decrease the η value. Theoretical investigation provides insights into the O-O bond formation mechanism and the activity difference between RuIIIRuIII(µ-OO) and RuIIIRuIV(µ-OO) for electrocatalytic water oxidation.

Cell surface receptor-specific scaffold requirements for adhesion to laminin-derived peptide-chitosan membranes.

Scaffolds are used for bioengineering to regulate cellular functions. Previously, we developed laminin-derived peptide-conjugated chitosan membranes for cell engineering. Here, we determined whether changes in the chitosan scaffold altered the cellular response. When an alphavbeta3 integrin-binding peptide A99a (ALRGDN) was conjugated on chitosan membranes of varying density (1.5-1500 ng/mm(2)), cell adhesion was altered depending on the amount of chitosan. 3 or 30 ng/mm(2) of the A99a-chitosan membrane effectively promoted cell attachment, cell spreading with well-organized actin stress fibers, phosphorylation of FAK Tyr397, and neurite outgrowth. In contrast, syndecan-binding peptide AG73 (RKRLQVQLSIRT) conjugated chitosan membranes density (1.5-1500 ng/mm(2)) promoted similar biological activities at all of the concentrations tested. These results suggest that integrin-mediated cell adhesion is sensitive to the scaffold condition. To improve the function of integrin-mediated biological activities on a large amount of scaffold, we designed an A99a/AG73 mixed peptide-chitosan membrane. The mixed peptide-chitosan membrane promoted the strongest biological activities at 150-1500 ng/mm(2) of chitosan membrane. We conclude that the A99a/AG73 mixed peptide-chitosan membrane effectively interacts with both integrins and syndecans and is a useful multi-functional biomaterial.