A series of Ru(bpy)32+-attached metallopeptides are being prepared with a tyrosine (phenol) separated from the metal by a rigid polyproline helix. We aim to experimentally establish the effects of distance on the observed rate of multiple-site concerted proton electron transfer (MS-CPET) by varying the polyproline helix length and comparing our observations to those seen in ET reactions. The polyproline helices have been prepared via solid-phase peptide synthesis on chlorotrityl-chloride resin, and the amine functionalized complex, Ru(bpy)2(bpy-NH2)2+, has been prepared by published procedures. We are currently developing conditions for efficient amide coupling to the electron-poor amine in Ru(bpy)2(bpy-NH2)2+, as many of the traditional carbodiimide reagents and conditions have failed to produce appreciable amounts of metallopeptide. We are also exploring metallopeptides which are synthesized in the reverse direction, coupled instead to the N-terminus with a Ru(bpy)2(bpy-Me-COOH)2+, as described in the literature. With the full constructs in hand, photo-oxidation to the ruthenium(III) form should be expected to lead to proton-coupled electron transfer (PCET) from the phenol, with the proton transferred to a hydrogen-bonded base and the electron transferred to the ruthenium(III) oxidant. This will likely occur by multiple-site concerted proton electron transfer (CPET), the simultaneous movement of an electron and a proton in a single kinetic step to or from separated sites. This is a common mechanism in many important energy conversion and enzyme catalyzed reactions. Studies toward the measurement of MS-CPET rate constants for a series of metallopeptides with varying polyproline helix length between the Ru(bpy)3 and tyrosine phenol will be described. We then compare the observed distance-dependence rate of MS-CPET to that observed in ET reactions for other, similar biomimetic systems.

Long-range, multiple-site concerted proton electron transfer in metallopeptide constructs

252nd National Meeting (2016)

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