Cross-Linked Crystals of Dirhodium Tetraacetate/RNase A Adduct Can Be Used as Heterogeneous Catalysts

Abstract

Due to their unique coordination structure, dirhodium paddlewheel complexes are of interest in several research fields, like medicinal chemistry, catalysis, etc. Previously, these complexes were conjugated to proteins and peptides for developing artificial metalloenzymes as homogeneous catalysts. Fixation of dirhodium complexes into protein crystals is interesting to develop heterogeneous catalysts. Porous solvent channels present in protein crystals can benefit the activity by increasing the probability of substrate collisions at the catalytic Rh binding sites. Toward this goal, the present work describes the use of bovine pancreatic ribonuclease (RNase A) crystals with a pore size of 4 nm (P3 2 21 space group) for fixing [Rh 2 (OAc) 4 ] and developing a heterogeneous catalyst to perform reactions in an aqueous medium. The structure of the [Rh 2 (OAc) 4 ]/RNase A adduct was investigated by X-ray crystallography: the metal complex structure remains unperturbed upon protein binding. Using a number of crystal structures, metal complex accumulation over time, within the RNase A crystals, and structures at variable temperatures were evaluated. We also report the large-scale preparation of microcrystals (∼10−20 μm) of the [Rh 2 (OAc) 4 ]/RNase A adduct and crosslinking reaction with glutaraldehyde. The catalytic olefin cyclopropanation reaction and self-coupling of diazo compounds by these cross-linked [Rh 2 (OAc) 4 ]/RNase A crystals were demonstrated. The results of this work reveal that these systems can be used as heterogeneous catalysts to promote reactions in aqueous solution. Overall, our findings demonstrate that the dirhodium paddlewheel complexes can be fixed in porous biomolecule crystals, like those of RNase A, to prepare biohybrid materials for catalytic applications.

Real-time observation of a metal complex-driven reaction intermediate using a porous protein crystal and serial femtosecond crystallography

“…Since the HEWL crystal used as a model template can immobilize various organometallic complexes in the crystal 45 , their catalytic reactions can be observed directly by TR-SFX. In addition, protein crystals generally form pores with tens to hundreds of nm, which can provide appropriate chemical environments for investigating reactions 45 – 47 . Thus, the TR-SFX experiment of synthetic metal complexes immobilized in the HEWL crystals is the first appropriate demonstration showing the potential of our method.…”