Biomimetic Crystallization of MnFe₂O₄ Mediated by Peptide‐Catalyzed Esterification at Low Temperature

Abstract

Enzymes are some of the most efficient catalysts in nature.I fs mall catalytic peptides mimic enzymes,t here is potential for broad applications from catalysis for new material synthesis to drug development, due to the ease of molecular design.R ecently ah ydrogel-based combinatory phage display library was developed and proteasemimicking peptides were identified. Here we advanced the previous discoverytoapply one of these catalytic peptides for the synthesis of bimetal oxide nanocrystals through the catalytic ester-elimination pathway.C onventional bimetal oxide crystallizationu sually requires high temperatures above several hundred 8C; however,t his catalytic peptide could grow superparamagnetic MnFe 2 O 4 nanocrystals at 4 8C. Superconducting quantum interference device (SQUID) analysis revealed that MnFe 2 O 4 nanocrystals grown by the catalytic peptide exhibit superparamagnetism. This study demonstrates the usefulness of protease-mimicking catalytic peptides in the field of material synthesis.Enzymes in nature are evolvede fficiently to catalyzem aterial growths in high yield and high selectivity at low temperature. Up to now,b iomineralizing enzymes and peptides that catalyze the growth of metal nanocrystals have been isolated from tissues and cells of animals andm icroorganisms.[1] Recent comprehensive proteomic studies discovered metal-binding proteins that playc ritical roles in biomineralization.[2] For instance, the proteins derived from magnetotactic bacteria (e.g., Mms6) [2a] control the morphologies of magnetite crystalsi nt he magnetosome organelles.[3] The biomineralization pathway starts from the uptake of metal precursors on metal-binding peptides ites, and then their catalytic properties nucleate and facilitatec rystal growths. The biomineralization process is so efficient that crystals can be grown with low energy consumption (e.g.,a tl ow temperature). Thus far,s everal promising peptides or proteins can be used to catalyzet he growth of inorganic nanomaterials. [4] Recently,p rotease-mimickingC P4 peptides were used to catalyzeZ nO nanocrystal formation through ester elimination.[5] Ester elimination favors the growth of metal oxides from metal acetate precursors through reverse hydrolysiso f esters in organic environments, such as alcohols at high temperature.[6] The CP4 peptide was discovered from ac ombinatorial phage-display peptide libraryt hrough ah ydrogel-based biopanning process where phage viruses possessing proteaselike activity can be purified by centrifugation due to product gel formation around peptides displayed at the tail of viruses. [5,7] Previously,t his type of phage biopanning was also applied to identify peptides that can target cancer and stem cells.[8] The CP4 peptidei sa ne fficient catalystf or metal oxide formation through the ester elimination pathway,a nd its amino acid residues (in particular, serine and lysine residues) could play an important role for crystallization.[5] While protease can catalyze the reverseh ydrolysis of ester, [9] natural pr...

Design of Catalytic Peptides and Proteins Through Rational and Combinatorial Approaches

“…The ester elimination reaction catalyzed by CP4 peptide can be a general way to synthesize industrially important metal oxides. CP4 peptide also catalyzes the crystallization of the spinel ferrite MnFe 2 O 4 (Figure 4e,f) (88a), which is used in electrode materials in lithium ion batteries (89, 90), magnetic storage (91), ferrofluids (92, 93), catalysts (94), and biomedical applications (95; Y. Maeda, J. Fang, Y. Kezoe, D. Pike, V. Nanda & H. Matsui, manuscript submitted). In a methanol–benzyl alcohol solvent system (50% volume ratio), CP4 peptide can crystallize MnFe 2 O 4 nanoparticles under ambient temperature.…”