Effect of a Mixed Peptide Ligand Layer on Au Nanoparticles for Optical Control of Catalysis

Abstract

Inorganic colloidal nanoparticles are known for their efficient catalytic reactivities due to their enhanced surface-to-volume ratio. As an alternative to conventional synthetic methods, bioinspired approaches can sustainably generate stable colloidal nanoparticles where their reactivity can be tuned by the biomolecular overlayer structure. Recent studies have shown that incorporation of light-activated photoswitches into material-binding peptides could be used to optically and reversibly switch the biomolecular overlayer structure on Au nanoparticle surfaces, which has significant ramifications on the material catalytic reactivity. In this contribution, we demonstrate that the optical photoswitching capability and catalytic reactivity in these materials are highly dependent upon the composition of the biomolecular overlayer. For this, mixed monolayer-capped Au nanoparticles were prepared where the ratio of the parent material-binding peptide and the peptide with photoswitch included were varied. Key trends related to the photoswitching capability of the peptides and their overall reactivity were identified, where slower reactivity was noted for materials prepared using only the photoswitchable peptide. Taken together, these results demonstrate that the composition of the overlayer structure on Au nanoparticles is highly important in tuning the overall optical, photoswitching, and catalytic properties of these materials and can be used to refine the properties of the structure for their intended application.

Traffic Lights for Catalysis: Stimuli‐Responsive Molecular and Extended Catalytic Systems

“…[51-53, 66, 127] Further, incorporation of photoswitches in extended structures, micelles, and nanoparticles has resulted in biomimetic systems modeling enzyme behavior. [61][62][63][64][65][66][113][114][115][116][117][118][119][120][121][122][123][124][125][126][127][128] In addition to photoswitchable catalysis, notable work utilizing alternative stimuli, such as pH and temperature, has improved catalyst recyclability. [148,150] The mentioned studies also demonstrate the importance of the stimulus choice for tailoring catalytic activity of a particular system.…”

“…While the peptide ligands exhibit strong binding to the NP surface through noncovalent interactions, these interactions can be weakened by small changes (e.g., point mutations affecting residue sequence) which alter the conformation of the peptide with respect to the NP surface. [122] With this in mind, integration of an azobenzene moiety within the peptide sequence could allow for light-induced "mutations" that alter the peptide ligand binding strength. In fact, the presence of transazobenzene coincided with an increased rate (10.5 � 0.2 × 10 À 2 s À 1 ) for the reduction of 4-nitrophenol to 4-aminophenol, which could be attributed to weaker binding and dissociation of some ligands to expose a larger portion of the catalytically active NP surface.…”

“…In contrast, irradiation with 365-nm light to yield cis-azobenzene was accompanied with stronger binding of the peptide ligands and reduced reaction rate (9.4 � 0.7 × 10 À 2 s À 1 ). [122] A different example coupled a proline organocatalyst with gold NPs by covalently bonding the proline functionality to an aliphatic tail which could be coordinated to the metal surface by a thiol end group. [64] An azobenzene spacer was used within the aliphatic chain, allowing for modulation of the distance between the proline catalyst and NP surface (Figure 14).…”

“…As a result, photoswitches represent an avenue toward control of enzyme activity through alteration of active site geometry [62] . A conceptually different approach to modulating larger systems is through coupling of photoswitches through formation of extended periodic structures, such as covalent‐ and metal–organic frameworks (COFs and MOFs, respectively) [64, 121–126] . Choice of inorganic, organic, or hybrid materials as platforms allows for strategic engineering of distances and angles between catalytically active sites and confirmation of their location using single‐crystal X‐ray diffraction analysis.…”

“…Choice of inorganic, organic, or hybrid materials as platforms allows for strategic engineering of distances and angles between catalytically active sites and confirmation of their location using single‐crystal X‐ray diffraction analysis. Finally, catalytic activity of nanoparticles (NPs) could be controlled through an external stimulus by addition of a layer of photoswitchable ligands at the NP surface to regulate access to the catalytically active core [64, 121–126] …”