Publication Date

2019-05-01

Availability

Open access

Embargo Period

2019-05-01

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Chemistry (Arts and Sciences)

Date of Defense

2018-11-15

First Committee Member

Marc R. Knecht

Second Committee Member

James N. Wilson

Third Committee Member

Jean-Hubert Olivier

Fourth Committee Member

Sapna K. Deo

Abstract

The incorporation of photoswitchable molecules, specifically azobenzene, into the passivating ligands along nanoparticle (NP) interfaces can allow for the modulation of catalytic response by means of optical irradiation. These results are apparent in metallic nanoparticles passivated with peptide ligands that have been functionalized with an azobenzene photoswitch. By passivating particles with this peptide-photoswitch hybrid, the catalytic response of such materials changed according to the isomerization state of the photoswitch, i.e. trans or cis, which is easily triggered with specific wavelength of light. Presented in this dissertation are different applications of such reconfigurable ligands with nanomaterials in order to ascertain how overlayer rearrangement can affect nanoparticle catalysis. This is accomplished by first passivating Au NPs with two variations of the parent peptide (AuBP1) through placement of the photoswitch at either the N- or C- terminus. This initial attempt confirmed that the state of the photoswitch induced changes in the rate of 4-nitrophenol reduction, where one conformation produced a greater catalytic response compared to the other. These results were further expanded upon by studying the effect of peptide sequence and photoswitch placement through preparation of a hybrid that placed the azobenzene in the middle of the 12-mer sequence (AuBP1 and Pd4). Additional molecular modeling was performed for the new peptide ensembles, uncovering different modes of binding at the Au metallic interface. From this data, the catalytic rates were influenced by photoswitch placement within the same parent peptide, with additional changes noted between the two peptide-photoswitch hybrids. Lastly, the metal component was modified across two different monometallic (Pd and Ag) and bimetallic (Pd:Au) nanomaterial compositions. Through these variations the data revealed that the metal composition of the NP influenced both switching and reactivity. Together, these results present pathways towards the realization of photoactuatable materials that can undergo direct property manipulation via remote stimuli. This work serves as the basis for the eventual generation of remotely controlled “on/off” functionality of nanomaterials, which could be highly important for applications in catalysis, biosensing, drug delivery, etc.

Keywords

nanoparticles; peptides; biointerface reconfiguration; catalysis; photoactivated switch; azobenzene

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