Helical Peptides Design for Molecular Dipoles Functionalization of Wide Band Gap Oxides

Abstract

The use of helical hexapeptides to establish a surface dipole layer on a TiO2 substrate, with the goal of influencing the energy levels of a coadsorbed chromophore, is explored. Two helical hexapeptides, synthesized from 2-amino isobutyric acid (Aib) residues, were protected at the N-terminus with a carboxybenzyl group (Z) and at the C-terminus carried either a carboxylic acid or an isophthalic acid (Ipa) anchor group to form Z-(Aib)6-COOH or Z-(Aib)6-Ipa, respectively. Using a combination of vibrational and photoemission spectroscopies, bonding of the two peptides to TiO2 surfaces (either nanostructured or single-crystal TiO2(110)) was found to be highly dependent on the anchor group, with Ipa establishing a monolayer much more efficiently than COOH. Furthermore, a monolayer of Z-(Aib)6-Ipa on TiO2(110) was exposed for different binding times to a solution of a zinc tetraphenylporphyrin (ZnTPP) derivative terminated with an Ipa anchor group (ZnTPP-P-Ipa). Photoemission spectroscopy revealed that ZnTPP-P-Ipa partly displaced Z-(Aib)6-Ipa, forming a coadsorbed monolayer on the oxide surface. The presence of the peptide molecular dipole shifted the HOMO levels of the ZnTPP group to lower energy by ∼300 meV, in accordance with a simple parallel plate capacitor model. These results suggest that a mixed-layer approach, involving coadsorption of a strong molecular dipole compound with a chromophore, is a versatile method to shift the energy levels of such chromophores with respect to the band edges of the substrate.

Bioinspired Phosphatase-like Mimic Built from the Self-Assembly of De Novo Designed Helical Short Peptides

“…The spectra displayed a double-negative Cotton effect around 204 and 214 nm along with a positive peak at 196 nm, which is the characteristic pattern of the helical conformation built by short peptides. − Compared with the spectrum of typical α-helix in proteins, the shorter length of the helix results in a slight blue-shift of the characteristic peaks by 3–7 nm and a lower intensity of the signals. , This result was also supported by attenuated total reflectance-infrared Fourier transform infrared (ATR-FTIR) and Raman spectra (Figures S7 and S8). − The secondary structure assignment based on amide I and amide III bands showed that helical structures dominated the backbones of both heptapeptides.…”