Chemistry Department , Rutgers University , 73 Warren Street , Newark , New Jersey 07102 , United States.
Department of Physics and Astronomy and Laboratory for Surface Modification , Rutgers University , 136 Frelinghuysen Road , Piscataway , New Jersey 08854 , United States.
J Am Chem Soc. 2020 Feb 19;142(7):3489-3498. doi: 10.1021/jacs.9b12001. Epub 2020 Feb 11.
The use of helical hexapeptides to establish a surface dipole layer on a TiO 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)-COOH or Z-(Aib)-Ipa, respectively. Using a combination of vibrational and photoemission spectroscopies, bonding of the two peptides to TiO surfaces (either nanostructured or single-crystal TiO(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)-Ipa on TiO(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)-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.
利用螺旋六肽在 TiO 基底上建立表面偶极层，以影响共吸附生色团的能级，这一策略得到了探索。两种螺旋六肽由 2-氨基异丁酸（Aib）残基合成，在 N 端用羧基苄基（Z）保护，在 C 端分别携带羧酸或间苯二甲酸（Ipa）锚定基团，形成 Z-（Aib）-COOH 或 Z-（Aib）-Ipa。通过振动和光电子能谱的结合，发现这两种肽与 TiO 表面（无论是纳米结构还是单晶 TiO(110)）的键合高度依赖于锚定基团，Ipa 比 COOH 更有效地形成单层。此外，Z-（Aib）-Ipa 在 TiO(110)上的单层暴露于具有 Ipa 锚定基团的锌四苯基卟啉（ZnTPP）衍生物的溶液中不同的结合时间。光电子能谱揭示了 ZnTPP-P-Ipa 部分取代了 Z-（Aib）-Ipa，在氧化物表面形成共吸附单层。肽分子偶极的存在将 ZnTPP 基团的 HOMO 能级向下移动了约 300 meV，符合简单的平行板电容器模型。这些结果表明，涉及与生色团共吸附强分子偶极化合物的混合层方法是一种灵活的方法，可以改变此类生色团相对于基底能带边缘的能级。
