Abstract
Multifunctional amide-containing self-assembled monolayers (SAMs) provide prospects for the construction of interfaces with required physicochemical properties and distinctive stability. In this study, we report the synthesis of amide-containing thiols with terminal phenylalanine (Phe) ring functionality (HS(CH2)7CONH(CH2)2C6H5) and the characterization of the formation of SAMs from these thiols on gold by reflection absorption infrared spectroscopy (RAIRS). For reliable assignments of vibrational bands, ring deuterated analogs were synthesized and studied as well. Adsorption time induced changes in Amide-II band frequency and relative intensity of Amide-II/Amide-I bands revealed two-state sigmoidal form dependence with a transition inflection points at 2.2 ± 0.5 and 4.7 ± 0.5 min, respectively. The transition from initial (disordered) to final (hydrogen-bonded, ordered) structure resulted in increased Amide-II frequency from 1548 to 1557 cm−1, which is diagnostic for a strongly hydrogen-bonded amide network in trans conformation. However, the lateral interactions between the alkyl chains were found to be somewhat reduced when compared with well-ordered alkane thiol monolayers.
Highlights
Self-assembled monolayers (SAMs) of functional thiol molecules at the gold metal surface modify interfacial physicochemical properties and provide a valuable platform for the investigation of specific interactions of the terminal functional group with solution components, provide the possibility to probe the mechanism of electron transfer reactions, and serve for the construction ofsensors and the development of biotechnological processes [1,2,3,4]
The MOPHE molecule consists of four molecular units: (i) the thiol group (SH), (ii) the chain (−(CH2 )7 −), (iii) the amide group (−CO−NH−), and (iv) the terminal Phe ring (Figure 1)
Each molecular group can be characterized by infrared spectroscopy
Summary
Self-assembled monolayers (SAMs) of functional thiol molecules at the gold metal surface modify interfacial physicochemical properties and provide a valuable platform for the investigation of specific interactions of the terminal functional group with solution components, provide the possibility to probe the mechanism of electron transfer reactions, and serve for the construction of (bio)sensors and the development of biotechnological processes [1,2,3,4]. Phe residue participates in a variety of noncovalent interactions involving the delocalized π-electron system, such as π-π stacking, CH-π, and cation-π [6,7,8,9]. These interactions are weak and difficult to study.
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