Reflection Absorption Infrared Spectroscopy Characterization of SAM Formation from 8-Mercapto-N-(phenethyl)octanamide Thiols with Phe Ring and Amide Groups

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.

Electrochemical Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy of Imidazole Ring Functionalized Monolayer on Smooth Gold Electrode

“…The spectral features at 1645, 1556, and 1264 cm −1 are assigned to amide bands, Am-I, Am-II, and Am-III, respectively, whereas the ones near 1460 and 1380 cm −1 to methylene scissoring and wagging deformations, δ(CH 2 ). The RAIRS-surface selection rule allows interrogating the orientation of molecular groups because the intensity of particular spectral mode directly depends on the projection of the mode’s transition dipole moment (TDM) on the surface normal [ 51 ]. While Am-I and Am-II have TDMs oriented perpendicular to each other in the amide bond plane, they also have perpendicular and parallel TDM orientations with respect to carbohydrate chain [ 51 ].…”

“…The RAIRS-surface selection rule allows interrogating the orientation of molecular groups because the intensity of particular spectral mode directly depends on the projection of the mode’s transition dipole moment (TDM) on the surface normal [ 51 ]. While Am-I and Am-II have TDMs oriented perpendicular to each other in the amide bond plane, they also have perpendicular and parallel TDM orientations with respect to carbohydrate chain [ 51 ]. Thus, for the neatly packed IMHA monolayer, the Am-II is expected to dominate the spectrum.…”

Electrochemical SEIRAS Analysis of Imidazole-Ring-Functionalized Self-Assembled Monolayers

“…Figure 3 shows ATR-FTIR spectra of IMHA, Frag, and an IMHA molecule recrystallized from ethanol-d 6 (IMHA-d). Assignments of the Im ring and amide spectral modes, based on the literature and our density functional theory (DFT) calculations, are given in Table 1 [ 4 , 6 , 7 , 8 , 11 , 25 , 26 , 27 , 28 , 29 ].…”

“…Figure 4 A shows the time-dependent adsorption SEIRAS spectra of the IMHA monolayer formation in the ethanol incubation solution. The planar amide bond, –CO–NH–, gives rise to Am-I and Am-II vibrations, for which the transition dipole moments (TDM) are orientated perpendicularly to each other ( Figure S1 ) [ 25 ]. Metal surface selection rule states that the intensities of spectral modes scale with respect to the TDM vector projection to the surface normal [ 36 ]; therefore, any changes in the amide plane orientation will be reflected in the altered Am-I and Am-II intensity patterns, which, conveniently, could be expressed as the intensity ratio Am-I/Am-II.…”

Zero-to-Two Nanoarchitectonics: Fabrication of Two-Dimensional Materials from Zero-Dimensional Fullerene

“…Functional materials in huge varieties have been prepared and fabricated through efforts in organic synthesis [ 7 , 8 , 9 , 10 ], polymer chemistry [ 11 , 12 , 13 ], coordination chemistry [ 14 , 15 , 16 , 17 ], supramolecular chemistry [ 18 , 19 , 20 , 21 ], and the other materials science especially for nanostructured materials [ 22 , 23 , 24 , 25 ]. Various fabrication techniques including the self-assembled monolayer (SAM) method [ 26 , 27 , 28 ], Langmuir–Blodgett (LB) technique [ 29 , 30 ], and layer-by-layer (LbL) assembly [ 31 , 32 ] have indispensable roles in the developments of functional materials as well as contributions with emerging materials such as nanocarbon materials [ 33 , 34 ] and nanoporous materials [ 35 , 36 ].…”