Hydrogen-Bond-Induced Dual Structural Response in Amide-Functionalized Self-Assembled Monolayers
- 1Institute for Basic Science (IBS
- 2Department of Chemistry
- 3Korea University
Abstract
Internal functionalization can reorganize intermolecular interactions across a self-assembled monolayer (SAM), yet its depth-dependent consequences remain poorly understood. Here, molecular dynamics simulations and vibrational sum-frequency generation (VSFG) spectroscopy reveal a dual structural response in N-(2-mercaptoethyl)heptanamide SAMs on Au(111). A persistent intermolecular hydrogen-bond network suppresses conformational fluctuations between the Au-S interface and the amide plane. Above this plane, however, the larger volume of the amide increases alkyl-chain separation and weakens van der Waals coupling and enhances conformational flexibility with temperature. Thus, a hydrogen-bond-stabilized, solid-like lower region coexists with a weakly coupled, liquid-like upper region. Simulated VSFG spectra reproduce the observed terminal CH3 stretching-mode intensities, including the enhanced asymmetric response. This response occurs without a correspondingly large average methyl tilt angle because inequivalent molecular environments produce broad, heterogeneous orientation distributions. Consequently, the conventional assignment of a single methyl tilt angle from VSFG intensity ratio breaks down for internally functionalized SAMs.
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BibTeX
@misc{sadiq2026hydrogenbondinduced,
title = {{Hydrogen-Bond-Induced Dual Structural Response in Amide-Functionalized Self-Assembled Monolayers}},
author = {Saima Sadiq and Hojeong Yoon and Junhyeok Park and Kyungwon Kwak and Minhaeng Cho},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15009617/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009617/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Hydrogen-Bond-Induced Dual Structural Response in Amide-Functionalized Self-Assembled Monolayers
AU - Saima Sadiq
AU - Hojeong Yoon
AU - Junhyeok Park
AU - Kyungwon Kwak
AU - Minhaeng Cho
PY - 2026
DA - 2026/09/29
PB - ChemRxiv
DO - 10.26434/chemrxiv.15009617/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009617/v1
AB - Internal functionalization can reorganize intermolecular interactions across a self-assembled monolayer (SAM), yet its depth-dependent consequences remain poorly understood. Here, molecular dynamics simulations and vibrational sum-frequency generation (VSFG) spectroscopy reveal a dual structural response in N-(2-mercaptoethyl)heptanamide SAMs on Au(111). A persistent intermolecular hydrogen-bond network suppresses conformational fluctuations between the Au-S interface and the amide plane. Above this plane, however, the larger volume of the amide increases alkyl-chain separation and weakens van der Waals coupling and enhances conformational flexibility with temperature. Thus, a hydrogen-bond-stabilized, solid-like lower region coexists with a weakly coupled, liquid-like upper region. Simulated VSFG spectra reproduce the observed terminal CH3 stretching-mode intensities, including the enhanced asymmetric response. This response occurs without a correspondingly large average methyl tilt angle because inequivalent molecular environments produce broad, heterogeneous orientation distributions. Consequently, the conventional assignment of a single methyl tilt angle from VSFG intensity ratio breaks down for internally functionalized SAMs.
ER -