Abstract
Assessment of van der Waals (VDW) interactions is fundamental to all of the central quest of structure that regulates the biological function. VDW interactions contributing to intramolecular weak hydrogen bonding are regarded as an important force to regulate the thermal stimuli-sensitive function of sulfobetaine methacrylate, DMAPS. We present here the conversion from the thermal-motion form at room temperature to the weak-hydrogen-bonded form against thermal motion as a terahertz spectral change with a definite isosbestic point from an absorption peak of one form to the other. Vibrational absorptions are used as a probe for assessing VDW interactions in conjunction with highly reliable and well-established density functional theory (DFT) calculations for analysis. Complicated spectral features and uncertain conformations of DMAPS in the amorphous state are clearly resolved under the polarizable continuum model and the dispersion correction for the pure DFT calculations.
Highlights
The van der Waals (VDW) interaction has become a hot topic in recent years as a constructing force of promising materials such as the VDW heterostructure[1,2,3,4], quantum liquid[5,6], the VDW bonded magnet[7], molecular diode[8], and Rydberg gas[9]
We have studied intermolecular weak hydrogen bonding of crystalline compounds using THz spectroscopy with density functional theory (DFT) calculations[30,31,32,33] and synchrotron FTIR microspectroscopy[34]
The far-infrared (FIR) spectral profile of DMAPS in the range from 140 to 700 cm−1 was measured by synchrotron FTIR microspectroscopy to investigate the behaviour at low temperature where VDW interactions become effective
Summary
The van der Waals (VDW) interaction has become a hot topic in recent years as a constructing force of promising materials such as the VDW heterostructure[1,2,3,4], quantum liquid[5,6], the VDW bonded magnet[7], molecular diode[8], and Rydberg gas[9]. DMAPS contains intramolecular weak hydrogen bonds predominantly governed by dispersion interactions such as the VDW force, and the formation of the intramolecular weak hydrogen bonds at low temperature is expected to affect the THz vibrations. To assess the VDW interaction, we study the low temperature behaviour of the biocompatible DMAPS molecule in the vibration absorption of THz spectroscopy and synchrotron FTIR microspectroscopy. We perform a gas-phase calculation for peak assignment instead of a solid-state calculation because the sample studied here is fully amorphous, Here, we incorporate the dielectric constant into the gas-phase calculation as the effect of the surrounding molecules with a large dipole moment, and perform the dispersion correction for the pure DFT calculation to describe the weak hydrogen bond
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