Optics and Spectroscopy, 2025 Volume 133, Issue 5,Pages 425–436(Mi os1910)
Proceedings of The XXVIII Annual International Conference "Saratov Fall Meeting 2024", September 23-27, 2024 Spectroscopy and physics of atoms and molecules
Raman structural analysis of polyethylene glycols: experimental study and quantum chemical modeling
Abstract:
In spite of wide and diverse practical applications of polyethylene glycols (PEG), dependence of Raman spectra of these substances on molecular weight, structure of terminal groups and conformational composition is still little studied. In this work we experimentally study Raman spectra of liquid samples of ethylene glycol, tri(ethylene glycol), tetra(ethylene glycol), PEG400 and PEG600 as well as methylated mPEG550 and mPEG750. With increase in the number of PEG monomeric units the most noticeable changes are observed for wavenumbers of the bands at 321, 832 and 1125 cm$^{-1}$ and intensities of the bands at 885, 1043 and 1125cm$^{-1}$. We showed that Raman spectra of mPEGs contain additional feature compared with the PEG spectra, namely the band at 2830 cm$^{-1}$. This band is related to the vibrations of O–CH$_3$ groups. In theoretical part of this work we analyze 16 approximations using the density functional theory for modeling the structure and Raman spectra of PEG molecules in the 7$_2$ helix conformation using the ethylene glycol nonamer as an example. By comparing with experimental data from Raman spectroscopy and X-ray diffraction, we show that the combination of the generalized gradient approximation functional OLYP and the basis set of the 4z of Gaussian functions type is the most suitable for calculating the structure and Raman spectra of PEG molecules.
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