Аннотация:Quantum chemical modeling is a powerful tool to study the conformational composition and the vibrational spectra of organic molecules. In particular, such modeling allows to identify the most probable molecular conformations, assign IR and Raman bands to the particular vibrations and determine the general regularities in dependences of the vibrational spectra on the chemical structure and the conformational composition of molecules.In this work, we used density functional theory (DFT) to study the structure and Raman spectra of L-lactide (LA) and ε-caprolactone (CL) oligomers with the aim to identify the Raman bands, which depend on the length and conformation of sequence of the monomeric units. This information is necessary for Raman evaluation of microstructure of LA/CL copolymers chains. These copolymers are very important as bioresorbable and biocompatible materials with adjustable degradation profile for novel applications in medicine.We showed that the most probable conformation of LA oligomers is helix 103. The conformation of helix 31 is much less probable. If we do not apply any constraints during geometry optimization procedure, it easily transforms to the conformation of helix 103.The DFT calculations showed that the most probable conformation of CL oligomers is all-trans conformation. For both LA and CL oligomers the simulated Raman spectra describe well the main bands of poly(L-lactide) and poly(ε-caprolactone).This study was supported by the Russian Science Foundation under the grant № 23-22-00347, https://rscf.ru/en/project/23-22-00347/. We are grateful to the Joint Supercomputer Center of the RAS for the possibility of using their computational resources for our calculations.
