Application Of Raman Optical Activity Spectroscopy In Structural Investigation Of Chiral Drug Penicillamine

Chirality is widespread in biomolecules such as amino acids,proteins,and most chiral drugs.The researches on these aspects gradually attract more attention.Raman Optical Activity(ROA)spectroscopy is an extremely powerful tool for studying chiral molecules,which can not only detect absolute configurations but also provide rich stereochemical information,including sophisticated and complex structure change information together with side-chain supplementary information.Compared with other traditional methods,ROA has another significant advantage of being very suitable to test in aqueous environments and physiological environments.In this study,ROA was exploited to investigate the structural characteristics of penicillamine for the first time under the assistance of the density functional theory(DFT)method.The conformational changes of penicillamine in different states and different pH environments were also explored.Besides,the information of penicillamine’s structural changes after interacting with various metal ions was recorded in this study.These results laid the foundation for further research of its pharmacological effects on the human body.Now the results are summarized as follow:(1)The Raman and ROA spectra of penicillamine in the solid state were obtained by using the 457 nm short-wavelength ROA spectrometer.The assignments of spectral peaks were achieved according to the results of DFT calculation in the gas state,which revealed that the corresponding relationship between the Raman and the ROA peaks,and the reasons for the change of the ROA spectra under different states were analyzed.(2)The ROA spectroscopy in combination with the DFT calculation was used to explore the structural changes of penicillamine under different acid-base states in aqueous solutions.The peak assignments of ROA spectra of penicillamine,as well as the relationship between conformations of penicillamine and ROA peaks,were intensively studied and elucidated for the first time.The most distinct part of the ROA spectra focus on the fingerprint region(600-1500 cm-1),where two ROA couplets and one ROA triplet with different patterns were recognized.The influence of pH on the conformational changes and the characteristics of ROA spectra of penicillamine were investigated,and the corresponding regular patterns were concluded.Moreover,the isotope exchange was carried out for verifying and separating the corresponding vibration modes,especially the ROA peaks of the deuterated amino group were sensitive to the change of ambient environments.(3)The ROA spectroscopy in combination with electronic circular dichroism spectroscopy was exploited to inspect the conformational changes of the penicillamine molecule after it was chelated with various metal ions in a monodentate,bidentate or tridentate fashion,respectively.The metal ions include silver ion,zinc ion,nickel ion,and mercury ion.The influence of different ratios of penicillamine to metal ions was also explored.The state of the electron acceptor and the donor as well as the steric hindrance effect of the molecule had an impact on the tendency of different groups(such as NH2)to interact with metal ions,which led to the changes of local vibrational environments and the spectra.