Raman Spectroscopy Of Triazole Compounds In Solutions

Triazole compounds have a wide range of biomedical activities and are the structural units of many clinical drugs.In the technical field,triazoles have been applied as corrosion inhibitors for metals and alloys protection.As an important ligand,triazole derivatives have also been used to synthesize novel organic metal framework materials with high catalytic performance in recent years.Triazole compounds have abundant chemical changes in solution,such as protonation,dephosphorization,molecular association,tautomerism and so on.Understanding their solution properties is of great significance for their applications in various fields.In this dissertation,the Raman spectra of some triazole compounds in solution were studied by means of spectroscopic experiments and quantum chemical calculations,and the characteristics of their molecular vibrations were analyzed in detail.These studies can not only deeply understand the structure and chemical changes of related molecules in solutions,but also provide a basis for using Raman spectroscopy as a tool to study their mechanism of drug action and corrosion inhibition.The first chapter briefly introduces the fundamental knowledge of Raman spectroscopy and quantum chemistry calculation,the properties and applications of triazole compounds,and the Raman studies of triazole compounds reported in literature.The research background and scientific significance of this dissertation are also briefly introduced.In the second chapter,the Raman spectra of 1,2,4-triazole-3-carboxylate(TC-anion)and its ring-deprotonated derivative(dpTC2-)in aqueous solutions were measured.The density functional theory(DFT)calculations were performed using MN15 function and PCM solvent model to investigate their structures,as well as the vibrational frequencies and Raman intensities.With the aid of the calculated spectra,all the observed Raman bands of dpTC2-were clearly assigned,when taking into account the deuteration shifts.Various protonic tautomers of TC-anion were compared in the present theoretical calculations,and 2H-tautomer was found more stable.The experimental Raman spectrum of TC solution was roughly consistent with the calculated spectrum of the monomeric 2H-tautomer of TC-,but some splits existed for a few bands when comparing to the calculated spectra,which might be contributed by the hydrogen-bonding dimers of TC-.In the third chapter,the Raman spectra of 1,2,4-triazole(Trz)in neutral,alkaline,and acidic aqueous solutions were measured.The solution conditions and spectral changes of neutral free base(HTrz),deprotonated anion(Trz-)and protonated cation(H2Trz+)were investigated.The vibration frequencies and Raman intensities were calculated with B3LYP functional and PCM solvent model.Based on DFT calculation and deuterated isotope shifts,the Raman bands of HTrz,Trz-and H2Trz+ were clearly assigned.The Raman spectra of Trz in methanol,acetone,acetonitrile and acetic acid were measured.It was found that the spectrum of Trz in the protic methanol is close to the neutral aqueous solution.In the aprotic acetone and acetonitrile,some Raman bands of Trz show large shifts or splitting in comparison with the aqueous solution,which is attributed to the formation of Trz dimer due to the intermolecular hydrogen bonding.In acetic acid,Trz exists in the form of neutral free base,but its Raman bands were significantly broadened.Meanwhile,the Raman spectrum has significant changes in the C=O stretching vibration region of the solvent molecules,reflecting the strong hydrogen bonding between HTrz and the solvent molecules.These studies revealed the spectral characteristics of Trz as a free base,protonated cation,or deprotonated anion,and also provided useful information on the solute-solute,solute-solvent intermolecular hydrogen bonding in different solvent environments.