Non-covalent Interactions Of Sulfur-bearing Five-member Rings Studied By High Resolution Rotational Spectroscopy

Sulfur-bearing five-member rings heterocycles are important components of many natural compounds and drug active intermediates with biological activity.The activity of these compounds especially in the gas phase is directly related to the non-covalent nature of the interaction with the receptor.However,there are few studies on the non-covalent interactions of sulfur-bearing five-member rings.Molecular complexes is studied in the gas phase can avoid the interference of factors such as solvation and crystal effect,and obtain detailed non-covalent interaction information.Rotation spectroscopy is a reliable experimental method to study molecular complexes,with high detection sensitivity and spectral resolution,and is the most direct and effective means to explore non-covalent interactions in the gas phase.Based on this,Fourier-transform microwave spectroscopy was used to explore with the non-covalent interactions characteristics of sulfur-bearing five-member rings.The2-thiophenecarboxaldehyde,thiazole,tetrahydrothiophen-3-one as model,was selected to study the rotational spectroscopy of these with water combining the theory of quantum chemistry calculation,to characterize the conformation,geometric structure and energy of complex,to reveal the structure and energy characteristics of non covalent interaction between them and water.The details are as follows:The first chapter is the introduction,which summarizes the research progress of non-covalent interactions of sulfur-bearing five-member rings,the theoretical and experimental techniques of rotational spectroscopy and the theoretical calculation methods of quantum chemistry,and points out the research purpose and significance of this paper.The second chapter to the fourth chapter are the main content of this paper,described the 2-thiophenecarboxaldehyde-water complex,thiazole-water complex and tetrahydrothiophen-3-one-water complex research results,respectively.The main results are as follows:2-thiophenecarboxaldehyde-water complex:The conformational optimization and frequency analysis of 2-thiophenecarboxaldehyde-water complex were carried out using MP2/6-311++G（d,p）level of theory.Then Fourier-transform microwave（FTMW）spectrometer was used to search rotational spectra of the different isomers of2-thiophenecarboxaldehyde-water complex.Finally,the existence of two stable isomers was confirmed by spectral analysis.The two isomers were the cis and trans conformers of 2-thiophenecarboxaldehyde monomer formed by the interaction with water（denotated as cis-w-1 and trans-w-1）.The experimental results showed that the population of cis-w-1 and trans-w-1 was about 4:1.In addition,the rotational spectra of four isotopologues of water(H₂¹⁸O,DOH,HOD and D₂O)of the two isomers have been measured,respectively.We determined the structural parameters of the observed isomers using the experimental parameters.According to NCI,QTAIM and NBO analyses,the two isomers all contain an O―H···O hydrogen bond and a C―H···O weak hydrogen bond.SAPT energy decomposition analysis showed that the non-covalent interactions of the two isomers were dominated by electrostatic,and the total interaction energies were-22.5 k J·mol^-1 and 26.5 k J·mol^-1,respectively.Thiazole-water complex:The structure and non-covalent interactions of thiazole-water complex were studied by supersonic jet FTMW spectroscopy and theoretical calculations.The experiment confirmed the existence of one isomer corresponding to the theoretically predicted minimum energy.In addition,the rotational spectra of nine isotopologues of this isomer,including isotopologues of five heavy atomic(³⁴S,¹³C,and ¹⁵N)from mono-substituted thiazoles and four isotopologues of water(H₂¹⁸O,DOH,HOD,and D₂O)were determined.We determined the structural parameters of the observed isomer using the experimental parameters.According to NCI,QTAIM and NBO analysis,thiazole and water are connected by an N···H―O hydrogen bond.SAPT energy decomposition analysis showed that the non-covalent interaction of the isomer was dominated by electrostatic,and the total interaction energy was-25.1 k J·mol^-1.Tetrahydrothiophen-3-one-water complex:We optimized the structure of Tetrahydrothiophen-3-one with water complex using the B3LYP-D3（BJ）/DEF2-TZVP level of theory.The structure and the non-covalent interaction were studied by using supersonic jet FTMW spectroscopy.The experiment confirmed the existence of one isomer corresponding to the theoretically predicted minimum energy.In addition,the rotational spectra of two isotopologues of oxygen(H₂¹⁸O and C=¹⁸O)of this isomer have been measured.We determined the structural parameters of the observed isomer using the experimental parameters.According to NCI,QTAIM and NBO analysis,an O―H···O（C=O）hydrogen bond and a C―H···O（H₂O）hydrogen bond have been established between tetrahydrothiophen-3-one and water.SAPT energy decomposition analysis showed that the non-covalent interaction of the isomer was dominated by electrostatic,and the total interaction energy was-23.3 k J·mol^-1.The fifth chapter summarizes the research results of this paper and prospects the problems to be solved in the future.