Weak Interaction Study Of Terahertz Spectra For Purines And Its Derivatives

Terahertz(THz)wave is a segment of electromagnetic wave between microwave and infrared radiation.The applications involved in THz technology are applied to the intersection domains of biomedicine,materials science and communication technology.THz time-domain spectroscopy(THz-TDS)technology is one of the typical applications for THz technology.It is an extremely efficient tool to study biomolecules by measured the sample optical parameters to obtain the unique structural and vibrational information of biomolecules via THz-TDS technology.In this paper,the THz absorption spectra of purine and its derivatives in the range of 0.3?1.9 THz at room temperature were measured by the THz-TDS system,and then the vibration and dispersion characteristics of the THz absorption spectra were analyzed in detail.The main research contents are as follows:1.The samples of purine and its derivatives were measured by THz-TDS and the THz absorption spectra of them were studied.The THz time-domain spectra of samples were measured,the frequency domain spectra of them were obtained after Fourier transform,and the THz absorption spectra of all samples were then stuided.The experimental results show that the amounts of characteristic absorption peaks of THz absorption spectra for each sample are increased gradually,and all of samples have their own fingerprint spectrum.Due to the difference in the molecular structure of isomers and the optimized stable configuration,the absorption characteristics of THz spectra of the two isomers are also significantly different.The THz absorption spectra can reflect the configuration and conformation changes of purines and its derivatives.2.The cluster model construction and theoretical simulation of purines and their derivatives were studied.The construction scheme of cluster model from known crystal structure was explored.Solid density functional theory(DFT)was employed to perform the theoretical calculation for all clusters,and the absorption phenomenon of THz spectra was demonstrated by theoretical calculation results.The theoretical calculation results show that the simulation results of DFT / B3 LYP combined with the molecular cluster model can predict the absorption peaks of THz absorption spectrum properly,and the absorption peaks of the theoretical simulation curves is basically consistent with the THz experimental spectra.3.The vibration characteristics of the THz absorption spectra of purines and its derivatives were studied.Potential energy distribution(PED)and vibration vector graphs of clusters were successfully appiled to identify the characteristic absorption peaks of theoretical calculation spectra.PED analysis results show that the vibration mode of hypoxanthine and allopurinol isomers shows a big difference.The vibration modes of hypoxanthine cluster are all dihedral angle torsion,while the vibration modes of allopurinol cluster are dihedral torsion and bond angle bend vibration.The total vibration modes of purine and allopurinol clusters are four types of vibrations,bond angle bend and dihedral angle torsion et al,which are related to a certain carbon,nitrogen and hydrogen atoms except oxygen atoms.However,the total vibration modes of uric acid,hypoxanthine and allantoin clusters are three types of vibrations,bond length bend and dihedral angle torsion et al,which vibration atoms are related to hydrogen,carbon,oxygen and nitrogen elements.4.The dispersion characteristics of the THz absorption spectra of purines and its derivatives were studied.The energy decomposition analysis based on molecular forcefield(EDA-FF)method and VMD software were carried on qualitative analysis and atomic coloring diagrams visualization for weak interaction of all clusters.The EDA-FF results show that the electrostatic interaction of hypoxanthine and Allopurinol clusters provides a primary contribution to total interaction energy,the contribution of dispersion interaction for second.The amounts of hydrogen bond of allopurinol system are double as hypoxanthine.In contrast,the dispersion interaction make a more contribution than electrostatic interaction to the total interaction energy of the purine,uric acid and allantoin clusters,and uric acid cluster has formed more hydrogen bonds because of more oxygen atoms than the purine.The dispersion visualization analysis shows that the dispersion of each cluster is primarily reflected on the donor and acceptor atoms directly interacted with hydrogen bonds.The above research results provide a new idea for the further exploration the structure and non-bond interactions of molecules,and inspired applications by THz-TDS technology,combined with DFT and DEA-FF method.