Study Of Density Functional Theory For Vibrational Spectrum And Surface-enhanced Raman Spectrum Of Local Anesthetic Molecules

Benzocaine（ABEE）,procaine（PRC）,tetracaine（TTC）and so on,as a kind of local narcotic drugs,are often added in cosmetics,livelihood supplies,and even drug fillers,which are more and more serious threats to human health.At present,most methods for detecting local anesthetics need to be pretreated,the detection process is complicated and the cost is high.As a highly sensitive fingerprint spectroscopy technology,Surface Enhanced Raman Spectroscopy（SERS）has attracted more and more attention in rapid drug detection and analysis of real and fake drugs due to its advantages such as no complicated pretreatment,convenient detection and less interference from water environment,etc.In this paper,the Raman spectra of three kinds of local anesthetics were studied by DFT theory and experiment:1.In the ABEE molecules,density functional theory（DFT）is used to optimize the structure of ABEE and Au-ABEE by using Lanl2dz pseudo potential basis set for Au clusters and 6-311+G（d,p）basis set for C,H,O,N atoms at B3LYP level.The calculated Raman spectra are in good agreement with the experimental SERS spectra.According to the analysis of molecular electrostatic potential,when ABEE molecules interact with metal substrates,it is predicted that O,N and benzene rings will mainly adsorb on the substrates.Among them,617,855,1034 and 1604 cm^-1can be used as the characteristic peaks for SERS rapid detection of ABEE.The difference between HOMO and LUMO energy levels is estimated to be between 296 nm and 455 nm.2.In the of PRC molecules,density functional theory（DFT）is used to optimize the structure of PRC and Au-PRC by using Lanl2dz pseudo potential basis set for Au clusters and6-311+G（d,p）basis set for C,H,O,N atoms at B3LYP level.The calculated Raman spectra are in good agreement with the experimental SERS spectra.the analysis of molecular electrostatic potential shows that when PRC molecules interact with metal substrates,it is predicted that the adsorption between PRC molecules and substrates mainly occurs through O,N and benzene rings.In the detailed identification of SERS spectrum,617,841,1244 and1599 cm^-1could be used as characteristic peaks.The difference between HOMO and LUMO energy levels is estimated to be between 254-453 nm.3.In the TTC molecule,DFT theory was used to optimize the structure and calculate the frequency of TTC molecule,and the Raman spectrum and infrared spectrum of TTC were obtained.The experimental and theoretical results were basically consistent.The main characteristic peaks in the experimental and theoretical spectra were linearly fitted,the correlation coefficients of infrared spectrum R=0.999 and Raman spectrum R=0.998 were basically consistent,which indicated that the DFT theoretical calculation method used in this paper was feasible.The difference of HOMO and LUMO is 4.78 e V,and the excitation wavelength isλ=259 nm.The analysis of molecular electrostatic potential shows that when TTC molecules interact with metal SERS substrate,it is predicted that the adsorption of O and N with substrate will produce chemical enhancement effect.By Mulliken layout analysis,the positive and negative charges of C atoms in the benzene ring of TTC molecules are alternately distributed,forming a large delocalizedπbond.The characteristic peaks of the three local anesthetics were 639,1175,1282,1605 and 1682 cm^-1,which provided a theoretical basis for the detection and subsequent development of local anesthetics.