Theoretical Study On The Spectrum And Active Sites Of Catecholamine Molecule

Catecholamines are a widely studied class of neurotransmitters and hormones,which are closely related to people’s health and diseases,and have important physiological functions and pharmacological properties.Firstly,Gentor software was used to search the molecular conformations of epinephrine,norepinephrine and dopamine,and the initial conformations of27,27 and 9 molecules were obtained respectively.Then these initial conformations were optimized and calculated by single point energy,and the most stable molecular conformations were obtained by energy comparison.Finally,the stable configurations of epinephrine,norepinephrine and dopamine were analyzed.Then Multiwfn3.7 software was used to draw their infrared spectra and conduct vibration analysis,and compare and analyze with the experimental data.Then,on the basis of stable structure optimization,based on time-dependent density functional theory（TD-DFT）,the excitation energies of the first 50excited states of epinephrine,norepinephrine and dopamine molecules were calculated,and the ultraviolet spectra were drawn and the excitation properties were analyzed,and compared with the experimental data.Finally,the active sites of epinephrine,norepinephrine,and dopamine were predicted by three methods:frontline orbit,Fukui function,and double descriptor.It can be seen from the analysis that the theoretical and experimental infrared spectra of epinephrine,norepinephrine and dopamine are in good agreement at 2500-400 cm^-1,but the spectra are quite different above 2500 cm^-1.This is due to the formation of hydrogen bonds between the epinephrine,norepinephrine and dopamine molecules,which weakens the o-H bond and leads to a decrease in absorption frequency,resulting in a wide peak between3500-2500 cm-1.Epinephrine has a uv absorption peak at 270.6652 nm and a molar absorption coefficient of 2655.3796 L/mol/cm at 200-400 nm,which is mainly generated byπ→π*transition in benzene ring.The corresponding main transitions are from the ground state to the 2,4,7,15,16,19,21 and 23 excited states respectively.Norepinephrine has two UV absorption peaks at 200.4603 nm and 288.5739 nm,respectively,and the molar absorption coefficients are 25501.8733 L/mol/cm and 3058.9046 L/mol/cm,respectively.It is mainly formed byπ→π*and n→σ*transitions at 200.4603 nm,and produced byπ→π*transitions at 288.5739 nm.The corresponding major transitions are from the ground state to the first,second,seventh,thirteenth,sixteenth,seventeenth,eighteenth and twenty-second excited states respectively.Dopamine has a uv absorption peak at 256.8166 nm at 200-400 nm,and the molar absorption coefficients are 5089.7810 L/mol/cm,which is mainly generated byπ→π*transition in benzene ring.The corresponding main transitions are from the ground state to the 4th,6th,11th,13th,14th,15th,16th and 17th excited states respectively.The active sites of epinephrine,norepinephrine and dopamine were predicted by the three methods of frontline orbit,Fukui function and double descriptor,and the prediction results of their active sites were consistent.The results showed that the N22 atom in epinephrine was most likely to be the electrophilic active site of the molecule,at the same time,the bond energies of N22-C14,N22-C18 and N22-H17 bonds were calculated to be 0.2746,0.3852,0.1687 Hartree;C2 and C5 were most likely to be the nucleophilic active site of epinephrine,The bond energies of C2-H7 and C5-H9 are 0.0799 Hartree and 0.1014 Hartree.Under different chemical conditions,it produces substances such as epinephrine red,3,4-dihydroxymandelic acid,and norepinephrine.The N21 atom in norepinephrine is most likely the electrophilic active site of the molecule,the bond energies of its N-H and C18-N21 bonds are 0.1635Hartree and 0.1781 Hartree,respectively;The C1 and C4 atoms may be the nucleophilic active site of norepinephrine,the bond energy of C1-H7 is 0.0756 Hartree and the bond energy of C4-H9 is 0.0942 Hartree.Under different chemical conditions,it produces substances such as adrenaline molecules and 3,4-dihydroxyphenylethylene glycol.The O19atom in dopamine is most likely the electrophilic active site of the molecule,the C6-O19 bond and O19-H20 bond energies are 0.1733 Hartree and 0.08698 Hartree,respectively;The C2and C5 atoms may be the nucleophilic active site of the dopamine molecule,the bond energies of C2-H7 and C5-H9 are 0.0721 Hartree and 0.0896 Hartree respectively.So when the dopamine molecule is disconnected from O19-H20,and its H20 atom will be replaced by other groups to generate 5-（2-aminoethyl）-2-methoxyphenol.This study is of great significance for the detection of catecholamine and their physical and chemical properties,and also provides theoretical basis for the metabolic mechanism,degradation reactions and drug safety of catecholamine.