Abstract：Epinephrine is a neurotransmitter and hormone transmitter. Studying the spectra and energy levels of the epinephrine molecules may help to understand their chemical stability and pharmacological effects. Based on density functional theory (DFT), the structure of epinephrine was optimized by using Software Gaussian 09 at the level of B3LYP/6-311G(d, p) in this article. On this basis, the first 20 excited states of epinephrine molecule were calculated by using the time-dependent density functional theory (TD-DFT) at the level of PBE/def2tzvp in the gas phase, and ultraviolet spectrum was drawn by using Multiwfn3.7 (dev) software and the properties of excitation are analyzed. The main transitions corresponding to the UV spectrum of adrenaline molecules are those from the ground state to the first, second, fourth, eighth, 15th and 16th excited states respectively. The oscillator strength of other excited states is lower than the threshold value of 0.03. The theoretical calculation showed two absorption peaks in the ultraviolet spectrum of epinephrine, which are located at 206.23 and 273.92 nm respectively. The peak at 206.23 nm is mainly formed from the ground state transition to the 16th excited state, and the peak at 273.92 nm is mainly formed from the ground state transition to the 2nd and 4th excited states. They are mainly produced by the transition from π band to π* band on the benzene ring, and they are in good agreement with the experimental spectrum. The analysis of the excited state properties of adrenergic molecules shows that the absorption peaks are generated in the adjacent orbital transitions of the highest occupied orbital and the lowest vacant orbital. Then, the PBE method based on density functional theory was used to calculate the infrared frequency and draw the infrared spectrum of adrenergic molecules at the base group level of 6-311g (d, p). The vibration analysis shows that the characteristic absorption peak is generated by the phenol hydroxyl O—H vibration at 3 738 and 3 662 cm-1, and the alcohol hydroxyl O—H vibration generates the characteristic absorption peak at 3 715 cm-1. Point 2 854 cm-1 is the characteristic absorption peak generated by the stretching vibration of the C18—H20 bond of methyl, point 1 516 and 1 439 cm-1 are the characteristic absorption peaks of the stretching vibration of the benzene ring, at 1 279 and 1 057 cm-1 respectively were the characteristic absorption peak of the stretching vibration of the C6—O10 and C12—O23 bond, and point 620 cm-1 is the characteristic absorption peak of the oscillation of the N22—H17 bond. The vibration analysis is consistent with the characteristic absorption peaks of various functional groups in the introduction to spectroscopy. By comparing the experimental infrared spectrum of epinephrine, it was found that the characteristic absorption peaks of each group in the theoretical spectrum were relatively obvious, and they were generally in good agreement with the experimental spectrum. Due to the hydrogen bond formed between the adrenergic molecular dimer and the polymer, the hydrogen bond formed between the molecules weakens the strength of the O—H bond. It reduces the stretching vibration frequency of the hydroxyl O—H that can form the inter-molecular hydrogen bond, which results in a wide peak of the experimental spectrum between 3 500 and 2 500 cm-1.
Key words：Epinephrine; Density functional theory; UV spectrum; Infrared spectrum (IR)
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