title: Structural investigation of the cocrystal formed between 5-fluorocytosine and fumaric acid based on vibrational spectroscopic technique.
abstract: The vibrational spectra of 5-fluorocytosine, fumaric acid and their cocrystal were measured using terahertz time-domain spectroscopy (THz-TDS) and Raman spectroscopy at room temperature. Experimental THz results show that the cocrystal has distinct fingerprint spectra in terahertz region. The absorption peaks observed in the terahertz spectra of the cocrystal were at 0.61 and 0.91THz. These are quite different from corresponding raw starting materials. Raman spectra also show similar results about differences between the cocrystal and corresponding raw starting materials. Density functional theory (DFT) was used to simulate the structure of the possible salt form and the cocrystal form between 5-fluorocytosine and fumaric acid. The theoretical terahertz result shows that the cocrystal form has absorption at 0.62 and 0.87THz, which is in agreement with the experimental result. The theoretical Raman result also indicates that the cocrystal form has more possibilities than the salt form. So, it is more reasonable that the structure between 5-fluorocytosine and fumaric acid could be the corresponding cocrystal form. The characteristic bands of the cocrystal between 5-fluorocytosine and fumaric acid are also assigned based on the simulation results from the DFT calculation.
authors.affiliation: Centre for THz Research, China Jiliang University, Hangzhou 310018, China. Electronic address: yongdu@cjlu.edu.cn.
authors.forename: Yong
authors.initials: Y
authors.lastname: Du
authors.affiliation: Centre for THz Research, China Jiliang University, Hangzhou 310018, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Cai
authors.affiliation: Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, China.
authors.forename: Jiadan
authors.initials: J
authors.lastname: Xue
authors.affiliation: Centre for THz Research, China Jiliang University, Hangzhou 310018, China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Centre for THz Research, China Jiliang University, Hangzhou 310018, China.
authors.forename: Dan
authors.initials: D
authors.lastname: Qin
keywords: 5-fluorocytosine; Cocrystal; Density functional theory; Fumaric acid; Raman spectroscopy; Terahertz time-domain spectroscopy