title: Raman spectroscopy and quantum-mechanical analysis of tautomeric forms in cytosine and 5-methylcytosine on gold surfaces.
abstract: Spectral differences between cytosine (Cyt) and 5-methylcytosine (5MC) were investigated by means of Raman spectroscopy with a combination of density functional theory (DFT) calculations. Surface-enhanced Raman scattering (SERS) revealed discriminating peaks of 5MC from those of Cyt upon adsorption on gold nanoparticles (AuNPs). Among the notable features, the multiple bands between 850 and 700cm-1for the ring-breathing modes of 5MC and Cyt could be correlated well with the simulated spectra based on the DFT calculations of the adsorbates on the gold cluster atoms. The relative energetic stabilities of the enol/keto and the amino/imino tautomeric forms of Cyt and 5MC have been estimated using DFT calculations, before and after binding six atom gold clusters. Among the six tautomeric forms, the 7H keto amino and the 4H imino trans forms are expected to be predominant in binding gold atoms, whereas the enol trans/cis conformers would coexist in the free gas phase. Our approach may provide useful theoretical guidelines for identifying 5MC from Cyt by analyzing Raman spectra on gold surfaces on the basis of quantum-mechanical calculations.
authors.affiliation: Department of Chemistry, Soongsil University, Seoul 156-743, Republic of Korea; Department of Information Communication, Materials, and Chemistry Convergence Technology, Soongsil University, Seoul 156-743, Republic of Korea.
authors.forename: Dinh Bao
authors.initials: DB
authors.lastname: Nguyen
authors.affiliation: Department of Chemistry, Soongsil University, Seoul 156-743, Republic of Korea; Department of Information Communication, Materials, and Chemistry Convergence Technology, Soongsil University, Seoul 156-743, Republic of Korea.
authors.forename: Thanh Danh
authors.initials: TD
authors.lastname: Nguyen
authors.affiliation: School of Systems Biomedical Science, Soongsil University, Seoul 156-743, Republic of Korea.
authors.forename: Sangsoo
authors.initials: S
authors.lastname: Kim
authors.affiliation: Department of Chemistry, Soongsil University, Seoul 156-743, Republic of Korea; Department of Information Communication, Materials, and Chemistry Convergence Technology, Soongsil University, Seoul 156-743, Republic of Korea. Electronic address: sjoo@ssu.ac.kr.
authors.forename: Sang-Woo
authors.initials: SW
authors.lastname: Joo
mesh_terms: D044503:5-Methylcytosine / Q000737:chemistry*; D000327:Adsorption; D003596:Cytosine / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D055595:Mechanical Phenomena; D011789:Quantum Theory; D013059:Spectrum Analysis, Raman; D013237:Stereoisomerism; D013499:Surface Properties; D013816:Thermodynamics; D014732:Vibration
chemical_list: D044503:5-Methylcytosine; D006046:Gold; D003596:Cytosine
keywords: 5-Methylcytosine; Cytosine; Gold atom cluster calculation; Raman ring-breathing mode; Tautomers