title: Energetic stabilities of thiolated pyrimidines on gold nanoparticles investigated by Raman spectroscopy and density functional theory calculations.
abstract: The adsorption structures of 2-thiocytosine (2TC) on gold surfaces were examined by means of vibrational Raman spectroscopy and quantum mechanical density functional theory calculations. The 1H-thione-amino form was calculated to be most stable among the six examined tautomers. The three plausible binding geometries of sulfur, pyrimidine nitrogen, and amino group binding modes were calculated to estimate the binding energies of the 1H-thione-amino form with six gold cluster atoms. Thiouracils including 2-thiouracil (2TU), 4-thiouracil (4TU), and 6-methyl-2-thiouracil (6M2TU) were also studied to compare their relative binding energies on gold atoms. The intracellular localization of a DNA base analog of 2TC on gold nanoparticles (AuNPs) in HeLa cells was identified by means of surface-enhanced Raman scattering. AuNPs were modified with 2TC by self-assembly. Our dark-field microscopy and z-depth-dependent confocal Raman spectroscopy indicated that 2TC-assembled AuNPs could be found inside cancer cells. On the other hand, we did not observe noticeably strong Raman peaks in the cases of thiouracils including 2TU, 4TU, and 6M2TU. This may be due to the additional amino group of 2TC, which can lead to a stronger binding of adsorbates on AuNPs.
authors.affiliation: Department of Chemistry, Soongsil University, Sangdo-dong, Dongjak-gu, Seoul 156-743, Republic of Korea.
authors.forename: Erdene-Ochir
authors.initials: EO
authors.lastname: Ganbold
authors.affiliation: Department of Chemistry, Soongsil University, Sangdo-dong, Dongjak-gu, Seoul 156-743, Republic of Korea.
authors.forename: Jinha
authors.initials: J
authors.lastname: Yoon
authors.affiliation: School of Systems Biomedical Science, Soongsil University, Sangdo-dong, Dongjak-gu, Seoul, Republic of Korea.
authors.forename: Kwang-Hwi
authors.initials: KH
authors.lastname: Cho
authors.affiliation: Department of Chemistry, Soongsil University, Sangdo-dong, Dongjak-gu, Seoul 156-743, Republic of Korea. Electronic address: sjoo@ssu.ac.kr.
authors.forename: Sang-Woo
authors.initials: SW
authors.lastname: Joo
mesh_terms: D001665:Binding Sites; D003596:Cytosine / Q000031:analogs & derivatives* / Q000032:analysis; D006046:Gold / Q000032:analysis*; D006367:HeLa Cells; D006801:Humans; D053768:Metal Nanoparticles / Q000032:analysis*; D011789:Quantum Theory; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013237:Stereoisomerism; D013816:Thermodynamics; D013889:Thiouracil / Q000031:analogs & derivatives / Q000032:analysis
chemical_list: C000599236:6-methyl-2-thiouracil; C058511:2-thiocytosine; C114719:4-thiouracil; D013889:Thiouracil; D006046:Gold; D003596:Cytosine
keywords: 2-Thiocytosine; Density functional theory; Gold nanoparticles; Intracellular delivery; Raman spectroscopy