Surface-enhanced Raman scattering of 5-fluorouracil adsorbed on silver nanostructures.
Raman and surface-enhanced Raman scattering (SERS) of 5-fluorouracil (5-FU) have been recorded under several experimental conditions. SERS spectra have been analysed according to a resonant charge-transfer (CT) mechanism similar to a resonance Raman (RR) process, involving the photoinduced transfer of an electron from the Fermi level of the metal to vacant orbitals of the adsorbate (SERS-CT). In order to detect the enhancement mechanism and to identify the chemical species that give rise to the spectra, the theoretical SERS-CT intensities for the dienolic and diketo forms, and its respective N1 and N3 deprotonated anions (5-FU(-)), have been calculated and compared with the experimental results. In this way, the presence of N1 deprotonated anion is confirmed by SERS given that the calculated SERS-CT intensities predict the selective enhancement of the band at ca. 1680 cm(-1) in agreement with the experiment. Therefore, the metal-to-adsorbate CT process involves the transient formation of the respective radical dianion (5-FU (2-)), which is new evidence of the relevance of the CT enhancement mechanism in SERS.
Sardo
Mariana
M
CICECO, Chemistry Department, University of Aveiro, Aveiro, 3810-193, Portugal.
Ruano
Cristina
C
Castro
José Luis
JL
López-Tocón
Isabel
I
Soto
Juan
J
Ribeiro-Claro
Paulo
P
Otero
Juan Carlos
JC
D000327:Adsorption; D000465:Algorithms; D000964:Antimetabolites, Antineoplastic / Q000737:chemistry; D005472:Fluorouracil / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*; D015394:Molecular Structure; D012834:Silver / Q000737:chemistry*; D013059:Spectrum Analysis, Raman / Q000379:methods; D014867:Water / Q000737:chemistry
D000964:Antimetabolites, Antineoplastic; D014867:Water; D012834:Silver; D005472:Fluorouracil