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Adsorption of 6-mercaptopurine and 6-mercaptopurine-riboside on silver colloid: A pH de-pendent surface enhanced Raman spectroscopy and density functional theory study. Part II. 6-mercaptopurine-riboside

Domenii publicaţii > Fizica + Tipuri publicaţii > Articol în revistã ştiinţificã

Autori: V. Szeghalmi, L. Leopold, S. Pînzaru, V. Chiş, I. Silaghi-Dumitrescu, M. Schmitt, J. Popp, W. Kiefer

Editorial: Biopolymers, 78, p.298-310, 2005.

Rezumat:

Surface-enhanced Raman spectroscopy (SERS) has been applied to characterize the
interaction of 6-mercaptopurine-ribose (6MPR), an active drug used in chemotherapy of acute lymphoblastic
leukemia, with a model biological substrate at therapeutic concentrations and as function
of the pH value. Therefore, a detailed vibrational analysis of crystalline and solvated (6MPR)
based on Density Functional Theory (DFT) calculations of the thion and thiol tautomers has been
performed. 6MPR adopts the thion tautomeric form in the polycrystalline state. The SERS spectra
of 6MPR and 6-mercaptopurine (6MP) recorded on silver colloid provided evidence that the ribose derivative shows different adsorption behavior compared with the free base. Under acidic conditions,
the adsorption of 6MPR on the metal surface via the N7 and possibly S atoms was proposed
to have a perpendicular orientation, while 6MP is probably adsorbed through the N9 and N3 atoms.
Under basic conditions both molecules are adsorbed through the N1 and possibly S atoms, but 6MP
has a more tilted orientation on the silver colloidal surface while 6MPR adopts a perpendicular orientation.
The reorientation of the 6MPR molecule on the surface starts at pH 8 while in the case of
6MP the reorientation starts around pH 6. Under basic conditions, the presence of the anionic
molecular species for both molecules is suggested. The deprotonation of 6MP is completed at pH 8
while the deprotonation of the riboside is finished at pH 10. For low drug concentrations under neutral
conditions and for pH values 8 and 9, 6MPR interacts with the substrate through both N7 and
N1 atoms, possibly forming two differently adsorbed species, while for 6MP only one species
adsorbed via N1 was evidenced. # 2005 Wiley Periodicals, Inc. Biopolymers 78: 298–310, 2005

Cuvinte cheie: adsorption; 6-mercaptopurine-riboside; 6-mercaptopurine; Raman and surfaceenhanced