title: Kinetics of porphyrin adsorption and DNA-assisted desorption at the silica-water interface.
abstract: Evanescent wave cavity ring-down spectroscopy (EW-CRDS) has been used to study in situ the kinetics of the adsorption of 5,10,15,20-tetrakis(4-N-methylpyridiniumyl)porphyrin (TMPyP) from pH 7.4 phosphate buffer solution (PBS) to the silica-water interface and the interaction of calf thymus DNA (CT-DNA) with the resulting TMPyP-functionalized surface. TMPyP was delivered to the silica surface using an impinging jet technique to allow relatively fast surface kinetics to be accessed. Adsorption was first-order in TMPyP, and the initial adsorption rate constant at the bare surface was found to be k = (4.1 +/- 0.6) x 10(-2) cm s(-1). A deceleration in the adsorption kinetics was observed at longer times that could be described semiquantitatively using an Elovich-type kinetic expression. The limiting value of the absorbance corresponded approximately to monolayer coverage (6.2 x 10(13) molecules cm(-2)). Exposure of the TMPyP-modified silica surface to CT-DNA, achieved by flowing CT-DNA solution over the functionalized surface, resulted in efficient desorption of the TMPyP. The desorption process was driven by the interaction of TMPyP with CT-DNA, which UV-vis spectroscopy indicated involved intercalative binding. The desorption kinetics were also simulated using complementary finite element modeling of convection-diffusion coupled to a surface process.
authors.affiliation: Department of Chemistry, University of Warwick, Coventry CV4 7AL, United Kingdom.
authors.forename: Meiqin
authors.initials: M
authors.lastname: Zhang
authors.forename: Hayley V
authors.initials: HV
authors.lastname: Powell
authors.forename: Stuart R
authors.initials: SR
authors.lastname: Mackenzie
authors.forename: Patrick R
authors.initials: PR
authors.lastname: Unwin
mesh_terms: D000327:Adsorption; D004247:DNA / Q000737:chemistry*; D007700:Kinetics; D011166:Porphyrins / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D014867:Water
chemical_list: D011166:Porphyrins; D014867:Water; D012822:Silicon Dioxide; D004247:DNA