K calc 9200 mol -1 dm -3

1. 4 3 2 1 0 0.00 0.04 0.08 0.12 [I-] / mol dm-3 0.5 0.4 0.3 0.2 0.1 0.0 0.00 0.02 0.04 0.06 0.08 K R R + M b f k k b f P r o d u c t s Ontheapplication of thePseudophaseModeltophotochemicalreaction in theslowexchangelimit 60 (KSV)obs / mol-1 dm3 • Eva Bernal, María Marchena and Francisco Sánchez*. Departamento de Química Física, Facultad de Química • Universidad de Sevilla 50 40 30 Introduction 20 10 0 5 10 15 20 25 • 104[DNA]/ mol dm-3 Wehavedeveloped a modelthatgiveananswertothisquestion and givesthemeaning of theparameters [6]. Thismodel produces equations 2-4: In ordertoapplythePseudophaseModeltoreactionsunderrestrictedgeometryconditions (rgc) theexchangebetween Rf and Rb (f: free, b: bound) mustbefast in relationtothe reactive steps [1]. PseudophaseModel [I-] / mol dm-3 1 SLOW EXCHANGE LIMIT STEADY-STATE MEASUREMENTS 2 3 Fast in realtionto Photochemicalreactions are usuallyfasterthantheseexchangeprocesses, so, in principle, thePseudphaseModelcannotexplainthechanges in reactivityobservedunderrgc. 4 • Assumption: • Homogeneousdistribution of Q In ordertocheckthismodel, the quenching of the excited state of 1-pyrene-carboxaldehyde by iodidewasstudied. Thesestudieswascarriedoutin the presence of DNA and β-cyclodextrin (β –CD), two receptors of different characteristics. However, thismodel has beenappliedtothiskind of reactions in thelimit of slowexchange [2-5]. This introduces thefollowingquestion: What is the meaning of parameters obtained by fitting the experimental data to the Pseudophase Model, in the case of photochemical reactions? The idea is to determine K by a classical procedure and compare the value obtained with that resulting from using equations 2-4. Results and Discussion Obtaining K: kinetic data Obtaining K: classicalprocedure Kapp= 1104 mol-1 dm3 Independent of [Q] K 9400 mol-1 dm-3 Independent of [Q] Kcalc 9200 mol-1 dm-3 DNA 1.0 0.8 0.6 Emissionintensity /a.u. Figure 2. Plot of (Ksv)obsvs. DNA concentration. The values of (Ksv)obs have been obtained from emission intensity of 1-pyrene-carboxaldehyde at different concentrations of quencher (iodide) as Figure 1. Stern-Volmer plot for the quenching of 1-pyrene-carboxaldehyde by iodide at fixed DNA concentration of 3·10-4 mol dm-3. 0.4 • 104[DNA]/ mol dm-3 . Figure 3. Plot of emission intensity of 1-pyrene-carboxaldehyde at different DNA concentrations. 0.2 0.0 0 5 10 15 20 25 100·[KI] (mol dm-3 ) Kapp (mol-1 dm3) Kcalc (mol-1 dm3) K 1100 mol-1 dm-3 3.0 1.83 1397 2465 3.5 1.99 1292 2475 bCD Kcalc(average) 1147 mol-1 dm-3 4.0 2.15 1214 2506 4.5 2.30 1198 2645 1.00 • Emissionintensity /a.u. 5.0 2.45 1091 2563 0.95 5.5 2.60 1043 2591 Figure 5. Stern-Volmer plot for the quenching of 1-pyrene-carboxaldehyde by iodide at different concentrations of -CD: 3 mM (), 5 mM (), 6 mM () and 9 mM (). . Figure 3. Plot of emission intensity of 1-pyrene-carboxaldehyde at different CD concentrations. 0.90 6.0 2.74 1013 2653 0.85 8.0 3.27 932 2909 0.80 0 2 4 6 8 10 12 14 Conclusions References • 103[b-CD] / mol dm-3 The developed treatment : · Explains that the Stern-Volmer constant can be dependent on the quencher concentration. · Establishes a quantitative relation between the true binding constant and the apparent binding constant, obtained from kinetic (quenching) data. · Has been applied to the quenching of 1-pyrene-carboxaldehyde by I- in the presence of two different receptors. Quantitative agreement has been found between the predictions of the treatment and the experimental data. [1] F.M. Menger, C.E. Portnoy, J. Am. Chem.Soc. 89 (1967) 4698-4703. [2] P. Lopez-Cornejo, F. Sanchez, J. Phys. Chem. B 105 (2001) 10523-10527. [3] P. López-Cornejo, J.D. Mozo, E. Roldán, M .Domínguez, F. Sánchez, Chem. Phys. Lett. 352 (2002) 33-38. [4] E. Pelizzetti, E. Pramauro, Inorg.Chem. 18 (1979) 882-883. [5] T. Lopes-Costa, F. Sanchez, P. Lopez-Cornejo, J. Phys. Chem. B 113 (2009) 9373-9378. [6] M. Marchena, F. Sanchez, Prog. React. Kinet. Mech. 35 (2010) 27-80.