Quenching of singlet oxygen in solid organic polymers

Abstract

The quenching of singlet molecular oxygen ('AgOz) by 1,4-diazabicyclo [2.2.2] octane (DABCO), triphenylamine (TPA), and nickel(II) bis [diisopropyl dithiophosphate] (N) was studied in solid polystyrene (PS) and poly(methyl methacrylate) (PMMA). Quenching rate constants (kq) were determined by monitoring the time-resolved 1 8 2 phosphorescence as a function of quencher concentration in photosensitized experiments. For the efficient quencher N and the moderately efficient quencher DABCO, the rate constants determined in the polymers are smaller than those determined in liquid-phase analogs [fcq(PMMA) < feq(PS) < Aq(liquid)]. Moreover, the solids have a "leveling effect" on the N and DABCO rate constants, minimizing differences in kq that are quite pronounced in the liquid. These observations track a decrease in the oxygen diffusion coefficient [Dq(PMMA) < Dq(PS) < Do(liquid)] and are consistent with a quenching process in the polymer that is principally controlled by solute diffusion to form the 1Ag02~quencher encounter pair. For the poorer quencher TPA, however, where the rate of quenching is determined more by events in the 1Ag02quencher encounter pair than by solute diffusion, feq(PMMA) > fcq(PS) > ^(liquid). These data are consistent with an increase in the number of collisions between the quencher and xAgC>2 in the more rigid solvent cage of the solid polymer. Because differences between fcq(polymer) and Aq(liquid) will vary greatly as a function of the quencher efficiency, published attempts to define the role of1 AgC>2 in a mechanism of polymer degradation may need reinterpretation; specifically, the common practice of comparing values of feq(liquid) with parameters that reflect photodegradation in quencher-doped polymers may be misleading.

Singlet Oxygen in a Cell: Spatially Dependent Lifetimes and Quenching Rate Constants

“…Although the latter is comparatively small (i.e., far removed from those in the diffusion-controlled regime), it can still be influenced by a change in viscosity. 46,47 In systems such as ours, where k T ~ k rem , the observed phosphorescence signal will indeed appear as a difference of two exponential functions. In the analysis of such data, one cannot, a priori, assign the rising portion of the observed signal to k T and the falling portion of the signal to k rem .…”

“…Although this viscosity-dependent phenomenon is general, it has been explicitly demonstrated for the quenching of singlet oxygen in a number of polymer-based systems. [46][47][48] We now quantify the phenomenon in aqueous liquid-phase systems suitable for comparison to data recorded from cells.…”

Morin Flavonoid Adsorbed on Mesoporous Silica, a Novel Antioxidant Nanomaterial

“…This could be explained by the interaction between the most acidic hydroxyl moiety of morin (the 2´-OH group on the B ring, pKa 5.2), with the amine group of the NP [53], the formation of dimers and other aggregates of morin on the NP surface, and the slower oxygen diffusion on the solid nanoparticle compared to neat solvents and lipid membranes. In solid organic polymers, the bimolecular quenching rate constants ( k q ) for deactivation of singlet oxygen by efficient quenchers are smaller than in homogeneous solutions because quenching process in polymers is mainly controlled by solute diffusion to yield the singlet oxygen-quencher encounter pair [84]. Indeed this reduction in reactivity would be compensated with the higher availability of quencher species, resulting in a potential promissory system for real applications…”

Luminescent oxygen channeling immunoassay: measurement of particle binding kinetics by chemiluminescence.

“…The diester HI was determined after centrifugation of the particles and dissolution in dioxane. It was assumed that the rates of reaction of 1A.02 with I and IV in particles were the same because of the rate-leveling effect of very fast reactions by polystyrene (9). The total light output was determined by extrapolation to zero irradiation time to account for light emitted during irradiation.…”