Lars Poulsen

Time-resolved Singlet Oxygen Phosphorescence Measurements from Photosensitized Experiments in Single Cells: Effects of Oxygen Diffusion and Oxygen Concentration

Time‐resolved singlet oxygen, O2(a1Δg), phosphorescence experiments have been performed in single cells upon pulsed laser irradiation of a photosensitizer incorporated into the cell. Data recorded as a function of the partial pressure of ambient oxygen to which the cell is exposed reflect apparent values for the intracellular oxygen diffusion coefficient and intracellular oxygen concentration that are smaller than those found in neat H2O. This conclusion is supported by O2(a1Δg) phosphorescence data and sensitizer triplet state absorption data recorded in control experiments on sucrose solutions with different viscosities. We recently demonstrated that the intracellular lifetime of O2(a1Δg) is comparatively long (∼3 μs) and does not differ significantly from that in neat H2O (∼3.5 μs). Despite this long lifetime, however, our estimate of an apparent intracellular oxygen diffusion coefficient in the range ∼2–4 × 10−6 cm2 s−1 means that the spatial domain of intracellular O2(a1Δg) activity will likely have a spherical radius of ∼100 nm. This latter point helps reconcile seeming inconsistencies between our direct O2(a1Δg) lifetime data and results obtained from independent photobleaching experiments that show a limited translational diffusion distance for O2(a1Δg) within a cell.

Direct Optical Detection of Singlet Oxygen from a Single Cell

Abstract Singlet oxygen has been detected in single nerve cells by its weak 1270 nm phosphorescence (a1Δg→X3Σg−) upon irradiation of a photosensitizer incorporated in the cell. Thus, one can now consider the application of direct optical imaging techniques to mechanistic studies of singlet oxygen at the single-cell level.

Metal-Enhanced 1270 nm Singlet Oxygen Phosphorescence†

The first excited state of molecular oxygen, singlet oxygen (O2(a Dg), or simply O2), is a reactive intermediate of importance in processes ranging from polymer degradation to cell death. The most unambiguous way to detect O2 is by its characteristic phosphorescence at 1270 nm. However, this emission is very weak because the overall deactivation of O2 is dominated by nonradiative pathways; typical phosphorescence yields (FP) are on the order of 10 !5 to 10. This can make optical detection of O2 difficult, particularly in spatially resolved experiments from small volumes. Thus, much would be gained if FP could be increased. Herein, we demonstrate that the 1270 nm radiative decay of O2 can be enhanced by coupling to localized surface plasmon resonances (LSPRs) in carefully designed gold nanostructures. O2 is commonly produced in a photosensitized process (Scheme 1) with FP expressed as a product of the O2 yield, FD, and the fraction of O2 molecules that decay radiatively, tDkr [Eq. (1)], where the O2 lifetime, tD= (knr+ kr), is

Photoinduced Degradation of the Herbicide Clomazone Model Reactions for Natural and Technical Systems

The photodegradation of the herbicide clomazone in the presence of S2O82− or of humic substances of different origin was investigated. A value of (9.4 ± 0.4) × 108 m−1 s−1 was measured for the bimolecular rate constant for the reaction of sulfate radicals with clomazone in flash‐photolysis experiments. Steady state photolysis of peroxydisulfate, leading to the formation of the sulfate radicals, in the presence of clomazone was shown to be an efficient photodegradation method of the herbicide. This is a relevant result regarding the in situ chemical oxidation procedures involving peroxydisulfate as the oxidant. The main reaction products are 2‐chlorobenzylalcohol and 2‐chlorobenzaldehyde. The degradation kinetics of clomazone was also studied under steady state conditions induced by photolysis of Aldrich humic acid or a vermicompost extract (VCE). The results indicate that singlet oxygen is the main species responsible for clomazone degradation. The quantum yield of O2(a1Δg) generation (λ = 400 nm) for the VCE in D2O, ΦΔ = (1.3 ± 0.1) × 10−3, was determined by measuring the O2(a1Δg) phosphorescence at 1270 nm. The value of the overall quenching constant of O2(a1Δg) by clomazone was found to be (5.7 ± 0.3) × 107 m−1 s−1 in D2O. The bimolecular rate constant for the reaction of clomazone with singlet oxygen was kr = (5.4 ± 0.1) × 107 m−1 s−1, which means that the quenching process is mainly reactive.

Regulation of FcepsilonARI synthesis in human eosinophils.

FcεRI, the high–affinity receptor for IgE, and eosinophils are thought to be key components of the allergic reaction underlying asthma and rhinitis. We provide evidence at the protein level that FcεRI is expressed in human blood eosinophils, and that the synthesis of FcεRI in purified human blood eosinophils is regulated by fibronectin in combination with IgE, IL–4, both involved in allergic reactions, and by RANTES, a strong chemotactic agent for eosinophils. This provides further evidence for a regulatory effect of IgE on human eosinophils in allergic disease.

Spatial and temporal electrochemical control of singlet oxygen production and decay in photosensitized experiments.

Active spatial and temporal modulation of domains of singlet oxygen activity is demonstrated using electrochemical tools. Using singlet oxygen microscopy in photosensitized experiments, it is shown that singlet oxygen concentrations around an ultramicroelectrode can be controlled by applying a bias voltage to the electrode. Two phenomena that can be exploited separately or collectively are examined: (1) the singlet oxygen concentration can be altered by local oxidation or reduction of the photosensitizer, which is the precursor to singlet oxygen, and (2) the reduction of oxygen to produce the superoxide anion which, among other things, is an effective singlet oxygen quencher, results in a local decrease in the concentration of singlet oxygen around the electrode. Both of these phenomena depend significantly on the diffusion of molecules along concentration gradients established by the biased electrode. The results reported herein demonstrate that one can indeed exert local electrochemical control and readily manipulate the population of singlet oxygen produced in a photosensitized process.

Rapid Communication: Direct Optical Detection of Singlet Oxygen from a Single Cell ¶

Singlet oxygen has been detected in single nerve cells by its weak 1270 nm phosphorescence (a1Δg→X3Σg−) upon irradiation of a photosensitizer incorporated in the cell. Thus, one can now consider the application of direct optical imaging techniques to mechanistic studies of singlet oxygen at the single‐cell level.