For more than 70 years, researchers in several areas of science have been intrigued by the physical and chemical properties of the lowest excited states of molecular oxygen. With two singlet states lying close above its triplet ground state, the O2 molecule possesses a very unique configuration, which gives rise to a very rich and easily accessible chemistry, and also to a number of important photophysical interactions. In particular, photosensitized reactions of the first excited state, O2(∆g), play a key role in many natural photochemical and photobiological processes, such as photodegradation and aging processes including even photocarcinogenesis. Reactions of O2(∆g) are associated with significant applications in several fields, including organic synthesis, bleaching processes, and, most importantly, the photodynamic therapy of cancer, which has now obtained regulatory approval in most countries for the treatment of several types of tumors. The development of both applications and novel observation techniques has strongly accelerated during the past few years. Significant recent advances include, for example, the development of novel luminescent singlet oxygen probes,1-4 the time-resolved detection of O2(∆g) in a transmission microscope,5 the first time-resolved measurements of singlet oxygen luminescence in vivo,6 and the observation of oxygen quenching of triplet-excited single molecules.7 Experimental and theoretical studies on the mechanisms of photosensitized formation of excited O2 states and of their deactivation have been performed for almost 40 years. While most early liquid-phase studies were exclusively concerned with O2(∆g), recent technological advances also made possible time-resolved investigations of the second excited state, O2(Σg), which can be formed in competition with O2(∆g) in many cases. A significant number of * Corresponding author. Tel.: ++49 69 79829448. Fax: ++49 69 79829445. E-mail: R.Schmidt@chemie.uni-frankfurt.de. 1685 Chem. Rev. 2003, 103, 1685−1757

Physical mechanisms of generation and deactivation of singlet oxygen.

A self-consistent kinetic model is developed to study dc flowing glow discharges in N/sub 2//O/sub 2/ mixtures. This model includes the calculation of electron energy distribution functions and electron rate coefficients coupled with detailed vibrational kinetics of N/sub 2/ molecules, chemical kinetics taking into account a large set of neutral, excited and charged species, interaction of N and O atoms at the discharge tube wall, and the thermal balance of the discharge. The results of this model agree reasonably well with the measurements of the electronic density, the gas temperature, the reduced electric field, the vibrational temperature of N/sub 2/ and the concentration of O, N atoms, NO molecules, N/sub 2/(C), N/sub 2//sup +/(B), and NO(/spl gamma/) excited states. The comparison was performed in a N/sub 2/-O/sub 2/ discharge at pressure p=2 Torr, for discharge currents I=15, 30, and 80 mA, a flow rate Q=100 sccm, and O/sub 2/ percentages ranging from 0 up to 100%,. >

Kinetic model of a low-pressure N/sub 2/-O/sub 2/ flowing glow discharge

http://engine.princeton.edu/Publications/Ombrello_2010-2.pdf

Flame propagation enhancement by plasma excitation of oxygen. Part I: Effects of O3

Bioluminescence is a phenomenon that has fascinated mankind for centuries. Today the phenomenon and its sibling, chemiluminescence, have impacted society with a number of useful applications in fields like analytical chemistry and medicine, just to mention two. In this review, a molecular-orbital perspective is adopted to explain the chemistry behind chemiexcitation in both chemi- and bioluminescence. First, the uncatalyzed thermal dissociation of 1,2-dioxetane is presented and analyzed to explain, for example, the preference for triplet excited product states and increased yield with larger nonreactive substituents. The catalyzed fragmentation reaction and related details are then exemplified with substituted 1,2-dioxetanone species. In particular, the preference for singlet excited product states in that case is explained. The review also examines the diversity of specific solutions both in Nature and in artificial systems and the difficulties in identifying the emitting species and unraveling the color...

Chemi- and Bioluminescence of Cyclic Peroxides.

We have modified the separated-surface-sensitizer singlet oxygen generating system previously described (Midden and Wang, 1983) for the efficient exposure to pure singlet oxygen of bacteria collected on membrane filters. Physical separation of the photosensitizer and the bacteria eliminates the possibility of direct interaction between bacteria and photoexcited sensitizers that could lead to Type I (non-singlet oxygen) photooxidation processes. This system was used to examine the bacterial cytotoxicity of singlet oxygen. The role of singlet oxygen was confirmed by measuring the decrease in cytotoxicity as the distance between the singlet oxygen source and the bacteria was increased. The gas phase half-life of the intermediate responsible for cell killing, determined from this distance dependence analysis (24 ± 6 ms), is the same as that calculated from literature data for the gas phase half-life of singlet oxygen (53 ± 37 ms). Killing of various strains of Salmonella lyphimurium and Escherichia coli was compared at the same dose of singlet oxygen. Bacteria were killed by singlet oxygen at levels several orders of magnitude lower than those effective in killing by H2O2. Altered DNA repair capacities (uvrB, recA, xth, nth, pKM101) did not affect survival. Incomplete cell wall lipopolysaccharide formation decreased survival following singlet oxygen exposure. Overproduction of the singlet oxygen quencher histidine increased survival, as did accumulation of the dipeptide carnosine (β-alanyl-L-histidine). No evidence for mutagenicity of exogenous singlet oxygen exposure was obtained in a variety of S. typhimurium strains killed to 35% survival.

W. Groth

Papers

The quenching of metastable O2(1Δg) and O2(1Σg+) molecules

Observation of carbon atoms in reactions of active nitrogen with organic compounds

Reactions of O2(1Δg) with ozone

The air glow reaction NO + O + (M) → NO*2 + (M) at low pressures

The ratio of the Franck-Condon factors q(0, 0)/q(0, 1) of the infrared atmospheric band system of oxygen