Ahsan U. Khan

Singlet Molecular Oxygen from Superoxide Anion and Sensitized Fluorescence of Organic Molecules

The superoxide anion, O2-, evolves singlet molecular oxygen in dimethylsulfoxide solution. Pronounced water quenching of superoxide-sensitized luminescence is indicative of the preferential generation of the 1σg+ state. Recent identification of O2- in the xanthine oxidase system suggests that the generation of singlet oxygen may also occur in enzymatic systems.

L-ascorbic acid quenching of singlet delta molecular oxygen in aqueous media: Generalized antioxidant property of vitamin C

L-ascorbic acid quenches singlet (1 delta g) molecular oxygen in aqueous media (pH 6.8 for [1H]H2O and pD 7.2 for [2H]D2O) as measured directly by monitoring (0,0) 1 delta g leads to 3 sigma-g emission at 1.28 micron. Singlet oxygen was generated at room temperature in the solutions via photosensitization of sodium chrysene sulfonate; this sulfonated polycyclic hydrocarbon was synthesized to provide a water soluble chromophore inert to usual dye-ascorbate photobleaching. A marked isotope effect is found; kHQ2O is 3.3 times faster than kDQ2O, suggesting ascorbic acid is chemically quenching singlet oxygen.

SENSITIZED PHOTOOXYGENATION REACTIONS AND THE ROLE OF SINGLET OXYGEN

Abstract— In this paper we discuss various theoretical and experimental aspects of the role of singlet oxygen in sensitized photooxygenation reactions. New spectroscopic observations on the photosensitized production of singlet oxygen molecules are presented. The various factors which control the generation and reactions of singlet oxygen molecules are considered in detail. A relatively simple theoretical procedure is developed to predict the relative reactivities of 1σ, 1δ and 3σ oxygen toward various organic acceptors, and is used to discuss the chemical and photochemical properties of some of the oxygenation products. Finally, the properties of dioxetanes are examined in connection with the role which they may play in chemi‐ and bioluminescence. While we have said rather little about photodynamic reactions per se, the results presented in this paper strongly support the suggestion that many of the observed photodynamic effects could be due to reactions of singlet oxygen. Clearly a careful reexamination of various photodynamic effects at the molecular level to establish whether or not reactions of singlet oxygen are involved is now in order.

Myeloperoxidase singlet molecular oxygen generation detected by direct infrared electronic emission

Myeloperoxidase in micromolar concentrations reacting with half-millimolar stock solution H2O2 in acetate buffer containing KBr and in 50% D2O (pH + pD = 4.5) at 298 K is shown to generate singlet delta molecular oxygen efficiently. The near infrared electronic emission of singlet oxygen at 1268 nm is detected directly by novel ultrasensitive IR spectrophotometer equipment. The quantum efficiency of singlet oxygen generation by the MPO X Br- X H2O2 reaction is shown to be comparable with that of the standard chemical reaction OCl- X H2O2 at identical peroxide concentrations.

Direct spectroscopic observation of 1.27 μm and 1.58 μm emission of singlet (1Δg) molecular oxygen in chemically generated and dye-photosensitized liquid solutions at room temperature

Abstract Direct spectroscopic observation of (0,0) at 1.27 μm and (0, 1) at 1.58 μm of 1 Δ g → 3 Σ g − transitions of molecular oxygen in H 2 O 2 -OCl − chemiluminescence reaction and in dye-sensitized fluorocarbon solutions at room temperature is reported. Observation of these weak and ultraweak emissions was accomplished by developing an extremely sensitive near IR spectrophotometer using a thermoelectrically cooled PbS detector, optimized optics, and a boxcar integrator, as a data processor.

Discovery of enzyme generation of 1Δg molecular oxygen: Spectra of (0.0) 1Δg → 3Σg− IR emission

Abstract Enzyme production of 1Δg molecular oxygen in dark reactions is revealed via near-IR emission spectroscopy. Singlet molecular oxygen emission (0,0) 1Δg → 3Σg− is observed in the enzyme systems chloroperoxidaseH2O2Cl− and lactoperoxidaseH2O2Br−. In the catalaseH2O2 system a strong emission at 1.64 μm with a bandwidth of 755 cm−1 is observed, but is as yet unidentified.

Solvation emission spectral peaks of single molecular oxygen

Abstract Distinct new emission peaks of solvated single (1Δg) molecular oxygen, generated by photosensitization, are observed in a series of oxygen-sa

Luminescence bands of molecular oxygen from a tungsten lamp.: The possible role of singlet molecular oxygen in surface catalyzed oxidation☆

Abstract Sharp emission bands superimposed on ordinary incandescent tungsten lamp output have been observed. These definite spectroscopic bands have been tentatively assigned to Single and Simultaneous Transitions in molecular oxygen. An alternative explanation of a perturbed molecular oxygen, [W·O2], has not been completely ruled out. A possible relation of this novel method of generation of Singlet Molecular Oxygen to heterogeneous catalysis has been pointed out.

Ultraviolet light amplification by the cool green phosphorus chemiluminescence flame: PO‐diatomic and PO‐excimer electronic excited states

Ultraviolet light amplification by the phosphorous chemiluminescence flame is observed in the 200–400‐nm region. PO γ‐system emission is identified in the light amplification spectrum. Gaps in the amplification spectrum are attributed to the forbidden transitions: 4II→X2II of PO at 30 590 cm−1 and 5Γ1→1,3Γ0 of PO excimer at 28 117 cm−1. Light amplification by the phosphorus chemiluminscence system is interpreted as an incipient lasing action.

Artifacts in emission spectral studies by the Cary 14 spectrophotometer. Corrigendum in the proposed singlet molecular oxygen emission from a tungsten lamp

Abstract Intense sharp bands previously observed in the emission spectrum from an incandescent tungsten lamp and tentatively assigned to transitions in molecular oxygen have now been shown to be artifacts of the single beam mode of the Cary 14 spectrophotometer.