CHEMILUMINESCENCE AND THE FORMATION OF SINGLET OXYGEN IN THE OXIDATION OF CERTAIN POLYPHENOLS AND QUINONES

Abstract— The possibility of ¹O₂ (¹Δ_g) participation in the oxidation of polyphenols and quinones has been investigated in two systems: (1) the system involving autooxidation leading to oxidative polymerization and destruction, and (2) the modified Trautz-Schorigin reaction, i.e. oxidation of polyphenols and HCHO with H₂O₂ in concentrated alkaline solutions. The red band with maximum at 635 nm observed in chemiluminescence of pyrocatechol, adrenaline, pyrogallol, gallic acid, adrenochrome and p -benzoquinone corresponds to the transition 2O₂(¹Δ_g) → 2O₂(³Σ^-_g). Emission bands in the range 475–540 nm arise from the superposition of the 2O₂(¹Δ_g) → 2O₂(³Σ^-_g) transition and radiative deactivation of excited oxidation products. In system (2) chemiluminescence has a broad band from 580 nm beyond 800 nm and much higher intensity than in system (1). Formaldehyde was found to enhance light emission in system (1) by a factor of about 30. The influence of solvents, including D₂O in which ¹O₂ has varying lifetimes, on kinetics of chemiluminescence as well as quenching effect of β-carotene, hydroquinone, cysteine, bilirubin and biliverdin strongly support the involvement of ¹O₂ in the chemiluminescence of both systems.     

CHEMILUMINESCENCE IN THE PEROXIDATION OF TANNIC ACID

Abstract— Peroxidation of tannins with alkaline H₂O₂ is accompanied by weak chemiluminescence in the spectral region 480–800 nm. o-Di and tri-hydroxy groups of polyphenols undergo oxidation by a free-radical mechanism and a green intermediate anion-radical with absorption Δ_max= 600 nm is formed. The radical mechanism is supported by the low activation energy 14–20 kJ/mol and the quenching effect of radical scavengers. The reaction of the green intermediate with peroxy anions is the chemiluminescence rate limiting step. In the presence of a-hydroxy-methylperoxide formed from H₂O₂ and formaldehyde, the alkaline peroxidation of tannins is accompanied by strong red luminescence (420–800 nm). The base catalyzed decomposition of peroxides gives only a weak red emission (460–800 nm). Light intensity is enhanced in D₂O by a factor 6.5. Quenchers of O₂(¹Δ_g) and 1,3-di-phenylisobenzofurane diminish light intensity in non-aqueous solutions. The data suggest ¹O₂ participation in the observed chemiluminescence. Thermo-chemical calculations give —ΔH values from 250–1000 kJ/mol for one elementary reaction step which limits the mechanism of chemi-enereization. Chemiexcitation of tannins is relevant to biochemical mechanisms of aerobic degradation of aromatic compounds, energy utilization as well as to defense and resistance processes in plants.     

PHOTOINDUCED LUMINESCENCE AND EPR SIGNALS OF POLYPHENOL AND QUINONE POLYMERS

Abstract— Aqueous basic solutions, pH 9.0 of humic acids and melanin-like, synthetic polymers, obtained with adrenochrome, hydroquinone and purpurogallin, were illuminated with visible light under N₂ or O₂ atmospheres. It has been found that light enhances a singlet electron-paramagnetic-resonance (EPR) signal of polymers both under N₂ and O₂, and induces ultra-weak luminescence in the presence of O₂. Degradative oxidation of polymers, accelerated by light, leads to a decrease of EPR signal intensity and generates weak chemiluminescence.     

CHEMILUMINESCENCE IN THE PHOTOOXIDATION OF HUMIC ACIDS*

Abstract— Photo-irradiation of aqueous basic solutions of soil humic acids and synthetic melanins with UV and visible light (Λ > 320 nm) under oxygen or nitrogen atmospheres generates electronic exicted states and radicals. These processes give rise to a long-lived chemiluminescence with emission maxima at 480–500, 570 and 615–650 nm, as well as a paramagnetic resonance (EPR) signal with g-value at 2.006 and ΔH～ 3Gs. Chemiluminescence intensity and EPR signals follow multistep kinetics. An increase of the ratio of OD at 260/400 nm and 400/600 nm and a decrease of amplitude of an EPR signal after prolonged photo-irradiation were observed. Long irradiation also causes a decrease of fluorescence intensity bands with maxima at 535 nm and 495 nm (Λ_ex 480 and 400 nm, respectively), and an increase of the short wavelength band with a maximum at 450 nm (Λ_ex 260 nm). The data indicate that a complex chain of reactions initiated by reactive species leads to the degradation of the aromatic core of the polymers. Oxygen efficiently enhances the chemiluminescence intensity and the rate of photodegradation. The mechanism of photodegradative oxidation and chemiluminescence probably involves an energy transfer process and singlet oxygen formation. The possibility of its occurrence in nature and its significance are discussed.     

Correction to: Spatiotemporal Pattern Extraction by Spectral Analysis of Vector-Valued Observables

Journal of Nonlinear Science - The original version of this article unfortunately contained an error in Acknowledgement section. The authors would like to correct the error with this erratum. The...     

Spatiotemporal Pattern Extraction by Spectral Analysis of Vector-Valued Observables

Journal of Nonlinear Science - We present a data-driven framework for extracting complex spatiotemporal patterns generated by ergodic dynamical systems. Our approach, called vector-valued spectral...