I. V. Sokolova

Laser Photolysis Study of the Triplet States of Fulvic Acids in Aqueous Solutions

The spectral and kinetic characteristics of short-lived intermediates formed during the photolysis of aqueous and alkaline (0.1 mol l−1 NaOH) solutions of fulvic acids (FA) were studied by the nanosecond laser photolysis technique. Laser photolysis of FA at 337 nm leads to the formation of short-lived triplet states of FA (3FA) with a quantum yield of about 1% and different relatively long-lived intermediates (with decay rate constants in deoxygenated solutions of 1.8 × 103–2.1 × 105 and 80–160 s−1, respectively), which are characterized by absorption spectra with maximums at λ ≤ 400 nm. 3FA are quenched by atmospheric oxygen with rate constants of 5.4 × 108–1.1 × 109 l mol−1 s−1. Introduction of phenols into the solutions at concentrations up to 0.1 mol l−1 has no appreciable effect on the decay kinetics of the detected intermediate products of FA photolysis.

Photolysis of Phenol and para -Chlorophenol by UV Laser Excitation

The photolysis of phenol and para-chlorophenol by irradiation with the fourth harmonic of a neodymium laser was examined using electronic absorption spectroscopy, fluorescence, and quantum-chemical techniques. It was found that the introduction of a chlorine atom into the phenol molecule increases the efficiency of photolysis of para-chlorophenol by excitation in the long-wavelength absorption band. The O–H and C–Cl bonds in the test compounds are ruptured via a predissociation mechanism in triplet states localized at the breaking bonds.

Quantum-Chemical Study of the Effect of Chlorine Substitution on Spectral and Luminescent Properties and Photolysis of Phenol and Its Complexes with Water

The effect of chlorine substitution on the spectral and luminescent properties and photolysis of phenol and its 1 : 1, 1 : 2, and 1 : 3 complexes with water was studied by quantum chemistry methods. The chlorine substitution in the para position of phenol was found to decrease the fluorescence quantum yield and to make it dependent on excitation energy in the absence of phototransformations. The nature of photodissociative states and a mechanism for the photocleavage of O–H and C–Cl bonds in p-chlorophenol were determined.

Phototransformations of Phenols in Aqueous Solutions under Different Excitation Modes

The photolysis of aqueous solutions of two widespread environmental organic ecotoxicants—phenol and 4-chlorophenol—on excitation by UV radiation from a KrCl exciplex laser and a glow-discharge KrCl excilplex lamp was studied. The irradiated solutions were studied by spectroscopic techniques. The laser and lamp photolyses were compared.

Effect of simulated solar radiation on the interaction of humic acids with naphthalene

The equilibrium constants of binding of naphthalene with a series of humic acids were determined by the fluorescence quenching method. The effect of irradiation on the extent of the interaction of naphthalene with humic acids was examined. Based on the data obtained, preliminary conclusions on the structure of humic acids of raised bog peat before and after modification were made.

Spectral and chromatographic study of the effect of UV preirradiation on the biodegradation of phenols

The effect of UV radiation of a KrCl excilamp on the biodegradation of 4-nitrophenol, 2,5-dinitrophenol, and their mixture by a Penicillium tardum H-2 isolate strain and microbiocenosis of activated sludge was studied. It was shown that the efficiency of the successive photodegradation and biodegradation of nitrophenols depended on the initial concentration and the time of UV preirradiation. UV irradiation increased the efficiency of the biodegradation of 2,5-dinitrophenol with respect to the biodegradation alone. Preliminary UV irradiation inhibited the subsequent biodegradation of 4-nitrophenol by a Penicillium tardum H-2 isolate strain and activated sludge.

Dependence of fluorescent ability on efficiency of intersystem conversion in psoralens

Results of theoretical research for seven psoralen molecules: psoralen, 5-methoxypsoralen, 8-methoxypsoralen, angelicin, pseudoisopsoralen, isopseudopsoralen, and allopsoralen, are presented. Schemes of photophysical processes in psoralens based on quantum chemical calculation by the INDO method are analyzed. Effects of isomerism and methoxysubstitution on the energy level diagram are demonstrated. The rate constants of intersystem and internal conversions are calculated. We obtained rather high intersystem conversion constant that influences on the fluorescent yield of psoralens.

The Nature of Electronically Excited States and Photoprocesses in Psoralen Molecules and Their Complexes

The nature of electronically excited states of molecules of psoralens and their complexes with methanol and the photoprocesses occurring in the molecules under exposure to light were studied by quantum chemistry methods. It was found that the principal deactivation pathway for all of the compounds examined is intersystem (S–T) crossing, which substantially affects their properties as sensitizers. It was shown that isomerization and substitution of the methoxy group do not lead to significant enhancement of the S–T transition.

The Efficiency of the Formation of Singlet Oxygen by a Sensitizer Based on Zinc Phthalocyanine

Using zinc octa(diethoxyphosphenylmethyl)phthalocyanine as an example, we determined experimentally the quantum yield of generation of singlet oxygen (ϕΔ) which makes it possible to evaluate quantitatively the efficiency of photogeneration of 1O2 and the influence of biomolecules on this parameter. It is shown that the efficiency of generation of singlet oxygen by the sensitizers used in photodynamic therapy depends on their state in a solution and increases with disaggregation of the dye and its interaction with biomolecules. It is established that phthalocyanine in an aqueous buffer solution sensitizes the formation of 1O2 with the quantum yield ϕΔ = 0.16 ± 0.02. On introduction of the detergent Triton X‐100 into the buffer solution of phthalocyanine, ϕΔ increases up to 0.48 ± 0.07. In a microheterogeneous medium (buffer + albumin) ϕΔ = 0.42.

Fluorescence Investigations of Phenol Phototransformation in Aqueous Solutions

Absorption and fluorescence techniques were used to study special features of the XeCl laser-induced phototransformation of phenols in water and to compare the results obtained with those of photolysis of phenol solutions exposed to the UV radiation from mercury lamps. XeCl laser-induced phenol photolysis provided photoproducts not found on exposure to UV radiation. This is related to the two-photon population of highly excited phenol states under high-power laser pumping, which gives rise to a new phototransformation reaction pathway.