Dezső Gál

Effect of photosensitizers in chemical and biological processes: The MTO mechanism in photodynamic therapy

It is suggested that in the course of the application of photosensitizers irradiated for cancer therapy a real competition occurs between the singlet oxygen mediated effects and the interactions between the triplet photosensitizers and doublet radicals formed in tumor cells while processes between photosensitizer radicals and molecules are negligible. This hypothesis is strongly supported by experimental findings and reveals a novel approach for the synthesis of new photosensitizers.

Sequence studies in liquid phase hydrocarbon oxidation. Part 5.—Temperature dependence of hydroperoxide–alcohol and hydroperoxide–ketone transitions

The temperature dependence of the transition of α-phenylethylhydroperoxide into acetophenone and phenylmethylcarbinol during the oxidation of ethylbenzene has been studied by radioactive tracer methods.It has been established that in these transitions the induced decomposition of the hydroperoxide molecules plays a decisive role within the temperature range investigated.The rate constant of the interaction between hydroperoxide molecules and the chain carrier peroxy radicals yielding ketone has been calculated at different temperatures, and the activation energy and pre-exponential factor were determined.

Quantitative studies on the respiratory burst generated in peritoneal macrophages

The luminol-dependent chemiluminescence of macrophages during the zymosan-stimulated respiratory burst has been studied both in the absence and in the presence of the radical inhibitor 3,5 di-tert-butyl-4-hydroxyphenyl propionic acid. In addition, the consumption of luminol and of the inhibitor has been followed analytically. Based on the rates of the consumption of the inhibitor, an iteration procedure yields a value of 2.2 x 10(-7) M for the steady-state concentration of radicals generated by cells at the maximum of the chemiluminescence in the presence of inhibitor. Approximate calculations have indicated that under the experimental conditions applied, additional formation of superoxide anion radicals by the oxidation of luminol is negligible. By assuming that in an inhibitor-free system the disappearance of radicals takes place via their combination process as well as by their interaction with luminol and/or with luminol-derived species, numerical integration yields a calculated curve of radical concentration versus time in fair agreement with experimental data and a rate-constant value for the combination of radicals of approximately 10(6) M-1 s-1, supporting literature findings according to which primarily superoxide anion radicals are formed.

Solvents effects in the photodegradation and reactivity of the various ionic forms of haematoporphyrin

The dependence of the ionic forms of haematoporphyrin(LX) dihydrochloride (HpdiCl) on solvent composition was investigated. In 2.8 x 10(-4) M solutions of HpdiCl in apolar (C6H6) and polar (CH3CN) solvents, HpdiCl exists in dicationic form. In hydrogen-bonding solvents, such as CH3OH, HpdiCl can exist in neutral, monocationic and dicationic forms. In C6H6-CH3OH solvent mixtures, the ionic forms in which HpdiCl is present depend on the composition of the solvent and on the acidity of the solution. The rate of oxidative photodegradation of HpdiCl excitation in its Q bands (WBI) and the ability to produce free radicals are different for the different ionic species. The highest values correspond to the dicationic form of HpdiCl and the lowest values correspond to the neutral species. In the absence of oxygen, the formation of free radicals due to the reaction of 3(Hp dication) is detected in the following solvent mixtures: CH3OH-toluene, CH3OH-ethylbenzene, CH3OH-hexane. The data obtained indicate that interaction of 3(Hp dication) with methine groups is an intermediate step in the formation of free radicals. In the HpdiCl concentration range studied, the presence of a phenolic antioxidant, such as beta-naphtol, inhibits the oxidative photodegradation of the dicationic form in a treated solution, but has little effect on the oxidative photobleaching of the monocation. The rate of oxidative photodegradation of the monocationic form increases with the addition of propionic acid to the solution.

Radical intermediates induced by porphyrin triplets

In the photochemical reactions of triplets of both protoporphyrin-IX-dimethyl-ester (PP) and haematoporphyrin dihydrochloride (HP) with alpha-phenyl-ethyl hydroperoxide (HROOH) in C6H6 at room temperature, both O-O and C-C bonds are broken yielding alkoxy and carbon-centred radicals. The ruptures of C-C and O-H bonds were observed in the photochemical reaction of PP with tert-butanol in the same solvent, yielding alkoxy and carbon-centred radicals at lambda greater than or equal to 366 nm, while HP did not react photochemically with tert-butanol at lambda greater than or equal to 334 nm.

Studies on the reactivity of ˙OH radicals in non-aqueous solvents using laser flash photolysis

The reactivity of ˙OH radicals toward stable molecules in acetonitrile has been studied using laser flash photolysis. ˙OH radicals have been generated by 260 nm photolysis of H2O2 and the rate of their disappearance was measured using N,N-dimethyl-p-nitrosoaniline as acceptor. It has been established that in acetonitrile ˙OH radicals manifest high reactivity towards ethylbenzene and its oxidation products (1-phenylethanol, 1-phenylethyl hydroperoxide, acetophenone). The corresponding rate coefficients were in the range 106–107 dm3 mol–1 s–1 and were lower than such coefficients observed in aqueous solutions.

Kinetic data on the interaction between triplet anthraquinone and 2-naphthol in oxygen

During the photooxidation of ethylbenzene in the presence of 2-naphthol a new interaction has been found between the sensitizer anthraquinone and the inhibitor. The quantum yield and the kinetics of this interaction have been investigated in the temperature interval of 28–98°C.AbstractИсследована новая реакция возбужденного триплета антранинона с β-нафтолом, обнаруженная при сенсибилизированном антрахиноном окислении этилбензола, измерен квантовый выход реакции в интервале температур 28–98°C и изучены продукты реакции, а также кинетика их накопления.

Quantification of the formation of free radicals in macrophage systems

A mechanism is suggested for the zymosan stimulated, luminol dependent chemiluminescence of macrophage system both in the absence and in the presence of free radical inhibitor. Based on the mechanism and relevant data of elementary rate constants computer simulation has been performed in order to describe the free radical formation and consumption, the kinetics of the chemiluminescence signal as well as the consumption of the inhibitor and luminol molecules in the course of the overall process.

Reactions of alkoxy and hydroxy radicals generated photochemically from hydroperoxide molecules

AbstractIn the present work