Dezso Gal

Photodynamic Effects of Antioxidant Substituted Porphyrin Photosensitizers on Gram-positive and -negative Bacteria¶

Photodynamic treatment of the gram‐negative bacteria Escherichia coli B and Acinetobacter baumannii and the gram‐positive bacterium Staphylococcus aureus was performed using two newly devised and synthesized antioxidant carrier photosensitizers (antioxidant carrier sensitizers‐2 [ACS‐2] and antioxidant carrier sensitizers‐3 [ACS‐3]), which are butyl hydroxy toluene and propyl gallate substituted haematoporphyrins, respectively. It was found that ACS‐2 is less reactive than other photosensitizers previously used for the same purpose, whereas ACS‐3 is very effective against the multidrug‐resistant bacterium A. baumannii, causing its complete eradication at a low fluence (∼7.5 J/cm) of blue light (407–420 nm) and a low concentration (10 μM). At a higher fluence (∼37.5 J/cm) complete eradication of E. coli B can be obtained under the same conditions. Furthermore, X‐ray microanalysis and ultrastructural changes indicate that ACS‐3, especially in the case of photodynamic treatment of A. baumannii, interferes with membrane functions and causes the inactivation of the bacterium. ACS‐3 may be suggested as a specific photosensitization agent for photoinactivation of gram‐negative bacteria.

A possible construction of a complex chemical reaction network

A procedure is suggested for the construction of chemical reaction networks. We define the kinetic communication as a transfer of atoms or atomic groups between two species and determine all the kinetic communications occurring in the possible mechanism of a complex chemical process. The set of kinetic communications is the basis of the communication matrices resulting in the complete network of the overall reaction.Limiting the consideration for certain types of kinetic communications we obtain the reaction subnetworks and selecting arbitrarily species among those participating in the possible mechanism we introduced the concept of the partial subnetworks which correspond to subsets of the complete network.By the simple analysis of the subnetworks it is easy to obtain the sequence network indicating the pathways via which the selected species are formed in the course of the overall process, by the transfer of chosen atoms or atomic groups.

Physico-chemical modeling of the role of free radicals in photodynamic therapy. I. Utilization of quantum yield data of singlet oxygen formation for the study of the interaction between excited photosensitizer and stable free radicals

The measurement of the relative quantum yield of singlet oxygen formation, a simple process without tedious sample deoxygenation, is shown to furnish data on the interaction of the excited photosensitizer with any additive (in this case stable free radicals) given to the sample. The rate constants derived from such measurements are in good agreement with direct determination of the corresponding values.

A possible construction of chemical reaction networks

The chemical reaction networks and the sequence networks represent the pathways of a complex chemical process. In order to study the pathways separately the systematization of the elementary processes included in the possible mechanism is inevitable.This systematization was realized by a special procedure based on linear algebraic methods and enabled us to select the corresponding processes from the possible mechanism. The efficiency of the procedure has been illustrated by its application to the liquid phase oxidation of ethylbenzene and the elementary processes have been selected using a computer program.

Type III photosensitization: attempt for quantification and a way toward new sensitizers

Earlier results studying the effect of excited triplet photosensitizer on the zymosan-stimulated and luminol- dependent chemiluminescence of macrophages have been quantitatively re-evaluated and rate constant data indicate that the effect is due to triplet-doublet interactions between sensitizer and free radicals generated. Such interactions, named Type III mechanism, compete with Type I and Type II mechanisms depending on the experimental environment. This suggestion resulted in the synthesis of new sensitizers being the first members of the Antioxidant Carrier Sensitizer (ACS) group of molecules. According to preliminary experiments the PDT treatment of tumor bearing mice seems promising with two of such compounds which demonstrate an inhibitory effect in chemical systems already in their ground state.

Determination of the Initiation Rates in the Liquid Phase Oxidation of Ethylbenzene

1. The appropriate method of the measurement of the initiation rate has been selected among those suggested in the literature. 2. It was established that in the case of non-integral stoichiometric factors, their values depend on the conditions of the experiment (inhibitor concentration; rate of initiation ; reaction time) and vary with the conversion. 3. Reactions regenerating the inhibitor have been studied and the upper limit of their rate constants, below which they become negligible, determined. The computer modeling enabled us to calculate the errors committed by neglecting different processes and thus it proved to be an objective procedure in order to diminish (or to enhance) the mechanism assumed.

Additional approach to PDT: type III mechanism and the role of native free radicals

It has been suggested by us earlier that interactions of excited triplet sensitizer (3PS) and native free radicals compete with Type I (sensitizer radical mediated) and Type II (singlet oxygen mediated) mechanisms during PDT. Evidence such as fall in the overall radical concentration in vivo ( in mice tumors) during PDT and in the life time of 3PS caused by free radicals supported this assumption In addition, following results have been obtained recently. 1.) Excited Photofrin II and m-THPC affected luminol dependent chemiluminescence (CL) generated by respiratory burst of macrophages like free radical inhibitors. 2.) Quantification of spin trapping for chemical and in vitro systems by kinetic ESR spectrometry yielded detailed knowledge of triplet-doublet interactions 3.)Measurements in open systems (tank reactor) yielded data for the interactions between 3PS and peroxy type radicals 4.)Simulation of experimental data based on mechanisms suggested gave fair agreement. Based on experimental results new PS-s called Antioxidant Carrier Sensiters (ACS-s) have been devised, synthesized and tested one of them showing enhanced activity for PDT.

STUDIES ON HOMOGENEOUS CATALYSIS IN OXIDATION

For studying the homogeneous catalysis in oxidation our approach starts with the determination of the reaction sequence network of the non-catalytic oxidation using the KIM. The next step is the study of the effect of the catalyst complex and the transformation of the catalyst in the subsystems. The rate parameters collected (referring to the reactions of the catalyst complex with stable and short lived intermediates) can be used to simulate the subsystems and the overall catalytic system.

Sequence studies in liquid phase hydrocarbon oxidation. Part 3.—Temperature dependence of alcohol–ketone transition in the oxidation of ethylbenzene

The consumption of 1-phenylethanol during oxidation of ethylbenzene has been measured at different temperatures. Using the equations of the kinetic isotope method a new procedure is suggested for the determination of reactivity ratios of the chain propagating steps. The activation energy obtained by this procedure for the chain propagation of the oxidation of the alcohol is in good agreement with the value computed from direct measurements and is supported by kinetic evidence.

Quantitative methods for studying the role of free radicals in biology

The mechanism of the primary sensitization steps in Photodynamic Therapy could be of essential importance concerning the efficiency of the treatment. Besides the well known mechanisms there is a possibility that the interaction between the excited triplet state sensitizer and the doublet state free radicals generated by the cells adds a significant contribution to the overall photodynamic effect. To support this hypothesis the quantification and identification of free radicals would be required. For this purpose chemiluminescence studies and spin trapping seemed to be the most suitable methods due to the extremely short lifetime of free radicals in biological systems. We present data on the kinetics of accumulation of free radicals: (1) by measuring luminol- dependent chemiluminescence of stimulated macrophages both in the absence and in the presence of a free radical inhibitor 3,5 di-tert-butyl-4-hydroxyphenyl propionic acid; (2) by following the production of primary, secondary and tertiary radical adducts using DMPO (5,5-dimethyl-1-pyrroline N-oxide) as spin trapping agent in chemical model systems. The measured data are used to determine the effect of the excited sensitizers on the kinetics of accumulation of free radicals under biological conditions. These results would serve to design new and more effective sensitizers used for therapy based on the triplet-doublet mechanism of action.