Photodynamic Hemolysis at Low Temperatures

Abstract

A large number of organic dyes may act as photosensitizers for oxidations by molecular oxygen; the substrate may be any one of a wide variety of organic or inorganic substances. When such photosensitized oxidation takes place in living systems it is commonly referred to as photodynamic action; the results are generally destructive. The name photodynamic action is not altogether appropriate since it seems to assign too general significance to the phenomenon. The term photooxidation, on the other hand, may be confusing since these same dyes may forward other photooxidations that do not produce the destructive effects characteristic of photodynamic action (see Blum, 1941).In photosensitized oxidation the dye is the light absorber, but how the energy of the absorbed quantum is employed in bringing about the oxidation of the substrate by molecular oxygen is not clearly understood. The over-all reaction may be written in the following wayin which D is the dye molecule, X the substmte, and Xoz the oxidized substrate after reacting with 02. The symbol hl is used to indicate that it is the dye molecule which captures the light quantum, but without commitment as to the way in which the energy of the quantum is used in forwarding the oxidation. D appears on the right hand side of the equation, indicating that the dye is unchanged at the end of the reaction, which may go in a cycle, the dye capturing successive quanta and repeatedly bringing about the oxidation of X molecnles by O, molecules. The evidence that a cycle occurs is very good. In simple inorganic solution the dye may photooxidize many times its equivalent of oxidizable substrate, say iodide ion. This is not a chain reaction; the quantum yield approaches but never exceeds unity. In the case of photodynamic hemolysis the same number of quanta must be absorbed per red cell by the dye (~---10 '° quanta per cell) in order to produce hemolysis, regardless of the concentration of the dye or the * Hemolysis by photosensitized oxidation. :~ Present address:

Photohemolysis Sensitized by the Furocoumarin Derivative Alloimperatorin and its Hydroperoxide Photooxidation Product

“…For example, transmembrane leakage of cations photoinduced by protoporphyrin and xanthene does not depend on the temperature in the 5–37°C interval , whereas the rate of photohemolysis augments somewhat with increasing temperature . For some photodynamic sensitizers, the hemolysis may be induced at a temperature as low as −79°C . The reasons for the failure with FC photosensitized hemolysis rests on the fact that the authors tried to photoinduce and observe it at room temperature , because the temperature was not very important with other known sensitizers.…”