A Kinetic Study of the Photodynamic Effect on Tryptophan Methyl Ester and Tryptophan Octyl Ester in DOPC Vesicles

Abstract

The photodynamic effect on tryptophan methyl ester (trpME) and tryptophan octyl ester (trpOE), using the O(2)((1)Delta(g))-photosensitizers Rose Bengal (RB) and Perinaphthenone (PN) has been studied in large unilamellar vesicles (LUVs) of the phospholipid 1,2-di-oleoyl-sn-glycero-3-phosphatidylcholine (DOPC) by stationary photolysis and time-resolved methods. This work reports on the influence of both the site (O(2)((1)Delta(g))) generation and the location of the tryptophan derivatives (trpD), on the photo-oxidation process in a compartmentalized system. The apparent rate constant values for chemical quenching of O(2)((1)Delta(g)) by trpOE (k(r,app)), was higher in vesicles than in water. Also, the ratio between apparent reactive and overall rate constant values for the deactivation of O(2)((1)Delta(g)) (k(r,app)/k(t,app)), increases in vesicles as compared with water, when the oxidative species is generated in the lipidic region or at the interface. Nevertheless, this quotient is lower than the corresponding value in water when O(2)((1)Delta(g)) is generated in the aqueous pseudophase. For trpME, the k(r,app)/k(t,app)values in vesicles and in water are quite similar, confirming the fact that trpME is located in the water pseudophase. Results are discussed in terms of relative protection against O(2)((1)Delta(g)) attack in a microheterogeneous medium as compared with water.

Effect of temperature on the photobehavior of Rose Bengal associated with dipalmitoylphosphatidyl choline liposomes

“…This type of data allows an evaluation of the dye distribution (from the change in absorbance at a given wavelength with DPPC concentration). This procedure has been previously employed to evaluate the incorporation of RB to macromolecules [6,7,20], micelles [21][22][23][24], and liposomes [11]. Furthermore, since the absorption of RB is determined by the characteristics of the solvent [7,8,16], the microenvironment of the bound dye can be estimated from the wavelength of maxima absorbance when most of the dye is bound to the dispersed microphase [7,8,25,26].…”

“…2 show that, at both temperatures, the absorbance tends to reach a plateau, indicative of total association of the dye to DPPC SUVs [11]. In order to obtain the value of the absorbance of the bound species (A N ), the data of Fig.…”

“…The absorbance of the sample at 567 nm, measured as a function of the lipid concentration, was employed to quantify the amount of dye associated to the liposomal pseudophase [6][7]11,15]. The visible spectrum at high DPPC concentrations, where most of the dye is bound to the liposomes, was considered to estimate the microenvironment of bound RB molecules [7][8]16].…”

“…On the other hand, the binding of RB to membrane-like structures has been less investigated considerably [11,12]. As a first step to get an insight on the factors determining the association of the dye to biological membranes, we report in this communication the extent of RB binding to dipalmitoylphosphatidyl choline (DPPC) small unilamellar liposomes (SUVs) over a temperature range that covers the gel and liquid crystalline states.…”

Photosensitization Reactions In Vitro and In Vivo

“…Pd-bacteriopheophorbide 14 had greater stability than 13 and 15, and also produced more reactive oxygen species (ROS) thereby generating hydroperoxides. Another porphyrin system was studied, namely 5,10,15,20-tetra-(phenoxy-3-car-bonyl-1-aminonaphthyl)-porphyrin (16), which was synthesized by a naphthylisocyanate condensation reaction (9). The absorption of the 4th Q-band extended out to ca 670 nm, while…”