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Properties of Chlorophyll and Derivatives in Homogeneous and Microheterogeneous Systems

2011; American Chemical Society; Volume: 115; Issue: 22 Linguagem: Inglês

10.1021/jp201278b

1520-6106

Adriana P. Gerola, Tayana Mazin Tsubone, Amanda Marília da Silva Sant’Ana, Hueder Paulo Moisés de Oliveira, Noboru Hioka, Wilker Caetano,

Protein Interaction Studies and Fluorescence Analysis

Chlorophyll (Mg-Chl) and its derivatives, zinc chlorophyll (Zn-Chl), copper chlorophyll (Cu-Chl), pheophytin (Pheo), pheophorbide (Pheid), and zinc chlorophyllide (Zn-Chld), were studied as to their acid–base equilibrium properties, hydrophobicity, stability, binding, and relative localization in neutral surfactant micellar systems. The stability order of metalochlorophyll (pHM) in acidic medium was found to be Cu-Chl > Zn-Chld > Zn-Chl > Mg-Chl. The apparent pKa for protonation of porphyrin ring nitrogens was around 1.0 for all derivatives. The pKa for protonation of carboxylate phorbide was 5.9 for Pheid and 2.4 for Zn-Chld. This difference was attributed to complexation of carboxylate with zinc. The hydrophobicity of chlorophyll in relation to the ability of partitioning the cell membrane lipid layer was estimated in the octanol/water biphasic system. Pheo, a more hydrophobic molecule, presented the highest partition coefficient (KP) in the organic phase, followed by Cu-Chl, Mg-Chl, Zn-Chl, Pheid, and Zn-Chld. The hydrophobic character was the key to relative drug location in the micellar systems. All studied derivatives interacted strongly with Tween 80 micellar systems, and particularly with P-123. For both surfactants, the order followed by binding constant (Kb) was Zn-Chld > Pheo > Cu-Chl > Mg-Chl > Zn-Chl > Pheid, while binding constants estimated for the Chl containing the phytyl group correlated with KP. Fluorescence quenching studies have shown that phorbides are located in a less hydrophobic region than the phytyl chain-containing derivatives, which are located preferentially in a deeper micellar microenvironment. Thus, the association of the chlorophylls with specific binding sites of micellar systems is strongly modulated by the presence of phytyl chains and metal coordinated to the porphyrinic ring.