Meso-Substituted Cationic Porphyrins of Biological Interest. Photophysical and Physicochemical Properties in Solution and Bound to Liposomes¶

Abstract

A series of cationic porphyrins with 1-4 positive charges are studied: mono(N-methyl-4-pyridyl)triphenylporphine chloride [Mono], cis(N-methyl-4-pyridyl)diphenylporphine chloride [Cis], tri(N-methyl-4-pyridyl)monophenylporphine chloride [Tri] and tetra(N-methyl-4-pyridyl)porphine chloride [Tetra]. Their photophysical properties are measured in small unilamellar vesicles and compared with those in homogeneous solution. Liposomes of L-alpha-dimyristoyl-phosphatidylcholine (100 nm diameter) and L-alpha-dipalmitoyl-phosphatidylcholine (50 nm diameter) in phosphate-buffered saline (pH = 7.4) or D2O 0.15 M NaCl were used. The effect of the medium microheterogeinity is discussed. The triplet quantum yields in liposomes for all the porphyrins are about 0.7, similar to the value obtained for Tetra in aqueous media. The singlet molecular oxygen quantum yields for the hydrophilic compounds Tri and Tetra are greater than those of the hydrophobic ones, Mono and Cis. Also, association constants (KL) of the dyes to liposomes and their localization within the membranes are determined from fluorescence and fluorescence polarization measurements, respectively. KL values are in the range of 10(4)-10(5) M-1 for all the compounds, indicating that hydrophobic and coulombic interactions between porphyrins and liposomes are responsible for the dye association. Fluorescence polarization experiments indicate that Mono and Cis can penetrate into the lipidic phase, and that Tri and Tetra are located near the polar heads of the lipidic molecules.

Photophysical properties of Zn(II) phthalocyaninates incorporated into liposomes

“…The magnitudes of K a , show that 1, 2 and 3 are more tightly bound to liposomes than 4 (see Table 1). For cationic porphyrins, K a is on the order of 10 4 but in this case only monomers are present in the system [18]. In the case of 4, the low value of the constant agrees with the hypothesis that states that when Pc monomers and dimers in aqueous solution encounter liposomes, only the monomers bind to them.…”

“…Cationic phthalocyanine, 4, presents a high value of quenching constant indicating dye is outside the membrane. In this case, heterogeneous quenching is due to the presence of aggregation and the fraction of accessible quenching (see footnote of Table 2) correspond to the monomer concentration associated with the polar heads of the phospholipids [18].…”

Alkane Chain‐extended Pterin Through a Pendent Carboxylic Acid Acts as Triple Functioning Fluorophore, 1O2 Sensitizer and Membrane Binder

“…Pterins have not yet been shown to be useful in this capacity in part due to their poor absorption of light in the visible and NIR. There is also wide interest in individual areas of highly emissive and amplified fluorescence materials (51)(52)(53), as well as sensitizers producing high yields of 1 O 2 (38,54). In our case, inroads…”

Lipid Membrane Adsorption Determines Photodynamic Efficiency of β-Imidazolyl-Substituted Porphyrins

“…In this regard, porphyrins with positively charged peripheral groups seem to be the most promising molecules for PDT [21][22][23][24]. Due to positive charge, such porphyrins pass through the cellular membranes more readily and bind to DNA molecules by intercalation [25].…”