In this work we investigate the localization and photophysical
properties of twelve synthetically derived chlorins in artificial
membranes, with the goal of designing more effective
photosensitizers for photodynamic therapy (PDT). The studied
chlorins incorporate substituents of varying lipophilicity at the
C(5)-meso-position (H to C(5)H(11)), while the C(13)- and
C(17)-positions have carboxylate "anchoring" groups tethered to the
tetrapyrrole by alkyl chains (CH(2))(n) (n = 1-3).
It was found that as n increases, the chromophoric part of the
molecule, and thus the point of generation of singlet oxygen, is
located at a deeper position in the bilayer. The vertical insertion
of the sensitizers was assessed by two fluorescence-quenching
techniques: by iodide ions that come from the aqueous phase and by
spin-probe-labeled phospholipids that are incorporated into the
bilayer, using the parallax method.
These results demonstrate that elongation of the side chains endows
the modified molecules with a larger affinity for artificial
membranes and also causes the tetrapyrrole ring to be localized
deeper in the lipid membrane. This location leads to a higher
effective quantum yield for the chemical reaction of singlet oxygen
with its chemical target 9,10-dimethylanthracene (DMA).
PMID: 19255676 [PubMed - indexed for MEDLINE]