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Relevant academic research and scientific papers

Additive effect of heparin on the photoinactivation of Escherichia coli using tricationic P-porphyrins

Polycationic porphyrins have received substantial attention in developing singlet oxygen-sensitizers for biological use such as in the photoinactivation of bacteria and photodynamic therapy (PDT) of tumor cells because they have strong binding affinities for DNA and proteins. However, these strong cellular interactions can retard elimination of the drug after PDT. Therefore, the studies on the interactions of porphyrins with other molecules present much interest, in order to modulate the sensitizers’ activity or even remove them from the human body after PDT. Here, we studied the additive effect of heparin on the photoinactivation by polycationic porphyrins using Escherichia coli as a model cell. Tricationic P-porphyrin sensitizers substituted with an N-alkylpyridinium group (alkyl = pentyl (1a), hexyl (1b), and heptyl (1c)) or N-hexylammonium (1d) as the axial ligand were used. Additionally, dicationic Sb-porphyrin substituted with an N-hexylpyridinium group (1e) was prepared. We studied the additive effect of heparin on the photoinactivation of E. coli by 1a–1e. The bactericidal activities were evaluated using the half-life (T1/2 in min) of E. coli and the minimum effective concentrations ([P]) of the porphyrin sensitizers. In the absence of heparin, the [P] values were determined to be 0.4–0.5 μM for 1a?1c and 2.0 μM for 1d?1e. The bactericidal activity of 1a?1c was completely retarded by the addition of heparin (1.0 μM). However, the addition of heparin (1.0 μM) could not completely retard the bactericidal activity of 1d?1e whose [P] values were relatively large. It is suggested that tricationic 1a?1c adsorbed onto the anionic heparin through electrostatic interactions. The adsorption of 1 on heparin disturbs the uptake of 1 into E. coli cells. Thus, the addition of heparin was found to be a useful method for retarding photoinactivation.

Spectroscopic analysis of the interaction of human serum albumin with tricationic phosphorus porphyrins bearing axial pyridinio groups

Much attention has been paid to water-soluble porphyrins and metalloporphyrins as potential sensitizers for photodynamic therapy (PDT). Thus, water-soluble tricationic phosphorus porphyrin complexes were prepared via the introduction of an N-alkylpyridinio group on the axial ligands of phosphorus porphyrins. The resulting tricationic phosphorus porphyrins readily dissolve in aqueous solutions without the formation of aggregates, even at high concentration. Moreover, the affinity of the porphyrins to human serum albumin (HSA) is a key factor in their application to PDT since HSA plays an important role in the transport of drug molecules to a target cell. Interactions between the tricationic phosphorus porphyrins and HSA were examined on the basis of changes in the Soret bands of the absorption and fluorescence spectra of phosphorus porphyrin solutions in the presence of HSA and the fluorescence quenching of HSA by the tricationic phosphorus porphyrins. Tricationic phosphorus porphyrins with moderately long alkyl chains on the pyridinio group were strongly adsorbed on the HSA at a position near the tryptophan residue of HSA. This result suggests that tricationic phosphorus porphyrins containing alkyl groups are good candidates as PDT reagents because of their high water solubility and high affinity for HSA.