title: Pd(II)-mediated assembly of porphyrin channels in bilayer membranes.
abstract: A membrane-spanning bis(meso-3-pyridyl) porphyrin 1 has been synthesized, embedded in EYPC vesicles, and upon Pd(II) addition has been shown to form ionophores that allow the passage of anionic 5/6-carboxyfluorescein through membranes. The geometric matching of bis(meso-3-pyridyl) porphyrin 1 and trans-Pd(II) was designed to give a cyclic porphyrin trimer [PdCl(2)(1)](3). However, solution-phase studies showed that PdCl(2)(PhCN)(2) cross linked 1 into linear oligomers at porphyrin concentrations above 10 mM, although the formation of cyclic species was inferred from studies at concentrations below 2 μM. Fluorescence titrations showed that embedding porphyrin 1 in bilayers greatly reduced its affinity for Pd(II), but the combination of porphyrin 1 and Pd(II) gave an ionophoric species that increased the rate of 5/6-carboxyfluorescein (5/6-CF) transit through the phospholipid bilayer 12-fold. A maximum in the 5/6-CF release rate was observed at a Pd(II) concentration of 4 μM, and the application of a solution-phase binding model to the membrane phase showed that this peak in ionophoric activity corresponded to the greatest extent of porphyrin oligomerization. Further studies suggested these Pd(II)/porphyrin oligomers transported 5/6-CF via a channel mechanism.
authors.affiliation: Manchester Interdisciplinary Biocentre, University of Manchester, Manchester, United Kingdom.
authors.forename: Usha
authors.initials: U
authors.lastname: Devi
authors.forename: James R D
authors.initials: JR
authors.lastname: Brown
authors.forename: Andrew
authors.initials: A
authors.lastname: Almond
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Webb
mesh_terms: D008051:Lipid Bilayers / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010165:Palladium / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry*
chemical_list: D008051:Lipid Bilayers; D011166:Porphyrins; D010165:Palladium