Characterization and Structure of Molecular Aggregates of a Tetracationic Porphyrin in LB Films with a Lipid Anchor

Citations Over TimeTop 16% of 2000 papers

Abstract

In this paper, the formation of the different aggregates of a water-soluble tetracationic porphyrin, TMPyP, anchored to an anionic phospholipid matrix, DMPA, and assembled in LB films has been investigated. The use of different solid substrates such as hydrophilic glass and supports modified by the transfer of monolayers of several lipids has been employed to assemble the TMPyP molecules in the mixed monolayer with DMPA (in a molar ratio of 1:4) as monomer (TMPyP4+), dimer, diprotonated monomer (TMPyPH26+), and tetramer aggregates. The porphyrin is organized as a monomer (TMPyP4+) when the mixed monolayer is directly transferred onto a hydrophilic glass plate. Also, if the glass and the porphyrin are separated by spacer layers such as a monolayer sequence EA↑/AA↓/EA↑/AA↓, the porphyrin monomer is identified. Porphyrin dimers are formed at the air−water interface in monolayers of 1:4 TMPyP/DMPA20 and may be transferred to solid substrates by the transfer of this system on top of the DMPA monolayer, i.e., (DMPA↓/TD↑)n. In these multilayers, a small fraction of porphyrin molecules is transferred as diprotonated monomer. Finally, the transfer on hydrophilic glass plates of 1:4 TMPyP/DMPA monolayers of the Y type assembled a packed tetramer of TMPyP. By applying the extended dipole approximation to the spectra measured, we proposed a model where the central planes of the two consecutive porphyrins are twisted by 22.5°, forming a helix.

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