Publication Type Journal Article
Title Reorganization of Self-Assembled Dipeptide Porphyrin J-Aggregates in Water-Ethanol Mixtures
Authors Raquel Teixeira Suzana M. Andrade Vanda Vaz Serra Pedro M. R. Paulo Antonio Sanchez-Coronilla M. Graca P. M. S. Neves Jose A. S. Cavaleiro Sílvia M. B. Costa
Groups MPPM
Journal JOURNAL OF PHYSICAL CHEMISTRY B
Year 2012
Month March
Volume 116
Number 8
Pages 2396-2404
Abstract The self-assembly of a neutral meso-methoxyphenylporphyrin functionalized with a dipeptide glycilglycine substituent (MGG) in water and in water-ethanol mixtures was studied by absorption and fluorescence spectroscopy. In water, hydrophobic interactions and the noncovalent intermolecular hydrogen bonding between the terminal carboxylate group of one porphyrin and the hydrogen atoms of the pyrrolic nitrogens of another porphyrin originate nonspecific disorganized H- and J-aggregates. The addition of ethanol (0.1-25\% v/v) to the water creates small clusters within which porphyrin J-aggregates reorganize as revealed by a narrow intense band detected by the Rayleigh light scattering (RLS) at 443 nm. Similar phenomenology is detected in SDS premicellar aggregates. Computational DFT calculations of a model dimer formation stabilized via intermolecular hydrogen bonding estimate an energy gain of -22 kJ mol(-1) and a center-to-center and interplane distances between porphyrin moieties of 16.8 and 3.7 angstrom, respectively. The kinetics of the J-aggregate formation could be fitted with a time-dependent model, and an activation energy of 96 kJ mol(-1) was estimated. The aggregate s morphology of MGG was followed by transmission electron microscopy (TEM) which showed rod-type structures of 5-8 mu m evolving to spherical particles with increased ethanol content. Similar images and sizes were obtained in analogous samples using fluorescence lifetime imaging microscopy (FLIM) and dynamic light scattering (DIS). The formation of excitonically coupled supramolecular MGG structures of brickwork or staircase types is proposed in these water-ethanol mixtures.
DOI http://dx.doi.org/10.1021/jp2115719
ISBN
Publisher
Book Title
ISSN 1520-6106
EISSN
Conference Name
Bibtex ID ISI:000300911900007
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