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Electrostatic Core Shielding in Dendritic Polyglutamic Porphyrins
Author(s) -
Vinogradov Sergei A.,
Wilson David F.
Publication year - 2000
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20000703)6:13<2456::aid-chem2456>3.0.co;2-p
Subject(s) - dendrimer , protonation , chemistry , porphyrin , fluorescence , free base , quantum yield , molecule , photochemistry , absorption (acoustics) , proton nmr , stereochemistry , polymer chemistry , organic chemistry , materials science , ion , physics , composite material , salt (chemistry) , quantum mechanics
Polyglutamic dendritic porphyrins of the general formula H 2 PophGlu N OR (H 2 Porph=free‐base meso ‐tetra‐4‐carboxyphenylporphyrin (H 2 TCPP), Glu=dendrimer layer composed of L ‐glutamates, N =1‐3: dendrimer generation number, R=terminal group (All, H)) were synthesized and characterized with NMR and MALDI‐TOF mass spectroscopy. The free‐acid terminated compounds were found to be highly soluble in water, with both their absorption and fluorescence spectra dependent on pH. The value of the porphyrin mono‐protonation constant, measured by fluorescence rationing, increased monotonously in the studied series of dendrimers (p K 3 =6.31, 6.70, and 6.98, for N =1, 2, 3, respectively). For the largest dendrimer, H 2 PorphGlu 3 OH, p K 3 was found shifted by almost two pH units relative to the non‐modified H 2 Porph. The second protonation constant ( K 4 ) was much less affected by the dendritic substituents. At pH values less than 3.5 there were noticeable changes in fluorescence intensity and quantum yield even for the highly soluble H 2 PorphGlu 3 OH. This suggests that interactions between individual dendritic molecules in solution are favored by full protonation of the peripheral glutamic carboxyls. The “dendrimer‐protected” porphyrins are convenient fluorescent pH sensors in the biological pH range.