Abstract |
Tetrapyrrole rings possess four nitrogen atoms, two of which act as Bröndsted bases in acidic media. The two protonation steps occur on a close pH range, particularly in the case of meso- tetraphenylporphyrin (TPP) derivatives. If the cause of this phenomenon is well known--a protonation-induced distortion of the porphyrin ring--data on stepwise protonation constants and on electronic absorption spectra of monoprotonated TPPs are sparse. A multivariate approach has been systematically applied to a series of glycoconjugated and hydroxylated TPPs, potential anticancer drugs usable in Photodynamic Therapy. The dual purpose was determination of protonation constants and linking substitution with basicity. Hard-modeling version of MCR-ALS (Multivariate Curve Resolution Alternating Least Squares) has given access to spectra and distribution profile of pure components. Spectra of monoprotonated species (H(3)TPP(+)) in solution resemble those of diprotonated species (H(4)TPP(2+)), mainly differing by a slight blue-shift of bands. Overlap of H(3)TPP(+) and H(4)TPP(2+) spectra reinforces the difficulty to evidence an intermediate form only present in low relative abundance. Depending on macrocycle substitution, pK values ranged from 3.5±0.1 to 5.1±0.1 for the first protonation and from 3.2±0.2 to 4.9±0.1 for the second one. Inner nitrogens' basicity is affected by position, number and nature of peripheral substituents depending on their electrodonating character. pK values have been used to establish a predictive Multiple Linear Regression (MLR) model, relying on atom-type electrotopological indices. This model accurately describes our results and should be applied to new TPP derivatives in a drug-design perspective.
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Authors | Benoît Chauvin, Athena Kasselouri, Pierre Chaminade, Rita Quiameso, Ioannis Nicolis, Philippe Maillard, Patrice Prognon |
Journal | Analytica chimica acta
(Anal Chim Acta)
Vol. 705
Issue 1-2
Pg. 306-14
(Oct 31 2011)
ISSN: 1873-4324 [Electronic] Netherlands |
PMID | 21962373
(Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
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Copyright | Copyright © 2011 Elsevier B.V. All rights reserved. |
Chemical References |
- Antineoplastic Agents
- Porphyrins
- Protons
- tetraphenylporphyrin
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Topics |
- Antineoplastic Agents
(chemistry)
- Humans
- Multivariate Analysis
- Neoplasms
(drug therapy)
- Photochemotherapy
- Photoelectron Spectroscopy
(methods)
- Porphyrins
(chemistry)
- Protons
- Quantitative Structure-Activity Relationship
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