Pagination not final (cite DOI) / Pagination provisoire (citer le DOI)
Zammit et al.
7
(2) Schneider, H.-J. Supramolecular Systems in Biomedical Fields; Royal Society of
Chemistry, Cambridge, UK, 2013.
(3) Katz, E. Molecular and Supramolecular Information Processing: From Molecular
Switches to Logic Systems; Wiley-VCH Verlag, Weinheim, Germany, 2012.
(4) de Silva, A. P.; Gunaratne, H. Q. N.; Gunnlaugsson, T.; Huxley, A. J. M.;
McCoy, C. P.; Rademacher, J. T.; Rice, T. E. Chem. Rev. 1997, 97, 1515. doi:10.
(5) Callan, J. F.; de Silva, A. P.; Magri, D. C. Tetrahedron 2005, 61, 8551. doi:10.
(6) Bissell, R. A.; de Silva, A. P.; Gunaratne, H. Q. N.; Lynch, P. L. M.; Maguire, G. E. M;
(7) de Silva, A. P.; Moody, T. S.; Wright, G. D. Analyst 2009, 134, 2385. doi:10.1039/
(8) de Silva, A. P.; McClenaghan, N. D. Chem. Eur. J. 2002, 8, 4935. doi:10.1002/
(10) Callan, J. F.; de Silva, A. P.; Ferguson, J.; Huxley, A. J. M.; O'Brien, A. M. Tetrahedron
(12) Montenegro, J.-M.; Perez-Inestrosa, E.; Collado, D.; Vida, Y.; Suau, R. Org. Lett.
(13) Pérez-Inestrosa, E.; Montenegro, J.-M.; Collado, D.; Suau, R.; Casado, J. J. Phys.
(14) de Silva, A. P.; Gunaratne, H. Q. N.; McCoy, C. P. Nature 1993, 364, 42.
(15) de Silva, A. P.; Gunaratne, H. Q. N.; McCoy, C. P. J. Am. Chem. Soc. 1997, 119,
(18) de Silva, A. P.; Gunaratne, H. Q. N.; McCoy, C. P. Chem. Commun. 1996, 2399.
(19) de Silva, S. A.; Zavaleta, A.; Baron, D. E.; Allam, O.; Isidor, E. V.;
Kashimura, N.; Percarpio, J. M. Tetrahedron Lett. 1997, 38, 2237. doi:10.1016/
(20) de Silva, S. A.; Loo, K. C.; Amorelli, B.; Pathirana, S. L.; Nyakirang'ani, M.;
Dharmasena, M.; Demarais, S.; Dorcley, B.; Pullay, P.; Salih, Y. A. J. Mater.
(21) Callan, J. F.; de Silva, A. P.; McClenaghan, N. D. Chem. Commun. 2004, 2048.
(22) Pais, V. F.; Remón, P.; Collads, D.; Andréasson, J.; Pérez-Inestrosa, E.;
(23) Coskun, A.; Deniz, E.; Akkaya, E. U. Org. Lett. 2005, 7, 5187. doi:10.1021/
(24) de Silva, A.P.; McClenaghan, N. D. J. Am. Chem. Soc. 2000, 122, 3965. doi:10.
(25) Ozlem, S.; Akkaya, E. U. J. Am. Chem. Soc. 2009, 131, 48.
(26) Li, Y.-P.; Yang, H.-R.; Zhao, Q.; Song, W.-C.; Han, J.; Bu, X.-H. Inorg. Chem. 2012,
(27) Georgiev, N.; Bojinov, V.; Nikolev, P. Dyes Pigm. 2011, 88, 350. doi:10.1016/j.
there are two possible sites of protonation in 3, the N2 atom of the
pyrazoline and (or) the carboxylate, makes it unclear as to which
is protonated at low extreme pH levels.
However, with 4, this is not an issue as the sulfonate is not
expected to be protonated even at pH 0 (i.e., the pKa of benzenesul-
fonic acid is –2.8).64 Furthermore, the sulfonate has a positive
p
of 0.35,63 which contributes to an exothermic PET. Thus, 4, with a
negative charge at a neutral pH, becomes a zwitterion on proto-
nation, and eventually positively charged at an extreme low pH.
The pKa values of 4 are generally similar to the other three com-
pounds. The highest measured pKa for 4 is in water. While the pKa
of the dimethylaniline moiety is identical in 0.1 mol/L NaCl, the
imine nitrogen is sensitive to ionic strength resulting in a pKa 0.6
lower. The
in 1:1 MeOH–water is shifted to shorter wave-
max
lengths by ϳ20 nm compared to 2 and the fluorescence quantum
yield is enhanced 25-fold relative to 2. The analogous compound
to 2 with a CN substituent (p = 0.66) on the 1-phenyl position of
the pyrazoline has a ⌬GPET of –0.13 eV.48 As the Hammett param-
eters for carboxylate, carboxylic acid, and sulfonate are 0.00, 0.45,
and 0.35, respectively, compounds 3 and 4 are predicted to have a
driving force for PET within –0.13 eV ≤ ⌬GPET < 0.13 eV.48
Further insight into the water-solubility properties of 1–4 was ob-
tained by performing partition coefficient (log P) calculations using
ChemSketch.65 The partition coefficient is a measure of the lipophi-
licity of the molecule between octanol and water under neutral con-
͑pHϪpKa͒
ditions using the equation log D = log P + log[1/(1 + 10
)], where
D is the distribution coefficient. The model compounds 1 and 2 have
calculated log P values of 3.9 0.6 in their neutral state. The intro-
duction of a negative charge on addition of the carboxy and sulfo-
nate groups on the 1-phenyl ring in 3 and 4 decreases the log P to 3.6
0.8 and 2.2 0.8, respectively. The positive numbers confirm the
molecules are naturally lipophilic and not readily soluble in water. It
was found that a negative log P requires two sulfonates.66 To account
for the pH dependence, we also calculated log D values at pH 3.0. The
determined log D values for 2–4 are 2.6, 3.3, and 0.3, respectively. A
similar calculation for CTAP-1 provided a log P of 5.0 1.2 and log D of
2.2 using a pKa of 5.8 (taken from an azacrown model).67 CTAP-2 had
a predicted log D of –0.1 1.4, in agreement with the water-solubility
properties reported.53
Conclusions
(28) Pais, V. F.; Lineros, M.; López-Rodríguez, R.; El-Sheshtawy, H. S.;
Fernández, R.; Lassaletta, J. M.; Ros, A.; Pischel, U. J. Org. Chem. 2013, 78,
(29) Magri, D. C.; Mallia, C. J. Metal Ion Sensing for Biomedical Uses in Supramolecular
Systems in Biomedical Fields; Schneider, H.-J., Ed.; Royal Society of Chemistry,
Cambridge, UK, 2013, Ch. 3, p. 38.
(30) Burtis, C. A.; Ashwood, E. R. Tietz Fundamentals of Clinic Chemistry, 5th ed.;
W.B. Saunders Company, Philadelphia, PA, 2001.
(31) Malvino, A. P.; Brown, J. A. Digital Computer Electronics, 3rd ed.; Glencoe, Lake
Forest, Illinois, 1993.
(32) Dollars, H; Schellhammer, C. W.; Schroeder, J. Angew. Chem., Int. Ed. Engl.
(33) Wagner, A.; Schellhammer, C.; Petersen, S. Angew. Chem., Int. Ed. Engl. 1966,
(34) Pragst, F.; Weber, E. J. Prakt. Chem. 1976, 318, 51. doi:10.1002/prac.
(35) Rurack, K.; Resch-Genger, U. Chem. Soc. Rev. 2002, 31, 116. doi:10.1039/
The photophysical properties of the 1,3,5-triaryl-2-pyrazoline
pH probes 1–4 were studied in methanol and (or) aqueous solu-
tions. Studies in aqueous solution were achieved with the sulfo-
nate pyrazoline 4. The fluorescence output is substituent, pH, and
solvent dependent. The fluorescent probes 2–4 are exceptional
examples of multilevel logic systems with a receptor1-fluorophore-
spacer-receptor2 format integrating PET and ICT mechanisms. The
molecules exhibit an off-on-off fluorescence character within a nar-
rowly defined pH range on sequential addition of proton inputs.55–58
The pH sensing involves two protonation equilibria yielding off-on-off
file.10 Implementation of the strategy demonstrated here could yield
a new approach for analyzing narrow concentration windows of ions
other than protons in clinical and environmental settings.
(36) de Costa, M. D. P.; de Silva, A. P.; Pathirana, S. T. Can. J. Chem. 1987, 65, 1416.
(37) Rivett, D. E.; Rosevear, J.; Wilshire, J. Aust. J. Chem. 1983, 36, 1649. doi:10.1071/
Acknowledgements
We are grateful for financial support from the University of
Malta, the Strategic Educational Pathways Scholarship (Malta) part-
financed by the European Social Fund (ESF) under Operational Pro-
gramme II, the European Cooperation in Science and Technology
(COST Action CM1005 Supramolecular Chemistry in Water), and the
European Regional Development Fund (ERDF). Prof. Robert M. Borg
is thanked for his assistance with the acquisition of the NMR data.
(38) Rivett, D. E.; Rosevear, J.; Wilshire, J. Aust. J. Chem. 1979, 32, 1601. doi:10.1071/
(39) Bricks, J. L.; Kovalchuk, A.; Trieflinger, C.; Nofz, M.; Bushcel, M.;
Tolmachev, A. I.; Daub, J.; Rurack, K. J. Am. Chem. Soc. 2005, 127, 13522.
(40) Rurack, K.; Bricks, J. L.; Schulz, B.; Maus, M.; Reck, G.; Resch-Genger, U.
(41) de Silva, A. P.; Dixon, I. M.; Gunaratne, H. Q. N.; Gunnlaugsson, T.;
Maxwell, P. R. S.; Rice, T. E. J. Am. Chem. Soc. 1999, 121, 1393. doi:10.1021/
(42) de Silva, A. P.; de Silva, S. A.; Dissanayake, A. S.; Sandanayake, K. R. A. S.
References
(1) de Silva, A. P. Molecular Logic-based Computation; The Royal Society of Chem-
istry, Cambridge, UK, 2013.
Published by NRC Research Press