Anomalous photophysics of H1 antihistamines in aqueous solution.
Electronic absorption, emission, and excitation spectra, and fluorescence lifetimes of two H1 antihistamines--tripelennamine and mepyramine--are investigated in detail to ascertain their usefulness as fluorescent probes for ligand binding to G-protein coupled receptors. The photophysical behavior of these compounds in aqueous solution is complex due to the presence of three protonable nitrogens, intramolecular hydrogen bonding, quenching due to the formation of a charge transfer state, and intramolecular fluorescence resonance energy transfer. At physiological pH values, anomalous photophysical behavior is observed: the compounds are found to be in a ground-state equilibrium mixture of two species, one with the alkylamine tail involved in an intramolecular hydrogen bond and a second without such a bond. This internal hydrogen-bonded tail has a profound effect on the ground and excited-state properties of both tripelennamine and mepyramine, which is further elucidated by comparing them to the reference compounds 2-aminopyridine and 2-(N,N-dimethylamino)pyridine.
Tardioli
Silvia
S
Department of Analytical Chemistry and Applied Spectroscopy, Laser Centre, Vrije Universiteit, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.
Gooijer
Cees
C
van der Zwan
Gert
G
D000042:Absorption; D000631:Aminopyridines / Q000737:chemistry; D004583:Electrons; D005453:Fluorescence; D006634:Histamine H1 Antagonists / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D011522:Protons; D012015:Reference Standards; D012996:Solutions; D013997:Time Factors; D014867:Water / Q000737:chemistry*
D000631:Aminopyridines; D006634:Histamine H1 Antagonists; D011522:Protons; D012996:Solutions; D014867:Water