Premium
Intermolecular chiral recognition probed by enantiodifferential excited‐state quenching kinetics
Author(s) -
Stockman Tonya Gowl,
Klevickis Cynthia A.,
Grisham G. M.,
Richardson F. S.
Publication year - 1996
Publication title -
journal of molecular recognition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.401
H-Index - 79
eISSN - 1099-1352
pISSN - 0952-3499
DOI - 10.1002/(sici)1099-1352(199634/12)9:5/6<595::aid-jmr307>3.0.co;2-v
Subject(s) - kinetics , intermolecular force , quenching (fluorescence) , excited state , intermolecular interaction , chemistry , chemical physics , materials science , photochemistry , fluorescence , organic chemistry , physics , molecule , atomic physics , optics , quantum mechanics
Time‐resolved chiroptical luminescence (TR‐CL) measurements are used to study the kinetics of chirality‐dependemt excited‐state quenching processes in aqueous solution. Experiments are carried out on samples that contain a racemic mixture of chiral luminophore molecules (L) in solution with a small, optically active concentration of chiral quencher molecules (Q). The luminophores are excited with a pulse of unpolarized light to create an initially racemic excited‐state population of ΛL* and ΔL* enantiomers, and TR‐CL measurements are then used to monitor the differential decay kinetics of the ΛL* and ΔL* subpopulations. Observed differences between the ΛL* and ΔL* decay kinetics reflect differential rate processes and efficiencies for ΛL*‐Q versus ΔL*‐Q quenching actions, and they are diagnostic of chiral discriminatory interactions between the luminophore and quencher molecules. In this study, the luminophores are either Eu(dpa) 3 3−or Tb(dpa) 3 3−coordination complexes (where dpa denotes a dipicolinate dianion ligand), and the quenchers are diastereomeric structures of Cr(H 2 O) 4 (ATP), Rh(H 2 O) 4 (ATP) and Rh(H 2 O) 3 (ATP) (where ATP≅adenosine triphosphate). The Ln(dpa) 3 3−(Ln≡Eu 3+ or Tb 3+ ) complexes have three‐bladed propeller‐like structures of D 3 symmetry, and in aqueous solution they exist as a racemic mixture of left‐handed (Λ) and right‐handed (Δ) configurational isomers (enantiomers). The results show that the chiral quencher molecules can distinguish between the Λ and Δ enantiomeric structures of the luminophores in their excited‐state quenching actions. The degree and sense of enantiomeric preference in these quenching actions are governed by the electronic and stereochemical properties of the quencher molecules. Twenty‐one different luminophore‐quencher systems are examined in this study, and they exhibit interestingly diverse enantiodifferential quenching kinetics. The results reflect the extraordinary sensitivity of chiral recognition and discrimination processes to relatively small, and somethimes subtle, changes in molecular electronic and stereochemical structure.