Excited-state chiral discrimination in aqueous solutions of lanthanide(III): 2,6-pyridinedicarboxylate complexes

Wu, Shao-Yi; Bedard, Thomas C.; Riehl, James P.

doi:10.1135/cccc19913025

Cited by 10 publications

(6 citation statements)

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“…The energy-transfer step in the kinetic scheme (6) has been described by Richardson et al8 as an activated process:…”

Section: Discussionmentioning

confidence: 99%

“…In the steady-state experiments, the observed CPL is due to a time-averaged excited-state population difference. 6 In more recent experiments, time-resolved CPL has been measured in the luminescence decay of an initially prepared racemic excited state. 1"5 Recently we have demonstrated that it is possible to determine accurate decay constants for the homochiral (AA = +) and heterochiral (AA = -) quenching of Tb(DPA)33" by A-(-)-Ru-(phen)32+ by a procedure in which the individual luminescence decay constants have been determined through a nonlinear least-squares fit of the luminescence decay curves in terms of a biexponential function.…”

Section: Introductionmentioning

confidence: 99%

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Ionic strength dependence of the enantioselective quenching of tris(2,6-pyridinedicarboxylate)terbium(3-) luminescence by resolved tris(1,10-phenanthroline)ruthenium(2+)

Rexwinkel¹,

Meskers²,

Dekkers³

et al. 1992

J. Phys. Chem.

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The enantioselective excited-state quenching of r~c-Tb(2,6-pyridinedicarboxylate)~~- [A,A-Tb(DPA)33-] by A-(-)-Ru-(1,lO-phenanthroline):' [A-R~(phen)~~+] has been studied in aqueous solution (298 K) and in methanol (298 and 255 K) as a function of solution ionic strength. The ionic strength of methanol and water solutions were controlled through the addition of NaBr. The bimolecular rate constants for homochiral (A-A or A-A) and heterochiral (A-A) quenching were obtained by numerical fitting of the biexponential decay of Tb(DPA)3f luminescence in a series of time-resolved experiments.It is shown that the diastereomeric quenching reactions can be modeled by a kinetic scheme in which the luminophore and quencher form an encounter complex and then undergo a reactive step leading to energy transfer. In water, it is demonstrated that the ionic strength dependence of the quenching rates can be accurately described by the predicted ionic strength dependence of a pseudoequilibrium constant for the encounter complex. Experimental results for a wide range of ionic strengths are presented, and it is shown that the enantioselectivity of the quenching in water at room temperature does not depend on ionic strength. Results for enantioselective quenching in methanol (which are opposite in sign to those measured in water) do show variations in enantioselectivity at room temperature due to interference from racemization of the lanthanide complex, which can be suppressed at lower temperatures. The remaining ionic strength dependence is attributed to a situation in which the reaction becomes nearly diffusion controlled. A theoretical description of chiral recognition in both solvent system is developed through calculations of diffusion and dissociation rates using DebyeSmoluchowski and Eigen equations, respectively, and it is concluded that most of the observed enantioselectivity is due to chiral differences in the reactive step. The analysis also yields a charge product that is very close to the expected value of -6 for both solvent systems and a reactive distance of 1.1 nm. This latter result indicates that the observed quenching is due to very short-range interactions.

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“…The energy-transfer step in the kinetic scheme (6) has been described by Richardson et al8 as an activated process:…”

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Ionic strength dependence of the enantioselective quenching of tris(2,6-pyridinedicarboxylate)terbium(3-) luminescence by resolved tris(1,10-phenanthroline)ruthenium(2+)

Rexwinkel¹,

Meskers²,

Dekkers³

et al. 1992

J. Phys. Chem.

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“…The results for a homologous series of cobalt trans-1,2diamine cyclohexane (dach) chelates, [142][143][144][145][146][147][148][149][150][151] clearly shows the sensitivity of the enantioselectivity to small structural changes in the quencher. Studies of quenching by Δ-Ru(phen) 3 2 + [152][153][154][155][156][157][158] showed opposite enantioselectivities of Ln(dpa) 3 3À in water and methanol, indicating that also the solvation shell around the coordination complexes can play an important role in the molecular recognition. Enantioselective quenching is not restricted to small inorganic complexes: also organic dye molecules, [159] vitamin B 12 derivatives [160] and vitamin B 12protein complexes, [161] transition metal-nucleotide complexes [162,163] and metal organic complexes with topological chirality [164] show chiral discrimination.…”

Section: Cpl From Isolated Small Moleculesmentioning

confidence: 99%

Circular Polarization of Luminescence as a Tool To Study Molecular Dynamical Processes

Meskers

2021

ChemPhotoChem

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Circular polarization of luminescence is a phenomenon that can be observed for chiral molecules in isotropic solution, for molecular aggregates and molecular materials. Also, the electroluminescence from chiral molecular materials in organic light emitting diodes can be nearly completely circularly polarized. In this review we focus on the latest developments in experimental results for the categories listed above. A unifying description of the origin of the circular polarization is still missing. We revisit the very earliest efforts to measure and understand circular polarization in light emission in order to better understand the present day confusion on the origins of the polarization. It seems that quantum field theory of electromagnetic interactions could provide leads for a comprehensive description of the circular polarization including contributions from helicity at all possible length scales from the molecular to the macroscopic.

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“…If kdm » Kket, then this system can be described by a preequilibrium step followed by energy transfer, and eq 6 reduces to = Kka (8) In this case the quenching process is "activation controlled". On the other hand, if Kkn »/earthen the overal reaction is diffusion controlled, and ^q = *diff (9) Results and Discussion Kinetic Analysis of the Diastereomeric Quenching. In Figure 3A we plot the natural log of the homochiral and heterochiral quenching rate constants versus 1/ for a 0.73 mM solution of Tb(DPA)33~i n water to which A-(-)-Ru(phen)32+ has been added.…”

Section: Theorymentioning

confidence: 99%

Thermodynamics of the enantioselective quenching of tris(2,6-pyridinedicarboxylate)terbate(3-) luminescence by resolved tris(1,10-phenanthroline)ruthenium(2+)

Rexwinkel¹,

Meskers²,

Riehl³

et al. 1993

J. Phys. Chem.

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The temperature dependence of the enantioselective quenching of racemic (A,A)-Tb(DPA)3j-(DPA = 2,6-pyridinedicarboxylate) by A-Ru( 1, 10-phenanthroline)32+ in HzO, D20, and methanol is reported. Rate constants for the two diastereomeric quenching reactions may be determined from a nonlinear least-squares fit of the decay of the total luminescence from excited Tb(DPA)33-. Analysis of the biexponential decay data in water (5-80 "C) indicates that the kinetics of the quenching reactions can be accurately described as a preequilibrium between isolated donor and quencher species and an associated ion pair, followed by energy transfer to the acceptor. In methanol a wider temperature range (-85 to 50 "C) can be studied, and it is demonstrated that, dependent on solution ionic strength, at high temperatures the preequilibrium limit is appropriate, but at the lowest temperatures studied, the quenching reactions become entirely diffusion controlled, and the enantioselectivity vanishes. In all three solvents at the higher temperatures the overall quenching reactions are associated with negative activation energies. All of the quenching reactions may be analyzed within activated complex theory to yield activation energies, enthalpies, and free energies for the diastereomeric reaction schemes in both solvents. In addition, the temperature dependence of the equilibrium constant for ion-pair association has been determined. From all of these data, it is concluded that, based on enthalpy considerations, the quenching of like enantiomers (A-A, homochiral quenching) is larger than the quenching of unlike enantiomers (A-A, heterochiral quenching) but that entropy considerations favor the reverse preference. These generalizations are used to explain the observed differences in enantioselectivity observed in methanol and water.

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Excited-state chiral discrimination in aqueous solutions of lanthanide(III): 2,6-pyridinedicarboxylate complexes

Cited by 10 publications

References 0 publications

Ionic strength dependence of the enantioselective quenching of tris(2,6-pyridinedicarboxylate)terbium(3-) luminescence by resolved tris(1,10-phenanthroline)ruthenium(2+)

Ionic strength dependence of the enantioselective quenching of tris(2,6-pyridinedicarboxylate)terbium(3-) luminescence by resolved tris(1,10-phenanthroline)ruthenium(2+)

Circular Polarization of Luminescence as a Tool To Study Molecular Dynamical Processes

Thermodynamics of the enantioselective quenching of tris(2,6-pyridinedicarboxylate)terbate(3-) luminescence by resolved tris(1,10-phenanthroline)ruthenium(2+)

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