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F S Richardson

Publications and source records attributed to F S Richardson.

17 recordsLinked to original sources
PubMed1977

Circularly polarized emission studies on Tb3+ and Eu3+ complexes with potentially terdentate amino acids in aqueous solution.

Circularly polarized emission (CPE) and total emission (TE) spectra are reported for Eu3+ and Tb3+ complexes of L-aspartic acid (L-asp), L-serine (L-ser), L-threonine (L-thr) and L-histidine (L-his) in D2O solution under various pH conditions. Variations in TE and CPE intensities and in CPE splittings and sign patterns as functions of solution pH are correlated with lanthanide ion/ligand binding characteristics and with structural changes in the coordination environment of the metal ion. In the Eu3+/amino acid systems, the emission bands associated with the 5D0 leads to 7F1 and 7F2 Eu3+ transitions are monitored, and in the Tb3+/amino acid systems the 5D4 leads to 7F5 Tb3+ emission is examined.

Amino Acids↗
PubMed1967

Considerations.

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Dentist-Patient Relations↗
PubMedDate not supplied

Intermolecular chiral recognition probed by enantiodifferential excited-state quenching kinetics.

Time-resolved chiroptical luminescence (TR-CL) measurements are used to study the kinetics of chirality-dependent 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 lambda L* and delta L* enantiomers, and TR-CL measurements are then used to monitor the differential decay kinetics of the lambda L* and delta L* subpopulations. Observed differences between the lambda L* and delta L* decay kinetics reflect differential rate processes and efficiencies for lambda L*-Q versus delta L*-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(H2O)4(ATP), Rh(H2O)4(ATP) and Rh(H2O)3(ATP) (where ATP identical to adenosine triphosphate). The Ln(dpa)3(3-) (Ln identical to En3+ or Tb3+) complexes have three-bladed propeller-like structures of D3 symmetry, and in aqueous solution they exist as a racemic mixture of left-handed (lambda) and right-handed (delta) configurational isomers (enantiomers). The results show that the chiral quencher molecules can distinguish between the lambda and delta 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 sometimes subtle, changes in molecular electronic and stereochemical structure.

Adenosine Triphosphate↗