Relative viscosities of some aqueous rare earth chloride solutions at 25.deg.

Spedding, F. H.; Witte, David L.; Shiers, Loren E.; Rard, Joseph A.

doi:10.1021/je60063a016

Cited by 25 publications

(29 citation statements)

References 14 publications

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“…Enzyme activity (reference 57) is inhibited by Mg 2+ binding to NAD(P)+ malic enzyme in the presence of 20 μM Ln 3+ . Viscosity parameter is for an aqueous solution of 1.0 M LnCl 3 at 25 °C (reference 55). …”

Section: Figurementioning

confidence: 99%

Enhancement of Anion Binding in Lanthanide Optical Sensors

Cable

Kirby²,

Gray

et al. 2013

Acc. Chem. Res.

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In the design of molecular sensors, researchers exploit binding interactions that are usually defined in terms of topology and charge complementarity. The formation of complementary arrays of highly cooperative, noncovalent bonding networks facilitates protein-ligand binding, leading to motifs such as the ‘lock-and-key.’ Synthetic molecular sensors often employ metal complexes as key design elements as a way to construct a binding site with the desired shape and charge to achieve target selectivity. In transition metal complexes, coordination number, structure and ligand dynamics are governed primarily by a combination of inner-sphere covalent and outer-sphere noncovalent interactions. These interactions provide a rich variable space that researchers can use to tune structure, stability and dynamics. In contrast, lanthanide(III)-ligand complex formation and ligand-exchange dynamics are dominated by reversible electrostatic and steric interactions, because the unfilled f shell is shielded by the larger, filled d shell. Luminescent lanthanides such as terbium, europium, dysprosium and samarium display many photophysical properties that make them excellent candidates for molecular sensor applications. Complexes of lanthanide ions act as receptors that exhibit a detectable change in metal-based luminescence upon binding of an anion. In our work on sensors for detection of dipicolinate, the unique biomarker of bacterial spores, we discovered that the incorporation of an ancillary ligand (AL) can enhance binding constants of target anions to lanthanide ions by as much as two orders of magnitude. In this Account, we show that selected ALs in lanthanide/anion systems greatly improve sensor performance for medical, planetary science and biodefense applications. We suggest that the observed anion binding enhancement could result from an AL-induced increase in positive charge at the lanthanide ion binding site. This effect depends on lanthanide polarizability, which can be established from the ionization energy of Ln3+ → Ln4+. These results account for the order Tb3+ > Dy3+ > Eu3+ ≈ Sm3+. As with many lanthanide properties, ranging from hydration enthalpy to vaporization energy, this AL-induced enhancement shows a large discrepancy between Tb3+ and Eu3+ despite their similarity in size, a phenomenon known as the ‘gadolinium break.’ This discrepancy, based on the unusual stabilities of the Eu2+ and Tb4+ oxidation states, results from the half-shell effect, as both of these ions have half-filled 4f-shells. The high polarizability of Tb3+ explains the extraordinarily large increase in the binding affinity of anions for terbium compared to other lanthanides. We recommend that researchers consider this AL-induced enhancement when designing lanthanide-macrocycle optical sensors. Ancillary ligands also can reduce the impact of interfering species such as phosphate) commonly found in environmental and physiological samples.

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Section: Figurementioning

confidence: 99%

Enhancement of Anion Binding in Lanthanide Optical Sensors

Cable

Kirby²,

Gray

et al. 2013

Acc. Chem. Res.

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“…Various physical and chemical properties of the series of rare earth ions in aqueous solution have been studied over the years (apparent molal volumes, relative viscosities, apparent molal heat capacities, heats of dilution and electrical conductance [3][4][5][6]). However, many thermodynamic and transport properties of rare earth ions in aqueous solution actually follow an irregular or S-shaped behavior when plotted against the atomic number or the ionic radius [3][4][5][6][7][8][9]. This behavior was seen as the result of the coordination number change of the first sphere in the middle of the lanthanide series following neodymium to terbium (see [7] and references therein).…”

Section: Introductionmentioning

confidence: 99%

On the Hydration of the Rare Earth Ions in Aqueous Solution

Rudolph

Irmer

2020

J Solution Chem

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The totally symmetric stretching mode 1 Ln-(OH 2 ) of the first hydration shells of all the rare earth (RE) ions across the series from lanthanum to lutetium has been measured on dilute aqueous perchlorate solutions at room temperature. An S-shaped relationship has been found between the 1 Ln-(OH 2 ) peak positions and the Ln-(OH 2 ) bond distances of the lanthanide(III) aqua ions. While the light rare earth ions form nona-hydrates, the heavy ones form octa-hydrates and the rare earth ions in the middle of the series show non integer hydration numbers between 9 and 8. A relationship between wavenumber positions 1 Ln-(OH 2 ) and the Ln-(OH 2 ) bond distances of the RE hydrates has been given. Recent quantum mechanical calculations support the given interpretation.

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“…Investigations in this laboratory, including the determination of partial molal volumes (43,46,49,50), heats of dilution (42), partial molal heat capacities (44), viscosities (45,(51)(52)(53), and electrical conductances (40,47,48) of aqueous rare earth solutions, have indicated that the thermodynamic and transport properties of these solutions are not simple functions of the ionic radii. It has been suggested (46) that changes in primary hydration coordination of the rare earth ions are partially responsible for the observed irregularities.…”

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confidence: 99%