Lanthanide ion probe spectroscopy

Dobbs, J.C., Susetyo, W., Knight, F.E., Castles, M.A., Carreira, L.A. and Azarraga, L.V (1989a) Characterization of metal binding sites in fulvic acids by lanthanide ion probe spectroscopy. Anal. Chem., 61, 483M-88. 

Dobbs J. C., Susetyo W., Carreira L. A., and Azarraga L. V. (1989) Competitive binding of protons and metal ions in humic substances by lanthanide ion probe spectroscopy. Anal. Chem. 61, 1519-1524. 

A powerful, but less frequently used, method for studying the complexation of trace metal cations by DOM is lanthanide ion probe spectroscopy (Dobbs et al., 1989). In this method, fluorescence intensities of Eu(lll) at two emission wavelengths are used to determine the proportions of complexed and free Eu(lll). When a competing metal cation is added to the solution, its complexation by DOM causes the fluorescence... 

Titration curves of HS fluorescence quenching versus concentration of added metal quencher have been used to obtain the CC values of HS ligands and the stability constants of HS-metal complexes (Saar and Weber, 1980, 1982 Underdown et al., 1981 Ryan et al., 1983 Weber, 1983 Dobbs et al., 1989 Grimm et al., 1991 Hernandez et al., 2006 Plaza et al., 2005, 2006). Two fluorescence techniques, lanthanide ion probe spectroscopy (LIPS) and fluorescence quenching of HSs by Cu-+, have been used in conjunction with a continuous distribution model to study metal-HS complexation (Susetyo et al., 1991). In the LIPS technique, the HS samples are titrated by Eu-+ ions, and the titration plot of the ratio of the intensities of two emission lines of Eu + is used to estimate the amount of bound and free species of the probe ion. In the other technique, titration curves of fluorescence intensity quenched by Cu versus the logarithm of total added Cu2+ are used. 

Structure Probes.—The introduction of fluorescing labels into nucleic acids can yield valuable structural information, and both organic compounds and metal ions [Tb (ref. 136) and Eu (ref. 137)] have been used as fluorescent probes for tRNA and other polynucleotides. The degree of secondary structure in RNA has been estimated from Raman scattering by the phosphate group vibrations. A number of n.m.r. studies have appeared, but discussion of these is more suited to a review on n.m.r. spectroscopy. Lanthanide ions have been used as contact shift reagents to probe tRNA structure. ... 

Lanthanide complexes of transferrin have been used for several purposes. Gd3+-transferrin gives a characteristic EPR signal at g = 4.96, quite unlike the spectra for other Gd3+ complexes (165) Eu3+ has been used to probe differences between the two sites by Eu(III) excitation spectroscopy (168) and the luminescence of excited Tb3+ ions bound in one site of mixed-metal Tb3+-Mn3+ and Tb3+-Fe3+ transferrin complexes has been used to determine the intersite distance (169). The value obtained, 35.5 A, compares well with the value of 42 A later obtained from the lactoferrin crystal structure (67). 

Reviews have appeared on the use of high resolution n.m.r. spectroscopy in the structural determination of complex carbohydrates and of some 3-0-, 4-0-, and 3,4-di-O-glycopyranosyl-substituted methyl D-gtycopyranosides. The latter publication includes complete assignments of and C-n.m.r. resonances as well as conformational studies using HSEA effect theory. The application of various njnj. techniques (multi-relayed correlation, H- H-correlated, triple quantum field H- H-correlated and H- H homonuclear Hartmann Hahn spectroscopy) to carbohydrate analysis has been reviewed in Japanese, and in a further Japanese review the interactions of metal ions with uronic acids and amino sugars as observed by the lanthanide-probe n.m.r. method are discussed/... 

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