Multi-Wavelength Fluorescence-Quenching Model for Determination of Cu2+ Conditional Stability Constants and Ligand Concentrations of Fulvic Acid

2003 ◽  
Vol 57 (4) ◽  
pp. 454-460 ◽  
Author(s):  
Michael D. Hays ◽  
David K. Ryan ◽  
Stephen Pennell
Keyword(s):  
Fulvic Acid ◽  
Data Sets ◽  
Conditional Stability ◽  
Intensity Data ◽  
Fluorescence Excitation ◽  
Ph Values ◽  
Synchronous Fluorescence Spectra ◽  
Multi Wavelength ◽  
Conditional Stability Constants

In this work, a multi-wavelength model (MWM) is developed. It uses fluorescence bands in the fulvic acid (FA) spectrum that quench upon binding of inorganic Cu2+ to FA. Quenching data at pH values of 5, 6, and 7 are placed in sets, containing fluorescence measures at select wavelengths versus added copper ( CM). Intensity data of wavelength set 1 are obtained from 25 nm constant offset synchronous fluorescence spectra (SyF), in which are observed distinct peaks (λex = 415 nm, λem = 440 nm; and λex = 471 nm, λem = 496 nm). Wavelength set 2 intensity data are obtained from the FA fluorescence excitation and emission maxima (λex = 335 nm, λem = 450 nm; and λex = 471 nm, λem = 496 nm). Application of MWM shows that the multi-wavelength data sets characterize ligands of different binding strength (log Kx) and concentration ( CLx). Corresponding to pH values of 5, 6, and 7, mean and standard deviation values for wavelength set 1 are log K415/440 = 4.66 (0.12), 5.03 (0.12), and 5.05 (0.08), log K471/496 = 4.93 (0.06), 5.27 (0.11), and 5.39 (0.09), C415/440 = 3.1 (1.5), 10.9 (4.5), and 7.9 (3.9) μM, C471/496 = 14.3 (3.0), 1.7 (0.6), and 1.4 (0.5) μM. And for wavelength set 2, log K335/450 = 4.50 (0.03), 4.96 (0.27), and 5.22 (0.08), log K471/496 = 5.02 (0.04), 5.42 (0.32), and 5.71 (0.09), C335/450 = 8.8 (0.5), 21.9 (7.9), and 18.7 (0.3) μM, C471/496 = 21.0 (2.5), 7.17 (1.2), and 7.09 (0.3) μM. The ability of the 415/440 nm SyF transect to characterize the main excitation and emission maximum of FA at 335/440 nm is evaluated. Relatively low concentration values returned by the model for this transect (415/440 nm) suggest that it is not entirely illustrative of the maximum. The model predictive capability is verified at pH 6 with two fluorescing Cu2+ chelating organic compounds, L-tyrosine and salicylic acid. This test confirms that the model is capable of providing good estimates of equilibrium binding parameters from multi-wavelength measurements of a mixed ligand system.

Direct phase determination in electron crystallography: small organic molecules

1992 ◽  
Vol 50 (2) ◽  
pp. 1166-1167
Author(s):  
Douglas L. Dorset
Keyword(s):  
Organic Molecules ◽  
Data Sets ◽  
Temperature Structure ◽  
3D Analysis ◽  
Intensity Data ◽  
Electron Crystallography ◽  
Phase Determination ◽  
Measured Intensity ◽  
3D Data

The quantitative use of electron diffraction intensity data for the determination of crystal structures represents the pioneering achievement in the electron crystallography of organic molecules, an effort largely begun by B. K. Vainshtein and his co-workers. However, despite numerous representative structure analyses yielding results consistent with X-ray determination, this entire effort was viewed with considerable mistrust by many crystallographers. This was no doubt due to the rather high crystallographic R-factors reported for some structures and, more importantly, the failure to convince many skeptics that the measured intensity data were adequate for ab initio structure determinations.We have recently demonstrated the utility of these data sets for structure analyses by direct phase determination based on the probabilistic estimate of three- and four-phase structure invariant sums. Examples include the structure of diketopiperazine using Vainshtein's 3D data, a similar 3D analysis of the room temperature structure of thiourea, and a zonal determination of the urea structure, the latter also based on data collected by the Moscow group.

Comparison of Mn2+, Co2+, and Cu2+ binding to fulvic acid as measured by fluorescence quenching

1983 ◽  
Vol 61 (7) ◽  
pp. 1505-1509 ◽  
Author(s):  
David K. Ryan ◽  
Carl P. Thompson ◽  
James H. Weber
Keyword(s):  
Fluorescence Quenching ◽  
Fulvic Acid ◽  
Binding Capacity ◽  
Outer Sphere ◽  
Conditional Stability ◽  
Complexing Capacity ◽  
Fluorescence Quenching Titration ◽  
Conditional Stability Constants ◽  
Slight Advantage ◽  
Binding Curves

The binding of Cu2+ to soil-derived fulvic acid (SFA) measured by fluorescence quenching titration is much stronger than Co2+ and Mn2+ which are similar. The conditional stability constants from curve fitting at pH 6 are 1.1 × 105 for Cu2+, 5.1 × 103 for Co2+, and 4.2 × 103 for Mn2+. The slight advantage in strength for Co2+ over Mn2+ is also demonstrated by the binding curves at pH 6 and 7. These two metal ions not only tend to bind more weakly but also bind to fewer sites, giving complexing capacity values of about 1.5 × 10−6 M compared to 2.0 × 10−5 for Cu2+ at pH 6. This lower binding capacity may be due to outer sphere complexation that does not allow access to some sites complexed by inner sphere binding Cu2+. Scattering experiments demonstrate that Cu2+ is more effective at precipitating and aggregating SFA than Co2+ and Mn2+. Cu2+ probably neutralizes the negative charges on SFA molecules allowing larger hydrophobic aggregates to form and precipitate.

Reactions of gallocyanine methyl ester with gallium(III) and indium(III) ions

1982 ◽  
Vol 47 (7) ◽  
pp. 1950-1963 ◽  
Author(s):  
Milan Kotouček ◽  
Josef Růžička ◽  
Pavla Vaculíková
Keyword(s):  
Methyl Ester ◽  
Stability Constants ◽  
Equilibrium Constants ◽  
Photometric Determination ◽  
Conditional Stability ◽  
Conditional Stability Constants

Reactions of gallocyanine methyl ester with gallium(III) and indium(III) ions in solutions in 15% (m/m) ethanol were studied spectrophotometrically. At pH 1.7-6.5, the GaL, GaL2, and Ga(OH)L3 complexes are formed; in the case of indium, the In(OH)2L2 and In(OH)L3 complexes appear at pH 4-6.5, and InL3B2 in tartrate solutions. The conditional stability constants and the equilibrium constants of the coordination equilibria were calculated, and procedures were worked out for a photometric determination of gallium and for a chelatometric determination of gallium and indium using gallocyanine methyl ester as metallochromic indicator.

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