METAL-FULVIC ACID CHELATION EQUILIBRIUM IN AQUEOUS NaNO3 SOLUTION. Hg(II), Cd(II), AND Cu(II) FULVATE COMPLEXES

1974 ◽  
Vol 54 (4) ◽  
pp. 413-417 ◽  
Author(s):  
VENGHUOT CHEAM ◽  
DONALD S. GAMBLE
Keyword(s):  
Fulvic Acid ◽  
Copper Complexes ◽  
Similar Type ◽  
Conditional Stability ◽  
Acid System ◽  
Cadmium Complexes ◽  
K Value ◽  
Metal Affinity ◽  
Mercury Complexes ◽  
Conditional Stability Constants

Conditional stability constants of some metal fulvate complexes have been determined at 25 C using specific ion electrodes. In aqueous 0.1 M NaNO3, solution, the log K values are: 4.86 and 5.08 at pH 3 and 4 for mercury complexes; 3.04 and 3.64 at pH 4.9 and 5.95 for cadmium complexes; and 3.22, 3.72, and 4.35 at pH 3, 4, and 5 for copper complexes. In 0.04 M NaNO3 solution, the log K value for mercury–fulvic acid system is 5.12 at pH 3.1. The order of metal affinity toward fulvic acid Hg > Cu > Cd is in general agreement with the literature for complexing of these metals with similar type donors.

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.

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.

Cadmium complexation by soil fulvic acid

1978 ◽  
Vol 56 (17) ◽  
pp. 2331-2336 ◽  
Author(s):  
Bill Brady ◽  
Gordon K. Pagenkopf
Keyword(s):  
Fulvic Acid ◽  
Stability Constants ◽  
Conditional Stability ◽  
Cadmium Complexation ◽  
Conditional Stability Constants

A soil fulvic acid bas been characterized and the complexation stability constants with cadmium have been evaluated. The average gram formula weight of the fulvic acid is 2775. Three complexes of stoichiometry CdFA, Cd2FA, and Cd3FA have been observed. The respective conditional stability constants at pH 5.7 are 105.3, 109.8, and 1014.0; at pH 6.7 they are 105.6, 1010.6, and 1015.5; and at pH 7.7 they are 106.0, 1010.7, and 1015.4.

Measurement of Complexing Materials Excreted from Algae and Their Ability to Ameliorate Copper Toxicity

1979 ◽  
Vol 36 (8) ◽  
pp. 901-905 ◽  
Author(s):  
C. M. G. Van den Berg ◽  
P. T. S. Wong ◽  
Y. K. Chau
Keyword(s):  
Stability Constants ◽  
Copper Complexes ◽  
Copper Toxicity ◽  
Copper Ion ◽  
Ion Concentration ◽  
Conditional Stability ◽  
Exchange Method ◽  
Ionic Copper ◽  
Conditional Stability Constants ◽  
Algal Exudates

The complexing capacities of three algal exudates and the conditional stability constants of their copper complexes have been determined by an ion exchange method. Their ability to ameliorate copper toxicity towards the primary production of Chlorella vulgaris is related to the conditional stability constants, which regulate the ionic copper concentration. Anabaena cylindrica, Navicula pelliculosa, and Scenedesmus quadricauda excreted 6.73, 2.86, and 0.66 μmol/L of complexing ligands, respectively, with conditional stability constants of 107.7, 108.1, and 108.6, respectively, for their corresponding copper complexes. When these constants were applied in calculations, a free copper ion concentration of 10−10.3 mol/L was found in each exudate. Key words: algal exudates, free copper ion concentration, complexing capacity, copper ion toxicity, primary productivity

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