Fluorescence quenching study of the effect of association on the structure of humic acids

Лаврик, Н. Л.; Mulloev, N. U.

doi:10.1007/s10812-010-9372-y

Cited by 5 publications

(7 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Only a few studies indirectly touching upon this problem have been published (see, e.g., [23,24]). The data directly related to the study of the forms of HA existence depending on concentration were only reported in [25], where the authors observed the bathochromic shift of HA fluorescence spectra with an increase in solution concentration. This shift was related to the possibility of HA association.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Association and colloid-chemical properties of humic acids in aqueous solutions

et al. 2013

View full text Add to dashboard Cite

Colloid chemical properties of humic acids in aqueous solutions have been studied as functions of their concentration, medium pH, and counterion nature. It has been established that, at pH < 4, Na form humic acids exist in aqueous solutions as 30-120 nm aggregates. At pH > 4, the state of humic acids depends on the solution concentration. At low concentrations, they exist as individual molecules; as the concentration is increased, they associate to form supramolecular structures at 5 mg/dm 3 and micelles at 8 g/dm 3 . An increase in the counterion charge has been shown to decrease the critical concentration of supramolecular structuring. Supramolecular structures have increased adsorbability on clay minerals and promote the mani festation of solubilizing properties of humic acids in solutions even at a concentration of 5 mg/dm 3 , which is three orders of magnitude lower than the critical micelle concentration (8 g/dm 3 ).

show abstract

Section: Resultsmentioning

confidence: 99%

“…Other authors also have noted this concentration as a critical one when studying HA molecular masses [36] and fluorescence spectra [25] in aqueous solutions.…”

Section: Resultsmentioning

confidence: 99%

Association and colloid-chemical properties of humic acids in aqueous solutions

et al. 2013

View full text Add to dashboard Cite

show abstract

“…This value was noticeably greater than the fluorescence quenching diffusion rate constant for dynamic quenching in water (~10 10 M -1 ⋅s -1 [16]). Quenching rate constants greater than the diffusion ones in experiments on FA and HA quenching by metal ions have been reported several times [4,5,8,11,12,21]. The greater values indicate that static quenching is present [16].…”

Section: Modeling K Svmentioning

confidence: 99%

“…Fluorescence spectroscopy (fluorescence spectra, fluorescence excitation) is a non-invasive method of observation and is currently one of the most informative and common methods for studying HA structural properties [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The polydispersity of HA is manifested in fluorescence spectroscopy as a dependence of the fluorescence spectrum maximum position on the wavelength of the exciting light and a dependence of the excitation spectrum on the observation wavelength [4][5][6][7].…”

mentioning

confidence: 99%

A method to study polydispersity of humic acid from fluorescence quenching by Cu2+ ions

Лаврик

Mulloev

2011

J Appl Spectrosc

Self Cite

View full text Add to dashboard Cite

The spectral dependence of Stern-Volmer constants (K SV λ ) for fluorescence quenching by Cu 2+ ions in a standard sample of humic acid (HA) (IHSS) with monochromatic excitation (λ ex = 337.1 nm) conditions has been studied in the spectral range 400-600 nm. This is interpreted within a concept implying that HA macromolecules possess the property of polydispersity, which means that fluorophore-containing sites are different in terms of chemical nature and spatial accessibility. Modeling data show that the minimum number of spectral components required for the simulated spectral dependence of K SV λ to agree as closely as possible with that observed experimentally is three.Keywords: humic acid, polydispersity, quenching of humic acid fluorescence, Cu 2+ ion, experimental and simulated spectral dependences of Stern-Volmer constants.Introduction. Humic (HA) and fulvic (FA) acids are very important environmental components that occur in soil, water (dissolved), and air (as aerosols). HA originate in organic matter and are synthesized via oxidation of such complex natural organic molecules as carbonylhydrates, proteins, and lignins. They also occur in the remains of dead plants and animals. HA play an important role in the chemistry and transport of hydrophobic organic molecules, bioactivity, and the maintenance of the pH of natural aquifers. HA macromolecules are composed of many functionally varied chemical groups (catechins, quinones, phthalates, phenolamines, salicylates, etc.) that are capable of forming complexes [1]. Owing to these acceptor properties, HA control the concentration of dissolved pollutants (amines, phenols, heterocyclic compounds, heavy metals, etc.) [1].The following model is generally accepted for the structure of HA. There is a core (aromatic carbon skeleton) and a periphery (polysaccharide or polypeptide chain) [1]. It is assumed that the molecular fragments of the core and periphery of a single HA molecule are chemically bonded. The groups imparting specific properties to HA are the condensed aromatic rings bonded to each other through chains with somewhat conjugated C-C and other bonds. The peripheral irregular structural elements (peripheral chains) are variable components. As a result, the structures of HA molecules, even those isolated from a single soil, are not rigidly fixed and are subject to statistical fluctuations. Therefore, a characteristic feature of HA macromolecules is their polydispersity that causes an HA sample to consist of macromolecules that differ in chemical and; therefore, structural properties.Numerous physicochemical methods [1], in particular those involving fluorescence [2,3], are used to obtain information about the structural and chemical properties of HA. Fluorescence spectroscopy (fluorescence spectra, fluorescence excitation) is a non-invasive method of observation and is currently one of the most informative and common methods for studying HA structural properties [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The polydispersity of HA is manife...

show abstract

“…The concentration-dependent acceptor capacity of the HA macromolecule to form complexes has already been discussed elsewhere. 11,12…”

Section: Introductionmentioning

confidence: 99%

Self-Association of the Macromolecules of Aldrich Humic Acid in Aqueous Solutions Using Ultraviolet–Visible (UV–Vis) Absorption Spectroscopy

Лаврик

Bazhin

2019

Appl Spectrosc

View full text Add to dashboard Cite

The ultraviolet–visible (UV–Vis) spectra of the aqueous solutions of humic acids (HA) Aldrich were obtained within the concentration range 1–20 mg/L (0.1–2ċ10–6 mol/L). A conclusion on the existence of the self-association (dimer formation) of HA macromolecules is based on the deviation of the concentration dependence of optical density (OD) from the linear one at [HA] > 10 mg/L (>10–6 mol/L). An original, mathematical algorithm is proposed to determine a dimerization constant K and a molar coefficient of dimer absorption [Formula: see text] The value of K was (2.56 ± 0.07) ċ 106 L/mol. The calculated molar coefficients of HA macromolecule dimer absorption, [Formula: see text], indicate an increase in the dimer extinction coefficient [Formula: see text] compared to the double value of the molar monomer absorption 2[Formula: see text]. It was established that the spectral dependence of the value β = [Formula: see text]/[Formula: see text] exhibits a minimum within a wavelength range of 300–450 nm, which is due to the difference in the efficiency of the interaction of various sites upon HA macromolecule dimerization. Thus, an approach of studying the processes of self-association is proposed using the method of UV–Vis absorption spectroscopy. This method is implemented for molecules that do not have characteristic absorption bands. The proposed method can also be successfully applied to molecules with characteristic absorption bands.

show abstract

Fluorescence quenching study of the effect of association on the structure of humic acids

Cited by 5 publications

References 17 publications

Association and colloid-chemical properties of humic acids in aqueous solutions

Association and colloid-chemical properties of humic acids in aqueous solutions

A method to study polydispersity of humic acid from fluorescence quenching by Cu2+ ions

Self-Association of the Macromolecules of Aldrich Humic Acid in Aqueous Solutions Using Ultraviolet–Visible (UV–Vis) Absorption Spectroscopy

Contact Info

Product

Resources

About