Evidence from surface tension and fluorescence data of a pyrene-assisted micelle-like assemblage of humic substances

Sierra, Maria Marta de Souza; Rauen, Thalita Grando; Tormen, Luciano; Debacher, Nito Ângelo; Soriano-Sierra, Eduardo Juan

doi:10.1016/j.watres.2005.07.005

Cited by 26 publications

(17 citation statements)

References 16 publications

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“…Sierra et al observed at neutral pH the partial neutralization of negative charges, associated with the hydrophobic-hydrophobic interactions between HA. The addition of pyrene molecules promoted the formation of relatively stable water-soluble agglomerates similar to micelle arrangements [46]. In our study, PAHs added to HS solution can also act as a nucleus for such arrangements.…”

Section: Aggregation and Conformational Behavior Of Hssupporting

confidence: 53%

Assessing desorption resistance of PAHs in dissolved humic substances by membrane-based passive samplers

Chen

Wang

2010

Journal of Colloid and Interface Science

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a b s t r a c tBinding of hydrophobic organic compounds (HOCs) to humic substances (HS) has significant influence on their fate and bioavailability in an aquatic environment, yet very little is known on the desorption behavior of HOCs in dissolved HS. In this study, triolein-embedded cellulose acetate membranes (TECAMs) were used as passive samplers in dissolved HS-containing solutions to extract the free polycyclic aromatic hydrocarbons (PAHs). The partitioning coefficients (K OC ) of PAHs in dissolved HS from different sources were determined. Then the rapidly desorbable fractions (f rd ) of HOCs in dissolved HS were quantified by a quasi-equilibrium model. Results show that the magnitude of K OC of PAHs correlated strongly with the O/C atomic ratio and molecular weight of HS. The PAHs with lower K OW values desorbed almost reversibly from an aquatic fulvic acid, a sediment humic acid (HA), a lignite HA, and Aldrich HA. However, for strongly hydrophobic chrysene binding to the lignite HA, some extent of desorption resistance was found and attributed to sorption hysteresis as well as steric hindrance. The present study illustrated that the quality of HS and the property of solute may play key roles in determining the desorption reversibility.

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Section: Aggregation and Conformational Behavior Of Hssupporting

confidence: 53%

Assessing desorption resistance of PAHs in dissolved humic substances by membrane-based passive samplers

Chen

Wang

2010

Journal of Colloid and Interface Science

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“…Moreover, several studies have shown that HA can aggregate inter and/or intramolecularly in aqueous solutions generating micelle-like agglomerates capable of sequestering hydrophobic pollutants. [44][45][46][47] The formation of such agglomerates, which is influenced by the concentration, pH, ionic strength and the presence of non-polar compounds, has been evidenced in HA, but not in FA, solutions of the same pool of HS studied here. 45,47 In HA bulk solutions the greater proximity of the aromatic moieties would then occur in the interior of such hydrophobic microdomains, explaining the strongest spectral displacement.…”

Section: D-fluorescence Of the Fractionsmentioning

confidence: 61%

“…[44][45][46][47] The formation of such agglomerates, which is influenced by the concentration, pH, ionic strength and the presence of non-polar compounds, has been evidenced in HA, but not in FA, solutions of the same pool of HS studied here. 45,47 In HA bulk solutions the greater proximity of the aromatic moieties would then occur in the interior of such hydrophobic microdomains, explaining the strongest spectral displacement. A few HA fractions (particularly fractions 6 and 7) exhibit, besides the main signal at 450 nm, a shoulder in the same wavelength range (~530 nm) as that of the bulk sample emission, indicating that in these fractions agglomerates might also be present, but here, the fluorescence signal of individual structures is still dominant.…”

Section: D-fluorescence Of the Fractionsmentioning

confidence: 61%

3D-fluorescence spectroscopic analysis of HPLC fractionated estuarine fulvic and humic acids

Sierra¹,

Giovanela²,

Parlanti³

et al. 2006

J. Braz. Chem. Soc.

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Seis amostras de ácidos fúlvicos (AF) e húmicos (AH) estuarinos foram fracionadas por meio de cromatografia líquida de alta performance em fase reversa, num gradiente de polaridade água → acetonitrila, com detecção por fluorescência. Diferenças entre os cromatogramas mostraram que os AH contêm mais componentes hidrofóbicos que os AF. Os espectros de fluorescência tridimensional das frações foram bastante similares entre si e também ao da amostra original, indicando que, apesar das polaridades distintas, a complexidade e as principais características do material original se mantêm. Um mesmo grupo de fluoróforos parece ser responsável pelas características de fluorescência, dos dois tipos de substâncias húmicas. Um deslocamento batocrômico dos espectros de emissão das soluções originais, com relação àqueles das frações, foi atribuído a uma maior proximidade destes fluoróforos, possivelmente devido à formação de agregados. Em geral, os resultados confirmam o conceito de que as "macromoléculas" húmicas consistem de associações de estruturas menores com características químicas semelhantes.Six estuarine fulvic (FA) and humic acids (HA) were fractionated with reversed-phase high performance liquid chromatography in a water/acetonitrile gradient, with fluorescence detection. Differences between FA and HA chromatograms pointed to a higher incidence of hydrophobic components in the latter. Excitation-emission matrix fluorescence diagrams of most fractions were similar to those of the bulk samples indicating that, in spite of their distinct polarities, the complexity and main spectral characteristics of the materials persisted. A primary group of fluorophores, which are present in most of the fractions, seems to be at the origin of the fluorescence properties of both kinds of HS. A bathochromic shift of the bulk solutions spectra in relation to the fraction emissions was attributed to a greater proximity of these fluorophores, possibly due to the formation of aggregates. Generally, the results reinforced concepts that humic macromolecules consist of assemblages of structurally similar building blocks. Keywords: RP-HPLC, fulvic acids, humic acids, EEM fluorescence IntroductionHumic substances (HS) are complex macromolecular products resulting from the chemical and biological degradation of plant and animal residues. They are widely distributed in soils, natural waters, and sediments, and represent a significant proportion of the organic carbon in the global carbon cycle.1-4 According to current estimates, HS constitute the major fraction of soil organic matter (up to 80%) and the largest fraction of natural organic matter (NOM) in aquatic systems (up to 60% of dissolved organic carbon). 5,6These organic materials can have a substantial impact on a variety of biogeochemical processes, for example, immobilizing anthropogenic organic chemicals and heavy metals. 7-11The elucidation of the HS molecular sizes, shapes, weights and structural arrangements is essential for an [15][16][17][18][19] In general, UV absorbance, and/or ...

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“…This is because the pyrene incorporated into the HS matrix has a less polar microenvironment compared to water. 15,16,19,22,24 The same should be true for the σ B 02 and σ F 02 values, which should change in the opposite direction. As a result, fluorescence quenching in the pyrene-HS system upon S 0 → S 1 excitation should be more pronounced compared to S 0 → S 2 excitation.…”

Section: Backgroundsmentioning

confidence: 91%

Experimental evidence of incomplete fluorescence quenching of pyrene bound to humic substances: implications for Koc measurements

Shirshin

Budylin

Grechischeva

et al. 2016

Photochem Photobiol Sci

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Fluorescence quenching (FQ) is extensively used for quantitative assessment of partition coefficients (K OC ) of polycyclic aromatic hydrocarbons (PAHs) to natural organic materials -humic substances (HS). The presence of bound PAHs with incompletely quenched fluorescence would lead to underestimation of the K OC values measured by this technique. The goal of this work was to prove the validity of this assumption using an original experimental setup, which implied FQ measurements upon excitation into two distinct vibronically coupled electronic states. Pyrene was used as a fluorescent probe, and aquatic fulvic acid (SRFA) and leonardite humic acid (CHP) were used as the humic materials with low and high binding affinity for pyrene, respectively. Excitation of pyrene into the forbidden (S 0 -S 1 ) and allowed (S 0 -S 2 ) electronic states yielded two pairs of nonidentical FQ curves. This was indicative of incomplete quenching of the bound pyrene, and the divergence of the two FQ curves was much more pronounced for CHP as compared to SRFA. The two component model of fluorescence response formation was proposed to estimate the K OC values from the data obtained. The resulting pyrene K OC value for CHP (220 ± 20) g L −1 was a factor 3 higher compared to the K OC value determined with the use of the Stern-Volmer. At the same time for aquatic FA the difference in FQ curves was almost negligible, which enables the use of the Stern-Volmer formalism for weakly interacting HS and PAHs. IntroductionInteractions of polycyclic aromatic hydrocarbons (PAHs) with natural organic matrices, e.g. humic substances (HS), are of serious environmental concern due to the multiple adverse effects of these hydrophobic contaminants on living organisms.1-3 Binding to HS causes an increase in mobility and a change in the bioavailability and toxicity of PAHs. Given that pyrene interacts with HS mostly via hydrophobic binding, incomplete quenching looks rather feasible. 25,26 Still, quantitative assessments of this phenomenon are missing. In this work, we propose an original experimental setup to acquire FQ measurements, which could enable observation of pyrene bound to HS. For this purpose we measured FQ curves of pyrene upon its excitation into two vibronically coupled states (the forbidden S 1 state and the allowed S 2 state). In the case of static quenching, both FQ curves should be identical. A difference between the FQ curves is indicative of the presence of pyrene-HS complexes with a nonzero fluorescence cross † Electronic supplementary information (ESI) available: Detailed description of the protocol of fluorescence measurements. See

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Evidence from surface tension and fluorescence data of a pyrene-assisted micelle-like assemblage of humic substances

Cited by 26 publications

References 16 publications

Assessing desorption resistance of PAHs in dissolved humic substances by membrane-based passive samplers

Assessing desorption resistance of PAHs in dissolved humic substances by membrane-based passive samplers

3D-fluorescence spectroscopic analysis of HPLC fractionated estuarine fulvic and humic acids

Experimental evidence of incomplete fluorescence quenching of pyrene bound to humic substances: implications for Koc measurements

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