A structural conformation study of aquatic humic acid

Zara, Luiz Fabrício; Rosa, André Henrique; Toscano, Ilda Antonieta Salata; Rocha, Júlio César

doi:10.1590/s0103-50532006000500028

Cited by 22 publications

(27 citation statements)

References 18 publications

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“…This parameter is commonly used as a degree of molecular condensation and polycondensated aromatic-ring structures of humic substances. 12,25,26 The E 4 /E 6 ratio decreases whereas the molecular weight and aromatic structures increase. Higher values of the ratio can indicate the presence of high amounts of aliphatic structures.…”

Section: Molecular Absorption Spectroscopymentioning

confidence: 99%

“…This AHA was isolated, purified and characterized as reported before. 12 Samples of peat humic acid (PHA) were obtained from peat soil fractions collected at the margins of the Mogi Guaçu river (47 o 9' W/21 o 5' S) in the town of Luiz Antonio (São Paulo, Brazil). This humic acid was isolated, purified and characterized as reported before.…”

Section: Chemicalsmentioning

confidence: 99%

“…These different additions were made in order to observe the pH influence on conformation of CHA, AHA and PHA structures. 12 …”

Section: Uv-vis Spectroscopymentioning

confidence: 99%

“…Structural conformation of macro molecules, like AH, is influenced by several factors as pH, ionic strength, charge density, ionization degree of acid groups, concentration, hydrogen bonds and intermolecular arrangements. 12 Besides, HA samples are able to form molecular aggregation in solution and their sizes are a function of pH. 2 From the molecular absorption spectroscopy, we can obtain the E 4 /E 6 index.…”

Section: Molecular Absorption Spectroscopymentioning

confidence: 99%

“…These amphiphilic molecules can form micelles, double layers or micelle-like structures. [10][11][12] In this present work, HA were studied by potentiometric and conductimetric titration in order to determine the charge tendencies on the surface of the material. Besides, UV-Vis molecular absorption and scanning electron microscopy (SEM) were performed in order to understand the relationship between the pH system and molecular aggregation of the HA macromolecule.…”

Section: Introductionmentioning

confidence: 99%

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Aspects of protonation and deprotonation of humic scid durface on molecular conformation

Prado¹,

Pertusatti²,

Nunes³

2011

J. Braz. Chem. Soc.

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As densidades superficiais de carga de ácidos húmicos foram determinadas por titulação potenciométrica e condutimétrica simultâneas. Também foi observada a influência do pH na conformação molecular através de espectroscopia de UV-Vis e microscopia eletrônica de varredura (MEV). A densidade de carga superficial para todas as amostras de ácido húmico é aproximadamente zero na faixa de pH 3,5-6,0. A influência do pH na condensação molecular foi observada pela determinação do índice b na equação de Doty e Steiner. Os altos valores de b foram obtidos na região ácida, indicando uma conformação condensada, devido à fraca interação atrativa. Além disso, na região alcalina, a densidade de carga na superfície da molécula é mais negativa, o que favorece o aumento da repulsão e dispersão das partículas, levando à formação de estruturas micelares como consequência da característica anfifílica dos ácidos húmicos.The surface charge densities for humic acids (HAs) were determined by simultaneous potentiometric and conductimetric titrations. It was also observed the pH influence on molecular conformation by UV-Vis spectroscopy measurements and scanning electron microscopy (SEM) images. The surface charge densities are approximately zero at the pH range 3.5 to 6.0 for all samples. The pH influence on molecular condensation level was observed by the determination of the b index from Doty and Steiner equation. High values of b were obtained at acid region indicating a condensed conformation due to weak attractive interactions whereas around the neutral region the repulsive intramolecular forces take place leading to an extended conformation of humic molecules. Moreover, at very alkaline region, the charge density on molecule surface is more negative, increasing repulsion and dispersion of the particles and also takes place formation of micelle-like structure because of the amphyphylic feature of HA samples.

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Section: Molecular Absorption Spectroscopymentioning

confidence: 99%

Section: Chemicalsmentioning

confidence: 99%

“…These different additions were made in order to observe the pH influence on conformation of CHA, AHA and PHA structures. 12 …”

Section: Uv-vis Spectroscopymentioning

confidence: 99%

Section: Molecular Absorption Spectroscopymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Aspects of protonation and deprotonation of humic scid durface on molecular conformation

Prado¹,

Pertusatti²,

Nunes³

2011

J. Braz. Chem. Soc.

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The physiology of fish in acidic waters rich in dissolved organic carbon, with specific reference to the Amazon basin: Ionoregulation, acid–base regulation, ammonia excretion, and metal toxicity

et al. 2021

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Although blackwaters, named for their rich content of dissolved organic carbon (DOC), are often very poor in ions and very acidic, they support great fish biodiversity. Indeed, about 8% of all freshwater fish species live in the blackwaters of the Rio Negro watershed in the Amazon basin. We review how native fish survive these harsh conditions that would kill most freshwater fish, with a particular focus on the role of DOC, a water quality parameter that has been relatively understudied. DOC, which is functionally defined by its ability to pass through a 0.45‐µm filter, comprises a diverse range of compounds formed by the breakdown of organic matter and is quantified by its carbon component that is approximately 50% by mass. Adaptations of fish to acidic blackwaters include minimal acid–base disturbances associated with a unique, largely unknown, high‐affinity Na+ uptake system that is resistant to inhibition by low pH in members of the Characiformes, and very tight regulation of Na+ efflux at low pH in the Cichliformes. Allochthonous (terrigenous) DOC, which predominates in blackwaters, consists of larger, more highly colored, reactive molecules than autochthonous DOC. The dissociation of protons from allochthonous components such as humic and fulvic acids is largely responsible for the acidity of these blackwaters, yet at the same time, these components may help protect organisms against the damaging effects of low water pH. DOC lowers the transepithelial potential (TEP), mitigates the inhibition of Na+ uptake and ammonia excretion, and protects against the elevation of diffusive Na+ loss in fish exposed to acidic waters. It also reduces the gill binding and toxicity of metals. At least in part, these actions reflect direct biological effects of DOC on the gills that are beneficial to ionoregulation. After chronic exposure to DOC, some of these protective effects persist even in the absence of DOC. Two characteristics of allochthonous DOC, the specific absorbance coefficient at 340 nm (determined optically) and the PBI (determined by titration), are indicative of both the biological effectiveness of DOC and the ability to protect against metal toxicity. Future research needs are highlighted, including a greater mechanistic understanding of the actions of DOCs on gill ionoregulatory function, morphology, TEP, and metal toxicity. These should be investigated in a wider range of native fish Orders that inhabit one of the world's greatest biodiversity hotspots for freshwater fishes.

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Sorption–desorption of fipronil in some soils, as influenced by ionic strength, pH and temperature

Singh

Srivastava

2015

Pest Management Science

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A structural conformation study of aquatic humic acid

Cited by 22 publications

References 18 publications

Aspects of protonation and deprotonation of humic scid durface on molecular conformation

Aspects of protonation and deprotonation of humic scid durface on molecular conformation

The physiology of fish in acidic waters rich in dissolved organic carbon, with specific reference to the Amazon basin: Ionoregulation, acid–base regulation, ammonia excretion, and metal toxicity

Sorption–desorption of fipronil in some soils, as influenced by ionic strength, pH and temperature

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