Luminescence properties of humic substances

Mazhul, V. M.; Ivashkevich, Ludmila S.; Shcherbin, D. G.; Pavlovskaya, N.A.; Naumova, G. V.; Ovchinnikova, T. F.

doi:10.1007/bf02683894

Cited by 13 publications

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“…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].…”

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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].…”

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

Лаврик

Mulloev

2011

J Appl Spectrosc

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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...

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

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Mulloev

2011

J Appl Spectrosc

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“…The RT phosphorescence spectra were measured using an automated spectrophosphorimeter [16][17][18] designed in the Proteomics Laboratory of the Institute of Biophysics and Cell Engineering (National Academy of Sciences of Belarus), allowing us to record the phosphorescence spectra in the 250-650 nm range with quantum yield up to 10 -6 . The RT phosphorescence spectra of cortical and nuclear lens tissues were measured under oxygen-free conditions.…”

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Mobility of Chromophores Absorbing Light in the 320–420 nm Range in Transparent and Cataract Lens Tissue

2014

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We have analyzed the spectral and kinetic characteristics of phosphorescence at room temperature on a millisecond time scale for transparent and cataract lens tissues. We have studied the nature of the change (with age and with cataract development in the lens tissues) in the molecular mobility of the products absorbing light in the 320-420 nm range.Keywords: bovine and human transparent lenses, human cataract lenses, phosphorescence at room temperature, age-related cataract.Introduction. Human lens tissue is characterized by a high level of posttranslational modifi cations of proteins accumulating with age, due to the very high content of protein macromolecules in them compared with other tissues in the body [1]. The main targets for modifi cation are crystallins, comprising ≈90% of all lens proteins [2]. A healthy lens contains low molecular weight substances absorbing UV radiation in the 300-400 nm range. These substances ("UV fi lters") are metabolites of tryptophan: kynurenine (KN) and its derivatives 3The main reason for age-related posttranslational modifi cations of lens proteins is fragmentation of the kynurenine-containing UV fi lters (3OHKG, KN, and 3OHKN) followed by their subsequent addition via covalent bonds to proteins [3] and reduced glutathione (GSH) [4] with formation of protein-bound kynurenines and the compounds GSH-KN, GSH-3OHKN, and GSH-3OHKG. Since these substances are more photochemically active than the original UV fi lters, they are responsible for the formation of active oxygen species promoting development of cataract with age [5]. The decrease of free, not protein-bound UV fi lters (KN, 3OHKG, 3OHKN) with age in lens tissue is ≈12% per decade [6].One more lens protein posttranslational modifi cation process is glycation. αB-Crystallin is the predominant protein in lenses and belongs to the family of small heat shock proteins, which is a large class of molecular chaperones that interact with partially denatured proteins to prevent their aggregation. It is generally thought that the function of chaperones is not vital for maintaining lens transparency and preventing cataract development. In model experiments, it was shown [7] that formation of advanced glycation end products (AGEs) leads to a decrease in chaperone activity of αB-crystallin relative to the proteins alcohol dehydrogenase, insulin, and citrate synthase selected as substrates.In lenses of the elderly, with cataract development we observe an increase in non-disulfi de protein crosslinks. Some researchers have identifi ed yellow chromophores bound to lens proteins. Hypothetically, many of these components are AGEs, which absorb light in the UV-A region (320-400 nm). Since 1000 times more light in the UV-A range is incident on the lens than in the UV-B range (280-320 nm), the presence of AGEs can enhance photo-induced damage to lens proteins. When the proteins are highly modifi ed, they become part of the water-insoluble fraction. This fraction consists of large protein aggregates that do not dissolve during homogenization. I...

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“…Structure of humic acids upon association (general case). According to the commonly accepted model for the structure of the humic acid macromolecule, it is a polyanion with a core containing mainly aromatic groups and a peripheral region containing both aromatic and aliphatic groups [22]. Association of humic acid leads to the sites in the HA core, as the most hydrophobic part of the molecule, being positioned as close to each other as possible, forming a stacking type structure and accordingly shielding each other from interaction with the quenching agent.…”

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

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Mulloev

2010

J Appl Spectrosc

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Using as an example the concentration dependence of the fluorescence quenching constants for quenching by Cd 2+ ions for different weight fractions of humic acid, we have demonstrated the application of the fluorescence quenching method for studying the effect of association on the structure of humic acids. We have established that the quenching constants for the light fraction (5-30 kD) decrease as the humic acid concentration increases and the quenching constants increase for the heavy fraction (60-100 kD). The observed dependences are interpreted in terms of the idea of oppositely directed effects of association on the structure of the environment of fluorophores located within the core and peripheral regions of the humic acid macromolecule.Introduction. Based on our experiments studying the concentration dependences of the fluorescence spectra for different weight fractions of humic acids, we previously [1] concluded that an increase in the humic acid concentration in alkaline solution is accompanied by association of the humic acids. This conclusion was based on data from a fluorescence experiment, in which we established the presence of a long-wavelength (bathochromic) shift of the humic acid fluorescence spectrum as the humic acid concentration increased, where the spectrum consisted of two components. The long-wavelength shift of the HA fluorescence spectrum was observed both for the short-wavelength and long-wavelength components of the spectrum. The proportion of the intensity from the long-wavelength component in the total fluorescence intensity increased, while the proportion from the short-wavelength component decreased.During association, partial structural reorganization of the original humic acid macromolecule is possible. However, no information is available about the characteristic features of the change in structure of the humic acid macromolecule upon association. With the goal of obtaining additional information about the change in the structure of humic acid macromolecules upon association, we decided to use the fluorescence quenching method: the Stern-Volmer (SV) method. The proposed approach for obtaining information about the change in humic acid structure as a consequence of the effect of association essentially involves determining the concentration dependence of the fluorescence quenching constants for humic acid with some molecule (ion) as the quenching agent. Then from the shape of these curves, a conclusion is drawn about the change in accessibility of the fluorophores for quenching, i.e., about the change in the structure of the humic acid macromolecule upon association. The possibilities for using the SV method to obtain information about the structure of different types of humic acids have been shown earlier in [2][3][4][5][6][7].The SV quenching constant K T is determined from the equation

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Luminescence properties of humic substances

Cited by 13 publications

References 2 publications

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

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

Mobility of Chromophores Absorbing Light in the 320–420 nm Range in Transparent and Cataract Lens Tissue

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

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