Sorption Equilibrium of a Wide Spectrum of Organic Vapors in Leonardite Humic Acid:  Modeling of Experimental Data

Aggregation and stability of multiwalled carbon nanotubes in aqueous solutions were investigated with two polysaccharide stabilizers (carboxymethyl cellulose and a water soluble starch) and a natural organic matter (leonardite humic acid).

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Atrazine hydrolysis in aqueous suspensions of humic acid at 25.0 °C

Canadian Journal of Chemistry ◽

10.1139/v88-409 ◽

1988 ◽

Vol 66 (10) ◽

pp. 2605-2617 ◽

Cited By ~ 11

Author(s):

Donald S. Gamble ◽

Shahamat U. Khan

Keyword(s):

Humic Acid ◽

Rate Constant ◽

Free Acid ◽

Equilibrium Constants ◽

Environmental Research ◽

Separate Determination ◽

Sorption Equilibrium ◽

Catalytic Sites ◽

Free Acid Form

The acidic properties of a Chernozemic humic acid were determined by equilibrium titration. The number of carboxyl groups is 2.828 (mmol/g) ± 0.5%. The results were used for an investigation of Brönsted acid catalysis of atrazine hydrolysis by a suspension of the humic acid. There is sufficient sorption so that the rates of change of atrazine and product hydroxyatrazine in solution differ both from each other and form the rate of atrazine conversion on the catalytic sites. An important objective of this work was the separate determination of the sorption equilibrium constants for atrazine and hydroxyatrazine, and the rate constant for atrazine conversion on the catalytic sites. All three constants are relevant to environmental research. The apparent rate constants for changes in solution are experimental artifacts however, not useful for such research. Calculated in terms of carboxyl sorption sites in the free acid form, the sorption equilibrium constants were 1.74 × 102, σ = 0.03 × 102 and 8.5 × 102, σ = 2.3 × 102, for atrazine and hydroxyatrazine, respectively. The rate constant for conversion on catalytic sites ranges from 1.8 × 10−1day−1 ± 20% to 2.9 × 10−1day−1 ± 20%, for atrazine coverage of sites from 9.0(μmol/g) to 1.0(μmol/g).

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Modeling and Thermodynamic Values of Complex Equilibrium of Cobalt(II) with Diethylenetriaminepentaacetic Acid in Aqueous Solution

Indonesian Journal of Chemistry ◽

10.22146/ijc.59169 ◽

2021 ◽

Author(s):

Ghusoon Faidhi Hameed ◽

Fawzi Yahya Waddai ◽

Nahla Shakir Salman

Keyword(s):

Experimental Data ◽

Aqueous Solution ◽

Complex Formation ◽

Stability Constant ◽

Wide Spectrum ◽

Equilibrium Constants ◽

Diethylenetriaminepentaacetic Acid ◽

The Stability ◽

Hoff Equation ◽

Potentiometric Data

The paper reports the study of the complex formation of cobalt (II) with diethylenetriaminepentaacetic acid (DTPA, H5L) based on spectrophotometric (SF) and potentiometric data (pH). Complexes of different compositions were found, and equilibrium constants, as well as the stability constants of these complexes, were determined. Accumulation of complexes in proportion is calculated based on the acidity of the medium. The experimental data have been carried out by using mathematical models to assess the solution's possible existence with a wide spectrum of complex particles and to point out those which are quite sufficient to copy the experimental data. In addition, thermodynamic parameters (ΔG°, ΔH°, and ΔS°) for the studying complexes were calculated according to the values of stability constant (KST) at 25 °C obtained from the temperature dependence of stability constant by using van’t Hoff equation.

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Link-Spring Model of Bump-Type Foil Bearings

Volume 6: Structures and Dynamics, Parts A and B ◽

10.1115/gt2009-59260 ◽

2009 ◽

Cited By ~ 3

Author(s):

Kai Feng ◽

Shigehiko Kaneko

Keyword(s):

Experimental Data ◽

Film Thickness ◽

Wide Spectrum ◽

Load Capacity ◽

Ambient Air ◽

Radial Clearance ◽

Interaction Forces ◽

Friction Forces ◽

Foil Bearings ◽

Foil Bearing

The field experiences of gas foil bearings (GFBs) from the 1960s prove that GFBs offer several advantages over traditional oil bearings and rolling element bearings. They have the potential to be applied in a wide spectrum of turbomachinery. Bump-type foil bearings, which are considered as the best structure for GFBs, can be simply described as a hydrodynamic bearing utilizing the ambient air as the lubricant and a smooth shell supported by a corrugated bump foil as the bearing surface. However, the performance predictions of bump-type foil bearings are difficult due to mechanical complexity of the support elastic structure, especially for the effects of four factors, elasticity of bump foil, interaction forces between bumps, friction forces at contact surfaces, and local deflection of top foil. In this investigation, an analytical model of bump-type foil bearings considering the effects of all above factors is presented. In this model, each bump of the bump strip is simplified to two rigid links and a horizontally spaced spring, whose stiffness is determined from Castigliano’ theorem. Then, interaction forces and friction forces can be coupled with the bump flexibility though the horizontal elementary spring. The local deflection of top foil is described using a Finite Element model and added to the film thickness for the pressure prediction with the Reynolds’ equation. The bump deflections of a strip with ten bumps under different load distributions are calculated with the presented model and the predictions show consistency with published results. Moreover, the predicted bearing load and film thickness of a full bump-type foil bearing using this model are very close to the experimental data. Also, radial clearance and friction force variations in the foil bearing are noted to change the stiffness of bump significantly. And the predictions from the calculation with a proper selection of radial clearance and friction coefficients show extremely good agreement with the experimental data. The assumption of minimum reachable film thickness is based on experimental data to determine the load capacity of bearing. The results demonstrate that the radial clearance of foil bearing has an optimum value for the maximum load capacity.

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Molecular Dynamics Simulations of the Standard Leonardite Humic Acid: Microscopic Analysis of the Structure and Dynamics

Environmental Science & Technology ◽

10.1021/acs.est.7b00266 ◽

2017 ◽

Vol 51 (10) ◽

pp. 5414-5424 ◽

Cited By ~ 37

Author(s):

Drazen Petrov ◽

Daniel Tunega ◽

Martin H. Gerzabek ◽

Chris Oostenbrink

Keyword(s):

Molecular Dynamics ◽

Humic Acid ◽

Molecular Dynamics Simulations ◽

Microscopic Analysis ◽

Structure And Dynamics ◽

Dynamics Simulations ◽

Leonardite Humic Acid

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Silver ion desorption kinetics from iron oxides and soil organic matter: effect of adsorption period

Soil Research ◽

10.1071/sr03056 ◽

2004 ◽

Vol 42 (1) ◽

pp. 59 ◽

Cited By ~ 8

Author(s):

Jian Li ◽

Andrew W. Rate ◽

Robert J. Gilkes

Keyword(s):

Experimental Data ◽

Humic Acid ◽

Significant Proportion ◽

Silver Ions ◽

Reaction Rates ◽

Contact Period ◽

Desorption Kinetics ◽

Fe Oxides ◽

Desorption Reaction ◽

Soil Constituents

In order to have a better understanding of the mobility and bioavailability of silver in the environment, it is important to investigate the desorption behaviour of silver from some environmentally relevant soil components. Four single soil constituents (charcoal, humic acid, ferrihydrite, goethite) were chosen to investigate the rate of desorption of silver ions. The effect of reaction period between silver and the soil constituents on subsequent desorption was also investigated. A significant proportion of Ag+ sorbed by Fe oxides, humic acid, and charcoal cannot readily be desorbed back into solution. For goethite and humic acid, a longer contact period between Ag+ and the adsorbing phase caused subsequent slower rates of desorption, and a smaller proportion of adsorbed Ag+ was desorbed back into solution. Two-site and log-normal equations, assuming the desorption reaction was first-order, gave excellent fits to experimental data, except for Ag+ desorption from charcoal, in which case the kinetic experimental data fitted to a 1-site model better. The parameters obtained from the modelling provide information regarding the possible changes in metal–oxide binding and metal–humic acid complexing mechanisms, and these changes can be interpreted as a re-arrangement of Ag ions to sites with slower desorption reaction rates. All the reaction sites on charcoal have very similar desorption rates (rate constants), and these sites are relatively slow to desorb Ag. Fe oxides, and humic acid and charcoal could be very important sinks for Ag. The longer the Ag interacts with soils in environment, the less mobile Ag becomes, and the less toxic and bioavailable it will be to living organisms.

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Modeling and theoretical analysis of ring specific mimicry in view of isomerism within medicinal promising oligomers of "DIVEMA"

Biomeditsinskaya Khimiya ◽

10.18097/pbmc20196502133 ◽

2019 ◽

Vol 65 (2) ◽

pp. 133-151

Author(s):

B.D. Bolshchikov ◽

V.B. Tsvetkov ◽

O.L. Alikhanova ◽

A.V. Serbin

Keyword(s):

Experimental Data ◽

Molecular Dynamics ◽

Wide Spectrum ◽

Water Soluble ◽

Structural Units ◽

Activation Barriers ◽

Elementary Reactions ◽

Design And Synthesis ◽

Chain Synthesis ◽

Accurate Computations

The furan or pyran related hetero cycles play basic role in structural units of nucleic acids (NA) and polysaccharides (PS), significantly predetermining their functional specifics. Some of such properties, in great relevancy for medicine, can be imitated through mimicry of polymers synthetic. Particularly, a formation of similar cycloisomeric chains is possible in process of free-radical cyclocopolymerization of divinyl ether (DVE) and maleic anhydride (MA). The products yielded (DVEMA) of general formula [DVE(MA)-alt-MA]n become precursors for a broad family of water-soluble derivatives capable of wide spectrum of bioactivity, including induction of interferon, immune-stimulated and direct antiviral protection. In this connection, the knowledge: what is content of different heterocyclic isomers in backbone of the preparations and what their partial contributions in promotion of the certain bioactivities observed, are in great importance. Available experimental data (NMR, IR, etc.), controversial for interpretations, didn't elucidate a required estimation of the DVEMA isomerism. The current work represents an independent exploration of the problem via quantum chemistry-based analysis of kinetic (activation barriers) and thermodynamic (enthalpies) priorities in competition between variable isomerism within the chain synthesis. The system is considered in maximal range of hypothetically allowable variations of two levels for double regioselective bifurcations: there are four competitive ways, each of which involves a sequence of four type elementary reactions for a diverse-isomeric formation of chain units. A genesis of six chiral centers (62 stereoisomers permitted) per every of the four part ways was accounted in view for up to 256 isomeric variations in total. The required time-minimized but precisely accurate computations were conducted via B3LYP/6-31G(d), M06-2X/6-311+G(d), M06-2X/6-31+G(2df,p) techniques, which were preselected through model test-systems. As a result, the mechanisms, crucial points and factors for the process-permitted regulation of isomeric content of DVEMA were studied in details. The narrow enough set of most probable enantiomers within highly competitive 5-exo- and 6-endo- ring closing sub-ways was revealed. The results obtained are very actual for an adequate modeling (docking / molecular dynamics) of DVEMA derivatives in their interactions with biopolymer targets, in search for purposed advancement of current background in design and synthesis of highly effective agents for combined antiviral protection (against HIV, flu, herpes, and other infections).

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