Aqueous Solutions Of Organic Acids Research Articles

Corrosion Resistance of Coatings Based on Chromium and Aluminum of Titanium Alloy Ti-6Al-4V.

Improvement of wear, corrosion, and heat-resistant properties of coatings to expand the operational capabilities of metals and alloys is an urgent problem for modern enterprises. Diffusion titanium, chromium, and aluminum-based coatings are widely used to solve this challenge. The article aims to obtain the corrosion-electrochemical properties and increase the microhardness of the obtained coatings compared with the initial Ti-6Al-4V alloy. For this purpose, corrosion resistance, massometric tests, and microstructural analysis were applied, considering various aggressive environments (acids, sodium carbonate, and hydrogen peroxide) at different concentrations, treatment temperatures, and saturation times. As a result, corrosion rates, polarization curves, and X-ray microstructures of the uncoated and coated Ti-6Al-4V titanium alloy samples were obtained. Histograms of corrosion inhibition ratio for the chromium-aluminum coatings in various environments were discussed. Overall, the microhardness of the obtained coatings was increased 2.3 times compared with the initial Ti-6Al-4V alloy. The corrosion-resistant chromaluminizing alloy in aqueous solutions of organic acids and hydrogen peroxide was recommended for practical application in conditions of exposure to titanium products.

Green extraction of berberine from Coscinium fenestratum (Gaertn.) Colebr. using ultrasound-assisted aqueous solutions of organic acids, polyalcohols, and deep eutectic solvents

Berberine displays many potential bioactivities and is found in several medicinal herbs, such as Coscinium fenestratum. The extraction of berberine from biomass was carried out using volatile organic solvents, inorganic acid solutions, and more recently, ionic liquids and deep eutectic solvents. In order to develop more efficient and sustainable extraction processes, this study used inexpensive green solvents, such as carboxylic acid and polyalcohol aqueous solutions, to extract berberine from Coscinium fenestratum. Initial screening was performed to compare the berberine extraction performance of various solvents, including aqueous solutions of carboxylic acids, polyalcohols, and their deep eutectic solvents. The obtained results showed that lactic acid was a potential solvent for extracting berberine. After optimizing the process using response surface methodology (RSM), the optimal ultrasound-assisted extraction conditions were determined to be a lactic acid concentration of 60 % (w/w), a liquid-to-solid ratio of 17.25 mL/g, an extraction time of 20 min, and an extraction temperature of 66 °C. This resulted in an extraction efficiency of 38.23 ± 0.69 mg/g, corresponding to a berberine concentration of 2.22 ± 0.04 mg/mL. Additionally, the use of lactic acid as the extraction solvent yielded superior extraction efficiency and berberine purity compared to conventional volatile organic solvents, and inorganic acids, bases. The recovery of berberine was achieved using macroporous resins, allowing for the recovery of 99.52 ± 0.67 % of berberine from aqueous lactic acid solutions. The lactic acid solvent and the AB-8 resin were successfully recovered and reused for a minimum of three consecutive extraction cycles, maintaining their full effectiveness throughout the entire process. The recovered berberine from the lactic acid extract exhibited stronger antibacterial activity than the extracts obtained using ethanol, methanol, and acetone, as well as berberine recovered from the limewater and sulfuric acid extracts. Furthermore, the lactic acid solvent and its extracts demonstrated no cytotoxicity toward the human embryonic kidney cell line. The findings of this investigation establish a foundation for future studies utilizing eco-friendly solvents for alkaloid extraction from medicinal plants. This lays the groundwork for implementing a large-scale extraction process of natural active compounds in a safe and environmentally conscious manner.

DECOMPOSITION OF PHOSPHORUS-CONTAINING COMPOUNDS IN AQUEOUS AND POLYSACCHARIDE SOLUTIONS OF ORGANIC ACIDS

The purpose was to study the patterns of dissolution (solubilization) of phosphorus-containing minerals in aqueous and polysaccharide solutions of organic acids in order to model the mechanism of mineral destruction by soil bacteria synthesizing organic acids and exopolysaccharides. Methods. Model, laboratory-analytical, microbiological, statistical. Results. The destructive effect of organic acids on minerals is manifested both in aqueous and polysaccharide solutions. The introduction of bacterial polysaccharide into an aqueous solution of acids increases the decomposition of phosphorus-containing minerals by 1.34̶ 4.96 times. The influence of the chemical structure of acid molecules on the intensity of mineral decomposition is mainly manifested in the presence of bacterial polysaccharide, while in an aqueous solution the effectiveness of acid action depends on the nature of the mineral being destroyed. To the maximum degree, polysaccharide increases the destruction of minerals in a solution of citric acid: molten magnesium phosphate ̶ 2.55 times, thermophosphate ̶ 2.11 times, phosphate flour ̶ 4.96 times. Decomposition of phosphorus compounds in solutions of ascorbic and oxalic acids enhances bacterial polysaccharide to a lesser extent than in citric acid solution. Modeling the destruction of phosphorus-containing minerals under non-sterile conditions (soil conditions) made it possible to establish that organic acids under non-sterile conditions are subject to consumption by soil microbiota, especially ascorbic and citric acids, and to a lesser extent - succinic. Aqueous solutions of organic acids after 18 hours of incubation in non-sterile conditions lose their leaching activity by 1.06 ̶12.1 times. The introduction of a polysaccharide into aqueous solutions of acids makes it possible to avoid their rapid consumption by microorganisms, because of which the efficiency of mineral leaching under non-sterile conditions decreasшes by only 5–20% compared to sterile ones. Conclusions. The introduction of a bacterial polysaccharide into a solution of organic acids enables the latter to be transferred to a sorbed state, as a result of which their susceptibility to consumption by microorganisms is sharply reduced. Thus, polysaccharide-forming bacteria not only destroy minerals more intensively than microorganisms synthesizing only low-molecular-weight metabolites, but also synthesize a more stable and long-term functioning leaching complex in the soil.

Improving yields by switching central metal ions in porphyrazine-catalyzed oxidation of glucose into value-added organic acids with SnO2 in aqueous solution.

Photocatalysis has exhibited huge potential in selective conversion of glucose into value-added chemicals. Therefore, modulation of photocatalytic material for selective upgrading of glucose is significant. Here, we have investigated the insertion of different central metal ions, Fe, Co, Mn, and Zn, into porphyrazine loading with SnO2 for access to more efficient transformation of glucose into value-added organic acids in aqueous solution at mild reaction conditions. The best selectivity for organic acids containing glucaric acid, gluconic acid, and formic acid of 85.9% at 41.2% glucose conversion was attained by using the SnO2/CoPz composite after reacting for 3h. The effects of central metal ions on surficial potential and related possible factors have been studied. Experimental results showed that the introduction of metalloporphyrazine with different central metal ions on the surface of SnO2 has a significant effect on the separation of photogenerated charges, changing the adsorption and desorption of glucose and products on the catalyst surface. The central metal ions of cobalt and iron contributed more to the positive effects toward enhancing conversion of glucose and yields of products, and manganese and zinc contributed more to the negative effects, resulting in the poor yield of products. The differences from the central metals may attribute to the surficial potential change of the composite and the coordination effects between the metal and oxygen atom. An appropriate surficial potential environment of the photocatalyst may achieve a better interactive relationship between the catalyst and reactant, while appropriate ability of producing active species matched with adsorption and desorption abilities would gain a better yield of products. These results have provided valued ideas for designing more efficient photocatalysts in selective oxidation of glucose utilizing clean solar energy in the future.

Comparative analysis of absorption capacity of Cr(VI) polyaniline and cellulose/polyaniline composites synthesized in aqueous solutions of organic acids

Samples of polyaniline (PAn) doped by different organic acids, namely PAn-FA, PAn-AA, PAn-OA, and PAn-CA, were synthesized by oxidation of aniline (An) with ammonium peroxydisulfate in the 0.5 M aqueous solutions of formic (FA), acetic (AC), oxalic (OA), and citric acids (CA) respectively. Samples of composites of cellulose (Cel) with doped polyaniline (Cel/PAn-FA, Cel/PAn-AA, Cel/PAn-OA, and Cel/PAn-CA)were produced by the same method under the presence of a suspension of microfibrillar bleached cellulose in the reaction mixture. The mass ratio of An : Cel was 1 : 1. The structure of obtained samples was studied using X-ray diffraction, FTIR spectral analysis, and scanning electron microscopy. Adsorption capacity as concerns Cr(VI) by produced samples of both individual polyanilines and composites and adsorption kinetics has been studied by electronic (UV) and fluorescence X-ray spectroscopy and also X-ray energy dispersion analysis methods. Practically full removal of Cr(VI) ions (98–100 %) of such investigated samples of PAns and its composites has been determined. The adsorption kinetics is well described by equations of pseudo first and second orders. According to the results, the Langmuir and Freundlich adsorption isotherms are plotted. It was found that the process of adsorption Cr(VI) ions by doped samples of PAn and Cel/PAn accords to adsorption model of Langmuir. It has been shown, that adsorbed chromium remains in the samples of adsorbents in the form of chromium (III). Keywords : polyaniline, cellulose, composites, structure, Cr(VI), adsorption.

Pressurized Liquid Extraction of Polyphenols and Anthocyanins from Saffron Processing Waste with Aqueous Organic Acid Solutions: Comparison with Stirred-Tank and Ultrasound-Assisted Techniques

Fοllow up with our previous study on the extraction of saffron processing waste polyphenols using deep eutectic solvents, the objective of this examination was a comparative evaluation of pressurized liquid extraction (PLE), stirred-tank extraction (STE) and stirred-tank extraction with ultrasonication pretreatment (STE/UP) with respect to the recovery of pigments and antioxidant polyphenols from saffron processing waste. Aqueous solutions of citric and lactic acids at two different concentrations were used as green solvents. The extracts obtained under the specified conditions were analyzed for total pigment and total polyphenol yields as well as for their ferric-reducing power and antiradical activity. Furthermore, each produced extract was analyzed with liquid chromatography–mass spectrometry to profile its analytical polyphenolic composition. In all cases, PLE provided inferior results compared to the two other techniques, producing extracts with lower polyphenolic concentration and weaker antioxidant properties. On the other hand, no specific pattern was detected concerning the effect of ultrasonication, acid type and acid concentration. Hierarchical cluster analysis indicated that stirred-tank extraction with 1% (w/v) lactic acid and ultrasonication pretreatment might be the highest-performing combination, providing extracts with increased polyphenol and pigment concentration; however, it also enhanced antioxidant activity. It was also concluded that the significantly shorter extraction time when using PLE might be an important element in further optimizing the process, buttressing the use of this technique for the establishment of innovative and sustainable-by-design extraction methodologies.

Aqueous solutions of organic acids as effective solvents for levodopa extraction from Mucuna pruriens seeds

• Aqueous solutions of organic acids are promising substitutes for organic solvents. • Performance in the extraction of L-dopa from the seeds of M. Pruriens was assessed. • High purity and yields of L-dopa have been achieved with the investigated compounds. Levodopa is an amino acid commonly used in the treatment of Parkinson’s disease found in several plants, such as Mucuna pruriens . The extraction of levodopa from biomass has been achieved using methanol, ethanol:water mixtures in presence of ascorbic acid, chloroform in alkaline media, and acetonitrile. Aiming at finding more sustainable solvents and develop efficient extraction processes, in this work, aqueous solutions of carboxylic acids (acetic, propionic, citric, glycolic, and lactic acid) and (poly)alcohols (ethanol, ethylene glycol and glycerol) were studied for the extraction of levodopa from Mucuna pruriens seeds. An initial screening with aqueous solutions of these compounds (at 50 wt%) was conducted at 50 °C, with an extraction time of 90 min at a solid/liquid (biomass/solvent) ratio of 1:10. Based on these results, citric acid aqueous solutions were identified as the best solvent, and an experimental design was carried out to optimize the temperature (T), solid/liquid ratio (S:L) and concentration of acid (wt.%), with the following optimal extraction conditions found: T = 60 °C, S:L = 1:7 and concentration of acid at 58 wt%. Under these optimal conditions, an extraction efficiency of 9.2 ± 0.1 wt% of levodopa was achieved. The recovery of levodopa from the acidic aqueous solution was achieved using an ion exchange column, allowing the recovery of approximately 84% of levodopa. The solvent was shown to be reusable in three successive extraction cycles, with no significant losses in the extraction efficiency of levodopa. The results here obtained show that citric acid aqueous solutions can lead to the effective extraction of levodopa from seeds of Mucuna pruriens, serving as basis for the development of more effective and environmentally friendly processes to recover natural products with therapeutic properties.

Effect of carbon chain length of chlorinated carboxylic acids on morphology of the carbon films electrodeposited from aqueous solutions

Diamond-like carbon films can be electrodeposited from organic acids in aqueous solutions. Chlorinated carboxylic acids with different chain lengths, ie. chloroacetic acid, 3-chloropropionic acid, 4-chlorobutyric acid and 5-chlorovaleric acid, were used as the carbon sources in the electrolytes. It showed an interesting even-odd effect of carbon chain length on the surface morphology of the electrodeposited carbon films. The odd carbon-numbered chlorinated carboxylic acids lead to smooth carbon films whose morphologies were insensitive to the deposition parameters. On the contrary, the morphologies of the films obtained from the even carbon-numbered chlorinated carboxylic acids were island-like and dependent on the film thickness. Fourier transform infrared and Raman analysis indicated that the electrodeposited diamond-like carbon films were hydrogenated and contaminated by oxygen.

Homogeneously Synchronous Degradation of Chitin into Carbon Dots and Organic Acids in Aqueous Solution

Biomass polysaccharides are natural biopolymers and are considered as energy storage structural materials and suppliers in animals and plants. Among various biomass polysaccharides, chitin is the s...

Direct Measurement of Acid Dissociation Constants of Trace Organic Compounds at Nanomolar Levels in Aqueous Solution by Condensed Phase-Membrane Introduction Mass Spectrometry.

We report the use of condensed phase-membrane introduction mass spectrometry as a novel method for the determination of acid dissociation constants for hydrophobic organic acids in aqueous solution at nanomolar concentrations. The technique is based on the pH-dependent permeation of analytes through a semipermeable polydimethylsiloxane membrane probe that is immersed directly in aqueous samples. We describe the method and report the dissociation constant (pKa ) values for compounds of biological and environmental relevance, including contaminants, pharmaceuticals, and naphthenic acids. The approach can be applied to individual compounds, combined suites, and complex mixtures at parts-per-billion levels. We report pKa values for 10 carboxylic acids with precision estimates and relative errors (where reliable literature values are available) of <0.1 log units. We report acidity constants for 2-methyl-3-methoxy-4-phenyl butanoic acid (a biomarker for microcystin algal toxins) and 4-t-butylcyclohexane carboxylic acid (a model naphthenic acid) as 4.28 ± 0.03 and 5.15 ± 0.05, respectively. Furthermore, we employ this approach to measure the effect of both temperature and deuterium oxide (heavy water) on acid dissociation, reporting the enthalpy and entropy changes for the ionization of a representative carboxylic acid and substituted phenol. Environ Toxicol Chem 2019;38:1879-1889. © 2019 SETAC.

Preparation, Structure and Properties of Acid Aqueous Solution Plasticized Thermoplastic Chitosan.

This work provides a simple method for the preparation of thermoplastic chitosan using the most common dilute inorganic and organic acids in aqueous solutions, namely hydrochloric acid (HCl) and acetic acid (HAc). The melting plasticization behavior of chitosan under different concentrations and types of acid solution was investigated. By means of infrared spectra (IR), scanning electron microscope (SEM), X-ray diffraction (XRD), and other characterization methods, as well as a mechanical property test, it was found that as the acid solution concentration increased, the protonation effect was stronger and the plasticization performance showed a better trend. The structure and performance of the modified chitosan were optimal when the concentration of HCl was around 8 wt %. In addition, it was found that HCl had a better effect on the plasticization of chitosan than HAc, which was because the protonation ability of HCl was stronger than that of HAc. Unlike the casting method, the structure and properties of chitosan sheets prepared by thermoplastic processing were directly affected by protonation, however not by the interaction of anionic-cationic electrostatic attractions between the –NH3+ groups of chitosan chains and the carboxyl groups of acetic acids or the chloridoid groups of hydrochloric acid.

FEATURES OF GRAIN GERMINATION WITH THE USE OF AQUEOUS SOLUTIONS OF FRUIT ACIDS

The paper describes some aspects of producing germinated cereal grain with the use of fruits acids of various concentrations. The technological process of grain germination (including washing grain, disinfection, hydration by alternate steeping and air resting, germination, and drying) has been analysed and studied. To intensify germination and disinfection of grain of various crops at the steeping stage, aqueous solutions of organic acids (citric acid, malic acid, and inactive tartaric acid) were used. The results of studying the effect of these organic acids on the energy and germination ability of grain, the flouriness of malt grain, the amino acid composition of malt, the microbiological status of grain have been presented. For each grain crop, concentrations have been determined of active substances in the solutions that activate germination and reduce the time of malt production. A higher flouriness of malt grain, being an important brewing parameter, has been shown. The effect of the considered growth stimulants on the amino acid composition of the finished product has been studied. An increase in the amino acids content indicates splitting the grain endosperm more deeply and obtaining a biologically valuable food product rich in essential amino acids. While studying the microbiological status of grain with the use of the said organic acids, their disinfecting ability towards the pathogenic microflora of the grain was observed. It has been found that the suggested method of intensifying grain germination allows obtaining eco-friendly products in a shorter time, namely, 3–6 days depending on the grain crop. It has been established that, compared to the classical technology, using fruit acids as growth stimulants allows obtaining malt of higher quality, rich in biologically active substances. These grain raw materials can be used both to brew beer and to make highly nutritious healthy food.

Explaining the role of vanadium in homogeneous glucose transformation reactions using NMR and EPR spectroscopy

Our contribution investigates the formation of various catalytically active vanadium species for different glucose transformation reactions. By applying both 51V-NMR (nuclear magnetic resonance) and continuous wave EPR (electron paramagnetic resonance) spectroscopy, we were able to identify the different vanadium species that catalyse glucose transformation to several organic acids in aqueous solution depending on the reaction atmosphere and type of vanadium precursor. Under aerobic conditions (20 bar oxygen atmosphere) we could prove that only the higher-substituted vanadium containing polyoxometalate HPA-5 (H8PV5Mo7O40) catalyses the desired glucose oxidation to formic acid at 90 °C. Moreover, our results suggest that substituted V5+ species are the predominantly catalytic active species in the production of formic acid. Using anaerobic conditions (20 bar nitrogen atmosphere), we could show that different vanadium species are formed depending on the nature of the precursor. Hereby, paramagnetic acid-bound vanadyl species formed from the VOSO4 and NH4VO3 as well as the HPA-5 precursor seem to be predominantly responsible for lactic acid formation from glucose under anaerobic conditions.

Planar microwave sensor for detection and discrimination of aqueous organic and inorganic solutions

A planar microwave sensor based on a coplanar waveguide (CPW) loaded with a circular split ring resonator (SRR) was developed for the detection and estimation of salts, sugars and organic acids in aqueous solution. The magnitudes of the spectra at resonance frequencies of 2.3–2.6 GHz were shown to provide a rapid and reliable way to measure concentrations of materials such as sucrose, sorbitol, glucose, fructose, CaCl2, NaCl, KCl, MgCl2, Na2CO3 and citric acid. We generated linear and nonlinear regression prediction models built from correlations between the magnitudes of the transmission coefficient (S21) and concentration of materials using coefficient of determination (R2). Principle component analysis (PCA) method was used for discrimination of liquid solution samples. The studies clearly showed sample concentrations in the range from 4 to 20% (w/V) were correlated with the magnitude of S21 and could be detected by using the proposed sensor. Aqueous solution samples could be discriminated into two groups based on magnitude of the spectra of S21 of different solutions at various concentrations. The proposed device can be used to distinguish between organic and inorganic materials in aqueous solution.

A polarizable embedding approach to second harmonic generation (SHG) of molecular systems in aqueous solutions

We present the extension to second harmonic generation (SHG) of the atomistic fully polarizable QM/FQ method that treats the solvent atomistically and embeds each atom in the solvent with a fluctuating charge (FQ) which responds to the solute quantum mechanical (QM) electrostatic potential in a self-consistent manner. The proposed approach is able to achieve an adequate modeling of solvent effects both in the quantum mechanical response equations and on the conformational properties of the system, which is sampled by resorting to molecular dynamics simulations. The application of the model to selected organic acids in aqueous solution, for which the interaction with the surrounding environment is dominated by HB interactions, shows a good agreement in both the modeling of solvent effects and in the reproduction of experimental SHG data extracted from hyper-Raman scattering experiments.

Carbon Nitride Nanocomposites with Layered Niobates as Photocatalysts for Hydrogen Evolution from Aqueous Solutions of Organic Acids by the Action of Visible Light

The efficiency of H2 evolution from aqueous solutions of organic acids using composite photocatalysts derived from layered KNb3O8 and C3N4 was found to be much higher than for individual C3N4. This enhanced photocatalytic activity may be attributed to better separation of the photogenerated charges between the composite components and suppression of unwanted electron–hole recombination.

Features of obtaining malt with use of aqueous solutions of organic acids

Recently, the traditional formulations of essential food products are actively including malt – a valuable dietary product rich in extractives and hydrolytic enzymes, obtained by germination in artificially created conditions. Containing a full set of essential amino acids and a high saccharifying ability of malt, obtained from grain cereals, determines its wide use in the production of beer, alcohol, mono- and poly-malt extracts, bakery products, special types of flour, food additives, cereals, non-alcoholic beverages, lactic acid products and, in particular, in the production of natural coffee substitutes. However, the classical germination technology, which includes 2-3 days of soaking and 5-8 days of germination due to the considerable duration and laboriousness of the process, does not meet the requirements of modern technology and the constantly growing rates of industrial production, so this problem requires finding new and improving existing scientific and technical solutions. The features of malt production using organic acids of different concentrations are presented. The malt production technology has been analyzed and investigated. It includes washing, disinfection, air and water soaking of grains, germination and drying. The feature of the technology under investigation is using of aqueous solutions of butadiene, 3-pyridinecarboxylic acid and pteroylglutamic acid. The results of the inquiry of the effect of these organic acids on energy and the ability of germination of the grain are presented. The optimal values of concentrations of active substances in solutions are revealed. The influence of organic acids on the absorption of grain moisture has been investigated. It has been established that in comparison with the classical technology, the use of these acids as a growth stimulator can reduce the overall length of the reproduction process of the material from 1.5 to 2 times and increase the yield of flour grains in the batch of malt.

Evaporation of aqueous solutions of organic acids through spread films of poly(diallyldimethylammonium chloride)/sodium dodecylsulfate complex

ABSTRACTThe films with the extreme concentration of poly (diallyldimethylammonium chloride)/sodium dodecylsulfate complex spread to the surface of aqueous solutions of formic and acetic acids reduce the evaporation rate of liquids by 3–6% and demonstrate selective properties increasing water content in the vapor by 1–3 abs.%. The concentrations of solutions were up to 30 vol.%. The formation conditions of such films were determined by means of the Wilhelmy plate technique. Surface tension isotherms of aqueous solutions of acids were also obtained.

Heterogeneous Reaction of SO2 with Ca Dissolved in Aqueous Solutions of Organic Acids

Heterogeneous Reaction of SO₂ with Ca Dissolved in Aqueous Solutions of Organic Acids

Evaporation of aqueous solutions of organic acids through spread films of sodium polystyrene sulfonate/dodecyl trimethyl ammonium bromide complex

The Wilhelmy plate technique was used to determine surface tension isotherms of aqueous solutions of formic and acetic acids with concentration up to 30 vol% and with a film of solution of sodium polystyrene sulfonate/dodecyl trimethyl ammonium bromide complex spread to the surface. The formation conditions of films with the extreme concentration of the complex were determined. Such films reduce the evaporation rate of binary liquids by 3-6% and demonstrate selective properties increasing the water content in the vapor by 2-5 abs%.