Carboxylic Acids In Aqueous Solution Research Articles

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.

Viscosity of Binary Aqueous Solutions Involving Malonic, Maleic, Malic, Tartaric, and Citric Acids in the Temperature Range between 303 and 363 K: Experimental Data and Modeling

Kinematic viscosity is a key property for the design of flow systems. This transport property is directly dependent on temperature and concentration and indirectly dependent on molecular interactions that take place in a mixture. Carboxylic acids are a class of chemical compounds with employment in a large variety of processes and applications. The viscosity of carboxylic acid solutions changes due to the acid size and its concentration. The application of models can provide property prediction and generate information about molecular interactions in a mixture. This work studies the kinematic viscosity of binary aqueous solutions of carboxylic acids (malonic, maleic, malic, tartaric, and citric acids) at different temperatures (from 303.2 to 363.2 K with an increment of 10 K) and concentrations (from 0.5 to 3.0 mol·kg–1 with an increment of 0.5 mol·kg–1). The data were treated by the Eyring equation combined with the UNIFAC model. The experimental results and thermodynamic properties indicate that the kinematic viscosity is strongly influenced by the size of carboxylic acid and the molar mass of the binary solution. The suggested modeling showed capability of correlating the experimental data.

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 Solvent on the Hydrodynamic Properties of Collagen.

In this study, the effect of solvent on the hydrodynamic properties of collagen extracted from tail tendons of young rats was researched. Collagen was dissolved in various aqueous carboxylic acid solutions, including acetic acid (AA), acetic acid with the addition of sodium chloride (AA/NaCl), formic acid (FA), lactic acid (LA), citric acid (CA), and also citrate buffer at pH = 3.7 (CB). The properties of collagen solutions at a concentration of 0.45 mg/mL were characterized based on the viscometric method. The reduced viscosity, intrinsic viscosity, and Huggins coefficient of collagen solutions and effect of solvent, temperature, and UV irradiation on these properties were investigated. Collagen solutions in acetic acid, acetic acid/NaCl, and citrate buffer were irradiated with UV light up to 1 h, and the viscosity of collagen solutions was measured. It was found that the organic acids used as solvent affected viscosity behavior, denaturation temperature, and stability of collagen solutions. The lowest values of studied parameters were obtained for the collagen solutions in acetic acid with the addition of sodium chloride. Thus, the effect of various aqueous carboxylic acid solutions on collagen solutions properties and denaturation temperature can also be affected by the sodium chloride addition. The results of this research can be crucial for the preparation of collagen solutions for both cosmetic and biomedical applications.

Improvement of Extractive Alkylation Gas Chromatography of Short-chain Carboxylic Acids in Aqueous Solution.

In the analysis of short-chain carboxylic acids such as formic acid and acetic acid in aqueous solution using extractive alkylation gas chromatography, tetrahexylammonium bromide (THAB) as a phase-transfer catalyst (PTC) causes a high intensity and broad peaks in the gas chromatogram, and interfere with the detection of carboxylic acid derivatives. By an easy treatment of the extractive alkylation solution with perchloric acid and n-hexane, it is possible to remove more than 95% of THAB, and to provide good gas chromatogram with a little admixture of carboxylic acid derivatives. The desensitization was 16% at the maximum, the contamination of the glass insert in gas chromatograph and liquid phase in column by THAB was minimized, and trouble in continuous measurement could be avoided.

Investigation of The Reaction Kinetics of Chromium(III) Ions with Carboxylic Acids In Aqueous Solutions and The Associated Effects on Chromium Deposition

Electroplated chromium is an important industrial coating. Both in the decorative and functional field, research is being carried out to develop trivalent chromium electrolytes. In this work, the interaction between CrIII ions and carboxylic acids (malonic acid, malic acid, oxalic acid and glycolic acid) is investigated. The use of carboxylic acids to improve the current efficiency in trivalent chromium plating baths has been known for a long time. But the thermodynamics and kinetics of the associated complexing reactions are not well understood. It is shown that the complexes form at different rates depending on the acid and its concentration and have a varying influence on chromium deposition. For the development of a technical bath, care must be taken to ensure that the molar ratios between chromium and carboxylic acids can be controlled. This is possible with the HPLC method presented here.

Freezing of Aqueous Carboxylic Acid Solutions on Ice.

We study the properties of acetic acid and propionic acid solutions at the surface of monocrystalline ice with surface-specific vibrational sum-frequency generation (VSFG) and heterodyne-detected vibrational sum-frequency generation spectroscopy (HD-VSFG). When we decrease the temperature toward the eutectic point of the acid solutions, we observe the formation of a freeze concentrated solution (FCS) of the carboxylic acids that is brought about by a freeze-induced phase separation (FIPS). The freeze concentrated solution freezes on top of the ice surface as we cool the system below the eutectic point. We find that for freeze concentrated acetic acid solutions the freezing causes a strong decrease of the VSFG signal, while for propionic acid an increase and a blue-shift are observed. This different behavior points at a distinct difference in molecular-scale behavior when cooling below the eutectic point. We find that cooling of the propionic acid solution below the eutectic point leads to the formation of hydrogen-bonded dimers with an opposite alignment of the carboxylic acid O–H groups.

Photo‐Mediated Decarboxylative Cross Coupling of Quinoxalin‐2(1H)‐ones with Aliphatic Carboxylic Acids in Aqueous Solution: Synthesis of Alkylated Quinoxalin‐2(1H)‐ones and Preliminary Antifungal Evaluation Against Magnaporthe Grisea

Photo‐Mediated Decarboxylative Cross Coupling of Quinoxalin‐2(1<i>H</i>)‐ones with Aliphatic Carboxylic Acids in Aqueous Solution: Synthesis of Alkylated Quinoxalin‐2(1<i>H</i>)‐ones and Preliminary Antifungal Evaluation Against <i>Magnaporthe Grisea</i>

Genetically Encoded Residue-Selective Photo-Crosslinker to Capture Protein-Protein Interactions in Living Cells

Summary The genetically encoded non-selective photo-crosslinkers suffer from unpredictable crosslinking sites and false positive interacting proteins, thus, the identification of protein interactions and mapping accurate interaction interfaces remain largely elusive in living systems. Here, we report genetically encoded, residue-selective protein photo-crosslinker enabling covalent crosslinking of the interacting proteins with proximal lysine, upon UV light activation in vitro and in living cells. Using this photo-crosslinker, we demonstrate a crosslinking strategy to capture protein-protein interactions with residue selectivity in a temporal-resolved manner. In addition, this crosslinking strategy produces the lysine-selective crosslinking site and predictable crosslinked peptide, which serve as the direct evidence for protein-protein interactions and facilitate mass spectrometry analysis. More importantly, this photo-crosslinker enables the capture of elusive enzyme-substrate interaction with directly interacting lysine and validation of acetylation site of the substrate. This strategy represents higher spatiotemporal resolution, accuracy, and reliability for investigating dynamic, transient, and weak protein-protein interactions in living systems.

Some Preformulation Studies of Pyruvic Acid and Other α-Keto Carboxylic Acids in Aqueous Solution: Pharmaceutical Formulation Implications for These Peroxide Scavengers

The purpose of this study is to assess some of the variables determining the aldol-like condensation of pyruvic acid (1), a peroxide scavenger, in aqueous solution to parapyruvic acid and higher oligomers. Its stability is compared to 3 other α-keto carboxylic acids, 2 with sterically hindered methylene groups alpha to the keto functionality (2-3) and phenylglyoxylic acid (4) with no methylene group. High-performance liquid chromatography, nuclear magnetic resonance, and liquid chromatography mass spectroscopy techniques are used in the kinetics and product analyses. 1 condensation is concentration dependent and base catalyzed above pH 7, consistent with the reaction mechanism proceeding through the attack of the fraction of the methylene group, alpha to the keto group, in its anionic form, at the keto group of a second molecule of 1. The major product is confirmed to be parapyruvic acid, but higher-order oligomers are also observed. All 3 of the other α-keto carboxylic acids 2-4 are considerably less reactive, with 4 being completely stable. Stable solutions of 1 can be prepared by the use of relatively dilute solutions maintained at slightly acidic pH values. 1 prevents the oxidation of methionine on addition of hydrogen peroxide.

Effect of organic acid concentration in lubricant on tribological characteristics of friction couple

Introduction.The possibility of using monocarboxylic acids as a lubricant composition additive, and the effect of their concentration in lubricant on the evolution of the friction factor of a brass-steel couple, as well as the morphology of the film surface under friction is considered. The work objective is to study the effect of the concentration of carboxylic acids in the lubricant composition on the evolution of the friction factor of copper – steel alloy.Materials and Methods.Tribological studies of a brass-steel friction couple in aqueous solutions of monocarboxylic acids with the concentrations of 0.025; 0.05; 0.1; 0.2; 0.5 mol/l are carried out. Using scanning electron microscopy, we have studied the morphology of the servovite film surface that is formed on a steel disk after frictional interaction of a brasssteel couple in aqueous solutions of acids with the concentration of 0.1 mol/l.Research Results.Tribological characteristics of the brasssteel tribocoupling in aqueous solutions of carboxylic acids of various concentrations are studied. The optimum acid concentration in the lubricant composition is specified. Herewith, a selective transfer and a wearless friction regime are implemented under friction of the brass 59–steel 40X couple. A decrease in the friction ratio to 0.009 and 0.007 is found out under friction in aqueous solutions of valeric and caproic acids, respectively. The formation of an anti-friction film on the steel surface is identified through the scanning electron microscopy. It is established that the film formed in an aqueous solution of caproic acid has a denser structure in comparison with the film formed under friction in aqueous solutions of butyric and caproic acids.Discussion and Conclusions.Thus, the tribological studies of a brass-steel friction couple in aqueous acid solutions show that the optimum molar acid concentration in the lubricant composition is 0.1 mol/l. At this acid concentration, the values of the friction factor characteristic of the wearless mode are attained.

Carboxylic acids in aqueous solutions: Hydrogen bonds, hydrophobic effects, concentration fluctuations, ionization, and catalysis.

In the frequency range between 100 kHz and 2 GHz, ultrasonic absorption spectra have been measured for a series of carboxylic acids from formic to enanthic acid, including constitutional isomers. Also investigated have been the spectra for mixtures with water of short-chain formic, acetic, propionic, butyric, and isobutyric acid, in each case covering the complete composition range. The neat carboxylic acids feature two Debye-type relaxation terms with relaxation times between 5.6 and 260 ns as well as 0.14 and 1.4 ns, respectively, at room temperature. Depending on the composition, mixtures with water reveal an additional Debye relaxation term in the intermediate frequency range (acetic acid) or a term subject to a relaxation time distribution (propionic, butyric, and isobutyric acid). The relaxations of the neat acids are assigned to the equilibrium between monomers and single-hydrogen-bonded linear dimers and between linear and twofold-hydrogen-bonded cyclic dimers. The latter equilibrium is considerably catalyzed by hydronium and carboxylate ions. Several mixtures with water indicate one of the up to three Debye relaxations to reflect the protolysis of the organic acid. The term with underlying relaxation time distribution is due to noncritical fluctuations in the local concentrations. The Debye relaxations are evaluated to yield the parameters of the relevant elementary chemical reactions, such as the rate and equilibrium constants and the isentropic reaction volumes. A comparison of the correlation length of concentration fluctuations with data for other aqueous systems confirms the idea that the hydrophobic part of the organic constituent promotes the formation of a micro-heterogeneous liquid structure, whereas the hydrophilic moiety is of minor importance in this respect. The high-frequency limiting absorption suggests the equilibrium between conformers of linear dimers to contribute to the spectra well above the frequency range of measurements.

MECHANICAL PROPERTIES OF SERVOVITE FILMS FORMED IN DURING FRICTION AQUEOUS SOLUTIONS OF CARBOXYLIC ACIDS

Introduction. The effect of the organic component nature in the systematic series of monocarboxylic acids on the tribological characteristics of the brass-steel friction pair in aqueous solutions is described. Dependence of the mechanical-and-physical properties of the antifriction films formed during friction on the nature of the lubricating composition is investigated. The work objectives are to study the applicability of carboxylic acids as an antifriction lubricant component; to assess their effect on the mechanical properties of the servovite film formed under the brass – steel friction.Materials and Methods. Tribological studies of the brass-steel friction pair on the AE-5 end-type friction machine are carried out. Roughness parameters of the servovite film were determined through the optical profilometry. The microgeometry and the object structure at the nanoscale were considered using atomic force microscopy. The mechanical characteristics of the antifriction film were investigated using the instrument nanoindentation.Research Results. Tribological characteristics of the brass-steel tribocoupling and mechanical-and-physical properties of the servovite film formed during friction in the “brass – aqueous solution of carboxylic acid – steel” system were studied. It is established that the friction factor reduces when increasing the hydrocarbon radical length. The dimensional effects are found in the mechanical and tribological properties of the servovite film formed on the surface of the friction interaction in the carboxylic acids.Discussion and Conclusions. The study results show that the friction interaction on the wearing surface in the aqueous solutions of carboxylic acids forms a nanostructured servovite film which drops the friction factor. Its mechanical, physical and tribological parameters depend on the composition of the model lubricating medium. It is determined that the local mechanical-and-physical properties depend on the method of producing the servovite layer, the load and the size of the deformation zone. The results obtained can be used in the development of lubricants.

Electrochemical Oxidation of Alcohols and Aldehydes to Carboxylic Acids Catalyzed by 4-Acetamido-TEMPO: An Alternative to “Anelli” and “Pinnick” Oxidations

An electrocatalytic method has been developed to oxidize primary alcohols and aldehydes to the corresponding carboxylic acids using 4-acetamido-2,2,6,6-tetramethylpiperidin-1-oxyl (ACT) as a mediator. The method successfully converts benzylic, aliphatic, heterocyclic, and other heteroatom-containing substrates to the corresponding carboxylic acids in aqueous solution at room temperature. The mild conditions enable retention of stereochemistry adjacent to the site of oxidation, as demonstrated in a 40 g-scale synthesis of a precursor to levetiracetam, a medication used to treat epilepsy.

Differential scanning calorimetry determination of phase diagrams and water activities of aqueous carboxylic acid solutions

We have investigated the solid-liquid equilibria phase diagrams and water activities of the several carboxylic acid/water binary systems using differential scanning calorimetry (DSC) method. These mixtures were formed by water and low molecular weight carboxylic acids (formic acid, acetic acid, propionic acid and butyric acid). Water activities of the investigated solutions were obtained from the freezing point depression data in the range of the ice melting envelope. The experimental results indicated that all the aqueous carboxylic acid systems present a eutectic point in their respective phase diagrams. The activity coefficients of two components in the liquid phase were used to adjust the parameters of the Wilson and NRTL models. For all of the investigated systems, the best correlations of the solid–liquid equilibrium data have been determined by using the NRTL model. Finally, the phase behaviors of the systems were compared to the ideal state and the influence of the chemical structure of the carboxylic acids on the magnitude of the deviation from the ideal state was discussed.

Atomic-Scale Understanding of Catalyst Activation: Carboxylic Acid Solutions, but Not the Acid Itself, Increase the Reactivity of Anatase (001) Faceted Nanocatalysts

Our ability to predict nanocatalyst reactivity has been hindered by our lack of atomic-scale understanding of nanocatalyst surface structure. Do nanocatalyst surfaces adopt a bulk-terminated structure or do they reconstruct to minimize their free energy, thereby lowering their reactivity as often observed in vacuum? Similarly, do nanocatalysts processed at high temperatures maintain their low reactivity, reconstructed surfaces when used at low temperatures? Using a new technique for the preparation of anatase nanocatalysts suitable for atomic-scale imaging and surface spectroscopy, we show that solution-prepared anatase is terminated by a monolayer of fluorine, which acts as an atomic-scale oleophobic coating, preventing the accumulation of adventitious carbon. We further show that the most common TiO2 functionalization chemistry, a carboxylic acid solution, causes the spontaneous reorganization of a reconstructed anatase nanocatalyst, leading to a five-fold increase in reactive sites. This reorganization is not observed when carboxylic acids are deposited from the gas phase, suggesting that model experiments in vacuum environments can lead to a nonequilibrium, kinetically trapped state that may not be catalytically relevant. Aqueous carboxylic acid solutions produce densely packed carboxylate monolayers with richer adsorption geometries than previously predicted. Ab initio simulations show that although the carboxylate termination is somewhat less effective at removing surface stress than the reconstruction, it is more effective in lowering the surface energy. This observation suggests that bulk-terminated metal-oxide nanocrystals may be common in reactive environments, even if high temperatures are used to process the nanocatalyst or if the reactant is later rinsed off. As such, the assumption of a bulk-terminated surface may be a reasonable starting point for “materials-by-design” approaches to computationally engineered nanocatalysts.

Practical and Scalable Synthesis of 7-Azetidin-1-yl-4-(hydroxy­methyl)coumarin: An Improved Photoremovable Group

7-Substituted 4-methylcoumarin derivatives are widely employed as photoprotecting groups in chemistry and biology. We have recently shown that the 7-azetidinylated version of this photocage releases carboxylic acids in aqueous solution more efficiently than the traditionally used 7-diethylamino variant. Here we present a robust and scalable route to prepare the 7-azetidinylated alcohol, a useful precursor for the photoprotection of a variety of leaving groups, and its use in the preparation of model phosphate, sulfonate, and carbamate derivatives.

ChemInform Abstract: Silver‐Catalyzed Decarboxylative Allylation of Aliphatic Carboxylic Acids in Aqueous Solution.

AbstractA facile protocol is developed for the decarboxylative radical allylation of a wide range of carboxylic acids with allyl sulfones.

Silver-Catalyzed Decarboxylative Allylation of Aliphatic Carboxylic Acids in Aqueous Solution.

Direct decarboxylative radical allylation of aliphatic carboxylic acids is described. With K2S2O8 as the oxidant and AgNO3 as the catalyst, the reactions of aliphatic carboxylic acids with allyl sulfones in aqueous CH3CN solution gave the corresponding alkenes in satisfactory yields under mild conditions. This site-specific allylation method is applicable to all primary, secondary, and tertiary alkyl acids and exhibits wide functional group compatibility.

ChemInform Abstract: Silver‐Catalyzed Decarboxylative Radical Azidation of Aliphatic Carboxylic Acids in Aqueous Solution.

AbstractAn efficient and general method for the decarboxylative azidation of aliphatic carboxylic acids is reported.