Acids Of Different Structures Research Articles

Study of the Cyanide Leaching of Gold from Low-Grade Raw Materials in the Presence of Amino Acids

The article discusses the interaction in amino acid–gold cyanide systems using amino acids of different structures. The formation of complex compounds of gold cyanide with amino acids with the participation of carboxyl and amino groups is shown. A relationship has been established between the formation of gold complexes with amino acids and the degree of its extraction in the process of leaching from low-grade ore with sodium cyanide together with amino acids: the higher the degree of participation of the amino group in the formation of the complex, i.e., covalent bond, the more pronounced the effect of the amino acid on the degree of gold leaching. The contribution to the formation of the complex of the carboxyl group (ionic bond) and the amino group (covalent donor–acceptor) can be assessed by the intensity of the band at a wave number of 1419 cm−1 of the IR spectra of the systems: gold cyanide–amino acid. This approach makes it possible to predict the effect of amino acid structure on gold recovery during cyanide leaching based on IR spectra.

Synthesis of Siloxane Derivatives of Phenylboronic Acids of Different Structures.

The synthesis of a storage-stable organosilicon modifier with a dioxaborolane-protecting group is described. Its high reactivity and selective anti-Markovnikov addition in hydrosilylation reactions to afford siloxanes of various structures are shown. The possibility of deprotection of both the initial modifier and its siloxane derivatives under mild conditions using water in yields up to 96% is demonstrated. The existence of an equilibrium between the organosilicon derivatives of phenylboronic acids and their cyclic six-membered boroxines was confirmed by 1H NMR spectroscopy and X-ray diffraction analysis data. The use of siloxane derivatives of phenylboronic acids in Suzuki-Miyaura and Chan-Lam cross-coupling reactions was studied. All synthesized compounds were characterized by NMR (1H, 11B, 13C, and 29Si), IR spectroscopy, and high-resolution mass spectrometry.

Retention Indices and Sorption Enthalpies of Pentaerythritol and С2–С8 Acid Esters on Nonpolar Stationary Phases

The retention and sorption enthalpy characteristics of 38 pentaerythritol esters of C2–C8 carboxylic acids of different structures were determined by gas-liquid chromatography on a nonpolar phase in the temperature range 433.2–563.2 K. The molecular structure was shown to affect the temperature dependence of the retention indices of the esters. The average change in the sorption enthalpy of pentaerythritol tetraesters per CH2 group is lower in magnitude than the similar contribution for normal alkanes. The excess mixing enthalpy at 298.2 K was evaluated for four fully substituted pentaerythritol esters.

Effects of Fatty Acid Compositions on Heavy Oligomer Formation and Catalyst Deactivation during Deoxygenation of Triglycerides

Deoxygenation of triglycerides (e.g., vegetable and microalgae oils) through hydro-upgrading is one of the most important routes to produce oxygen-free hydrocarbon fuels from biomass. Even though natural triglycerides are composed of fatty acids of different structures, their effects on catalytic selectivity and deactivation during deoxygenation have not been comprehensively investigated. In this study, we used three different reactant triglycerides including palm oil, soybean oil, and linseed oil for catalytic deoxygenation over Pt/γ-Al2O3. These oils consist of fatty acids with increasing degrees of unsaturation in the order of palm oil (number of C═C per fatty acid: 0.55) < soybean oil (1.33) < linseed oil (2.18). The catalytic results showed that the increased unsaturation of the triglycerides caused enhanced formation of heavy products by oligomerization (mostly dimers) of unsaturated fatty acid derivatives through Diels–Alder reaction and/or radical addition. These heavy products were readily transf...

Thermodynamics and kinetics of calcium oxalate crystallization in the presence of amino acids

Specific features of the crystallization of calcium oxalates (CaC2O4) in the presence of amino acids have been established based on thermodynamic and experimental modeling. Phase formation in the Ca2+–C2O4 2-–H2O–amino acid system in a wide range of variation in the component concentrations and solution pH have been theoretically investigated. The influence of pH on the thermodynamic stability of crystallizing compounds is considered. The effect of amino acids of different structures on the formation of the CaC2O4 solid phase in a prototype of physiological solution is analyzed. The kinetic crystallization parameters (induction period and rate constant) and crystallite growth are determined.

Raman spectroelectrochemical study of electrodeposited polyaniline doped with polymeric sulfonic acids of different structures

Polyaniline (PANI) films were prepared by electrochemical polymerization of aniline on Pt-electrode in aqueous medium in the presence of polymeric sulfonic acids distinguished by different flexibility of the polymer chain: (1) poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA, flexible chain); (2) poly(4-styrenesulfonic acid) (PSSA, flexible chain), (3) poly-4,4′-(2,2′-disulfoacid)-diphenylene-iso-phthalamide (i-PASA, semi-rigid chain); and (4) poly-4,4′-(2,2′-disulfoacid)-diphelylene-tere-phthalamide (t-PASA, rigid chain). Raman spectroelectrochemical studies using 532 nm laser excitation were carried out in aqueous HCl. The conventional HCl-doped PANI films were also studied for comparison. The results allowed one to distinguish the potential-dependent vibrations belonging to PANI and potential-independent vibrations belonging to the polyacids. In addition, amide C=O vibration was separated in the spectra by comparing the results for amide-containing (PAMPSA, i-PASA, and t-PASA) and amide-free (PSSA) PANI-polyacid complexes. The films of PANI-polyacid complexes demonstrated increased content of radical cation moieties at low potentials compared to PANI–HCl films.

Complexes of poly-3,4-ethylenedioxythiophene with polymeric sulfonic acids of different structures: Synthesis and optical and electric properties

Chemical polymerization of 3,4-ethylenedioxythiophene is carried out in the presence of polymeric sulfonic acids of different structures, such as flexible-chain polyacids with a uniform distribution of sulfonic acid groups along the macromolecular chain, namely, polystyrene sulfonic (PSSA) and poly-2-acrylamido-2-methyl-1-propanesulfonic (PAMPSA) acids, and rigid-chain polysulfonic acid with a nonuniform distribution of sulfonic acid groups along the macromolecular chain—namely, poly-p,p′-(2,2′-disulfonic acid)-diphenylene terephthalamide. The polymerization process and the properties of solutions and films of the synthesized complexes of poly-3,4-ethylenedioxythiophene (PEDOT) with the above polyacids are studied by the UV, visible, and near-IR spectroscopy. The electric properties of the films are investigated. The effects of the concentration ratio between the oxidizer and monomer and of the structure of polymeric acid on the kinetics of the PEDOT synthesis, as well as on the spectral and electric properties of the obtained polymer, are revealed. A correlation between the absorption of the PEDOT/PSSA complexes in the near-IR range and their specific conductivity is established.

Mechanochemical synthesis of polyaniline in the presence of polymeric sulfonic acids of different structure

We demonstrate that the solvent-free mechanochemical method, previously used for the synthesis of polyaniline (PANI) protonated with low molecular weight inorganic acids, can be extended to the preparation of conductive, all-polymeric PANI/polyacid molecular composites. Two polymeric sulfonic acids differing in their chain rigidity were selected as PANI protonating agents, namely: poly-(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA, flexible backbone polyacid) and poly(p,p′-(2,2′-disulfonic acid)-diphenylene-tere-phthalamide) (t-PASA, rigid backbone polyacid). Spectroscopic (UV–vis–NIR, FTIR, EPR), morphological, structural (TEM), electrochemical and spectroelectrochemical properties of the mechanochemically prepared molecular composites were compared with those determined for their analogs synthesized by oxidative polymerization in aqueous solution. The mechanochemically synthesized molecular composites show a characteristic layer-type morphology, distinctly different from that observed for the composites prepared chemically in aqueous solutions. UV–vis–NIR and FTIR spectroscopy clearly indicate better polaron delocalization in the mechanochemically prepared samples. These results are in line with those obtained in ESR, electrochemical and spectroelectrochemical investigations unequivocally showing better charge carrier delocalization in the mechanochemically prepared composites. The measured dc-conductivity of the mechanochemically prepared samples is 24mS/cm and 31mS/cm for PANI/PAMPSA and PANI/t-PASA, respectively.

UV-Vis Spectroscopy and Dynamic Light Scattering Study of Gold Nanorods Aggregation

Gold nanorods (AuNRs) were used as spectroscopic sensing elements to detect specific DNA sequences with a single-base mismatch sensitivity. The assay was based on the observation that the stabilizing repulsive forces between CTA(+)-coated AuNRs can be removed by citrate ions, which causes aggregation among AuNRs; whereas nucleic acids of different structures[ i.e., peptide nucleic acid (PNA), single-stranded DNA (ssDNA), PNA-DNA complex, and double-stranded DNA (dsDNA)] can retard the aggregation. Moreover, the dsDNA PNA-DNA duplexes provide larger retardation than that by unhybridized ssDNA and PNA probe. This assay can differentiate single-base mismatched targets with base substitution at different locations (center and end) with AuNRs of a larger aspect ratio. Besides ultraviolet-visable spectroscopy measurement of particle assembly-induced plasmonic coupling that in turn provides a spectroscopic detection of the specific DNA, dynamic light scattering and transmission electron microscope (TEM) were used to measure smaller degree of aggregation that can reveal sodium citrate- and dsDNA-AuNRs interactions in fine detail.

Thermochemistry of Heteroatomic Compounds: Analysis and Calculation of Thermody-namic Functions of Amino Acids and Some Peptides of Different Space Structure

The values of free energies, the heats of combustion and formation in condensed and gaseous phases over 30 amino acids of different structure were analyzed. Entropies and heat capacities in standard conditions were considered too. Twenty one equations of such type as Yо = i ± f (N – g) +Σ(hc)j, in which Yо is thermodynamic function or heat capaci-ty, i and f are stoichiometric coefficiens, Σ(hc)j are the sums of the number (j) of the heat corrections for the mentioned thermodynamic magnitudes, N is the number of valence electrons, from which a number of lone electron pairs (g) is ex-cepted for. The obtained equations were used for the calculations of a new such parameters for four phosphorylated amino acids, two enkephalines and two human peptides of low molecular weights.

Subtle Changes to Polymer Structure and Degradation Mechanism Enable Highly Effective Nanoparticles for siRNA and DNA Delivery to Human Brain Cancer

Polymeric materials can be used to deliver nucleic acids such as DNA plasmids and siRNA, but often have low efficacy in human cells. To improve gene delivery, an array of over 70 hydrolytically degradable and bioreducible poly(beta-amino ester)s are synthesized and the properties of over 200 nanoparticle formulations fabricated from these biomaterials are evaluated. The effect of different polymer structures on the delivery of nucleic acids of different structures and sizes, including siRNA, linear DNA, and circular DNAs (1.8-26 kb), is evaluated. Significantly, leading hydrolytically degradable polymeric nanoparticles deliver DNA to 90 ± 2% of primary human glioblastoma cells with <10% nonspecific cytotoxicity, better than leading commercially available reagents (p < 0.01). Bioreducible polymeric nanoparticles optimized for siRNA delivery cause up to 85 ± 0.6% knockdown in these cells as well while maintaining high viability. From a single dose, knockdown is higher than for Lipofectamine 2000 (p < 0.01) and persisted for one month. Polymer molecular weight is a driving factor of transfection efficacy for some polymer structures (correlation of r(2) = 0.63), but has no influence on transfection for other structures (r(2) = 0.01). Polymers with a reducible cystamine functional group dramatically improve siRNA delivery by facilitating quick release while generally decreasing DNA delivery compared with non-reducible counterparts (p < 0.01). Other material properties facilitate DNA delivery compared with siRNA delivery or increase delivery of both DNA and siRNA.

Interactions of Three s-Triazines with Humic Acids of Different Structure

The adsorption of three s-triazines (atrazine, terbutylazine, and simazine) on three different humic acids (HAs), before and after acidic hydrolysis, was studied at four diverse pH values from 3 to 4.5. The Freundlich sorption affinity (K(f)) and intensity (1/n) of s-triazines were related to the chemical and structural composition of HA and used in a multivariate statistical analysis. At low pH, the sorption values for s-triazines were not directly justified by the content of carboxyl groups in original HA, while only an increase of phenolic carbons in hydrolyzed HA supported the increased s-triazine adsorption. The structural composition of both s-triazines and humic samples explained 86% of the significance in multivariate analyses, whereas the role of pH remained hidden in only 14% of the statistical significance. Adsorption of s-triazines was mainly related to carbon content, hydrophobicity, and aromaticity of HA, thereby implying a predominant binding role of weak dispersive forces. Steric properties explained the larger adsorption affinity of atrazine and terbutylazine with respect to simazine. The occurrence of charge-transfer interactions between atrazine and mainly hydrolyzed HA was further suggested by the increased number of free radicals detected in atrazine-HA complexes at different pH values. Charge-transfer interactions were postulated to occur when HA conformations became progressively controlled by aromatic components. This work indicates that humic matter rich in hydrophobic and aromatic constituents is more likely to adsorb s-triazines and reduce their environmental mobility.

Capillary electrophoretic study of dibasic acids of different structures: Relation to separation of oxidative intermediates in remediation

Dicarboxylic acids are important in environmental chemistry because they are intermediates in oxidative processes involved in natural remediation and waste management processes such as oxidative detoxification and advanced oxidation. Capillary electrophoresis (CE), a promising technique for separating and analyzing these intermediates, has been used to examine a series of dibasic acids of different structures and conformations. This series includes malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, fumaric acid, phthalic acid, and trans, trans-muconic acid. The CE parameters as well as structural variations (molecular structure and molecular isomers, buffer composition, pH, applied voltage, injection mode, current, temperature, and detection wavelength) that affect the separations and analytical results have been examined in this study. Those factors that affect the separation have been delineated. Among these parameters, the pH has been found to be the most important, which affects the double-layer of the capillary wall, the electro-osmotic flow and analyte mobility. The optimum pH for separating these dibasic acids, as well as the other parameters are discussed in detail and related to the development of methods for analyzing oxidation intermediates in oxidative waste management procedures.

Selectivity of chemically bonded zwitterion-exchange stationary phases in ion chromatography

A number of zwitterion-exchange stationary phases were prepared by immobilization of amino acids of different structure (Asp, Glu, Val, Tyr, Pro, Hypro, Arg and Lys) on a silica surface. The occurrence of oppositely charged groups in a single ion-exchange site provided cation-, anion- and zwitterion-exchange properties. The chromatographic behaviour of these stationary phases was evaluated by the retention of a series of test organic compounds of different ionogenic nature. The role of the type and structure of the ion-exchange site was considered. The structure of the bonded molecules and the pH of the eluent were shown to be key parameters influencing the ion-exchange properties of amino acid-bonded silicas. The cation-exchange selectivity of phases containing primary or secondary amino groups was investigated for alkali and alkaline earth metal ions. The application of amino acid-bonded silicas to the ion chromatographic separation of anions and cations is described.

The Reactivities of the Histidine Residues at the Active Site of Ribonuclease toward Halo Acids of Different Structures

The Reactivities of the Histidine Residues at the Active Site of Ribonuclease toward Halo Acids of Different Structures