Adsorption of organic substances with different physicochemical properties

The linear regions of the adsorption isotherms of freon 13B1 (CF₃Br) on active carbons with different porous structures were studied by gas chromatography at 343–573 K. The Henry's constants were determined, and the isosteric heats of adsorption (Q) were calculated in the region of zero filling. It was established that theQ values for active carbons with different pore size distributions are almost the same and vary within 38–41 kJ mol^–1. This coincidence can be explained assuming that the interaction between the adsorbed molecules and the active carbons occurs in the pores whose sizes are comparable with those of the adsorbed molecules.For part 1, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 439–441, March, 1995.     

Changes in the physicochemical properties of transferrin upon chemical derivatization with ceramides

The interaction of native and derivatized transferrin with lecithin, cholesterol and their mixtures was studied using monomolecular layers of phospholipids. Moreover, the thermodynamic parameters corresponding to these interactions: the mixing excess free energy, interaction energy, and interaction parameter were also calculated.The ability of these two proteins to insert into monolayers was studied working at constant area.The formation of aggregates or secondary structures in solution was determined by the fluorescence and polarization values of ANS (anilinonaphthalene sulfonate), measured at different protein/ANS relationships.Abbreviations TF Transferrin - DTF derivatized transferrin - PC lecithin - CHOL cholesterol - CER ceramides - ANS anilinonaphthalene sulfonate - TNBS trinitro benzenesulfonate method     

Thorium compounds with non-metals: Electronic structure, chemical bond, and physicochemical properties

The current state of research on the nature of the chemical bond and the physicochemical properties of binary Th-X (X = H, B, C, N, O, P, S, As, Se, Sb) and ternary (carbonitrides, thorates, and silicates) thorium compounds by modern ab initio methods of the band structure theory is reviewed. The possibilities of the ab initio band structure methods in describing the structural states, phase stability, elasticity characteristics, X-ray emission, absorption, and photoelectron spectra of thorium-containing systems are discussed.     

Investigation into the structures and physicochemical properties of multi-component crystals of voriconazole

Voriconazole (VZL) is a second-generation and broad-spectrum triazole against fungal infections. Being a BCS (biopharmaceutics classification system) class II compound, the poor aqueous solubility has limited its bioavailability and clinical efficacy. Aims to overcome this disadvantage, a cocrystallization strategy based on crystal engineering principles has resulted in five new multi-component crystals of VZL with maleic acid, L-tartaric, protocatechuic, gallic, and 3,5-dinitrobenzoic acids. Structure analysis revealed that the hydroxyl/carboxylic acid···triazole N₃ hydrogen bonding interaction appears as a main supramolecular heterosynthon in the VZL multi-component crystals with organic acids. And VZL molecule has a flexible conformation in each of the five multi-component structures. The newly synthesized multi-component crystals showed impressive solubility improvement compared to that of the raw material of VZL. Molecular electrostatic potential surfaces (MEPS) analysis based on density functional (DFT) calculations revealed that hydrogen bond interactions in cocrystals mainly involved pairwise interactions in the global maxima and minima sites, but this rule is not always followed. This study indicates the potential of cocrystals to improve the solubility and dissolution rate of VZL     

Effect of chemical structures of amines on physicochemical properties of active layers and dehydration of isopropanol through interfacially polymerized thin-film composite membranes

Effect of chemical structures of amines on the performance of isopropanol dehydration by pervaporation through the polyamide thin-film composite membranes prepared by various amines reacting with TMC on the surfaces of the modified asymmetric polyacrylonitrile (mPAN) membranes was investigated. ATR-FTIR, SEM, AFM and water contact angle were used to characterize the chemical structures, morphologies and hydrophilicity of the polyamide active layers of the composite membranes. To investigate the correlation between the free volume of polyamide active layer and pervaporation performance, the free volume variation of the polyamide active layers was probed by positron annihilation spectroscopy (PAS) experiments performed using the slow positron beam. It was found that the pervaporation performance for separating 90 wt.% aqueous isopropanol solutions at 25 °C decreased in the order of EDA–TMC/mPAN membrane > MPDA–TMC/mPAN membrane > PIP–TMC/mPAN and HDA–TMC/mPAN membranes. The relationship between the performance of isopropanol dehydration and the physicochemical properties of the polyamide layers, that is, the free volume, surface roughness and hydrophilicity seemed very well.     

Comparison of different soft chemical routes synthesis of nanocrystalline LiMn2O4 and their influence on its physicochemical properties

A comparative study of nanocrystalline spinel LiMn₂O₄ powders prepared by two different soft chemical routes such as solution and sol-gel methods using lithium and manganese acetates are the precursors under different calcination temperatures. The dependence of the physicochemical properties of the spinel LiMn₂O₄ powder has been extensively investigated by using thermal analysis (TGA/DTA), FTIR, X-ray diffraction studies, SEM, specific surface area (BET) and electrical conductivity measurements. The results show that pure LiMn₂O₄ can be prepared from acetate precursors as starting materials at a low temperature of 600°C from solution route and 500°C from sol-gel method. The charge-discharge characteristics and the cycling behavior of Li/1M LiBF₄-EC/DEC electrolyte / LiMn₂O₄cells revealed that LiMn₂O₄ calcined at higher temperatures showed a high initial capacity, while the LiMn₂O₄calcined at lower temperatures exhibited a good cycling behavior.     

Crystal structures and physicochemical properties of mixed salts of ammonium nitrate and sulfate

Mixed salts (NH₄)₂SO₄·2NH₄NO₃ (1) and (NH₄)₂SO₄·3NH₄NO₃ (2) were synthesized and studied by X-ray diffraction analysis. The unit cell parameters of these salts were determined and their crystal structures were solved. The thermal stability of the salts was studied by differential scanning calorimetry and thermogravimetric analysis. The temperatures and enthalpies of incongruent melting of compounds 1 and 2 were determined. The enthalpies of formation from the constituent salts were estimated.     

Electro chemical properties of porous PVdF-HFP membranes prepared with different nonsolvents

Porous poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) membranes were prepared by solvent–nonsolvent evaporation technique. Morphology and porosity of the membranes were varied with different nonsolvents and had an effect on electrochemical properties. The porous membranes were functionalized with different liquid electrolyte solutions such as p-toluene sulfonic acid/phosphoric acid/sulfuric acid. Maximum electrolyte uptake and minimal electrolyte leakage were tailored by the optimized porosity of the membranes. Thermal behavior obtained in this study ensures the complete evaporation of nonsolvents and ensures its thermal stability. The pTSA-activated PVdF-HFP/THF membrane exhibited high ionic conductivity of about 27.27 mS/cm and a lower methanol permeability in the range of 9.7 × 10⁻⁸ cm²/s. High compatibility between pTSA solution and porous PVdF-HFP polymer electrolyte membrane enhances its electro chemical behavior than that of conventional liquid electrolytes.     

Physicochemical properties of multicomponent polyhydroxyalkanoates: Novel aspects

The physicochemical properties such as the degree of crystallinity and temperature and molecularmass characteristics of a number of polyhydroxyalkanoates of various chemical composition synthesized on a complex carbon substrate by bacteria Cupriavidus eutrophus В10646 have been investigated. Two-, three-, and four-component copolymer samples have different sets and ratios of monomers with various lengths of carbon chains: 3-hydroxybutyrate (3HB), 4-hydroxybutyrate (4HB), 3-hydroxyvalerate (3HV), 3-hydroxyhexanoate (3HH), 3-hydroxy-4-methyl valerate (3H4MV), and diethylene glycol (DEG). It has been shown that weight-average molar mass М _w and polydispersity vary in a wide range with no correlation existing with the composition of copolymer polyhydroxyalkanoates and that thermal stability is preserved in the temperature interval between the melting temperature and the thermal degradation temperature from 100 to 120–140°С. The composition and ratio of monomers most notably affect the degree of crystallinity of polyhydroxyalkanoates. Significant differences between the degrees of crystallinity of three- and four-component polyhydroxyalkanoates have been found for the first time. The degree of crystallinity for copolymers P(3HB/3HV/4HB) is 9–22%, and the degree of crystallinity for copolymers P(3HB/3HV/3HH) and P(3HB/3GV/3H4MV) is 41–63%; this value is close to the degree of crystallinity for diblock copolymers P(3HB)/DEG, which is 56–69%. For the four-component copolymers P(3HB/3GV/4HB/3HH), the degree of crystallinity is 30–41%. The values of М _w for the copolymers P(3HB/DEG) are inhomogeneous and the polymers contain fractions uneven with respect to molecular mass: a high-molecular-mass polymer (М _w from 2700 to 4900 kDa) and a low-molecular-mass polymer (М _w = 46–167 kDa). For the copolymers P(3HB)/DEG and P(3HB/3HV/3H4MV), two peaks are observed in the region of melting with the gap between these peaks being 4–20°С. All of the types of copolymer samples, regardless of the monomer ratio, show an increase in elongation at break against the background of a decrease in tensile stress and Young’s modulus, with these effects being pronounced to different extents. On the whole, the properties of multicomponent polyhydroxyalkanoates differ appreciably.     

Accurate crystal structures and chemical properties from NoSpherA2

The relationship between the structure and the properties of a drug or material is a key concept of chemistry. Knowledge of the three-dimensional structure is considered to be of such importance that almost every report of a new chemical compound is accompanied by an X-ray crystal structure – at least since the 1970s when diffraction equipment became widely available. Crystallographic software of that time was restricted to very limited computing power, and therefore drastic simplifications had to be made. It is these simplifications that make the determination of the correct structure, especially when it comes to hydrogen atoms, virtually impossible. We have devised a robust and fast system where modern chemical structure models replace the old assumptions, leading to correct structures from the model refinement against standard in-house diffraction data using no more than widely available software and desktop computing power. We call this system NoSpherA2 (Non-Spherical Atoms in Olex2). We explain the theoretical background of this technique and demonstrate the far-reaching effects that the improved structure quality that is now routinely available can have on the interpretation of chemical problems exemplified by five selected examples.

NoSpherA2 brings quantum crystallography to routine structure determination and to the analysis of chemical properties for any class of materials.     

The physicochemical properties of complexones,tetrapyridylporphin derivatives

We synthesized complexones based on tetrapyridylporphin (I), namely, tetra(pyridinium-4-N-carboxymethylene) porphin tetrachloride (II), tetra(pyridinium-4-N-carboxymethylene)porphin tetrabromide (III), complete ethyl ester of (pyridinium-4-N-carboxymethylene)porphin tetrachloride (IV), and tetra(pyridinium- 4-N-methyl)porphin tetraiodide (V). Data on the electronic absorption spectra of the compounds, the enthalpies of their solution in water, and the enthalpies of complex formation with copper(II) and zinc acetates were obtained, and the acid properties of the ligands and their stability under thermooxidative destruction conditions were studied. The conclusion was drawn that the enthalpy of solution of complexone-porphyrins in water was determined by the strength of their crystal lattices and, when different anions (Cl^?, Br^?, and I^?) were present, by the difference of the enthalpies of their hydration. As distinct from Cu²⁺, complex formation between Zn²⁺ and porphyrin ligands occurred with sensible energy expenditures likely caused by the electronic inconsistency between the zinc cation and porphyrin ligands. The stability of water-soluble porphyrins to thermooxidative destruction was limited by temperatures of 200–260°C.     

The formation and physicochemical properties of magnesium manganates

The effects of calcination temperature, molar ratio and the doping by CeO₂ on the solid–solid interactions, surface and catalytic properties of Mn/Mg mixed oxide system have been studied by XRD, nitrogen adsorption at −196 °C and the catalytic decomposition of hydrogen peroxide at 20, 30, and 40 °C.

The results revealed that the manganese oxides interacted with magnesium oxide to yield well crystallized magnesium manganates at temperatures starting from 600 °C, this reaction found to be affected by the molar ratio of the reacted oxides present and also by the dopant content. However, the treatment of the Mn/Mg mixed oxide system with increasing amounts of manganese and cerium oxides followed by calcination at 400–800 °C brought about an increase in the catalytic activity of the resulting solids, whilst the opposite effect was observed in the surface area of the investigated solids. These treatments resulted in an increase in the particle size of MgO and a decrease in both the activation energy of sintering of the investigated system and that necessary for hydrogen peroxide decomposition reaction.     

New cyanine-oligonucleotide conjugates: relationships between chemical structures and properties

Because the influence of the chemical structure of monomethine cyanine-oligo-2'-deoxyribonucleotide (ODN) conjugates on their binding and fluorescence properties has remained largely undetermined, we synthesized and studied a wide range of conjugates with various structural patterns. Different cyanine dyes such as thiocyanine, quinocyanine, and thiazole orange isomers were obtained. In the case of unsymmetrical cyanines, the linker was attached to either the quinoline or the benzothiazole nucleus. The influence of the ODN counterpart was evaluated by linking the cyanines to the 5'-end or to an internucleotidic phosphate. In the first case, the influence of neighboring nucleic bases was studied, whereas in the second, the stereochemical configuration at the phosphorus atom bearing the cyanine was investigated. We report here on relationships between the structures of the dyes and conjugates and some of their properties, such as the stability and fluorescence changes observed on their hybridization with the target sequence. This study provides useful information towards the design of ODN-cyanine conjugates.     

Enzymatic transformation of bacterial polyhydroxyalkanoates into repolymerizable oligomers directed towards chemical recycling

The enzymatic transformation into an oligomer was carried out with the objective of developing the chemical recycling of bacterial polyesters. Poly(R-3-hydroxyalkanoate)s (PHAs), such as poly[(R-3-hydroxybutyrate)-co-12%(R-3-hydroxyhexanoate)] and poly[(R-3-hydroxybutyrate)-co-12%(R-3-hydroxyvalerate)], were degraded by granulated Candida antarctica lipase B immobilized on hydrophilic silica (lipase GCA) in a diluted organic solvent at 70 degrees C. The degradation products were cyclic oligomers having a molecular weight of a few hundreds. The obtained cyclic oligomer was readily repolymerized by the same lipase (lipase GCA) to produce the corresponding polyester in a concentrated solution. The cyclic oligomer was copolymerized with epsilon-caprolactone using lipase to produce the corresponding terpolymers having an Mw of 21,000. This is the first example of the enzymatic chemical recycling of bacterial PHAs using lipase. Poly(R-3-hydroxybutyrate) [P(3HB)] was also degraded into the linear-type R-3HB monomer to trimer by P(3HB)-depolymerase (PHBDP) in phosphate buffer at 37 degrees C. The degradation using PHBDP required a longer reaction time compared with the lipase-catalyzed degradation in organic solvent. The monomer composition of the oligomer depended on the origin of the PHBDP. The R-3HB monomer was predominately produced by PHBDP from Pseudomonas stutzeri, while the R-3HB dimer was produced by PHBDP from Alcaligenes faecalis T1. Repolymerization of these oligomers by lipase in concentrated organic solvent produced a relatively low-molecular-weight P(3HB) (e.g., Mw=2,000). Degradation of P(3HB) by lipase in organic solvent into repolymerizable cyclic oligomer and degradation of P(3HB) by PHBDP in buffer into hydroxy acid type R-3HB dimer.     

Effect of different capping agents on physicochemical and antimicrobial properties of ZnO nanoparticles

This research aims to investigate the influence of soluble starch; lactose; carboxymethyl cellulose; urea; and polyvinylpyrrolidone on synthesis of zinc oxide nanoparticles (ZnO-NPs). Zinc acetate was used as a precursor under alkaline conditions to produce ZnO-NPs as a low-cost and efficient antimicrobial and UV-blocking agent. Characterization and antimicrobial functional properties of prepared nanoparticles were investigated and reported using FTIR, TGA, XRD, TEM, analysis, as well as antimicrobial assay, respectively. The results revealed that the thermal decomposition profile, size of ZnO-NPs, IR spectra, as well as antimicrobial activity of the prepared ZnO-NPs is governed by the type of capping agents. Crystallinity analysis showed identical patterns in peak intensities and width irrespective of the used capping agents. On the other hand, the obtained results disclosed that using soluble starch as a capping agent results in attaining lower particle size of 3–5 nm and higher antimicrobial efficacy as compared with the other capping agents.     

Design of a gas chromatograph for chemical kinetic studies and measurement of other physicochemical properties

A simple gas chromatograph was constructed for the purpose of studying reaction kinetics parameters and physicochemical properties. The instrument has a large oven that can accommodate rather long and straight columns; an efficient air circulation makes the temperature gradients inside the oven negligible. The injector has a small dead volume and a thermal conductivity detector was used.

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Microbial synthesis,physical properties,and biodegradability of polyhydroxyalkanoates

Poly((R)-3-hydroxybutyrate), P(3HB), is produced by Alcaligenes eutrophus from fructose or butyric acid. The kinetics and mechanism of P(3HB) biosynthesis are presented. Four types of copolymers, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly (3-hydroxybutyrate-co-3-hydroxypropionate), poly (3-hydroxybutyrate-co-3-hydroxyhexanoate), and poly (3-hydroxybutyrate-co-4-hydroxybutyrate), are produced by several bacterial strains from various carbon substrates. These microbial polyesters are biodegradable thermoplastics whose physical properties can be regulated by varying the molecular structure and composition of copolymers.