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Comprehensive adsorption and spectral studies are performed for the interaction between caffeic acid and pyrogenic alumina in aqueous solutions. It is shown that sorption begins at pH >2.5 and reaches its maximum values in a neutral medium. The sorption isotherm of caffeic acid is the H-type isotherm characteristic of chemisorption. It is found that adsorption proceeds according to two mechanisms simultaneously: due to interaction between the surface groups of the sorbent and (a) the carboxyl group of caffeic acid or (b) the ortho-hydroxyl group of the acid to form a chelate complex, the relative fraction of which grows along with the pH of the solution.

The spectral characteristics (absorption band intensity and position) of structurally similar natural cinnamic acids absorbed on an aluminum oxide surface were found to depend on the surface concentration and aqueous solution pH. The conditional molar absorption coeffi cients [g/(mol∙cm)] of adsorbed cinnamic $$ \left({\upvarepsilon}_{274 nm}^S=1766\right), $$ coumaric $$ \left({\upvarepsilon}_{286 nm}^S=2056\right), $$ ferulic $$ \left({\upvarepsilon}_{290 nm}^S=1139\right), $$ and caffeic acids $$ \left(\left({\upvarepsilon}_{350 nm}^S=1163\right.\right) $$ were determined. The optical densities of the adsorbed cinnamic acids were found to correlate with their concentrations in the initial solutions being analyzed. Owing to this, highly disperse aluminum oxide could be recommended as a solid-phase reagent for evaluation of cinnamic, coumaric, ferulic, and caffeic acids in plant-derived products using spectrophotometric or visual test methods. The possibility of selective determination of caffeic acid was also shown.

The sorption of rutin on aluminum oxide from aqueous ethanol solutions is studied in the range of physiological pH values. It is found that sorption begins at pH >3 and reaches its maximum values in a neutral medium. It is established that the isotherm of rutin sorption belongs to the H-type, which is characteristic of chemisorption. It is shown that rutin is sorbed on aluminum oxide due to the interaction between a pair of hydroxyl and carbonyl groups alongside the undissociated ≡AlOH group, resulting in the formation of a chelate on the sorbent surface similar to the complex formed with Al(III) in solutions.

Quercetin and rutin upon adsorption on alumina were found to form colored chelate complexes with alumina surface groups similar to complexes with Al(III) ions in solution. The optical density of the alumina dispersion in the presence of these hydroxyflavones is greatest in neutral media and linearly dependent on their concentration in the initial solution. The conditional molar absorption coefficients of the surface quercetin (eS434 = 4386 g/(mole·cm)) and rutin complexes (eS403 = 5280 g/(mole·cm)) were determined. Highly dispersed alumina can be proposed as a solidphase reagent for the determination of quercetin and rutin in preparations of medicinal plants by a spectrophotometric or visual test method.

A comprehensive study of the interaction of a natural flavonol, quercetin, with highly dispersed alumina in a water–ethanol medium has been carried out by adsorption and spectral methods. It has been shown that the sorption of quercetin on alumina begins at pH > 2.5 and reaches maximum values in the neutral medium in correlation with the content of nondissociated surface ≡ AlOH groups. The sorption isotherm of quercetin is of H type, which is characteristic for chemosorption. The coincidence between the spectral characteristics of the flavonol on the surface of highly dispersed alumina and in solutions containing Al(III) ions suggests the formation of similar chelate complexes in these systems.

It has been shown that adsorption of natural antioxidants, such as 3-phenylpropenic (cinnamic), 3-(4-hydroxyphenyl)propenic (coumaric), and 3-(3-methoxy-4-hydroxyphenyl)propenic (ferulic) acids, on the surface of cerium dioxide is characterized by S-type isotherms, while adsorption of 3-(3,4-dihydroxyphenyl)propenic (caffeic) acid is described by an H-type isotherm. A linear correlation between adsorption values and hydrophobicity parameter logP has been found in initial regions of the S-type isotherms, with such correlation being typical for parallel orientation of adsorbed molecules relative to an adsorbent surface. The maximum adsorption values (≈2.9 × 10–4 mol/g), as well as dissociation constants (pKCOOH = 4.4–4.6), are almost identical for all acids, thereby suggesting that adsorbate molecules are predominantly bound to the adsorbent surface via carboxyl groups. The presence of hydroxyl groups in molecules of coumaric, ferulic, and caffeic acids widens the рН range of their adsorption as compared with cinnamic acid and promotes their oxidation on the cerium dioxide surface.

The effect ethonium, a dicationic surfactant, has on the physicochemical properties of a natural flavonoid, rutin, is studied spectrophotometrically in a wide range of concentrations in the region of physiological pH. It is found there are a bathochromic shift of the bands in the absorption spectra of rutin, a drop in the apparent constant of its dissociation $${\text{p}}{K}_{{{\text{a1}}}}^{{\text{a}}}$$ , and an increase in solubility and adsorption on the surface of nanosilica relative to aqueous solutions. The constant of bonding between rutin and ethonium is calculated.

The formation of supramolecular complexes with ethonium, a cationic gemini surfactant having a broad-spectrum antimicrobial activity, is shown to significantly alter the physicochemical properties (spectral, protolytic, and adsorption properties and solubility) of a natural f lavonol, quercetin. The constant of binding between quercetin and ethonium is calculated. Apparent dissociation constants pK a1 a of quercetin in solutions of this cationic surfactant are for the first time determined within a broad concentration range. A shift in the pH dependence of quercetin adsorption by 0.5 units to the alkaline region upon the transition from a premicellar ethonium solution to a micellar one correlates with an increase in pK a1 a under these conditions. The value of quercetin adsorption from aqueous ethonium solutions depends on the concentration of the cationic surfactant, pH of a solution, and the pK a1 a value of the f lavonol bound into the supramolecular complex.

The state of water in hydrated powders of KCl and KCl/AM1/H2O composite system before and after addition of hydrophobic organic substances was investigated using 1H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial waters. It is found that water retention in the nanocomposite consisting of hydrated powder of KCl and hydrophobic silica AM1-300 (model of stimulating protective composition “ECOSTIM”) is significantly higher than in the powders of mineral fertilizers. When KCl/AM1/H2O composite system is in contact with a hydrophobic substance, imitating the hydrophobic sites of the seed surface, the additional growth of interfacial water binding is observed. This takes place probably due to the gain of free energy as a result of water cluster defragmentation in nanoscale systems containing hydrophobic and hydrophilic constituents. The state of water in hydrated powders of KCl and KCl/AM1/H2O composite system was studied. It is found that water retention in the nanocomposite is significantly higher than in the powders of KCl. When a composite system is in contact with a CDCl3, the growth of water binding is observed. The growth of free energy as a result of water cluster defragmentation in nanoscale systems.

The effect of a hydrophobic medium on the hydrated properties of a powdered nanocomposite based on the cationic surfactant miramistin and silica was studied using low-temperature PMR spectroscopy. The thermodynamic parameters of strongly and weakly bound water layers and the interfacial energy of water in pore cavities of the nanocomposite were determined.

It has been shown that the spectral characteristics (intensity, position of the absorption band) and the acid-base properties in a series of structurally similar hydroxyflavones depend on the concentration of the cationic surfactants miramistin and decamethoxin in aqueous solutions, and the extent of their changes is more pronounced for hydrophobic quercetin than for hydrophilic rutin. For the first time, we have determined the apparent dissociation constants of quercetin and rutin in solutions of these cationic surfactants (pKa1) over a broad concentration range and we have established that they decrease in the series water–decamethoxin–miramistin.

The structure of hydrate cover layers of SiO2-DNA-Dox (where Dox: doxorubicin) and SiO2-DNA-Dox-C60 fullerene hybrids was studied by means of low-temperature 1H NMR spectroscopy in tetrachloromethane. The hydration properties of SiO2-DNA-Dox nanomaterials combined with fullerenes and their derivatives are extremely important for their further use as therapeutics in cancer treatment and for safety reasons. The findings reveal that the hydration properties of the hybrids differ from those of the solid DNA particulates or SiO2-DNA systems due to the existence of different types of water clusters, namely the weakly (WAW) and strongly associated water (SAW) clusters. For SAW clusters the radial distributions as well as the distributions of change in Gibbs free energy due to adsorptive interactions at the surfaces of the investigated systems were obtained.

The effect of the cationic surfactants decamethoxine and miramistin on the physicochemical properties of the natural flavonoids quercetin and rutin is studied spectrophotometrically in the range of physiological pH values. It is established that the interaction with these cationic surfactants changes the spectral characteristics of the flavonoids in solutions and essentially increases their adsorption on the surface of highly dispersed silica as compared with their aqueous solutions. It is shown that the efficiency of flavonoid adsorption from decamethoxine and miramistin solutions is governed by solution pH, flavonoid hydrophobicity, and the nature of a cationic surfactant.

The effect of a cationic surfactant, Decamethoxin, on the physicochemical properties of structurally related natural flavonoids, quercetin and rutin, was studied by spectrophotometry. The spectral and protolytic properties and the solubility of quercetin and rutin strongly depend on the Decamethoxin concentration in solution. The presence of Decamethoxin in the solution favors the tautomeric transition of the enol form of quercetin to the keto form.

The adsorption of a universal antiseptic agent, the cationic surfactant miramistin, on the surface of highly dispersed silica has been studied. It has been shown that, when miramistin is adsorbed from acidic premicellar solutions, the main contribution to miramistin binding with the surface is made by hydrogen bonding between amide groups of surfactant molecules and silanol groups of silica, which is, at higher pH values, accompanied by ionic interaction between positively charged quaternary nitrogen atoms of miramistin and negatively charged dissociated silanol groups. In the case of adsorption from a micellar solution, an increase in the surface concentration of miramistin is almost independent of solution pH, because the second layer is predominantly formed due to hydrophobic interactions.

Low-temperature 1H NMR spectroscopy was used to examine the effect of external factors (temperature and environment) on the hydrate properties of nanocomposite powder materials based on hyaluronic acid and hydroxyapatite. Thermodynamic parameters of layers of strongly and weakly bound water and the nanocompositewater interface energy were determined.

Pyrolysis of biologically active cinnamic acid derivatives: cinnamic, coumaric, ferulic and caffeic acids was studied by the method of thermal programmed desorption mass spectrometry. It was found that pyrolysis of coumaric and caffeic acid proceeds as a thermal decarboxylation reaction of the first order. Kinetic parameters of the reaction of decarboxylation including its order, the activation energy and pre-exponential factor were calculated. Under conditions of TPD MS experiment cinnamic acid sublimates at temperatures above 200 °C. Thermal decomposition of ferulic acid proceeds in several stages.

The effect of the anticancer drug--doxorubicin (Dox) on hydration properties of a nanocomposite material deposited on silica and modified by small amount of DNA (0.6 wt%) was studied by means of (1)H NMR spectroscopy at low temperatures (in the range of 200-280 K). Signals of either weakly (WAW) or strongly (SAW) associated water, as well as water associated with electrondonor groups of the composite surface (ASW), were observed. The findings reveal that, depending on the temperature and the composition of the dispersion medium, fast molecular exchange takes place between different forms of interphase water. The presence of Dox (0.1-0.2 wt%) in the dispersion medium leads to change of the relative concentrations of different forms of water.

Nanocomposites modified with small amounts of C 60 fullerenes were investigated by means of thermogravimetric analysis and 1 H NMR- and IR-spectroscopy. The nanocomposite materials were generated on the basis of highly dispersed silica and DNA. The findings revealed that a small amount of fullerenes, settled down on the surface of the nanocomposite, leads to significant modifications in the structure of adsorbed water clusters. The radius of the strongly associated water clusters increased and the interphase energy of the nanocomposite–water system decreased. These composites can be used to control a ratio between the weakly and strongly bound clusters of water adsorbed by DNA molecules.

Hydrated starch alone and in composition with nanosilica A-300 and quercetin (natural antioxidant) was studied in the form of powders (mechanical mixture) and gels using 1H NMR (at 200–280 K), FTIR (293 K), TG (293–573 K), TSDC (90–265 K) and quantum chemistry methods. Influence of weakly polar (chloroform-d, CDCl3) and polar ((CD3)2SO, DMSO) deuterated solvents on bound water structure in these systems was also analysed at 200–280 K. The energetic and structural boundaries between weakly (unfrozen at 250–260

The interactions of bioactive ferulic acid with fumed silica were studied by UV/vis spectroscopy, FT-IR, TPD MS techniques and quantum chemical methods. It was found that surface complexes may form through phenol or carboxyl group of ferulic acid depending on its coverage value. The structure of surface complexes and mechanisms of the ferulic acid chemosorption on the silica surface are discussed. The kinetic parameters of the chemical reactions on silica surface are calculated. The mechanisms of thermal transformations of the ferulic chemosorbed surface complexes are proposed.

It is shown that the interaction of polyvinylpyrrolidone and human serum albumin with a natural flavonoid quercetin in aqueous medium results in the formation of 1 : 1 supramolecular complexes. As a result of complexation, the optical and protolytic properties of the flavonoid change and its concentration in solution increases considerably. The adsorption of quercetin on silica particles in the presence of polymers is discussed.

It is demonstrated that NMR in combination with a liquid-phase freezing technique can be successfully used for the investigation of hydration processes in tablets, depending on the production technology.

The adsorption of cinnamic and caffeic acids on initial and partially silylated highly dispersed silica A-300 from polar (water-ethanol solution), low polar (chloroform and dichloroethane), and apolar (hexane and carbon tetrachloride) solvents is investigated. The dependence of adsorption on solvent polarity is established. It is disclosed that the dependences of the adsorption of cinnamic and caffeic acids on the degree of surface hydrophobization have different characters.

The interaction of cinnamic acid with the surface of highly dispersed silica is studied. The mechanisms of adsorption, chemisorption, and thermal transformations of cinnamic acid on the silica surface are proposed. The kinetic parameters of the chemical reactions on the surface of silica are calculated.

Interfacial water at a surface of nanosilica (SBET = 378 m2/g) with various amounts of adsorbed 1,3,5-trihydroxybenzene (phloroglucinol, PG), which as an ice-nucleator can strongly affect water structure, was studied using 1H NMR method with layer-by-layer freezing-out of bulk and interfacial water at 200

It is established that the adsorbability of cinnamic acid from solutions on the surface of highly dispersed silica decreases with an increase in the polarity and electron-donor ability of a solvent. The adsorption process is considerably affected by the hydrophobization of the surface. The adsorption curve passes through a maximum when methyl groups are substituted for 40–55% of the total number of hydroxyls on the silica surface. Probable structures of adsorption complexes are suggested.

A new test method for measuring the antioxidant power of herbal products, based on solid-phase spectrophotometry using tetrabenzo-[b,f,j,n][1,5,9,13]-tetraazacyclohexadecine-Cu(II) complex immobilized on silica gel, is proposed. The absorbance of the modified sorbent (lambda(max) = 712 nm) increases proportionally to the total antioxidant activity of the sample solution. The method represents an attractive alternative to the mostly used radical scavenging capacity assays, because they generally require complex long-lasting stages to be carried out. The proposed test method is simple ("drop and measure" procedure is applied), rapid (10 min/sample), requires only the monitoring of time and absorbance, and provides good statistical parameters (s(r)or= 0.2). The method was approved in the analysis of the most popular herbal beverages (black and green teas) and drugs (Echinacea products). The results obtained were compared with the content of total flavonoids and tannins of teas and total caffeic acid derivatives of Echinacea, determined spectrophotometrically.

PMR and electrophoresis have been applied to examine hydration changes in protein molecules due to the presence of the electron donor dimethylsulfoxide DMSO, which influences the radiolysis of human serum albumin HSA. The reactions of aqueous HSA with added DMSO show that the DMSO on the one hand acts as a protector, which prevents the formation of low-molecular protein forms on reaction with hydroxyl radicals, and on the other alters the protein hydration, which facilitates thiol-di-sulfide exchange, which leads to oligomers.

Thermally stimulated depolarization spectra of frozen aqueous suspensions of fumed silica show a dependence of relaxation processes on the concentration of silica (CSiO2) due to a change in the particle-particle interaction (their electrical double layers) and the concentration of bulk water (ice) with increasing CSiO2. A significant fraction of agglomerates of primary particle aggregates are not decomposed in aqueous suspensions of fumed silica. The thickness of an interfacial water layer perturbed by the silica surface or protein molecules was estimated from the dependence of 1H NMR signal intensity of unfrozen water on temperature below 273 K, separating the signals of water molecules weakly and strongly bound to the surface. Protein molecules adsorbed on fumed silica aggregates form hydrogen bonds with identical withSiOH or identical withSiO- groups by amino groups, e.g., H+NR from the zwitterion fragments. Aqueous suspensions of mechanochemically activated fumed silica do not lose protein adsorption ability during a long period in which the particles remain as microscaled agglomerates. According to AM1-SM1 calculations, complexes such as identical withSiO(H)middot;middot;middot;H+NRCOO- are stabilized in aqueous suspensions of silica and the protein desorption rate decreases with increasing molecular weight of proteins.

Hydrogen bonds in which thiocarboxylic acids participate have received little quantitative study [i]. In [2, 3], in an investigation of the association of certain thiocarboxylic acids with electron donors by the methods of NMR and IR spectroscopy, the frequencies of the stretching vibrations and the chemical shifts of the protons of the SH groups were measured, but the energies of the hydrogen bonds were not calculated. Only in [4] was it shown that thioacetic acid forms stronger bonds with triethylamine than does propanethiol. This result is in qualitative agreement with the fact that thiocarboxylic acids are characterized by greater proton-donor capacity than mercaptoalcohols; however, from the quantitative standpoint this cannot be considered reliable, since in a calculation of the strength of the hydrogen bonds according to the data of the UV spectra, processes of protonation of the amide that follow the formation of hydrogen bonds were not considered.

The reaction of human serum albumin (HSA) with dimethyl sulfoxide (DMSO) was studied by the PMR method according to the intensity of the proton signal of non-freezable water in the temperature range of 230–273°K. It was shown that the concentration of DMSO in the non-frozen liquid phase is much higher than should be expected for the simple eutectic. This is attributable to the binding of N molecules of DMSO with a molecule of HSA (at 270°K, N = 7–10). It was found that in the presence of DMSO, the amount of non-freezable water markedly increased, which is possibly due to a reaction between DMSO and proton-active centers of the protein through the intermediate water molecules.

The kinetics and mechanism of proton exchange between thiocarboxylic acids and o-substituted phenols with intramolecular hydrogen bonds (IMHB) were studied by dynamic PMR spectroscopy. Fast uncatalyzed exchange in cyclic binary complexes is observed for phenols with weak IMHB. In systems with strong IMHB fast exchange occurs only in the presence of an alkaline catalyst, the reaction of which with the phenol leads to cleavage of the IMHB. Concerted transfer of two protons and a cation is realized in the final step of the reaction. According to the proposed mechanism, the measured energy of activation of proton exchange is the sum of the energies of activation of the steps involving cleavage of the IMHB and strictly proton transfer.