Conductometric Method Research Articles

Intensifying the process of methane gas hydrates crystallization in the presence of surface-activated substances

The crystallization process of gas hydrates during their formation in the presence of surface-active substances (SAS) is studied. The research is conducted in two directions – theoretical and experimental. Experimental data on the crystallization rate of methane gas hydrates formation in the presence of surfactants have been obtained: high-molecular compounds are used on the basis of polymeric quaternary ammonium salts containing side aliphatic radicals of various lengths in the acyl fragment, as well as a number of specific surfactants. The process of methane gas hydrates formation is performed using a laboratory setup of the NPO modification for the gas hydrates creation. To analyse the experimental data, technical and metrological instruments are used: stalagmometric method with automatic photoelectric drop counting, conductometric method, Wheatstone bridge, spectrophotometric titration of amino end-groups, viscometer VPZh-1. It has been substantiated that the crystal formation rate depends on the surfactant concentration. New experimental dependences of the gas hydrates formation on surfactants under thermobaric conditions in the presence of surfactants have been found. It has been revealed that the crystallization process during the methane gas hydrates formation is accelerated in the presence of a surfactant. As a result of their application, the effect of solubilization and catalysis arises with the formation of the so-called “diffusion zone”, the size of which decreases in the presence of surfactants, thereby accelerating the substance transfer to the surface on which crystallization occurs. An increase in the surfactant concentration leads to an increase in the rate of molecular diffusion, and also creates a more intense turbulent diffusion.

Development of the orodispersible films based on CO2 extract of Ziziphora bungeana with antimicrobial activity

The present work was intended to develop the new drug in the form of film soluble in the oral cavity: development of its composition, production technology, the study of its antimicrobial activity. The relevance of the problem is caused by the absence of drugs in the form of films on the domestic pharmaceutical market. The optimal composition of films was selected by evaluating a number of physical, chemical and technological indicators of the obtained films. The article indicates the materials used to obtain the drugs in question, presents the technology for their preparation and quality determination methods: unit measurement methods and potentiometric determination of pH, tensiometric and conductometric methods, thin-layer and gas chromatography and others. Antimicrobial activity of the resulting films has been proven in vitro. Staphylococcus aureus ATCC 6538-p and Escherichia coli ATCC 8739 have been used as the test microorganisms in order to study them by disk diffusion method in agar. The introduction of СО2 extract of Z. bungeana from medicinal plant raw materials as active ingredients in medicinal films will expand the range of complex phytopreparations of the domestic pharmaceutical market for the treatment of inflammatory diseases of the oral mucosa.

Interactions between promethazine hydrochloride drug and sodium benzoate hydrotrope mixtures in various solvent media at different temperatures

The current study investigated the mixed micellization of a phenothiazine drug, promethazine hydrochloride (PMT), with the anionic hydrotrope sodium benzoate (NaB) using a conductometric method in three different solvent media: water, 50 mmol.kg−1 sodium chloride (NaCl), and 300 mmol.kg−1 urea (U). Five different temperatures, ranging from 293.15 to 313.15 K, were chosen for the current study of both pure and mixed systems. PMT belongs to a class of drugs known as antihistamines, which are used to treat allergy symptoms. Various physicochemical parameters of both pure and mixed systems (PMT+NaB) were evaluated at different compositions and temperatures, using numerous theoretical models associated with mixed micellization. The attained critical micelle concentration (cmc) and ideal cmc (cmcid) values indicated the formation of mixed micelles due to interactions between the components. The evaluated cmc value for PMT, the minimum hydrotropic concentration (mhc) of NaB, and the cmc value for the PMT+NaB mixture decreased in the NaCl system and increased in the U system compared with these values in the aqueous solution. The cmc values of the studied mixed systems decrease due to an upsurge in the mole fraction (α1) of NaB, indicating the non-ideality of the evaluated solution mixtures. The interaction parameter (β) was negative, revealing that the interaction between the constituents increased with the increasing α1 of NaB in aqueous solution. In the NaCl solution, the β value increased, whereas, in the U solution, the value decreased. The degree of dissociation (g) values decreased by increasing the α1 of NaB in the solution mixture. Various thermodynamic parameters were also evaluated in detail. The activity coefficient values in all cases were below unity, which further indicated the non-ideality of the system. The assessed excess free energy (∆GexRb) of the system was found to be negative in all cases, displaying the stability of the formed mixed micelles. Across the different solvents, their magnitudes were observed in the following order: ∆GexRb in NaCl > ∆GexRb in water >∆GexRb in U. An ultraviolet (UV)-visible study showed a clear interaction between NaB and PMT in the aqueous system. A Fourier-transform-infrared (FT-IR) spectroscopy investigation revealed a shift in the frequency bands of the components due to the interactions between them.

Association behavior of the amphiphilic drug and sodium p-toluenesulfonate mixtures: Effect of additives

The interaction between an amphiphilic phenothiazine drug—promethazine hydrochloride (PMT)—and anionic hydrotrope sodium p-toluenesulfonate (NaTS) mixtures was analyzed and the effect of different mole fractions (α1) of NaTS along with the variation of temperature was also investigated in three different media, water/NaCl (50 mmol.kg−1)/urea (U) (300 mmol.kg−1), using a conductometric method. Drug PMT is mainly utilized to cure allergic symptoms. From the study of pure components along with solution mixtures of components, various physicochemical parameters were evaluated and discussed thoroughly. The obtained results show that the experimental critical micelle concentrations (cmcs) are less than their corresponding ideal cmc (cmcid) values, showing the interaction amongst the constituents (PMT and NaTS). Mixing of dissimilar kinds of amphiphiles has an opportunity to bring about additional valuable acts owing to their attractive interaction. As hydrophobicity of the PMT + NaTS mixtures increased, therefore the cmc values remarkably decreased. The degree of dissociation (g) of the studied system was also evaluated and found to increase with a rise in temperature and decrease via an increase in α1 of NaTS. In salt (NaCl) solution, cmc and g-value of PMT and PMT+ NaTS at all compositions were decreased compared with an aqueous system while in U solution their value was found to be greater than in aqueous solution. Various theoretical models were also considered to estimate the fraction of hydrotrope in mixed micelles PMT + NaTS, the parameter is named the micellar mole fraction (X1Rb (Rubingh model), X1Rd (Rodenas model) and their ideal value is X1id), and the obtained value shows the higher composition of NaTS in mixed micelles along with their value increasing through an increase of α1 of NaTS in the solution mixture. One other parameter, called the interaction parameter (β), was observed as negative throughout the study, also proving the attractive interaction/synergism amongst the components of the solution mixture (PMT + NaTS). Assessed activity coefficients were all below one, showing the nonideality of the studied system. Several thermodynamic parameters of micellization, such as Gibbs free energy (ΔGm0), enthalpy (ΔHm0), and entropy (ΔSm0) have been determined in all studied media and compositions. UV–visible spectroscopy also confirmed the interaction amongst PMT and NaTS. Scanning electron microscope (SEM) images depicted a clear-cut interaction of PMT and NaTS interaction. The outcomes from the current study are significant in the expansion of the operative model drug delivery process.

Evaluation of the frost resistance of concrete in real operating conditions

The article proposes a method for evaluating the frost resistance of concrete at actual operating temperatures, using measurement results at temperatures that are regulated by current standards. Frost resistance was evaluated by determining the amount of water freezing at different temperatures, based on the measured adsorption isobars and the obtained relationship between the freezing temperature of water in concrete pores and relative humidity. A comparison of the calculated values of the frost resistance of concrete with those got based on direct measurements showed the adequacy of the calculation model. To get information about the frost resistance of concrete during unilateral freezing, a conductometric method was used to determine the kinetics of moisture diffusion and ice formation. It is shown that the use of this method allows one to establish the propagation speed of the ice formation and water diffusion front and the corresponding freezing depth of concrete samples depending on their capillary-porous structure and initial storage conditions. In general, the studies conducted allowed us to get a more reliable picture of the behaviour of concrete under alternating temperature load than is provided for by current regulatory documents.

Conductometric determination of trospium chloride by silver nitrate and phosphomolybidic acid

Two simple, accurate, sensitive and precise conductometric methods were developed for determination of trospium chloride in pure form and in pharmaceutical formulations. It is based on using two precipitating reagents; Phosphomolybdic acid (PMA) and Silver nitrate (AgNO3). The mean recovery for Silver nitrate is in the range (98-100.95%) and for Phosphomolybdic acid in the range (98-101.69%). A molar ratio has been determined conductometrically for the two reagents, revealed (1/1) for (drug/reagent). The proposed methods were validated and successfully applied for the determination of the studied drug in pure form and in its pharmaceutical preparation. The results of the proposed methods were compared to the results of reported method with no significant difference between them.

Component complexation study of Ni(II) with 1,3-diphenyl-2-(2-hydroxy-4-nitrophenylhydrozo) propodion-1,3

The effect of various components, including α,α′-dipyridyl (α,α′-dip), phenanthroline (Phen) and bathophenanthroline (B-phen), on the complexation of Ni(II) with 1,3-diphenyl–2-(2-hydroxy-4- nitrophenylhydrozo)propodion-1,3 (R) was studied. Homogeneous (Ni(II)-R) and mixed-ligand (Ni(II)-R-α,α'- dip, Ni(II)-R-Phen and Ni(II)-R-B-phen) complex compounds are determined to form at pH = 6, 5.5 and 5, respectively. The yield of the Ni(II)-R complex is established to be maximal at R concentration of 8·10 -5 M; Ni(II)-R-α,α'-dip – at concentration R and α,α'-dip of 8·10 -5 and 5.2·10 -5 M, respectively; Ni(II)-R-Phen – at concentration R and Phen of 8·10 -5 and 4.8·10 -5 M, respectively; Ni(II)-R-B-phen – at concentration of R and B-phen 8·10 -5 and 4·10 -5 M, respectively. All complexes, which differ in stability, were determined to form immediately after mixing the solutions of the components. The ratio of reacting components in the composition of homogeneous (1:2) and mixed (1:2:1) ligand compounds is established in terms of conformity to Beer's law. The equation coefficients for the calibration curve were obtained by the method of least squares. In the complexation of nickel(II), the А = f(c) dependence was shown to be expressed by linear equations. The stability constants of homogeneous (Ni(II)-R) and mixed-ligand (Ni(II)-R-α,α'-dip, Ni(II)-R-Phen and Ni(II)-R-B-phen) complexes were calculated. Under optimal complexation conditions, Ni(II)-R was titrated with a solution of the components, including α,α'-dip, Phen and B-phen, using the conductometric method. The effect of foreign ions on the complexation of nickel(II) with R both in the absence and presence of other components was studied. In the presence of other components, the selectivity of complexation reactions was established to increase significantly. These reagents were proved to be more selective for spectrophotometric determination of nickel(II) in comparison with reagents known from the literature. The developed technique was applied for nickel(II) determination in three varieties of apples.

Influence of Additives and Temperature on the Interaction of Acid Red 151 Dye with Cetyltrimethylammonium Bromide: A Conductometric Study

AbstractThe interaction of an anionic textile dye, acid red 151 (AR), with a cationic surfactant, cetyltrimethylammonium bromide (CTAB), in aqueous electrolyte medium (e.g., KCl, NaCl) and in H2O + ethanol medium was observed using the conductometric method. Two critical micelle concentrations (CMC) were found for the AR + CTAB system in water and H2O + ethanol medium, but only one CMC was detected for AR + CTAB in salt+H2O media and for pure CTAB in all solutions. The change in CMC behavior of CTAB in the presence of AR indicates the occurrence of strong interaction between AR and CTAB. The extent of solubility increases with an increase of temperature, which disfavors micellization. The CMC values in NaCl solution are comparatively lower than those found in KCl solution, which signifies that the micelle formation is more favorable in attendance of NaCl. In aqueous ethanol solution, two CMC values were also observed for AR + CTAB that are higher than those obtained in water. The free energy of micellization () was negative, which illustrates a thermodynamically spontaneous micellization process. The values of enthalpy () and entropy () of micellization show that the process was entirely entropically driven at a lower temperature; but, enthalpic events are favored at elevated temperature in electrolyte medium, whereas both enthalpy and entropy are reduced in attendance of ethanol. In aqueous medium, the thermodynamic parameters signify the presence of electrostatic interaction between AR and CTAB at higher temperatures, while the hydrophobic interaction is the main driving force at a lower temperature. A linear expression of as a function of demonstrates enthalpy‐entropy compensation over the experimental conditions employed in this study.

Synthesis of olephilic aminoester from the triglyceride of soybean oil and methyldyethanolamine

The aminoester of the mixture of soybean oil’s fatty acids has been obtained through the interaction of methyldyethanolamine with triglycerides. The composition and structure of obtained aminoester have been identified via the IR-spectroscopy. High surface activity of aminoester on the water-air boundary has been revealed with the strain measuring and its colloid-chemical parameters calculated as well. The electrical conductivity of aminoester in various concentrations of agent’s water solutions has been studied via conductometric method. The laboratory researches justified that the aminoester and its 5 % water solutions have high oil-collecting property in the waters of different mineralization degree.

CONSTANTS OF ELECTROLYTIC DISSOCIATION OF THE LITHIUM, SODIUM AND POTASSIUM SULFATES IN AQUEOUS ISOPROPANOL SOLUTIONS

At introduction of isopropyl alcohol in saturated aqueous solutions of sulfates of lithium, sodium and potassium at 25 °C physico-chemical properties of the studied systems Li2SO4-H2O-C3H7OH, Na2SO4-H2O-C3H7OH and K2SO4-H2O-C3H7OH are changed. This reduces the density of solutions and salt content in aqueous isopropanol solutions due to a decrease in solubility of salts. It is shown that the variation of the volume content of alcohol from 0% to 90% results in the decrease of Li2SO4 solubility 1280 times, Na2SO4 – 548 times, K2SO4 – in 278 times. Alcohol additives also affect the degree of electrolytic dissociation of salt in aqueous isopropanol solutions. To study the electrochemical properties of salts we used conductometric method based on the measurement of the molar conductivity of solutions depending on salt concentration. In aqueous solutions, alkali metal sulfates exhibit the properties of strong electrolytes and almost completely dissociate into ions. When the volume content of isopropanol in the solution is more than 30%, alkali metal sulfates begin to show the properties of weak electrolytes, as evidenced by the correlation of the molar conductivity of the diluted solution with the salt concentration under the equation describing the state of weak electrolytes. From the transformations of experimental data in the coordinates of this equation, the values of the electrolytic dissociation constants of the studied salts were determined, which vary (8.30 ± 0.01)·10-5 to (4,35 ± 0,01)·10-8 (mol/l)2 when varying the alcohol content from 30 to 90% volume. It is shown that isopropanol additives reduce the constant (and hence the degree) of electrolytic dissociation of alkali metal sulfates: the higher the alcohol concentration in the solution, the weaker the salt becomes as an electrolyte. The value of the electrolytic dissociation constant depends on the nature of the salt: with an increase in the size of the sulfate cation, the electrolytic dissociation constant decreases.

Lewis Acidity Scale of Diaryliodonium Ions toward Oxygen, Nitrogen, and Halogen Lewis Bases.

Equilibrium constants for the associations of 17 diaryliodonium salts Ar2I+X- with 11 different Lewis bases (halide ions, carboxylates, p-nitrophenolate, amines, and tris(p-anisyl)phosphine) have been investigated by titrations followed by photometric or conductometric methods as well as by isothermal titration calorimetry (ITC) in acetonitrile at 20 °C. The resulting set of equilibrium constants KI covers 6 orders of magnitude and can be expressed by the linear free-energy relationship lg KI = sI LAI + LBI, which characterizes iodonium ions by the Lewis acidity parameter LAI, as well as the iodonium-specific affinities of Lewis bases by the Lewis basicity parameter LBI and the susceptibility sI. Least squares minimization with the definition LAI = 0 for Ph2I+ and sI = 1.00 for the benzoate ion provides Lewis acidities LAI for 17 iodonium ions and Lewis basicities LBI and sI for 10 Lewis bases. The lack of a general correlation between the Lewis basicities LBI (with respect to Ar2I+) and LB (with respect to Ar2CH+) indicates that different factors control the thermodynamics of Lewis adduct formation for iodonium ions and carbenium ions. Analysis of temperature-dependent equilibrium measurements as well as ITC experiments reveal a large entropic contribution to the observed Gibbs reaction energies for the Lewis adduct formations from iodonium ions and Lewis bases originating from solvation effects. The kinetics of the benzoate transfer from the bis(4-dimethylamino)-substituted benzhydryl benzoate Ar2CH-OBz to the phenyl(perfluorophenyl)iodonium ion was found to follow a first-order rate law. The first-order rate constant kobs was not affected by the concentration of Ph(C6F5)I+ indicating that the benzoate release from Ar2CH-OBz proceeds via an unassisted SN1-type mechanism followed by interception of the released benzoate ions by Ph(C6F5)I+ ions.

Thermodynamic insights into molecular interactions of sodium lauryl sulfate (SLS) with caffeine and theophylline in aqueous media at different temperatures

Molecular interactions of the caffeine and theophylline with anionic surfactant sodium lauryl sulfate (SLS), in aqueous media, has been explored by thermodynamic parameters of micellization obtained by the conductometric method. The standard relations associated with micellization were used for the correlation and interpretation of molecular interactions by utilizing the experimental data. The various micellization parameters such as standard free energy ΔGmico, enthalpy ΔHmico and entropy ΔSmico of micellization were calculated. The increase of micellization for SLS in theophylline with an elevated temperature is attributed to the prevailing hydrophobic-hydrophobic increased interactions. The resonance and the dispersal charge on the electron-rich N atoms in caffeine tend to form an ion-dipolar interaction in the vicinity of the polar opposite charge. The thermodynamic parameters indicate that the micellization process in caffeine and theophylline with SLS are spontaneous, enthalpy and entropy controlled.

CONSTANT OF ELECTROLYTIC DISSOCIATION OF LITHIUM, SODIUM AND POTASSIUM SULPHATES IN AQUEOUS ETHANOL SOLUTIONS

Constants of electrolytic dissociation of the lithium, sodium and potassium sulphates in aqueous ethanol solutions at 25 °C were determined by conductometric method. Li2SO4, Na2SO4, K2SO4 were shown to decrease their ability to dissociation. It is generally accepted that the degree of electrolytic dissociation of electrolytes in a solution depends on the dielectric constant of the solvent. Water and ethanol differ greatly in their dielectric constant. For this reason, it is possible to prepare the solvent with different dielectric permittivity by changing the alcohol content in a mixture with water, thus, influencing the equilibrium state of the salt in solution. Therefore, in water-ethanol solutions with an increase in the alcohol content, sulfates of lithium, sodium and potassium should exhibit the properties of a weak electrolyte. In this case, the dependence of the molar conductivity on the concentration of sulfates of lithium, sodium and potassium in water-ethanol solutions will have a different appearance. Indeed, with an increase in the alcohol content in aqueous ethanol solutions, the molar conductivity decreases due to a decrease in the degree of electrolytic dissociation. With a decrease in the salt concentration in the solution, the molar electrical conductivity increases, approaching λ0, for both water and water-alcohol solutions. As it follows from the obtained data, the dependence of λ on the total concentrations of Li2SO4, Na2SO4, K2SO4) for the water solution with a high correlation coefficient is transformed into a straight line in the coordinates of the Kolraush equation since the sulfates of lithium, sodium and potassium act as strong electrolytes in the aqueous medium. For water-ethanol solutions, a high correlation coefficient in the coordinates of the equation 4λ3· C0(M2SO4)2 = КDIS · λ03 - КDIS - λ02·λ is observed in the case of [C2H5OH]> 50% of the volume. This means that in these solutions lithium, sodium and potassium sulphates exhibit the properties of a weak electrolyte. When the alcohol content is from 10% to 40% by volume, sulfates of lithium, sodium and potassium are medium-strength electrolyte and, therefore, low correlation coefficients are characteristic of transformations in the coordinates of the equations Kohlrausch and 4λ3· C0(M2SO4)2 = КDIS · λ03 - КDIS - λ02·λ.

Aggregation and antimicrobial properties of gemini surfactants with mono- and di-(2-hydroxypropyl)ammonium head-groups: Effect of the spacer length and computational studies

Cationic gemini surfactants, alkanediyl-α,ω-bis[(2-hydroxypropyl)dodecylammonium] dibromide (abbreviated as C12-s-C12[iso-Pr(OH)] and C12-s-C12[iso-Pr(OH)]2, with s = 2, 3, 4 and 5) have been synthesized, and their aggregation properties in aqueous solution have been studied by surface tension, electrical conductivity and dynamic light scattering methods. On the basis of the results of studying aqueous solutions of the synthesized gemini surfactants by tensiometric and conductometric methods, their principal surfactivity parameters, such as the degree of counterion binding (β), critical micelle concentration (CMC), effectiveness of surface tension reduction (πCMC), surface excess concentration (Γmax), area per molecule at the interface (Amin), changes of Gibbs free energies of adsorption (ΔGad) and micellization (ΔGmic) have been calculated. For both classes of these gemini surfactants, a character of the surfactivity parameters change with an elongation of the spacer chain was defined and comparative analysis with other ammonium-type gemini surfactants having different head-groups was performed. Using dynamic light scattering method, regularities of variation of the aggregates sizes were studied depending on the number of 2-hydroxypropyl groups and the spacer chain length was investigated. Meanwhile, it was revealed that the mentioned gemini surfactants possess antimicrobial properties. The mechanism of the epoxide ring opening and salt formation reactions were calculated by using Kohn–Sham DFT with the B3LYP functional. The epoxide ring opening via primary (dodecylamine) and secondary (INT2) amines was determined as exergonic (13.4 and 4.4 kcal/mol) reactions as observed experimentally.

Interactions of cationic surfactants with polyvinylpyrrolidone (PVP): Effects of counter ions and temperature

The interactions between the polymer polyvinylpyrrolidone (PVP) and conventional surfactants such as cetyltrimethylammonium chloride (CTACl) and cetyltrimethylammonium bromide (CTABr) were investigated using a conductometric method. The critical micelle concentrations (CMCs), the critical aggregation concentrations (CACs) and degrees of ionization (α) of aqueous solutions of the surfactants and PVP were determined via electrical conductivity measurements at various temperatures. The thermodynamic parameters (Gibbs free energy, enthalpy and entropy) of the surfactants were calculated in the absence and presence of the polymer, and the results were compared to determine the effects of counter ion on the micellization of the surfactants and the energetics of the process. The main goal of this work is to elucidate the various driving forces that lead to complexation between the surfactants and polymer. Electrostatic interactions play a major role in the binding of surfactants to polymers or surfaces in aqueous systems. The strength of the interaction is found to depend on the nature of the surfactant counter ion type.

Conductometric determination of Betahistine dihydrochloride and Heptaminol hydrochloride using silver nitrate

A simple, precise and cost effective conductometric method was developed for determination of betahistine dihydrochloride and heptaminol hydrochloride in pure form and pharmaceutical formulations. The method is based on the precipitation of chloride ions present in cited drugs with silver ions, yielding silver chloride, the conductance of the solution is measured as a function of the volume of titrant. Effect of solvent, reagent concentration, temperature were studied and evaluated. The suggested method was applied for determination of betahistine dihydrochloride and heptaminol hydrochloride in pure forms and pharmaceutical preparations. The described procedure allowed the determination of betahistine dihydrochloride and heptaminol hydrochloride in the range of 2-10mg/ml and 2-13mg /ml respectively.The molar ratio was (2:1),(1:1) (drug:reagent) between betahistine dihydrochloride and heptaminol hydrochloride with silver nitrate respectively. The suggested procedure was applied successfully to the analysis of these drugs in their pharmaceutical formulations, and the results obtained were in agreement with those given by the official methods

Thermodynamic Studies of Complexes of Amlodipine Besylate with Ni2+, Mg2+, Co2+ and Ca2+ cations in pure and in mixed binary solvent systems at 303.15, 313.15 and 323.15 K by Conductometric Method

The present work relates to the complexation reaction between Amlodipine Besylate[AML] with Ni2+, Mg2+, Co2+ and Ca2+ cation in dimethylsulfoxide (DMSO), pure methanol (MeOH) and their binary mixtures(DMSO-MeOH and DMSO-Water) by conductometric method. The conductance data show that the stoichiometry of the complexes formed between AML with Ni2+, Mg2+, Co2+ and Ca2+ cation in pure DMSO, pure MeOHas well as in the binary solvent mixtures was 1:1. The stability of AML complexes with Ni2+ , Mg2+, Co2+ and Ca2+ metal ion was observed to be sensitive to the nature of the solvent system. In case of DMSO-Water binary solvent systems there was a linear change in LogKf values but in case of DMSO-MeOH binary solvent systems non linear change in LogKf values observed.The negative values of ΔG0 show that the reaction is spontaneous and ability of the AML ligand to form stable complexes. However, the result shows positive value of ΔH0 which indicates that enthalpy is not driving force for the formation of the complexes. Furthermore, the positive value of ΔS0 indicates that entropy is a driving force for the complexation. The values of ΔH0 and ΔS0 for formation of the complexes were obtained from temperature dependence of the stability constants.

The use of surface plasmon resonance band of green silver nanoparticles and conductometry for quantitative determination of minor concentrations of doxycycline hyclate and oxytetracycline HCl in pure and pharmaceutical dosage forms

Two novel and sensitive methods for quantitative determination of doxycycline hyclate and oxytetracycline HCl were developed. The first method (method A) is based on the reducing character of the cited drugs which causes chemical reduction of silver ions to silver nanoparticles (Ag-NPs) in the presence of polyvinyl pyrrolidone (PVP) as a stabilising agent producing surface plasmon resonance which has absorption peaks at 424 and 428 nm for doxycycline hyclate and oxytetracycline HCl, respectively. The nanoparticles were characterised by UV-VIS spectrophotometry and transmission electron microscopy (TEM). The plasmon absorbance of the Ag-NPs was used for the quantitative spectrophotometric determination of the cited drugs. The second method (method B) is a conductometric method which is based on the reaction of the cited drugs with phosphotungstic acid to form ion associates in aqueous system. Validation of the proposed methods was carried out.

Synthesis, structural peculiarities, theoretical study and biological evaluation of newly designed O-Vanillin based azomethines

Two azomethines: (E)-2-(((2-hydroxyethyl)imino)methyl)-6-methoxyphenol (1) and (E)-3-(((2-hydroxyethyl)imino)methyl)benzene-1,2-diol (2) were synthesized and characterized in solid state by FT-IR spectroscopy and single crystal X-ray crystallography, whereas in solution state by NMR (1H, 13C) and GC-MS. The titled compounds exist in a zwitter ionic form with a strong intramolecular N–H⋯O hydrogen bond between the NH+ and the phenolate O− as observed both in solution states as well as in solid state. Both the compounds are stabilized in 3D network due to C–H⋯O, N–H⋯O and O–H⋯O types of hydrogen bondings. The optimized molecular geometries were calculated by DFT (density functional theory) with B3LYP functional with 6–31G(d,p) basis set was used using GAUSSIAN 09 program package. The simulated geometries showed excellent correlation with experimentally found structures. The synthesized compounds were investigated for DNA binding interactions using UV–visible spectroscopy and viscometery giving the intercalative mode of interaction with SS-DNA (Salmon sperm DNA). In order to explore the binding modes of compounds with DNA, docking simulations were further performed, that also support the aforementioned results. The compounds were also screened for their in vitro antimicrobial activities and the results showed that their antibacterial activity is even higher than that of the standard drug, Cefixime while their antifungal activity is lower than the standard drug, Terbinafine. The interaction of the titled compounds with cetyl trimethy lammonium bromide (CTAB) was investigated by conductometric method to know the critical micelle concentration (CMC) of CTAB in the absence and presence of compounds. The conductivity measurements revealed higher CMC value in the presence of compounds (For compound 1 CMC = 0.003 M while for compound 2 CMC = 0.0031 M), proposing a stable compound-CTAB system.

Static and dynamic approach to estimation of spring water mineralization stability as a factor of groundwater ecological safety

To assess the degree of influence of technogenic factors on the groundwater mineralization, it is proposed to consider simultaneously in a static and dynamic position the results of conductometric determination in spring water of generalized indicators, such as electrical conductivity and the coefficient of identification of the mineral composition of water. This is shown by the example of four springs located in the territory of Kaluga. This made it possible to establish the average annual background values of electrical conductivity and the coefficient of identification of the mineral composition of water, as well as to justify the permissible or weakly expressed degree of influence of technogenic factors on the quality of groundwater in the period from November 2017 to October 2018 by the criterion of exceeding the error of the conductometric method (2%) by 3 or more times.