The enthalpies of dilution of solutions of hexamethylenetetramine (HMTA), the well-known pharmaceutical urotropine, in water (H2O) and heavy water (D2O) were determined with a new heat conduction calorimeter at 298.15 K. The enthalpy-related homotactic coefficients of pairwise, h22, and triplet, h222, interactions between hydrated solute molecules were computed using the excess thermodynamic function concept (based on the McMillan-Mayer theory formalism). The h22 and h222 values were found to be large and positive in both H2O and D2O due to a partial overlapping of solute hydrophobic hydration shells and appearance of solute - solute correlations at rather large distances. This phenomenon is stronger pronounced in heavy water both for pairwise and for triplet HMTA - HMTA interactions indicating a highly ordered hydration structure in D2O. The established correlation between the h22 values and the corresponding solvent isotope effects, delta h22(H2O -> D2O), for HMTA and tetramethylurea mono- and bicyclic derivatives as solute species confirms the hypothesis of the differentiating effect of a solvent isotopic substitution on both the energetics of solvation and solute - solute interactions in aqueous solutions of proton-accepting non-electrolytes. In other words, the more negative or positive the h22 value due to stronger homo- and heterocomponent D-bonds, the more negative or positive the corresponding isotopic effect is.

The intermolecular interactions of 18-crown-6 with L-carnosine, β-alanine and histidine in water and in an aqueous-ethanol solvent with a composition of 0.1 mol fr ethanol at T = 298.15 K were studied using the method of isothermal titration calorimetry. The enthalpy of dissolution of crystalline β-alanine was determined using the method of dissolution calorimetry in an aqueous solution of ethanol with an ethanol content of 0.1 mol fr at T = 298.15 K. The thermodynamic parameters of the reactions of the formation of molecular complexes between 18-crown-6 and amino acids were analyzed. The enthalpy of combustion of 18-crown-6 was determined using bomb calorimetry, and the enthalpy of formation of crystalline 18-crown-6 was calculated.

Enthalpies of dilution of urea (U) solutions in formamide (FA), ethylene glycol (EG) and water were mea- sured calorimetrically in the temperature range between (288.15 and 318.15) K. Based on the results obtained, the enthalpy-homotactic coefficients of pairwise (h22) and triplet (h222) interactions between the solvated U molecules were computed and compared with the similar data for the respective solutions of tetramethylurea (TMU). An analysis was done of how temperature influences the solvophilic and solvophobic effects manifested in the h22 and h222 parameters for U and TMU in the studied organic sol- vents with a spatial H-bonding network.(c) 2022 Elsevier B.V. All rights reserved.

Enthalpies of dilution of solutions of urea (U) in formamide (FA) and ethylene glycol (EG), and solutions of tetramethylurea (TMU) in FA, are measured at 298.15 K to study displays of solvophilic and solvophobic effects in solvents with a spatial hydrogen-bond network. Homotactic enthalpic coefficients of pair (h22) and triple (h222) interactions between solvated molecules of the solute (U or TMU) are calculated from the calorimetric results. Calculated values are compared to literature data for U and TMU solutions in water (H2O) and TMU solutions in EG. It is established that unlike the effects of 2–2 interaction in (EG + U) and (H2O + U) systems, the h22 parameter for U in FA has a positive sign and is quite low in absolute value (~160 J kg mol−2). It is therefore concluded that there is complementarity in Н-bond-associated structures of the solvent (in bulk) and the U–FA solvatocomplex formed in it. The character of distribution of the h22 values for TMU in the FA (~587) < EG (~649)  $$ \ll $$  H2O (~2346 J kg mol−2) series of solvating media is evidence of the considerably greater role of solvophobic effects in aqueous solution.

In this work, four novel pharmaceutical cocrystals of nitrofurantoin, an antibacterial drug, with isonicotinamide, picolinamide, 2-hydroxybenzamide, and 2-aminobenzamide have been obtained and thoroughly characterized by various analytical techniques. The crystal structures of the solid forms have been elucidated by single-crystal X-ray diffraction, and the energy distribution of intermolecular interactions has been further quantified on the basis of QTAIMC analysis. Eight distinct supramolecular heterosynthons of hydrogen bonding have been identified in the studied crystals, and their relative stability has been ranked in terms of total interaction energies. The thermodynamics of the cocrystallization reactions has been systematically investigated using two independent experimental techniques, namely solution calorimetry and phase solubility diagram, which allowed us to assess both the enthalpic and the entropic contributions to the cocrystal formation driving force. The pH-solubility behavior of the cocrystals has been investigated at different pH values using eutectic concentrations of the components. Although all of the cocrystals reported here were found to be more soluble than the parent drug, their advantage in thermodynamic solubility did not translate into enhanced dissolution performance due to a rapid solution-mediated phase transformation in aqueous media. In addition, the effect of cocrystallization on other pharmaceutically relevant properties of nitrofurantoin, including photostability and membrane permeability, has been considered and analyzed.

The interaction of the dicationic photosensitizers (PSs) of the porphyrin {13(3),17(3)-bis-N-(2-N',N',N'-trimethylammonioethylamide) diiodide of deuteroporphyrin-IX} and chlorin {3(1),3(2)-bis-(N,N,N-trimethylammoniomethyl)-13(1)-N-methylamide-15(2),17(3)-dimethyl ester of chlorin e 6 diiodide} types with a nonionic surfactant Tween 80 (a potential delivery means) in the region of spherical micelles was studied by spectrophotometric and fluorescent titration. It was found that stable PS–Tween 80 complexes formed, with two binding modes with their own interaction constants and stoichiometry revealed on the titration curves; the most probable reasons for this are discussed. It was concluded that PS molecules lie in the outer layer of the micelle, where they are surrounded by polar oxyethylene groups and where hydrated iodide ions can penetrate. In the presence of various electrolytes, the size of Tween 80 micelles changed, which was detected by dynamic light scattering.

The interactions between the cationic polyelectrolyte poly(dimethyldiallyl ammonium chloride) (VPK402, PDADMAC) and the anionic polyelectrolyte Acremon B-1 (Ac), widely used as auxiliary materials in the textile industry, as well as Ac aggregation have been studied by isothermal titration calorimetry. The thermodynamic characteristics of Ac micelle formation and of interpolyelectrolyte complex formation between Ac and VPK-402 have been obtained in an aqueous solution at 298.15 K. It has been revealed that the entropy factor was favorable to the Ac micellization process. It has been found that at a low concentration of Ac in a solution, the interaction between Ac and VPK402 was also controlled by the entropy contribution. On the contrary, the formation of Ac - VPK-402 interpolyelectrolyte complexes at high Ac concentrations was enthalpycally favorable. (c) 2022 Elsevier B.V. All rights reserved.

The molar enthalpies of dissolution of N-tetramethylglycoluril, a known psychotropically active pharmaceutical mebicar (Meb) (solute x), in aqueous solutions of D-monosaccharide glucose (Glu), fructose (Fru) and galactose (Gal) as well as disaccharide sucrose (Suc) and a -lactose (Lac) (cosolute y), were mea-sured by the precision calorimetry method at T = 298.15 K and ambient pressure. Unlike the heat absorp-tion in aqueous monosaccharides or Lac, the endothermicity of Meb dissolution in {water (W) + Suc} decreases as the sugar content becomes higher. The enthalpy-heterotactic coefficients for pair interac-tions between the solute and cosolute molecules, hxy,were determined using the McMillan-Mayer theory formalism. Similar to the homotactic parameters hyy,the hxy values (in J.kg.mol(-2)) were found to be pos-itive, increasing in the series Suc (86) << Lac (32 9) < Fru (456) < Glu (545) < Gal (663), despite the exist-ing unusually large (in magnitude) negative hxx value, which is about-2000 J.kg.mol(-2). Overall, the number of hydroxy groups and their axial(a)/equatorial(e) positions as well as the peculiarities of a gly-coside bond and intramolecular H-bonding in cosolute saccharide molecules cause a stereospecificity of Meb hydration manifested in pair-interaction enthalpic coefficients h(xy). So, the inequality h(xy) > h(yy) was found to be characteristic of monosaccharide containing aqueous Meb solutions (down to h(yy) ? 0.2hxy for Gal), and h(xy) < h(yy) - to be related to disaccharide containing aqueous Meb solutions. Thus, if h(xy) for (W + Lac + Meb) is ca. 0.65hyy,then it is only about 0.15h(yy) in the case of (W + Suc + Meb). (C) 2022 Elsevier B.V. All rights reserved.

The molar enthalpies of dissolution of 1,3,6,8-tetraazatricyclo[4.4.1.1(3,8)]dodecane or TMDETA (tetramethylenediethylenetetramine: the teotropine pharmaceutical) in ordinary (H2O) and heavy (D2O) water were measured calorimetrically at T = (278.15, 288.15, 298.15, 308.15, and 318.15) K and p = 0.1 MPa. The standard molar enthalpies and heat capacities of TMDETA dissolution/hydration, along with D2O-H2O solvent isotope effects (IEs) in these quantities, were computed. Solution enthalpies and corresponding IEs were found to be negative, decreasing in magnitude as the temperature is rising. It was concluded that hydrophobic effects are the predominant part in the TMDETA hydration and they are enhanced in D2O and weakened going from TMDETA to its lower-molecular aminal derivative, hexamethylenetetramine (HMTA) being the known drug urotropine. Unlike the aqueous HMTA, the "dualistic" character of TMDETA hydration is less dependent on the initial structure state of a solvent isotopologue. The results of analyzing the contributions to the solvation enthalpy within the scope of Scaled Particle Theory showed that IEs in the enthalpy of TMDETA - water interaction and the solvent cavity formation is almost cancelling each other at T > 288.15 K. (C) 2020 Elsevier B.V. All rights reserved.

The research findings related to synthesis and study of water–sodium dodecyl sulfate–1-pentanol–triethanolamine–2-iodoheptafluoropropane and water–sodium dodecyl sulfate–1-pentanol–triethanolamine–1,2-dibromotetrafluoroethane microemulsions at the standard temperature were summarized. Use of microemulsions provides a promising means of combining with water chemically active inhibitors such as halohydrocarbons, which are water-immiscible under ambient conditions. This affords fire extinguishing agents integrating different flame suppression mechanisms: chemical inhibition of the combustion reaction and flame cooling. The electrical conductivities and heat capacities of the microemulsions synthesized were determined and used for analyzing the structural changes caused in them by changes in their composition. Using the dynamic light scattering method, the size of the microdroplets of the microemulsions was determined, and their size distribution was examined. Based on the data obtained, the fire extinguishing performance of the microemulsions (cooling capacity, possible applications, and mechanism of action) was described. Laboratory tests of the fire extinguishing efficiency of the microemulsions were carried out.

In this paper, we have discussed the results of densimetric and calorimetric studies of dissolution process in water for the (1:1) cocrystal consisting of two heterocyclic isomers being cis- and trans-coordinated dimethylglycolurils (2,8-DMGU and 2,6-DMGU, respectively) in the temperature range from (278.15 to 318.15) K at the ambient pressure. The standard (apparent or partial at infinite dilution) molar volumes and isobaric expansibilities of cocrystal as a solute in water were derived from the experimental data on solution density. Using thermochemical measurements, the standard molar enthalpies and isobaric heat capacities of the dissolution of cocrystal in water were also determined at the temperatures of interest. Based on the previously obtained similar results for aqueous 2,6-DMGU and 2,8-DMGU, a comparative analysis of packing and interaction changes in the hydration complex induced by the cocrystallization process has been carried out. It was found that the formation of cocrystal leads to a peculiar “synergism” in both volume and heat capacity effect of N,N′-dimethylglycoluril hydration at all temperatures studied.

In this work, we studied the thermodynamic parameters of the complexation reaction between europium and N,N '-diethyl-N,N '-difluorophenyl-2,2'-bipyridyl-6,6'-dicarboxamides in ethanol. The complexation reaction lead to one complex particle with 1 : 1 metal : ligand composition. Spectrophotometric and calorimetric titration methods were used for determination of the stability of complexes. According to our data, the fluorine atom in the meta-position in the ligand (log K = 3.59) increases the stability of complexes, enthalpy and entropy compared with the para-position (log K = 3.26). Comparison of two parameters ΔrH and TΔrS for the 3-F ligand (–8.6 and 14.15 kJ/mol, respectively) shows that they are lower than that of for the 4-F ligand (–15.5 and 10.19 kJ/mol, respectively).

This paper focuses on the solute – solute interactions in dilute solutions of a typically hydrophobic solute tetramethylurea (TMU) in ethylene glycol (EG) which forms the three-dimensional hydrogen-bond network at the supramolecular level. The results of our experimental efforts based on dilution calorimetry and phase partition techniques are able to make a conclusion that thermodynamics of the TMU – TMU pairwise interaction in EG is to a great extent similar to that occurs in liquid water. All effects, however, are weaker expressed in the non-aqueous medium. In particular, the integrand of the potential of mean force, i.e. the second virial coefficient, between two TMU molecules becomes negative only at elevated temperatures indicating the appearance of a rather weak solvophobic interaction in EG. Since C=O-groups of TMU are well-incorporated into the H-bond network of EG, it is reasonable to assume that the attraction observed should be mainly induced by apolar methyl groups. The correlation between the enthalpy- and volume-related parameters of pairwise interaction provides the additional confirmation of the existence of the solvent-induced solvophobic interaction between TMU molecules in EG.

Based on the identified inconsistencies in the existing literature data on the enthalpies and heat capacities of dissolution (solvation) of hexamethylenetetramine (HMTA) in ordinary (H2O) and heavy (D2O) water, we carried out carefully the calorimetric study of these two binary systems at seven temperatures from (278.15 to 318.15) K. It is established that the considered D2O-H2O enthalpy-isotopic effect exhibits a pronounced exothermic maximum between two sign-inversion points near 293 K and 318 K. The same goes the negative (up to similar to 305 K) solvent isotope effect (IE) in the partial molar heat capacity of HMTA in water. Such an unusual temperature-dependent behavior of the thermodynamic IEs points out the dualistic character of the HMTA hydration process which is dependent on the initial structure state of the solvent. (C) 2019 Elsevier B.V. All rights reserved.

The enthalpies of dissolution of propanol and butanol isomers in mixtures of water with methanol have been measured by the calorimetric method at 298 K and the enthalpies of solvation have been calculated over the entire composition range of mixed solvent. The enthalpy coefficients of methanol-alkanol pair interactions in water and the enthalpy coefficients of water-alkanol interactions in methanol have been computed. The influence of the composition of the mixture, structure and properties of the solutes on the enthalpy characteristics has been considered. The contributions of the structural fragments of alkanol molecules to the enthalpy characteristics of their solutions have been determined within the framework of the previously proposed additive scheme. It is allowed to quantitatively analyze the role of nonspecific and specific solvations of alkanols in solution. It has been shown that the features of solvation of propanol and butanol isomers in a water-methanol mixture are mainly determined by the contribution of specific solvation of hydroxyl groups associated with primary, secondary, and tertiary carbon atoms. (C) 2019 Elsevier B.V. All rights reserved.

Методами динамического светорассеяния и электронной спектроскопии поглощения изучены процессы агрегации и дезагрегации моно-, ди- и трикатионного хлоринов (соединения I—III) как потенциальных фотосенсибилизаторов (ФС) для фотодинамической терапии (ФДТ) в воде и водных растворах поливинилпирролидона (ПВП), определен средний размер частиц и характер их распределения. Образование наноагрегатов соединений I—III фиксируется при СФС в интервале 0.7—1.2 ммоль/кг, причем размер частиц увеличивается при хранении раствора. Распределение частиц дисперсной фазы по размерам имеет мономодальный характер только для ФС с более высокой растворимостью в воде. Минимальные добавки ПВП приводят к разрушению крупных (200—300 нм) агрегатов ФС; при этом, согласно спектрам поглощения, агрегаты небольшого размера не разрушаются полностью даже при 100-кратном мольном избытке полимерного ПАВ.