Data on the apparent and standard partial molar volumes, V empty set ,2 and V 2 o (equivalent to V phi , 2 infinity ), as well as the standard partial molar expansibilities, E p , 2 o , of N,N-dimethylglycoluril-N'-aminoisobutyric acid (DMGU-AIBA) in water were derived from density measurements of the corresponding aqueous solutions between 278.15 and 318.15 K and at ambient pressure. The uncertainty in density experiments did not exceed 0.10 kg m-3, and the solution molality for the aqueous DMGU-AIBA ranged from 0.002 to 0.06 molkg-1. Using the previously obtained results, it was established that the N'-alkyl-chain isomerization of N,N-dimethylglycoluril-aminobutyric acid (DMGU-ABA) as a solute in water, to form DMGU-AIBA, leads to squeezing of the structure packing of the formed "hydration complex". This effect, being increasingly pronounced with rising temperature, is supposed to be due to a change in the solute-solvent interaction balance, against the background of an increase in the effect of solvent electrostriction near the solute molecule. It was concluded that the decisive role in the hydration of amino acid glycoluril derivatives belongs to hydrophilic effects, associated mainly with heterocomponent interactions through proton-donating/-accepting pharmacophore moieties, despite partial dissociation of DMGU-AIBA and DMGU-ABA in the aqueous medium.

Densities of solutions of ordinary (H2O) and heavy (D2O) water in tetramethylurea (TMU) were measured with an uncertainty of ≤0.05 kg∙m−3 at T = (278.15, 288.15, 298.15, 308.15, and 318.15) K under ambient pressure using a precision densimeter equipped with the oscillating U-shaped tube. The solution molality, m, was ranged from (0.055 to 1.16) mol·(kg TMU)−1 in both H/D isotopically distinguishable water-containing systems. Standard molar volumes, V¯wo≡V¯w∞, and isobaric expansibilities, E¯p,wo≡E¯p,w∞, for H2O and D2O as solutes in TMU were computed. The temperature-dependent behavior of the solute D2O–H2O isotope effects (IEs) in the standard (partial) volume properties of water in TMU was discussed taking account of structure-packing and interaction-related peculiarities of the solvation complex formed. The factors influencing the structure state of water H/D isotopologues dissolved in TMU were considered. Attention was also paid to correlations between the currently available IEs of interest for water-containing aprotic protophilic media including TMU and some interaction-related properties of the latter.

As a first step to investigating the thermodynamic and physicochemical properties of previously unstudied aqueous solutions of N,N-dimethylthiourea (1,1-DMTU), precision data were obtained on the density of solutions for this “asymmetrically substituted” compound in water between (278.15 and 318.15) K, in 10 K increments, at the ambient pressure. Based on the results of density measurements, the temperature-dependent standard (partial at infinite dilution) molar volumes and expansibilities for 1,1-DMTM as a solute in water were calculated. Using the available literature data on the corresponding volume properties for the oxygen-containing counterpart, N,N-dimethylurea (1,1-DMU), in water, the influence of oxo→thioxo-substitution in 1,1-DMU, to form 1,1-DMTU, on the temperature-dependent structure-packing effects of the solute hydration was discussed. It was inferred that the effect of a slight increase in the free (excluded) volume or “loosening” of the structure packing of the hydration complex at the replacement of 1,1-DMU with 1,1-DMTM is in overall caused by a decrease in the thermal stability of the heterocomponent H-bonds formed. A non-trivial fact of the identity in changing at both oxo→thioxo-substitution in the isomeric N-dimethyl-substituted urea derivatives, and the corresponding equimolecular transfers from N(1,1)- to N(1,3)-methyl-containing ureas or thioureas in water was established. Also, the previously advanced assumption that each of functional >N(1)- and >N(3)-fragments bonded with the thiocarbonyl (>C=S)-group of the molecule of the thiourea alkyl-substituted derivative is solvated independently in water was confirmed, as in the similar case with the carbonyl (oxo-substituted) counterparts. For citation: Ivanov E.V. Influence of oxo→thioxo-substitution in molecules of N,N-dimethylurea as a solute in water on structure-packing hydration effects between (278.15 and 318.15) K. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2026. V. 69. N 8. P. 96-106. DOI: 10.6060/ivkkt.20266908.7085.

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.

Densities of water solutions in tert-butylamine (t-BuNH2) with the solute molality from ca. (0.015 to 0.35) mole (kg solvent)-1 were measured at six temperatures, from T = (278.15 to 303.15) K, and p similar to 0.1 MPa. The uncertainty in density measurements did not exceed 0.03 kg m(- 3). The standard (apparent at infinite dilution) molar volumes and expansibilities of water as a solute in t-BuNH2 were calculated. The origins for the phenomenon of the temperature-induced relative partial molar isobaric compaction of a solute (PMICS) in the system under study were discussed based on Ben-Naim's concept of the "relative affinity parameter".

We have examined the effect of the nitrogen oxide concentration on the ratio between λ557.7 nm and λ427.8 nm emission intensities in auroras caused by precipitating electron fluxes, using the numerical simulation method. The ratio I₅₅₇.₇/I₄₂₇.₈ has been shown to strongly depend on the NO concentration: the ratio decreases from 7 to 2 with increasing NO maximum concentration at the height profile from 10⁷ to 3·10⁹. This fact is in satisfactory agreement with experimental data.The effect of nitric oxide on the ratio has been demonstrated to occur through the excitation channel of the emission λ557.7 nm, namely, the dissociative recombination of the molecular oxygen ion O⁺₂+eₜₕ due to the ion deactivation by collision reaction with nitric oxide O⁺₂+NO.

We have examined the effect of the nitrogen oxide concentration on the ratio between lambda(557.7) nm and lambda 427.8 nm emission intensities in auroras caused by precipitating electron fluxes, using the numerical simulation method. The ratio I-557.7/I-427.8 has been shown to strongly depend on the NO concentration: the ratio decreases from 7 to 2 with increasing NO maximum concentration at the height profile from 10(7) to 3.10(9). This fact is in satisfactory agreement with experimental data. The effect of nitric oxide on the ratio has been demonstrated to occur through the excitation channel of the emission lambda 557.7 nm, namely, the dissociative recombination of the molecular oxygen ion O-2(+) e(th) due to the ion deactivation by collision reaction with nitric oxide O-2(+) NO.

Densities of dilute solutions of urea (U) in tert-butylamine (t-BuNH2) with molalities being up to similar to 0.023 molkg(-1) were measured at T = 278.15, 283.15, 288.15, 293.15, 298.15, and 303.15 K and p = 99.6 kPa. All experiments were carried out using a sealed U-tube vibrating densimeter. The total uncertainty in the density measurements did not exceed 0.03 kgm(-3). The standard (apparent at infinite dilution) molar volumes and expansibilities of U as a solute in t-BuNH2 were computed. Similar to infinitely dilute solutions of U in methanol (MeOH) and tert-butanol (t-BuOH), the phenomenon of the so-called "negative partial molar expansibility" or "partial molar isobaric compaction of a solute" was found in the studied binary system. The mixed structural aggregate or "solvation complex" formed by a U molecule in the t-BuNH2 medium becomes increasingly compact as the temperature rises because the solute-to-solvent affinity more and more noticeably prevails over the affinity of the solvent molecules for each other. In doing so, the stronger heterocomponent H-bonding leads to the marked increase in the compactness of solvation complexes formed in U solutions going from t-BuOH to t-BuNH2.

It has been shown that when drops fall on a solid surface, the physicochemical properties of water change. After drops fall on a solid surface, water saturated with atmospheric gases luminesces in the blue region of the spectrum. The luminescence intensity decreases exponentially after exposure. The concentration of gases (molecular oxygen and carbon dioxide) in water decreases. In this case, both the size and the number of nano-sized gas bubbles in the water do not change. It has been established that when drops fall on a solid surface in water saturated with atmospheric gases, hydrogen peroxide and hydroxyl radicals are formed. As the fall height increases, the intensity of generation of hydrogen peroxide and hydroxyl radical increases. The formation of hydrogen peroxide is probably associated with two independent mechanisms.

The electrical and luminescent characteristics of the heterostructure with a 20 nm-wide n-InAsSbP/n-InAs0.95Sb0.05/p-InAsSbP single quantum well, grown on an n-InAs substrate by the MOVPE method, have been studied. An intense room temperature electroluminescence (EL) with a maximum near the photon energy of 0.34 eV and a FWHM of 32 meV was discovered. It was established that the EL in such single quantum well has been emitted due to type I radiative transitions between the ground levels of electrons and holes both at forward and reverse bias. The characteristics of heterostructures with a single quantum well and the active region based on a bulk InAsSb layer of the same composition have been compared.

The detailed reply to brief comments by G.I. Egorov [J. Mol. Liq. 383 (2023) 122128] on our previous paper [J. Mol. Liq. 370 (2023) 121039] concerning the terminology of the phenomenon of relative partial isobaric compression of a solute (PICS) or its "negative partial molar expansibility" are contained in this short communication. The phrase "partial isobaric compression" has been justifiable renamed the partial molar isobaric compaction of a solute (PMICS). The origins for the phenomenon in question are also discussed here.

The data on density of dilute solutions of urea (U) in ethylene diamine (EDA) with the molality from similar to 0.018 to similar to 0.39 mol(kg solvent)-1 were experimentally obtained between (288.15 and 328.15) K and at ambient pressure. The uncertainty in density measurements did not exceed 0.03 kg m-3. The standard (partial at infinite dilution) molar volumes, V 2 circle, and expansibilities, E p,2 circle, of U as a solute in EDA were computed. The unusual phenomenon of the thermally activated partial molar isobaric compaction of the solute (PMICS) caused by the presence of a negative sign at E p,2 circle was discovered. The origin of this atypical volumetric effect in both the system under consideration and some other urea-containing amphiprotic media was discussed based on the thermodynamic approach including the Ben-Naim's concept of the "relative affinity parameter".

We propose a method for estimating average energy of precipitating electrons from 427.8 nm emission intensity measurements. This method is based on the experimental dependence of the ratio of λ630.0 and λ427.8 nm emission intensities on the λ427.8 emission intensity and model calculations of the dependence of the average auroral electron energy on the I₆₃₀.₀/I₄₂₇.₈ ratio. We present numerical estimates of the influence of three factors on this dependence: the shape of the auroral electron energy spectrum, the atomic oxygen concentration, and the NO concentration. The dependence of the average energy of the auroral electron flux on the 427.8 nm emission intensity is obtained and its analytical approximation is presented.

The results of theoretical and experimental studies of impact ionization processes and charge carrier heating in multi-valley AIIIBV semiconductors at high electric field are presented and their relationship with the features of the band structure is discussed. A role of subsidiary L- and X-valleys, complex structure of the valence band and orientation dependence of the ionization coefficients are taken into account. A new approach to the choice of semiconductor materials with a large ratio of the ionization coefficients of holes and electrons to create the noiseless avalanche photodiodes due to monopolarity of hot charge carrier multiplication is proposed.

Based on our own and some literature results, we have carried out a detailed analysis of concentration regions of the aqueous-organic mixture in which the temperature dependences of both excess molar heat capacity, CEp, and apparent molar heat capacity of each component, Cp,phi,i, are intersected. It is established that the partial differential CEp / partial differential T and partial differential Cp,phi,w/ partial differential T derivatives (W is water) for the {(W+ hexamethylphosphoramide (HMPA)} and {(W + tert-butanol (t- BuOH)} mixtures intersect in a rather narrow concentration interval between (0.30 and 0.35) and (0.35 and 0.40) mole fractions of the organic component, respectively. This fact we have interpreted as evidence that the decisive role in the mutually overlapping heat-capacity contributions to CEp resulting in such a situation plays the abnormal change in the isobaric molar heat capacity of W (Cp,w), which has a minimum at T approximate to 308 K, when the temperature increases.

It is shown that the efficiencies of excitation of optical emissions λ = 391.4, 557.7, and 630.0 nm and the efficiency of formation of the total electron density weakly depend on the shape of the energy spectrum of precipitating electrons and are mainly determined by the values of the average energy of the electron flux.

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.