Spin-lattice relaxations study of water mobility in natural natrolite

The mobility of water molecules in natural natrolite (Na₂Al₂Si₃O₁₀?2H₂O) is investigated by the ¹H NMR method. The spin-lattice relaxation times in the laboratory and rotating frames (T₁ and T_1ρ) are measured as a function of the temperature for a polycrystalline sample. From experimental T₁ data it follows that at T > 286 K the diffusion of water molecules along channels parallel to the c axis is observed. From experimental T_1ρ data it follows that at T > 250 K the diffusion of water molecules in transversal channels of natrolite is also observed. At a low temperature (T < 250 K) the dipolar interaction with paramagnetic impurities (presumably Fe³⁺ ions) becomes significant as a relaxation mechanism of ¹H nuclei.     

Excited States of Weak Interacting Complexes of Formaldehyde and Alkali Metal Ions

The electronically excited states of formaldehyde and its complexes with alkali metal ions are investigated with the time-dependent density functional theory (TD DFT) method. Vertical transition energies for several singlet and triplet excited states, adiabatic transition energies for the first singlet and triplet excited states S₁ and T₁, the adiabatic geometries and vibrational frequencies of the ground state S₀ and the first singlet and triplet excited states S₁ and T₁ for formaldehyde and its complexes are calculated. Better agreement with the experiment than that of the CIS method is obtained for CH₂O at the TD DFT level. The nonlinear C=O?M⁺ interaction in the excited states S₁ and T₁ is weaker than the linear interaction in the ground state. In the S₀ and S₁ states, the C=O bond is elongated by cation complexation and its stretching frequency is red-shifted, but in the T₁ state the C=O bond is shortened and its frequency is blue-shifted.     

Compositions and structures of nanoparticles of pentagonal axial symmetry <Emphasis Type="Italic">D</Emphasis><Subscript>5<Emphasis Type="Italic">d</Emphasis></Subscript>: Nanotubes

The method of determination of the structure and the number of atoms in the shells of nanoparticles as a function of the arrangement of atoms at the symmetry elements of a symmetry group has been developed. The formulas for the calculation of the number of particles with symmetry group D _5d are reported. The number of particles in these shells is determined by three structurally invariant numbers and the “quantum number” of the group order n. The classification of all possible nanostructures with symmetry group D _5d is given: C _θ+10z , z = 0, 1, 2, …, where the basic shells are C _θ = C ₂, C ₁₀, C ₁₂. The sum rule has been obtained for the coordination numbers of shell sites located at symmetry axes. Pentagonal axial nanoparticles are shown to be the initial shells for obtaining (5,5) and (10,10) armchair nanotubes or (5,0) and (10,0) zigzag nanotubes. The general formula of these nanotubes closed with icosahedral and dodecahedral caps is N _20+10p , N _60+10p (p = 1, 2, …). The graphical constructions of all classes of nanoparticles and nanotubes of the pentagonal axial type are reported.     

Numerical Calculation of Permittivity and Dielectric Loss of Aqueous KF Solution Depending on State Parameters

Based on the analytical expressions for permittivity ε₁(ω) and dielectric loss ε₂(ω) are obtained by the kinetic equation method, the frequency spectra of these coefficients are analyzed for an aqueous KF solution in a wide variation range of the density ρ, the concentration C, and the temperature T. With a certain choice of the solution model, the potential interaction energy Φab(|r|), and the radial distribution function g_ab(|r|) of a- and b-type ions, ε₁(ω) and ε₂(ω) of an aqueous KF solution are numerically calculated depending on ρ, C, T, and ω.     

Properties of solvate shells and the mobility of ions,according to molecular dynamics data

The solvate shells of an ion, its velocity autocorrelation function, and diffusion coefficient D are found, and the interrelations between them are analyzed. A single ion in the system of atoms of a liquid is considered a model system. The interaction between the ion and atoms of the liquid is described by polarization potential U(r); the interaction between atoms of the liquid alone is described by the Lennard–Jones potential. A classical molecular dynamics method is used. Five solvate shells around the ion are found, and the lifetimes of atoms on each shell are calculated. It is found that the velocity autocorrelation function is of a vibrating nature. The spectrum of the autocorrelator and the frequency of cluster vibrations in a linear approximation are compared. Dependences D on parameters of potential U(r) are found. No dependence D on the ion mass is found; this is explained by solvation. The Einstein–Stokes formula and the HSK approximation are used in discussing the results. It is shown that at small radii of the ion, dependence D on parameters U(r) is described by such a model. When the ion radius is increased, the deviation from this dependence and an increase in D are observed. The results are compared to experimental mobilities of O₂^- and Ar₂⁺ ions in liquid argon.     

Concentration,temperature, and isotopy effects on the heat capacity of aqueous urea

Relations for the apparent molar heat capacity ?_c of urea in an aqueous solution depending on the molality m and temperature were obtained. A transition to the relations ?_c(m,T) for D₂O-(ND₂)₂CO and T₂O-(NT₂)₂CO systems was effected by temperature scaling. At low temperatures, the isotherms of the molar heat capacity C _p(m) of the protium and deuterium systems have minima shifted to more dilute solutions at elevated temperatures. At m = 1, C _p of a solution does not depend on temperature in both systems. The dependences C _p(T) also have minima at constant concentrations. The temperature of the minimum heat capacity is most effectively lowered by small additions of urea. For m = 0.25, T _min is 7.5 K lower than T _min of pure water, and its heat capacity is 0.08 J/(mol K) higher. A transition from m = 1.5 to m = 2 lowers the temperature of the minimum heat capacity by 3.6 K; thus, the heat capacity of solutions differs by 0.02 J/(mol K) only.     

Analysis and characterization of the transition from the Arrhenius to non-Arrhenius structural relaxation in fragile glass-forming liquids

We have studied the transition from an Arrhenius-like to a non-Arrhenius-like structural relaxation behavior in fragile glass-forming liquids. This transition is denoted by the temperature T_A that usually occurs above the melting point T_m and the dynamic crossover temperature T_B. Recent studies reveal that T_A is a characteristic temperature related with the dynamical properties of the system. However, its unambiguous determination is not easy. In this work, a method to obtain the temperature T_A from the experimental data of α-relaxation time is presented. The obtained T_A is compared with the cooperativity onset temperature T_x extracted from the bond strength–coordination number fluctuation model. The result reveals that T_A is close to T_x for fragile liquids. From the result of the present analyses combined with the linear relation T_x \(\propto\) T₀, where T₀ is the Vogel temperature, the Arrhenius crossover phenomenon in fragile liquids is linked to the low-temperature structural relaxation dynamics.     

The thermal properties of water-n,n-dimethylformamide solutions at 278–323.15 K and 0.1–100 MPa

The isothermal compressibility coefficients κ _T , volumetric thermal expansion coefficients α, and pressure coefficients (?p/?T) _v were calculated for water-N,N-dimethylformamide (DMFA) mixtures of 12 compositions over the temperature and pressure ranges 278–323.15 K and 0.1–100 MPa. The composition dependences of κ _T passed minima, and the corresponding α and (?p/?T) _v dependences passed maxima. The structural features of water and hydrophobic hydration effects were found to play a determining role in changes in the thermodynamic properties of water-DMFA solutions.     

Structure and dynamics of a free aquaporin (AQP1) by a coarse-grained Monte Carlo simulation

Structure and dynamics of a free aquaporin (AQP1) are studied by a coarse-grained Monte Carlo simulation as a function of temperature using a phenomenological potential with the input of a knowledge-based residue–residue interaction. Response of the radius of gyration (R _g) of the protein to the temperature (T) is found to be nonlinear: Decay of R _g at T ≤ T _c is followed by a continuous increase at T ≥ T _c before reaching its saturation. In thermo-responsive regime, the protein exhibits segmental globularization with the persistence of three regions along its sequence involving residues ¹M–²⁵V and ²⁵⁰V–²⁶⁹K toward the beginning and end segments with a narrow intermediate region around ¹⁵⁵A–¹⁶³D. A detail analysis of the structure factor S(q) shows a global random coil conformation at high temperatures with an effective dimension D _e ~ 1.74 and a globular structure (D _e ~ 3) at low temperatures. In thermo-responsive regime, the variation of S(q) with the wave vector q reveals a systematic redistribution of self-organizing residues (in globular and fibrous sections) that depends on the length scale and the temperature.     

Differential thermogravimetric curves for a mixture of evaporable and degradable chain oligomers

Since the boiling point of oligomers increases with increasing chain length, differential thermogravimetric (DTG) curves of polymerization products are uniquely related to the molecular mass distribution of the oligomers in the chain length region in which the degradation rate is less than the rate of evaporation. Degradation is manifested by narrow, chain length-invariant peaks of the DTG curves so that they are distinguishable from broad DTG bands due to the evaporation of the mixture of oligomers. The detachment of the terminal groups at a temperature T₁ and main chain scission at T_d > T₁ are accompanied by dimerization of macroradicals, evaporation of the dimers in the T₁ < T < T_d interval, and appearance of the full degradation peak at T ≈ T_d. The pattern of DTG curves based on these concepts has been calculated on the assumption of free convection in the boundary layer and a spatially uniform degradation in the melt. As an example, DTG curves for the products of tetrafluoroethylene polymerization in liquid solutions have been considered.     

Estimation of boiling points of organic compounds at various pressures using recurrent relations

A new approach is proposed for the estimation of boiling points (T _b) of organic compounds at reduced pressure from their values at atmospheric pressure based on the application of a recurrent relation: T _b (log P + Δlog P) = aT _b (log P) + b. Estimation of coefficients in this relation for the compounds different by their chemical nature gives the following average values: a = 1.126, b = ?41.7. Successive application of this relation with Δlog P = 1 (that corresponds to 10-fold decrease in pressure) allows estimation of the T _b values at the pressure values of 100, 10 and 1 torr from the value of T _b (760 torr) by simple arithmetic calculation with an average accuracy about 8°C.     

Computer Simulation of the Cathode Active Layer in Hydrogen–Oxygen Fuel Cell with Polymer Electrolyte: The Nature of the Overall Current Variations

Full computer simulation of the cathode structure in hydrogen–oxygen fuel cell with polymer electrolyte is performed. Both transport, support grains (agglomerates of carbon particles onto whose surface Pt-catalyst is deposited), and the current generation in active layer are simulated. The active layer operation in potentiostatic mode is studied. The effect of variations of the active layer and the fuel cell temperature (T_s and Т, respectively) on the cathode overall current I and the support grain flooding with water is calculated. The changes in the temperature difference T_s–Т was shown for the first time, experimentally and by the simulation, to generate variations of I and the degree of the support grain flooding with water. In particular, with the increasing of T_s–Т the current I increased, whereas the support grain flooding with water decreased; and vice versa, with the decreasing of T_s–Т the current I drops down, while, the support grain flooding with water grows. An explanation of the phenomena is presented, which takes account of structure of the support grains in which О₂ reduction and Н₂О generation occur. There exist intrinsic channels for protons and О₂ molecules transportation to the catalyst. Water releasing in the support grains is able to fill partially or even entirely the gas pores through which oxygen is supplied to the platinum. As a result, the current generated in the support grains can drop down significantly; at the same time, the value of I also drops down. The degree of the support grainfilling with water is determined by two processes, namely, the flooding and draining. The source of flooding is the current generation; that of draining, the water saturated vapor diffusion and water filtration in nanopores. The lower cathode potential, the higher the flooding rate, whereas the water removal rate grows or drops down with the increasing of decreasing of the temperature difference Т_s–Т, respectively. Thus, the temperature difference variations naturally lead to those of the quantity I.     

A comparison of energy changes accompanying growth processes by <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

Calculations are made using the equations Δ_r G = Δ_r H ? TΔ_r S and Δ_r X = Δ_r H ? Δ_r Q where Δ_r X represents the free energy change when the exchange of absorbed thermal energy with the environment is represented by Δ_r Q. The symbol Q has traditionally represented absorbed heat. However, here it is used specifically to represent the enthalpy listed in tabulations of thermodynamic properties as (H _T  ? H ₀) at T = 298.15 K, the reason being that for a given substance TS equals 2.0 Q for solid substances, with the difference being greater for liquids, and especially gases. Since Δ_r H can be measured, and is tangibly the same no matter what thermodynamics are used to describe a reaction equation, a change in the absorbed heat of a biochemical growth process system as represented by either Δ_r Q or TΔ_r S would be expected to result in a different calculated value for the free energy change. Calculations of changes in thermodynamic properties are made which accompany anabolism; the formation of anabolic, organic by-products; catabolism; metabolism; and their respective non-conservative reactions; for the growth of Saccharomyces cerevisiae using four growth process systems. The result is that there is only about a 1% difference in the average quantity of free energy conserved during growth using either Eq. 1 or 2. This is because although values of TΔ_r S and Δ_r Q can be markedly different when compared to one another, these differences are small when compared to the value for Δ_r G or Δ_r X.     

Thermoresponsive behavior of water-salt solutions of a graft copolymer with a main polyimide chain and side poly(<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylamino-2-ethyl methacrylate) side chains

The water-salt solutions of the graft copolymer bearing a polyimide main chain and poly(N,N-dimethylamino-2-ethyl methacrylate) side chains (M = 4.7 × 10⁵, the density of grafting with side chains z = 0.44) are studied by static and dynamic light scattering and turbidimetry. The solutions are investigated in a tenfold range of NaCl concentrations (from 0.015 to 0.15 mol/L) at the polymer concentration from 0.002 to 0.015 g/cm³ and pH from 8 to 12. The temperature dependences of the intensity of scattered light, optical transmission, hydrodynamic radius of scattering objects, and their concentrations in solutions are derived. The temperatures of phase separation onset T ₁ and end T ₂ are determined. It is shown that an increase in the salt content in solution leads to reduction in the polymer solubility and in temperatures T ₁ and T ₂. The watersalt solutions retain all the regularities of phase-separation temperature variation observed for aqueous solutions with change in the concentration of solution and pH of a medium: the values of T ₁ and T ₂ increase upon dilution and growth of acidity.     

Method for calculating the sizes of nucleation centers upon homogeneous crystallization from a supercooled liquid

An alternative approach to calculating critical sizes l_k of nucleation centers and work A_k of their formation upon crystallization from a supercooled melt by analyzing the variation in the Gibbs energy during the phase transformation is considered. Unlike the classical variant, it is proposed that the transformation entropy be associated not with melting temperature T_L but with temperature T < T_L at which the nucleation of crystals occurs. New equations for l_k and A_k are derived. Based on the results from calculating these quantities for a series of compounds, it is shown that this approach is unbiased and it is possible to eliminate known conflicts in analyzing these parameters in the classical interpretation.     

Influence of sodium dodecyl sulfate on the phase transition of thermoresponsive hyperbranched polymer in water

The influence of sodium dodecyl sulfate(SDS) on the cloud point temperature(Tcp) of the aqueous solution of thermoresponsive hyperbranched polyethylenimine derivative HPEI-IBAm was studied systematically. When p H was below 8.5, HPEI-IBAm was positively-charged. Initially, the Tcp of HPEI-IBAm decreased significantly, followed by an obvious increase with the increase of SDS concentration. The lower the p H was, the higher the SDS concentration was required to achieve the minimum Tcp. When p H was above 8.5, HPEI-IBAm was neutral and raising the SDS concentration led to the gradual increase of Tcp. Compared to linear poly(N-isopropyl acrylamide)(PNIPAm), the Tcp of the current hyperbranched HPEI-IBAm was more sensitive to SDS. The thermoresponsive HPEI-IBAm/SDS complex was used as host to accommodate the non-polar pyrene in water. The lowest SDS concentration for effectively enhancing the solubility of pyrene in water was around 6.4 mmol·L~(-1). When HPEI-IBAm was present, the SDS concentration threshhold was decreased to about 0.31 mmol·L~(-1). Fluorescence technique with pyrene as the hydrophobic probe demonstrated that the SDS concentration of 7.2 mmol·L~(-1) was required to form the hydrophobic domain to accommodate pyrene guests without HPEI-IBAm, while only 0.2 mmol·L~(-1) of SDS was required in the presence of HPEI-IBAm.     

Dielectric properties of films of Ag-ED20 epoxy nanocomposite synthesized in situ. Temperature dependence of direct current conductivity

The influence of silver myristate used as a precursor of silver nanoparticles on the direct current conductivity σ _dc of epoxy polymer within the concentration range of ≤0.8 wt % was investigated. The value of direct current conductivity was determined on the basis of analysis of the frequency dependence of complex permittivity within the frequency range of 10^?2–10⁵ Hz. The temperature dependence of σ _dc is composed of two regions. The dependence corresponds to the Vogel-Fulcher-Tammann empirical law σ _dc = σ _dc0exp{?DT ₀/(T-T ₀)} (where T ₀ is the Vogel temperature and D is the strength parameter) at temperatures higher than the glass transition temperature T _g. At the same time, T ₀ does not depend on the concentration of nanoparticles. The Arrhenius temperature dependence characterized by activation energy about 1.2 eV is observed at temperatures lower than T _g. The observed shape of the temperature dependence is related to the change in the mechanism of conductivity after “freezing” of ionic mobility at temperatures lower than T _g. The value of σ _dc is increased as the concentration of nanoparticles is raised within the temperature range of T > T _g. The obtained dependence of σ _dc on silver myristate concentration is similar to the root one, indicating the absence of percolation within the studied range of concentrations.     

Apparent Molar Volumes of Aqueous Solutions of Magnesium Tetraborate from 283.15 to 363.15 K and 0.1 MPa

Densities for aqueous solutions of magnesium tetraborate MgB₄O₇(aq) at the molalities of (0.00556–0.03341) mol·kg^?1 were measured with an Anton Paar Digital vibrating-tube densimeter at temperature intervals of 5 K from 283.15 to 363.15 K and 0.1 MPa. Apparent molar volumes were obtained based on the experimental density data, and the 3D diagrams of the apparent molar volume (V _? ) of MgB₄O₇(aq) against temperature (T) and molality (m) were plotted. On the basis of the Vogel–Tamman–Fulcher equation, the coefficients of the correlation equation for densities of MgB₄O₇(aq) against temperature and molality were parameterized. According to the Pitzer ion-interaction model of the apparent molar volume, the temperature correlation equations of Pitzer single-salt parameters F(i,p,T)?=?a₀?+?a₁?×?T?+?a₂?×?T ²?+?a₃/T?+?a₄?×?ln(T)?+?a₅?×?T ³ (where T is temperature in Kelvin, a _i are model parameters) for MgB₄O₇ were obtained for the first time.     

On hydrolysis of Ba–Bi–O and K–Ba–Bi–O oxide systems

Fundamentally different behavior of Ba–Bi–O (Ba : Bi = 11 : 4, 1 : 1, 2: 3, and 1 : 5 mol/mol) and K_nBa_mBi_m+nO_y (m = n = 1, 2,...; exhibiting superconducting properties with T_c = 28–32 K) oxides and BaO₂ in hydrolysis reactions has been revealed by means of potentiometry and chemical analysis. Products of the oxides treatment with water do not contain H₂O₂, evidencing the absence of peroxide ions in their structure. The perovskite-type barium-bismuth(III) oxides are completely hydrolyzed into Ba(OH)₂ and Bi₂O₃ at room temperature.     

Molecular Dynamics Study on Carbon Dioxide Absorbed Potassium Glycinate Aqueous Solution

Molecular dynamics (MD) simulations have been performed to investigate the effects on structure, transport properties, and dynamical properties in the potassium glycinate aqueous solution caused by carbon dioxide (CO₂) absorption. The optimized structure and charges of constituents of the solution, such as the glycine zwitterion, have been determined by Gaussian09 using the density functional theory. The obtained pair distribution functions, g _ij (r)’s, show the significant distribution difference of bicarbonate ion, \({\text{HCO}}_{3}^{ - }\), around the glycine anion and glycine zwitterion. The shear viscosity and diffusion coefficient obtained by MD show different CO₂ concentration dependences. The frequency dependent diffusion coefficient D _i (ν) for N and C in glycine ions are mainly influenced by the cage effect of surrounding water molecules, whereas D _i (ν) for H show the characteristic vibration due to the structure difference of the glycine ions.