Thermochemistry of the Dissolution of Dipeptides Containing DL-α-Alanine in Aqueous Solutions of Sodium Dodecyl Sulfate at 298.15 K

Enthalpies of the dissolution of DL-α-alanylglycine (AlaGly), DL-α-alanyl-DL-α-alanine (AlaAla), DL-α-alanyl-DL-α-valine (AlaVal), and DL-α-alanyl-DL-norleucine (AlaNln) in an aqueous solution of sodium dodecyl sulfate (SDS) at SDS concentration of m = 0–0.07 mol kg^?1 and temperature Т = 298.15 K are measured via calorimetry. The standard values of the enthalpy of dissolution (Δ_solH ^m ) and the transfer of dipeptides (Δ_trH ^m ) from water to aqueous SDS solutions are calculated using the experimental data. The dependences of Δ_solH ^m and Δ_trH ^m the SDS concentration at a constant concentration of dipeptide are established. Thermochemical characteristics of the transfer of AlaGly, AlaAla, AlaVal, and AlaNln in the investigated range of SDS concentrations are compared. The results are interpreted by considering ion–ion, ion–polar, and hydrophobic–hydrophobic interactions between SDS and dipeptide molecules.     

Synthesis,Crystal Structures,and Biological Activity of Manganese(III) Complexes Derived from BIS-Schiff Bases

Two new manganese(III) complexes, [Mn^IIIL¹(Dca)(MeOH)] (I) and [Mn^IIIL₂(N₃)₂] (II), where L¹ and L² are the dianionic form of N,N'-3,4-chlorophenylene-bis(5-methylsalicylaldimine) (H₂L¹) and N,N'-3,4-nitrophenylene-bis(5-methylsalicylaldimine) (H₂L₂), respectively, and Dca is dicyanoamide, have been synthesized and characterized. The complexes were characterized by elemental analyses, IR, UV-Vis spectra, molar conductivity, and single crystal X-ray diffraction (CIF files nos. 1054200 (I), 1054336 (II)). The Mn atoms in the structures are in octahedral coordination. In the crystal structure of complex I, molecules are linked through intermolecular O–H···N hydrogen bonds to form 1D chains running along the x axis. In both complexes, there exist π···π interactions among molecules. The complexes and the Schiff bases were assayed for antibacterial activities against three Gram-positive bacterial strains (B. subtilis, S. aureus, and St. faecalis) and three Gram-negative bacterial strains (E. coli, P. aeruginosa, and E. cloacae) by MTT method.     

Thermodynamic characteristics of the dissolution of glycine,glycylglycine, and glycylglycylglycine in aqueous solutions of sodium dodecyl sulfate at <Emphasis Type="Italic">Т</Emphasis> = 298.15 K

the enthalpies of dissolution of glycine (Gly), glycylglycine (GlyGly), and glycylglycylglycine (GlyGlyGly) are measured in aqueous solutions of sodium dodecyl sulfate (SDS) at SDS concentrations m = 0–0.7 mol kg^?1 and Т = 298.15 K by means of calorimetry. The obtained data are used to calculate the standard values of enthalpies of dissolution (Δ_sol H ^m ) and enthalpies of transfer (Δ_tr H ^m ) of glycine and its oligomers from water to SDS aqueous solutions. The dependences of Δ_sol H ^m and Δ_tr H ^m on SDS concentration in an aqueous solution at a constant concentration of glycine and its oligomers are determined. A comparative analysis of the thermodynamic characteristics of Gly, GlyGly, and GlyGlyGly transfer within the studied range of SDS concentrations is performed. The results are interpreted in terms of ion–ion, ion–polar, and hydrophobic interactions between SDS and molecules of glycine and its oligomers.     

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.     

Synthesis and crystal structure of a new Schiff base ligand and its cobalt(II) complex

The crystal structures of cobalt(II) Schiff base complex (Co^IIL₂ · H₂O) and Schiff base ligand 3,5-dichlorosalicylidene-2-chlorophenylmethylamine (HL) have been determined by single-crystal X-ray analysis. The geometry around cobalt in Co^IIL₂ · H₂O is distorted tetrahedral. Co^IIL₂ · H₂O crystallizes in the monoclinic system, in space group C2/c, with crystallographic parameters: a = 12.9143(16) Å, b = 8.8326(16) Å, c = 25.115(3) Å, β = 92.791(10)°, V = 2861.4(7) ų, Z = 4, F(000) = 1420, and the final R indices (I > 2σ(I)) are R ₁ = 0.0440, wR ₂ = 0.1272. HL crystallizes in the monoclinic system, in space group P2₁/c, with crystallographic parameters: a = 11.9764(15), b = 8.2331(10), c = 14.2211(17) Å, β = 98.723(6)°, V = 1386.0(3) ų, Z = 4, F(000) = 640, and the final R indices (I > 2σ(I)) are R ₁ = 0.0397, wR ₂ = 0.1018.     

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.     

Syntheses,Structures, and Properties of Two Coordination Polymers Based on 2-Pyrimidineamidoxime

Two coordination polymers, {[Cd(L¹)₂(L₂)] · 0.25H₂O} _n (I) and {[Cd(L¹)(L₃)H₂O] · 2H₂O} _n (II) (L¹ = 2-pyrimidineamidoxime, L² = 4-sulfobenzoate dianion and L³ = 5-sulfosalicylate dianion), has been synthesized and structurally characterized by single-crystal X-ray diffraction (CIF files CCDC nos. 1565646 (I) and 1565728 (II)). Complex I crystallizes in monoclinic space group P2₁/n with a = 10.1462(3), b = 16.0152(5), c = 14.0349(5) Å, β = 93.267(3)°, V = 2276.87(13) ų, C₆₈H₆₆N₃₂O₂₉S₄Cd₄, M = 2373.36, ρ_calcd = 1.731 g/cm³, μ(MoK_α) = 1.109 mm^?1, F(000) = 1186, GOOF = 0.806, Z = 1, the final R¹ = 0.0287 and wR² = 0.0733 for I > 2σ(I). Complex II crystallizes in monoclinic space group P2₁ with a = 6.882(2), b = 17.138(2), c = 7.883(2) Å, β = 103.83(3)°, V = 902.8(4) ų, C₁₂H₁₆N₄O₁₀SCd, M = 520.75, ρ_calcd = 1.916 g/cm³, μ(MoK_α) = 1.388 mm^?1, F(000) = 520, GOOF = 1.047, Z = 2, the final R¹ = 0.0739 and wR² = 0.2041 for I > 2σ(I). Crystal structural analysis reveals that complex I possesses the corrugated 1D chain structure extending along the \([\bar 101]\) direction. However, complex II displays a 2D coordination network lying on the ab crystal plane, which can be simplified as a binodal 3-connected 6³ topological network by considering Cd²⁺ ions and L³ ligands as 3-connected nodes. Their photoluminescent and thermal properties were also investigated.     

Investigation of the Binding Properties of the Cosmetic Peptide Argireline and Its Derivatives Towards Copper(II) Ions

Isothermal titration calorimetry, potentiometric titration and circular dichroism spectroscopy were used to study the interaction of copper(II) ions with Argireline (Ac-Glu-Glu-Met-Gln-Arg-Arg-NH₂) and three of its point mutation derivatives: Glu-Ala-Met-Gln-Arg-Arg-NH₂ (AN1), Glu-Ala-His-Gln-Arg-Arg-NH₂ (AN2) and Glu-Ala-Met-Gln-Ala-Arg-NH₂ (AN3). Under the experimental conditions (20 mmol·L^?1 Caco solution, pH 6, 298.15 K), copper(II) ions form 1:1 complexes with the peptides Argireline, AN1, and AN2. The complexation reactions are entropy-driven processes. The stability of the resulting complexes increases in the order log₁₀K_Cu(AN1) < log₁₀K_{Cu(Argireline)} < log₁₀K_Cu(AN2). The relationship between the point mutations of Argireline and the binding properties of these peptides towards copper(II) ions is discussed.     

Synthesis and crystal structures of cobalt(III) and zinc(II) complexes with Schiff bases

Two new cobalt(III) and zinc(II) complexes, [Co(L¹)₂ (H₂O)] · ClO₄ (I) and [Ni(L²)₂ (H₂O)₂] · 2ClO₄ (II), where L¹ is the deprotonated form of 5-methoxy-2-[(2-morpholin-4-ylethylimino)methyl]phenol, and L² is the zwitterionic form of 2-[(2-isopropylaminoethylimino)methyl]-5-methoxyphenol, were synthesized and structurally characterized by elemental analyses, IR spectra, and single-crystal X-ray diffraction. The crystal of I is monoclinic: space group P2₁/c, a = 11.1512(4), b = 28.2424(11), c = 10.9655(4) Å, β = 95.746(2)°, V = 3436.1(2) ų, Z = 4. The crystal of II is triclinic: space group P2₁/c, a = 8.1441(2), b = 10.4531(3), c = 10.8849(3) Å, α = 84.0240(10)°, β = 76.9800(10)°, γ = 74.2280(10)°, V = 867.92(4) ų, Z = 1. Complex I consists of a mononuclear cobalt(III) complex cation and a perchlorate anion. Complex II consists of a crystallographic centrosymmetric mononuclear nickel(II) complex cation and two perchlorate anions. Each metal atom in the complexes is in an octahedral coordination.     

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.     

Spacer-armed binuclear copper(ii) complexes with salicylidene hydrazones of N-benzoylaminodicarboxylic acids

The structure and EPR spectra of copper(II) complexes with bis(salicylidene)hydrozones of N-benzoyl-L-aspartic and N-benzoyl-L-glutamic acids have been described. The compounds have been studied by chemical and thermal analyses, IR spectroscopy, and EPR spectroscopy. The molecular and crystal structure of the copper(II) complex with bis(salicylidene)hydrozone of N-benzoyl-L-aspartic acid (H₄L) of composition [Cu₂L · 2Py] · 2CH₃OH · H₂O has been determined by X-ray single-crystal diffraction. The crystals are monoclinic: a = 10.3316(7) Å, b = 16.7552(9) Å,c = 11.0137(6) Å, β = 105.758(3)°, space group P2₁, Z = 2. The complex has a polymeric structure composed of alternating copper-containing binuclear fragments bound to each other either via phenoxy bridges or via an aliphatic spacer (the Cu…Cu distances are 3.471 Å and 8.939 Å, respectively). The EPR spectra of the solutions of the complexes under study shows an isotropic signal comprising seven HFS lines due to two equivalent copper nuclei with the spin Hamiltonian parameters g = 2.115–2.122 and a _Cu = (36.1–36.9) × 10^?4 cm^?1, which indicates the reaization of weak exchange coupling of the paramagnetic centers.     

Laterally non-symmetric aza cryptand molecules stitched by water

Crystal structure of the compound L·4H₂O (L = aza cryptand) and its supramolecular assembly via H-bonding through water molecules are described here. The compound crystallizes in the cubic space group Pa3 (no. 205) with the following lattice parameters: a=b=c=19.023(2) Å, V=6883.9(4) Å³, Z=8, R ₁=0.0592, wR ₂ = 0.1572, S=0.964.     

Molecular dynamics simulations of the characteristics of sodium carboxymethyl cellulose with different degrees of substitution in a salt solution

Sodium carboxymethyl cellulose (SCMC) with different degrees of substitution (DS) possesses structural characteristics and physicochemical properties that are important in broad areas of industrial applications. This reported work investigated the structural characteristics, including the effective length (L _ef), the radius of gyration (R _g), and the hydrodynamic radius (R _H), and the physicochemical properties, including intrinsic viscosity ([η]) and salt tolerance, of SCMC with a DS more than 1.0 in NaCl solution using molecular dynamics (MD) simulations. In the MD simulations, the DS of SCMC varied from 1.2 to 2.8, and the NaCl concentration varied from 0 to 1.4 mol/L. MD simulation results showed that with the increment of NaCl concentration, the L _ef (or R _g or R _H) of SCMC decreased; with the increment of the DS, the L _ef of SCMC increased. Also, the variation tendency of [η] in the NaCl solution was consistent with its L _ef (or R _g or R _H). It was noted that the salt tolerance (represented by D) of SCMC increased as the DS increased. In addition, the sharp variation of the D value of SCMC occurred in the range of DS of 1.6 to 2.0, which agreed with the reported experimental results. Radial distribution function analyses showed that the Na⁺ cations had a stronger interaction with the carboxyl groups in SCMC with lower DS when it was present in a salt solution of higher concentration, which also reasonably explained the variation of L _ef, R _g, R _H, [η], and D of SCMC in NaCl solution.     

Structural features of monomeric octahedral <Emphasis Type="Italic">d</Emphasis><Superscript>2</Superscript>-rhenium(V) monooxo complexes with oxygen atoms of bidentate-chelating neutral and acidic ligands (O,P)

The structural features of 38 mononuclear d ²-Re(V) octahedral monooxo complexes (I–XXXVIII) with oxygen atoms of bidentate-chelating (O, P) ligands (L ⁿ ) are considered. The atoms O(L ⁿ ) are mostly in trans positions to O(oxo) ligands. In three compounds of general formula [ReO(L_mono)(L ⁿ )₂] (XXXVI–XXXVIII), the O atoms of two L ⁿ ligands occupy both trans and cis positions to oxo ligands. In one complex, namely, in [ReO(L ⁿ )(L _tri ¹¹ )], n = 3 (XXXV), the atom O(L³) is in the cis position to the oxo ligand; the trans position to O(oxo) is occupied by the atom O(L _tri ¹¹ ).     

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.     

Determination of thermal to epithermal neutron flux ratio (f), epithermal neutron flux shape factor (α) and comparator factor (F<Subscript>c</Subscript>) in the Triga Mark II reactor,Malaysia

The thermal to epithermal neutron flux ratio (f or Ø _th /Ø _e ), epithermal neutron flux shape factor (α) and comparator factor (F _c ) are essential parameters when calculating the concentration of sample using k ₀-standardization method in the neutron activation analysis (NAA). The work was performed in the Triga Mark II reactor of Malaysian Institute for Nuclear Technology Research (MINT) using Au/Zr monitor couple. Twenty channels in the reactor have been evaluated and the corresponding thermal to epithermal neutron flux ratios (f) ranged from 11.69 to 47.89. The epithermal neutron flux shape factors (α) were found in the range of ?1.50·10^?1 to 1.59·10^?1 and the comparator factors (F _c ) were calculated within the range of 9.85·10³ to 6.70·10⁴. These results allowed us to study the neutron flux distribution more precisely and established the goodness of fit for k ₀-NAA.     

Synthesis and crystal structure of <Emphasis Type="Italic">N,N</Emphasis>-dimethylbiguanidinium hexafluorosilicate

The complex [(CH₃)₂NC(NH₂)NHC(NH₂)NH₂]SiF₆ (I) was synthesized and its structure was determined by X-ray crystallography. The crystals are monoclinic: a = 7.4346(10) Å, b = 12.7628(10) Å, c = 11.0828(10) Å, β 104.080(10)°, V = 1020.01(18) ų, ρ_calc = 1.780 g/cm³, μ(MoK _α) = 0.302 mm^?1, Z = 4, space group P2₁/c. The crystals of I are composed of SiF ₆ ^2? anions (Si-F, 1.657(2)–1.699(2) Å) and N,N-dimethylbiguanidinium (H₂L²⁺) cations combined in a framework by interionic H-bonds NH···F. In the cations, protonation sites are the terminal imide groups.     

The thermodynamic properties of the [(Me<Subscript>3</Subscript>Si)<Subscript>7</Subscript>C<Subscript>60</Subscript>]<Subscript>2</Subscript> fullerene complex

The temperature dependence of the heat capacity C _p ^o of the [(Me₃Si)₇C₆₀]₂ fullerene complex was measured for the first time using precision adiabatic vacuum calorimetry over the temperature range 6.7–340 K and high-accuracy differential scanning calorimetry at 320–635 K. For the most part, the error in the C _p ^o values was about ±0.5%. An irreversible endothermic effect caused by the splitting of the dimeric bond between fullerene fragments and the thermal decomposition of the complex was observed at 448–570 K. The thermodynamic characteristics of this transformation were calculated and analyzed. Multifractal analysis of the low-temperature (T < 50 K) heat capacity was performed, and conclusions were drawn concerning the character of the heterodynamicity of the structure. The experimental data obtained were used to calculate the standard thermodynamic functions C _p ^o (T), H ^o (T) ? H ^o (0), S ^o (T) ? S ^o (0), and G ^o (T) ? H ^o (0) over the temperature range from T → 0 to 445 K and estimate the standard entropy of formation of the compound from simple substances at 298.15 K. The standard thermodynamic properties of [(Me₃Si)₇C₆₀]₂ are compared with those of the (C₆₀)₂ dimer, the [(η⁶-Ph₂)₂Cr]⁺[C₆₀]^?? fulleride, and the initial C₆₀ fullerene.     

Synthesis,characterization, and crystal structures of two Schiff base zinc(II) complexes with urease inhibitory activities

Two Schiff base zinc(II) complexes, [ZnBr₂L¹] · 2CH₃OH (I) (I) and [ZnBr₂L²] (II), where L¹ is 4-chloro-2-[(2-piperazin-1-ylethylimino)methyl]phenol and L² is 4-chloro-2-[(3-diethylaminopropylimino)methyl]phenol were synthesized and structurally characterized. The crystal of I is monoclinic: space group P2₁/c, a = 9.831(3), b = 18.680(6), c = 11.879(4) Å, β = 94.660(6)°, V = 2174.3(11) ų, Z = 4. The crystal of II is monoclinic: space group P2₁/n, a = 7.2310(14), b = 16.037(3), c = 15.856(3), β = 90.01(3)°, V = 1838.7(6) ų, Z = 4. The Zn atom in each complex is four-coordinated by one phenolate O and one imine N atoms of the Schiff base ligand and two bromide atoms, forming a tetrahedral coordination. The urease inhibitory activities of the complexes were evaluated.     

Binuclear copper(II) complexes with acyldihydrazones of <Emphasis Type="Italic">N</Emphasis>-benzenesulfonyl-<Emphasis Type="Italic">L</Emphasis>-aspartic acid

The structure and the EPR spectra of copper(II) coordination compounds with acyldihydrazones of N-benzenesulfonyl-L-aspartic acid and salicylaldehyde (2-hydroxyacetophenone) were described. The compounds were studied by chemical and thermal analyses, IR spectroscopy, and EPR. The molecular and crystal structures of copper(II) complexes with N-benzenesulfonyl-L-aspartic acid bis(salicylidene)hydrazone (H₄L¹) [Cu₂L¹ · 2Py] · 1.5 H₂O was determined by X-ray diffraction. The crystals are triclinic: a = 10.4714(4) Å, b = 12.9702(5) Å, c = 14.6187(9) Å, α = 104.763(2)°, β = 93.082(2)°, γ = 111.4240(10)°, space group P \(\bar 1\), Z = 2. The binuclear complexes containing copper cations whose coordination polyhedra are connected by an aliphatic spacer (Cu...Cu, 8.669 Å) are additionally linked by phenoxy bridges (Cu...Cu, 3.398 Å). The EPR spectra of these compounds in solutions exhibit an isotropic signal of seven HFS lines due to two equivalent copper ions with the spin Hamiltonian parameters g = 2.115?2.120, a _Cu = (35.5?38.0) × 10^?4 cm^?1, which is indicative of weak exchange interactions between the paramagnetic sites.