Low-Temperature Heat Capacity and Glassy Behavior of Lysozyme Crystal^†

Heat capacities of tetragonal hen egg-white lysozyme crystals containing different amounts of water have been measured in the temperature region between 8 and 300 K. A broad glass transition was observed at about 150 K for the crystals with more than 24.0 wt % water content. These crystals also exhibited a spontaneous exothermic effect due to crystallization of the supercooled water contained in the crystals and melting process of the water above the glass transition temperature. The crystals containing 13.6 and 7.4 wt % of water gave rise to only a glass transition at 165 and 218 K, respectively. The fully dried crystal showed no thermal anomaly in the temperature up to 300 K. The amounts of the freezable and unfreezable water were estimated from the enthalpies of fusion of the crystal water. The water content dependence of the glass transition temperature and the magnitude of the excess heat capacity suggest that the observed glass transition arises from the cooperative motion between the segments of the lysozyme molecules and the bound water molecules

Mixing Schemes in a Urea−H₂O System: A Differential Approach in Solution Thermodynamics

The excess partial molar enthalpies of urea (UR), HURE, were experimentally determined in UR−H2O at 25 °C. The HURE data were determined accurately and in small increments in the mole fraction of UR, xUR, up to xUR ≈ 0.22. Hence it was possible to evaluate one more xUR-derivative graphically without resorting to any fitting function, and the model-free UR−UR enthalpic interaction, HUR−URE, was calculated. Using previous data for the excess chemical potential, μURE, the entropy analogue, SUR−URE, was also calculated. The xUR-dependences of both HUR−URE and SUR−URE indicate that there is a boundary at xUR ≈ 0.09 at which the aggregation nature of urea changes. From the results of our earlier works, we suggest that a few UR molecules aggregate at xUR ≈ 0.09, while the integrity of H2O is retained at least up to xUR ≈ 0.20. Together with the findings from our previous studies, we suggest that in the concentration range xUR < 0.22, UR or its aggregate form hydrogen bonds to the H2O network, reducing the degree of fluctuation characteristic to liquid H2O. However, up to at least xUR = 0.20 the hydrogen bond network remains intact. Above xUR ≈ 0.22, the integrity of H2O is likely be lost. Thus, in discussing the effect of urea on H2O and in relating it to the structure and function of biopolymers in aqueous solutions, the concentration region in question must be specified

Unexpected Rise of Glass Transition Temperature of Ice Crystallized from Antifreeze Protein Solution

Antifreeze protein (AFP) is known to bind to a single ice crystal composed of hexagonally arranged waters, hexagonal ice. To investigate the effect of the AFP binding to a general ice block that is an assembly of numerous hexagonal ice crystals, thermodynamic properties, dynamics, and the crystal structure of the ice block were examined in the presence of type I AFP (AFP-I). Previously, it was found that hexagonal ice has a glass transition based on the proton ordering in the ice lattice at low temperature. Measurements of heat capacity under adiabatic conditions, dielectric permittivity, and powder X-ray diffraction revealed that the glass transition occurs around 140 K in the ice containing 0.01–1% (w/w) of the AFP-I, which is greater than the value for the pure hexagonal ice (ca. 110 K). These data imply that AFP affects the glass transition kinetics, i.e., the slowness of the proton migration in the ice block. Hence, adsorption of AFP molecules to each hexagonal ice is thought to change the physicochemical properties of the bulk ice

Quantitative Analysis of Cs Extraction by Some Dialkoxycalix[4]Arene-Crown-6 Extractants

Cesium extraction from acidic media by seven dialkoxy-calix[4]arene-crown-6 compounds in several diluents was studied. 2-Nonanone was found to be a suitable diluent for cesium extraction. Nitric acid concentration variation reveals a maximum distribution ratio, whose position depends on extractant and diluent. This maximum was explained quantitatively by a competitive extraction of H+. An analytical mass-action extraction model accounting for activity effects is proposed that fits correctly the different datasets. The analysis showed a nitrate hyper-stoichiometry in alkyl ketone diluents. This effect yields efficient back-extraction at low acidity. Benzo substitution on the crown ether lowers nitric acid extraction, improves sodium separation, but also degrades potassium and rubidium separation.</p

Effects of Carboxylate Anions on the Molecular Organization of H₂O as Probed by 1-Propanol

We characterized the effects of carboxylate anions, formate (OFm^–), acetate (OAc^–), and propionate (OPr^–), on the molecular organization of liquid H₂O by the 1-propanol (1P) probing methodology. The latter thermodynamic methodology provides two indices: one pertaining to the hydration number, <i>n</i>_H, and the other being related to the net increase/decrease of the entropy–volume cross fluctuation of the system. The results indicated that OFm^– is a hydration center with <i>n</i>_H = 1.2 ± 0.5 and leaves the bulk H₂O away from the hydration shell unperturbed. We suggest that this single H₂O hydrates preferentially one of the O’s in the COO^– group, showing the hydration center character. The values of <i>n</i>_H for OAc^– and OPr^– were found to be 3.7 ± 0.8 and 9 ± 2, respectively, out of which one H₂O molecule is used for hydrating the COO^– side and the remaining 2.7 and 8 H₂O molecules hydrate the respective alkyl group. Hence, OPr^– is more hydrophobic than OAc^– in terms of the hydration number. However, both alkyl moieties seem to equally retard the hydrogen bond probability of bulk H₂O away from hydration shells around nonpolar sites, as much as the probing 1P does

Gene expression profile of <i>zeitlupe/lov kelch protein1</i> T-DNA insertion mutants in <i>Arabidopsis thaliana</i>: Downregulation of auxin-inducible genes in hypocotyls

<p>Elongation of hypocotyl cells has been studied as a model for elucidating the contribution of cellular expansion to plant organ growth. ZEITLUPE (ZTL) or LOV KELCH PROTEIN1 (LKP1) is a positive regulator of warmth-induced hypocotyl elongation under white light in <i>Arabidopsis</i>, although the molecular mechanisms by which it promotes hypocotyl cell elongation remain unknown. Microarray analysis showed that 134 genes were upregulated and 204 genes including 15 auxin-inducible genes were downregulated in the seedlings of 2 <i>ztl</i> T-DNA insertion mutants grown under warm conditions with continuous white light. Application of a polar auxin transport inhibitor, an auxin antagonist or an auxin biosynthesis inhibitor inhibited hypocotyl elongation of control seedlings to the level observed with the <i>ztl</i> mutant. Our data suggest the involvement of auxin and auxin-inducible genes in ZTL-mediated hypocotyl elongation.</p

Magnetostructural Study of 2-(4-<i>N</i>-<i>tert</i>-Butylaminoxylphenyl)benzimidazole

The heat capacity of the title organic free radical, PhBABI, was measured over 0.3−300 K by adiabatic calorimetry and relaxation methods in the presence of external magnetic fields up to 9 T. A hump in the magnetic heat capacity was observed with a maximum at about 15 K in zero field, which did not shift at fields up to 9 T. The experimental magnetic entropy was in good agreement with the theoretical value of R ln 2 (= 5.76 J K−1 mol−1) for S = 1/2 systems. The higher temperature, field-insensitive feature was fitted to several antiferromagnetic Heisenberg models. The best fits were obtained using spin ladder and coupled spin bilayer models

Lanthanide Intra-series Separation by a 1,10-Phenanthroline Derivative: Counterion Effect

The demand for rare earths is expected to keep increasing throughout the following years. Separation of lanthanides in particular is especially challenging because of their chemical similarities. Therefore, improving the separation process is essential. In this work, we present the effect of the counterion nature on the lanthanide extraction by a 1,10-phenanthroline derivative, the N-octyl-N-tolyl-1,10-phenanthroline-2-carboxamide in chloroform. Modification of the counterion yields a drastic change in selectivity, with a shift in the maximum of extraction from the light lanthanides (Pr, Nd, Sm) in the nitrate system to the heavy lanthanides (Dy, Ho) in the perchlorate system. Other salts (NaCl, NaNO2) showed a gradual increase in extraction along the whole lanthanide series or no effect (Na2SO4). This selectivity shift was explained by possible different coordination in the organic phase. The reversed behavior depending on the anion is especially interesting because a cycling extraction/back-extraction of light lanthanides in nitrate/chloride media or a cycling extraction/back-extraction of heavy lanthanides in perchlorate/nitrate media can enhance the separation factors of Nd and Dy/Ho, respectively.</p

Heat Capacities of the <i>S</i> = ¹/₂ Two-Dimensional Heisenberg Antiferromagnet Bis(2-amino-5-chloropyridinium) Tetrabromocuprate(II) [(5CAP)₂CuBr₄] and Its Diamagnetic Analogue [(5CAP)₂ZnBr₄]^‖

Heat capacities of the spin quantum number S = 1/2 two-dimensional Heisenberg antiferromagnet bis(2-amino-5-chloropyridinium) tetrabromocuprate(II) [(5CAP)2CuBr4] crystal and its nonmagnetic analogue, the bis(2-amino-5-chloropyridinium) tetrabromozincate(II) [(5CAP)2ZnBr4] crystal, were measured by adiabatic calorimetry. For the (5CAP)2ZnBr4 crystal, single-crystal X-ray diffraction was also performed. The (5CAP)2ZnBr4 crystal belongs to the orthorhombic space group Pbca, with a = 16.074(2) Å, b = 7.688(2) Å, c = 30.538(6) Å, and Z = 8. In the (5CAP)2CuBr4 crystal, an antiferromagnetic phase transition occurred at TN = 5.08 K, and a thermal anomaly arising from the short-range order characteristic of two-dimensional magnetic substances was found above TN; the heat capacity of the (5CAP)2ZnBr4 crystal showed no thermal anomaly. The enthalpy and entropy gains due to the magnetic transition were estimated to be 49.3 J mol-1 and 5.65 J K-1 mol-1, respectively. The value of the entropy gain coincides well with the R ln 2 (5.76 J K-1 mol-1, R stands for the gas constant) expected for S = 1/2 spin systems. The thermal anomaly observed above TN is well accounted for in terms of the S = 1/2 two-dimensional antiferromagneic Heisenberg model of a square lattice with J/kB = −4.3 K. Spin wave analysis of the magnetic heat capacities below TN suggests that the (5CAP)2CuBr4 crystal is in a three-dimensional antiferromagnetic state, which is realized by a weak interlayer magnetic interaction between the two-dimensional layers

2-(4,5,6,7-Tetrafluorobenzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1- <i>H</i>-imidazole-3-oxide-1-oxyl, A Hydrogen-Bonded Organic Quasi-1D Ferromagnet

The title radical (F4BImNN) is a stable nitronylnitroxide that forms hydrogen-bonded NH···ON chains in the solid state. The chains assemble the F4BImNN molecules to form stacked contacts between the radical groups, in a geometry that is expected to exhibit ferromagnetic (FM) exchange based on spin polarization (SP) models. The experimental magnetic susceptibility of F4BImNN confirms the expectation, showing 1-D Heisenberg chain FM exchange behavior over 1.8−300 K with an intrachain exchange constant of Jchain/k = +22 K. At lower temperatures, ac magnetic susceptibility and variable field heat capacity measurements show that F4BImNN acts as a quasi-1-D ferromagnet. The dominant ferromagnetic exchange interaction is attributable to overlap between spin orbitals of molecules within the hydrogen-bonded chains, consistent with the SP model expectations. The chains appear to be antiferromagnetically exchange coupled, giving cusps in the ac susceptibility and zero field heat capacity at lower temperatures. The results indicate that the sample orders magnetically at about 0.7 K. The magnetic heat capacity ordering cusp shifts to lower temperatures as external magnetic field increases, consistent with forming a bulk antiferromagnetic phase below a Néel temperature of TN(0) = 0.72 K, with a critical field of Hc ≈ 1800 Oe. The interchain exchange is estimated to be zJ/k ≅ (−)0.1 K