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

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

An Enantiopair of Organic Ferromagnet Crystals Based on Helical Molecular Packing of Achiral Organic Radicals

We report the ferromagnetic ordering phenomena occurring in organic molecular crystals with structural chirality. Achiral radical <b>1</b> has been found to crystallize in two enantiomorphs with chiral space groups of <i>P</i>4₃ and <i>P</i>4₁. The <i>P</i>4₃ form (<b>1L</b>) has left-handed stacking of the molecules, giving the helical chirality in a crystalline solid. In the other form of <i>P</i>4₁ (<b>1R</b>), the right-handed stacking corresponds to a mirror image of <b>1L</b>. Magnetic susceptibility measurements show that both the crystals undergo a ferromagnetic phase transition at <i>T</i>_C = 1.1 K. The ferromagnetic ordering has been confirmed by heat capacity measurements. The magnetic heat capacity exhibits a λ-shaped peak at <i>T</i>_C = 1.1 K with an entropy change of <i>R </i>ln 2, as expected for <i>S</i> = 1/2 spins. This is the first example of genuinely organic molecule-based ferromagnetism associated with the structural chirality based on the helical molecular packing in the crystalline solid

An Enantiopair of Organic Ferromagnet Crystals Based on Helical Molecular Packing of Achiral Organic Radicals

We report the ferromagnetic ordering phenomena occurring in organic molecular crystals with structural chirality. Achiral radical <b>1</b> has been found to crystallize in two enantiomorphs with chiral space groups of <i>P</i>4₃ and <i>P</i>4₁. The <i>P</i>4₃ form (<b>1L</b>) has left-handed stacking of the molecules, giving the helical chirality in a crystalline solid. In the other form of <i>P</i>4₁ (<b>1R</b>), the right-handed stacking corresponds to a mirror image of <b>1L</b>. Magnetic susceptibility measurements show that both the crystals undergo a ferromagnetic phase transition at <i>T</i>_C = 1.1 K. The ferromagnetic ordering has been confirmed by heat capacity measurements. The magnetic heat capacity exhibits a λ-shaped peak at <i>T</i>_C = 1.1 K with an entropy change of <i>R </i>ln 2, as expected for <i>S</i> = 1/2 spins. This is the first example of genuinely organic molecule-based ferromagnetism associated with the structural chirality based on the helical molecular packing in the crystalline solid

Multifunctional One-Dimensional Rhodium(I)–Semiquinonato Complex: Substituent Effects on Crystal Structures and Solid-State Properties

Two new one-dimensional (1D) rhodium­(I)–semiquinonato complexes formulated as [Rh­(3,6-DBSQ-4,5-PDO)­(CO)₂]_∞ (<b>4</b>; 3,6-DBSQ-4,5-PDO^•– = 3,6-di-<i>tert</i>-butyl-4,5-(1,3-propanedioxy)-1,2-benzosemiquinonato) and [Rh­(3,6-DBSQ-4,5-(<i>N</i>,<i>N</i>′-DEN))­(CO)₂]_∞ (<b>5</b>; 3,6-DBSQ-4,5-(<i>N</i>,<i>N</i>′-DEN)^•– = 3,6-di-<i>tert</i>-butyl-4,5-(<i>N</i>,<i>N</i>′-diethylenediamine)-1,2-benzosemiquinonato) were synthesized to explore the nature of the unusual structural phase transition and magnetic and conductive properties recently reported for [Rh­(3,6-DBSQ-4,5-(MeO)₂)­(CO)₂]_∞ (<b>3</b>; 3,6-DBSQ-4,5-(MeO)₂^•– = 3,6-di-<i>tert</i>-butyl-4,5-dimethoxy-1,2-benzosemiquinonato). Their crystal structures and magnetic and conductive properties were investigated. Compounds <b>4</b> and <b>5</b> comprise neutral 1D chains of complex molecules stacked in a staggered arrangement with fairly short average Rh–Rh distances of 3.06 Å for <b>4</b> and 3.10 Å for <b>5</b>. These distances are similar to those for <b>3</b> (3.09 Å); however, the molecules of <b>5</b> are strongly dimerized in the 1D chain. Compound <b>4</b> undergoes a first-order phase transition at <i>T</i>_trs = 229.1 K, and its magnetic properties drastically change from antiferromagnetic coupling in the room-temperature (RT) phase to strong ferromagnetic coupling in the low-temperature (LT) phase. In addition, compound <b>4</b> exhibits a long-range ordering of net magnetic moments originating from the imperfect cancellation of antiferromagnetically coupled spins between the ferromagnetic 1D chains at <i>T</i>_N = 10.9 K. Furthermore, this compound exhibits an interesting crossover from a semiconductor with a small activation energy (<i>E</i>_a = 31 meV) in the RT phase to a semiconductor with a large activation energy (<i>E</i>_a = 199 meV) in the LT phase. These behaviors are commonly observed for <b>3</b>. Alternating current susceptibility measurements of <b>4</b>, however, revealed a frequency-dependent phenomenon below 5.2 K, which was not observed for <b>3</b>, thus indicating a slow spin relaxation process that possibly arises from the movements of domain walls. In contrast, compound <b>5</b>, which possesses a strongly dimerized structure in its 1D chain, shows no sign of strong ferromagnetic interactions and is an insulator, with a resistivity greater than 7 × 10⁷ Ω cm

Multifunctional One-Dimensional Rhodium(I)–Semiquinonato Complex: Substituent Effects on Crystal Structures and Solid-State Properties

Two new one-dimensional (1D) rhodium­(I)–semiquinonato complexes formulated as [Rh­(3,6-DBSQ-4,5-PDO)­(CO)₂]_∞ (<b>4</b>; 3,6-DBSQ-4,5-PDO^•– = 3,6-di-<i>tert</i>-butyl-4,5-(1,3-propanedioxy)-1,2-benzosemiquinonato) and [Rh­(3,6-DBSQ-4,5-(<i>N</i>,<i>N</i>′-DEN))­(CO)₂]_∞ (<b>5</b>; 3,6-DBSQ-4,5-(<i>N</i>,<i>N</i>′-DEN)^•– = 3,6-di-<i>tert</i>-butyl-4,5-(<i>N</i>,<i>N</i>′-diethylenediamine)-1,2-benzosemiquinonato) were synthesized to explore the nature of the unusual structural phase transition and magnetic and conductive properties recently reported for [Rh­(3,6-DBSQ-4,5-(MeO)₂)­(CO)₂]_∞ (<b>3</b>; 3,6-DBSQ-4,5-(MeO)₂^•– = 3,6-di-<i>tert</i>-butyl-4,5-dimethoxy-1,2-benzosemiquinonato). Their crystal structures and magnetic and conductive properties were investigated. Compounds <b>4</b> and <b>5</b> comprise neutral 1D chains of complex molecules stacked in a staggered arrangement with fairly short average Rh–Rh distances of 3.06 Å for <b>4</b> and 3.10 Å for <b>5</b>. These distances are similar to those for <b>3</b> (3.09 Å); however, the molecules of <b>5</b> are strongly dimerized in the 1D chain. Compound <b>4</b> undergoes a first-order phase transition at <i>T</i>_trs = 229.1 K, and its magnetic properties drastically change from antiferromagnetic coupling in the room-temperature (RT) phase to strong ferromagnetic coupling in the low-temperature (LT) phase. In addition, compound <b>4</b> exhibits a long-range ordering of net magnetic moments originating from the imperfect cancellation of antiferromagnetically coupled spins between the ferromagnetic 1D chains at <i>T</i>_N = 10.9 K. Furthermore, this compound exhibits an interesting crossover from a semiconductor with a small activation energy (<i>E</i>_a = 31 meV) in the RT phase to a semiconductor with a large activation energy (<i>E</i>_a = 199 meV) in the LT phase. These behaviors are commonly observed for <b>3</b>. Alternating current susceptibility measurements of <b>4</b>, however, revealed a frequency-dependent phenomenon below 5.2 K, which was not observed for <b>3</b>, thus indicating a slow spin relaxation process that possibly arises from the movements of domain walls. In contrast, compound <b>5</b>, which possesses a strongly dimerized structure in its 1D chain, shows no sign of strong ferromagnetic interactions and is an insulator, with a resistivity greater than 7 × 10⁷ Ω cm

Measurement of Extreme Hyperfine Fields in Two-Coordinate High-Spin Fe²⁺ Complexes by Mössbauer Spectroscopy: Essentially Free-Ion Magnetism in the Solid State

Mössbauer studies of three two-coordinate linear high-spin Fe²⁺ compounds, namely, Fe­{N­(SiMe₃)­(Dipp)}₂ (<b>1</b>) (Dipp = C₆H₃-2,6-^<i>i</i>Pr₂), Fe­(OAr′)₂ (<b>2</b>) [Ar′ = C₆H₃-2,6-(C₆H₃-2,6-^<i>i</i>Pr₂)₂], and Fe­{C­(SiMe₃)₃}₂ (<b>3</b>), are presented. The complexes were characterized by zero- and applied-field Mössbauer spectroscopy (<b>1</b>–<b>3</b>), as well as zero- and applied-field heat-capacity measurements (<b>3</b>). As <b>1</b>–<b>3</b> are rigorously linear, the distortion(s) that might normally be expected in view of the Jahn–Teller theorem need not necessarily apply. We find that the resulting very large unquenched orbital angular momentum leads to what we believe to be the largest observed internal magnetic field to date in a high-spin iron­(II) compound, specifically +162 T in <b>1</b>. The latter field is strongly polarized along the directions of the external field for both longitudinal and transverse field applications. For the longitudinal case, the applied field increases the overall hyperfine splitting consistent with a dominant orbital contribution to the effective internal field. By contrast, <b>2</b> has an internal field that is not as strongly polarized along a longitudinally applied field and is smaller in magnitude at ca. 116 T. Complex <b>3</b> behaves similarly to complex <b>1</b>. They are sufficiently self-dilute (e.g., Fe···Fe distances of ca. 9–10 Å) to exhibit varying degrees of slow paramagnetic relaxation in zero field for the neat solid form. In the absence of EPR signals for <b>1</b>–<b>3</b>, we show that heat-capacity measurements for one of the complexes (<b>3</b>) establish a <i>g</i>_eff value near 12, in agreement with the principal component of the ligand electric field gradient being coincident with the <i>z</i> axis

Bistable Multifunctionality and Switchable Strong Ferromagnetic-to-Antiferromagnetic Coupling in a One-Dimensional Rhodium(I)–Semiquinonato Complex

We present a comprehensive study of the synthesis, heat capacity, crystal structures, UV–vis−NIR and mid-IR spectra, DFT calculations, and magnetic and electrical properties of a one-dimensional (1D) rhodium­(I)–semiquinonato complex, [Rh­(3,6-DBSQ-4,5-(MeO)₂)­(CO)₂]_∞ (<b>3</b>), where 3,6-DBSQ-4,5-(MeO)₂^•– represents 3,6-di-<i>tert</i>-butyl-4,5-dimethoxy-1,2-benzosemiquinonato radical anion. The compound <b>3</b> comprises neutral 1D chains of complex molecules stacked in a staggered arrangement with short Rh–Rh distances of 3.0796(4) and 3.1045(4) Å at 226 K and exhibits unprecedented bistable multifunctionality with respect to its magnetic and conductive properties in the temperature range of 228–207 K. The observed bistability results from the thermal hysteresis across a first-order phase transition, and the transition accompanies the exchange of the interchain C–H···O hydrogen-bond partners between the semiquinonato ligands. The strong overlaps of the complex molecules lead to unusually strong ferromagnetic interactions in the low-temperature (LT) phase. Furthermore, the magnetic interactions in the 1D chain drastically change from strongly ferromagnetic in the LT phase to antiferromagnetic in the room-temperature (RT) phase with hysteresis. In addition, the compound <b>3</b> exhibits long-range antiferromagnetic ordering between the ferromagnetic chains and spontaneous magnetization because of spin canting (canted antiferromagnetism) at a transition temperature <i>T</i>_N of 14.2 K. The electrical conductivity of <b>3</b> at 300 K is 4.8 × 10^–4 S cm^–1, which is relatively high despite Rh not being in a mixed-valence state. The temperature dependence of electrical resistivity also exhibits a clear hysteresis across the first-order phase transition. Furthermore, the ferromagnetic LT phase can be easily stabilized up to RT by the application of a relatively weak applied pressure of 1.4 kbar, which reflects the bistable characteristics and demonstrates the simultaneous control of multifunctionality through external perturbation