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

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]∞ (4; 3,6-DBSQ-4,5-PDO•– = 3,6-di-tert-butyl-4,5-(1,3-propanedioxy)-1,2-benzosemiquinonato) and [Rh­(3,6-DBSQ-4,5-(N,N′-DEN))­(CO)2]∞ (5; 3,6-DBSQ-4,5-(N,N′-DEN)•– = 3,6-di-tert-butyl-4,5-(N,N′-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]∞ (3; 3,6-DBSQ-4,5-(MeO)2•– = 3,6-di-tert-butyl-4,5-dimethoxy-1,2-benzosemiquinonato). Their crystal structures and magnetic and conductive properties were investigated. Compounds 4 and 5 comprise neutral 1D chains of complex molecules stacked in a staggered arrangement with fairly short average Rh–Rh distances of 3.06 Å for 4 and 3.10 Å for 5. These distances are similar to those for 3 (3.09 Å); however, the molecules of 5 are strongly dimerized in the 1D chain. Compound 4 undergoes a first-order phase transition at Ttrs = 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 4 exhibits a long-range ordering of net magnetic moments originating from the imperfect cancellation of antiferromagnetically coupled spins between the ferromagnetic 1D chains at TN = 10.9 K. Furthermore, this compound exhibits an interesting crossover from a semiconductor with a small activation energy (Ea = 31 meV) in the RT phase to a semiconductor with a large activation energy (Ea = 199 meV) in the LT phase. These behaviors are commonly observed for 3. Alternating current susceptibility measurements of 4, however, revealed a frequency-dependent phenomenon below 5.2 K, which was not observed for 3, thus indicating a slow spin relaxation process that possibly arises from the movements of domain walls. In contrast, compound 5, 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

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