Anomalous Enhancement of Proton Conductivity for Water Molecular Clusters Stabilized in Interstitial Spaces of Porous Molecular Crystals

In an investigation into the proton conductivity of crystallized water clusters confined within low‐dimensional nanoporous materials, we have found that water‐stable nanoporous crystals are formed by complementary hydrogen bonding between [Co^III(H₂bim)₃]³⁺ (H₂bim: 2,2′‐biimidazole) and TATC^3? (1,3,5‐ tricarboxyl‐2,4,6‐triazinate); the O atoms in the ?COO^? groups of TATC^3? in the porous outer wall are strongly hydrogen bonded with H₂O, forming two types of WMCs (water molecular clusters): a spirocyclic tetramer chain (SCTC) that forms infinite open 1D channels, and an isolated cyclic tetramer (ICT) present in the void space. The ICT is constructed from four H₂O molecules as a novel C₂‐type WMC, which are hydrogen bonded with four‐, three‐, and two‐coordination spheres, respectively. The largest structural fluctuation is observed at elevated temperatures from the two‐coordinated H₂O molecules, which begin to rapidly and isotropically fluctuate on heating. This behavior can be rationalized by a simple model for the elucidation of pre‐melting phenomena, similar to those in ice surfaces as the temperature increases. Moreover, high proton conductivity of SCTCs (ca. 10^?5 S cm^?1 at 300 K with an activation energy of 0.30 eV) through a proton‐hole mechanism was observed for pellet samples using the alternating impedance method. The proton conductivity exhibits a slight enhancement of about 0.1×10^?5 S cm^?1 at 274 K due to a structural transition upon approaching this temperature that elongates the unit cell along the b‐axis. The proton‐transfer route can be predicted in WMCs, as O(4) of an H₂O molecule at the center of an SCTC shows a motion that rotates the dipole in the b‐axis direction, but not the c‐axis; the thermal ellipsoids of O(4) based on anisotropic temperature factors obtained by X‐ray crystallography reflect a structural fluctuation along the b‐axis direction induced by [Co^III(H₂bim)₃]³⁺.     

Structural studies of polyformals. II. Crystal structure of poly-1,3-dioxolane: Modification II1

The structure of poly-1,3-dioxolane, [? OCH₂O? (CH₂)₂? ]_n was studied by x-ray diffraction and infrared spectroscopy. Three crystal modifications were found. The crystal structure of modification II was determined: four molecular chains of glide type pass through the orthorhombic unit cell; Pbca-D_2h¹⁵, a = 9.07 Å, b = 7.79 Å, and c (fiber axis) = 9.85Å. The molecular conformation is The molecular chain consists of regular head-to-tail sequences. This fact shows that the ring opening of 1,3-dioxolane occurs exclusively at the same type of CO bond in the cationic polymerization, just as in the case of 1,3-dioxepane.     

Crystal structure of stable protein CutA1 from psychrotrophic bacterium Shewanella sp. SIB1

CutA1 is widely found in bacteria, plants and animals, including humans. The functions of CutA1, however, have not been well clarified. It is known that CutA1s from Pyrococcus horikoshii, Thermus thermophilus and Oryza sativa unfold at temperatures remarkably higher than the growth temperatures of the host organisms. In this work the crystal structure of CutA1 from the psychrotrophic bacterium Shewanella sp. SIB1 (SIB1-CutA1) in a trimeric form was determined at 2.7?? resolution. This is the first crystal structure of a psychrotrophic CutA1. The overall structure of SIB1-CutA1 is similar to those of CutA1 from Homo sapiens, Escherichia coli, Pyrococcus horikoshii, Thermus thermophilus, Termotoga maritima, Oryza sativa and Rattus norvergicus. A peculiarity is observed in the β2 strand. The β2 strand is divided into two short β strands, β2a and β2b, in SIB1-CutA1. A thermal denaturation experiment revealed that SIB1-CutA1 does not unfold completely at 363?K at pH 7.0, although Shewanella sp. SIB1 cannot grow at temperatures exceeding 303?K. These results indicate that the trimeric structural motif of CutA1 is the critical factor in its unusually high stability and suggest that CutA1 needs to maintain its high stability in order to function, even in psychrotrophs.     

Solid-state polymerization and polymer crystallization

Effects of the molecular and crystal structures of polymerizable substances on their radiation-induced solid-state polymerization are considered for two cases; the solid state polymerization of cyclic oligomers of formaldehyde and the canal polymerization of some monomers.

Cyclic oligomers of formaldehyde (–CH₂–O–)m from m = 3 to 6 are transformed into three-dimensionally oriented crystalline polyoxymethylene by irradiation. The polymer crystals are characteristically oriented, depending upon the parent oligomer crystal structures. A small amount of an oriented, unstable modification (orthorhombic) polyoxymethylene is also obtained in X-ray in-source polymerization of hexoxane.

Highly 1,4-trans tactic polymerization of 2,3-dichloro-1,3-butadiene and 2,3-dimethy1-1,3-butadiene in the thiourea canals is shown by structural evidence, based upon the crystal structure determinations of the monomerthiourea complexes, the polymer-thiourea complexes, and the resultant polymers for both dienes. The conversion of the monomer-thiourea complexes to the polymer-thiourea complexes by irradiation is performed, retaining the original single crystal habit, though in the canals the monomer-monomer distances are shortened by polymerization. The polymer samples obtained from the single crystals of polymer-thiourea complexes by removal of thiourea are uniaxially oriented and have unusual fine structures.     

Crystal structure of isotactic poly(4-methyl-1-pentene)

The crystal structure of isotactic poly(4-methyl-1-pentene) was determined by x-ray analysis. The unit cell is tetragonal, P4 b2, with α = 18.70 Å and c (fiber axis) = 13.68 Å; it contains four molecular chains each consisting of seven monomeric units in the fiber period. The molecular conformation is essentially a (7/2) helix, but deviates slightly from the uniform (7/2) helix. The unusual low density is discussed from the structural point of view.     

Molecular confirmation and crystal structure of the β form of poly(ethylene oxybenzoate)

The crystal structure of the β form of poly(ethylene oxybenzoate) was analyzed by x-ray diffraction. Four nearly extended molecular chains pass through a unit cell with parameters a = 8.19 Å, b = 11.07 Å, c (fiber axis) = 19.05 Å, β = 114.8°, and the space group P2₁/n-C. The structural difference between the α and β forms is mainly due to the internal rotation angles for the virtual bond and the ? CH₂? CH₂? bond. They are essentially in trans confirmation in the β form, while the α form contains cis and gauche (? CH₂? CH₂? ) conformations.