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K Hagiya

Publications and source records attributed to K Hagiya.

5 recordsLinked to original sources
PubMed2001

Commensurate structure of Ca(2)CoSi(2)O(7), a new twinned orthorhombic structure.

The crystal structure of the commensurate phase of Ca(2)CoSi(2)O(7), dicalcium cobalt disilicate, has been derived from the modulated structure described in (3 + 2)-dimensional space. The structure is orthorhombic P2(1)2(1)2; a = 23.510 (4), b = 23.510 (4), c = 5.025 (1) A (at 170 K), Z = 18. Since the crystal is twinned and the apparent diffraction symmetry is 4/mmm, the parameters were refined by a newly developed least-squares program for the refinement of twinned crystals. The structure is essentially similar to the known structure of the melilite group, but with regular arrangement of the bundles along [001] formed with four arrays of the sixfold coordinated Ca polyhedra and an array of CoO(4) tetrahedra. The distribution of the bundles found in the present structure is different from that reported by Riester et al. [(2000), Z. Kristallogr. 215, 102-109].

Journal Article↗
PubMed2001

Entropy-controlled asymmetric synthesis. How differential activation entropy is induced in chiral tethered reactions.

[figure: see text] Kinetic measurements to determine effective molarities of intramolecular reactions using 2,4-pentanediol and related tethers showed that methyl groups on the tether accelerate the major diastereomeric process but decelerate the minor process. The efficient promotion of stereocontrol is suggested to be due to chiral perturbation of the reaction rate through the entropy term. The conformation of the encounter complex of the reagent and reactant moieties was deduced by stereochemical analysis of the intramolecular adducts.

Journal Article↗
PubMed2000

Two-dimensional incommensurately modulated structure of (Sr0.13Ca0. 87)2CoSi2O7 crystals.

The incommensurate structure of (Sr(0.13)Ca(0.87))(2)CoSi(2)O(7) at room temperature has been determined from single-crystal X-ray diffraction data. The compound has a non-centrosymmetric tetragonal basic cell of a = 7.8743 (4) and c = 5.0417 (2) A with the space group P4;2(1)m. The refinements of the basic structure converged to R = 0.038 for 757 main reflections. The two-dimensional incommensurate structure is characterized by the wavevectors q(1) = 0.286 (3)(a* + b*) and q(2) = 0.286 (3)(-a* + b*), where a*, b* are the reciprocal lattice vectors of the basic structure. With the (3 + 2)-dimensional superspace group P(p4mg)(P4;2(1)(m)), the refinements converged to R = 0.071 for 1697 observed reflections (757 main and 940 satellite reflections). The structure is described in terms of displacement of the atoms, rotation, distortion of CoO(4) and SiO(4) tetrahedra, and the partial ordering of the Sr and Ca atoms accompanied with the modulation. Correlated evolution of these features throughout the crystal gives rise to various oxygen coordination around Ca/Sr. Comparison of the derived modulated structure to that of Ca(2)CoSi(2)O(7) clarified that the partial substitution of Ca by large alkaline-earth atoms such as Sr should decrease the distortion of the polyhedra around the cations.

Journal Article↗
PubMed2000

Mental disturbances during isolation in bone marrow transplant patients with leukemia.

The mental status of 39 leukemia patients, who received bone marrow transplants (BMT), was studied during the period of isolation. Mental disorders (diagnosed according to DSM-IV criteria) occurred in 16 patients (41%) during the observation period. The most frequent diagnoses were adjustment disorders, with anxiety and/or depression. Logistic regression analysis suggested higher Tension-Anxiety score in the Profile of Mood States (POMS) prior to isolation (P = 0.011), donation of the bone marrow from unrelated subjects (P = 0.026) and in female patients (P = 0.033). The results are preliminary, but indicate a high frequency of mental disturbances and highlight the importance of psychiatric intervention in BMT patients. Bone Marrow Transplantation (2000) 25, 315-318.

Adolescent↗