Kazuya Kawabata

Osaka University, Suika, Ōsaka, Japan

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Publications (8)30.75 Total impact

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    ABSTRACT: m-Diethynylbenzene macrocycles (DBMs), buta-1,3-diyne-bridged [4(n)]metacyclophanes, have been synthesized and their self-association behaviors in solution were investigated. Cyclic tetramers, hexamers, and octamers of DBMs having exo-annular octyl, hexadecyl, and 3,6,9-trioxadecyl ester groups were prepared by intermolecular oxidative coupling of dimer units or intramolecular cyclization of the corresponding open-chain oligomers. The aggregation properties were investigated by two methods, the (1)H NMR spectra and the vapor pressure osmometry (VPO). Although some discrepancies were observed between the association constants obtained from the two methods, the qualitative view was consistent with each other. The analysis of self-aggregation by VPO revealed unique aggregation behavior of DBMs in acetone and toluene, which was not elucidated by the NMR method. Namely, the association constants for infinite association are several times larger than the dimerization constant, suggesting that the aggregation is enhanced by the formation of dimers (a nucleation mechanism). In polar solvents, DBMs aggregate more strongly than in chloroform due to the solvophobic interactions between the macrocyclic framework and the solvents. Moreover, DBMs self-associate in aromatic solvents such as toluene and o-xylene more readily than in chloroform. In particular, the hexameric DBM having a large macrocyclic cavity exhibits extremely large association constants in aromatic solvents. By comparing the aggregation properties of DBMs with the corresponding acyclic oligomers, the effect of the macrocyclic structure on the aggregation propensity was clarified. Finally, it turned out that DBMs tend to aggregate more readily than the corresponding phenylacetylene macrocycles, acetylene-bridged [2(n)]metacyclophanes, owing to the withdrawal of the electron density from the aromatic rings by the butadiyne linkages which facilitates pi-pi stacking interactions.
    No preview · Article · Jun 2002 · Journal of the American Chemical Society
  • Source
    Y Fukuoka · M Sonoda · T Terashi · K Kawabata · K Sannou · H Uenomachi · Y Tanaka · T Arima
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    ABSTRACT: A 51-year-old man presented under a diagnosis of angina pectoris manifesting as exertional chest pain. First coronary angiography showed severe stenosis with ulceration and spontaneous dissection at the proximal right coronary artery and linear dissection-like filling defects extending to the distal right coronary artery. After about 3 months, repeat coronary angiography showed the previously observed stenosis with unclear dissection, and better developed collaterals from the left coronary artery to the right coronary artery showing the linear dissection-like filling defects. The bilateral coronary angiography did not clearly show filling defects. This phenomenon suggested that the collateral flows were related to filling of the defects. Intravascular ultrasonic imaging demonstrated severe atherosclerotic lesions at the proximal right coronary artery, but no dissection in the distal right coronary artery. Percutaneous transluminal coronary angioplasty for the stenosis was performed successfully with a stent. Coronary angiography after the angioplasty showed no collaterals, and the right ventricular branch appeared, suggesting that the linear dissection-like filling defects extending to the distal right coronary artery were due to the collateral flows. Filling defects extending distal to a severe stenosis must be distinguished carefully from coronary dissection.
    Preview · Article · Dec 2001 · Journal of Cardiology
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    ABSTRACT: A 70-year-old female patient presented and ECG with QS patterns and ST elevation in V1-3. Left ventriculography showed severely abnormal wall motion of the anteroseptal similar to a left ventricular aneurysm. Based on previous experience that 201Tl myocardial scintigraphy revealed possible myocardial viability in a patient with left ventricular aneurysm suspected of having apparently no myocardial viability, percutaneous transluminal coronary angioplasty (PTCA) was performed for severe stenosis of the left anterior descending artery. Follow-up images 3 months later showed a remarkable improvement in parietal motility of the left ventricle and recovery of almost normal cardiac function. This case demonstrates that exercise myocardial scintigraphy is useful for diagnosing hibernating myocardium associated with severely abnormal parietal motility, such as left ventricular aneurysm.
    No preview · Article · Jun 2001 · Kaku igaku. The Japanese journal of nuclear medicine
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    ABSTRACT: Butadiyne-bridged [44](2,6)pyridinophane and [46](2,6)pyridinophane derivatives were synthesized, and their heteroassociations with the corresponding metacyclophanes and complexations with organic cations were investigated.
    No preview · Article · Jan 2001 · ChemInform
  • Y Tobe · A Nagano · K Kawabata · M Sonoda · K Naemura
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    ABSTRACT: Butadiyne-bridged [4(4)](2,6)pyridinophane and [4(6)](2, 6)pyridinophane derivatives were synthesized, and their heteroassociations with the corresponding metacyclophanes and complexations with organic cations were investigated.
    No preview · Article · Nov 2000 · Organic Letters
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    ABSTRACT: GRAPHICS Butadiyne-bridged [4(4)](2,6)pyridinophane and [4(6)](2,6)pyridinophane derivatives were synthesized, and their heteroassociations with the corresponding metacyclophanes and complexations with organic cations were investigated.
    No preview · Article · Oct 2000 · Organic Letters
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    ABSTRACT: Coronary arterial embolization is an extremely rare and potentially lethal complication of atrial myxomas. A 61-year-old male patient was admitted on 3 April 1997 for chest pain accompanied by cold sweat and dyspnea after he had pruned trees in his garden. ST segment elevation in leads II, III, and aVF was indicated by electrocardiogram (ECG) at time of admission, and an echocardiogram showed severe hypokinesis of inferior-wall motion and a mobile tumor in the left atrium; however, emergency coronary angiography showed no significant finding, and there was no ST elevation in the ECG during the catheter examination. Further, the patient recalled having had severe lassitude of the legs in 1995 and 1996, and because systemic embolization, a common complication of this disease, suggested arterial embolization of the legs, he was assumed to have had an acute myocardial infarction caused by coronary embolism from the left atrial myxoma, which reperfused before the coronary angiography was conducted. A 40x40x30-mm tumor that protruded from the interatrial septal wall to the left atrium was surgically removed on 30 April 1997. Histologic examination of this tumor confirmed as a myxoma.
    No preview · Article · Jan 2000
  • Yoshito Tobe · Naoto Utsumi · Kazuya Kawabata · Koichiro Naemura
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    ABSTRACT: We synthesized diethynylbenzene macrocycles (DBMs), cyclic oligomers of diethynylbenzene, having functional groups in the periphery of the macrocyclic framework and investigated their self-association properties in solution resulting from π-π stacking interaction. The tetrakis-DBM having hexadecyl ester groups showed dimerization behavior not only in chloroform-d, but also in o-dichlorobenzene-d4.
    No preview · Article · Dec 1996 · Tetrahedron Letters

Publication Stats

298 Citations
30.75 Total Impact Points

Institutions

  • 1996-2002
    • Osaka University
      • Department of Chemistry
      Suika, Ōsaka, Japan
  • 2001
    • Kagoshima University
      • Faculty of Medicine
      Kagosima, Kagoshima, Japan