Tsutomu Kai

C66 fullerene encaging a scandium dimer.

The geometry of carbon cages (fullerenes) is governed by the isolated-pentagon rule (IPR), which states that the most stable fullerenes are those in which all pentagons are surrounded by five hexagons. Although this rule has been verified experimentally, it is impossible for fullerenes in the range C60 to C70 to obey it. Here we describe the production and characterization of an IPR-violating metallofullerene, Sc2@C66, a C66 fullerene encaging a scandium dimer. Our results indicate that encapsulation of the metal dimer significantly stabilizes this otherwise extremely unstable C66 fullerene.

A Scandium Carbide Endohedral Metallofullerene: (Sc2C2)@C84

Not Sc2 @C86 but Sc2 C2 @C84 : that is the conclusion of 13 C NMR spectroscopic and synchrotron X-ray powder diffraction studies on a new metallofullerene obtained by arc discharge of Sc2 O3 /graphite rods. The picture shows a schematic representation of the deduced structure, in which the novel scandium carbide cluster Sc2 C2 is encaged in D2d -C84 .

Production and isolation of an ellipsoidal C80 fullerene

We report the first successful production and isolation of a new C80 isomer together with 13C NMR structural and UV–VIS–NIR spectroscopic studies of the purified sample; 13C NMR results unambiguously suggest that the new C80 isomer has an ellipsoidal structure with D5d symmetry.

Sc2@C76(C2): a new isomerism in fullerene structure

Abstract Sc 2 @C 76 was for the first time isolated and characterized spectroscopically. It is suggested from the 13 C NMR spectroscopy ( 13 C NMR pattern: 38×2) that this metallofullerene has a C 2 symmetry, in contrast to the D 2 symmetry of an empty C 76 fullerene cage. Ab initio calculations were performed to explore the symmetry changes for C 76 (from D 2 to C 2 ) induced by the endohedral scandium ions. It is found that the scandium ions are located at two of the three main C 2 axes of C 76 ( D 2 ). The two isomers Sc 2 @C 76 ( D 2− x ) (Sc 2 was put along the C 2 x axis of C 76 ( D 2 )) and Sc 2 @C 76 ( D 2− y ) (Sc 2 was put along the C 2 y axis of C 76 ( D 2 )) are nearly iso-energetic in their optimised geometrical structures, and their energies are much lower than that of the third isomer Sc 2 @C 76 ( D 2− z ) (Sc 2 was put along the C 2 z axis of C 76 ( D 2 )). Each of the two iso-energetic isomers, i.e., Sc 2 @C 76 ( D 2− x ) and Sc 2 @C 76 ( D 2− y ), contributes 19 NMR lines ( 13 C NMR pattern: 19×4), so the mixture of them shows overall 38 NMR lines ( 13 C NMR pattern: 38×2) for this metallofullerene.

Measurement of thermodynamic quantities in the heating-rate dependent thermal transitions of sequenced polytripeptides

Abstract The apparent excess heat capacities ( C p ) of sequenced polytripeptides, (Pro-Pro-Gly) 10 and (Pro-Hyp-Gly) 10 in various solutions were measured using a differential scanning calorimeter. The dependence of the peaks of the C p curves on heating rates was identical for all solutions studied. The apparent enthalpy changes of the transition did not depend on the heating rate. The equilibrium thermodynamic data, Δ H and Δ S of the transition, obtained calorimetrically in this system, are found to be linear to each other, indicating an enthalpy–entropy compensation. These results are discussed in terms of the phase transition.

Two states of the triple helix in the thermal transition of the collagen model peptide (Pro-Pro-Gly)10.

Abstract The collagen model peptide (Pro-Pro-Gly)10 is known to fold into a triple helix in solution. So far, the triple helix has been considered to exist as a single state. However, our previous study of (Pro-Pro-Gly)10 in solution has indicated the presence of two different states of the triple helix, a lower (HL) and a higher temperature state (HH). In the present study, these triple-helical states were investigated in more detail by NMR. Complete stereospecific assignments of the methylene protons of the proline residues were accomplished by the use of NOESY and TOCSY spectra. The temperature dependence of the 1H chemical shifts showed that the HL-to-HH thermal transition can be attributed to a conformational change of the first proline (Pro1) residues of the (Pro-Pro-Gly) triplets. Since TOCSY spectra with a 10 ms mixing-time confirmed a down puckering of these Pro residues in the HL state, but interconverting down and up puckerings in the HH state, the HL-to-HH thermal transition corresponds to conformational changes of the pyrrolidine rings of the Pro1 residues from an uniform down puckering to a more flexible state. The results confirm that thermal unfolding of the triple helix proceeds through the intermediate HH state.

NMR OBSERVATION OF TWO STATES OF TRIPLE HELIX IN THE THERMAL TRANSITION OF(PRO-PRO-GLY)10

Abstract The thermal transition of (Pro-Pro-Gly) 10 in D 2 O solution has been studied by NMR. The 1 H and 13 C spectra measured at different temperatures are assigned using homo- and heteronuclear two-dimensional NMR methods. It is confirmed that the triple helix undergoes a preliminary transition between two distinct states; the higher state is considered to be a preparatory state for the transition to the statistical coil. The observed change in the helix content is explained in terms of an extended first-order phase transition.

Density measurements and differential scanning calorimetry of collagen model peptides

Susumu Uchiyama, Tetsuo Tomiyama, Tsutomu Kai, Kazuhiro Hukada, Koichi Kajiyama, and Yuji Kobayashi 1 Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, 5650871, Japan; 2 Graduate School of Science, Nagoya University, Chikusa, Nagoya, 460814, Japan; Faculty of Science, Tokyo Metropolitan University, Hachioji, Tokyo, 1920364, Japan; and Admon Science Inc., Fujieda, Shizuoka, 4260007, Japan.