Structural elucidation and regioselective functionalization of an unexplored carbide cluster metallofullerene Sc2C2@C(s)(6)-C82

A Sc(2)C(84) isomer, previously assumed to be Sc(2)@C(84), is unambiguously identified as a new carbide cluster metallofullerene Sc(2)C(2)@C(s)(6)-C(82) using both NMR spectroscopy and X-ray crystallography. The (13)C-nuclei signal of the internal C(2)-unit was observed at 244.4 ppm with a 15% (13)C-enriched sample. Temperature-dependent dynamic motion of the internal Sc(2)C(2) cluster is also revealed with NMR spectrometry. Moreover, the chemical property of Sc(2)C(2)@C(s)(6)-C(82) is investigated for the first time using 3-triphenylmethyl-5-oxazolidinone (1) which provides a 1,3-dipolar reagent under heating. Regarding the low cage symmetry of this endohedral which contains 44 types of nonequivalent cage carbons, it is surprising to find that only one monoadduct isomer is formed in the reaction. Single-crystal X-ray results of the isolated pyrrolidino derivative Sc(2)C(2)@C(s)(6)-C(82)N(CH(2))(2)Trt (2) reveal that the addition takes place at a [6,6]-bond junction, which is far from either of the two Sc atoms. Such a highly regioselective addition pattern can be reasonably interpreted by analyzing the frontier molecular orbitals of the endohedral. Electronic and electrochemical investigations reveal that adduct 2 has a larger highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap than pristine Sc(2)C(2)@C(s)(6)-C(82); accordingly, it is more stable.     

Rational development of caged-biotin protein-labeling agents and some applications in live cells

Biotin-(strept)avidin complex is widely used in biotechnology because of its extremely high binding constant, but there is no report describing spatiotemporally controlled formation of the complex in live cells. Here, based on X-ray crystal structure analysis and calorimetric data, we designed and synthesized photoreleasable biotins, which show greatly reduced affinity for (strept)avidin, but recover native affinity after UV irradiation. For application at the cell surface, we introduced an amine-reactive moiety into these "caged" biotin molecules. Specific fluorescence imaging of live cells that had been labeled with these agents and then UV-irradiated, was accomplished by addition of streptavidin conjugated with a fluorophore. We also demonstrated the applicability of these compounds for UV-irradiated-cell-specific drug delivery by using caged-biotin-labeled cells, a prodrug, and streptavidin conjugated with a prodrug-activating enzyme.     

Thermal [2+2] cycloaddition of morpholinoenamines with C60 via a single electron transfer

The thermal reaction of C(60) with five- and six-membered morpholinocycloalkenes in refluxing toluene exclusively gave the [2+2] cycloadducts in high yields. However, a seven-membered homologue sluggishly reacted with C(60) because of the increasing steric hindrance. This cycloaddition reaction is likely to proceed via a single electron transfer (SET), a radical-coupling, and subsequent ion cyclization rather than the prior proton transfer between the radical ions.     

Stabilization mechanism of clarithromycin tablets under gastric pH conditions

It has been reported that tablets of clarithromycin (CAM), a 14-membered macrolide antibiotic, are especially stable under low pH conditions such as in gastric fluid, and showed excellent antibacterial efficiency even though CAM molecules themselves are rapidly decomposed. Therefore, we aimed to clarify the stabilization mechanism of CAM tablets under low pH conditions. From the results of stability and dissolution tests, the optimal decomposition rate constant (K(dec)) and dissolution rate constant (K(dis)) at various pH values were calculated by curve-fitting to consecutive reactions. Consequently, log(K(dec)) increased as pH decreased. On the other hand, log(K(dis)) increased as pH decreased from 3.0 to 1.5, but decreased as pH decreased from 1.5 to 1.0. In addition, the disintegration time of commercially available tablets at pH 1.0 and 1.2 was found to be delayed, resulting in a decrease of K(dis). Furthermore, from powder X-ray diffraction, HPLC and elemental analysis, the delay in disintegration time might be attributable to the formation of a transparent gel, formed by the reaction between CAM molecule and hydrochloric acid under low pH conditions, on the surface of CAM tablet. On the basis of these results, this report can be considered the first case where a transparent gel prevents gastric fluid from penetrating the tablet, resulting in reduced decomposition of CAM following oral administrating.     

(E)- and (Z)-β-borylallylsilanes by alkyne silaboration followed by regio- and stereoselective double-bond migration

Double take: β-Borylallylsilanes have been synthesized by the regioselective silaboration of terminal alkynes followed by palladium-catalyzed double-bond migration of the resulting β-borylalkenylsilanes. The stereoselectivity of the double-bond migration can be controlled by additives, thus leading to the stereocomplementary synthesis of (E)- and (Z)-β-borylallylsilanes.     

Solving the Segregated Storage Problem with Benders' Partitioning

We investigate the application of Benders' partitioning to a mixed integer programming formulation of the segregated storage problem. The dual subproblem reduces to an efficiently-solvable network flow problem. This approach is compared empirically to Neebe's multiplier adjustment procedure. Benders' procedure is shown to be computationally effective for an important class of practical applications having high demand-to-capacity ratios and fewer products than compartments.     

Interior Imperfect Ignition Cannot Occur on a Set of Positive Measure

For the differential inequality , it is proved that the dead core of the solution with cannot be enclosed inside a bounded domain with positive Lebesgue measure. (Accepted July 11, 1996)     

169Re的转动带结构研究

利用在束γ谱学方法,通过反应¹⁴⁴Sm(²⁸Si,1p3n)¹⁶⁹Re研究了¹⁶⁹Re的激发态能级结构.实验进行了X-γ符合、γ-γ符合、DCO系数和带内B(M1)/B(E2)比率测量.基于这些测量,建立了组态为π9/2^－[514]的强耦合带和组态为π1/2^－[541]的退耦合带.通过比较¹⁶⁹Re的转动带与邻近奇质子核已知转动带的结构和B(M1)/B(E2)比率,指定了¹⁶⁹Re转动带的组态.实验观测到π9/2^－[514]和π1/2^－[541]转动带的中子AB带交叉的转动频率分别为0.23和0.27MeV.着重讨论了¹⁶⁹Re转动带的中子AB带交叉频率、转动角动量顺排和旋称劈列等,并讨论了奇ARe核转动带结构的系统性