Classical Valence Similarity in Fullerene Derivatives

Summary.  The generalized Pauling bond order was enumerated in the C₆₀ fullerene cage molecule (truncated icosahedral symmetry). This index measures chemical similarity in fullerene derivatives such as dihydrofullerene (C₆₀H₂), anionized monohydrofullerene (C₆₀H⁻), N-substituted monohydrofullerene (C₅₉NH), the fullerene dimer ((C₆₀)₂), and the dianionic fullerene dimer ((C₆₀)₂ ²⁻). It is also useful in judging the chemical stability of isomers. Received October 9, 2001. Accepted November 9, 2001     

Cation binding properties of crown ether-modified polyethylenimines

Crown ether-modified polyethylenimines (PEI-CR) were prepared to elucidate their cation binding efficiency and selectivity by liquid-liquid and solid-liquid extraction methods. With alkali metal cations it was found that polyethylenimines containing benzo-15-crown-5 moieties (Ia and Ib) extracted all cations examined more efficiently than their monomeric analogs, especially in the cases of K⁺ and Rb⁺ cations. The solid-liquid extraction revealed clearly that the polymers complexed with K⁺ and Rb⁺ cations according to a 1:2 cation-to-crown stoichiometry. The high selectivities of the polymers for K⁺ and Rb⁺ were interpreted in terms of the favourable conformation of the polymer chain for the formation of intramolecular 1:2 complexes. On the contrary, these polymers bound alkali earth cations less effectively with low selectivities.     

Synthesis and analgesic activity of novel heterocycles, [1]benzothiopyrano[3,4-b]pyrrole derivatives

In order to develop analgesic compounds possessing a sulfur atom in the alicyclic ring, novel cis-fused heterocycles, [1]benzothiopyrano[3,4-b]pyrrole derivatives (II) were synthesized via a unique cyclization reaction starting from 4-(4-methoxyphenylthio)-2-butanone (1) or 6-methoxy-3,4-dihydro-2H-1-benzothiopyran-4-one (7). The analgesic effects of benzothiopyranopyrroles (16, 18) were measured by means of the writhing test. The phenolic derivative 18 completely inhibited the appearance of writhing at the dose of 50 mg/kg, but the methoxy derivative 16 had no analgesic effect.     

Homogeneous palladium catalyst suppressing Pd black formation in air oxidation of alcohols

In homogeneous catalyst systems, there is the persistent problem that metal aggregation and precipitation cause catalyst decomposition and considerable loss of catalytic activity. Pd black formation is a typical example. Pd catalysts are known to easily aggregate and form Pd black, although they realize a wide variety of useful reactions in organic synthesis. In order to overcome this intrinsic problem of homogeneous Pd catalysis, we explored a new class of Pd catalyst by adopting aerobic oxidation of alcohols as a probe reaction. Herein we report a new catalyst system that suppresses the Pd black formation even under air and with a high substrate to catalyst molar ratio (S/C: more than 1000) in oxidation of alcohols. The novel pyridine derivatives having a 2,3,4,5-tetraphenylphenyl substituent and its higher dendritic unit at the 3-position of the pyridine ring were found to be excellent ligands with Pd(OAc)2 in the palladium-catalyzed air (balloon) oxidation of alcohols in toluene at 80 degrees C. Comparison with structurally related pyridine ligands revealed that introduction of the 2,3,4,5-tetraphenylphenyl substituent at the 3-position of pyridine ring effectively suppresses the Pd black formation, maintaining the catalytic activity for a long time to give aldehydes or ketones as products in high yields.     

Radiation-induced emission from golden hamster embryo cells

Emission from high-energy-electron-irradiated golden hamster embryo (GHE) cells has been studied over the temperature range 12–300 K both by a one-shot-single-photon-counting method and by photocurrent measurements with an oscilloscope. Emission from the irradiated phosphate buffered saline (PBS) also has been studied. The emission spectra from PBS at 12 and 77 K show a maximum around 330 and 380 nm, respectively, which are the same spectra as those from irradiated pure H₂O. The emission from irradiated GHE consists of the new band at 480 nm in addition to the emission from H₂O. The 480 nm emission is observed at the temperature range of 12–300 K, though the emission at 300 K is much lower than that at low temperature. The 480 nm emission is ascribed to the transition from excited organic substances in GHE cells. The intensity of 480 nm emission at 300 K increases linearly with increasing irradiation-dose in the range of 11–600 Gy.     

Dansyl-Modified γ-Cyclodextrin as a fluorescent sensor for molecular recognition

The crystal structure of thiamine iodide sesquihydrate has been determined by X-ray diffraction methods as a host-guest model for coenzyme-substrate interactions. The asymmetric unit contains two chemical units. Both the thiamine molecules A and B, which are crystallographically independent, assume the usualF conformation and have a disordered hydroxyethyl side chain. An iodide anion (or a water molecule) bridges the pyrimidine and thiazolium rings of molecule A (or B) by forming a hydrogen bond with the amino group and an electrostatic contact with the thiazolium ring to stabilize the molecular conformation. In the crystal the thiamine molecules self-associate to form a pipe-like polymeric structure, in which four thiamine hosts surround an iodide guest and hold it through C(2)-H...I hydrogen bonds and thiazolium...I electrostatic interactions. Crystal data: C₁₂H₁₇N₄OS⁺·I^– · 1.5 H₂O, monoclinic,P2₁/c, a=12.585(2), b=25.303(5), c=12.030(2) Å, =115.15(1)°,V=3468(1) ų,Z=8,D _c=1.606 g cm^–3,R=0.045 for 3328 observed reflections. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP. 82156 (13 pages).     

Heterogeneous structure of silk fibers from Bombyx mori resolved by 13C solid-state NMR spectroscopy

The molecular conformation of silk fibrion is characterized by solid-state 13C NMR before spinning (silk I structure) and after spinning (silk II structure). We compare native silk fibers with the quasi-crystalline Cp-fraction and a synthetic model peptide (Ala-Gly)15, both of which can be converted either into silk I by dialysis from 9 M LiBr or into silk II by treatment with formic acid. Our results demonstrate that silk II fibers are intrinsically heterogeneous, consisting of beta-sheets, distorted beta-turns, and distorted beta-sheets. This higher-order heterogeneity is revealed by the 13C-NMR Cbeta-peak of Ala, indicating that the Ala side chains are stacked partially in parallel and partially face-to-face, at a ratio of 1:2.     

Antithrombogenicity of cultured endothelial cell-detached surface

To examine the antithrombogenicity of cultured endothelial cell-detached surface, a simple hybrid vascular model tube consisting of a glass tube and endothelial cells was constructed. To detach the endothelial cells from the inner surface of the model tube, a steady shear stress of 2 or 8 N m(-2) was imposed onto the surface of endothelial cell monolayer by means of a coaxial double cylinder rotational-type apparatus. Coagulation of blood in contact with the endothelial cell-detached surface was examined using a damped oscillation rheometer. Coagulation of whole blood in the cell-detached tube occurred at about 40 min, which was almost the same as that in the endothelial cell-coated tube. A few platelets without shape change adhered to the endothelial cell-detached surface. These data suggest that the endothelial cell-detached surface may exhibit antithrombogenic and anticoagulant surfaces. Biochemical analyses showed that the glass surface, where endothelial cell was detached, was covered with components such as collagen type IV that is considered to be produced from the endothelial cells on the glass surface.     

Method of the orthonormality-constrained variation

The orthonormality-constrained variation method is developed, the application of which gives an exact SCF equation. The variational procedure used in deriving the equation clarifies the source and meaning of two kinds of arbitrary parameters which appear by the use of the method of lagrangean multipliers.     

A theoretical study of the dielectric solvent effect on vicinal spin coupling constants

The dielectric solvent effect on HCCH, HCNH and HCNC spin coupling constants in ethane, tetrachloroethane and trans N-methylformamide has been calculated by finite perturbation theory based on the INDO and CNDO/2 approximations incorporating solvaton theory. The available experimental data are interpreted using the calculated variations of spin coupling constants. The effect of dielectric constant on the general form of the Karplus relation is included in the finite perturbation calculations.