Rotational vibration of poly(tetrafluoroethylene) chains by the electron spin resonance method

Temperature‐dependent electron spin resonance spectra of main‐chain free radicals, ? CF₂(β)? C · F(α)? CF₂(β)? , in poly(tetrafluoroethylene) (PTFE) were analyzed by the change in the hyperfine splitting due to β‐fluorines, which was a decreasing function of the observation temperature. The results were interpreted in terms of the rotational vibration around the C_α? C_β bond. The amplitude of the vibration was estimated on the assumption of its harmonic oscillation. The vibration of the PTFE chain was found to have a large amplitude in comparison with that of a polyethylene chain in single crystals. The vibration of the large amplitude was caused by a weak interchain interaction in the PTFE matrices. The amplitude of the vibration in crosslinked PTFE was much larger than that in noncrosslinked PTFE. This result indicated that the free radicals in crosslinked PTFE were trapped in the amorphous region, which had the disordered sites of crosslinking, whereas the free radicals in noncrosslinked PTFE were mainly trapped in the paracrystalline region. The decay reaction of the free radicals in the PTFE matrices was also related to the heterogeneity in the structure and the rotational vibration. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1539–1547, 2004     

Electronic states of lanthanide in the ternary thiogallate CaGa2S4

The electronic states of lanthanide (Ln) doped CaGa₂S₄ are investigated by the molecular orbital calculations for a spherical cluster of LnCa₈Ga₁₂S₂₄ using the FORTRAN program DVSCAT on the basis of the Discrete Variational method with Xα potentials (DV-Xα). In view of the SCF convergence, the Ln-doped lattice should contract to 85-90% of the mother crystal around the Ln atom for the lightweight lanthanides from Ce to Sm. On the other hand, the lattice contraction is very small for the heavyweight lanthanides, especially for Er, Tm and Yb in contrast to the generally known lanthanide contraction for Ln³⁺ ions. This is probably attributed to the effective charges of Ln atoms calculated here to be less than +1 for all lanthanides contrary to the chemically accepted value of +3. The energy level scheme of 4f and 5d related molecular orbitals is proposed for each Ln substituting Ca in CaGa₂S₄, showing that the optical processes relating to the 5d→4f transition must be complicated especially for the lightweight Ln-doped CaGa₂S₄.     

Physicochemical Properties of Large-Ring Cyclodextrins (CD 18 ∼CD 21

Cyclomaltooctadecaose(CD₁₈),cyclomaltononadecaose(CD₁₉),cyclomaltoeicosaose(CD₂₀) andcyclomaltoheneicosaose(CD₂₁) are cyclic oligosaccharides composed of 18, 19, 20 and 21 D-glucose units, respectively. This report describes the physicochemical properties of CD₁₈, CD₁₉, CD₂₀ and CD₂₁ in terms of aqueous solubility, surface tension, optical rotation and acid-catalyzed hydrolysis.     

Effect of water content on the solid-state stability in two isomorphic clathrates of cephalosporin: cefazolin sodium pentahydrate (alpha form) and FK041 hydrate

This study clearly demonstrates that clathrated water molecules can contribute to both chemical stabilization and destabilization of clathrates. The solid-state stabilities for two isomorphic clathrates of cephalosporin, cefazolin sodium and FK041, were investigated in terms of the effects of water content. The isomorphic ranges of water content were estimated to be 3.5-5 mol/mol for alpha-form cefazolin sodium and 2-4 mol/mol for FK041 hydrate. Upon the isomorphic dehydration, alpha-form cefazolin sodium was destabilized as the water content decreased below 4.25 mol/mol owing to the disruption of hydrogen bonding network in lattice channels. In this case, the hydration of clathrated water up to 4.25 mol/mol contributed to the physical and chemical stability of the crystals. On the contrary, the isomorphic hydration in FK041 hydrate contributed to the chemical destabilization owing to the high water activity. The difference in water activity between alpha-form cefazolin sodium and FK041 hydrate could be attributed to the size of water channels.     

Syntheses of chiral oxazolo[2,3-a]tetrahydroisoquinoline and its asymmetric alkylation. Synthesis of (S)-(−)- and (R)-(+)-sa1solidines

The isoquinolinium bromide (4), on treatment with base, underwent cyclization to give the chiral oxazolotetrahydroisoquinoline (5) with a high diastereoselectivity, which was converted to optically pure salsolidine.     

Dynamic characteristics of a peptide-binding groove of human HLA-A2 class I MHC molecules: normal mode analysis of the antigen peptide-class I MHC complex

Class I major histocompatibility complex (MHC) binds antigen peptides with various sequences. We performed a normal mode analysis of HLA-A2 MHC that binds three peptides with different affinity. HLA-A2 MHC has a peptide-binding groove composed of two alpha-helices (residue 49-84, residue 140-179). Some residues in the center of the groove showed an increase in fluctuations and some residue pairs between two helix groups showed a negative change in correlations by removing the antigen peptide. The extent of the fluctuation and correlation changes correlated well with the experimental ranking of the three peptides in binding affinity. Some definite anti-correlative motions were found between two helix groups in low frequency modes (<50 cm(-1)) by removing the antigen peptide. We propose that the above anti-correlative motions play an important role to bind the antigen peptide, especially in obtaining a "dynamic fit."     

Vibrational spectra and density functional study of propylgermane

Raman and infrared spectra of propylgermane, CH₃CH₂CH₂GeH₃, and its Ge-deuterated analog, CH₃CH₂CH₂GeD₃, were investigated in their gaseous, liquid and solid states. The normal coordinate treatment was carried out by density functional theory (DFT) calculation, using B3LYP/6-31G^* and 6-311++G^** basis sets, and the corresponding fundamental vibrations were assigned. The trans (T) and gauche (G) forms around the central C–C bond coexisted in the gaseous and liquid states and only the T form existed in the solid state. From the temperature dependent measurements of the Raman spectra in the liquid state, the enthalpy difference was found to be ΔH(T−G)=−0.36±0.02 kcalmol⁻¹ with the T form being more stable. The energy differences between the isomers obtained by DFT calculations were ΔE(T−G)=−0.46 kcalmol⁻¹ and ΔE(T−G)=−0.87 kcalmol⁻¹ by the 6-31G^* basis set and 6-311++G^** basis set, respectively.     

Novel superstructure of nondiscoid mesogens: uneven-parallel association of half-disk molecules, 3,4,5-trialkoxybenzoic anhydrides, to a columnar structure and its one-directionally geared interdigitation

Compact and simple nondiscoid mesogens, trialkoxybenzoic anhydrides 2-11 ((RO)(3)C(6)H(2)-CO-O-CO-C(6)H(2)(OR)(3), R = C(2)H(5), n-C(3)H(7), n-C(4)H(9), n-C(6)H(13), n-C(8)H(17), n-C(10)H(21), n-C(12)H(25), n-C(14)H(29), n-C(16)H(33), and (S)- and (R)-3,7-dimethyloctyl) were designed and synthesized, and their superstructures were investigated by polarized light microscopy, differential scanning calorimetry, calculation (MM2 and AM1), circular dichroism spectroscopy, and X-ray diffraction. As the result, in the cases of 5-9 and 11, the half-disk molecules in the liquid crystal phases were self-assembled by the dipole-dipole interaction between their carbonyl groups to a column in which the molecules were piled up in an alternately antiparallel manner, and the columns were interdigitated each other. The observed interdigitations were highly directional in the perpendicular direction to the column axis. In the case of compound 11 which has (S)- or (R)-3,7-dimethyloctyl groups, a helical organization of the molecules in the column was estimated from the peaks in the circular dichroism spectra. This is the first report of a one-directionally interdigitated columnar phase, and these compounds are the first liquid crystalline acid anhydrides. It was demonstrated that a -CO-O-CO- moiety is useful as a polar junction in liquid crystalline compounds.     

Synthesis of C-nor-4,6-secocamptothecin and related compounds

C-nor-4,6-Secocamptothecin 2 , 4-ethyl-4-hydroxy-6-(2-quinolinyl)-1H-pyrano[3,4-c]pyridine-3,8(4H,7H)-dione, lacking the C-ring of camptothecin 1 , and its related compounds 3 and 4 were prepared from ethyl quinoline-2-carboxylate 7 . By an analogous reaction sequences, synthesis of 6-(2-pyridinyl)-1H-pyrano[3,4-c]-pyridine-3,8(4H7H)-dione derivatives 5 and 6 , which contain the B, D, and E ring of 1 , were achieved.     

Continuous flotation of trace amounts of nitrite ion in water

A flotation method in which sample is continuously fed at flow rates of 2–3 1 h^-1 into a separation tube is described. The nitrite (3–40 μg l^-1) is continuously converted to an azo dye for spectrophotometric measurement at 15-min intervals.