7,10,14-Tri-t-butyl-3-amino-1,8-bisdehydro[14]annulene

Tri-t-butylcarboxybisdehydro[14]annulene was converted by the Curtius reaction into unstable aminoannulene, which could be characterized as N-acetyl derivative. The pK_a-value of the aminoannulene reflects aromatic nature of the annulene nucleus.     

Localization of Iα and Iβ phases in algal cellulose revealed by acid treatments

Highly crystalline I-rich type Cladophora cellulose, which had been kept in never-dried condition, was treated in 60wt% sulfuric acid at 100°C, for 1–48h. The cellulose microcrystals thus obtained were analysed by X-ray diffractometry, FT-IR, and transmission electron microscopy. The I component was found to be more degraded than the I component. The cellulose I/I ratios of the samples acid-treated for 0, 24, and 48 h were about 8:2, 6:4, and 4:6, respectively. After the acid treatment, the microcrystals became narrower in width, and very sharp at their ends. These results indicate that the I phase is mostly located at the surface of the microcrystals, which is morphologically more susceptible to the acid treatment.     

Studies on diacetylenic vinyl compounds. VI. ESR studies on the polymerization of diacetylene containing acrylate and methacrylates

A number of diacetylene containing acrylate and methacrylates have been synthesized and the interaction between their propagating radicals and the diacetylene groups was studied by ESR spectroscopy. In the case of polymerization at 70°C using AIBN as an initiator, the propagating radicals of methacrylates are temporarily trapped with the diacetylenes with rapid exchange of the electron, thus showing strong signals of the propagating radicals. Gamma irradiation of the frozen state produces a blue color in samples, and the ESR signals were found to be those of uninteracted acrylate and methacrylates. From a comparison of spectral widths, there seems to exist an intramolecular interaction between the radicals and the diacetylene group at the frozen state. © 1992 John Wiley & Sons, Inc.     

Spatial geometric arrangements of disulfide-crosslinked loops in nonplanar proteins

The method presented earlier [T. Kikuchi, G. Némethy, and H.A. Scheraga, (1986) J. Comput. Chem. 7 , 67] for the classification of patterns of the three-dimensional folding of a covalently crosslinked polypeptide chain has been extended to nonplanar proteins. The procedure described earlier was applicable only to proteins termed planar, i.e., with a connexity of the crosslinks (e.g., disulfide bonds) that can be represented in a planar diagram. The procedure described in the present work is applicable to any (planar or nonplanar) pattern of crosslinking. The classification is based on a systematic and objective method of enumeration of spatial geometric arrangements of loops (SGAL) using no information other than the location of the disulfide bonds in the amino acid sequence. Various SGAL classes correspond to the presence of different ways of mutual penetration of loops, called thrustings and entanglements. Information on SGAL classes can be of use in structural predictions of folding patterns of proteins.     

3-Aroylmethyl derivatives of 2(1H)quinoxalinone and 2H-l,4-benzoxazin-2-ones existing in the enamine form

Seventeen derivatives of 2(1H)quinoxalinone and 2H-l,4-benzoxazin-2-one have been synthesized for structural study. All of the compounds having a substituted phenacyl, isonicotinoylmethyl, or 2-furoylmethyl side chain are shown to exist in the enamine form with an internal chelation both in the crystalline and solution states as evidenced by the ir and pmr spectra, respectively. In the gas phase, however, o-hydroxyphenacyl derivatives can exist in another type of intramolecularly hydrogen-bonded form which is supported by their mass spectra.     

Theoretical study of endohedral metallofullerenes: Sc3−nLanN@C80 (n=0–3)

To provide theoretical insight into the structures and properties of Sc₃N@C₈₀, which has been isolated in high yield and purity as a new stable endohedral metallofullerene, density functional calculations are carried out for the Sc_3?nLa_nN@C₈₀ (n=0–3) series. Because of electron transfer from Sc₃N to C₈₀, the electronic structure of Sc₃N@C₈₀ is formally described as (Sc₃N)⁶⁺C$_{80}^{6-}$. The encapsulated Sc₃N cluster takes a planar structure with long Sc–Sc distances and is highly stabilized inside the I_h cage of C₈₀, which rotates rapidly. As the number of La atoms increases, the Sc_3?nLa_nN cluster is forced to maintain a pyramidal structure in Sc_3?nLa_nN@C₈₀. In addition, the C₈₀ cage takes an open‐shell electronic structure due to an increase in the number of electrons transferring from Sc_3?nLa_nN. These make the endohedral structure less stable and more reactive. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1353–1358, 2001     

Mössbauer spectroscopic studies of (n-C n H2n +1NH3)2SnX6 (n=0-4; X = Cl or Br) and their related complexes

Complexes of the type (n-C _n H_2n +1NH₃)₂SnX₆ (0n 4 and X=Cl or Br) have been investigated with a variety of physico-chemical techniques. The structural phase transitions were found in some of these complexes. The temperature dependence of the Mössbauer spectral absorption area for (C₂H₅NH₃)₂SnCl₆ and (C₂H₅NH₃)₂SnBr₆ changed sharply at phase transition temperatures. The temperature dependences for (n-C₄H₉NH₃)₂SnCl₆ and (n-C₄H₉NH₃)₂SnBr₆ decreased gradually with an increase in temperature. The correlation between the temperature dependence of the spectral absorption area and the motion of n-C _n H_2n+1NH₃ ⁺ ions is discussed.