Nobutami Kasai

Raman spectroscopic studies of silk fibroin from Bombyx mori

This study was focused on the conformational characterization of Bombyx mori silk fibroin in film, fiber and powder form by means of Fourier transform Raman spectroscopy. Native and regenerated silk fibroin films prepared by casting dilute silk fibroin solutions (<1%, w/v) display characteristic conformationally sensitive bands at 1660 cm-1 (amide I), in the range 1276–1244 cm-1 (a complex amide III region with multiple detectable maxima) and at 1107 and 938 cm-1. This spectral pattern can be related to a prevalently random coil conformation, with traces of α-helix. Liquid silk, prepared by casting the silk gland content (fibroin concentration 20–25%, w/v), shows almost the same wavenumbers in the amide I and III ranges, while differences appear below 1000 cm-1, where three bands at 952, 930 and 867 cm-1 increase in intensity. The spectral differences between films and liquid silk are discussed with a view to identifying possible markers for silk I structure, a crystalline modification of silk fibroin. The treatment of both native and regenerated films with 50% (v/v) methanol solution induces the conformational transition to a β-sheet structure, as demonstrated by the shift of amide I to 1665 cm-1 and the appearance of new maxima at 1262 and 1236 cm-1 (amide III) and at 1084 cm-1. When liquid silk is cast at above 50°C, the prevailing conformation taken by silk fibroin is β-sheet, whatever the rate of drying. By comparing the Raman spectra of silk fibroin fiber and powder, both having a β-sheet structure, a difference in the tyrosine doublet bands and in the amide I band can be observed. The value of the I853/I830 (Rtyr) intensity ratio increases in the powder while amide I shifts to lower wavenumbers, suggesting that the hydrogen bonds involving the tyrosil residues are weaker in the powder than in the fiber.

Single-Helical Structure of Native Curdlan and its Aggregation State

ABSTRACT One of the polymorphs of β-(1→3) glucan, curdlan, was studied by X-ray diffraction and thermal analyses. Different from the molecular models proposed so far, the molecular structure of native curdlan (Form I) was found to be a 6/1-single stranded helix. Therefore, the transformation from Form I to Form II is a conversion process from single to triple. Form I specimen has three kinds of water, bound- and amorphous-water in the crystalline micelles and free water in the intermicelles. The amount of bound water is estimated to be more than 10 %wt. If the specimen is kept at less than 98%RH, the effusion of free water and amorphous water occurs very easily, which causes a drastic decrease of the specimen weight. The bound water is left even at 0%RH.

Synthesis, Structure and Reactivities of [6]Paracyclophanes.

Abstract The synthesis, structure and reactivities of [6]paracycophanes 2a-c, the smallest bridged [n]paracydophanes so far isolated, are described. The parent hydrocarbon 2a has been efficiently synthesized by oxidative decarboxylation of [6.2-2]propellenecarboxylic acid (7) by lead tetraacetate. The 8-carbomethoxy derivative 2b has been quantitatively synthesized by thermal valence isomerization of the [6.2.2]propelladiene (4b) (Dewar isomer of 2b). X-Ray structure analysis of the crystalline 2c has revealed that the benzene ring of 2c severely deformed into a boat conformation with deformation angles of α= 20.5° and β = 18.5°. Furthermore, the bond angles of the bridging chain (C(2), C(3), C(4) and C(5)) are considerably expanded from the normal sp3 angle. Vaporphase thermolysis of 2a gives the spiro triene 12 via homolysis at the benzyl position. Add-catalyzed isomerization of 2a with trifluoroacetic add takes place readily to afford the meta and ortho isomers 13a and 14a in a ratio of 1:3. UV irradiation of the ester 2b brings about valence isomerization to the Dewar isomer 4b which isomerizes slowly to the prismane derivative 15a on further irradiation. A [4+2] cycloaddition of 2a with N-phenyl-l,2,4-triazoline-3,5-dione occurs at room temperature to give mainly adduct 16. Addition of bromine to 2a takes place to furnish quantitatively the unstable 1,4-addition product 18. Oxidation of 2a with mCPBA readily takes place to give the dienone dimer 20 which affords on UV irradiation the cage diketone 21 derived from intramolecular photocycloaddition.

The crystal and molecular structure of a 3:2 mixture of laminarabiose and O-α-d-glucopyranosyl-(1→3)-β-d-glucopyranose

Abstract The crystal and molecular structure of a 3:2 mixture of laminarabiose and 3-O-α- d -glucopyranosyl-β- d -glucopyranose has been determined by X-ray diffraction. The crystal belongs to the monoclinic system, space group P2, a 14.778(1), b 4.794(1), c 10.516(1) A and β 98.10(1)c, Dm 1.54 g. cm-3, Z 2. The structure was solved by the direct method and refined by the block-diagonal, least-squares procedure to R 0.057 for 1034 observed reflections. Difference synthesis showed all hydrogen atoms and indicated a partial (∼39%), random substitution of the β anomer molecules by the α anomer molecules, which are accompanied by water molecules on the crystallographic two-fold axis (∼19%). The molecule shows a conformation, different from the fully-extended one, which is stabilized by an intramolecular hydrogen-bond between O-1-H and O-5 [2.786(7) A]. The ring-to-ring conformation can be described as (Φ, Ψ)=(27.9·–37.5·), according to the definition of Sathyanarayana and Rao, and it is located in the comparatively low-energy region of the energy-contour diagram of laminarabiose. Four intermolecular hydrogen-bonds hold molecules together to form infinite sheets, which are approximately parallel to the ab-plane and linked by additional hydrogen-bonds in the c-direction.

The Crystal and Molecular Structure of trans -Bis(trimethylphosphine)propynyl-1-(4′-dicyanomethylene-cyclohexa-2′-5′-dien-1-ylidenl-3,3-dicyano-2-methyl-prop-2-en-1-ylplatinum, a Reaction Product of trans -Bis(trimethylphosphine)bis(propynyl)platinum and 7,7,8,8-Tetracyanoquinodimethane

The molecular structure of the title complex has been determined from three-dimensional X-ray diffraction data. The crystal belongs to the monoclinic system, space group P21/c, a=14.934(2), b=8.997(1), c=20.221(3)A, β=97.44(2)°, Z=4. The molecular structure showed that the tetracyanoquinodimethane (TCNQ) molecule has reacted with one of the propynyl groups of trans-{(PMe3)2Pt(C≡CMe)2} : part of the TCNQ is bonded to the α-carbon atom and the other part to the β-carbon of the propynyl ligand. The platinum atom has a squareplanar geometry; Pt–P=2.302(5) and 2.290(5), Pt–C(C≡CMe3)=2.009(15) and Pt–C(reacted)=2.057(15) A.

A simplest isolable monocyclic thiepin. Synthesis, structure, and thermal stability of 2,7-di-tert-butylthiepin

Abstract As an example of a simplest isolable monocyclic thiepin, 2,7-di-tert-butylthiepin (2) has been synthesized from 2,6-di-tert-butylthiopyrylium salt, and the thermal properties together with the X-ray crystal structure of (2) have been examined.

The crystal structure of the polymerization catalyst of acetaldehyde and its derivatives I. The crystal structure of dimethylaluminum N-phenylbenzimidate dimer, [(CH3)2AlOC(6H5)N(C6H5)]2

Abstract The crystal structure and molecular configuration of the highly stereospecific polymerization catalyst of acetaldehyde, dimethylaluminum N-phenylbenzimidate dimer, [(CH3)2AlOC(C6H5)N(C6H5)]2 have been determined from three-dimensional X-ray data collected photographically. The crystal belongs to the monoclinic system, space group P21/c, with two dimer formula units in a cell of dimensions: a=6.64±0.03, b=12.05±0.01, c=18.28±0.01 A, and β=94.9±0.02°. The structure has been refined by block-diagonal least-squares using anisotropic temperature factors for the nonhydrogen atoms. Hydrogen atoms with isotropic temperature factors were also included in the refinement. The final R index is 0.107 for 1096 non-zero reflections. The dimeric molecule is composed of a centro-symmetrical eight-membered ring; the aluminum atoms are bridged by OCN groups. The environmental of the aluminum atom is distorted tetrahedron: AlO = 1.805(6), AlN = 1.947(7), AlC = 1.940(11) and 1.940(11) A. The environments of the N and C atoms (of the eight-membered right) are trigonal. The configuration of the two adjacent benzene rings about the NC bond is cis.

The preparation and X-ray molecular structure of a novel dialkylpalladium(II) compound containing bridged thiophenoxymethyl groups

Abstract A stable homoleptic palladium compound, [Pd(CH 2 SC 6 H 5 ) 2 ] 4 was isolated by treatment of (C 6 H 5 CN) 2 PdCl 2 with LiCH 2 SC 6 H 5 , and its molecular structure has been determined by means of three-dimensional X-ray diffraction data at −160°C. The CH 2 Cl 2 solvate ([Pd(CH 2 SC 6 H 5 ) 2 ] 4 · CH 2 Cl 2 ) forms orange-yellow, monoclinic crystals; a 16.302(3), b 19.394(4), c 18.552(3)A and β 91.28(2)° at −160°C, space group P 2 1 / n with Z = 4. The structure was solved by the conventional heavy atom method, and refined by the least-squares procedure to R = 0.089 for 4363 independent non-zero reflections. The fairly rigid cyclic tetramer is formed, which has approximate 222 symmetry. Four palladium atoms occupy the corners of a distorted rectangle and two averaged Pd···Pd distances are 4.051 and 3.304 A, respectively. Four coordination planes around the palladium atom, the geometries of which are essentially square-planar, are equivalent with each other. The CH 2 SC 6 H 5 groups bridge four palladium atoms (mean SC(methylene) 1.82, SC(phenyl) 1.80 A).

Structure and molecular conformation of tussah silk fibroin films treated with water–methanol solutions: Dynamic mechanical and thermomechanical behavior

The thermal response of tussah (Antheraea pernyi) silk fibroin films treated with different water–methanol solutions at 20°C was studied by means of dynamic mechanical (DMA) and thermomechanical (TMA) analyses as a function of methanol concentration and treatment time. The DMA curves of α-helix films (treated with ≥80% v/v methanol for 2 min and 100% methanol for 30 min) showed the sharp fall of storage modulus at about 190°C, and the loss peak in the range 207–213°C. The TMA curves were characterized by a thermal shrinkage at 209–211°C, immediately followed by an abrupt extension leading to film failure. Both storage and loss modulus curves significantly shifted upwards for β-sheet films, obtained by treatment with ≤60% methanol for 30 min. The loss peak exhibited a maximum at 236°C. Accordingly, the TMA shrinkage at above 200°C disappeared. The films broke beyond 330°C, failure being preceded by a broad contraction step. Intermediate DMA and TMA patterns were observed for the other solvent-treated films. The loss peak shifted to higher temperature (219–220°C), and a minor loss modulus component appeared at about 230°C. This coincided with the onset of a plateau region in the storage modulus curve. The TMA extension–contraction events in the range 200–300°C weakened, and the samples displayed a final broad contraction (peak temperature 326–338°C) before breaking. The DMA and TMA response of these films was attributed to partial annealing by solvent treatment, which resulted in the formation of nuclei of β-sheet crystallization within the film matrix. The increased thermal stability was probably due to the small β-sheet crystals formed, which acted as high-strength junctions between adjacent random coil and α-helix domains.

Studies of organometallic compounds : XLIII. Reactions of organotin chlorides with sodium azide

Abstract Dialkyltin dichlorides R 2 SnCl 2 (R  CH 3 , C 2 H 5 , n-C 3 H 7 , and n-C 4 H 9 ) react with sodium azide in the presence of water to give hexaalkyl-1,5-diazidotristannoxanes N 3 R 2 Sn(OSnR 2 ) 2 N 3 , tetraalkyl-1,3-dichlorodistannoxanes also give the same products. The configuration of the tristannoxane compound was established by X-ray diffraction study. On the other hand, dioctyltin dichloride yielded octaoctyl-1,7-diazidotetrastannoxane. Hexamethyl-1,5-diazidotristannoxane was treated with boiling methanol to give tetramethyl-1-azido-3-methoxydistannoxane, N 3 (CH 3 ) 2 -SnOSn(CH 3 ) 2 OCH 3 .