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  • Electronic Resource  (265)
  • Chemistry  (259)
  • General Chemistry  (42)
  • crystal structure  (6)
  • 1
    Electronic Resource
    Electronic Resource
    Cyanophenoxy-containing microbial polyesters: Structural analysis, thermal properties, second harmonic generation and in-vivo biodegradability (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Polymer International 39 (1996), S. 205-213 
    Details
    ISSN: 0959-8103
    Keywords: Pseudomonas putida ; poly(β-hydroxyalkanoate) ; microbial polyesters ; poly[3-hydroxy-6(4-cyanophenoxy)hexanoate] ; non-linear optics ; in-vivo biodegradation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Pseudomonas putida KT 2442 was utilized as biocatalyst to form optoactive poly(β-hydroxyalkanoate)s (PHAs) from a cosubstrate mixture of octanoate and the achiral polarizable carbon source 6(4-cyanophenoxy)hexanoate, CPH. COSY and heteronuclear multiplet quantum correlation experiments were used to assign 1H and 13C NMR signals of 3-hydroxy-6(4-cyanophenoxy)hexanoate (3HCPH) repeat units. The methine carbon of 3HCPH repeat units was sensitive to repeat unit sequence effects, indicating that a substantial fraction of 3HCPH centered triad sequences in the product contain neighboring 3-hydroxyoctanoate and 3-hydroxhexanoate repeat units. Comparing the thermal properties of 0 and 19.6 mol% 3HCPH samples by differential scanning calorimetry shows that 3HCPH incorporation results in melting at temperatures 〉64°C (not seen for the 0 mol% sample), more rapid crystallization and a new Tg transition at ∼ -21°C. These characteristics indicate that chains and/or chain segments are formed that are enriched in 3HCPH which phaseseparate and form a unique crystal structure. Measurements of second harmonic generation (SHG) intensities carried out using in-situ corona-poled samples showed weak SHG signals that increased by a factor of 8 for an increase in the 3HCPH content from 26 to 34 mol%. Comparatively higher SHG intensities (5 times) were found for PHAs which contained 5.1 mol% 3-hydroxy-6(4-nitrophenoxy)hexanoate (3HNPH) repeat units relative to a PHA with 17 mol% 3HCPH. In-vivo biodegradation studies of microbial polyesters prepared with and without 3HCPH repeat units showed that PHA chains with 3HCPH degraded to lesser extents (weight loss of ∼ 20 and 50% over 72 h incubations). The large increase in polydispersity from 1.9 to 4.3 observed during in-vivo biodegradation of microbial polyesters containing 3HCPH repeat units was attributed to the existence of chains with highly variable contents of 3HCPH repeat units.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular gears: Structures of (9,10-triptyceno) crown ethers (1999)
    Springer
    Journal of chemical crystallography 29 (1999), S. 513-521 
    Details
    ISSN: 1572-8854
    Keywords: nanotechnology ; molecular devices ; triptycene ; crown ether ; crystal structure ; thallium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The incorporation of 9,10-triptycene unit in a crown ether is examined from a structural perspective. Insertion of a triptycene group into 18-crown-6 stretches the crown into an ellipse, as seen in structures presented here of 9,10-triptyceno-22-crown-6 and its thallium complex. Symmetric addition of two triptycene groups into 18-crown-6 results in the sterically congested bis(9,10-triptyceno)-26-crown-6, whose crown cavity is filled with the π-clouds of two arene groups. The larger bis(9,10-triptyceno)-32-crown-8 is more sterically relaxed. The structures of these bis(triptyceno)crown ether molecules are the first with two triptycene groups simultaneously linked through their 9 and 10 positions, thereby forming a simple molecular gearing mechanism. The compound 9,10-triptyceno-22-crown-6 (1) crystallizes in the orthorhombic space group Pbca with a = 10.7962(7), b = 15.826(3), c = 31.147(5) Å, V = 5321.8(12) Å3, and Z = 8; its complex with TlNO3 (Tl-1) crystallizes in the monoclinic space group P21/c with a = 8.1884(14), b = 19.552(2), c = 20.575(4) Å, β = 97.062(8)°, V = 3269.2(9) Å3, and Z = 4; bis(9,10-triptyceno)-26-crown-6 (2) crystallizes in the triclinic space group P $$\bar 1$$ with a = 8.6488(11), b = 10.7718(12), c = 12.3324(12) Å, α = 111.58(1), β = 100.55(1), γ = 106.43(1)°, V = 970.3(5) Å3, and Z = 1; and bis(9,10-triptyceno)-32-crown-8 (3) crystallizes in the orthorhombic space group Pna21 with a = 20.186(3), b = 8.558(2), c = 25.623(2) Å, V = 4426.2(14) Å3, and Z = 4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009535632237
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  • 3
    Electronic Resource
    Electronic Resource
    Reactions of the dirhenium(II) complexes Re2X4(dppm)2 (X= Cl, Br; dppm = Ph2PCH2PPh2) with isocyanides. Part IX. New isomeric forms of the mixed carbonyl-isocyanide dirhenium(II) Complexes Re2 Cl4(dppm)2(CO)(CNxyl) and [Re2Cl3(dppm)2(CO)(CNxyl)2]O3SCF3 The X-ray crystal structure of [(xyl NC)2ClRe(μ-dppm)2ReCl2(CO)] O3SCF3 (1996)
    Springer
    Journal of cluster science 7 (1996), S. 155-166 
    Details
    ISSN: 1572-8862
    Keywords: Rhenium ; dirhenium complexes ; rhenium-rhenium multiple bonds ; isocyanide ligands ; carbonyl ligand ; structural isomers ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The monocarbonyl complex Re2Cl4(µ-dppm)2(CO) reacts with xylyl isocyanide in acetonitrile to afford the bioctahedral complex (CO)Cl2Re(µ-dppm)2 ReCl2(CNxyl), 2b. This is a different structural isomer from the edge-sharing bioctahedral complex Cl2Re(µ-Cl)(µ-dppm)2ReCl(CNxyl) or this same stoichiometry which A formed when acetone is be reaction solvent. The complex2b reacts with a further equivalent of xylNC in the presence of TlO3SCF3 in dichloromethane to form a red complex of composition [Re2Cl3(µ-dppm)2 (CO)(CNxyl)2]O3SCF3. 3, which has the open bioctahedral structure [(xylNC)2ClRe(µ-dppm)2ReCl2(CO)]O3SCF3. This is a third isomeric form of this dirhenium cation: the previously isolated green and yellow forms have edge-sharing bioctahedral structures. Crystal data for3 at 295 K: orthorhombic space group Pbca (No. 61) witha=22.654(5) Å,b=22.717(4) Å,c=27.324(4) A,V= 14061(7) Å3, andZ = 8. The structure was refined to R = 0.059 (R, = 0.134 ) for 14164 data. The Re-Re distance is 2.3833(8) Å.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01166054
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis of a new dibenzo-14-crown-4 lariat ether and structure of its sodium perrhenate complex (1999)
    Springer
    Journal of chemical crystallography 29 (1999), S. 1255-1259 
    Details
    ISSN: 1572-8854
    Keywords: crown ether ; crystal structure ; lariat ; sodium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A dibenzo-14-crown-4 ether with a novel monooxyacetone sidearm is prepared and its structure with sodium perrhenate is determined. The structure crystallizes in P21/c with cell dimensions: a = 8.107(2) Å, b = 28.138(3) Å, c = 10.293(2) Å, and β = 104.173(9)°; giving a volume of 2276.6(7) Å3. This structure is compared to other sodium complexes of dibenzo-14-crown-4 lariat ethers and is found to be the only one with intramolecular bonding between the sidearm and the cation. Possible reasons for this observation are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009552806586
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  • 5
    Electronic Resource
    Electronic Resource
    Nucleophilic additions of primary and secondary amines to pentacyclo[5.4.0.02,6.03,10.05,9]undecane-8,11-dione (1995)
    Springer
    Journal of chemical crystallography 25 (1995), S. 633-640 
    Details
    ISSN: 1572-8854
    Keywords: Amines ; crystal structure ; pentacycloundecane-8,11-dione
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The crystal structures of three compounds formedvia nucleophilic attack of a heterocyclic secondary amine on PCU-8,11-dione, with the concomitant intramolecular attack of one keto oxygen on the carbon of the other ketone, are presented. In all three compounds, the bridging oxygen contains substantial p-character, and the bonds to the “attacking” nitrogen are significantly shorter than would be expected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01665969
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  • 6
    Electronic Resource
    Electronic Resource
    Reactions of the Dirhenium(II) Complexes Re2 X 4(μ-dppm)2 (X=Cl, Br; dppm=Ph2PCH2PPh2) with Isocyanides. Part XV: A Fifth Structural Isomer of the [Re2Cl3(μ-dppm)2(CO)(CNXyl)2]+ Cation (Xyl = 2, 6-Dimethylphenyl) (1997)
    Springer
    Journal of cluster science 8 (1997), S. 547-551 
    Details
    ISSN: 1572-8862
    Keywords: Rhenium ; dirhenium complexes ; rhenium–rhenium multiple bonds ; isocyanide ligands ; carbonyl ligand ; structural isomers ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The reaction of the unsymmetrical, coordinatively unsaturated dirhenium(II) complex [(XylNC)(OC)CIRe(μ-dppm)2ReCl2]O3SCF3 (dppm = Ph2PCH2PPh2) with one equivalent of XylNC in CH2Cl2 affords a fifth structural isomer of the [Re2Cl3(μ-dppm)2(CO)(CNXyl)2] + cation; this is believed to have a CO-bridged structure of the type [(XylNC)ClRe(μ-Cl)(μ-CO)(μ-dppm)2ReCl(CNXyl)]+. The latter complex reacts with a further equivalent of XylNC in the presence of Tl+ to form the [Re2Cl2(μ-dppm)2(CO)(CNXyl)3]2+ cation, which has been shown by IR spectroscopy, and by the X-ray crystallographic characterization of its neutral congener Re2Cl2(μ-dppm)2(CO)(CNXyl)3, to contain a very weak and unsymmetrical CO bridge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022609214775
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  • 7
    Electronic Resource
    Electronic Resource
    Multiple denaturational transitions in fibrillar collagen (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1875-1893 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The heat denaturation of pepsinized bovine nonfibrillar and fibrillar collagen was studied by differential scanning calorimetry. For fibrillar preparations that had been rapidly precipitated with stirring at low ionic strength, then resuspended at physiological ionic strength, multiple denaturational transitions were observed. At heating rates of 10°C/min, melting endotherms occurred at about 44, 50, 53, and 57°C. Fibrillar collagen that was slowly gelled without stirring at physiological ionic strength exhibited a similar series of endotherms, but the lower melting transitions were less conspicuous. In contrast, nonfibrillar bovine collagen in acidic solution showed only a single denaturational transition at 40°C. Nonfibrillar solutions at pH 7, to which inhibitors of fibrillogenesis were added, showed a major endotherm as high as 46°C. These results suggest that reconstituted fibrillar collagen contains a heterogeneous fibril population, possibly including molecules in a nonfibrillar state. It was proposed that the multiple melting endotherms of such preparations were due to sequential melting of molecular and fibril classes, each with a distinct melting temperature. The fibrillar classes may represent three or more types of banded and nonbanded species that differ from each other in packing order, collagen concentration, and possibly also in fibril width and level of cross-linking.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360251006
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  • 8
    Electronic Resource
    Electronic Resource
    Optical activity of polypeptides in the infrared. Predicted CD of the amide I and amide II bands (1975)
    New York : Wiley-Blackwell
    Biopolymers 14 (1975), S. 173-196 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Miyazawa-Blout-Krimm (M-B-K) treatment of polypeptide absorption in the infrared is extended to the calculation of circular dichroism (CD), linear dichroism, and oriented CD for the amide I and amide II transitions. Matrix methods are applied to the α helix and β structures using measured values for the strengths and directions of the transition dipole moments and empirical values from M-B-K for the coupling constants.Relatively small aggregates, a 36-residue helix, and 8-chain × 4-residue β sheets, are large enough to show calculated absorption agreeing with M-B-K results, which are based on infinite lattices.In all cases the predicted CD is an approximately conservative couple. The strongest CD should appear in the α helix, Δε/ε ≃± 10-3 for both transitions. The amide II transition should show moderate CD couples in both β structures, Δε/ε ≃ (+2 to -1) × 10-4. The amide I transitions in β structures should show weak CD couples, Δε/ε = (+3 to -2) × 10-5, except that the negative branch in the antiparallel structure may be detectable (Δε/ε ≃ -2 × 10-4) because absorption is very low at its wavelength peak.CD on oriented samples should be enhanced over the unoriented cases, giving values as large as Δε/ε = 3 × 10-3 because particular directions of observation allow the light to avoid much of the absorption in the sample.If all three structures are considered as helices, then the larger distance of the transition dipoles from the axis in the α helix, and the orientations of the transitions in the different structures, are the factors that, in terms of our previous theoretical work [Snir and Schellman (1973) J. Phys. Chem. 77, 1653] satisfactorily explain the calculated results. Simple dipole-dipole interaction is calculated to make a substantial contribution to the coupling between groups.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1975.360140113
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  • 9
    Electronic Resource
    Electronic Resource
    The sieving of spheres during agarose gel electrophoresis: Quantitation and modeling (1989)
    New York : Wiley-Blackwell
    Biopolymers 28 (1989), S. 1475-1484 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By use of agarose gel electrophoresis, the sieving of spherical particles in agarose gels has been quantitated and modeled for spheres with a radius (R) between 13.3 and 149 mm. For quantitation, the electrophoretic mobility has been determined as a function of agarose percentage (A). Because a previously used model of sieving [D. Rodbard and A. Chrambach (1970) Proc. Natl. Acad. Sci. USA 65, 970-977] was found incompatible with some of these data, alternative models have been tested. By use of an underivatized agarose, two models, both based on the assumption of a single effective pore radius (PE) for each A, were found to yield PE values that were independent of R and that were in agreement with values of PE obtained independently (PE = 118 nm × A-0.74): sieving by altered hydrodynamics in a cylindrical tube of radius, PE, and sieving by steric exclusion from a circular hole of radius, PE. The same analysis applied to a 6.5% hydroxyethylated commercial agarose yileded a steeper PE vs A plot and also agreement of the above tow models with the data. The PE vs A plot was significantly altered by both further hydroxyethylation and factors that cause variation in the electro-osmosis found in commercial agarose.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360280811
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  • 10
    Electronic Resource
    Electronic Resource
    Editorial (1995)
    New York : Wiley-Blackwell
    Biopolymers 37 (1995), S. 176-176 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360370302
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