NMR and X-ray diffraction

Poly(vinyl fluoride) [24981-14-4] (PVF) is a semicrystaltiae polymer with a planar, zig-zag configuration (50). The degree of crystallinity can vary significantly from 20—60% (51) and is thought to be primarily a function of defect stmctures. Wide-line nmr and x-ray diffraction studies show the unit cell to contain two monomer units and have the dimensions of a = 0.857 nm, b = 0.495 nm, and c = 0.252 nm (52). Similarity to the phase I crystal form of poly (vinytidene fluoride) suggests an orthorhombic crystal (53). 

Glass-forming systems other than siUca have been examined. The fraction of three- and four-coordinated boron in borate glasses can be determined by nmr (29). Both nmr and x-ray diffraction (30) results led to the suggestion that the boroxyl ring is the stmctural unit of vitreous The... 

The recognition that short chain / -peptides can form regular secondary structures initially came from detailed conformational analysis of y9 -peptides 1 and 66 (which incorporates a central (2S,3S)-3-amino-2-methylbutanoic acid residue) by NMR in pyridine-d5 and CD3OH [10, 103, 164] and homooUgomers (as short as four residues) of trons-2-amino-cyclohexanecarboxyhc acid (trans-ACHC) (e.g. hex-amer 2 for the (S,S) series) by NMR and X-ray diffraction [6, 126, 159]. 

Thomas and co-workers [277] reported that irradiation of (382) with a 450 W high-pressure mercury lamp brought about photocyclisation to a constrained analogue (394). The structure of the product was elucidated through NMR and X-ray diffraction analysis. The compound retained high affinity for the CBi receptor (Xj = 48 nM) and good selectivity over the CB2 receptor (K[ — 3,340 nM). 

Quinone methide complexes were characterized by standard spectroscopic techniques. It is possible to elucidate the structural and electronic properties of the QM complexes and also to estimate the reactivity tendencies of the coordinated QM moiety based on IR, NMR, and X-ray diffraction spectroscopes. 

Polarized Raman and fluorescence spectroscopies, NMR and X-ray diffraction allow the determination of at least (P2) and (P4) for uniaxial systems. This is a great advantage since the shape of the orientation distribution can then be estimated [7], even if not all the coefficients of the ODF s expansion are known. While P2 has fixed boundary limits, those of (P4) depend on the (P2) value such as... 

Unusual example of bidentate ligand involved in linkage isomerism. Forms characterized by P nmr and x-ray diffraction. (ly isomer favored at 40 °C pH 6.5. No kinetic data on rearrangement. 

The reaction of amidophosphito cavitands with Cr, Mo, and W hexacar-bonyl, and C5H5Mn(CO)3 resulted in the formation of the binuclear complexes. The structure was elucidated by and NMR and X-ray diffraction analysis, and showed that the distal bi-nuclear structure was formed. The tetra-nuclear complex was only obtained with tetra-phosphitocavitand 14 and Cr or Mo hexacarbonyl (Scheme 19) [72]. 

An interesting difference in the diastereoselectivity of the ring closure was found in the cyclizations of the cis amino alcohols 21 (R = H, Me) (84T3587). Depending on the A-substituent, C-2 epimers were isolated. The structures were determined by NMR and X-ray diffraction [82ACH(109)39 84T3587],... 

Cys residues spaced i, i + 3 apart have been covalently linked to obtain cyclic peptides which fold into a 310-helix. Balaram et al.[159l synthesized Boc-c[-Cys-Pro-Aib-Cys-]-NHMe, wherein a disulfide bond links the two Cys residues. Pro and Aib residues were used to restrict conformational flexibility. NMR and X-ray diffraction studies revealed a highly folded, compact formation of an incipient 3i0-helix, with the S—S bridge lying approximately parallel to the helix axis. 

S. Brunak and R.M.J. Cotterill (Technical University of Denmark) pursued the approach further, based upon data inputs from NMR and x-ray diffraction. The neural network approach remains very active so that encoding of the intricacy of interconnections may be achievable. 

In another failed approach, addition of 1-pyrrolidinocyclohexene 32 to ( )-( l-melhyl-2-oxoindolin-3-ylidene)acetophenone 31, followed by acid hydrolysis, could be controlled simply by changes in the reaction temperature, and was found to give diastereoselectively compounds 33 or 34. The latter compound was shown by NMR and X-ray diffraction data to have the suitable geometry to allow the creation of the crucial bond between the position adjacent to the cyclohexanone carbonyl and the oxindole C-4 position. 

We thank L.E. Manzer, V.N.M. Rao, A.E. Feiring and B.E. Smart for many helpful discussions during the course of this work. We also thank A.J. Vega and R.L. Harlow for NMR and X-ray diffraction studies of Ag10F8C2, respectively. 

To draw conclusions concerning the templating effect of different molecules, comparable conditions for the crystallization process must be used. In this paper we present a systematic investigation on the effect of mono-, di- and tri-n-alkylamine and tetraalkylammonium compounds (alkyl = C. - C,) upon the rate of crystallization, yield and the properties of the products. Also the field of a template-free synthesis is studied. The products were characterized by magic-angle-spinning nuclear magnetic resonance spectroscopy (MAS NMR) and X-ray diffraction. 

Characterization of Substituted Boron. We used solid state -B NMR and X-ray diffraction data to distinguish occluded borates from boron substituted into the zeolite framework. When an element replaces aluminum or silicon in a zeolite structure, the local coordination environment changes to accommodate the new ion. Since B + is a much smaller ion than Al "1", the unit cell axes contract when boron replaces aluminum in the framework. The ionic radii of trivalent B and A1 in a tetrahedral environment are 0.25 and 0.53, respectively (1). The magnitude of the contraction is dependent upon the level of substitution (17). 

The NMR and X-ray diffraction data are only consistent with substitution of boron into the framework structure of the mordenite. Although we prepared boron substituted mordenite directly from modified gels, direct synthesis has severe limitations. The solution chemistry of the substituting element can interfere with zeolite nucleation and crystallization, as... 

McChesney JD, Dou J, Slndelar RD, Goins DK, Walker LA, Rogers RD (1997) Tirucallane-type Trlterpenolds NMR and X-ray Diffraction Analyses of 24-Epi-piscidinol A and Plscldlnol A. J Chem Crystallogr 27 283... 

A range of imidazabole derivatives have been described recently. These compounds may be considered as aza- (69a) or carbene-borane (69b) adducts. However, NMR and X-ray diffraction data of these compounds (69) indicate that they are dimers of carbene borane adducts rather than dimers of... 

The compound can be isolated in pentane, recrystallized, and characterized by IR, H NMR and x-ray diffraction. The bis(cyclopentadienyl)lanthanide(f -allyl) complexes are also stable decomposition occurs at greater than 200°C... 

This molecule presents a lithium-boratirane (C-B-Li) ring formed by 1,2-migration of a trimethylsilyl group to a neighboring boron atom, generating a boron-stabilized carbanion. The X-ray stmcture of this derivative revealed two independent molecules per asymmetric unit. The two boratirane derivatives have been thoroughly characterized by multinuclear NMR and X-ray diffraction analysis. 

Wozniak, K., He, H., Klinowski, J., Jones, W., and Barr, T. L., ESCA, solid-state NMR, and X-ray diffraction monitor the hydrogen bonding in a complex of 1,8-bis(dimethylamino)naph-thalene with 1,2-dichloromaleic acid, J. Phys. Chem. 99, 14667-14677 (1995). 

The techniques to follow aggregation of amyloidogenic proteins and to determine their molecular conformation range from spectrometric assays (thiohavin T, Congo red) over spectroscopic assays (FTIR and CD) and visualization techniques (AFM and TEM) to methods that provide detailed insight into the atomic coordinates (solid-state NMR and X-ray diffraction). 

Molecular structure determination (solid-state NMR and x-ray diffraction)... 

Reaction of Mo(NMe2)4 with four equivalents of dry 02 produces a rare homoleptic amido complex, blue Mo(NMe2)6, and an oxide by-product. The octahedral complex has been characterized by JH (6 3.22) and 13C (6 51.8) NMR and X-ray diffraction (Th symmetry, fi (Mo—N) 2.0338(14) A).176 Reaction of MoNC13 with Me3SiNPR3 (R = Me, Ph) produces... 

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