Partial structures determination

B. Antiviral and Antifungal Mycoticin (A and B) Partial Structure Determination... 

We also need to identify the gene for PBAN. The gene can provide additional information about the nature of pro-PBAN (if it is different from PBAN), and also allow us to clone it in a baculovirus. A melanization and reddish coloration hormone (MRCH) was isolated from the head extracts of B. mori (16). Partial structure determination of the MRCH revealed that the amino acid sequence of this hormone and that of PBAN from B. mori are identical (12.). It has also been observed that Hez-PBAN causes intense melanization in H. zea larvae (Raina, unpublished). Such larvae either die or produce deformed pupae. Infestation of H, zea and possibly larvae of other species of moths with the recombinant virus containing the PBAN gene may be... 

Subunit c ofEcFo [or subunit III ofchloroplast CFo] consists of 79 amino-acid residues and has a molecular mass of 8.3 kDa. Because of its hydrophobic character it is soluble only in non-polar solvents. Girvin and Fillingame examined the monomeric subunit c of E. coli Fq by NMR spectroscopy and were able to make a partial structure determination ofresidues 9-25 and 52-79 in the N- and C-terminal regions, respectively. Subunit c appears to span the membrane as a hairpin of two hydrophobic helices separated by a polar loop of about 18 amino-acid residues exposed to the cytoplasmic side ofthe membrane, as shown in Fig. 3 8 (C). NMR spectroscopic measurement shows subunit c to consist oftwo gently curved a-helices crossing at a slight angle of -30° [also see Fig. 39 (A)]. 

Applying these steps mm/ allow assignment of the structure of an unknown compound. However, without additional information about a substance, such as its molecular formula or the chemical reaction(s) by which it was formed, only a partial structural determination may be possible. Other chemical or spectral data may be required to make a complete assignment. In any case, structural assignments based exclusively on interpretation of spectra must be confirmed by comparing the spectra of the unknown with those of an authentic specimen, if the compound is known, or by chemically converting the unknown to a known compound. 

X-r crystal structure determinations have been completed on two salts containing bicyclo[2.2.1]heptyl cations (Fig. 5.12). Both are more stable than the 2-norbomyl cation itself 18 is tertiary whereas 19 contains a stabilizing methoxy group. The crystal structure of 18 shows an extremely long (1.74 A) C—C bond between C-1 and C-6. The C(1)—C(2) bond is shortened to 1.44 A. The distance between C-2 and C-6 is shortened from 2.5 A in norbomane to 2.09 AThese structural changes can be depicted as a partially bridged structure. 

For a long time the structural classification of the mineral todorokite was uncertain, until Turner and Buseck [4] could demonstrate by HRTEM investigations that the crystal structure of that mineral consists of triple chains of edge-sharing octahedra, which form [3 x 3] tunnels by further corner-sharing. These tunnels are partially filled by Mg2+, Ca2+, Na+, K+, and water (according to the chemical analysis of natural todorokites). In 1988 Post and Bish could perform a Rietveld structure determination from XRD data taken for a sample of natural todorokite [25], This diffraction study confirmed the results of Turner and Buseck. The cations... 

We reacted 2 first with bromine in chloroform at 10 C. iH NMR studies have revealed that the reaction mixture was very complex and consisted of six products. This mixture was submitted to silica gel column chromatography. Careful repeated chromatography followed by fractional crystallization allowed us to isolate ten products (Scheme 3). IR analysis indicated that a hydroxyl group was incorporated in compounds lfi-19. Therefore, we assume that these products have been formed by partial hydrolysis of compounds lfl-14. Structural determination of compounds lfl-19 revealed that the barrelene skeleton was rearranged completely. 

Instead of measuring only the time-dependent dipolar interaction via NOE, it is also possible to determine dipolar couplings directly if the solute molecule is partially aligned in so-called alignment media. The most important resulting anisotropic parameters are RDCs, but residual quadrupolar couplings (RQCs), residual chemical shift anisotropy (RCSA) and pseudo-contact shifts (PCSs) can also be used for structure determination if applicable. 

The general computational mechanism of Bayesian crystal structure determination in presence of various sources of partial phase information was first outlined by... 

In this section we will discuss perturbation methods suitable for high-energy electron diffraction. For simplicity, in this section we will be concerned with only periodic structures and a transmission diffraction geometry. In the context of electron diffraction theory, the perturbation method has been extensively used and developed. Applications have been made to take into account the effects of weak beams [44, 45] inelastic scattering [46] higher-order Laue zone diffraction [47] crystal structure determination [48] and crystal structure factors refinement [38, 49]. A formal mathematical expression for the first order partial derivatives of the scattering matrix has been derived by Speer et al. [50], and a formal second order perturbation theory has been developed by Peng [22,34],... 

Fig. 56a-c. Reduced relaxation rates Q (Q)/Q3 for diblock PIP stars under various conditions and theoretical predictions using the partial structure factors of Gaussian stars (dashed lines) or the experimental determined ones (solid line), a core contrast, b shell contrast, c average contrast. (Reprinted with permission from [154]. Copyright 1990 American Chemical Society, Washington)... 

There is strong cross-reaction between S11A and S18. The partial structures proposed for S18 (Refs. 1 and 38), 17 and 18, with glycerol phosphate and the O-acetyl group linked to positions not yet determined, are also remarkably similar to that of S11A. 

An X-ray crystal structure determination of calciferol (vitamin D-2,71) showed that steric crowding in the s-cis diene system resulted in a twisted conformation with a dihedral angle of 53° [59], On irradiation with a mercury lamp, it was partially converted into ergosterol (72) and tachysterol (73) [60, 61]. When a solution of calciferol in light petroleum containing a trace of iodine was exposed to diffuse daylight, the vitamin was photoisomerized to (74) [62],... 

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