Structure working

Finally, note that the ions produced by the combined inlet and ion sources, such as electrospray, plasmaspray, and dynamic FAB, are normally molecular or quasi-molecular ions, and there is little or none of the fragmentation that is so useful for structural work and for identifying compounds through a library search. While production of only a single type of molecular ion may be useful for obtaining the relative molecular mass of a substance or for revealing the complexity of a mixture, it is often not useful when identification needs to be done, as with most general analyses. Therefore,... 

The structural work on many other tautomeric pyrimidines is summarized in the reviews previously quoted <63AHC(1)339, 76AHC(Sl)7l). 

Three more antibiotics, all discovered about 1953, are also derivatives of cytosine. Amicetin, bamicetin and plicacetin may all be isolated from Streptomyces plicatus and all have some activity against some acid-fast and Gram-positive bacteria as well as some other microbial systems (69MI21301). Structural work in this area is fascinating (62JOC2991). 

In addition to developing solid RP structures, work has been conducted on sandwich structures such as filament-wound plastic skins with low-density foamed core or a plastic honeycomb core to develop more efficient strength-to-weight structures. Sandwich structures using a syntactic core have been successfully tested so that failures occurred at prescribed high-hydrostatic pressures of 28 MPa (4,000 psi). 

Nodularia spwnigena has also been shown to produce a peptide with hepato-toxic activity. The more recent reports come from Australia (76), the German Democratic Republic (77), Denmark (78), Sweden (79), and Finland (80,81). Recently structure information on Nodularia toxin has been presented by Rinehart (97) for waterbloom material collected in Lake Forsythe, New Zealand, in 1984 by Eriksson et al. (81) from waterbloom material collected in the Baltic Sea in 1986, and Runnegar et al. (82) for a field isolate from the Peel Inlet, Perth, Australia. Structure work by Rinehart, Eriksson, and Runnegar all indicate that the peptide is smaller than the heptapeptide toxins. Rinehart s work (97) indicates the toxin is a pentapeptide with a similar structure to the heptapeptides and containing fi-methylaspartic acid, glutamic acid, arginine, dehydrobutyrine, and ADDA (MW 824). 

Work with European toxic cyanobacteria was partially supported by a NATO collaborative research grant between W.W. Carmichael and G.A. Codd, University of Dundee, Scotland, and O.M. Skulberg, Norwegian Water Research Institute, Oslo, Norway. Toxin structure work on European and North American peptide toxins is supported in part by U.S. AMRDC contract DAMD17-87-C-7019 to W.W. Carmichael. Portions of the work represent part of the Ph.D. dissertation research of N.A. Mahmood and E.G. Hyde. Their work was supported in part by fellowship support from the Biomedical Ph.D. Program, Wright State University. 

Saraiva, P.. and Stephanopoulos, G Data-Driven Learning Architectures for Proce.ss Improvement in Complex Systems with Internal Structure, Working paper. Massachusetts Institute of Technology, Dept. Chem. Eng., Cambridge, MA, 1992d. 

The way that Miller Indices arose CcUi be understood by considering the history of crystal structure work, accomplished by many investigators. 

Preparative HPLC of component II was difficult. Component II was collected with a resolution comparable to that shown in Figure 2. Higher resolution showed the presence of at least 5 minor peaks. Slowing the water/methanol gradient finally produced a single peak, which when collected, totaled 14 mg of slightly yellow oil from 2.1 gms OFAs extracted with ODS silica (16). Structural work on II has not yet appeared in the literature, so more detail is included. 

Equipment erection, including foundations and minor structural work. 

Although less common than zinc chlorides, there has been much synthetic and structural work carried out on zinc bromide and iodide complexes. For example, the 1 1 adduct of N,N,N, A -tetramethyl-o-phenylenediamine with zinc bromide has been structurally characterized.630 The ion exchange properties of zinc bromide and iodide have been studied in ethylene glycol.631 The electrolytic behavior of zinc bromide in propylene carbonate has been studied and the conductance data shows the existence of dimers.632... 

Ylide complexes of gold are unique in that they exhibit an exceptional chemical and thermal stability, which facilitates preparative and structural work very considerably. It was in this class of compounds that a large variety of true organogold(ll) and mixed valence organogold(l)/(lIl) complexes was discovered. These are rare in the remainder of organogold chemistry. 

Linear coordination complexes are also observed with carbenes rather than carbonyl ligands. However, recent structural work carried out on bis(carbene) complexes indicates that coordination of the counteranion can lead to significant deviation of the Ccalbene-Hg-Gcalbene angle from linearity. In 70, for example, the two chloride anions are... 

It is timely to review the reactivity of plastocyanin in the light of recent aqueous solution studies, and the elegant structural work of Freeman and colleagues on both the PCu(I) and PCu(II) forms (1 2) Plastocyanin now ranks alongside cytochrome c (3) as the electron-transfer metalloprotein for which there is most structural information. 

Structural work reported here was performed by Dr. H. W. Chen and Dr. C. Paparizos. The National Science Foundation NSF-CHE 80-13141 and the donors of the Petroleum Research Fund as administered by the American Chemical Society have supported this work. 

Studies involving 2,6-diacetylpyridine derivatives. Detailed studies by Nelson and coworkers supported by X-ray structural work by Drew and coworkers have elucidated many aspects of the template synthesis of metal complexes of a Schiff-base ligand series which includes the N4-donor system (83) and the N5-systems (84)-(86) (Nelson, 1980). Since... 

There was some evidence that the preparations of gramicidin used in this structural work were not completely... 

In a review paper, Dr. Synge recapitulated the early structural work on gramicidin and indicated that x-ray diffraction was incapable of distinguishing a gramicidin fraction purified by counter current analysis from the heterogeneous starting material. 

A large number of chemicals, which are used for communication, attack or defense, are secreted by ants. In general, these substances are small molecules, and their availability in minute amounts (50 p,g per ant) does not allow the use of the traditional isolation and characterization procedures. Thus all of the structural work on ant substances rests on gas chromatography (GC), mass spectroscopy, and chemical synthesis. Two review articles have been published on the chemicals from the glands of ants (128, 128a) and we shall mention here only the work relevant to the pyrrolidine field. 

A remarkable feature of the structural work on the derivatives with unsaturated side chains is the method by which the double bonds were located. Thus a micromethod has been devised, based on the Markovnikov selectivity of olefin... 

All of this structural work is backed up by total synthesis, which will be developed later. These syntheses often produce mixtures of cis-trans isomers. The natural products have a trans configuration and have the longest GC retention times. This attribution is based on an analogy with the hydrogenation of 2,5-dimethylpyrrole. 

Most structural work on xylan has been done on that from esparto grass and the principal attack made by way of the methyl ether. Xylan can be methylated by heating with methyl iodide and silver oxide,92-93 but complete etherification is difficult and considerable degradation probably occurs. On the other hand, complete etherification is attained by methylation in two operations with potassium hydroxide and dimethyl sulfate to give a dimethylxylan in almost quantitative yield70 showing [< ]22d — 92° in chloroform. Methylation with potassium hydroxide appears to proceed more readily than with sodium hydroxide.70-92... 

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