Structural examination

The cycloadducts formed from ethenetetracarbonitrile and the three isomerically pure methyl methyl-1//-azepine-l-carboxylates, 4, 5 and 6, have been subjected to a rigorous structural examination, from which it was concluded that adducts bearing the methyl groups at the bridgehead positions are not formed.251 Thus, the 2-methyl and the 4-methyl isomers, 4 and 5, each yield only one adduct, 7a and 7b, respectively, whereas methyl 3-methyl-1//-azepine-l-car-boxyate (6) gives 66 % yield of a 45 55 mixture of the 4-methyl 7 c and 7-methyl 7 d cycloadducts. 

Tschiersky and Baltes96 prepared di-D-fructose dianhydrides by heating fructose. Mass spectra of the permethyl ethers were obtained. Although the dianhydrides were of unknown structure, examination of the spectra indicate that all are difuranose dianhydrides (mlz 101 as the base peak, and low intensities of the ions mlz 88 and 277) and at least one is reminiscent of a 2,3-linked difuranose structure (relatively intense mlz 363 [M — 45]+).95-98... 

An alternative technique to NMR spectroscopy is chromatography. The partially functionalized sample is completely fimctionahzed with a group different from the one present, the product carefully de-polymerized, its structure examined with a chromatographic technique. For example, partially substituted CA was further derivatized with methyl vinyl ether, the product hydrolyzed, the monomers produced examined with gas chromatography [241]. HPLC has been advantageously applied for the determination of substitution pattern for CAs with DS 0.8 to 3.0, by employing the same approach, i.e., further derivatization of the partially derivatized polymer with methyl trifluoroacetate, followed by de-polymerization. The results obtained by this technique compared favorably with those obtained by NMR [242]. 

Now that automated diffractometers and sophisticated computer data-reduction systems have become routinely used, the task involved in conducting an X-ray crystal-structure examination has been enormously simplified. As a result, the number of structures determined each year by crystallography has escalated dramatically. The logistics of maintaining this series in the original form would now entail such stupendous demands on our space that a volume of Advances could be completely occupied by this one article alone. As the original purpose of this series... 

The first structural examination of Mn-Al electrodeposits was made by Read and Shores [144] in 1966. Since then, several structural studies of both as-deposited and thermally annealed films have been reported [126-129, 133, 134, 145-151], As is often the case with electrodeposited alloys, several phases with varying degrees of deviation... 

N-Alkylhydroxamic acid hydrolysis Methyl Violet + OH" Cl C12H25S03Na + H30+, CTABr + OH". An attempt made to separate electronic and hydrophobic effects on the micellar reaction Anionic and cationic micelles. Effect of surfactant structure examined Berndt el at., 1984 Malaviya and Katiyar, 1984... 

Protein X is abnormal and lacks biological function. The problem is in the quaternary structure. Examine the following statements, determine whether each is true of false, and in either case explain why ... 

Structural data are readily available from the database, but it must be assumed that they were not originally collected with the requirements of the particular correlation in mind. It is essential that the substructure investigated be tightly defined, and that this is confirmed by careful checks of structures in the data set retrieved. (This requirement is squarely at odds with that for statistical respectability, for which the largest possible data set is generally desirable.) A last resort, if the question is important enough, is to collect new data. The structures examined can then be designed to answer specific questions. The answers to the questions will not, however, be available for months or even years. 

Interpenetration of Reactants. A detailed structural examination (Figure 1) reveals the inherent difficulties in attempting to define a "contact" separation for reactants of the type considered here. In spite of the deceptively high symmetry (e.g., the Tg point group assumed in Figure 1 and (13)), the... 

Davidson, G., Choudhury, S. B., Gu, Z., Bose, K., Roseboom, W., Albracht, S. P. and Maroney, M. J. (2000) Structural examination of the nickel site in chromatium vinosum hydrogenase Redox state oscillations and structural changes accompanying reductive activation and CO binding. Biochemistry, 39, 7468-79. 

Hrapka, I. (1977, 1978). Structural Examination of Inorganic Fibrous Materials (Hungarian with English Abstract). Wojnarovitsne, Part 1. Epitoanyag, Budapest 29 498—503 Part 2. Epitoanyag, Budapest 30 13—18. 

Browse through three articles in Chemical Research in Toxicology or the Journal of Agricultural and Food Chemistry. For each article, copy and paste into a text document one sentence from each IMRD section that is consistent with the hourglass structure. Examine each group of four sentences. Is the hourglass structure apparent in these four sentences Explain. 

The crystal structures of lupanine (15) and its derivatives were investigated as free bases (54-56) as well as protonated forms (57-60). In all structures examined ring A was a half-chair. The conformation of ring C is a boat, and rings B and D have chair conformations. In other cases rings B, C, and D had chair conformations (54-57,59). Lupanine derivatives mamanine (16) and pohakuline (17), possible metabolites in the biosynthesis of sparteine, were studied by... 

Following this work on NMR spectra of ozonides, there is an extensive paper by the Griesbaum group" where 35 ozonides (6-14 with different stereochemistries) have been studied. The widely different structures examined allowed the influences of structural features on "O NMR spectra of ozonides to be shown. Five structurally different types of ozonides can be recognized symmetrically tetrasubstituted (type 6), unsymmetrically tetrasubstituted (type 7), unsymmetrically tri- and tetrasubstituted (type 8), unsymmetrically disubstituted (type 9-13) and bicyclic ozonides (type 14). "O NMR chemical shifts of peroxidic and ethereal oxygens are collected in Table 3. All spectra were obtained at natural isotopic abundance, in benzene-dg solution mainly at 25 °C, although in some cases higher temperatures had to be used. These experimental conditions make for an easy comparison with the previously discussed data. 

Ackerberg, D. 2003. Advertising, Learning, and Consumer Choice in Experience Good Market A Structure Examination. International Economic l eview 44 1007-1040. 

Finally, many complex software programs are modified or evolved from other programs. The result may be convoluted dead end pathways, nonfunctioning dead code, and inefficient module looping structures. Examination of code to determine the elegance or simphcity that avoids these non-parsimonious problems provides an important element in the evidence supporting continued reliabihty. 

High resolution electron microscopy (HREM) is also used extensively for structural examination of zeolites, particularly for intergrowths and faults. EXAFS has been used to determine the local coordination geometry of the exchangeable cations and how this changes on reaction or dehydration. 

O Keeffe (1991Z)) has used bond valences to model the coherent interface that occurs between the semiconductors Si and MSi2 with M = Ni or Co (27139). Although these systems contain Si-Si bonds and therefore do not obey the assumptions of the bond valence model (condition 3.2), the mathematical formalism of the model still works because of the high symmetry. As both Si-Si and Si-Ni bonds are found in NiSi2, the cubic structure is strained (cf. BaTiOs in Section 13.3.2) and this strain affects the structure of the interface. Of the six possible interfacial structures examined, the two with the lowest BSI eqn (12.1) are those that are believed to occur in NiSi2 and CoSi2 respectively, and in both cases the strain introduced at the interface is correctly predicted. 

Young male Wistar rats were given 2000 mg/kg bw di(2-ethylhexyl) phthalate per day by gavage for periods of 3-21 days (Lake et al, 1975). Treatment caused increases in relative liver weight and in microsomal cytochrome P450 content. Ultra-structural examination revealed marked peroxisome proliferation and a dilation of the smooth and rough endoplasmic reticulum. Rats were also treated with mono(2-ethyl-hexyl) phthalate, 2-ethylhexanol and phthalic acid at doses equimolar to 2000 mg/kg bw per day di(2-ethylhexyl) phthalate for seven days. While phthalic acid had no effect, both mono(2-ethylhexyl) phthalate and 2-ethylhexanol increased relative liver weight and produced hepatic peroxisome proliferation. 

Male Fischer 344 rats (body weight, 100-150 g) were fed 0.5-4% di(2-ethyl-hexyl) phthalate in the diet for one or four weeks and male Swiss Webster mice (20-30 g) were fed 2 or 4% di(2-ethylhexyl) phthalate in the diet for one or four weeks (Reddy etal., 1976). Di(2-ethylhexyl) phthalate increased relative liver weights and markedly induced hepatic carnitine acetyltransferase activity in both species (up to 25-fold in rats and 10-fold in mice). Some increase in hepatic catalase activity (approximately two-fold) was observed and subjective (non-morphometric) ultra-structural examination revealed marked peroxisome proliferation. This study also demonstrated that di(2-ethylhexyl) phthalate was a hypolipidaemic agent, as serum triglyceride levels were reduced to one seventh of control values in rats and one third of control values in mice. 

Hepatocytes isolated from male Wistar rats (180-250 g) were treated with 0.2 mM mono(2-ethylhexyl) phthalate or 1 mM 2-ethylhexanol for 48 h (Gray et al., 1982). Both di(2-ethylhexyl) phthalate metabolites increased carnitine acetyltransferase activity about nine-fold. In studies with hepatocytes from male Sprague-Dawley rats (180-220 g), treatment with 0.2 mM mono(2-ethylhexyl) phthalate and 1.0 mM 2-ethylhexanol for 48 h resulted in induction of carnitine acetyltransferase activity about 15-fold and six-fold, respectively (Gray et al., 1983). Mono(2-ethylhexyl) phthalate was also shown to induce cyanide-insensitive palmitoyl-CoA oxidation and, by ultra-structural examination, to increase numbers of peroxisomes. Hepatocytes were isolated from Wistar-derived rats (180-220 g) and treated for 72 h with 0-0.5 mM mono(2-ethylhexyl) phthalate and some mono(2-ethylhexyl) phthalate metabolites (Mitchell etal., 1985). Treatment with mono(2-ethylhexyl) phthalate and metabolites VI and IX (see Figure 1) resulted in a concentration-dependent induction of cyanide-insensitive palmitoyl-CoA oxidation. In addition, 0-0.5 mM mono(2-ethylhexyl) phthalate and 0-1.0 mM metabolite VI produced concentration-dependent increases in lauric acid hydroxylation. Treatment with metabolites I and V resulted in only small effects on the enzymatic markers of peroxisome proliferation. In another study with hepatocytes from Wistar-derived rats (180-220 g), metabolite VI was shown by subjective ultrastructural examination to cause proliferation of peroxisomes (Elcombe Mitchell, 1986). 

A comparison of metal-metal bond-length variations for a given metal in differing environments among structures of homonuclear rhenium, molybdenum, and chromium dimers reveals that the flexibility of strong multiple chromium-chromium bonds is distinctly different from the behavior of the two heavier metals. Both rhenium and molybdenum display relatively constant quadruple bond lengths in most structures examined to date, while chromium exhibits a wide range of metal-metal distances. 

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