Structures 2-substituted

Phenazines — These are dibenzopyrazine derivatives with fnnctional groups (hydroxy-, carboxy-) at C, and Cg and an oxygen or methyl gronp at Nj and N,o. There are also more complex structures, substituted phenazines, terpenoidal, and carbohydrate-containing phenazines and phenazines derived from saphenic acid. ... 

The parent phase is a stoichiometric oxide M02 with the fluorite structure. Substitution of a lower valence cation for Zr4+ is compensated by oxygen vacancies (Section 1.11.6 and Section 4.4.5). Taking calcia-stabilized zirconia as an example, addition of CaO drops the metal to oxygen ratio to below 2.0, and the formula of the oxide becomes Ca Zrj -x02-x. 

The Ti4+ distribution in TS-1 has also been studied by computational methods (34,62,160-163). The actual location of the Ti atoms in the framework of titanosilicates is difficult to determine experimentally because of the low Ti content (Section II), and information obtained from theoretical methods is, therefore, of considerable interest. In the orthorhombic MFI structure, substitution can take place at 12 crystallographically different tetrahedral (T) sites (T1-T12) (Fig. 1 and Section II.A.l.b). In the monoclinic MFI framework, the mirror symmetry is lost and 24 crystallographically different T sites can be distinguished (Fig. 31) (160). 

Polymerization was carried out in NaOH aqueous solution. Table 4 summarizes the reaction conditions and polymer yields. The first step of the polymerization was hydrolysis and oligomerization of the silylethers at low temperatures from 90°C to 150 °C. In order to increase the polymer yield and the softening point of the polymers, the second step was carried out at higher temperatures under reduced pressure, removing alcohol and water, 1H-NMR, 13CNMR and IR spectroscopy of each polymer show that these polymers have the polysiloxane structure substituted with a phenol group. 

The nitrenium ion +NH2 has been the subject of a detailed, comprehensive calculation. Calculations on (48) with 15 different X substituents reveal a large substituent sensitivity, and also that aqueous solvation preferentially stabilizes the singlet state. This substiment sensitivity agrees with the results of a time-resolved IR study of the diphenylnitrenium ion (49), which shows that resonance contributors such as (50) and (51) are very important to the overall structure. Substituted 4-biphenyl nitrenium ions... 

Fig. 3.27 data of structurally substituted sulfur in carbonate and in barite vs time (Prokoph et al. 2008)... 

Fig. 6.9 Left Relationship between the Curie (Tc) and Morin (Tm) temperature of hematite and the extent of structural substitution of Fe " by Al, Ga, Cr and In (M) (Svab Kren, 1979, with permission). Right Relationship between the Morin temperature and the inverse mean crystal dimension (MCD) for different hematites ( ) natural from Elba ( ) heating lepido-...

It is interesting to note that in magmatic apatites the luminescence of uranium containing centers have not been discovered before or after oxidizing heating. Thus it is reasonable to suppose that uranium is present mainly in the 11" + form. The U with an ionic radius of 0.97 A may be located in the apatite structure instead of Ca with the ionic radius of 0.99 A. The most likely way for achieving the excess charge compensation is the Na" for Ca " structural substitutions. 

In equation (1) the parameter (9) expresses the length of substituent R. to the rest of the molecule. W. is the width upward of R. when one views it from the connecting end along the bond axis defining L. The electronic parameter, a, was estimated for the structure substituted on the common aspartyl-amino moeity, so that the electronic effect is directed to the peptide bond. Ten compounds of the original 61 do not fit equation (1) hence n=51, not 61. 

Sulfonic and phosphonic acids contain sulfur and phosphorus in their structures, substituting for carbon in the carboxyl function group. They are fairly abundant, but have not been studied extensively. 

Zeolites are tectosilicates and their structure is based upon the feldspar model. The major chemical and structural substitution is M+A1 = Si, i.e., silicon replaces aluminum plus one (or in the case of calcium) ion. Usually the exchange of one ion for two is accompanied by an increase of free, zeolite water in the structure. As this substitution increases in importance, the structure becomes more "open" and more variable substitutions can take place, for example NII for K+, and so forth. 

The activity of ebselen can be altered by modifying its structure. Substitution of the hydrogen atom of the benzene ring with a nitro group in the ortho-position to selenium has been shown to increase of the GPx activity of ebselen. The sulfur analog of ebselen and the compounds having no Se-N bond in the ring are inactive [18, 20, 247],... 

The approximate nature of a model of this kind, the large number of parameters needed for its description, and the likely occurrence of many overlapping interactions, can make the results ambiguous and lead to systematic errors in the refined parameter values. Usually, therefore, diffraction data for a single solution are not sufficient for a complete and unbiased derivation of the structure of a specific complex. If iso-structural substitution can be used to eliminate some of the pair interactions, then much more precise and detailed information about the... 

A graphene sheet can be rolled up in different ways to form a certain type of CNT. Similarly, various defects in the graphene plane (flaws in the regular hexagonal structure, substitution of carbon atoms by other atoms, etc.) may form new types of CNTs. Multi-walled, functionalized, capped and opened CNTs broaden this list. 

Zeolite Y. We also substituted boron into dealuminated zeolite Y. We dealuminated zeolite Y by EDTA treatment using standard methods (4). The presence of hydroxyl nests in the product was confirmed using 29Si CPMAS NMR spectroscopy. The dealuminated material incorporated 33 times more boron than zeolite Y when treated with KOH/B2O3. These data are summarized in Table 3. The boron substituted faujasite exhibits a single sharp resonance in the NMR spectrum, consistent with structural substitution. Since the substitution level was low and would not be expected to cause large shifts in the diffraction pattern, no corrected XRD data were obtained on substituted zeolite Y. 

Fig. 9. Proximity relationships for residues in Cl relative to 316 in H8. Example of R1 distance mapping in rhodopsin. For each distance measurement, only two R1 side chains were in the protein, one fixed at the reference site 316, and the other at a site in the sequence 55-75. The R1 side chains were modeled based on crystal structure data with energy minimization subject to the experimentally determined distance constraint (shown). In each case, the measured distances in solution were in good agreement with those expected from the rhodopsin crystal structure. Substituted cysteine residues 65 and 68 most rapidly formed disulfide cross-links with the reference cysteine at 316 in H8. This is indicated by the dark bars connecting the potential disulfide partners.

If we take a series of compounds which are related by structural substitutions, such as benzene derivatives, then we can assign the effects of the structural changes to the ratio KBJKB. if we select this property as a standard. Such a system of correlation was first proposed by Hammett and revised and extended by Jaff " to account for the effects of meta and para substituents on the reactivity of benzene derivatives. For convenience, the ionization constant of benzoic acia queous solution at 25°C was chosen as standard and for each meta or para substituent a, a value of ionization constant for benzoic acid and Ka the ionization constant of the corresponding, substituted benzoic acid. 

In the orthorhombic MFI structure, substitution can take place at 12 crystallographically different tetrahedral (T) sites (numbered T1-T12). In the monoclinic MFI framework, the mirror symmetry is lost and 24 crystallographically different T-sites can be distinguished (see Figure 23). 

For Fe oxides, FTIR spectroscopy provides a rapid means of identification. It can detect traces (1-2%) of goethite in a sample of hematite. In addition, low levels of impurities arising from insufficient washing, for example nitrate in ferrihydrite (band at 1384 cm ) and carbonate in goethite (ca. 1300 and 1500 cm ) can be detected. Broadening of the absorption bands reflects a decrease in crystal perfection (Cambier, 1986). Structural substitution of Fe by A1 (Schulze Schwertmann, 1984), Mn (Stiers Schwertmann 1985), and Cr (Schwertmann et al. 1989) causes a shift in the positions of the bands. 

Photodimerization and cross-cycloaddition of coumarins are improved by Lewis acids [74]. Similarly, photochemical [2-1-2] cycloadditions [75] of 1- and 2-naphthols [76] with ethylene are promoted by aluminum halides yielding the [2-1-2] adduct from the (complexed) enone form. According to the structure, substitution (e. g., methyl) vicinal to the OH group in 1-naphthol gives rise to ring-contracted indanone products. The formation of (ring-contracted) benzo-bicyclo[3.1.0]bicyclohexenone was already observed by irradiation (AICI3) of 1-naphthol without ethylene (Scheme 6) [77],... 

Table VII lists the six other amino acids occurring in low frequency at position 34 in the H chain. Some of these could play a role in specificity or some might be acceptable structural substitutions for Met. It is of interest that all are hydrophobic except for one Arg and one Ser.

Kampschulte, A. Strauss, H. (2004) The sulfur isotope evolution of Phanerozoic seawater based on the analysis of structurally substituted sulfate in carbonates. 

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