Molecular ions, viii

Twelve volatile acyclic amines and amides (114-120,125-129) (Table VIII) from ponerine ants in the genus Mesoponera have been identified by gas chromatography-mass spectrometry and mass spectral comparison with authentic synthetic samples 41). The major aliphatic amine, A-isoamylnonylamine (114), shows a molecular ion at m/z 213, a-cleavage fragments at miz 156 (M — C4H9)... 

Two of amides from melon flies of the genus Dacus (Table VIII) have been identified as V-isoamylacetamide (122) and V-(2-methylbutyl)acetamide (123) by comparison of their mass spectra and chromatographic properties with those of authentic samples 103). The third amide, previously reported neither as a component of an insect secretion nor as a synthesized derivative, was assigned as A-isoamyl-2-methoxyacetamide (124) from the mass spectrum, showing a molecular ion at m/z 159 and fragment ions at m/z 129 (M" — CHjO) and 102 (M + — C4Hg), and its structure was confirmed by comparison with a synthetic au-... 

The TLC purified diphosphoryl lipid A fractions (TLC -3, -5, and -7) were analyzed by FAB mass spectrometry in the negative mode as previously described (23) and the results are shown in Table X. TLC-3 gave a molecular ion (M-H) at m/z 1796 TLC-5, m/z 1586 TLC-7, m/z 1360. As expected, these values were 80 amu or (P03H2 H) larger than those for the corresponding monophosphoryl lipid A s of the series as shown in Table VIII. These results established the structural relationship between the mono- and diphosphoryl lipid A s. 

The mass spectrum of cyclooctatetraeneiron tricarbonyl shows stepwise loss of the three carbonyl groups from the molecular ion, followed by elimination of acetylene giving C6H6Fe+, and further breakdown gives Fe+ (119). The mass spectra of two substituted cyclooctatetraene complexes (see Table VIII) show the molecular ion and stepwise loss of the carbonyl groups (83). 

Tables VIII and IX demonstrate reasonable agreement between the two analyses in regard to the range in molecular weight for both Z(N) and Z(N,0) volatile bases. The Z(N) and Z(N,0) carbon-number distributions (35) reveal that the differences in Tables VIII and IX reflect low-intensity molecular ions at higher m/z values in the LV/EI/MS than in the FI/MS. Thus, the good agreement in the weight percents for the various Z(N) and Z(N,0) series between the two analyses is not an artifact.

Smith, G.P., L.C. Lee, and P.C. Cosby, Photodissociation and photodetachment of molecular negative ions, VIII. Nitrogen oxides and hydrates. J Chem Phys 71, 4464, 1979. 

Other than the formation of compound V and the higher molecular weight compound (IV), three other stable photoproducts (VI, Vll, and VIII) are formed in minor amounts. These products possess molecular ion peaks at 270, 242, and 228 respectively (Scheme 1 and Table I). 

Compound VIII, whose molecular ion peak appears at 228 could have been formed by the loss of the CH2 moiety (m/e = 14) from VII, and/or from the cleavage of a n-propyl moiety from VI. VIII does not appear to possess the isopropy1idene group as evidenced by large differences in the fragmentation patterns of VIII and bisphenol A. Although the structures indicate only one isomer other isomers are possible. 

The development of scanning probe microscopies and x-ray reflectivity (see Chapter VIII) has allowed molecular-level characterization of the structure of the electrode surface after electrochemical reactions [145]. In particular, the important role of adsorbates in determining the state of an electrode surface is illustrated by scanning tunneling microscopic (STM) images of gold (III) surfaces in the presence and absence of chloride ions [153]. Electrodeposition of one metal on another can also be measured via x-ray diffraction [154]. 

These equations indicate that the energy of the scattered ions is sensitive to the mass of the scattering atom s in the surface. By scanning the energy of the scattered ions, one obtains a kind of mass spectrometric analysis of the surface composition. Figure VIII-12 shows an example of such a spectrum. Neutral, that is, molecular, as well as ion beams may be used, although for the former a velocity selector is now needed to define ,. ... 

The nature of reaction products and also the orientation of adsorbed species can be studied by atomic beam methods such as electron-stimulated desorption (ESD) [49,30], photon-stimulated desoiption (PDS) [51], and ESD ion angular distribution ESDIAD [51-54]. (Note Fig. VIII-13). There are molecular beam scattering experiments such... 

Table VIII. Tabulation of Important Ions Present in Mass Spectra, GC Retention Times (t ), Molecular Weights of Unknown and Standard Compounds r...

Giuffrida S, De Guidi G, Miano P, Sortino S, Condorelli G, Costanzo LL. Molecular mechanism of drug photosensitization VIII effect of inorganic ions on membrane damage photosensitized by naproxen. / Inorg Biochem 1996 63 253-63. 

This sequence explains Price s observations adequately and seems to be required in this particular case. The oxidative elimination of halide ion from salts of phenols does not always follow this course, however. In the peroxide-initiated condensation of the sodium salt of 2,6-dichloro-4-bromophenol (Reaction 23) molecular weight continues to increase with reaction time after the maximum polymer yield is obtained (Figure 5) (8). Furthermore, Hamilton and Blanchard (15) have shown that the dimer of 2,6-dimethyl-4-bromophenol (VIII, n = 2) is polymerized rapidly by the same initiators which are effective with the monomer. Obviously, polymer growth does not occur solely by addition of monomer units in either Reaction 22 or 23 some process leading to polymer—polymer coupling must also be possible. Hamilton and Blanchard explained the formation of polymer from dimer by redistribution between polymeric radicals to form monomer radicals, which then coupled with polymer, as in Reaction 11. Redistribution has indeed been shown to occur under... 

The static - double-layer effect has been accounted for by assuming an equilibrium ionic distribution up to the positions located close to the interface in phases w and o, respectively, presumably at the corresponding outer Helmholtz plane (-> Frumkin correction) [iii], see also -> Verwey-Niessen model. Significance of the Frumkin correction was discussed critically to show that it applies only at equilibrium, that is, in the absence of faradaic current [vi]. Instead, the dynamic Levich correction should be used if the system is not at equilibrium [vi, vii]. Theoretical description of the ion transfer has remained a matter of continuing discussion. It has not been clear whether ion transfer across ITIES is better described as an activated (Butler-Volmer) process [viii], as a mass transport (Nernst-Planck) phenomenon [ix, x], or as a combination of both [xi]. Evidence has been also provided that the Frumkin correction overestimates the effect of electric double layer [xii]. Molecular dynamics (MD) computer simulations highlighted the dynamic role of the water protrusions (fingers) and friction effects [xiii, xiv], which has been further studied theoretically [xv,xvi]. 

Table VIII. Fractionation of High Molecular Weight Asphaltenes by Ion Exchange Chromatography...

Our knowledge of porcine pancreatic phospholipase comes from the laboratory of G. H. de Haas and his co-workers. The enzyme is quite different from pancreatic lipase (Table VIII). Its molecular weight is quite small, it is a metalloenzyme that requires Ca ion as a cofactor, and it is excreted from the pancreas as a proenzyme which is then activated by trypsin with removal of a heptapeptide. The molecule has six... 

The free dimensions of the windows in zeolite A are 4.3A and those in mordenite are 6.7 X 7.0A. Any of the sorbates of Table VIII could migrate therefore into the crystals with minimal values of E, were it not for an influence of the ions (diameter 2.66A). These ions must obstruct the diffusion paths partially in each case. Indeed, ion exchange is one of the most effective ways of changing the molecular sieve characteristics of zeolites. Decationation, as in H-mordenite or H-clinoptilolite, produces maximum clearance of diffusion paths from metallic ions, so... 

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