Isomerism identification

Anacleto, J. E., Ramaley, L., Boyd, R. K., Ploeasance, S., QuiUiam, M. A., Sim, P. G., and Benoit, F. M., Analysis of polycychc aromatic compounds by supercritical fluid chromatography mass spectrometry using atmospheric-pressure chemical ionization. Rapid Commun. Mass Spectrom., 5, 149-155,1991. Mansoori, B. A., Isomeric identification and quantification of polycychc aromatic hydrocarbons in environmental samples by liquid chromatography tandem mass spectrometry using a high pressure quadrupole collision cell, Rapid Common. Mass Spectrom., 12, 712-728, 1998. 

Qi, F, Yang, R., Yang, B., Huang, C Wei, L., Wang, J., Sheng, L Zhang, Y. (2006) Isomeric Identification of Polycyclic Aromatic Hydrocarbons Formed in Combustion with Tunable Vacuum Ultraviolet Photoionization. Rev. Sci. Instrum. 77 084101. 

Step 3 Once formed the thiazolone derivative isomerizes to a more stable phenylthiohydantom (PTH) derivative which IS isolated and characterized thereby providing identification of the N terminal ammo acid The remainder of the peptide (formed m step 2) can be isolated and subjected to a second Edman degradation... 

The above considerations indicate the complex nature of the hydrocarbons known as caryophyllene. For practical purposes, however, the compounds indicated are obtained of practically definite melting-points, and, in spite of the complicated isomerism existing amongst most of them, are useful for identification of the sesquiterpene or mixture of sesquiterpenes, occurring naturally and known as caryophyllene . 

An examination of the mass spectra of these isomeric compounds and of their D20-exchanged analogs leads to the conclusions that the spectra can be interpreted in terms of the structures 4-6 and that structural differences lead to extensive differences in fragmentation. These mass spectra now can be used for identification purposes and as models to aid in the interpretation of the mass spectra of similar compounds, possibly of unknown structure. 

FIG. 16 Identification of isomeric C14 monosulfonates using a light scattering detector. 

Structural Identification of Isomeric O-Trimethylsilyl Derivatives of Some Hexuronic Acids, J. F. Kennedy, S. M. Robertson, and M. Stacey, Carbohydr. Res., 57 (1977) 205-214. 

Co2(CO)8 has also been studied in low-temperature matrices (19,20), the photochemical behavior of which led to the identification of three isomeric forms of the dimer complex (19). Two of these are the accepted forms, 1 and 2, whereas the third has no bridging, CO ligands. The structure most... 

Yang, B. et al.. Identification of combustion intermediates in isomeric fuel-rich premixed butanol-oxygen flames at low pressure. Combust. Flame, 148, 198, 2007. 

Absolute identification of the isomeric structure of primary standard materials by single crystal techniques ... 

Masamoto, K. et al.. Identification of a gene required for cis-to-trans carotene isomerization in carotenogenesis of the cyanobacterium Synechocystis sp. PCC 6803, Plant Cell Physiol. 42, 1398, 2001. 

When the aim is isolation for identification by direct probe insertion mass spectrometry (MS), plastic materials, filter papers, and blenders should be avoided to prevent contamination during extraction and chromatography. It is also very important to avoid the cis-trans isomerization of carotenoids in solution, which is accelerated by heat, light, acids, and active surfaces. Therefore, a pure carotenoid or even a crude extract should never be stored in solution it should be kept completely dry in an inert atmosphere at low temperature. 

The identification of surface adsorbed species has been carried out with FT-IR [69] and Raman spectroscopy [70] during reaction and with GC-MS after epoxidation reaction [72]. The aggregation of gold NPs is not appreciable during reaction at temperatures below 473 K [69,72]. Catalyst deactivation, which happens within a few hours causing a decrease in C3FI6 conversion by about 50%, can be accounted for by the accumulation of successively oxidized compounds after isomerization and cracking of... 

During the 1940s, more than 15 years before the structure of (67) was elucidated as the major psychoactive constituent of marijuana [90] and 40 years before the identification of specific cannabinoid receptors, Adams and co-workers [91, 92] demonstrated that a T,2 -dimethylheptyl (T,2 -DMH) side chain was the optimal 3-alkyl substituent for carmabinoid activity in vivo in the A ° -THC series. In this early research, the ataxia test in dogs was used as a standard measure of psychoactive cannabinoid activity. The isomeric l, l -DMH side chain was found to be less potent than the l, 2 -DMH one in the series, but the two side chains have similar... 

Cacia, J., Keck, R., Presta L. G., and Frenz, J., Isomerization of an aspartic acid residue in the complementarity-determining regions of a recombinant antibody to human IgE identification and effect on binding affinity, Biochemistry, 35, 1897, 1996. 

NMR spectroscopy is commonly used for the identification of isomeric tetrazolium salts. There are significant differences in the chemical shifts of C-methyl and /V-methyl protons as shown in Table 4 for compounds 128... 

HPLC-NMR analysis in a closed-circuit reveals the stereochemical information for elucidating the structures of unknown compounds (Albert 2002). In contrast to the technique of off-line separation, sample collection, and peak identification closed-circuit analysis guarantees the absence of isomerization and degradation. Very often only small amounts of sample are available after extraction. 

Englert, G. and Vecci, M. 1980. Trans/cis isomerization of astaxanthin diacetate/isolation by HPLC and identification by 1H-NMR spectroscopy of three mono-civ- and six di-civ-isomers. Helv. Chim. Acta 63 1711-1717. 

A dry, thin lycopene layer heated at 50°C, 100°C, and 150°C showed first-order kinetic decay (Lee and Chen 2002). At 50°C, isomerization dominated in the first 9h however, degradation was favored afterward. On the other hand, at 100°C and 150°C degradation proceeded faster than isomerization. Although cis isomer identification was not confirmed by standards, the mono-civ lycopene isomers, 5-cis-, 9-cis-, 13-cis-, and 15-m-, degraded at the same rate as did all-trans-lycopene,... 

Wiles, D. R. Search for the pj isomeric states in Tc101 and identification... 

The reactions and identification of small isomeric species were reviewed by McEwan in 199223 Since that time, additional experimental data have been obtained on more complex systems. In the present review, smaller systems will only be mentioned where there has been an advance since the previous review and emphasis here will be concentrated on the correlation between reactivity, the form of the potential surface, and the isomeric forms. There is also a wealth of kinetic data (rate coefficients and product ion distributions) for ion-molecule reactions in the compilations of Ikezoe et al.24 and Anicich,25,26 some of which refer to isomeric species. Thermochemical data relevant to such systems, and some isomeric information, is contained in the compilations of Rosenstock et al.,27 Lias et al.,28 29 and Hunter and Lias.30... 

In general, intramolecular isomerization in coordinatively unsaturated species would be expected to occur much faster than bimolecular processes. Some isomerizations, like those occurring with W(CO)4CS (47) are anticipated to be very fast, because they are associated with electronic relaxation. Assuming reasonable values for activation energies and A-factors, one predicts that, in solution, many isomerizations will have half-lives at room temperature in the range 10 7 to 10 6 seconds. The principal means of identifying transients in uv-visible flash photolysis is decay kinetics and their variation with reaction conditions. Such identification will be difficult if not impossible with unimolecular isomerization, particularly since uv-visible absorptions are not very sensitive to structural changes (see Section I,B). These restrictions do not apply to time-resolved IR measurements, which should have wide applications in this area. 

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