Secondary products formation fragmentation

Since nicotine is the major precursor to NNN in tobacco and tobacco smoke, the reaction of nicotine with sodium nitrite was studied to provide information on formation of other tobacco specific nitrosamines, especially NNK and NNA, which could arise by oxidative cleavage of the l -2 bonds or l -5 bond of nicotine followed by nitrosation (26). The reaction was investigated under a variety of conditions as summarized in Table I. All three nitrosamines were formed when the reaction was done under relatively mild conditions (17 hrs, 20 ). The yields are typical of the formation of nitrosamines from tertiary amines (27). At 90 , with a five fold excess of nitrite, only NNN and NNK were detected. Under these conditions, both NNK and NNA gave secondary products. NNK was nitrosated a to the carbonyl to yield 4-(N-methyl-N-nitrosamino)-2-oximino-l-(3-pyridyl)-1-butanone while NNA underwent cyclization followed by oxidation, decarboxylation and dehydration to give l-methyl-5-(3-pyridyl)pyrazole, as shown in Figure 4. Extensive fragmentation and oxidation of the pyrrolidine ring was also observed under these conditions. The products of the reaction of nicotine and nitrite at 90 are summarized in Table II. 

Melanine, ammelide and cyanuric acid were not detected in the HCOOH extracts and the identification of s-triazines previously reported does not prove that s-triazines are indigenous. This kind of compound can easily be formed during the experimental and analytical procedures. Nevertheless, this last conclusion is not definitive. As pointed out by Stoks and Schwartz33, the carbonaceous chondrites are far from homogenous. Important variations from sample to sample exist, even if all these samples are fragments of the same chondrite. Moreover, and as previously reported, the sample treatment is of prime importance. It can lead to the formation of secondary products or liberate molecules unobservable after milder treatment. To conclude, it seems clear that nitrogen heterocycles are present in carbonaceous chondrites and that pyrimidine derivatives are less abundant than purine derivatives. 

Peroxynitrite, like other oxidants, reacts with proteins, first oxidizing cysteine methionine and tryptophan residues (A7). The reaction products are sulfones, carbonyl moieties, and dityrosines (K23, M29). Formation of protein hydroperoxides and protein fragmentation was also observed (B7, G6). Nitric oxide induces oxidation of methionine residues, thus effecting oxidative damage to proteins (Cl 1). It also reacts with Fe-S clusters of aconitase (D15), though in most cases it is difficult to assess whether these effects are produced by the NO itself, or rather by a more reactive secondary product such as peroxynitrite (C5). At physiological... 

Despite the unlikelihood of secondary mineral formation by ion substitution into or movement within an existing solid, some secondary 2 1 layer silicates apparently are formed by solid-phase changes of mica fragments inherited from the parent material. Hydrous mica, for example, is a product of chemical weathering as well as mechanical breakdown of mica. Hydrous mica, in turn, can be modified directly to vermiculite, montmorillonite, or chlorite. The process is not completely understood, but seemingly involves the outward diffusion of K+ from between the layer lattices and a subsequent or simultaneous reduction of charge within the layer lattice. 

On the other hand, the pyrograms observed in flash Py-GC at 720°C almost entirely consisted of the fragments formed via homolytic degradations, although many were identical with those observed by Py-FMS. In addition, the difference between Nomex and Kevlar with Py-GC was much less than those observed in Py-FIMS. Moreover, the formation of secondary products, such as biphenyl derivatives in Py-GC, was much less than that in Py-FIMS. The differences between the results by Py-GC and by Py-FIMS could be attributed to the difference in the flnal pyrolysis temperature and the heating rate. 

GC-MS-fragmentation patterns indicated the following secondary products isomers resulting from the formylation of toluene dimethylbenzophenone (30). di(methylphenyl)-methane ( ), tri(methylphenyl)methane (29) and di(methylphenyl)-methanol (26). The formation of the various side-products is explicable in terms of a two-step mechanism. 

HPLC MS/MS. Unlike SORI-CAD, there is no issue with blind spots in the IRMPD product ion spectrum. However, product ions produced on-axis may also absorb the IR radiation to produce secondary fragments. Care must be taken when performing IRMPD to eliminate or minimize the formation of secondary product ions, which are of lower analytical utility than the primary products. This requires that the duration of the event be selected so that no more than half of the precursor ions undergo fragmentation. In contrast with SORI-CAD, 100% of the precursor ions can be converted into products. 

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