4-HHE

Figure 11.2 Representative product-ion mass spectrometric analyses of carnosine-derivatized 4-hydroxyalkenal species. Carnosine-4-hydroxyaIkenal adducts were prepared by incubating individual 4-hydroxyalkenal species with carnosine as previously described [39]. Product-ion ESI-MS analyses of carnosine-derivatized 4-hydroxynonenal (4-HNE, a), 4-hydroxyhexenal (4-HHE, c), and 4-hydroxynondienal (4-HNDE, d) were performed on a QqQ mass spectrometer (Thermo Fisher TSQ Vantage). Collision activation was carried out at collision energy of 25 eV and gas pressure of 1 mTorr. The fragmentation pattern of protonated 4-HNE-carnosine adduct was proposed (b). Wang et al. [39]. Reproduced with permission of the American Chemical Society.

Consider now the behaviour of the HF wave function 0 (eq. (4.18)) as the distance between the two nuclei is increased toward infinity. Since the HF wave function is an equal mixture of ionic and covalent terms, the dissociation limit is 50% H+H " and 50% H H. In the gas phase all bonds dissociate homolytically, and the ionic contribution should be 0%. The HF dissociation energy is therefore much too high. This is a general problem of RHF type wave functions, the constraint of doubly occupied MOs is inconsistent with breaking bonds to produce radicals. In order for an RHF wave function to dissociate correctly, an even-electron molecule must break into two even-electron fragments, each being in the lowest electronic state. Furthermore, the orbital symmetries must match. There are only a few covalently bonded systems which obey these requirements (the simplest example is HHe+). The wrong dissociation limit for RHF wave functions has several consequences. 

In relation to cancer, there is some evidence that highly oxidized and heated fats may have carcinogenic characteristics. HNE (4-hydroxy-2-frans-nonenal), a secondary lipid peroxidation product derived from linoleic acid oxidation, has assumed particular interest because it has shown cytotoxic and mutagenic properties. Its toxicity, as well other secondary lipid peroxidation products (HHE 4-hydroxy-2-frans-hexenal and HOE 4-h yd roxy-2-trans-oc ten al), is explained through the high reactivity with proteins, nucleic acids, DNA, and RNA. Research links them to different diseases such as atherosclerosis, Alzheimer s, and liver diseases (Seppanen and Csallany, 2006). Research is rapidly progressing, but results are still not conclusive. 

Fig. 4. Polarograms of several monomers. Monomer concentration 10-8 mol/1, hHe = 70 cm, Temp. 25° C, Supporting electrolyte 0.1 M Bu4NC104...

BoflHbifl pacTBop OMEIA HeftTpaJieH (pH 7) h ycroHHHB b Te HHe pa a JieT [4] B kmcjiux pacTBopax oh pa3jiaraercH 6bicTpo, a b mejion-hhx MeflaeHHO (cm. TaSji. 57). 

If the system contains three electrons, the two occupying 4 will be stabilized, and the other one, localized in XV2, destabilized. Here, the stability of the molecule depends upon the relative energies of 4, Tf, and the AOs thus, HHe dissociates spontaneously, but the three-electron bond in He2+ is moderately robust. Note that, in contradiction with Lewis theory, a covalent bond may be formed with one or three electrons. Electron-deficient bonds (where there are fewer than two electrons per bond) are particularly prevalent amongst boron compounds. 

---