Glyoxal chemistry

Polyquinoxalines (PQ) have proven to be one of the better heat-resistant polymers with regard to both stabiUty and potential appHcation. The aromatic backbones are derived from the condensation of a tetramine with a bis-glyoxal, reactions first done in 1964 (61,62). In 1967, a soluble, phenylated version of this polymer was produced (63). The chemistry and technology of polyquinoxalines has been reviewed (64). 

An intramolecular variant of the above chemistry has been used for the preparation of pyrroloindolizines. A -Allyl- and iV-propargyl-glyoxals react with tetrahydroisoquinoline to give 231 and 232, respectively (Equations 28 and 29). Furthermore, these reagents have been linked through the (V-substituent to a polymeric resin for further use in solid-phase and combinatorial chemistry <1997JA6153>. 

Glyoxal-based fixatives work faster than formalin. Small biopsies may be ready to process after only an hour while properly grossed larger specimens are ready in about 6h. Structural detail is remarkable in its clarity (Fig. 12.9). Red blood cells are lysed, but that rarely presents a problem. Eosinophilic granules are reduced in prominence (see below). Special stains work well, except for tests for iron (the mildly acidic pH is detrimental) and the silver detection methods for Helicobacter pylori. Most notably, glyoxal-fixed tissues retain strong immunoreactivity for most antigens. The chemistry behind most of this is known. 

The ability to direct conjugation or modification specifically through arginine residues using this chemistry has been exploited in the availability of the only photoreactive glyoxal derivative, APG. 

In 1997, four laboratories reported their results on (phenoxyl)copper(II) structural model compounds that stressed various aspects of the coordination chemistry of GO and glyoxal oxidase in its various oxidation levels. 

Nature has designed the active sites in the enzymes GO and glyoxal oxidase in order to perform a hydrogen-atom abstraction reaction from the a-carbon atom of an O-bound alcoholate (or aldehyde) in the rds. The essence of this chemistry is depicted in Fig. 8. 

The uncatalysed Belousov-Zhabotinsky (B-Z) reaction between malonic acid and acid bromate proceeds by two parallel mechanisms. In one reaction channel the first molecular products are glyoxalic acid and carbon dioxide, whereas in the other channel mesoxalic acid is the first molecular intermediate. The initial reaction for both pathways, for which mechanisms have been suggested, showed first-order dependence on malonic acid and bromate ion.166 The dependence of the maximal rate of the oxidation of hemin with acid bromate has the form v = [hemin]0-8 [Br03 ] [H+]12. Bromate radical, Br02, rather than elemental bromine, is said to play the crucial role. A mechanism has been suggested taking into account the bromate chemistry in B-Z reactions and appropriate steps for hemin. Based on the proposed mechanism, model calculations have been carried out. The results of computation agree with the main experimental features of the reaction.167... 

Volkamer, R., L.T. Molina, M. J. Molina, T. Shirley, and W.H. Brune DOAS measurement of glyoxal as an indicator for fast VOC chemistry in urban air, Geophysical Research Letters, 32 (2005a) L08806, doi 10.1029/2005GL022616. 

Volkamer, R., U. Platt, and K. Wirtz Primary and Secondary Glyoxal Formation from Aromatics Experimental Evidence for the Bicycloalkyl-Radical Pathway from Benzene, Toluene, and p-Xylene, Journal of Physical Chemistry A, 105 (2001) 7865-7874. 

Volkamer, R., P. Spietz, J.P. Burrows, and U. Platt High-resolution absorption cross-section of Glyoxal in the UV/vis and IR spectral ranges. Journal of Photochemistry and Photobiology A Chemistry, 172 (2005b) 35-42, doi 10.1016/j.jphotochem.2004.11.011. 

Velisek J., Davidek T. and Davidek J. (1998) Reaction products of glyoxal with glycine. 6th Int. Symp. on Maillard react., The Maillard Reaction in Foods and Medicine, O Brien J., Nursten H.E., Crabbe J.C. and Ames J.M. Eds Royal Society of Chemistry, London, pp. 204-8. 

Figure 3.9 Typical capillary gas chromatogram of the derivatives of dicarboxylic acids (C2 Cg), ketocarboxylic acids ( C0C2, C0C4, pyruvic acid), and dicarbonyl (glyoxal) isolated from sea water (Sample collected in the Bay of Marseille (northwestern Mediterranean Sea) in September 2005. Reprinted with permission from Determination of low molecular weight dicarboxylic and ketocarboxylic acids in seawater sample) Tedetti, M, et ai, Analytical Chemistry (1 Sep 2006), 78 ( 7), 6012-6018. Copyright (2006) American Chemical Society).

---