Amino acids models

Chlorination of Individual Amino Acids. HPLC analysis of an extract of chlorinated humic acids indicated that the chlorination products compose a highly complex mixture of organic material. Thus, the task of identification of mutagenic products of chlorination would not be simplified by the use of the humic acid model. In contrast, the amino acid model of production of mutagenic compounds can be readily simplified by the use of individual compounds as precursors. 

Fig. 19.3 Relationship between turnover number (TN) of Ru-red confined in a coaed iNafior membrane for electrocatalytic 02 evolution and the catalyst concentration ir the absence of amino acid model compound (a), in the presence of 5.0 x 1U 2Mp-Cre (b), and witl toluene (c). The solid line and dashed line are calculated curve .. The dash-dotted curve (I) is a simulated curvt in the presence of / -Cre when r0 and rd are the same as those in the absenc< of p-Cre, and curve (II) is a simulated curve in the presenci of p-Cre when r0 and kQ2 an the same as those in the absence ofp-Cre.

V. Fogliano, R. C. Borrelli, and S. M. Monti, Characterization of melanoidins from different carbohydrate amino acids model system, in Melanoidins in Food and Health, Vol. 2, J. M. Ames (ed), European Communities, Luxembourg, 2001, 65-72. 

Competitive effects for the interactions of cisplatin with various active sites in the cellular environment are discussed in papers of Deubel.55,56 In the earlier paper, energetic and structural data of complexes with the different substituted ligands were explored. The more recent work deals with kinetic factors in the relation to the transition state (TS) for water replacement of the semihydrated cisplatin complex (cis-[Pt(NH3)2(H20)Cl]+ ) with either an N- or S-containing ligand (thiopheneimidazol, dimethyl sulphide, or methanethiolate which serve as amino acid models). Deubel concluded the kinetic preference of N-sites over S-nucleophiles where the important role is played by the electrostatic terms. In addition, the aliphatic/aromatic character of the substituent as well as the influence of different dielectric constants of the environment are very important. A more realistic model for the aqua-ligand replacement with adenine and guanine was studied in works of Chval et al.53,57 and Eriksson and coworkers.58 They performed independently the estimation of the thermodynamic and kinetic parameters of this process. 

A phenohc a-amino acid. Model compound Tyrosine (1). 

In search for the key intermediates to meat flavor development in heated cysteine-sugar systems, it was found that in addition to thiazolidine derivatives also the tetrahydro-l,4-thiazine derivatives are being formed. These tetrahydro-l,4-thiazines, which are the cyclic form of Amadori compounds of cysteine, have excellent meat flavor precursor properties and are likely to play a prominent part in meat flavor development. Another major pathway to meat flavor development is the reaction of cysteine with the Amadori compounds of other amino acids. Model experiments showed that both pathways are probably of about equal importance for flavor development in boiled meat and process flavorings, this in spite of the low reactivity of cysteine with sugars. It seems that the first pathway is general-acid-catalyzed by the other amino acids, whereas the second pathway is inhibited by cysteine. 

Koehler P.E., Mason M.E. and Newell J.A. (1969) Formation of pyrazine compounds in sugar-amino acid model systems. J. Agric. Food Chem. 17, 393-6. 

As mentioned before, the sites A to F of the map now can be occupied by different amino acids presenting the necessary chemical properties. The available biochemical information, such as amino acid sequence, bacteriorho-dopsin homology, alignment studies, etc., has led us to construct the amino acid model of the 5-HT2a receptor presented in Fig. 24.6. Interaction energies for the complexes formed between ligands and the receptor model were calculated as described in Section H. D. 

Deakyne and Allen (1979) have used semiempirical CNDO/2 calculations to attempt to define the amino acid residues at the active site of RNase involved in binding and catalysis in the cyclization step of the reaction. As these workers state, such calculations are not absolute, but demonstrate trends. They suffer from the limitations of the level of calculation and the minimal model structures that may be used for substrate and aetive site. The cyclization step is considered in two parts the first, attachment and partial protonation of the substrate the second, deprotonation/protonation of the TBP intermediate. For attachment and partial protonation, dimethyl phosphate is used as a model for the nucleotide substrate and interactions with amino acid models analysed. Several conclusions are drawn ... 

Table 2 Stability constants of receptor 20 with Boc-N-protected amino acids (model of binding 1 1).

Guerra P.V., Yaylayan V.A. Thermal generation of 3-amino-4,5-dimethylfuran-2(5H)-one, the postulated precursor of sotolone, from amino acid model systems containing glyoxylic and pyruvic acids. Journal of Agricultural and Food Chemistry, 59 4699-4704 (2011). 

---