Gy. Kóródi, J. Rikk and T. Szarvas
BGF Methodology Department, Budapest, Hungary
INTRODUCTION: The moderate wine intake causes more healthy benefits than other types of alcohol because of it’s high antioxidant content. On the orther hand we have to investigate all the methods, which can be useful in reducing the toxic effects of the ethanol metabolits. It has been supposed for a long time that methilation of amines by acetaldehyde occurs only extreme conditions. Recently hungarian authors have reported on the spontaneous reaction between acetaldehyde and Llysine yielding N-methylated products at room temperature. This reaction extended to L- arginie as well, so a tentative theoretical explanation of the experimental findings is outlined.
METHODS: We did potentiometric titration using combined glass electrodes, UV, H-NMR and mass were recorded by mass spectrometer, respectively. strong cationic exchange plates were used in a citrate bufer for thin layer chromatography. The content of the methylol-arginine derivate was examined by a radiochromatographic method thinlayer chromatographic system. Electrostatic isopotential maps were calculated by the ELPO programme. Geometries of lysine and arginine were taken from neutron diffraction studies.
RESULTS: Changes in pH L-lysine and L-arginine correspond to the Sörensen formole titration While L-lysine reacts slowly, it’s methylated products appear only 5 hours after neutralization, N-hydroxymethyl derivates of arginine can be detected instantaneously on the plate. Methylation reacton products for L-lysine could be identified as N-mono-, di- and trimethyl-L-lysine. No hydroximethyil derivates could be detected at all. On the other hand, reaction between L-arginine and acetaldehyde is slow; the products could be identified as N-hydroxymethyl derivates with thin layer chromatography.
DISCUSSION: Two problems arise when studying the reaction between acetaldehyde and L-argnine: 1., what are the products formed; 2., how the essential difference between reactivities of L-lysine and L-arginine can be explained.
It is evident that if the imino nitrogen of the arginin guanidino miety is blocked by methyl groups the reaction gets practically impossible. On the other hand N-monomethyl and N-N-dimethyl derivates of arginine reacts with acetaldehyde at about a same rate. Consequently it is the imino nitrogen atom which reacts readily with acetaldehyde to yield the monosustituted hydromethyl derivate. Most probably the second acetaldehyd molecule enters at the terminal amino nitrogen atom. This is understood by inspection of the lectrostatic isopotential map of the zwitterionic, Nprotonated form of L-arginine. The N-proteonated form of lysine reacts with acetaldehyde to yield an unstable adduct, afterwards a proton is transformed to the alkoxide group and hydroxymethyl-L-lysine is formed. This reacts at once with a second molecule of acetaldehyde and the intermediate product is reducced via an azomethin structure to N-methyl-Llysine. The diffference in the reaction rate between L-lysine and L-arninine with acetaldehyde is explained with the different nucleophilicity of the amino group in lysine and that of the imino group in argininine. The minima of the electrostatic potential around the corresponding atoms are -481 kJ/mol and -749 kJ/mol, respectively. These values explain the higher affinity of arginine, as related to lysine towards the acetaldehyde molecule.
Keywords: L-Lysine, L-Arginin, wine intake.