Methylation is a substitution of a hydrogen, halogen or metal atom by a methyl group – CH3. It is carried out by various methylating agent, for instance, iodide methyl CH3I, dimethyl sulfate (CH3O)2SO2, methyl sulfuric acid CH3OSO3H, methyl ester of organic sulfuric acid, and methanol, CH3OH, and dimethyl ester (CH3)2O. It is widely used in industrial organic synthesis (Carvalho, 2000).
Thus, methylation with dimethyl sulfate is used in the synthesis of drugs, such as analgene; methylation is carried out with formaldehyde and a reducing agent, usually formic acid, in producing of amidopirin. Methylation is very important in preparative organic chemistry in the laboratory and in the factory production, for instance, in technology of aniline dyes, drugs. Methylation is of great importance to elucidate the structure of certain classes of organic compounds, for instance, carbohydrate.
The processes of methylation in body of warm-blooded creatures have been known for long time: the formation of telluride methyl from telluride acid (Hof-meister), finding in the urine of dogs poisoned with phosphorus, methylated amino butyric acid, which was formed from glutamic acid; methylation of the injected into the body nitrogenous substances, for instance, pyridine and nicotine acid, formation of sarcosine КН(СН3)-СН2-СОО, nizglycine 1Sh2-COOH (H2N—СН2—СООН), and increase the selection of creatine and creatinine in feeding with guanidine acetic acid: HN = C (NHa)-NH-CH2-COOH-+ guanidine acetic acid HN=C(NHa)-N(CH,)-CH2-COOH methyl guanidine acetic acid=creatine (Mauro, 2001). An indication of the fact that the processes of methylation take place in the animal body is a constant presence in it of methylated nitrogenous compounds such as creatine, methyl- and dimethylguanidine, adrenaline, trimethylamine, betaine, carnitine, methylated purines, etc.
The process of methylation occurs in mercury as well but it is very complicated. Sulfate-reducing bacteria in the sediments are dominated in this process. It is known that each bacterial cell is able to methylate mercury and any bacterial membrane is capable to dimethylate. The mercury becomes a non-polar compound after methylation, it passes through the membrane and exhibits all the properties of the heavy metal inside the cell. There are accumulation of it and functional changes of characteristics of individual proteins. Mercury goes the way of the trophic chain and methylated mercury accumulated in vivo.
Carvalho, C.V.d., Payão, S.L.M., Smith, M.d.A.C. (2000). DNA methylation, ageing and ribosomal genes activity. Biogerontology, 1(4), pp. 357-360.
Mauro, J.B.N., Guimarães, J.R.D., Melamed, R. (2001). Mercury Methylation in Macrophyte Roots of a Tropical Lake. Water, Air, and Soil Pollution, 127(4), pp. 271-275.