Diazomethane is a highly reactive, explosive organic compound with the chemical formula CH2N2. It is a colorless gas or pale yellow liquid that is used as a methylating agent in organic synthesis. Diazomethane is prepared by the reaction of nitrosomethane with a base such as potassium hydroxide.

It is important to handle diazomethane with care, as it can be explosive and toxic. It should only be used in well-ventilated areas, and protective equipment such as gloves and safety glasses should be worn. Diazomethane should not be stored for long periods of time, as it can decompose spontaneously and release nitrogen gas.

Diazomethane is used to introduce methyl groups into organic molecules in a process called methylation. It reacts with carboxylic acids to form methyl esters, and with phenols to form methyl ethers. Diazomethane is also used to synthesize other organic compounds such as pyrazoles and triazoles.

It is important to note that the use of diazomethane in the laboratory has declined due to its hazardous nature, and safer alternatives are now available for many of its applications.

Methylation, in the context of genetics and epigenetics, refers to the addition of a methyl group (CH3) to a molecule, usually to the nitrogenous base of DNA or to the side chain of amino acids in proteins. In DNA methylation, this process typically occurs at the 5-carbon position of cytosine residues that precede guanine residues (CpG sites) and is catalyzed by enzymes called DNA methyltransferases (DNMTs).

DNA methylation plays a crucial role in regulating gene expression, genomic imprinting, X-chromosome inactivation, and suppression of repetitive elements. Hypermethylation or hypomethylation of specific genes can lead to altered gene expression patterns, which have been associated with various human diseases, including cancer.

In summary, methylation is a fundamental epigenetic modification that influences genomic stability, gene regulation, and cellular function by introducing methyl groups to DNA or proteins.