A method of forming a self-connective structure (a hairpin structure, a four-stranded structure, etc.) of a single-stranded oligonucleotide chain by forming a mimetic base pair of a mismatch base pair failing to form any normal base pair among base pairs of the single-stranded oligonucleotide chain with the use of a compounds represented by the following general formula (I): A-L-B (I) wherein A represents a chemical structural moiety capable of forming a pair with one base of a base pair failing to form any normal base pair; B represents a chemical structural moiety capable of forming a pair with the other base of the base pair failing to form any normal base pair; and L represents a linker structure by which the chemical structures A and B are linked to each other; and a method of inhibiting the activity of enzyme according to the previous method.