LONG-RANGE ATTRACTION BETWEEN NUCLEOSIDES WITH SHORT-RANGE SPECIFICITY - DIRECT MEASUREMENTS

The structure of DNA is the result of highly specific interactions bet ween nucleotides (adenine and thymine, cytosine and guanine) based on hydrogen bonds and size complementarities. We performed direct measure ments of the forces between adenosine and thymidine using a surface fo rce apparatus [J. Chem. Soc. Faraday I 74, 975-1001 (1978)]. These mea surements showed that without the size effect hydrogen bonds alone gen erate the specificity. Bond energies obtained in our experiments are c onsistent with estimates indirectly obtained through other methods. We have also observed an unexpected long-range nonspecific attraction.