Effect of the electronic coupling in dinucleotides and oligonucleotides of adenine and thymine from synchrotron radiation absorption and circular dichroism

Absorption and circular dichroism measurements were performed on specifically chosen DNA mononucleotides, dinucleotides and oligonuclotides with combinations of adenine (A) and thymine (T), namely 2′-deoxyadenosine 5′-monophosphate (dAMP), thymidine 5′-monophosphate (TMP), dApdA, dTpdT, dApdT, dTpdA and dAp(dTp)ndA (n = 1, 2 or 3) to study the importance of electronic coupling between bases for various bands. The coupling is stronger in the VUV region than in the UV region. In the VUV, it is possible to distinguish between dApdT and dTpdA sequences whereas in the UV the spectra are almost identical. A simple sequence dependent nearest neighbour model is used to explain the observations from both types of spectroscopy, underlining the importance of not only the nature of nearest neighbour nucleobases but the sequence as well.