DNA duplex. The modified nucleotide is described in:
Haugland et al. (2016) J. Am. Chem. Soc. 138, 9069-9072.

These shifts are what is obtained in 1H2O.
The amino protons of the Cytosine N4 is H bonded.

These shifts are what is obtained in 1H2O.
The amino protons of the Cytosine N4 is not H bonded.

2'-Alkynyl spin-labelling is a minimally perturbing tool for DNA structural analysis.