Figure 4.

(a) Attachment of the porphyrin to the 2′-position of the ribose through tethers (left)⁴⁰ or direct amidation (right)⁴¹ will position the substituents in the minor groove of the DNA. (b) Conjugation to the phosphate backbone leads to external placement, and face-to-face stacked dimers can lead to a stabilizing effect in the duplex, which is dependent on the central metal and its potential additional axial ligands. Reprinted with permission from ref (42). Copyright 2008 American Chemical Society.