Effects of G-Quadruplex Topology on Electronic Transfer Integrals. PubMed Central. Sun, Wenming; Varsano, Daniele; Di Felice, Rosa. 2016-01-01. G-quadruplex is a quadruple helical form of nucleic acids that can appear in guanine-rich parts of the genome. The basic unit is the G-tetrad, a planar assembly of four guanines connected by eight hydrogen bonds.