To deliberate the chirality of the supramolecular architecture, solid state circular dichroism spectra were measured in a KCl matrix for GMP ligand and the single-crystals of complex 1 (Fig. 3(b)). There is a red-shift in the solid state CD spectrum of GMP compared with its liquid CD spectrum. The negative band about the conformation of the sugar moiety has nearly disappeared. In solid-state, mutarotation is more difficult and the negative band at the 260 nm nearby can be detected which indicates that the GMP ligand is mainly β-anomers. In the spectrum of complex 1, the weak negative band at 215–225 nm indicates that the GMP exists as l-ribo [5], which is induced by the strong π–π and hydrogen bonding interaction. For solid samples, CD spectroscopy is highly sensitive to even a very small distortion from planarity of the aromatic chromophore [12]. The strong negative CE centered at 297 nm (θ ≈ − 10 mdeg) is due to the excitation coupling of π → π* transitions of the aromatic chromophores, including the intra- and intermolecular coupling of the guanine chromophores [13], which is consistent with the single crystal structure.
solid state CD spectrum of GMP
negative band
260 nm
nm
spectrum of complex 1
negative band
215–225 nm
nm
strong negative CE
297 nm
nm
θ
≈ − 10 mdeg
mdeg