Implications of Guanidine Substitution on Copper Complexes as Entatic‐State Models

Abstract

The guanidine–quinoline ligand dimethylethyleneguanidinoquinoline (DMEGqu) is able to stabilise bis(chelate) copper complexes in an intermediate geometry between tetrahedral and square‐planar environments. The structures of the obtained complexes model the entatic state and have been investigated in solid state by single‐crystal X‐ray diffraction and in the solid state and in solution by X‐ray absorption spectroscopy. The dimethylethyleneguanidine (DMEG) unit of the DMEGqu ligand displays a smaller steric encumbrance than the tetramethylguanidine (TMG) counterpart; this allows slightly larger structural changes upon oxidation than those for the TMG counterparts. Moreover, triflate coordination was possible for the CuII DMEG complexes. DFT analyses revealed that good structural and optical descriptions are possible through the use of the hybrid functionals B3LYP and TPSSh in combination with the triple‐zeta basis set def2‐TZVP and the inclusion of empirical dispersion with Becke–Johnson damping and a suitable solvent model. The orbital analysis gives insights into the electronic structure of the complexes and their charge‐transfer behaviour.

Copper Guanidinoquinoline Complexes as Entatic State Models of Electron‐Transfer Proteins

“…Copper guanidinoquinoline complexes could act as good entatic state models. The geometries of their molecular structures of both oxidation states are highly distorted from the ideal tetrahedral (for Cu I ) and ideal square‐planar (for Cu II ) coordination geometry . The structures resemble each other strongly (Figure ).…”

“…The imine donor of neutral guanidines simulates the donor function of histidine and, therefore, the ligands are used in model complexes of type 1 and type 3 copper enzymes …”

Jet delivery system for Raman scattering on bio-inorganic compounds

“…1, 29 These complexes consist of a Cu I center with the hybrid guanidine-quinoline ligands TMGqu or DMEGqu.…”

“…1, 29 The center ion is bound to four nitrogen atoms, which belong to two quinoline and two guanidine groups. The dominant copper-core related vibration modes at 530 cm…”

“…1,6,[29][30][31][32] For the optimization of the Raman signal it was important to fit the jet size to the optical Raman spot size with regard to the measurements with the UT-3. We needed to optimize the laser power deposited into the jetting sample without disrupting the jet.…”