Chair vs. Boat: Conformational Impacts on DNA Binding Capacity in Cu(II) Complexes Featuring cis‐1,4‐Cyclohexanedicarboxylate

This work reports the syntheses of two new Cu(II) coordination complexes using cis-1,4 cyclohexanedicarboxylic acid (cis-1,4-H₂chdc) linker; and 4,4′-dimethyl-2,2′-bipyridine (1)/5,5′-dimethyl-2,2′-bipyridine (2) auxiliary ligands, wherein, cis-1,4-chdc adopts chair form in 1 and boat conformation in 2. Intriguingly, this conformational change impacts the DNA binding capacities of the complexes as revealed by spectrophotometry, circular dichroism spectroscopy and docking studies.

Abstract

Two new coordination complexes were synthesized, which are formulated as [Cu₂(cis-1,4-chdc)(4,4′-Me₂bpy)₄] ⋅ 2(ClO₄ ⁻) ⋅ H₂O (1) and [Cu₂(cis-1,4-chdc)(5,5′-Me₂bpy)₄] ⋅ 2(ClO₄ ⁻) ⋅ H₂O (2), using cis-1,4-cyclohexanedicarboxylic acid (cis-1,4-H₂chdc), 4,4′-dimethyl-2,2′-bipyridine (4,4′-Me₂bpy), 5,5′-dimethyl-2,2′-bipyridine (5,5′-Me₂bpy). Interestingly, cis-1,4-chdc adopts chair form in 1 and boat conformation in 2. This conformational change impacts the DNA binding capacities of the complexes as revealed by spectrophotometry, circular dichroism (CD) spectroscopy and docking studies. The complex 1 having the chair conformation shows higher affinity towards the DNA base pairs due to anti-alignment of the planar aromatic pyridyl rings of 4,4′-Me₂bpy, which strongly intercalates with the adenosine base pairs of DNA by formation of three π–π stacking and two extra π-positive stacking interactions between adenosine bases and positively charged nitrogen. Conversely, 5,5′-Me₂bpy with planar aromatic pyridyl rings of complex 2 shows bis-intercalation with weak affinities toward base pairs by formation of two π–π stacking and one π-positive stacking interactions.

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