pH Modulates the Coordination Mode and Pentose Ring Conformation Response Mechanism of Inosine 5′-Monophosphate Metal Complexes

Abstract

Nucleotides are the core of life genetics and metabolism, and are also excellent ligands for the construction of metal–organic frameworks. However, the site selectivity and conformational response of their metal complexes at different pH values are still unclear. In this study, using inosine 5′-monophosphate (IMP) as the main ligand and 1,2-bis(4-pyridyl)ethylene (bpe) as the auxiliary ligand, three crystalline complexes were synthesized under two distinct pH conditions: [Co(HIMP)2(H2O)4]·(bpe)·2H2O (1), [Cd(HIMP)2(H2O)4]·(bpe)·2H2O (2), {[Co2(IMP)2(bpe)2(H2O)6]·17H2O}n(3), which were characterized using various spectroscopic and diffraction techniques. Crystallographic analysis shows that under acidic conditions (pH = 4.03), metal ions coordinate with the purine nitrogen atom of IMP, while bpe does not participate in coordination but induces the pentose ring to adopt a compact twisted (T) conformation through intermolecular forces; under weakly basic conditions (pH = 7.12), the metal ion coordinates with the phosphate oxygen atom of IMP and the pyridine nitrogen atom of bpe; the expanded coordination environment, in conjunction with intramolecular forces, causes the pentose ring to revert to a more extended envelope (E) conformation. Screening across a range of pH values and the switching of metal ions confirmed the universality and controllability of this regulation. Single-crystal analysis and solid-state circular dichroism (CD) spectroscopy revealed that 1–3 exhibit, respectively, axial chirality of the auxiliary ligand, supramolecular helical chirality (P configuration), and extended axial chirality (M configuration). This study visually reveals the intrinsic relationship among pH, coordination patterns, and the conformation of the pentose ring, providing a new perspective for the regulation of nucleotide metal complexes and the design of chiral biomaterials.