Synthesis and Characterization of Novel Quinolyl Porphyrins as Receptors. Study of their Association with Halophenols and 4-Nitrophenol as a Reference

In this work, new receptors built on the porphyrin scaffold were synthesized for halophenols recognition. A quinolyl group was introduced on the porphyrin's periphery as binding site, to form two series of molecules based on two distinct porphyrin frames and which were obtained in free base and zinc forms. The binding between these porphyrin-based receptors and halophenols (2,3,4,6-tetrachlorophenol, 2,4,6-trichlorophenol or 2,4,6-tribromophenol) was studied. As established by H-1 NMR spectroscopy, the binding constants are in the range of two-digit numbers, which value is correlated with the porphyrin structure (substitutive pattern, form of the free base or Zn-II complex) and the pK(a) of the respective phenol. These data, supplemented by a X-ray structure of one adduct complex, indicate a single interaction between the phenolic proton and the nitrogen of the quinolyl group. The binding with p-nitrophenol was tested for comparison. The association constant increases at a scale of one order of magnitude. This net stabilization of the adduct complex in this case is explained by additional hydrogen bonds implying the nitro function, as also witnessed by X-ray diffractometry.