Binding of Heteropolyarenes to Protein

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Abstract
The interaction of 14 aza-aromatic compounds, substituted DB[a, h]ACRs and DB[c, g]Cs with human serum albumin, as well as their hydrophobicity have been studied. The binding constants of DB[a, h]ACRs with the electron-donative nitrogen are in the range of (0.05 – 1.10) × 102M−1, for DB[c, g]C with the electron-accepting nitrogen, two orders higher. Consequently, the acridines are of low affinity and carbazoles of high affinity to protein, i.e. the relative nucleophilicity of the ligand has a considerable effect on the protein binding affinity of aza-PAHs. The association constant values for the methyl-DB[c, g]C studied differ by a factor of over 270, suggesting the importance of localization of the substituent. At the same time, for 14-alkyl-substituted DB[a, h]ACRs the hydrophobic, steric and electronic effects of the substituent characterize the protein binding affinity. The presence of two ligands B[a]P and 7H-DB[c, g]C, in the system leads to a mutual inhibition of their binding to albumin. Water solubility of DB[a, h]ACRs is very low (0.69–2.60 nM). The hydrophobicities of both classes of aza-PAH studied differs within a series only by a factor of 4, i.e. the influence of the substituent is less significant. The binding affinity of carbazoles to protein decreases with their increasing water solubility, while that of acridines increases.

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