Analysis of the interaction of para-sulfonatocalix[8]arene with free amino acids and a six residue segment of β-amyloid peptide as a potential treatment for Alzheimer’s disease

In this paper we examined the host–guest complex formation between para-sulfonatocalix[8]arene, and the amino acids l-alanine (A), l-arginine (R), l-isoleucine (I), l-leucine (L), l-lysine (K), l-phenylalanine (F), l-valine (V), and a six residue peptide (KLVFFA) based on the central hydrophobic cluster of the β-amyloid peptide. In the 1H NMR spectra, the addition of sCX[8] results in upfield and downfield shifts of selective proton resonances of the native seven amino acids, and the side-chain protons of the residues in the KLVFFA peptide of between + 0.3 and − 1.02 ppm. From a Job Plot, it was found that sCX[8] can form a 1:2 host–guest complex with the amino acid phenylalanine. The nature of the host–guest interactions was further examined by fluorescence spectrophotometry, whereby sCX[8] quenched the fluorescence of phenylalanine, both as the free amino acid, and as a residue within the KLVFFA peptide, at host–guest ratios of 1.37 and 0.24, respectively. It was also found that sCX[8] binds to the β-amyloid fibril staining dye, Thioflavin-T, and enhanced its fluorescence by 347%; this interaction could have implications in future fibrillation research using sCX[8]. Overall, the findings of this study provide an insight into the mechanism by which sCX[8] can reduce the aggregation of β-amyloid peptide, and supports further research into the potential use of sCX[8] in the treatment, or prevention, of Alzheimer’s disease.