Sonication-induced instant amyloid-like fibril formation and organogelation by a tripeptide

A terminally protected tripeptide Boc-Val(1)-Phe(2)-Phe(3)-OMe 1 having sequence similarity with Aβ18–20 (the central hydrophobic fragment 18–20 of the amyloid β-peptide Aβ42) forms sonication induced organogels. The peptide forms a very weak gel only in 1,2-dichlorobenzene after heating, cooling and ageing for 3 days. But ultrasound energy induces instant fibril formation and gelation in a wide range of organic solvents starting from hexane, cyclohexane, petrol, kerosene to benzene, toluene, xylene and ethanol. CD, FT-IR, NMR and wide angle X-ray scattering (WAXS) studies of the peptide 1 exhibit distinct structural changes before and after sonication. Atomic force microscopy (AFM) and field emission scanning electron microscopy (FE-SEM) of the xerogels reveal a nanofibrillar morphology, which is obtained by the sonication induced self-assembly of the gelator. These gels bind with Congo red, a physiological dye, and show a green-gold birefringence under polarized light, a characteristic feature of amyloid fibrils.