Triiodide ion-induced inhibition of amyloid aggregate formation: A case study of α-synuclein

•The effect of ethylammonium iodide (EAI) on the formation of amyloid aggregates of α-synuclein (α-SynA) was investigated.•Concentrated EAI solutions exhibited an ability to inhibit α-SynA formation.•The formation of triodide (I3–) ion in this media relates to the inhibition of α-SynA formation.•The inhibition ability of ammonium-based iodides for α-SynA formation are stronger than alkali-iodides.