Biointeractions of C.I. Acid Red 2 and its structural analogues with transporter albumin: Fluorescence, circular dichroism, and ligand docking approaches

•Vector protein may be used to assess the potential harms of food color additives.•The contribution of benzene ring to overall toxicity is less than naphthalene ring.•Artificial food colorants can disrupt the orderly structure of transport protein.•Ser-202, Ala-210, and Trp-214 residues are critical in the recognition processes.•Hydrophobicity of food colorings has a pivotal role in their toxicological actions.

In this contribution, the toxicological effects of C.I. Acid Red 2 and 1-(2-pyridylazo)-2-naphthol (PAN) have been elucidated by utilizing plasma albumin as a biological model. Fluorescence data indicated that the Trp-214 residue was quenched by both azo compounds, but the quenching degree of C.I. Acid Red 2 is less than PAN. According to the results of time-resolved fluorescence decay, it may be observed that the quenching of Trp-214 residue is controlled by static type; this corroborates the Stern–Volmer analyses and the conformational transition of protein was concurred. The experiments also found that azo colorants are situated within subdomain IIA, several amino acid residues, such as Ser-202, Ala-210, and Trp-214 were believed to be yielded direct interaction with the two chemicals, yet the operating distances between C.I. Acid Red 2 and relevant residues are greater than PAN. Interestingly, we may ascertain that the azo colorants with naphthalene ring possess stronger affinity with protein than those just having benzene ring in their molecular structure. This suggested that the existence of naphthalene ring substituent could hold relatively great risk for the human body due to large hydrophobicity (cLogP); therefore, the hydrophobicity of azo colorants can probably be a major element of its toxicological activities.

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