Abstract
Herein, we have investigated principally with the use of UV and fluorescence (steady-state and time-resolved) spectroscopy the interactions between selected pentapeptides with tyrosine residue (EYHHQ, EHYHQ, EHHQY, and KYHHE) and various metal ions (Cu2+, Mn2+, Co2+, Ni2+, Zn2+, Cr3+, Cd2+, Ag+, Pb2+, Sr2+, Ba2+, Ca2+, Mg2+, Al3+, Fe2+, and Ga3+) in order to establish the relationship between the position of a tyrosine residue in the peptide sequence and the metal ion-binding properties. Among the peptides studied, EHYHQ was evaluated as an efficient and selective ligand for developing a chemosensor for the detection of copper(II) ions. While significant fluorescence emission quenching was observed for that peptide in the presence of Cu2+ cations, other metal cations used at the same and at considerably higher concentrations caused a negligible change of the fluorescence emission spectrum, indicating a high selectivity of EHYHQ for Cu2+ ions. Under optimum conditions, fluorescence intensity was inversely proportional to the concentration of Cu2+ ions. The limit of detection of Cu2+ ions with the use of EHYHQ was determined at the level of 26.6 nM. The binding stoichiometry of the complexes of the studied peptides with Cu2+ ions was evaluated spectrophotometrically and fluorimetrically (as in the case of EHYHQ confirmed by mass spectrometry) and found to be 1:2 (Cu2+-peptide) for all the investigated systems. Furthermore, the stability constant (K) values of these complexes were determined. The reversibility of the proposed Cu2+ ions sensor was confirmed, the pH range where the sensor acts was determined, while its analytical performance was compared with some other reported recently fluorescent sensors. The mechanism of the interactions between EHYHQ and Cu2+ was proposed on the basis of NMR spectroscopy investigations.
Highlights
In recent years, there has been a particular emphasis on the development of new highly selective molecular sensors for cations with biological interest because of their potential applications to clinical biochemistry and environmental research [1]
Disorders in cellular homeostasis of Cu2+ ions have been proven to result in various diseases, such as Alzheimer’s disease, Parkinson’s disease, prion diseases, or amyotrophic lateral sclerosis [7]
The main goal of our work was to investigate the interactions between selected pentapeptides with a tyrosine moiety including EYHHQ, EHYHQ, EHHQY, and KYHHE, where E denotes glutamate, Y tyrosine, H histidine, Q glutamine, K lysine, and a list of chosen metal ions (Cu2+, Mn2+, Co2+, Ni2+, Zn2+, Cr3+, Cd2+, Ag+, Pb2+, Sr2+, Ba2+, Ca2+, Mg2+, Al3+, Fe2+, and Ga3+) to evaluate the relationship between the position of a tyrosine residue in the pentapeptide sequence and the metal ion-binding properties
Summary
There has been a particular emphasis on the development of new highly selective molecular sensors for cations with biological interest (such as Na+, Ca2+, Cu2+, and Zn2+) because of their potential applications to clinical biochemistry and environmental research [1]. Among these ions, the Cu2+, ion as the third most abundant essential transition metal in a human organism [2], plays a significant role in a variety of fundamental physiological processes (many proteins use Cu2+ ion as a cofactor for electron or oxygen transport as well as a catalyst for oxidation–reduction reactions [3]). The US Environmental Protection Agency set the limit of copper in drinking water at 1.3 ppm (∼20 μM) [6]
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