Contents lists available at ScienceDirect Microchemical Journal journal homepage: www.elsevier.com/locate/microc Chiral recognition and quantitative analysis of tyrosine enantiomers using L- cysteine capped CdTe quantum dots: Circular dichroism, fuorescence, and theoretical calculation studies Foroozan Feizi, Mojtaba Shamsipur ⁎ , Ali Barati, Mohammad Bagher Gholivand, Farimah Mousavi Department of Chemistry, Razi University, Kermanshah, Iran ARTICLEINFO Keywords: Enantiomeric excess Chiral recognition L-Cys/CdTe quantum dots Circular dichroism Fluorescence ABSTRACT In this work, L-cysteine-capped CdTe quantum dots (L-Cys/CdTe QDs) were used as novel chiral probes for in enantioselective recognition and quantitative determination of tyrosine (Tyr) enantiomers using both fuores- cence and circular dichroism (CD) spectroscopies. Diferent quenching percentages in fuorescence of L-Cys/ CdTe QDs in the presence of similar concentrations of Tyr enantiomers were clearly observed. Quantum me- chanical (QM) calculations were also used to confrm such diferent interactions of L- and D-Tyr enantiomers with L-Cys/CdTe QDs. However, the CD spectroscopy exhibited higher capability and sensitivity, compared to fuorescence spectroscopy, to distinguish between these enantiomers. While, Tyr enantiomers provided no sensible CD signals at micromolar concentration levels, they exhibited remarkable and opposite CD spectra at these concentration levels in the presence of L-Cys/CdTe QDs. Under the optimized conditions, the CD signals of L- and D-Tyr enantiomers showed good linear relationships with the concentrations of both enantiomers over the range of 10–80 µM with limit of detections (LODs) of 1.5 and 1.6 µM, respectively. This method was also successfully applied to enantiomeric excess determination of Tyr at the total concentration of 50 μM with a LOD of 1.2%. 1. Introduction Due to diferent functionality of enantiomers of the most chiral species, their identifcation and enantiomeric excess determination is of highly importance especially for clinical applications [1]. Until now, many diferent methods such as chiral electrophoresis methods [2], chiral chromatography methods [3], enzymatic methods [4], and spectroscopic and fuorimetric methods based on a number ofdiferent chiral probes [5,6] have been employed for enantiomeric excess de- termination, chiral identifcation, and enantio-separation of various chiral species. In recent years, the use of fuorescent chiral nanoparticles as chir- optical probes for enantiomeric excess determination and chiral iden- tifcation has attracted an increasing research interest [7–10]. The chiral optical activity of these nanoparticles is commonly originated from the intrinsic chiral structure of the nanoparticles [11–14], the chiral properties of their capping chiral ligands [15] or from the chiral memory efects [16]. The chiral semiconductor quantum dots (QDs) [17–19] are among the widely reported chiral nanoparticles that have been applied for various purposes from enantiomeric sensing to enantiomeric separation [20,21], and cell imaging [22,23]. The frst chiral QDs were reported by Yurii K. Gun’ko et al. who capped the surface of CdS QDs by D- or L-penicillamine ligands. The circular dichroism studies of these QDs produced intense mirror CD spectra and those capped with a racemic mixture of penicillamine li- gands showed only a very weak signal [24]. This simple method has been extensively used to preparation of chiral QDs with the aim of chiral recognition and enantiomeric excess determination of chiral components. For example, the fuorescence signal of chiral L-cysteine (Cys)-capped CdSe(ZnS) QDs exhibited selective responses to carnitine enantiomers in aqueous solution. The fuorescence intensities of L-Cys- capped QDs and D-Cys-capped QDs were only quenched in the presence of D- and L-carnitine enantiomers, respectively, and were not afected by the other enantiomer [25]. Cyclodextrins have also been used as chiral agents for capping the surface of QDs [20,26]. In this regard, Haibing Li and co-workers modifed the surface of CdSe/ZnS QDs with cyclodextrin through a simple sonochemical method to prepare an en- antioselective fuorescent sensor for amino acid enantiomers [26]. In- terestingly, when cyclodextrin‐QDs treated with L‐amino acids, they showed a much greater fuorescence enhancement, compared with https://doi.org/10.1016/j.microc.2020.105168 Received 28 February 2020; Received in revised form 12 June 2020; Accepted 13 June 2020 ⁎ Corresponding author. E-mail address: mshamsipur@yahoo.com (M. Shamsipur). Microchemical Journal 158 (2020) 105168 Available online 15 June 2020 0026-265X/ © 2020 Elsevier B.V. All rights reserved. T