Highly Conductive Crown Ether/Ionic Liquid Crystal-Carbon Nanotubes Composite Based Electrochemical Sensor for Chiral Recognition of Tyrosine Enantiomers

Abstract

A new insight is presented in the fabrication of a simple chiral electrochemical sensor for tyrosine enantiomers which are the biomarkers of depression. The conductive sensor is based on modifying the glassy carbon electrode with two consecutive layers namely multiwalled carbon nanotubes-ionic liquid crystal (CNT+ILC) and 18-crown-6 (CW); GC/(CNT+ILC)/CW. CW is introduced for the first time as an excellent receptor for the chiral recognition of Ty enantiomers due to its perfect host-guest size matching principle. On the other hand, β-cyclodextrin (β-CD) does not recognize Ty enantiomers as its cavity size was larger, and needs extra modifications. Moreover, it was observed due to the opposite steric configurations of the Ty enantiomers, CW preferably forms strong complexes with L-Ty compared to D-Ty enantiomers, resulting in significantly noticeable electrochemical differences in their peak current responses with ratio of (L-Ty to D-Ty) about 3.09. The GC/(CNT+ILC)/CW showed excellent current responses for the electrochemical analysis of L-Ty and D-Ty enantiomers in the concentration ranges of 0.01-60 μmol L −1 and 0.09-60 μmol L −1 with low detection limit values of 1.42 nmol L −1 and 9.36 nmol L −1 , respectively. The practical impact of the sensor was illustrated in accurate determination of the percentage of enantiomers in Ty racemic mixture. Moreover, the electro-oxidation of AA, UA, and L-Ty in their ternary mixture was successfully achieved to three well-separated peaks using the GC/(CNT+ILC)/CW sensor.

Enantioselective Limiting Transport into a Fixed Cavity via Supramolecular Interaction for the Chiral Electroanalysis of Amino Acids Regardless of Electroactive Units

“…At present, most of the reported work has synthesized chiral materials immobilized on the surface of the working electrode (WE), such as proteins, 16−18 polymers, 1,19,20 nanohybrids, 3,5,6,8 and small organic molecules. 4,10 Among them, ferrocene (Fc) is supposed to be an appropriate precursor due to its redoxactive subunit. 21−26 In general, two approaches are carried out for the synthesis of chiral electroconductive materials derived from Fc.…”

“…One is that the isomers being tested should have electrochemical activity to provide electrical signals. Therefore, electroactive amino acids, including tryptophan, − tyrosine, , cysteine, , and phenylalanine, − have been widely recognized by using appropriate chiral sensing platforms. However, detecting chirality is still difficult when enantioselective electroanalysis is used to detect nonelectroactive isomers, thus limiting the further application of this electrochemical method for the analysis of chiral drugs or for screening asymmetric reactions.…”

“…At present, most of the reported work has synthesized chiral materials immobilized on the surface of the working electrode (WE), such as proteins, − polymers, ,, nanohybrids, ,,, and small organic molecules. , Among them, ferrocene (Fc) is supposed to be an appropriate precursor due to its redox-active subunit. − In general, two approaches are carried out for the synthesis of chiral electroconductive materials derived from Fc. One is that Fc as an achiral conductive unit mixes with a chiral selector as the modification of the WE. , However, it has little difference on the redox peak response of the ferrocene unit toward different configurations.…”

Enantioselective Voltammetric Sensors Based on Amino Acid Complexes of Cu(II), Co(III), and Zn(II)

“…Present-day strategies for creating enantioselective sensors suggest the use of the molecular imprinting technology [5][6][7][8] or chiral modifiers of various nature [9][10][11][12][13][14][15][16][17], which form a chiral layer on the electrode surface. The latter, in fact, determines enantioselectivity with respect to optical isomers of the analytes.…”

“…Despite certain advances in the development and application of enantioselective sensors based on composite glassy carbon electrodes, the search for optimal chiral modifiers has still remained an important and an urgent task. Indeed, the currently widely used modifiers, such as amino acids and their derivatives [9,10], cyclodextrins [11][12][13], crown ethers [14], and chiral biopolymers (proteins, polysaccharides) [13,15,16], most often do not simultaneously satisfy all the requirements for chiral modifiers: to have low cost, stability, reproducibility, and be easy to manufacture.…”