Development of a selective fluorescence derivatization strategy for thyroid hormones based on the Sonogashira coupling reaction.

A new fluorescence derivatization technique for the determination of the thyroid hormones, 3,3',5-triiodo-L-thyronine (T3, triiodothyronine) and 3,3',5,5'-tetraiodo-L-thyronine (T4, L-thyroxine), in human serum was developed based on the Sonogashira coupling reaction. This derivatization reaction was recently utilized by our research group as a promising solution for the derivatization of ortho-substituted aryl halides that suffer from steric hindrance. T3 and T4 possess amino groups that could be derivatized by many reagents; however, these reagents are not useful in the case of biological analysis as they could non-selectively react with many biogenic amines and amino acids. Thus, herein we aimed at labeling the iodo-phenyl group of T3 and T4 as a selective fluorescence labeling approach suitable for biological analysis. The fluorescent alkyne, 2-(4-ethynylphenyl)-4,5-diphenyl-1H-imidazole (DIB-ET), can label the ortho-substituted aryl halides T3 and T4 in the presence of palladium and copper as catalysts, overcoming the steric hindrance of ortho-substitution. Furthermore, the application of the proposed method for the selective analysis of T3 and T4 in biological samples was successfully performed even in the presence of numerous biological components. The formed fluorescent derivatives produced from the reaction of DIB-ET and T3 and T4 could be determined by an HPLC system with fluorescence detection. The proposed method was successfully applied for the selective and sensitive determination of T3 and T4 in human serum with detection limits (S/N = 3) of 4.0 and 6.1 ng/mL and the recovery rate in the ranges of 84.3-92.1% and 81.3-84.9%, respectively. Therefore, the proposed method could be used as a new simple tool for the simultaneous determination of T3 and T4 in biological samples.

A new chemosensor for cyanide in blood based on the Pd complex of 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]phenol.

A new indirect chemosensor for the detection of cyanide in blood is developed. 2-(5-Bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]phenol, a yellow dye, forms a blue-coloured complex with palladium ions. The yellow colour of this complex is regained upon reaction with cyanide ions. The complex shows high selectivity for the detection of cyanide over 16 other anions. The system was applied to two different methods for the detection of cyanide in human whole blood. As a quantitative absorbance method, blood samples were mixed with acid, and the resulting vaporised hydrogen cyanide was absorbed in an alkaline solution containing the complex in a Conway cell. The resulting absorbance response of the solution at 450 nm is linear over the range 4-40 µM (R2 = 1.000), and the limit of detection is 0.6 µM. Furthermore, the complex-soaked paper is applicable as a test strip for cyanide detection. When a test strip is used with 0.5 mL of blood, the limit of detection is 15 µM. The detection limits of these two methods are below the toxic blood cyanide concentration (19 µM). Therefore, both methods allow the quantification and screening of cyanide in blood samples. Furthermore, the test strip is low cost and enables on-site analysis.

The Utility of Sonogashira Coupling Reaction for the Derivatization of Aryl Halides with Fluorescent Alkyne.

Aryl halides are a very important category of compounds that include many vital drugs and key industrial additives, such as clofibrate and bromobenzene, respectively. Due to their importance, our research group previously developed a novel fluorescence labeling approach for their analysis using a fluorescent aryl boronic acid as a reagent, based on the Suzuki coupling reaction. This coupling reaction was successfully applied for the determination of aryl halides in biological fluids; however, there was a limitation of low reactivity towards ortho-substituted aryl halides. In the present study, a novel fluorescence derivatization approach for aryl halides was developed using, 2-(4-ethynylphenyl)-4,5-diphenyl-1H-imidazole (DIB-ET) as a fluorescent alkyne reagent, based on the Sonogashira coupling reaction. DIB-ET reacted with aryl bromides in the presence of palladium and copper as catalysts, yielding fluorescent derivatives that could be subsequently determined by an HPLC system with fluorescence detection. The detection limits (S/N = 3) for aryl bromides were in the range of 14 - 23 nM, which is 3.5 - 18-times more sensitive than our previously developed approach, Suzuki coupling derivatization. Moreover, in contrast to the previous technique, the reactivity of DIB-ET to ortho-substituted aryl bromides was almost equivalent to that of the para-substituted aryl bromides. Hence, by using this newly developed approach we could label the aryl halides with more sensitivity and reactivity. Finally, the proposed method was successfully applied for the selective determination of aryl bromides in human serum with good recovery (84.6 - 107%), which proves the ability of the developed method to determine occupational exposure to aryl halides.