Synthesis of Upper-Rim Sulfanylpropyl- and p- Methoxyphenylazo-Substituted Calix[4]arenes as Chromogenic Sensors for Hg2+ and Ag+ Ions

Jia-De Lian; Hsin-Yu Hu; Yi-Han Lin; Putikam Raghunath; Ming-Chang Lin; Wen-Sheng Chung

doi:10.1021/acs.joc.3c00943

Synthesis of Upper-Rim Sulfanylpropyl- and p- Methoxyphenylazo-Substituted Calix[4]arenes as Chromogenic Sensors for Hg²⁺ and Ag⁺ Ions

J Org Chem. 2023 Oct 20;88(20):14292-14302. doi: 10.1021/acs.joc.3c00943. Epub 2023 Sep 28.

Authors

Jia-De Lian¹, Hsin-Yu Hu², Yi-Han Lin², Putikam Raghunath³, Ming-Chang Lin³, Wen-Sheng Chung^{1

2}

Affiliations

¹ Department of Applied Chemistry, National Chiao Tung University, Hsinchu 30050, Taiwan.
² Department of Applied Chemistry, National Yang Ming Chiao Tung University, Hsinchu 30050, Taiwan.
³ Center for Interdisciplinary Molecular Science, Department of Applied Chemistry, National Yang Ming Chiao Tung University, Hsinchu 30050, Taiwan.

PMID: 37768859
DOI: 10.1021/acs.joc.3c00943

Abstract

A series of calix[4]arenes with upper-rim sulfanylpropyl and p-methoxyphenylazo groups (compounds 8-10) were synthesized and found to be effective chromogenic sensors for selectively detecting Hg²⁺, Hg⁺, and Ag⁺ ions among 18 screened metal perchlorates. In comparison to previously reported diallyl- and dithioacetoxypropyl-substituted calix[4]arenes (5, 6, 14, 15, and 16) and the newly synthesized compound 7, the distal (5,17)-disulfanylpropyl-substituted di-p-methoxyphenylazocalix[4]arene 9 demonstrated superior performance with a limit of detection of 0.028 μM for Hg²⁺ ions in a chloroform/methanol (v/v = 399/1) cosolvent. Job's plot revealed 1:1 binding stoichiometry for all these upper-rim sulfanylpropyl- and p-methoxyphenylazo-substituted calix[4]arenes 8-10 with Hg²⁺ ions, and Benesi-Hildebrand plots from ultraviolet/visible (UV-vis) titration spectra were used for the determination of their association constants. Our findings indicated that the distal orientation of two p-methoxyphenylazo and two sulfanylpropyl groups in calix[4]arenes 8-10 is more favorable for binding Hg²⁺ ions than the proximal (5,11-) orientation; moreover, the adjacent sulfanylpropyl groups exhibited superior coordination as ligands compared to the allyl and thioacetoxypropyl groups. Notably, compounds 8-10 displayed a comparable trend in their association with Ag⁺ ions, albeit with 1 order of magnitude lower binding constants and a distinct binding mode compared to Hg²⁺ ions. UV-vis spectroscopy, Job's plots, high-resolution mass spectrometry, and ¹H nuclear magnetic resonance titration studies are presented and discussed.