Tuning the recognition properties of urea based receptor towards cyanide in aqueous medium: Effect of fluorine substitution on strength and selectivity of the anion receptor

Vanthana Jeyasingh; Kumaresan Murugesan; Sudha Lakshminarayanan; Selvapalam Narayanan; Lakshminarayanan Piramuthu; I V Muthu Vijayan Enoch; Mosae Selvakumar Paulraj

doi:10.1016/j.saa.2019.02.084

Tuning the recognition properties of urea based receptor towards cyanide in aqueous medium: Effect of fluorine substitution on strength and selectivity of the anion receptor

Spectrochim Acta A Mol Biomol Spectrosc. 2019 May 15:215:233-243. doi: 10.1016/j.saa.2019.02.084. Epub 2019 Feb 21.

Authors

Vanthana Jeyasingh¹, Kumaresan Murugesan¹, Sudha Lakshminarayanan², Selvapalam Narayanan¹, Lakshminarayanan Piramuthu³, I V Muthu Vijayan Enoch⁴, Mosae Selvakumar Paulraj⁴

Affiliations

¹ International Research Centre, Centre for Supramoleular Chemistry, Department of Chemistry, Kalasalingam University (KARE), Anand Nagar, Krishnankoil, Srivilliputtur, Tamil Nadu 626 126, India.
² International Research Centre, Centre for Supramoleular Chemistry, Department of Chemistry, Kalasalingam University (KARE), Anand Nagar, Krishnankoil, Srivilliputtur, Tamil Nadu 626 126, India; Department of Chemistry, J.P. College of Arts & Science, Agarakattu, Ayikudi, Tamil Nadu 627852, India.
³ International Research Centre, Centre for Supramoleular Chemistry, Department of Chemistry, Kalasalingam University (KARE), Anand Nagar, Krishnankoil, Srivilliputtur, Tamil Nadu 626 126, India. Electronic address: p.lakshminarayanan@klu.ac.in.
⁴ Department of Chemistry, Karunya University, Karunya Nagar, Coimbatore, Tamil Nadu 641114, India.

PMID: 30826582
DOI: 10.1016/j.saa.2019.02.084

Abstract

In this report, we have successfully tuned the selectivity and sensitivity of an anion receptor L¹ by substituting electron withdrawing natured fluorine atoms directly on to the rim of the phenyl ring. Despite the fact that, we have two electron withdrawing natured nitro substituents on the other side of receptor L¹; two fluorine substitutions made dramatic change in the sensing ability as well as the selectivity of the receptor L¹ towards anions. The acetonitrile solution contains L¹ with tetrabutyl ammonium salts of fluoride, cyanide, acetate and dihydrogen phosphate results sudden color changes from yellow to brown; almost negligible spectral/color change for azide and bifluoride, where as there is no color change observed with any other anionic guests with L¹. Solution state binding studies of L¹ are carried out by UV-Vis spectrometry titration in 100% acetonitrile and it is found to be the receptor L¹ selectively binds cyanide, phosphate and fluoride stronger than acetate; it is also found that receptor binds fluoride 100 times stronger than that of the receptor L and L¹ has almost similar efficiency in binding towards acetate ion (AcO^-). The strength of the receptor L¹ towards fluoride, cyanide, acetate and dihydrogen phosphate bindings are found to be in the order of 1.271 × 10⁵ M^-1 > 1.245 × 10⁵ M^-1 > 1.368 × 10³ M^-1, 1.23 × 10³ M^-1 respectively. When we used aqueous environment (10% of water in acetonitrile) as testing solvent system, the receptor L¹ selectively sense cyanide ion. Over all, strength of the receptor is increased towards anions with an increasing the number of fluorine atom onto the receptors. Here in we have also prepared a reference compound L² in which the receptor molecule is substituted with only one fluoride atom. The acetonitrile solution of reference receptor L² with help of naked-eye colorimetric experiment and spectrometric ammonium salts of fluoride, cyanide, acetate and bifluoride results sudden color changes from faint-yellow to brown in color. Unlike receptor L¹, receptor L² does not recognize H₂PO₄^-, but instead of H₂PO₄^-, it recognizes bifluoride as evidenced from UV-Vis spectroscopic and naked-eye colorimetric studies.

Keywords: Anion recognition; Colorimetric sensors; Fluorine chemistry; Urea receptors.