Elsevier

Polyhedron

Volume 223, 1 September 2022, 115959
Polyhedron

Novel Zn-dppy based receptor for selective sensing of pyrophosphate anion in aqueous acetonitrile medium

https://doi.org/10.1016/j.poly.2022.115959Get rights and content

Abstract

A new zinc(II) complex (ZnCl2L) of 4-N,N-dimethylaminophenyl substituted 2,6-dipyrazinylpyridine (dppy) ligand L was synthesized and used as a probe for selective sensing of pyrophosphate anion (P2O74-, PPi) in the presence of other anions in aqueous acetonitrile (1:1 v/v) solution (buffered with 10 mM HEPES). The sensing study was visualized through colorimetric method and measurements were done using UV–Visible spectroscopy. Further, the results were also investigated by DFT calculations in order to provide an explanation to the selectivity of the Zn-dppy hybrid receptor for PPi.

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A new zinc (II) complex (ZnCl2L.) of 4-N,N-dimethylaminophenyl substituted 2,6-dipyrazinylpyridine (dppy) ligand L is reported for selective sensing of pyrophosphate anion (P2O74-, PPi) in aqueous acetonitrile (1:1 v/v) solution (buffered with 10 mM HEPES). The colorimetric study and UV-Visible spectroscopy study showed that the zinc (II) complex selectively detects PPi over other anions. DFT calculations indicate that high exergonic reaction process as well as formation of a six-membered chelate ring between the Zn-dppy hybrid receptor and PPi enable the receptor to sense PPi with high selectivity.

Introduction

In recent years, a substantial amount of interest has been invested in recognizing the biologically essential anions such as pyrophosphate (PPi, P2O74-), as it has emerged as a potential biomarker for various disease monitoring processes as well as physiological functions.[1], [2], [3], [4] PPi is involved in various biochemical and metabolic processes, including cellular ATP hydrolysis, enzymatic reactions, cellular metabolism, DNA and RNA polymerization, cell metabolic/apoptosis, etc.[5], [6], [7], [8], [9] Abnormal concentration of PPi may result in various diseases, viz, elevated levels of PPi may cause arthritis, cartilage breakage, calcium pyrophosphate deposition disease (CPPD), chondrocalcinosis, muscle weakness, pseudogout, vascular calcification, etc. whereas its deficiency may result in arteriosclerosis.[10], [11], [12], [13], [14], [15], [16] PPi concentration can be used for real-time monitoring of DNA sequencing, telomerase elongation process during diagnosis of early-stage cancer.[2], [3], [12], [17], [18], [19] Hence, measuring an abnormal PPi concentration can be utilized as a potential biomarker for early-stage diagnosis of arthritis, cancer, chondrocalcinosis, CPPD, infectious disease, pseudogout, urolithiasis, etc.[1], [2], [20], [21], [22], [23], [24] Considering its importance in the field of diagnosis and medical applications, [17] various analytical methods were employed for the sensing of PPi among which spectroscopic and colorimetric techniques served the purpose best due to their fast detection, low cost, high efficiency, selectivity, sensitivity, and simple operations.[25], [26], [27], [28], [29]

The nitrogen-based heterocyclic ligands and their transition metal complexes have fascinating photophysical and electrochemical properties and can be employed in various anion sensing, amino acid sensing, halogen bonding, hydrogelation, etc.[18], [30], [31], [32], [33], [34], [35] Several zinc based receptor of terpyridine (tpy), bis(2-pyridylmethyl)amine (DPA), amide functionalized macrocycles have been reported for sensing of PPi; [17], [18], [36], [37], [38] however, strong hydration nature of the anion and low solubility of the organic receptor inhibited the sensing of the same in an aqueous medium to some extent which could be overcome by utilizing metal ion displacement approach.[4], [39], [40], [41] Pyrazine and its derivatives are less basic and have low toxicity which enabled them to be incorporated in designing novel biologically active molecules, and hence, can be used as potential drugs for a wide range of diseases since pyrazine derivatives show potential physiological activities including antibacterials, antidepressants, antifungals, antioxidants, antitumor, etc.[42], [43], [44], [45], [46].

Considering the potential physiological activities of pyrazine derivatives, herein we report a simple zinc(II) complex ZnCl2L of 4-N,N-dimethylaminophenyl substituted 2,6-dipyrazinylpyridine (dppy) ligand L, which selectively detects PPi anion in an aqueous acetonitrile (1:1 v/v) solution (buffered with 10 mM HEPES) at micromolar level, having excellent selectivity over other anions, such as F-, I -, AcO-, SO42-, Cl-, HCO3, CO32–, HPO42-, Br-, SO32-, NO3. To the best of our knowledge, this is the first time a substituted 2,6-dipyrazinylpyridine (dppy) receptor is reported for sensing of PPi anion. The sensing study was performed by UV–Visible spectroscopy and is well supported by naked eye colorimetric detection. Further, we have also performed a DFT study in order to evaluate the energy associated to the displacement of the ligand L by the anion PPi in ZnCl2L complex and provide an explanation for the selectivity of the receptor to PPi.

Section snippets

Experimental section

Materials and Methods: All the chemicals used were of analytical grade reagents, purchased commercially and used without further purification. The ligand L was synthesized according to literature method.[47] 1H NMR spectra were recorded on a 400 MHz Bruker NMR spectrometer. Chemical shifts were expressed in ppm. UV–Visible absorption spectra were recorded on a Mortas Scientific UV plus MSGUI3.1.0 absorption spectrophotometer. Mass spectra were measured on maXis impact q-TOF mass spectrometer.

Results and discussion

The ligand L was synthesized according to the literature method by reacting 2-acetylpyrazine with 4-N,N-dimethylaminobenzaldehyde in methanol in the presence of KOH and conc. NH3 [47]. The receptor zinc(II) complex ZnCl2L was synthesized by stirring an equimolar reaction mixture of L (in dichloromethane) and ZnCl2 (in methanol) at room temperature for 2 h. The synthesis of ZnCl2L is given in Scheme 1, while 1H NMR data given in the experimental section. The 1H NMR spectra of L and ZnCl2L are

DFT study

Scheme 2 shows the equations to evaluate the energies involved in the process of displacement of ligand L in the receptor complex for monoatomic (halides) and polyatomic anions. It should be mentioned that two equivalents of halide ions are needed for the substitution reaction, although only one equivalent of anion was used in the experiments.

Table 1 summarizes the energetic results (obtained using the reactions shown in Scheme 2) associated to the dissociation of the metal complex upon

Conclusions

In conclusion, we have synthesized a simple Zn-dppy complex for selective sensing of PPi anion in an aqueous acetonitrile HEPES buffer solution. The receptor selectively detects PPi anion in the presence of other anions with LOD and LOQ values 4.29 µM and 13 µM, respectively. The above results are well supported by DFT study which shows that the substitution of L by PPi in the Zn-dppy complex is largely exergonic. The reason is that PPi is the only anion that is able to form a six-membered

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

Authors DD, PS and SS would like to thank NIT Silchar for Institute Fellowship. This research was funded by MICIU/AEI of Spain (project PID2020-115637GB-I00 FEDER funds).

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      Considering the importance of PPi recognition, several methods such as capillary electrophoresis, mass spectrometry, spectroscopic techniques, colorimetry, enzymatic analysis, and others were used, with colorimetric and spectroscopic techniques emerging as the most advantageous due to in-vivo and in-vitro imaging facilities, cost-effectiveness, high efficiency, and sensitivity, etc [14–20]. Several transition metal complexes of nitrogen ligands such as terpyridine, dipyrizinylpyridine, amide functionalized macrocycles, etc. as receptors were also reported for PPi detection [7,18,21–30]. Terpyridines and their transition metal complexes have considerable attention among nitrogen-based ligands for their remarkable electrochemical and photophysical properties.

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