Zn(II)-dicarboxylato-terpyridyl coordination polymer - A ‘Turn on’ fluorogenic platform for Al3+ sensing in aqueous medium and life cell imaging

https://doi.org/10.1016/j.molstruc.2022.134559Get rights and content

Highlights

  • Dicarboxylato bridged Zn(II) Coordination Polymer chelated with 4′-Chloro-2,2′:6′,2′′-terpyridine is characterised.

  • Noncovalent interactions (Cl—Cl, C-H—π, π⋅⋅⋅π) make 3D superstructure

  • Upon binding with Al3+ the fluorescence enhancement of the CP is recorded.

  • LOD (0.2 µM) is far below the EPA recommended data (7.4 µM) and method is used in real water sample analysis.

  • Intracellular Al3+ is determined in MDA-MB 231 cells by adding CP using Fluorescence imaging microscope.

Abstract

Recently, coordination polymers (CPs/MOFs) have emerged as a desirable hybrid material for sensing analytes- such as ions, amino acids, nitroexplosives due to their versatility, stability, reusability, economic benefits and sustainability. Herein, [Zn(bdc)(4-Cltpy)(H2O)]n (CP) [4-Cltpy = 4′-Chloro-2,2′:6′,2′′-terpyridine, H2bdc = Benzene-1,4-dicarboxylic acid], a coordination polymer, is structurally characterized. The structure reveals that the bdc2− bridges Zn(II) via dicarboxylato-O and propagates to form a 1D Coordination Polymer. The 1D CP further undergoes Cl⋯Cl interaction to form a 2D sheet and H-bonding and π⋅⋅⋅π interactions help to construct a 3D supramolecular architecture. Photoluminescence study exposes that the CP is weakly emissive while the fluorescence intensity is significantly enhanced upon interaction with Al3+ in aqueous medium even in presence of quenchable ions like Fe3+ and Cr3+. The detection limit (LOD) is 0.2 ± 0.005 µM (3σ/M method) which is much lower than the permissible limit in drinking water recommended by U.S. Environmental Protection Agency (0.2 mg/L or 7.4 µM). The toxicity of CP has been checked by MTT Assay and intracellular imaging of Al3+ is vivid in human breast cancer MDA-MB 231 cells. The reagent is used for real water sample analysis by fluorescence spectroscopic technique.

Graphical abstract

[Zn(bdc)(4-Cltpy)(H2O)]n (CP) [4-Cltpy = 4′-Chloro-2,2′:6′,2′′-terpyridine, H2bdc = Benzene-1,4-dicarboxylic acid] forms a 3D superstructure through coordination and noncovalent interactions. The coordination polymer shows turn-on fluorescence sensing to Al3+ out of 17 ions in aqueous medium with a detection limit (LOD), 0.2 µM. The CP is nontoxic to 100 µg and helps intracellular imaging of Al3+ in MDA-MB 231 cells.

Image, graphical abstract
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Introduction

Sensors have many applications in health monitoring, environmental sustainability, food quality control etc. Water quality measurement is one of the important applications of sensing technology for WQI (Water Quality Index) [1]. Recently, Al (Aluminium) toxicity in food, drinks, and beverages is in focus because of the neurodegenerative symptoms [2]. Presumably excess of Al3+ in cells causes Alzheimer's disease, Parkinson's syndrome [3,4], etc. World Health Organization or WHO recommends the permissible limit of daily Al uptake is 0-0.6 mg/kg (kg depicts the person's weight) and 7.41 µM in drinking water [5]. Design of molecular sensor for Al3+ is recently focused [6]. In this regard, use of coordination polymers (CPs) or Metal-Organic Frameworks (MOFs) for selective sensing of environmentally/biologically important ions/molecules has taken a real challenge [7], [8], [9]. The CPs has been formed with the combination of metal nodes and organic/inorganic linkers. The CPs, a class of hybrid multifunctional crystalline materials of fascinating structural architectures and topologies, have been widely explored due to their unique properties and diverse potential applications like - gas storage and separation [10], [11], [12], catalysis-[13], [14], chemical sensor [15], [16], [17], magnetism [18], drug delivery [19], biological activity [20,21] and electrical conductivity [22], [23], [24], [25] etc. In recent literature, there has been a significant development in using CPs as fluorescence sensors to recognize molecules/cations [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], anions [37], [38], [39], [40], [41], [42], [43], [44], [45], [46] etc. The luminescent CPs can detect analytes by either quenching of luminescence or turn-off, enhancement of luminescence or turn-on or fluorescence shift [47].

Herein, we have structurally characterized, [Zn(bdc)(4-Cltpy)(H2O)]n (CP) (4-Cltpy = 4-chloroterpyridine; H2bdc = 1,4-Benzene-dicarboxylic acid) in which dicarboxylato serves as linker agent to constitute 1D CP and turned to be 3D supramolecular structure by Cl—Cl, C-H—π and π—π interactions. 4-Cltpy acts as N, N, N-chelating agent to block propagation while extended conjugation may help to bring optical sensitivity to the material. Thus, it can be useful as chemosensor. Keeping this on mind, fluorescence activity has been explored which shows that the CP is weakly emissive, but fluorescence emission is considerably enhanced by selective addition of Al3+ ion in aqueous medium among other metal ions. This indicates that the CP seems to be a highly selective and sensitive “turn-on” fluorescence sensor for detection of Al3+ ion. Further, this CP is also biologically active and its in-vitro cell cytotoxicity assay (MTT assay) appears that the CP is nontoxic even at 100 µg and intracellular fluorescence imaging of Al3+ is vivid in MDA-MB 231 cells (human breast cancer). It is believed that the cells readily uptake the CP and can detect Al3+ within the biological medium. Hence, CP is biocompatible and favourable for biological application.

Section snippets

Materials and physical measurements

All the chemicals used during synthesis of the CP are of reagent grade from different commercial resources. Zn(NO3)2.6H2O purchased from TCI, 1,4-benzene dicarboxylic acid (H2bdc) and 4′-chloro-2, 2′: 6′, 2′′-terpyridine (4-Cltpy) from Sigma-Aldrich and used without further purification. Apart from these chemicals all the organic and inorganic materials used in the experiment had been purchased from Merck. Millipore or Milli Q water used for preparation of aqueous solution throughout the

Structural description of CP

The X-ray crystal structure determination of CP reveals that the compound crystalizes in monoclinic crystal system having 'C2/c' space group and Z = 4. The asymmetric unit contains one Zn (II) cation coordinated with three N atoms of 4-Cltpy in a tridentate chelating fashion and two carboxylate-O of the bdc2− moiety in monodentate linking following a distorted square pyramidal ZnN3O2 coordination motif. The five coordinated environment around the metal is fulfilled by two carboxylate-O atoms

Conclusion

Carboxylato Zn(II) Coordination Polymer, [Zn(bdc)(4-Cltpy)(H2O)]n, is characterized by X-ray structure determination ([H2bdc = Benzene-1,4-dicarboxylic acid; 4-Cltpy = 4′-Chloro-2,2′:6′,2′′-terpyridine]. The bridging of bdc2− to Zn(II) makes 1D coordination polymer which undergoes noncovalent interactions like- Cl—Cl, C-H—π, π⋯π stacking to construct a 3D supramolecular structure. The emissivity of CP is enhanced on selective binding with Al3+ out of other seventeen ions in aqueous medium with

Author Contributions

All of the authors contributed equally.

CRediT authorship contribution statement

Angeera Chandra: Data curation, Methodology, Formal analysis, Writing – original draft. Satyajit Halder: Data curation, Formal analysis, Writing – original draft. Suprava Bhunia: Data curation. Sukanya Pal: Formal analysis. Kuladip Jana: Investigation, Writing – review & editing, Resources, Supervision. Chittaranjan Sinha: Conceptualization, Formal analysis, Writing – review & editing, Funding acquisition, Project administration, Resources, Supervision, Visualization.

Declaration of Competing Interest

The authors declare no competing financial interest.

Acknowledgments

A. C. is thankful to Jadavpur University for providing lab and all infrastructural facilities; S. P is thankful to CSIR and S. B. is thankful to UGC (Award Number. 127894); C. S. is thankful to UGC-CAS-II and RUSA 2.0. A special thanks to Dr. Basudeb Dutta for his selfless help.

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