Synthesis of Polynorbornene Based Molecular Self-Assembly for the Detection of Copper Ions Present in the Environmental Water Samples

Introduction

Nature organized itself with a wide variety of molecular architecture with different types of nanostructural self-assembly which includes DNA double helix, tubulin assembly lipid build blocks, etc. Molecular self-assembly is a highly efficient process that involves non-covalent interactions such as hydrogen bonding, hydrophobic forces, π-stacking interactions, van der Waals forces, metal coordination, and electrostatic interactions. These forces help in transforming a disordered system into an ordered one, with well-organized shapes, sizes, and dimensions ¹. Molecular self-assembly   assists   in   the spontaneous   association   of   the macromolecules to adopt dynamic supramolecular assemblies such as nanofibers, nanoparticles, and nanotubes. By connecting the unique properties of host-guest with molecular self-assembly, it is possible to unlock new frontiers in optoelectronics, sensing, and catalysis. This simple and efficient approach offers tremendous potential for advancing cutting-edge technologies and solving complex scientific challenges. In this article, it is proposed to make a polymer-based metal-assisted molecular self-assembly. Its sensing properties have enough potential for real-life application in the sensing area^2-5. Heavy metals, particularly copper (II) ions, are crucial for the metabolism of living organisms⁶. Copper (II) ions serve as a cofactor for cuproenzymes and help regulate various metabolic processes in our bodies, including neuro-signal transduction and gene expression⁷. This highlights the importance of copper (II) ions in maintaining optimal physiological functions. Excessive intake of copper can be extremely harmful to our health as it is highly toxic and can result in various health complications such as liver function abnormalities, liver cirrhosis, or Wilson’s disease. Industries that use copper without proper regulation can lead to contamination of environmental water, and it can ultimately enter our bodies through the food chain⁸. Therefore, it is important to detect and monitor Cu²⁺ ions in water or other aqueous solutions to ensure environmental safety and promote good health. Numerous methods have been reported in the scientific literature for detecting and monitoring the presence of copper (II) ions in water. Most of these methods involve electromagnetic or mass spectroscopy techniques such as ICP-MS, ICP-OES, atomic absorption spectrometry, laser-induced breakdown spectroscopy, voltammetric techniques, and atomic emission spectrometry ⁹. However, the major drawback of these techniques is that they require expensive equipment and difficult sample preparation procedures, which makes them less widely available and restricts their application for detection of copper. On the other hand, colorimetric sensors derived from polymers are in high demand due to their unique self-assembly based on host-guest interaction ^10-11. They are also very economical and easily accessible for detecting copper ions. Our present work represents a new sensor for the detection of copper ions from environmental samples. A fluorescein-derived norbornene-based monomer, Nor-Flu, and its polymer, PNor-Flu, are introduced in this article. These compounds demonstrate exceptional selectivity and sensitivity for copper ions detection. With this new work, it is possible to detect copper ions with greater accuracy and efficiency, making it a highly valuable tool for environmental monitoring and analysis. It was previously reported that copper has a higher affinity to make coordination bonds with the electronegative nitrogen atom of the imine bond and oxygen atom of the hydroxyl group which presents very adjacently to make a stable complex along with color change of the solution in the presence of the copper due to the formation of the highly stable ligand to metal charge transfer complex. It was confirmed that both the monomer (Nor-Flu) and the polymer (PNor-Flu) exhibited excellent LOD which is quite below the limit stated by US-EPA. Also in the case of the polymer due to the presence of amphiphilicity within the polymeric macromolecules, it is showing interesting host-guest molecular self-assembly in the presence and the absence of the copper ions with unique molecular architecture.

Materials and Methods

Chemicals

Organic chemicals such as cis-5-norbornene-exo-2,3-dicarboxylic anhydride, 4-aminophenol, Acetic acid, Hexamethelene diamine (HMTA), Trifluoroacetic acid, Fluorescein, Hydrazine hydride, Ethanol, Grubb’s 2nd generation Grubbs catalyst, Ethyl vinyl ether, Dimethyl sulfoxide (DMSO), Dichloromethane (DCM), Diethyl ether (Et₂O), CDCl₃, DMSO-d₆, Sodium Hypochlorite, Hydrogen peroxide, and Tertiary butyl hydroperoxide are bought from from Sigma Aldrich, Spectrochem, and Combiblocks.  The stock analyte solutions of CuSO₄, MgCl₂, FeSO₄, K₂CO₃, PbNO₃, AgNO₃, NiCl₂, CdSO₄, CaSO₄, and AlCl₃ were prepared by using analar chermicals.

Analysis

NMR characterizations were performed on a Bruker 500 MHz instrument for both ¹³C and ¹H NMR and  ¹³C NMR spectroscopic techniques, employing DMSO-D₆ and CDCl₃ as the NMR solvents. Throughout the experiments, Tetramethylsilane (TMS) served as the internal standard for calibration. Acquity Advanced Polymer Chromatography (APC) was used to get thhe molecular weight of the polymer with Omnisec Reveal detector, employing refractive index (RI), light scattering (RALS 90°, LALS 7° angle), and a viscometer for detection.

UV-visible absorption studies were performed using a Perkin-Elmer Lambda35 UV-Vis spectrometer, with a scan rate of 480 nm/min. Each absorption spectrum was measured individually in a 1 cm quartz cell for every solution. Sample preparation for UV-Vis studies were done with utmost care. All stock solutions of Nor-Flu and PNor-Flu were initially prepared in DMSO and later diluted with water for various experiments. Metal solutions were exclusively prepared in water. UV-Vis spectroscopy involved maintaining fixed concentrations of Nor-Flu (μM) and PNor-Flu (μM). Spectroscopic titrations were conducted by introducing fixed concentrations of Nor-Flu solution to successive increasing concentrations of Cu²⁺ ions. Real samples were consistently prepared using water as the solvent. Scanning electron microscope (SEM) was employed the high-performance variable pressure FE-SEM (Zeiss SUPRA 55VP-Field Emission Scanning Electron Microscope) to determine the size of the nano-aggregates. This FESEM utilizes patented GEMINI column technology and a Schottky type field emitter system, with a single condenser featuring a crossover-free beam path. In high vacuum mode, the resolution is 1.0 nm at 15 kV and 1.6 nm at 1 kV, while in variable pressure mode, it is 2.0 nm at 30 kV.

Synthesis

Though synthesis of polynorbornene (PNor-Flu) is not main objective of the research article, the synthetic methodology is shown in Scheme-1. The equential procedures of synthesis of polynorbornene is done using simple organic compounds available in the Indian market. Synthesis of the compounds 1-3, Nor-Flu and PNor-Flu involves synthetic procedures as detailed below. Synthesis of Compound-1 was synthesized first from analar chemicals. Cis-5-Norbornene-exo-2,3-dicarboxylic anhydride (1 g, 0.006 mol) was taken in a 100 mL roundbottom flask followed by the addition of glacial acetic acid. The mixture was stirred for 15 minutes. To the mixture 4-aminophenol (0.665 g, 0.006 mol) was added and refluxed at 110 ºC for 24 hours. After completion of the reaction, the mixture was cooled to room temperature. The formed precipitate was filtered and recrystallized from ethanol to obtain Compound 1 as brown solid (1.2 g, 77%). Synthesis of Compound-2 was synthesized from Compound-1. First Compound-1 (1 g, 0.004 mol) was taken in a 250 mL round-bottom flask and 50 mL of TFA added to it. After complete solubility of Compound-1, HMTA (660 mg, 0.0048 mol) was added to the reaction mixture and kept in refluxing condition for 24 hours. After completion of the reaction, the mixture was cooled to room temperature. The cooled reaction mixture was transferred to a 250 mL separating funnel with DCM and extracted with 2(N) HCl solution, water, and brine. Then combined DCM layer was dried over anhydrous sodium sulfate and the solvent was removed under reduced pressure to obtain the crude product. Flash column chromatography was carried out t:o obtain Compound 2 as a white powder (700 mg. 64%). Synthesis of Compund-3 was synthesized from Compound-2. First Compound-2 (500 mg, 0.0018 mol) was dissolved in DMF and K₂CO₃ (300 mg, 0.0022 mol) was added to it. The reaction mixture was stirred for 5 minutes followed by the addition of ethyl iodide (280mg, 0.0018 mol). The overall mixture was stirred for 24 hours at room temperature and the progress of the reaction was monitored using TLC. After completion of the reaction, the mixture was poured into ice-cold water. A white-colored precipitate was observed, which was filtered and washed with cold water to remove unreacted compounds. After drying, Compound-3 was obtained as a white-colored powder (490 mg, 90%). Compounds 1-3  were characterized using ¹H-NMR and ¹³C-NMR spectral techniques ^12-17.

Scheme 1: (A) Synthetic scheme for Nor-Flu (B) Synthetic scheme for PNor-Flu. Click here to View Scheme

Synthesis of monomer Nor-Flu was obtained from Compounds-2&3. In a 100 mL round-bottom flask, 732 mg (2.116 mmol) of Compound-3 was dissolved in 5 mL of ethanol with the assistance of a stirring magnetic bar. Following this, 600 mg (2.116 mmol) of Compound-2 was introduced into the flask, accompanied by the addition of 5 drops of acetic acid, and the mixture was refluxed for 18 hours. After the reaction concluded, the reaction mixture was concentrated and poured into a beaker containing cold water, resulting in the formation of a white precipitate. This precipitate was subsequently filtered and subjected to multiple washes with water. Finally, the precipitate was dried to obtain the absolutely pure product as a white solid, yielding 486 mg (81%). Synthesis of polymer PNor-Flu was accomplished from Nor-Flu. It involves a ring-opening polymerization. Nor-Flu (0.0816 mmol, 1 eq.) was placed in a dried 10 mL polymerization vial under a complete nitrogen atmosphere and dissolved in 1 mL of dry DCM. Subsequently, a catalytic amount of Grubbs second-generation catalyst (0.01 eq.) was added by dissolving 200 μL of dry DCM solution, and the reaction mixture was stirred at a specified temperature for 7 hours under a nitrogen atmosphere. The polymerization reaction was then quenched using ethyl vinyl ether. The resulting reaction mixture was precipitated in diethyl ether to obtain a white solid random copolymer. Confirmation of polymerization was achieved through ¹H NMR spectroscopy.  Additionally, confirmation was obtained from Advanced Permeation Chromatography to get number average molecular weight and polydispersity index ^12-17.

Results and Discussion

Photophysical studies of Nor-Flu

After successfully synthesizing Nor-Flu and PNor-Flu, it is the examination of its photophysical properties of the sensor application. It is anticipated that the sensor molecule would form a stable complex in the solution in the presence of copper ions, resulting in colourimetric responses. To achieve this, UV-Vis spectroscopic studies of Nor-Flu in the presence and absence of copper (II) ions was performed. Initially, optimization of the solvent system by varying nonpolar to polar and protic to aprotic solvents was done.

Figure 1: (A) Time-dependent study of the Nor-Flu (100 µM) in the presence of Copper (II) ions. (B) Selectivity study of the Nor-Flu (100 µM) in the presence of the different types of cations (100 µM) (C) Pictorial images of the Nor-Flu in the various metal ions in the naked eye. Click here to View Figure

The present observations revealed that Nor-Flu exhibited an excellent response only in the case of DMSO. The photophysical studies of Nor-Flu were conducted in DMSO. It was observed that in the absence of copper ions, Nor-Flu showed an absorption peak at a wavelength of 343 nm. However, in the presence of copper ions, Nor-Flu exhibited a new, red-shifted absorption peak at a wavelength of 417 nm, accompanied by a change in the color of the solution from colorless to yellow. To determine the full response time of the monomer, a time-dependent study was carried out. This study revealed that the absorption maxima at 417 nm reached saturation within one minute, indicating that the sensing of copper in the presence of Nor-Flu is instantaneous (Fig.1-A). To assess the selectivity properties of Nor-Flu, UV-Vis spectroscopic studies were performed in the presence of different types of metal ions. The results, shown in Fig.1-B and Fig.1-C, clearly indicated that Nor-Flu only responds in the presence of copper (II) ions, as evidenced by both UV-Vis spectroscopy and pictorial visualization. Having obtained positive results in the selectivity and time-dependent studies of Nor-Flu, it is quite essential to investigate its sensitive properties. UV-Vis spectroscopic titration of Nor-Flu with successive increases in the concentration of copper(II) ions from 0 µM to 80 µM was performed (Fig.2).

Figure 2: (A) UV-Vis spectroscopic titration of the Nor-Flu (100 µM) with increasing the concentration of the copper ions from 0 µM to 80 µM.  Click here to View Figure

A ratiometric titration curve was obtained, where the absorption maxima at 417 nm increased and the absorption maxima at 343 nm decreased with the addition of the copper(II) ions. It is observed that after adding 50 µM of copper(II) ions, the absorption intensity at 417 nm and 343 nm became saturated. To determine the lower limit of detection of copper, the calibration curve has been drawn in the lower concentration region (0 µM to 30 µM) and achieved an excellent linearity with R² value of 0.98087. From the calibration curve, the LOD value of 78 nM was obtained, which is well below the limit provided by the WHO for environmental water. Based on the obtained results, it was found that Nor-Flu can detect copper(II) ions instantly with excellent selectivity and sensitivity, with an LOD of 78 nM.

Determination of the binding constant and stoichiometry

The positive results in the case of selectivity, time-dependent study, and titration have motivated us to further investigate the photophysical properties of Nor-Flu, as shown in Fig.3. It is hypothesized that Nor-Flu forms a complex in the presence of copper(II) ions by creating a coordination bond with the nitrogen atom of the imine bond and the oxygen atom of the hydroxyl bond ^12-17. Additionally, ligand-to-metal charge transfer likely occurs during the formation of the complex, leading to the observed color change in the presence of copper(II) ions. The binding constant was determined from the UV-Vis titration to be approximately 2.47×10⁵, using the Benesi-Hildebrand equation. Furthermore, employing Job’s method, UV-Vis spectroscopy analysis was performed with increasing mole fraction of Nor-Flu and calculated a binding ratio of 1:2 for Nor-Flu and copper(II) ions.

Figure 3: (A) Binding constant of Nor-Flu with copper,  (B) Job’s plot of Nor-Flu. Click here to View Figure

Photophysical studies of PNor-Flu

After achieving excellent results in the photophysical studies of the monomer (Nor-Flu), It proceeded to investigate the photophysical properties of the polymer (PNor-Flu). Although Nor-Flu demonstrates exceptional photophysical properties for the selective and sensitive detection of copper(II) ions, its practical application is limited. Due to the lack of amphiphilicity, the challenge lies in producing films, paper strips, and unique self-assembly properties. To overcome this issue, synthesis was accomplished by ring-opening metathesis-based polynorbornenes for the selective and sensitive detection of copper(II) ions, as well as to study its host-guest self-assembly with copper(II) ions. Following the synthesis of the final polymer, the average molecular weight of PNor-Flu was determined using advanced polymer chromatography, which was found to be approximately 8000 Da with a PDI value of 1.10. To assess the photophysical properties of PNor-Flu,  UV-Vis spectroscopic study was conducted in the presence and absence of copper(II) ions (Fig.4). In the absence of copper(II) ions, PNorFlu exhibited an absorption peak at 350 nm in DMSO. Upon addition of copper(II) ions to the PNor-Flu solution in DMSO, the peak at 350 nm decreased, and a new red-shifted peak at 416 nm emerged, accompanied by a change in the color of the solution from colorless to yellow.

Figure 4: (A) UV-Vis titration of the PNor-Flu (100 µM) (100 µM) with increasing the concentration of the copper ions from 0 µM to 100 µM. Click here to View Figure

Furthermore, a time-dependent study was performed to determine the time required for the complete sensing of copper(II) ions by PNor-Flu. The sensing of copper(II) ions by PNor-Flu is instantaneous, as the peak OD₄₁₆/OD₃₅₀ reaches its maximum within one minute after the addition of the copper (II) ions. Afterwards, the LOD was determined. For that purpose, the concentration-dependent UV-Vis titration of the PNor-Flu was obtained with the increase of the concentration of Copper(II) ions from 0 µM to 100 µM. It was observed that with an increase of the copper(II) ions concentration, the absorption maxima at 416 nm increased and absorption maxima at 350 nm decreased which suggests that it was ratiometric titration pattern with the isobestic point of 370 nm. Also from the OD₄₁₆/OD₃₅₀ vs concentration of the PNor-Flu at a lower concentration range, the calibration curve was plotted with an excellent R² value of 0.99319 and from the 3σ/K equation, the LOD of 0.27 µM was obtained. So far the obtained result related to the PNor-Flu, it looks that like the Nor-Flu, PNor-Flu has a higher selectivity and the sensitivity of LOD value 0.27 µM for the detection of the copper(II) ions instantaneously within one minute. The lower LOD value suggests that PNor-Flu can be utilized as a sensor for the detection of copper ions in environmental contaminants.

Morphological analysis of the PNor-Flu in the presence of copper(II) ions

Metal-based molecular self-assembly is another important aspect of this work. The results obtained in the sensing study of the Nor-Flu and PNor-Flu clearly show that a definite self-assembly pattern will observed in the absence and the presence of the copper(II) ions. Along with that, a definite level of amphiphilicity is there in the polar solvent of PNor-Flu because of the presence of a large number of hydroxyl groups in the PNor-Flu. To check the morphological properties of the PNor-Flu, initially, the dynamic light scattering study of the PNor-Flu was done by increasing the concentration from 0.025 mg/ml to 0.05 mg/ml. It was observed that in between the concentration range from 0.03 mg/ml to 0.05 mg/ml the size of the PNor-Flu becomes fixed which is about to be 91 nm. Also, form the same DLS study was repeated with the addition of the copper ions. In this case, the hydrodynamic diameter of 100 nm with the concentration range of the polymer 0.035 mg/ml was obtained. Next work performed was checking the SEM images of the PNor-Flu in the presence and absence of the copper(II) ions. It was observed that in the absence of copper(II) ions, the PNor-Flu is showing rod-like self-assembly (Fig.5, B, C). Whereas in the presence of copper(II), it shows spherical-like self-assembly (Fig.5, E, F). All the self-assembly properties were investigated in the THF and water 1:1 mixture. Each of the monomers contains three hydroxyl groups, they take part in higher-order hydrogen bonding in the polymeric form and form rod-shaped self-assembly. Whereas in the presence of the copper(II) ions, it is forming a coordination bond with the oxygen atom of the hydroxyl group next to the imine group which lifted the possibility of the hydrogen bonding. That’s why in the presence of the copper(II) ions it forms spherical self-assembly.

Figure 5: (A) DLS study of the PNor-Flu (0.03 mg/ml). (B, C) Corresponding SEM images of PNor-Flu (0.03 mg/ml). Click here to View Figure

Real sample analysis

It has been observed that copper(II) contamination often occurs due to the uncontrolled release of copper-based metal derivatives into the environment, which pollutes water bodies. To assess the ability of PNor-Flu to detect unknown amounts of copper(II) ions in environmental water, a real sample analysis was conducted. First, a calibration curve has been drawn using known concentrations of copper(II) ions in the presence of PNor-Flu. Then, different unknown concentrations of copper(II) ions were introduced into pond water (India) and added a fixed concentration of PNor-Flu to each solution. Subsequently, UV-Vis spectroscopy was recorded and were compared the OD₄₁₆/OD₃₅₀ with the calibration curve to determine the corresponding copper(II) ion concentrations. The present polymeric sensor PNor-Flu is capable of determining the unknown concentration of copper(II) in environmental contaminants with more than 98% accuracy (Table 1).

Table 1: Real sample analysis using PNor-Flu solution

Sample	Spiked, [Cu2+] µM	Obtained, [Cu2+] µM	% of accuracy
Water in Pond 1	0	0	100
Water in Pond 2	8	7.92±0.104	99.00
Water in Pond 3	16	15.75±0.235	98.43
Water in Pond 4	22	21.87±0.355	99.40
Water in Pond 5	32	31.65±0.025	98.90

 

Conclusions

Synthesis of the fluorescein-based polynorbornenes has been completed, PNor-Flu, for the selective and sensitive detection of copper(II) ions from environmental contaminants. Through concentration-dependent titration, it has been demonstrated that PNor-Flu exhibits very high sensitivity and selectivity for copper(II) ions, with a limit of detection (LOD) value of 0.27 µM, which is lower than the limit permitted by the EPA. Additionally, It has been investigated the host-guest molecular self-assembly of PNor-Flu in the absence and presence of copper(II) ions. The present observations revealed that in the absence of copper(II) ions, PNor-Flu exhibits rod-like self-assembly, whereas in the presence of copper(II) ions, it forms spherical aggregates. Furthermore, present investigation based on real sample analysis indicates that PNor-Flu has an efficiency of over 98% in determining the copper(II) ion content in contaminated water.

Acknowledgement

Author’s special thanks goes to his wife and son for their continuous moral support.

Conflict of Interests

There is no conflicts of interests in this work

References

1. Huang, G.; Wen, R.; Wang, Z.; Li, B. S.; Tang, B. Z. Novel chiral aggregationinduced emission molecules: self-assembly, circularly polarized luminesce9nce, and copper (II) ion detection. Mater. Chem. Front. 2018, 2 (11), 1884–1892.
   CrossRef
2. Xu, X.; Van Guyse, J. F. R.; Jerca, V. V.; Hoogenboom, R. Metal Ion Selective SelfAssembly of a Ligand Functionalized Polymer into [1+1] Macrocyclic and Supramolecular Polymer Structures via Metal–Ligand Coordination. Macromol. Rapid Commun. 2020, 41 (24), 1900305.
   CrossRef
3. Pastore, V. J.; Cook, T. R. Coordination-Driven Self-Assembly in Polymer–Inorganic Hybrid Materials. Chem. Mater. 2020, 32 (8), 3680–3700.
   CrossRef
4. Wang, W.; Wong, N.-K.; Sun, M.; Yan, C.; Ma, S.; Yang, Q.; Li, Y. Regenerable Fluorescent Nanosensors for Monitoring and Recovering Metal Ions Based on Photoactivatable Monolayer Self-Assembly and Host–Guest Interactions. ACS Appl. Mater. Interfaces. 2015, 7 (16), 8868–8875.
   CrossRef
5. Mondal, S.; Ghosh, T. K.; Chowdhury, B.; Ghosh, P. Supramolecular Self-Assembly Driven Selective Sensing of Phosphates. Inorg. Chem. 2019, 58 (23), 15993–16003.
   CrossRef
6. Ruiz, L. M.; Libedinsky, A.; Elorza, A. A. Role of Copper on Mitochondrial Function and Metabolism. Front. Mol. Biosci. 2021, 8, 740547.
   CrossRef
7. Fan, X.; Gao, Y.; Yang, F.; Low, J. L.; Wang, L.; Paulus, B.; Wang, Y.; Trampuz, A.; Cheng, C.; Haag, R. A Copper Single-Atom Cascade Bionanocatalyst for Treating Multidrug-Resistant Bacterial Diabetic Ulcer. Adv. Funct. Mater. 2023, 33, 2301986.
   CrossRef
8. Izydorczyk, G.; Mikula, K.; Skrzypczak, D.; Moustakas, K.; Witek-Krowiak, A.; Chojnacka, K. Potential environmental pollution from copper metallurgy and methods of management. Environ. Res. 2021, 197, 111050.
   CrossRef
9. Liberelle, B.; Dil, E. J.; Sabri, F.; Favis, B. D.; De Crescenzo, G.; Virgilio, N. Immobilizing Enzyme Biocatalysts onto Porous Polymer Monoliths Prepared from Cocontinuous Polymer Blends. ACS Appl. Polym. Mater. 2021, 3 (12), 6359–6365.
   CrossRef
10. Zheng, C.; Zhou, Y.; Zhang, H. Facile Preparation of Well-Defined Uniform Hydrophilic Hairy Hollow Functional Polymer Micro- and Nanoparticles. ACS Appl. Polym. Mater. 2020, 2 (2), 220–233.
    CrossRef
11. Ram, B.; Jamwal, S.; Ranote, S.; Chauhan, G. S.; Dharela, R. Highly Selective and Rapid Naked-Eye Colorimetric Sensing and Fluorescent Studies of Cu²⁺ Ions Derived from Spherical Nanocellulose. ACS Appl. Polym. Mater. 2020, 2 (11), 5290–5299.
    CrossRef
12. Das, N.; Samanta, T.; Gautam, S.; Khan, K.; Roy, S.; Shunmugam, R. Caprolactone Based Biodegradable Polymer for Selective, Sensitive Detection and Removal of Cu²⁺ Ions from Water. ACS Polym. Au.  2024, 4 (3), 247–254
    CrossRef
13. Das, N.; Samanta, T.; Patra, D.; Kumar P.; Raja Shunmugam, R. A Unique Stimuli-Responsive Reversible Hierarchical Spherical to Twisted-Rod-Shape Organization from Fluorescein-Derived Polynorbornene Copolymers. Macromolecules. 2024, 57 (3), 976–984.
    CrossRef
14. Samanta T.; Das N.; Patra D.; Kumar P. Shunmugam R.Reaction-Triggered ESIPT Active Water-Soluble Polymeric Probe for Potential Detection of Hg2+/CH3Hg+ in Both Environmental and Biological Systems. ACS Sustainable Chem. Eng. 2021, 9(14), 5196–5203.
    CrossRef
15. Samanta T.; Das N.; Shunmugam R. Intramolecular Charge Transfer-Based Rapid Colorimetric In-Field Fluoride Ion Sensors. ACS Sustainable Chem. Eng. 2021, 9(30), 10176– 10183.
    CrossRef
16. Patra D.; Kumar p; Pal d.; Chakraborty I. Unique Random-Block Polymer Architecture for Site-Specific Mitochondrial Sequestration-Aided Effective Chemotherapeutic Delivery and Enhanced Fluorocarbon Segmental Mobility-Facilitated 19F Magnetic Resonance Imaging. Biomacromolecules. 2022, 23(6), 2428–2440
    CrossRef
17. Singha, J., Samanta, T. and Shunmugam, R., Unusual redshift due to selective hydrogen bonding between F− ion and sensor motif: a naked eye colorimetric sensor for F− ions in an aqueous environment. Materials Advances, 2020, 1, 2346-2356. DOI: 10.1039/D0MA00092B
    CrossRef

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