Colorimetric fluorescent schiff base molecular sensor for the detection of pb (II)

Abstract

ABSTRACT A highly fluorescent Skiff base molecular sensor for the cliometric detection of the hazardous precarious heavy metal Pb(II) ion is submitted here. The presented Schiff base is synthesized by one pot synthesis under normal atmospheric condition without the use of any , solvent or sophisticated equipments. This method is definitely a green method, devoid of solvent pollution or formation of pollution causing unimportant side products. The yield is 98Z.The compound is simple, less expensive and highly stable, with a shelf life of more than three years under room temperature without the requirement of any special storage procedure. The detection process is feasible in aqueous methanol medium which is ecofriendly. The detection of Pb(II) ion could be observed with naked eye; the yellow color of the Schiff base solution in methanol medium is decolonized by Pb(II) ion in water medium. The Schiff base could detect Pb(lI) ions present even in trace amount which is as low as 1 x 10' 4M molar. The detection mechanism is delineated as due to the foundation of coordination complex between the Schiff base compound and the heavy metal ion Pb(H).The presented Schiff base molecular sensor could also be recovered back with the help of EDTA so that can be request. The presence of other metal ions do not cause interference to the detection of Pb(H) metal. The sensing efficiency is applied in the analysis of real water samples.

Description

FIELD OF INVENTIONThe present invention is about a simple organo mine compound which could detect the presence of the heavy metal namely Pb(II). This compound comes under the category of molecular sensors, more specifically colorimetric sensors, some more specifically phemosensors, still more specifically Schiff base chemosensors, farther more specifically fluorescent Schiff base chemosensors, still further more specifically Schiff base chemosensor prepared from 3-methoxy-2-hydroxy benzaldehyde, 4-hydroxy benzaldehyde and ammonium acetate.BACKGROUND ARTThe application of sensors in naked eye detection of hazardous metal ions is gaining importance due its significance among common people, because Pb(II) ions if present even in very low concentration can cause serious health problems. So the development of colorimetric and. fluorescent chemosensors are of great demandfDiganta Kumar Das et al]. The toxicity of Pb(Il) ion may be due to its soft acidic nature which allows the Pb(II) ions to bind with the sulfhydryle groups present in enzymes. Lead is considered as the second most toxic metal in the environment. Exposure to Pb(Il) ion causes physical growth impairment, mental retardation, anemia and muscle paralysis but the use of lead cannot be ignored due to its applications in storage batteries, electronics and paints. Some techniques like inductively coupled plasma atomic emission spectroscopy (ICP - AES), atomic absorption spectroscopy (AAS) has been used for the quantitative detection of Pb(II) ions[Anupam Ghorai et al]. Since these techniques are expensive, the synthesis of simple and cost effective fluorescent chemosensors are highly useful for the detection of Pb(II) ions.DETAILED DESCRIPTION OF THE INVENTIONA new Schiff base metal ion sensor is synthesized by one pot synthesis method without the use of any solvent. 3-methoxy-2-hydroxy benzaldehyde is made to react with 4-hydroxy benzaldehyde and ammonium acetate in the presence of triethylamine. The resulting mixture is dissolved in very minimum amount of (5 ml) methanol and the Schiff base is separated as a solid product. This solid product is washed well with petroleum ether and dried between the folded filter papers and kept in a vial. The Schiff base thus obtained is characterized by IR, UV-Vis, 'H NMR, ,3C NMR and Mass spectral studies. The melting point of the Schiff base is156°C. It is soluble in methanol, ethanol, DMSO and ACN. The SchifFbase is highly stable and has a shelf life of more than three years. The total time required for the preparation of the SchifFbase is less than 30 minutes.The SchifFbase obtained is a moderately fluorescent compound. The emission is found to occur at 323 nm with an intensity of 343 a.u.The metal ion detection efficiency of this new Schiff base is studied in aqueous methanolic medium. 15 metal ions are taken for the detection analysis. All metal solutions are prepared in water and the SchifFbase solution is prepared inmethanol medium. The SchifFbase is made to interact with one equivalent of each of metal ion taken for study. The Pb2+ ion is found to be exclusively detected over the other studied metal ions. The detection process is studied in three modes namely absorption, emission and colorimetric methods. The point to be highlighted here is that the presence of Pb2+ion is observed in naked eye namely the yellow coloured Schiff base solution is decolourised immediately and becomes colourless solution in the presence of Pb2+ ions. This colorimetric detection is found to be caused by a veiy dilute solution of theSchifFbase which is 10'4 M (1 / 10,000 M) solution. Another importance of the detectionprocess is the presented SchifFbase could detect Pb2+ ions even if it is present in a very very small quantity of the order of 10'3 M (1 / 1000 M). The naked eye colour change is clearly visible in these dilute solutions (very low concentration).The recognition process is also explored by absorption mode and emission mode which are also occurring with notable observations.SPECTRAL CHARACTERISATIONYield: 98% ; M. P. 156°C; m.w(g / mol): 406.43; EI-MS: 406.22; IR (Solid state, cm1): v(O-H) 3400.81[Sambamoorthy Santhi et al]; v(C=N) l625[Muhammad Pervaiz et al]; v(C-O). - 1253.30[Sambamoorthy Santhi et al]; v(C-H) 783.93; 'H NMR (In DMSO-de, ppm): 813.27(s); 5 8.77(s); 5 6.40-7.13(m)[Masumeh Galini et al]; 8 3.82; 13C NMR (In DMSO-de, ppm); 8 I65.82(s); 5 151.13(s)[Muhammet Kose]; 8 112.01 - 8 127.34(m)[Thierry Youmbi Fonkui et al]; 8 40.46(m).METAL ION SENSING STUDIESThe metal ion sensing process is studied by three modes namely colorimetric detection, absorption method and emission method. Colorimetric method involves the change in colourof the Schiff base solution in the presence of metal ion solution at normal laboratoricalconditions. In the present case yellow colour of the Schiffbase disappears on adding Pb(II) ion solution. On performing absorption and emission studies significant changes are observed in the absorption pattern and emission intensity of the submitted Schiffbase molecular sensor.The cation recognising potential of the Schiff base molecular sensor is studied by keeping the concentration of the Schiffbase at I x 10 '4 M in methanol medium. The metal ion solutions are prepared in triply distilled water with a concentration of 3 x 10'3 M. The studies are performed in aqueous methanolic medium.COLORIMETRIC METHODIn this method the presence of Pb(II) metal is indicated by the decolourisation of the Schiff base solution which is yellow in colourfP. Vijayakumar et al]. Here 1 equivalent of Pb(Il) solution prepared in water medium is added to the Schiff base solution prepared in methanol. Spontaneous decolourisation is observed. This type of decolourisation is not caused by any of the other 15 metal ions studied. The decolourisation in the presence of just 1 equivalent is highly advantageous when taken to society. Fig. 1.ABSORPTION METHODIn absorption method the Schiffbase molecular sensor is made to interact with 1 equivalent of 15 metal ions such as Na(I), Mg(ll), Ca(ll), Mn(II), Fe(lTl), Co(II), Ni(II), Cu(II), Zn(ll), Sr(II), Cd(II), Ba(II), Hg(II), Pb(II) and Al(III). The free Schiffbase molecular sensor exhibits three peaks of 416 nm, 282 nm and 220 nm. The addition of 1 equiv. of Pb(II) ion to the Schiffbase molecular sensor lead to the appearance of a new peak at 339 nm. The peak at 282 nm is also blue shifted to 268 nm[Kalyani Rout et al]. The presence of other metal ions does not produce noticeable change in the absorption pattern Fig. 1I & III.The interaction between the Schiff base and the Pb(LE) ion is further confirmed by performing absorption titrations[Tao Sun et al]. The sequential addition of Pb(II) ion results in the appearance of new peak at 341 nm. The intensity of new peak increases on addition of more amount of Pb(II) ion and the intensity of the peak at 416 nm gradually decreases Fig. IV & V. These changes confirm the complex formation between the Schiff base and Pb(Il) ion and the image of the complex is shown in Fig VI. Through Benesi-Hildebrand plot the stability of the complex is determined as 1.38 x 103[Salman A. Khan et al] Fig. VII.EMISSION STUDIESThe Schiffbase exhibits fluorescence emission at 323 nm with an intensity of 343 a.u. The excitation wavelength is kept at 283nm. Addition of Pb(II) ion to the ShifF base molecularsensor casued enhancement of emission whereas the addition of other metal ions does not produce significant spectral changesfReza Azadbakht et al][Wei Liu et al]. The fluorescence enhancement might be due to the coordination of Pb(IT) ion with imine nitrogen atoms thereby blocking the photo induced electron transfer (PET) process. The detection of Pb(II) by the patent claimed Schiff base molecular sensor can be expounded as because of the formation of co-ordination complex between the two mentioned reactants. This is due to the fact that the Schiff base contains four donor atoms which are easily got coordinated with the Pb(Il) ion. This way of interaction is corroborated by IR titration, CV titration, 'HNMR titration and Mass titration experiments. The enhancement of emission is further confirmed by performing fluorescence titrations. Gradual addition of Pb(II) ion to the Schiff base leads to the slow increase in the emission intensity Fig. VIII - XI.The Limit of Detection of the presented Schiff base sensor is 1.729 * 10" 4 M that is thepresented Schiff base could detect Pb2+ ions even if they present to an extent of 0.0001 g per litre. The metal ion detection is applied in real water samples. Water samples collected from Puthupatty, Dindigul, Thuvakudi, Trichy, SEDCO Industrial Estate, Ambattur, Residential area in Ambattur, ground water, Seethalakshmi Ramaswami College are tested for the presence of Pb2+ ions. The sample of water from SIDCO Industrial Estate-Ambattur, Chennai is found to contain Pb2+ ions; in that sample alone decolourisation occurred.SELECTIVITY OF THE SCHIFF BASE MOLECULAR SENSOR IN THE SENSING PROCESSThe Schiff base molecular sensor is highly selective towards Pb(II) ion. The presence of other metal ions does not interfere in the selective sensing of Pb(II) ion. Competitive titrations were performed to study the selectivity of the Pb(II) ion[Shanshan Zhang et al]. In this study l equiv. of Pb(II) ion in the presence of 1 equiv. of each of the other metal ions is made to interact with the Schiff base solution. These results confirm that the enhancement in emission intensity of the Schiff base in the presence of Pb(ll) ion is not affected by the presence of other metal ions Fig. XII.REVERSIBLE NATURE OF SENSING PROCESSThe Schiff base molecular sensor is found to be reversible with respect to Pb(II) ion and the reversible nature of the Schiff base molecular sensor is proved by the addition of EDTA. The addition of EDTA leads to the removal of Pb(II) ion, thereby preventing the complex formation and the Schiff base molecular sensor can be recovered and used again without any destruction[Liping Bai et al].The enhancement of emission intensity may also be illustrated as due to the formation of rigid chelate system by the presented Schiff base and Pb(II) ion. This is described as chelate Enhanced Fluorescence Effect.The interaction between the Schiffbase and Pb(Il) ion is studied by IR, CV, 'H NMR and Mass titrations. These studies confirm the coordination between the Schiffbase and Pb(II) ion.DR titrationsIR titrations were performed by recording the ER spectrum of Schiff base followed by the addition of l equiv. and 2 equiv. of Pb(Il) ion to the Schiffbase. The emergence of new bands at 405.4 cm-1 and 616.04 cm-1 on adding 1 equiv. of Pb(II) ion and the bands at 403.51 cm-1 and 577.5 cm-1 on adding 2 equiv. of Pb(II) ion corresponds to M-N and M-0 bonds[S. Santhi et al]. The shifts in the azomethine band from 1658.42 cm-1 to 1651.06 cm-1 and the shift in the phenolic -OH band at 3436.60 cm-1 further confirms the coordination between the Schiff base and Pb(II) ion through azomethine nitrogen and phenolic oxygen atomsfDevika Vashisht et al] Fig. XIII a, b, c.CV titrationsIn the case of CV titrations, the free Schiffbase exhibits two oxidation (Eox - -0.7570 and Eox = 0.6358) and two reduction peaks (Ered = -0.5079 and Ered = 0.6495)[Sambamoorthy Santhi et al]. The addition of 1 equiv. of Pb(II) ion showed two oxidation (Eox = -0.9408 and Eox =0.6862) and two reduction peaks (Ered = -1.0579 and Ered = 0.5256) and the addition of 2 equiv. of Pb(II) ion showed three oxidation (Eox = -0.8455, Eox = -0.4673 and Eox = 0.5474 and two reduction peaks (Ered = -0.8374 and Ered = 0.7312). After the addition of Pb(II) ion there is also a considerable change in AE value. These observations further stands as an additional evidence for the interaction between the Schiffbase and Pb(II) ion Fig. XIV a, b, c. lH NMR titrationsThe complexation behaviour of Schiff base molecular sensor with Pb(II) ion is studied in DMSO - de medium. The addition of Pb(Il) to the Schiffbase molecular sensor caused shift in the phenolic -OH group and there is also a considerable change in the aromatic protons peak after the addition of Pb(II) ion. These changes confirms the complexation of metal ions with Schiffbase molecular sensor through imine and phenolic groups[S. G. Jebastin Andrews et al] Fig. XV a, b.Mass titrationsMass titrations are performed to further confirm the interaction between the Schiff base molecular sensor and Pb(II) ion. Mass spectrum of Schiff base molecular sensor shows molecular ion peak at 406.1714 (calcd. 406.4339). The presence of 1 equiv. ofPb(II) ion results in the appearance of peak at 675.8959 (calcd. 675.7009) which corresponds to [Pb(HYHB)(CH3OH)2] complex[Gauthier J. P. Deblonde et al] Fig. XVI, STOICHIOMETRY AND DETECTION LIMITFrom the Job's plot the stoichiometry of the complex formed by the presented SchifFbase with Pb(Il) ion is determined as l:l[Tao Hu et al] Fig. XVII.The limit of detection-the quantity of the patent applied compound needed for the detection of Pb(II) is determined as1.729 X 10'4M.DETECTION OF Pb(II) IONS IN REAL WATER SAMPLESWater samples collected from different areas of Trichy, Chennai and Dindigul are tested for the presence of Pb(II) ions. To a sample of 10 ml of water 9 ml of 1x10* 4M solution of theSchiff base molecular sensor is added and then irradiated under UV light for an hour .The yellow colour of the SchifFbase is decolourised in the water sample collected from the SIDCO Industrial Estate-Ambattur, Chennai, proving the presence of Pb(II) ion.REFERENCESDas, D. K., Deka, S., & Guha, A. K. (2019). SchiffBase Derived from 4,4'-methylenedianiline and p-anisaldehyde: Colorimetric Sensor for Cu2+, Paper Strip Sensor for Al3+ and Fluorescent Sensor for Pb2+, Journal of Fluorescence, 29, 1467-1474.Ghorai, A., Mondal, J., Saha, R., Bhattacharya, S., & Patra, G. K. (2016). A highly sensitive reversible fluorescent-colorimetric azino bis-Schiff base sensor for rapid detection ofPb2+ in aqueous media. Analytical Methods, 8(9), 2032-2040.Amala, S., Santhi, S., & Subashini, S. (2018). 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Novel schiff base synthesis of EN-(1-(1H-phenothiazin-2yi)-ethylidene)-3-((E)-(2-phenylhydrazono) methyl) aniline "Tum-on" fluorescent chemosensor for sensitivity and selectivity of detection of Cr3+ and Pb2+ ions. Materials Today: Proceedings, 42, 1050-1064.Rout, K., Manna, A. K., Sahu, M., Mondal, J., Singh, S. K., & Patra, G. K. (2019). Triazole-based novel bis Schiffbase colorimetric and fluorescent tum-on dual chemosensor for Cu2+ and Pb2+: application to living cell imaging and molecular logic gates. RSC advances, 9(44), 25919-25931,Sun, T., Niu, Q., Guo, Z., & Li, T. (2017). A simple highly sensitive and selective tum-on fluorescent chemosensor for the recognition of Pb2+. Tetrahedron Letters, 5S(3), 252-256.1388-1394.27-Feb-2024 / 30741 / 202441014066 / Form 2(Title Page)Khan, S.A., Ullah, Q., Almalki, A S., Kumar, S., Obaid, RJ., Alsharif, M.A., Alfaifi, S.Y. and Hashmi, A. A. (2021). Synthesis and photophysical investigation of (BTHN) Schiffbase as off-on Cd2+ fluorescent chemosensor and its live cell imaging. Journal of Molecular Liquids, 328, 115407. 'Azadbakht, R., Veisi, H., Mohamadvand, H., & Khanabadi, J. (2015). A new fluorescent chemosensor for Pb2+ ions based on naphthalene derivatives. Spedrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 145, 575-579.Liu, W., Wu, G., Gu, X., Yuan, X,, Li, J., & Wang, H. (2015). Synthesis of Schiffbase-Based 1, 2, 4-Oxadiazole Derivative as Fluorescence Turn-On Sensor for High Selectivity of Pb2+ Journal of Fluorescence, 25, 557-561.Zhang, S., Niu, Q., Lan, L., & Li, T. (2017). Novel oligothiophene-phenylamine based Schiff base as a fluorescent chemosensor for the dual-channel detection of Hg2+ and Cu2+ with high sensitivity and selectivity. Sensors and Actuators B: Chemical, 240, 793-800.Bai, L., Xu, Y., Li, G., l ian, S:, Li, L., Tao, F., Deng, A., Wang, S. and Wang, L, (2019), A highly selective tum-on and reversible fluorescent chemosensor for Al3+ detection based on novel salicylidene Schiff base-terminated PEG in pure aqueous solution. Polymers, 11(4), 573.Santhi, S., Amala, S., Renganathan, R., Subhashini, M., & Basheer, S. M. (2019). Colorimetric and fluorescent sensors for the detection of Co(II), Ni(II) and Cu(lT) in aqueous methanol solution. Research on Chemical Intermediates, 45, 4813-4828.Vashisht, D., Sharma, S., Kumar, R., Saini, V., Saini, V., Ibhadon, A., Sahoo, S.C., Sharma, S., Mehta, S.K. and Kataria, R. (2020). Dehydroacetic acid derived Schiffbase as selective and sensitive colorimetric chemosensor for the detection of Cu(II) ions in aqueous medium. Microchemical Journal, 155, 104705.Santhi, S., Amala, S., & Basheer, S. M. (2018). Experimental and computational investigation of highly selective dual-channel chemosensor for Al(III) and Zn(II) ions: construction of logic gates. Journal of Chemical Sciences, 130, 1-13.Andrews, S. J., Silviya, S. B. J., Jeyanthi, D., Devi, E. S., Jebaraj, J. W., & Balakrishnan, C. (2020). Biocompatible alkyne arms containing Schiff base fluorescence indicator for dual detection of Cd(II) and Pb(Il) at physiological pH and its application to live cell imaging. Analyst, 145(13), 4576-4586.Deblonde, G. J. P., Lohrey, T. D., An, D. D., & Abergel, R. J. (2018). Toxic heavy metal-Pb, Cd, Sn-complexation by the octadentate hydroxypyridinonate ligand archetype 3, 4, 3-L1 (1, 2-HOPO). New Journal of Chemistry, 42(10), 7649-7658.Hu, T., Cheng, J., Li, L., Zhan, Y., Li, W., Chang, Z" & Sun, C. (2019). A new Schiffbase fluorescent-colorimetric probe containing fluorene-naphthalene structure: Multifunction detection. Inorganica Chimica Acta, 498, 119131.ADVANTAGES OF THE EMBODIMENT1. The compound submitted here is a very simple and highly stable molecular sensor.2. The compound can be easily prepared in a single step (by one pot method) under normal atmospheric condition using very basic apparatus such as beaker and glass rod.3. No solvent is required for the preparation, thus devoid of pollution.4. No formation of side products, assuring greater than 95% purity.5. Preparation requires less than half-an-hour time, and the product can be obtained in a pure form in a day, time effective preparation.6. Starting materials are very less cost and easily available - cost effective sensor compound,7. The presented compound is highly stable, requires no special, sophisticated equipments for preservation. Shelf life more than three years.8. The submitted compound could 'detect the highly hazardous lead ions "Colorimetrically".9. The detection is possible in the presence of more than 15 other metals.10. Very less quantity of the presented Schiff base is enough to detect the presence of Pb(II)12. Detection is possible in highly ecofriendly solvent medium (aqueous methanol medium).13. The submitted Schiff base sensor can be "recovered back" after sensing process and "reused" again.14. Real water samples could be tested for the presence of Pb(II) metal.In a nut shell, the presented Schiff base metal ion chemosensor is,metal.11. Very very less quantity ofPb(II) (10'4 M) could also be detected.Eco friendly with respect to points 2,3,4,13Time effective with respect to point 5Cost effective with respect to points 7,8,11,14 and possessingGreat social application with respect to points 9,10,121. The Pb(II) metal detection property of the submitted Schiffbase sensor could be applied in testing real water samples for the presence of Pb(LL) by very simple colorimetric method.2. The Pb(II) metal present in any sample could be completely removed from the sample. This is feasible due to the co-ordinating ability of the Schiffbase sensor with the Pb(II) metal.PREAMBLEA new fluorescent Schiffbase molecular sensor - Solvent free, time effective, cost effective, one pot green synthesis - High shelf life under normal atmospheric conditions - naked eye colorimetric recognition of Pb(II) in eco-friendly solvent - Fluorescence enhancement -perceiving even trace amounts of Pb(II)- Application in real water samples-

Claims

1. For a new Organo Imine Compound (Schiff base ) namely 6,6,-(((4-hydroxyphenyhmethylene)bis(azanylylidene)) bis(methanylylidene))biST-methoxyphenol) for the colorimetric detection of Pb(II), favoured by I. Solvent free, pollution free, time effective and cost effective onepot synthesis using very basic apparatus such as beaker and glass rod.

2. High stability with a shelf-life of more than three years under normal atmospheric conditions.

3. Harmlessness4. Efficiency to detect Pb(ll) present in trace amount (0.000 lg / litre) COLORIMETRICALLY.

5. Reusability