Browsing by Author "Wanniarachchi, D. D. S. de S."

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Comparison of structural, electronic, and fluorescent properties of Zn-terpyridine, Zn- 1,10-phenanthroline, and Zn-hydroxyquinoline metal complexes
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Lakshika, W. A. I.; Wanniarachchi, D. D. S. de S.
Terpyridine is a heteronuclear, N-N-N tridentate ligand while 1,10-Phenanthroline (1,10-Phen) and 8- hydroxyquinoline (8-HQ) are N-N and N-O bidentate ligands that are commonly used for the synthesis of metal complexes. Although the Cu2+, Ag+, and Ru2+ complexes of these ligands have been investigated, the Zn2+ complexes of these ligands have not gained much attention. One-pot Kröhnke type synthesis of 4/-(4-Nitrophenyl)-2,2/:6/,2//-terpyridine ligand (Nitrotyp) and 4/-(phenyl)-2,2/:6/,2//- terpyridine ligand (Phentyp) using 2-acetylpyridine and aryl aldehyde is followed by the characterization using UV-visible, FT-IR, and H1 NMR spectroscopy. Then Nitrotyp and Phentyp were separately coupled with Zn(II) and characterized by UV-visible and FT-IR spectroscopy. According to the UV-visible spectroscopy, after the coordination with Zn(II), both Nitrotyp and Phentyp ligands exhibit a red shift in absorption maxima (λmax) from 272 nm to 284 nm and from 277 nm to 283 nm, respectively. All these electronic transitions are ligand-centered π π* transitions. According to the FTIR spectroscopy, the C=N stretching frequencies for the Nitrotyp and Phentyp free ligands are 1593 cm- 1 and 1582 cm-1, respectively. Compared to the FT-IR spectra of the Zn complexes of the same ligand, the stretching frequency for the C=N bond is 1601 cm-1 and 1552 cm-1, respectively. The shift of the IR stretching frequency of the C=N bond compared to the relevant free ligand indicates the coordination of the ligands with Zn(II). In addition, commercially available 1,10-phen and 8-HQ ligands were combined with Zn(II) and characterized by UV-visible, and FT-IR spectroscopy. The formation of the Zinc complex in the 8-HQ ligand leads to a significant red shift of λmax from 241 nm to 259 nm. In contrast, free 1,10-Phen exhibits a blue shift from λmax= 229 nm to λmax= 225 nm upon coordination with Zn. As reported by FT-IR spectroscopy, the C=N stretching frequencies for the 1,10-Phen and 8- HQ free ligand are 1582 cm-1 and 1576 cm-1, respectively. Compared to the FT-IR spectra of the Zn complexes of these ligands the stretching frequency for the same bond is 1589 cm-1 and 1587 cm-1, respectively. The Zn(II)-to-metal ratio of all complexes was identified as 1:1 using the job’s plot method. Hence, it is concluded that the chemical formulae for the synthesized Zn(II) complexes are [Zn(Nitrotyp)Cl]+, [Zn(Phentyp)Cl]+ [Zn(1,10-Phen)Cl2], and [Zn(8-HQ)Cl2]. According to the fluorescence spectra, all the free ligands exhibit less fluorescence intensity compared to the corresponding Zn(II) complex and, [Zn(Nitrotyp)Cl]+ complexes exhibit hypsochromically (blue) shifted emission spectra, compared to the corresponding free ligand. In contrast, [Zn(Phentyp)Cl]+, [Zn(1,10-Phen)Cl2], and [Zn(8-HQ)Cl2] complexes demonstrate a bathochromically (red) shifted emission spectra. Out of the four complexes, [Zn(Phentyp)Cl]+ ((2.4 × 10-7 M) shows a higher fluorescence intensity, even at low concentrations than other complexes. Replacing one of the pyridine rings with a phenyl group triggers the diminution of the fluorescence intensity and it is indicated by the high fluorescence intensity of the [Zn(Phentyp)Cl]+ complex compared to the [Zn(1,10-Phen)Cl2] complex. These results make the [Zn(Phentyp)Cl]+ complex a more promising agent for the detection of anions in a given medium, than the other three complexes.
A novel method for spectrophotometric detection of Glyphosate using a simple terpyridine-based Zn complex
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Tharaka, K. S.; Diyabalanage, R. S.; Wanniarachchi, D. D. S. de S.
Glyphosate (N-[phosphomethyl] glycine, GLP) is an organophosphorus and widely applied as an herbicide. Also, it is a non-selective, effective, and broad-spectrum herbicide. Nevertheless, excessive use, misapplication, and residue of glyphosate adversely affect the environment. Therefore, it is very important to detect the glyphosate in environment samples. The current techniques for detection of glyphosates include chromatographic methods and spectrophotometric methods. However, these methods still confront many challenges such as complexity, requirement of sample preparation, time consuming, and low sensitivity. Thus, there is an exclusive need of a rapid and high sensitive system for detection of glyphosate. Therefore, in the present study, a simple terpyridine-based Zinc-complex (Zn-GLP) was successfully employed for the detection of GLP. 2,2’:6,2”-Terpyridine is a tridentate ligand which contain three coordination sites belonging to three N-heteroaromatic rings. A range of applications of terpyridine based compounds has been reported including catalysis, supramolecular chemistry, medicinal applications, and as sensors. The capability of metal-terpyridine as a sensor is least studied for Glyphosate. A 4-functionalized terpyridine ligand, 4-(4-N,N-dimethylaminophenyl)-2,2’:6,2”-terpyridine was synthesized through the Krohnke reaction by condensation of 2-acetylpyridine with 4-Dimethylaminobenzaldehyde followed by oxidation under ammonium hydroxide and finally a green colored solid was obtained in yield 54% . This product was recrystallized with ethanol to obtain the ligand in pure form. Then its Zn-complex was synthesized by treating 4-(4-N,N-dimethylaminophenyl)- 2,2’:6,2”-terpyridine ligand with ZnCl2 in methanol. The ligand and Zn-complex were fully characterized by a combination of 1H NMR spectroscopy, UV-Vis spectroscopy, FT-IR spectroscopy and Fluorescence spectroscopy. The UV-Vis spectrum of Zn-complex exhibited bands at 240 nm, 285 nm, 315 nm, and a characteristic band at 410 nm. GLP content was tested at 410nm using UV-visible spectroscopy with method LOQ 18 ppm GLP, LOD 18 ppm GLP and the method sensitivity was found to be 10 ppb. Here, the yellowish colour of solution of Znterpyridine in methanol instantly disappeared when the concentration of added Glyphosate was above 1 ppm, and this could be observed in naked eye. Therefore, this work evident the Znterpyridine complex as a novel method for the detection of GLP.