Potentiometric and spectrophotometric study of a new dipodal ligand N,N'-bis{2-[(2-hydroxybenzylidine)amino]ethyl}malonamide with Co(II), Ni(II), Cu(II) and Zn(II)

Pyrogallol-based dipodal optical probe as new smart analytical tool for sustainable detection of cobalt in biosystem

The present research focuses on the micro-level detection of cobalt ions in biological and environmental samples using a new probe. The probe is a multifunctional symmetrical dipodal molecule with two pyrogallol binding units attached to the malonate scaffold through a propylene spacer. It was synthesized and characterized by 1H NMR, 13C NMR, IR, electronic spectroscopy, and mass spectrometry. The molecule's binding, thermodynamic, and photophysical properties are also described. The designed probe demonstrates an excellent sensing ability for Co(II) based on the ESIPT "OFF-ON" fluorescence mechanism. The experiments explore the high selectivity of the ligand for cobalt sensing over a wide range of metal ions of biological and environmental importance. The fluorescence intensity shows a linear response to Co(II) in 5-100 μM concentration with a detection limit of 8.75 x 10-5 and a 2.65-fold enhancement in the intensity. These results establish its potential application as a fluorescence sensor. The probe is also employed as a colorimetric sensor for the qualitative determination of cobalt ions in DMSO solution. The interesting behavior of the probe motivated us further to study its coordination properties with divalent cobalt in solution. The pre-organized assembly with an appropriate cavity size favors the ligand for an efficient Co(II) encapsulation by coordinating through imine-Ns and aromatic ring-Os donors, giving high formation constants.

Photophysical Studies of a Catechol Based Polyfunctional Dipodal Chelator: Application for Optical Probe for Selective Detection of Fe(III)

A novel catechol based dipodal fluorescent chelator N,N'-bis[3-[(E)-(2,3-dihydroxyphenyl)methyleneamino]propyl]propanediamide(MPC), has been developed and its photophysical behaviour was studied by experimental (UV-VIS and fluorescence) and DFT method. The design of the molecule has been inspired from the naturally occurring siderophore enterobactin, a catechol based chelator with amide linkage, that shows an excellent binding efficiency towards Fe(III). The dipodal molecule (MPC) presented here, carries two catechol pendant binding moieties linked to the malonate central unit through propylene spacers by amide linkage. MPC showed good selectivity for Fe(III) at 10^-4 M concentration in aqueous medium amongst the biologically and environmentally important metal ions chosen viz., Na(I), K(I), Al(III), Cr(III), Fe(III), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II), by demonstrating a remarkable quenching in the fluorescent emission from 262 a.u. to 55 a.u. at λ_max = 477 nm. Also, the pre-organized assembled ligand favored an efficient Fe (III) encapsulation through coordination by imine nitrogen and catecholate oxygen donors. High formation constant (log β = 31.3) for 1:1 metal-ligand complex evaluated by both potentiometric and spectrophotometric methods, established the strong binding efficiency of the ligand for Fe(III) metal ion. The binding stoichiometry in the complex was also confirmed from Stern -Volmer and Hill Plot analysis. Further investigation on the emission behavior of MPC in a completely DMSO system explored its suitability for extensive applications in the areas such as, metallurgy, material science, iron contamination remedial in the materials etc.. DFT studies suggest that the ligand displays a U-shaped geometry with a parallel π-stacking and the hydrogen bond between two arms. The experimental infrared, electronic, fluorescence, ¹H nmr, ¹³C nmr spectra were correlated with the theoretical results. The nature of electronic transitions were identified from the TDDFT calculation. The ligand forms a hexa-coordinated complex with six Fe-O bonds extending an orthorhombic geometry due distortion from a regular octahedron.

Fluorescent organic nanoparticles (FONs) for selective recognition of Al3+: application to bio-imaging for bacterial sample

(a) Changes in fluorescence upon successive addition of Al³⁺ ions to salpn-ONPs; (b) titration profile of fluorescence; (c) recognition of Al³⁺ through bio-fluorescence Staphylococcus aureus bacterial cells.

Spectroscopic, potentiometric and theoretical studies of novel imino-phenolate chelators for Fe(III)

The present study was targeted to explore the binding properties of two strong chelators for Fe(III) based on tripodal-iminophenolate moiety. Complexation behavior of the tripodal systems cis-cis cyclohexane-1,3,5-tricarboxylic acid tris-({2-[(2-hydroxy-benzylidene)-amino]-ethyl}-amide (CYCOENSAL, L(1)) and cis-cis cyclohexane-1,3,5-tricarboxylic acid tris-({3-[(2-hydroxy-benzylidene)-amino]-propyl}-amide (CYCOPNSAL, L(2)) is described. Three protonation constants obtained are assigned for three hydroxyl groups of aromatic ring were employed for the evaluation of the formation constants of the metal complexes. Both ligands liberate three protons each forming monomeric complexes of type FeLH3, FeLH2, FeLH and FeL (L=L(1) and L(2)). The first species FeLH3 depicted at low pH, where the ligands were coordinated through three imine nitrogen and other species form subsequently from FeLH3 in steps upon deprotonation and coordination of the phenolic oxygen giving encapsulated tris(phenolate) complexes. The probable structures of the metal complexes formed in solution were proposed through molecular modeling calculations. L(2) was observed to be highly selective towards Fe(III) as compared to L(1).

Synthesis of Imine-Naphthol Tripodal Ligand and Study of Its Coordination Behaviour towards Fe(III), Al(III), and Cr(III) Metal Ions

A hexadentate Schiff base tripodal ligand is synthesized by the condensation of tris (2-aminoethyl) amine with 2-hydroxy-1-naphthaldehyde and characterized by various spectroscopic techniques like UV-VIS, IR, NMR, MASS, and elemental analysis. The solution studies by potentiometric and spectrophotometric methods are done at 25 ± 1°C, µ = 0.1 M KCl, to calculate the protonation constants of the ligand and formation constants of metal complexes formed by the ligand with Fe(III), Al(III), and Cr(III) metal ions. The affinity of the ligand towards Fe(III) is compared with deferiprone (a drug applied for iron intoxication) and transferrin (the main Fe(III) binding protein in plasma). Structural analysis of the ligand and the metal complexes was done using semiempirical PM6 method. Electronic and IR spectra are calculated by semiempirical methods and compared with experimental one.

Spectroscopic and pH-metric studies on the complexation of a novel tripodal amine-phenol ligand towards Al(III), Ga(III) and In(III)

The aqueous coordination chemistry of a newly synthesized tripodal amine-phenol ligand, cis,cis-1,3,5-tris{(2-hydroxybenzyl)aminomethyl}cyclohexane (THAC) towards H+, Al3+, Ga3+ and In3+ ions have been investigated in aqueous medium of 0.1 M KCl ionic strength and 25±1 °C by potentiometric and spectrophotometric methods. Three protonation constants assigned to phenolic hydroxyl groups were determined and were used as input data to evaluate the formation constants of the metal complexes. The ligand formed various monomeric metal complex species MLH3, MLH2, MLH, ML and MLH(-1) with Ga(III) and In(III); MLH3, ML and MLH(-1) with Al(III). The calculated stability constants followed the order Ga(III)>In(III)>Al(III), and their pM values at physiological condition were found to be higher than the corresponding transferrin complexes.

Synthesis, spectroscopic and theoretical studies of two novel tripodal imine-phenol ligands and their complexation with Fe(III)

Two novel tripodal imine-phenol ligands, cis,cis-1,3,5-tris{(2-hydroxybenzilidene)aminomethyl}cyclohexane (TMACHSAL, L(1)) and of cis,cis-1,3,5-tris{[(2-hydroxyphenyl)ethylidene]aminomethyl}cyclohexane (Me(3)-TMACHSAL, L(2)) have been synthesized and characterized by elemental analyses and various spectral (UV-vis, IR and (1)H and (13)C NMR) data. The complexation reactions of the ligands with H(+) and Fe(III) were investigated by potentiometric and spectrophotometric methods at an ionic strength of 0.1M KCl and 25 +/- 1 degrees C in aqueous medium. Three protonation constants each for ligands L(1) and L(2) were determined and were used as input data to evaluate the formation constants of the metal complexes. Formations of metal complexes of the types FeLH(3), FeLH(2), FeLH, FeL and FeLH(-1) were depicted in solution. Experimental evidences suggested for a formation of tris(iminophenolate) type metal complex by the ligands. The ligand L(1) showed higher affinity towards iron(III) than L(2). The pFe value related to L(1) (pFe = 20.14) is approximately four units higher than L(2) (pFe = 16.41) at pH = 7.4. The structures of the metal complexes were proposed through the molecular mechanics calculation using MM3 force field followed by semi-empirical PM3 method.

Spectrophotometric and conductometric study of complexation of salophen and some transition metal ions in nonaqueous polar solvents

The complexation reaction between Cu2+, Co2+ and Ni2+ metal cations with N,N'-bis(salicylidene)-1,2-phenylenediamine (salophen), in three nonaqueous polar solvents such as: acetonitrile (AN), dimethyl sulfoxide (DMSO), methanol (MeOH) and two binary mixtures of AN:DMSO and AN:MeOH at 25 degrees C were studied by spectrophotometric and conductometric methods. All investigated metal ions form 1:1 ML complex which their stability constants were determined and increase as Irving-Williams stability order of Co2+ < Ni2+ < Cu2+ in all solvent systems except in the pure MeOH and binary mixture of AN:MeOH 20:80; in which, Ni2+ < Co2+ < Cu2+ was observed. The values of the thermodynamic parameters (DeltaH degrees , DeltaS degrees and DeltaG degrees ) for complexation reactions obtained from the temperature dependence of the stability constants and the results show that for all metal ion complexes, the value of DeltaH degrees , DeltaS degrees and DeltaG degrees are solvent dependent.