Design and Development of Arylether Based Receptors for Electroanalytical Applications

Abstract

Different derivatives of di- and triphenylether molecules were synthesized by aromatic nucleophilic substitution reactions. Molecules named SMR-1 to SMR-16 were synthesized using various organic tools, which were then analyzed for their ion-recognition studies using spectrophotometric and voltammetric techniques. All the molecules were studied for their analytical applications as chemical sensors for target ions without interference from other ions. Complexation or interaction studies were also supported by theoretical studies using DFT calculations on Gaussian 03W software. 4-(2,4-dinitrophenoxy)-3-methoxybenzaldehyde (SMR-1) and (4-(2,4-dinitrophenoxy)-3-methoxyphenyl)methanol (SMR-2) were investigated for their complexation behaviors with various cationic species (Na(I), K(I), Mg(II), Cu(II), Ba(II), Cr(III), Fe(III), Co(II), Ni(II), Zn(II), Cd(II) and Pb(II)) in HEPES buffered CH3CN:H2O system. Both receptors showed high degree of selectivity for Fe(III) over other cations. Electrochemically, SMR-1 facilitated reduction of nitro group due to the presence of electron withdrawing (carbonyl) group and peak potentials of the cathodic two curves (for SMR-1) appeared at -1.16 V (Epc1) and -1.39 V (Epc2) respectively. In SMR-2, due to electron donating character of the methanolic group made reduction of the nitro group a little difficult due to which peak potentials occur at higher potential as compared to SMR-1 i.e. at -1.30 V (Epc1) and -1.43 V (Epc2), respectively. SMR-1 and SMR-2 can be projected as Fe(III) chemosensors with no interference from any other metal ion. SMR-3 and SMR-4 were studied for their binding ability with some selected anions like fluoride, cyanide, acetate, bisulphate, etc. by spectrophotometric and voltammetric methods, supported by theoretical studies. Results of the study showed that SMR-3 has high selectivity for fluoride ions over other anions in the acetonitrile medium. More importantly, SMR-3 displays naked-eye detection of fluoride ions at room temperature with a linear response in the range 0.1 to 20 μM. SMR-15 molecule with ether-imine functional groups was analyzed for its interaction with different cations, anions and lanthanides. SMR-15 showed instant visual color change on addition of fluoride, cyanide and cobalt ions, which led to the study of interaction of SMR-15 with Co(II), F- and CN-. A sharp color change from light yellow to colorless was observed for CN− through a nucleophilic addition mechanism, while F− was detected through H-bonding mechanism with a distinct color change from light yellow to dark yellow. Co(II) was detected x

by formation of complex in pseudocavity in SMR-15 causing color change from yellow to blue. Paper strips of SMR-15 receptor were also prepared to detect the presence of Co(II), F- and CN-. SMR-15 was also studied for its interaction with various lanthanides and has been developed as a new sensitive and selective chemosensor for the determination of cerium ions. The proposed receptor works as an excellent receptor by spectrophotometry and voltammetric methods in CH3CN:H2O (95:5, v:v) solvent medium. Detection limit obtained by this sensor is 5×10-7 M without any interference in CH3CN:H2O medium, which makes it a potent sensor for cerium detection. SMR-16 with unique ether-imine combination was also analyzed for its binding behavior with various cationic species (Na(I), K(I), Ag(I), Cu(II), Ni(II), Ca(II), Mg(II), Pb(II), Cd(II), Li(II), Co(II), Zn(II), Hg(II), Fe(II), Al(III)) in CH3CN:H2O system. Observable color change from dark yellow to colourless was the first signalling system for the interaction of SMR-16 with Cu(II) ions. Binding constant calculted from UV-visible spectrophotometric studies was 2.0×105 M−1 and the detection limit obtained was 50 nM. Highlight of the work is ratiometric sensing of water content by SMR-16-Cu(II) complex in pure acetonitrile medium. Detection limit for the detection of water content in a medium was determined as low as 0.06 ppb. Electrochemically, SMR-16 showed a major anodic peak at 1.05 V and a cathodic peak at 0.95 V along with small peaks at 1.35 V (anodic peak) and 0.5 V (cathodic peak). The anodic and cathodic peaks were found shifted in presence of copper ions only. Chemosensor showed 1:1 complexation with Cu(II) ions by sandwitching two copper ions between two SMR-16 molecules as observed by theoretical studies as well. The optimized electrochemical method was successfully used for the detection of copper (II) ions from real samples. In addition to arylether molecules, zinc oxide nanoparticle coupled imine linkage based receptors (SNR-4, SNR-5 and SNR-6) were also studied for their electrochemical characteristics. SNR-4 and SNR-5 having electron withdrawing and electron donating substituents at meta-position of the imine linkage showed prominent cathodic (reduction of imine group) peaks at -0.930 V and -1.850 V, respectively, while SNR-6 (without any substituent) showed a cathodic peak at -1.220 V. Voltammograms of the receptors indicated that SNR-4 and SNR-5 responded quantitatively for aluminium ions, while SNR-6 responded for cobalt ions. All the three receptors exhibited a linear dynamic range between 0.1 μM to xi

0.42 μM with regression coefficients ≥0.98. The proposed analytical method has been validated with complexometric method for metal detection in real time samples. Further, Levofloxacin (LFX), an antimicrobial agent has also been determined by using picric acid (PA) as an anionic reagent in aqueous medium using voltammetric method. On mixing the reactants in distilled water, yellow colored product was separated within two minutes as an ion-association complex (LFX-PA) of both the reactants. Voltammetric studies were carried out to explain the interaction between levofloxacin and picric acid. In voltammetric experiments, a shift of 70 mV from that of LFX was noticed in an anodic peak of LFX-PA (1.64V) accompanied with a large decrease in peak current. In addition, a number of new peaks appeared in voltammogram of LFX-PA. A calibration curve was drawn using the peak current values of the LFX. The linear increase in peak current with increasing LFX concentration was obtained in the concentration range 1.5×10-3 M – 6.0×10-3 M with R2 = 0.994. A study on the solvent effect by voltammetric methods for LFX suggested that water is the best medium for the study. Stability of the complex was also determined by computational methods using DFT/B3LYP/6-31G basis sets. Further, analysis of LFX in commercially available drug tablets proved that the proposed method is valid in real life sample analysis.