Aamir Hassan Shah

Synthesis, pH dependent photometric and electrochemical investigation, redox mechanism and biological applications of novel Schiff base and its metallic derivatives

A novel Schiff base, 1-((2, 4-dimethylphenylimino)methyl)naphthalen-2-ol abbreviated as (HL) and its four metallic complexes were synthesized and confirmed by 1H and 13C NMR, FTIR, TGA and UV-Visible spectroscopy. Schiff base was also characterized by X-ray analysis. The photometric and electrochemical responses of all the synthesized compounds were investigated in a wide pH range. Structures of the compounds were optimized computationally for the evaluation of different physico-chemical parameters. On the basis of electrochemical results the redox mechanistic pathways of the compounds were proposed. The cytotoxicity analysis on Hela cells revealed that HL and its complexes inhibit cell growth as revealed from their IC50 values (HL):106.7μM, (L2VO): 40.66μM, (L2Sn): 5.92μM, (L2Zn): 42.82 and (L2Co): 107.68μM. The compounds were tested for anti-diabetic, triglyceride, cholesterol, anti-microbial, anti-fungal and enzyme inhibition activities. The results revealed that HL and its complexes are promising new therapeutic options as these compounds exhibit strong activity against cancer cells, diabetics, fungal and microbial inhibition.

pH-dependent redox mechanism and evaluation of kinetic and thermodynamic parameters of a novel anthraquinone

The redox behavior of 1,4-dihydroxy-2-(3-hydroxy-3-(trichloromethyl)pentyl)-8-methoxyanthracene-9,10-dione (HCAQ) was investigated at a glassy carbon electrode over a wide pH range of 3–12 by using cyclic, square wave and differential pulse voltammetry (CV, SWV and DPV). CV results of HCAQ obtained at different temperatures were used for the evaluation of thermodynamic parameters like ΔG#, ΔH# and ΔS#. The values of diffusion coefficient and heterogeneous electron transfer rate constant were also determined by CV. Limits of detection and quantification were determined by SWV. The numbers of electrons and protons involved in the oxidation processes were evaluated by DPV. The value of apparent acid dissociation constant (pKa) was obtained from the intersection of two linear segments of the Ep vs. pH plot. The effect of pH on the UV-visible spectral response was also monitored which allowed the determination of pKa of HCAQ. The values of apparent acid dissociation constant obtained from electrochemical techniques and electronic absorption spectroscopy were found to be in very good agreement. On the basis of experimental results, a pH-dependent oxidation mechanism was proposed in order to provide useful insights into the unexplored pathways by which anthraquinones exert their biochemical action.

Thiamine-functionalized silver nanoparticles for the highly selective and sensitive colorimetric detection of Hg2+ ions

Hg2+ contamination is a serious threat to the environment; hence, the development of methods for its trace level detection is urgently required. To contribute in this domain, we report for the first time the application of a highly sensitive and selective colorimetric sensing platform for Hg2+ ions using thiamine-functionalized silver nanoparticles (Th-AgNPs). Upon the addition of Hg2+ ions to the solution, the AgNPs exhibited a noticeable color change from yellow to violet-blue. This color change was monitored by the UV-vis spectrophotometric observation of a significant decrease in the absorption band at 395 nm along with the appearance of a new peak at 550 nm. The designed sensor demonstrated good sensitivity in the concentration range of 1 × 10−8 to 5 × 10−6 M with a detection limit of 5 nM. The sensor also showed high selectivity for Hg2+ when tested in the presence of several competing metal ions. Moreover, the method was found to be applicable to river water samples with satisfactory percentage recoveries.

Biological activity, pH dependent redox behavior and UV-Vis spectroscopic studies of naphthalene derivatives

Two naphthalene derivatives, naphthalene-2,3-dicarboxylic acid (NDA) and 1,8-dimethoxynaphthalene (DMN) were screened for antioxidant and anti-diabetic activities. Biological antioxidant studies revealed NDA as more effective antioxidant as compared to DMN. Both compounds significantly increased the cholesterol level but showed varied biological activities as regards glucose and triglyceride concentrations. The cytotoxicity results evidenced DMN to significantly inhibit the cell proliferation in a dose dependent manner with IC₅₀ of 0.13 mM. Like the biological antioxidant studies, the electrochemical results also witnessed NDA as stronger antioxidant than DMN. The pH dependent spectrophotometric and electrochemical behavior was investigated in order to provide useful mechanistic insights about the biological role of the selected compounds.