S. K. Ashok Kumar

Viologen substituted anthrone derivatives for selective detection of cyanide ions using voltammetry

Electrochemical behavior of anthrone derivatives 1 (1-(2,7-dioxo-3,7-dihydro-2H-naphtho[1,2,3 de]quinolin-1-yl)-1′-heptyl-4,4′-bipyridine-1,1′-diium) and 2 (1-(2,7-dioxo-3,7-dihydro-2H-naphtho[1,2,3-de]quinolin-1-yl)-[4,4′-bipyridine]-1-ium functionalized with viologen group are inspected extensively using cyclic voltammetry. Colorimetric studies indicate their selectivity towards anions like cyanide, acetate and fluoride. Cation selectivity of anthrone derivative changes to anions because of the viologen group. Anthrone derivative stabilizes viologen through conjugation, reducing one of its two redox couples which are characteristic of viologen group for molecule 1. Mechanisms are proposed and supported by theoretical studies carried out using Guassian 03W for the electrochemical behaviour of compounds 1 and 2. Voltammograms of dicationic viologen derivative 1 show near quenching of anodic peaks (a decrease of almost 90% of current) as well as cathodic peaks (a decrease of almost 100% current) in the presence of 1 equivalent of cyanide ions. The molecule 2 undergoes quenching of the cathodic peak while anodic peak survives in the presence of the anions, cyanide, acetate and fluoride. The proposed electrochemical sensors are selective for CN−, OAc− and F− based on binding constants which are much larger than for anions like Cl−, Br−, I−, HSO4−. The proposed voltammetric method for the cyanide determination is compared with potentiometric and spectrophotometric methods for cyanide determination. The proposed voltammetric method has also been used for quantitative determination of cyanide in unknown samples.

Pyridoxal-thiosemicarbazide: its anion sensing ability and application in living cells imaging

A new anion selective chemosensor L was derived through a direct condensation reaction between pyridoxal and thiosemicarbazide. Sensor L showed selective recognition and sensing ability towards F− and AcO− anions through a naked-eye detectable color change from colorless to light yellow, appearance of a new charge transfer absorption band at 404 nm and significant “turn-on” fluorescence at 506 nm. The detection limit of L as a fluorescent ‘turn-on’ sensor for the analysis of F− and AcO− was estimated to be 0.10 μM. The anion sensing mechanisms of L was supported by 1H NMR and DFT results. Finally, the cytotoxicity effect of L and its ability to image intracellular F− ions in the living HeLa cells was investigated.

Chemically modified cellulose strips with pyridoxal conjugated red fluorescent gold nanoclusters for nanomolar detection of mercuric ions

One-pot approach was adopted for the synthesis of highly luminescent near-infrared (NIR)-emitting gold nanoclusters (AuNCs) using bovine serum albumin (BSA) as a protecting agent. The vitamin B6 cofactor pyridoxal was conjugated with the luminescent BSA-AuNCs through the free amines of BSA and then employed for the nanomolar detection of Hg2+ in aqueous medium via selective fluorescence quenching of AuNCs. This nano-assembly was successfully applied for the real sample analysis of Hg2+ in fish, tap water and river water. The study also presents chemically-modified cellulosic paper strips with the pyridoxal conjugated BSA-AuNCs for detecting Hg2+ ion up to 1nM.

Nanoscale materials as sorbents for nitrate and phosphate removal from water

Excessive nitrogen (N) and phosphorous (P) release into run-off waters from human activities is a major cause of eutrophication. Several techniques are available to remove N and P-containing pollutants, such as chemical precipitation, biological treatment, membrane processes, electrolytic treatment, ion-exchange and adsorption. In order to remove low concentration levels of nitrate and phosphate, adsorption is a cost-effective solution. In this review, we present a list of nanoscale adsorbents such as zero-valent metal, metal oxides/metal hydroxides, and carbon-based materials. We discuss their adsorption capacities, isotherms, kinetics and mechanisms.

Function of substituents in coordination behaviour, thermolysis and ligand crossover reactions of phosphine oxides

Some selected aminophosphine oxides (AmPOs) of the type OP(NMe2)3, OPPh(NMe2)2, OP(NC2H4O)3, OPPh(NC2H4O)2 and their corresponding La(III) and Th(IV) complexes are synthesized and analyzed by FT-IR, 1H-NMR, 31P{1H}-NMR, elemental analysis and TGA data. The coordination behavior of AmPOs was compared with some of the known ligands that include trioctylphosphine oxide (TOPO), tributylphosphate (TBP) and diethylphosphite (DEP). Thermogravimetric analysis of these complexes showed a distinct decomposition trend either by a single step or multi-step elimination of ligand species, which are strongly dependent on the electronic and steric behaviour of substituents on the PO group and the nature of the metal. Phosphine oxide based La(III) and Th(IV) complexes undergo three unique intermolecular ligand exchange reactions at room temperature: relative competition among phosphine oxides to form a strong complex by exchanging the weaker ligand and complete ligand transfer from La(III) to Th(IV) metal centers. Ligand crossover is well controlled by priority rules and the trend is TOPO > TBP > DEP > AmPO > Ph3PO. This tendency closely agrees with the stability constants of metal complexes. On comparison, Th(IV) complexes showed slightly higher stability than La(III) analogues.

Highly efficient performance of activated carbon impregnated with Ag, ZnO and Ag/ZnO nanoparticles as antimicrobial materials

A simple and efficient route for the synthesis of Ag, ZnO and Ag/ZnO nanostructures impregnated on highly porous activated carbon (AC) was developed. The antibacterial activities of AC, Ag–AC, ZnO–AC and Ag/ZnO–AC nanohybrids were evaluated against Gram negative and Gram positive bacteria by the disc diffusion method. Among the four nanostructures, we found that Ag/ZnO–AC exhibited the highest zone of inhibition, killing kinetics and post agent effect compared to the other nanohybrid materials. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the Ag/ZnO–AC nanohybrid against standard reference cultures were found to be 0.20 mg ml−1 with E. coli and 0.30 mg ml−1 with S. aureus while MBC was found to be 0.35 mg ml−1 with E. coli and 0.6 mg ml−1 with S. aureus. The killing kinetics (3 log10 decrease in 5 h) and post agent effect (2.45 h) were conducted only with E. coli. The Ag/ZnO–AC nanohybrid material showed the highest antimicrobial activity on selected microorganisms and the order of antibacterial activity was AC < ZnO–AC < Ag–AC < Ag/ZnO–AC.

A novel method for the determination of individual lanthanides using an inexpensive conductometric technique

A new conductometric titration method is established to determine quantitatively lanthanide ions (Lns) using ethylenediaminetetraacetic acid (EDTA) as a ligand and α-hydroxy isobutyric acid (α-HIBA) as a co-ligand. The detection limit of Ln(III) ions was found to be 1 × 10−5 M using a 5-ring conductivity sensor of cell constant 0.774 cm−1. The proposed method is tested for selective determination of individual lanthanides in the presence of interfering ions like selected alkali, alkaline earth, and transition metal ions. The method does not suffer from interference from any of these species. A mechanism for selective detection by conductometry is given. Gd(III) determination is verified with the spectrophotometric method.

Selective Removal of Nitrate and Phosphate from Wastewater Using Nanoscale Materials

Excessive nitrogen (N) and phosphorous (P) release into runoff from human activities is a major cause of eutrophication, which degrades freshwater and ecosystems. Phosphate and nitrate pollutants can be removed by chemical precipitation, biological treatment, membrane processes, electrolytic treatment, ion-exchange and adsorption process to remove these pollutants from water sources effectively. Adsorption is a cost-effective solution for efficient nitrate and phosphate ions removal. In this review various nanoscale adsorbents such as zero-valent metal, metal oxides, functionalized materials and carbon-based materials are surveyed. Their adsorption capacities under various conditions are compared.

A new Al 3+ selective fluorescent turn-on sensor based on hydrazide-naphthalic anhydride conjugate and its application in live cells imaging

In this communication, we have developed an optical chemosensor 2-amino N-(6-bromo-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)benzamide (NAPH) for selective detection of Al3+ by reacting 4-bromo-1,8-naphthalic anhydride with 2-aminobenzohydrazide. In (DMSO:H2O, 1:1, v/v) medium, the selective and specific nature of NAPH towards Al3+ was observed by the quenching along with a blue-shift in the absorption of NAPH at 465 nm that resulted in the distinct colour change from light brown to colourless. The selective complexation that occurred between NAPH and Al3+ was investigated by 1H NMR and DFT methods. Under similar conditions, the weakly fluorescent receptor NAPH showed a distinct fluorescence enhancement at 555 nm in the presence of Al3+ among the other tested metal ions and anions. The NAPH·Al3+ complex formation is reversible upon addition of strong chelating agent EDTA. The receptor NAPH can be applied to detect Al3+ down to 2.9 μM without any interference from other tested metal ions. In addition, the receptor NAPH was successfully applied to detect Al3+ in live HeLa cells.

Highly selective iodide sensing ability of an anthraquinone-derived Schiff base in semi-aqueous medium and its performance in antioxidation, anti-inflammation and HRBC membrane protection

In this study, a new iodide (I−) ion selective chromogenic receptor (3) was developed by reacting 9,10-anthraquinone with 2,4-dinitrophenylhydrazine. The sensing ability of the receptor 3 was studied with different anions such as F−, Cl−, Br−, I−, HSO4− and H2PO4− through naked-eye detection and UV-Vis spectroscopy in pure THF and mixed THF : H2O (1 : 1, v/v) media. In semi-aqueous medium, the receptor 3 showed a strong absorption band at 420 nm due to the presence of donor and acceptor units that resulted in an intense ligand-to-ligand charge-transfer (LLCT). Upon the interaction with I−, the receptor 3 showed a selective colour change from yellow to dark blue along with the formation of a new UV-Vis band at 615 nm. The absorption spectral studies indicate the formation of a complex between the receptor 3 and the I− ion with an estimated association constant of 1.37 × 104 M−1. The binding interaction of the receptor 3 with I− was examined by using 1H NMR, FTIR and density functional theory (DFT) calculations. The receptor 3 can detect I− at the concentration as low as 2.7 μM without any interference from other tested anions. Additionally, the pharmacological significance of the receptor 3 was explored. The receptor exhibited COX-2 inhibition of 70.18%, antioxidant activity of 73.42% and HRBC membrane protection ability of 67%.