Raghubir Singh

Schiff base tailed silatranes for the fabrication of functionalized silica based magnetic nano-cores possessing active sites for the adsorption of copper ions

One pot fabrication of functionalized magnetite nanoparticles using Schiff base tethered silatranes as modifiers is reported. In this work a new Schiff base functionalized silane and the corresponding silatrane were synthesized by the condensation of 2-hydroxy-4-methoxybenzophenone with 3-aminopropyltriethoxysilane and -silatrane, respectively. The latter was purified by convenient recrystallization. Thus, the silatrane, which was characterized by elemental analysis, spectroscopic techniques and single crystal X-ray diffraction, was used as a modifier to functionalize magnetite nano-cores to introduce active lone-pair donor systems on their surface. The Schiff base functionalized magnetite nano-particles were characterized by Powder X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Vibrating Sample Magnetometry (VSM). These studies revealed superparamagnetic nanoparticles of polydispersed spherical shape. Although functionalization of the nano-cores introduces some organic moieties onto the surface, some properties of the nano-particles have not been altered significantly, i.e. their magnetic nature, spherical shape and XRD patterns were retained even after the modification. Moreover, Langmuir adsorption isotherm measurement revealed that the Schiff base functionalized nanoparticles possess better adsorption capacity for copper ions (0.207 mmol g−1) as compared to magnetite nanocores coated with silica (0.141 mmol g−1). The Schiff base functionalized magnetic nanomaterial can be used for the adsorption of copper ions without interferences because the adsorption remained unaffected in the presence of other metal ions up to certain limits.

Development of molecularly imprinted microspheres for the fast uptake of 4‐cumylphenol from water and soil samples

Molecularly imprinted microspheres containing binding sites for the extraction of 4-cumylphenol have been prepared for the first time. The imprinted microspheres were synthesized by a precipitation method using 4-cumylphenol as a template molecule, methacrylic acid as a functional monomer and divinylbenzene-80 as a cross-linker for polymer network formation. The formation and the morphology of molecularly imprinted microspheres were well characterized using infrared spectroscopy, thermogravimetric studies, and scanning electron microscopy. The Brunauer-Emmett-Teller analysis revealed the high surface area of the sorbent indicating formation of molecularly imprinted microspheres. The developed microspheres were employed as a sorbent for the solid-phase extraction of 4-cumylphenol and showed fast uptake kinetics. The sorption parameters were optimized to achieve efficient sorption of the template molecule, like pH, quantity of molecularly imprinted microspheres, time required for equilibrium set-up, sorption kinetics, and adsorption isotherm. A standard method was developed to analyze the sorbed sample quantitatively at 279 nm using high-performance liquid chromatography with diode array detection. It was validated by determining target analyte from synthetic samples, bottled water, spiked tap water, and soil samples. The prepared material is a selective and robust sorbent with good reusability.

Imprinted silica nanoparticles coated with N‐propylsilylmorpholine‐4‐carboxamide for the determination of m‐cresol in synthetic and real samples

m-Cresol-imprinted silica nanoparticles coated with N-propylsilylmorpholine-4-carboxamide have been developed that contain specific pockets for the selective uptake of m-cresol. Silica nanoparticles were synthesized by a sol-gel process followed by functionalization of their surface with N-propylsilylmorpholine-4-carboxamide. The formation of m-cresol-imprinted silica nanoparticles was confirmed by UV-Vis spectrophotometry, infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy. Electron microscopic studies revealed the formation of monodispersed imprinted silica nanoparticles with spherical shape and an average size of 83 nm. The developed nanoparticles were filled in a syringe and used for the extraction of m-cresol from aqueous samples followed by quantification using high-performance liquid chromatography with diode array detection. Various adsorption experiments showed that developed m-cresol-imprinted silica nanoparticles exhibited a high adsorption capacity and selectivity and offered a fast kinetics for rebinding m-cresol. The chromatographic quantification was achieved using mobile phase consisting of acetonitrile/water (70:30 v/v) at an isocratic flow rate of 1.0 mL/min using a reversed-phase C18 column and detection at λmax = 275 nm. The limits of detection and quantification were 1.86 and 22.32 ng/mL, respectively, for the developed method. The percent recoveries ranged from 96.66-103.33% in the spiked samples. This combination of this nanotechnique with molecular imprinting was proved as a reliable, sensitive and selective method for determining the target from synthetic and real samples.

Fluorescent biogenic Schiff base compounds of dimethyltin

Herein, biologically crucial amino acids have been explored for the synthesis of fluorescent organotin compounds. One-pot reaction of dimethyltin oxide, 2-hydroxy-4-methoxybenzophenone and α-amino acids, i.e., glycine, L-isoleucine and L-methionine, afforded respective organotin compounds with biogenic Schiff base skeletons 1–3. Although all the compounds were constituted from similar ONO type Schiff base units, only compound 1 (derived from glycine) crystallized as a hexacoordinated organotin compound of the type (ONO)SnMe2(MeOH) with a tridentate chelating Schiff base ligand. Analogous syntheses with L-isoleucine and L-methionine did not afford the related Schiff base compounds 2 and 3. Instead, some kind of precursors, namely 2′ and 3′, crystallized as solvent mediated Sn4O4 ladders and two Schiff base ligand moieties bound to the terminal Sn atoms via carboxylate moiety only. Interestingly, solution NMR spectroscopy (1H, 13C, 119Sn) of 1 unambiguously complied with its solid state structure while for 2′ and 3′ the behaviour was entirely different suggesting their transformation to mononuclear compounds 2 and 3 in solution phase. The distinctive structural aspects of 2′/2 and 3′/3 in solid and solution phase were also supported by solid state 119Sn CP/MAS NMR studies. All the compounds were found to be fluorescent when excited at 365 nm and the solutions of compound 3′ experienced quenching in the presence of paramagnetic metal ions due to chelation enhanced quenching.

Recent Progress, Challenges and Prospects in Monitoring Plastic-Derived Xenoestrogens Using Molecularly Imprinted Sorbents

Indoor and outdoor exposure to plastic-derived xenoestrogens, such as phthalates and phenolic compounds, can adversely affect endocrine and reproductive systems in humans and wildlife. To accomplish the extraction of plastic-derived xenoestrogens from environmental samples, molecularly imprinted polymers (MIPs) have been proved to be selective, efficient, and reliable sorbents. Despite some problems associated with the use of MIPs as sorbents, these have been found to be of considerable interest due to their advantages of selectivity, easy synthetic procedures, and better stability over commercially available solid sorbents. Modifications in their synthetic strategies are continuously in progress and new approaches are being made through graphene oxide substrates, nanostructured platforms, nanoferrites, cryogels, and co-electropolymerization to design better sorbents. Apart from this, efforts to create molecularly imprinted solid phase microextraction (SPME) fibers have also been successful in improving the efficiency of the methodology. In future, the use of MIPs developed from advanced synthetic strategies, or as sorbents for more robust techniques like SPME and microextraction on packed sorbents, will add new horizons to explore the potential of MIPs in the field of plastic-derived xenoestrogens. This review presents various challenges, as well as progress and prospects associated with the extraction of plastic-derived phthalates and phenolic compounds using molecularly imprinted sorbents.

Exploration of solvent responsive Cr 3+ -Schiff base conjugates formonitoring Cr 3+ ions and organophosphates: Fabrication of spot-testingdevices

Herein, we report 2-((2-hydroxybenzylidene)hydrazono)(phenyl)methyl)-5-methoxyphenol (SB) synthesized by Schiff base condensation and characterized by spectroscopic techniques, elemental analysis and X-ray crystallography. In solution phase, it interacts with Cr3+ ions and exhibits a prominent fluorimetric switch due to the formation of SB·Cr3+ conjugate. The dual behavior of SB·Cr3+ conjugates i.e. self-aggregation in high water fraction (fw > 50%) and dissolution in low water fraction (fw < 50%) proves this conjugation excellent tool for monitoring Cr3+ ions. The SB·Cr3+ conjugate in methanol-water (70:30 v/v) allows quantification of Cr3+ ions with limit of detection 0.44 μM and its self-aggregation in high water fraction facilitates extraction of Cr3+ ions with 95% extraction efficiency. Although SB interacts with Zn2+ ions which causes inference in the determination of Cr3+ ions however the interferent can be easily masked with SCN- ions. Besides, the SB·Cr3+ conjugates are also able to quantify organophosphate neurotoxins; i.e. diethyl chlorophosphate (with LOD 4.1 nM) and diethyl cyanophosphonate (with LOD 3.3 nM) from aqueous solutions. Moreover, SB and SB·Cr3+ conjugates can be coated on solid surfaces to fabricate portable devices for the on-spot detection of targets from real samples. Hence, the conjugation of Schiff base and Cr3+ ions can be explored for the recognition, quantification and extraction of Cr3+ ions and detection of organophosphates.

Exploration of fluorescent organotin compounds of α-amino acid Schiff bases for the detection of organophosphorous chemical warfare agents: quantification of diethylchlorophosphate

Herein, fluorescent di-methyltin(IV) compounds (1–4) of an azomethinic ligating system derived from the template assisted condensation of α-amino acids (i.e.L-alanine, L-leucine, L-glutamine, and L-isoleucine) and 2-hydroxybenzaldehyde are reported. The synthesized di-methyltin derivatives were characterized using FT-IR spectroscopy, multi-nuclei NMR (1H, 13C and 119Sn) spectroscopy, mass spectrometry and single crystal X-ray diffraction. The compounds 1–4 exhibited fluorescence emission centred at 470 nm when excited at a wavelength of 380 nm. The emission band experienced quenching in the presence of various organophosphates, therefore, a representative compound was explored for the fluorogenic chemo-sensing of various organophosphates. The fluorescence response was found to be maximum for diethylchlorophosphate (a potential mimic of chemical warfare agents) and offered detection up to 0.023 mM. To explore the practicality of the test compound, it was successfully incorporated into portable devices of variable designs, such as fluorescent strips and silica tablets, for the on-the-spot detection of chemical warfare agents.

Molecular Cloning and Characterization of Microneme Gene 10 (MIC10) of Kolkata Isolate of Toxoplama gondii

The present study dealt with cloning and molecular characterization of MIC10 gene of T. gondii Kolkata isolate. TgMIC10 is a small microneme protein that lacks a putative transmembrane domain and appears not to remain associated with the parasite membrane after micronemal discharge. MIC10 gene of T. gondii “Kolkata isolate was PCR amplifi ed and cloned into a TA cloning vector (Promega) to facilitate sequencing and subsequent characterization. The product revealed 597bp in size and has 99.2% homology with the published sequence. The difference was observed at 22, 210, 235, 378 and 513 positions. When the gene was deduced for amino acids, the homology was 98% with published sequence. The total amino acids number was 198 with predicted mass of 23 kDa molecular weight. The changes were observed at 8, 115 and 171th amino acid positions.