Harjeet D. Juneja

Chemical Speciation of Chromium in Water: A Review

The investigation of a groundwater resource impacted with Cr(VI) requires analysis of groundwater for Cr(VI) and total Cr. Most notably, Cr(III) is considered to be a trace element essential for the proper functioning of living organisms, whereas Cr(VI) may exert toxic effects on biological systems. The nature and behavior of various Cr forms found in wastewater can be quite different from those present in natural waters because of altered physicochemical conditions of the eluents originating from various industrial sources. The chromium content in surface waters is usually at the low μgL−1 level, typically between 0.3 and 6 μgL−1. Speciation of Cr(III) and Cr(VI) has been a longstanding analytical challenge. The selective determination of Cr(VI) is of particular importance because of its toxicity. Due to the importance of Cr(III) and Cr(VI), the accurate and sensitive determinations of these ions are the important part of the analytical chemistry. Chromium speciation is very important in different branches of natural sciences. Therefore, total chromium measurements alone cannot determine the actual environmental impact. This requires speciation techniques with sufficient selectivity and high sensitivity. Speciation of trace levels of chromium in water sample requires high-capacity separation and high sensitivity detection. The authors present a review of presently available analytical possibilities of chromium speciation investigations in water samples.

Chelate polymer compounds with bis(bidentate) ligand: synthesis, spectral, morphological and thermal degradation studies

Four divalent transition chelate polymer compounds (1–4) were synthesised by condensation of ibpmpc (isophthaoyl bis(paramethoxyphenylcarbamide)) with metal acetate in a dimethylformamide medium. The synthesised polymer compounds 1–4 were characterised by elemental analyses, FT-IR, diffuse reflectance, magnetic moment measurements and thermal studies. Each metal ion is coordinated through an oxygen atom of the carboxylate group and a nitrogen atom of the amide group of ligand and two aqua ligands by the coordinated bond which formed a six-member heterocyclic ring and significantly formed octahedral geometry for 1–3, whereas distorted octahedral geometry for 4. The thermal properties were studied by TG/DTG/DTA analyses. It was found that the thermal stabilities of polymer compounds follow the order: 4 > 3 > 1 > 2 Also, their physical properties including solubility, colour and melting point were studied, and the result showed insolubility in common organic solvents. Moreover, SEM and XRD studies were carri...

Computational evaluation and experimental in vitro antibacterial, antifungal and antiviral activity of bis-Schiff bases of isatin and its derivatives

A computational model has been developed for the rational design of bioactive pharmacophore sites as an antibacterial, antifungal and antiviral candidates based on available X-ray structures of bis-Schiff bases (Blagus et al., Maced J Chem Chem Eng 29:117–138, 2010; Nabei et al., Polyhedron 28:1734–1739, 2009; Zhang et al., Inorg Chem Commun 14:1636–1639, 2011; Zhong et al., Eur J Med Chem 41:1090–1092, 2006; Zhou et al., Inorg Chim Acta 359:1442–1448, 2006). A dozen of bis-Schiff bases 3–14 of isatin, benzylisatin and 5-fluoroisatin 1a–c were designed using this model. The compounds were screened for antibacterial, antifugal and antiviral activity against a panel of DNA and RNA viruses. The most potent of these compounds 8 and 11 was tested in viral cultures for their ability to present a potential (Oδ−–Nδ−) antiviral pharmacophore site. Compounds 8 and 11 were the most cytotoxic in HEL cells. All these synthesized bis-Schiff bases were also tested for their antibacterial and antifungal activities. They did not display activity against S. cerevisiae (ATCC 28383) or C. albicans (CIP 1180-79); may be because they did not have an antibacterial pharmacophore site (Xδ−–Yδ+). The best inhibitors tested in vitro against HIV-1 are genetically predisposed to be inhibited by similar pharmacophore sites. The results from all the aspects of this bioinformatic approaches are discussed as par with our experience with screening candidates.Graphical Abstract

Synthesis of new series of 3-hydroxy/acetoxy-2-phenyl-4H-chromen-4-ones and their biological importance

Abstract3-Hydroxy-2-aryl/heteroaryl-4H-chromones 4(a–n) were synthesized from appropriate chalcones 3(a–n) and acetylated to afford the corresponding acetoxy derivatives 5(a–n). All compounds were evaluated for antimicrobial activity against Staphylococus aureus, Bacillus subtillis, Escherichia coli and Pseudomonas aeruginosa as well as fungi e.g., Candida albicans and Aspergius niger. Inhibition caused by hydroxy flavones was relatively low, whereas that of their acetoxy ester analogues was substantially high. Structure of 6-chloro-2-(furan-2-yl)-4-oxo-4H-chromen-3-yl acetate (5j) was also supported by means of single crystal X-ray diffraction. Graphical AbstractAn effective microwave-assisted synthesis of 3-acetoxy-2-aryl/heteroaryl-4Hchromones 5a-n has been achieved through a series of reactions starting from phenols. These compounds have been screened against gram (+) ve and (-) ve bacteria. The acetoxy flavones were biologically more active than the corresponding hydroxyflavones.

Evaluation of kinetic parameters from TG/DTG data of chelate polymer compounds of isophthaoyl bis (paramethoxyphenylcarbamide)

The four divalent transition metal chelate polymer compounds such as {[Mn (ibpmpc)(H2O)2] 2H2O}n, {[Co (ibpmpc)(H2O)2] 2H2O}n, {[Ni (ibpmpc)(H2O)2] 3H2O}n and {[Cu (ibpmpc)(H2O)2] 2H2O}n (ibpmpc = isophthaoyl bis (paramethoxyphenylcarbamide) were characterized by thermal properties. The thermal properties like decomposing temperature, thermal stability and presence of hydration water were studied by thermogravimetry (TG), differential thermal gravimetry (DTG) and differential thermal analysis (DTA) and the decomposition steps of these four chelate polymer compounds were investigated. The kinetic and thermodynamic parameters such as the pre-exponential Arrhenius factor (A), order of reaction (n), activation energy (Ea), activation entropy (ΔS#), activation enthalpy (ΔH#) and activation free energy (ΔG#) were calculated using Chen–Liu method. On the basis of thermal analysis technique and thermodynamic kinetic parameter studies, the thermal stability of chelate polymer compounds follows the order Cu (II) > ...

Synthesis, characterization and thermal properties of phthaloyl bis (paramethoxyphenylcarbamide) chelate polymers of divalent transition metals

Seven novel divalent transition metal chelate polymer complexes commonly known as coordination polymers or chelate polymers or coordination complexes such as [Mn (pbpmpc) (H2O)2]n (1), {[Co(pbpmpc) (H2O)2] 4H2O}n (2), {[Ni (pbpmpc) (H2O)2] 2H2O}n (3), {[Cu (pbpmpc) (H2O)2] 1H2O}n (4), {[Zn (pbpmpc)]}n (5), {[Cd (pbpmpc)]}n (6) and {[Hg (pbpmpc)] 1H2O}n (7) were synthesized under an aprotic solvent with phthaloyl bis (paramethoxyphenylcarbamide) (pbpmpc) as a polydentate ligand. The authenticities of these chelate polymers were characterized by elemental analyses: diffuse reflectance spectroscopy, magnetic susceptibility measurements, Fourier transform infrared (FT-IR), X-ray diffraction (XRD), thermal analyses and scanning electron microscope (SEM) techniques. SEM and XRD investigations significantly revealed a distinct morphology behavior of ligand and chelate polymers. The infrared spectroscopy supports the interaction of nitrogen and oxygen atoms of a polydentate ligand with a metal ion, while diffuse reflectance study is a powerful technique that suggests an octahedral geometry for all the chelate polymers except zinc, cadmium and mercury ions, which were further supported by other instrumental techniques. The decomposition steps and thermal stabilities of these chelate polymers were studied by thermal analysis techniques. The thermal stabilities of chelate polymers were identified on the basis of release of coordinated water and decomposition of backbone structure (ligand).

SYNTHETIC AND THERMAL STUDIES OF POLYMERIC CHELATES OF SOME BIS-BIURETS WITH FIRST TRANSITION SERIES METALS

Some new coordination polymers have been synthesized by combining adipyl bis-biuret and azelyl bis-biuret with metals of first transition series viz Mn(II), Co(II), Ni(II), Cu(II) and Zn(II). They were characterized by elemental analysis, infrared and reflectance spectral and magnetic studies. A detailed thermal study was carried out and thermal stability compared. The results obtained have been discussed.

Copper nanoparticles catalysed an efficient one-pot multicomponents synthesis of chromenes derivatives and its antibacterial activity

ABSTRACT In this study, copper nanoparticles (Cu NPs) were synthesised by using diethylenetriamine as a protective agent in chemical reduction method. The obtained nanoparticles were characterised by various spectroscopic techniques like powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR), UV–visible spectroscopy, energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermal analysis (TG/DTA). The structure and composition were estimated by PXRD, FTIR, EDS, UV–visible and TG/DTA techniques, while particles size and morphology behaviours were investigated by SEM and TEM instrumentation. A noteworthy, average particle size of nanoparticles was found around 40 nm with spherical shapes. Furthermore, the applications part of NPs were studied as a catalyst for one-pot solvent-free green synthesis of 3,4-dihydropyrano[c]chromenes from different aromatic aldehydes, malonitrile and 4-hydroxycoumarin by stirring at 80 °C. Moreover, the antibacterial properties of NPs were assessed in vitro against human bacterial pathogen such as Staphylococcus aureus, Escherichia coli, Klebsiella sp. and Pseudomonas aruginosa using agar well diffusion method. Gram positive bacteria S. aureus (18 mm) exhibited a maximum zone of inhibition at 60 µg/ml of Cu NPs. Nonetheless, antibacterial activities of Cu NPs (10–100 µg) were compared with four well-known antibiotics likes amikacin (30 mcg), ciprofloxacin (5 mcg), gentamicin (5 mcg) and norfloxacin (10 mcg). This study indicates that Cu NPs exhibited a strong antibacterial activity against all the test pathogens even at lower concentration.

Synthesis, antibacterial screening, and POM analyses of novel bis-isoxazolyl/pyrazolyl-1,3-diols

This research article reports the synthesis of 4,6-bis(5-aryl/heteroaryl-1,2-oxazol-3-yl)benzene-1,3-diol 4a–4f and 4,6-bis(5-aryl/heteroaryl-1H-pyrazol-3-yl)benzene-1,3-diol 5a–5f from 1,1′-(4,6-dihydroxybenzene-1,3-diyl)bis(3-aryl/heteroarylpropane-1,3-dione) 3a–3f. The compounds were fully characterized using spectroscopic analyses and tested for their antibacterial activity. A correlation of structure and activities relationship of these compounds with respect to molecular modeling, Lipinski rule of five, drug likeness, toxicity profiles, and other physico-chemical properties of drugs are described and verified experimentally.Graphical AbstractThis article reports the synthesis of bis-isoxazoles 4a–4f and bis-pyrazoles 5a–5f. A good correlation of structure and activities relationship of these compounds with respect to molecular modeling, Lipinski rule of five, drug likeness, toxicity profiles and other physico-chemical properties of drugs are described and verified experimentally.

Outstanding effect of the conformational restriction of isoquinolines: hints for the development of optimized antimicrobial agents

Conformational restriction constitutes a useful strategy of molecular modification for the design of new potential drug candidates. Herein we present the planning, antimicrobial evaluation, and establishment of structure–activity relationship (SAR) data for some isoxazole (3a–k, 8a–c, and 9a–c) and pyrazole (5a–h) derivatives. These derivatives were structurally designed by conformational restriction followed by bioisosteric exchange of previously described antimicrobial isoquinolines (1a–c). Some of these more conformationally restricted derivatives present improved properties as new antibacterial drug candidates.