R. Geetha Balakrishna

Chromones as a privileged scaffold in drug discovery: A review

The chromone and its derivatives are the most important heterocyclic compounds, which is a common and integral feature of a variety of natural products and medicinal agents. These heterocycles show a variety of pharmacological properties, and change of their structure offers a high degree of diversity that has proven useful for the search of new therapeutic agents. A large volume of research has been carried out on chromone and their derivatives, which has proved the pharmacological importance of this heterocyclic nucleus. The present review focuses on the pharmacological profile of chromone derivatives in the current literature with an update of recent research findings on this nucleus and the perspectives that they hold for future research.

Synthesis and Comparative Study of Nano‐TiO2 Over Degussa P‐25 in Disinfection of Water

Nanostructured TiO2 crystals were synthesized by gel to crystalline conversion. The crystals obtained were anatase form of titania averaging in 30 nm particles with an intrinsic band gap of 3.1 eV. The photocatalytic behavior was evaluated for the bactericidal effect in water, contaminated with the indicator organism Escherichia coli. The 100% photoinactivation of E. coli was achieved within 60 min with suspended nano‐TiO2. The catalytic activity of synthesized nanosample was observed to be 2.6 times more than that of commercial TiO2 sample referred to as Degussa P‐25. The photoinactivation of E. coli was tested with irradiation source of different wavelengths to substantiate the influence of particle size and nano crystallinity on electronic band structure. The photoactivity of nano titania enhanced to 1.625 times when the source of irradiation shifted from 360 to 400 nm while Degussa P‐25 showed no change.

Elucidation of cell killing mechanism by comparative analysis of photoreactions on different types of bacteria.

The mechanism of biocidal action of nano titania on Escherichia coli and Staphylococcus aureus has been evaluated by various biochemical techniques like lipid peroxidation, hydrolysis of orthonitrophenol β‐d‐galactopyranoside, estimation of protein–amino acid and bacterial nucleic acids leakage into solution, in addition to morphology studies by electron microscopy (TEM and SEM) and K+ ion leakage by inductively coupled plasma optical emission spectrometry. The active anatase phase of nano titania has been synthesized by sol‐gel and pulverization techniques to obtain particle sizes averaging around 11 nm. The nano semiconductor with a bandgap of 3.2 eV responds well to the UV source to liberate reactive oxygen species (ROS). Gram negative bacteria easily succumb to the ROS at a faster rate than gram‐positive bacteria with an observable difference in the mode of attack. The use of analytical techniques revealed the release of peroxidized lipid (26 nmol mL−1) and protein content (370 μg mL−1) with a K+ ion concentration of 22 000 ppb on complete destruction of E. coli.

Nanostructured binary and ternary metal sulfides: synthesis methods and their application in energy conversion and storage devices

Metal sulfides, known as being analogous to metal oxides, have emerged as a new class of materials for energy conversion and/or storage applications due to their low cost and high electrochemical activity. They have shown fascinating properties such as excellent redox reversibility, conductivity, and capacitance. Further, binary metal sulfides have gained enormous attention due to their large redox reaction sites and high electrical conductivity compared to metal sulfides. Recently, use of binary metal sulfides as electrode materials for various applications such as lithium-ion batteries (LIBs), supercapacitors (SC), and solar cells has been extensively studied by various research groups and this review critically overviews the strategies and advances made towards attaining high performances from these sulfides in an effort to provide leads for scale-up and to find long term solutions for energy and environment crisis. Finally, challenges in achieving superior performances and the future scope of research for metal sulfide based energy materials have been outlined.

Preparation and Characterization of Chitosan Thin Films on Mixed-Matrix Membranes for Complete Removal of Chromium.

Herein we present a new approach for the complete removal of CrVI species, through reduction of CrVI to CrIII, followed by adsorption of CrIII. Reduction of chromium from water is an important challenge, as CrIV is one of the most toxic substances emitted from industrial processes. Chitosan (CS) thin films were developed on plain polysulfone (PSf) and PSf/TiO2 membrane substrates by a temperature-induced technique using polyvinyl alcohol as a binder. Structure property elucidation was carried out by X-ray diffraction, microscopy, spectroscopy, contact angle measurement, and water uptake studies. The increase in hydrophilicity followed the order: PSf < PSf/TiO2 < PSf/TiO2/CS membranes. Use of this thin-film composite membrane for chromium removal was investigated with regards to the effects of light and pH. The observations reveal 100 % reduction of CrVI to CrIII through electrons and protons donated from OH and NH2 groups of the CS layer; the reduced CrIII species are adsorbed onto the CS layer via complexation to give chromium-free water.

Enhanced Bactericidal Activity of Modified Titania in Sunlight against Pseudomonas aeruginosa, a Water‐Borne Pathogen

Photocatalyst‐mediated inactivations generate reactive oxygen species and OH radicals, which induce oxidative destruction of membrane integrity, causing damage to membrane phospholipids of gram negative bacteria like Pseudomonas aeruginosa. Nanosized TiO2 was synthesized by gel to crystalline conversion and Zr‐doped TiO2 was synthesized by pulverization using appropriate precursor. The doped nanocrystals retained the anatase phase with a marginal increase in crystallite size, averaging at 25 nm. SEM–EDX analysis of the doped sample depicts the substantial growth of grain size with 1.33 atomic weight % of zirconium. The created electron states in the doped sample act as charge carrier traps suppressing recombination which later detraps the same to the surface of the catalyst causing enhanced interfacial charge transfer. Zr‐doped TiO2 at the molecular scale exhibits better photocatalytic activity with lower bandgap energy that can respond to visible light. The redshift caused by the dopants in absorption spectra of TiO2 facilitated the nonintrinsic sample to exhibit nearly 2‐fold enhancement of photoinactivation in sunlight. Extent of photoinactivation of P. aeruginosa was observed to be complete (100%) within 150 min of sunlight exposure in the presence of modified TiO2.

Photoactive titania float for disinfection of water; evaluation of cell damage by bioanalytical techniques.

A photoactive float was fabricated with the modified titania to cause a feasible disinfection of water, contaminated with E. coli. The commercially available titania was doped with neodymium by pulverization technique to enhance its activity in sunlight and a multiapproach technique was used to evaluate the extended efficiency of the doped sample. X‐ray diffraction patterns depicted the retention of anatase phase on doping and the existence of neodymium was confirmed by the energy dispersive atomic X‐ray analysis and the X‐ray photoelectron spectroscopy. Transmission electron microscopy and Bruner–Emmett–Teller analysis depicted a marginal increase in the particle size and a decrease in the surface area, respectively. Doping induces semiconductor behavior with lower band energy that could respond to visible light and exhibit better disinfection activity. The “f” and “d” transitions of the lanthanide in doped sample caused new electronic behavior of trapping/detrapping effect together with bandgap narrowing. The amount of malondialdehyde, protein, DNA and RNA released on destruction of E. coli was observed to be 0.915 × 10−3 μg mL−1, 859.912 μg mL−1, 20.173 μg mL−1 and 1146.073 μg mL−1, respectively. The above analytical methods along with standard plate count method substantiated the enhanced disinfection efficiency of the doped sample in sunlight.

Preparation and Characterization of High Activity Zirconium-Doped Anatase Titania for Solar Photocatalytic Degradation of Ethidium Bromide

Abstract Ethidium bromide is a fluorescent tag and is used in biomedical applications. It is a potent mutagen because of its DNA intercalating nature. A catalyst composition for the feasible elimination of ethidium bromide using a broad spectrum of solar radiation was investigated. Nanostructured anatase TiO2 was synthesized by gel to crystalline conversion and its bandgap was engineered by doping with zirconium to effectively harness sunlight. The doped nanocrystals were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis, and UV-Vis spectroscopy. The formed crystals retained the anatase phase with a marginal increase in size. The pulverization process used to dope Zr into titania resulted in a nano and doped lattice with an increased and extended light absorption range, which gave a nearly five-fold increase in photoactivity over pure titania. The catalytic effect of the modified titania, the dopant concentration, and the dynamics of the dopant concentration on the charge carriers (trapping-recombination) for the degradation of the mutagen was investigated. The modified titania is capable of total ethidium bromide elimination in sunlight. The loss of its mutagenic property was confirmed by an Ames test. The induced revertant colonies observed were nil in the treated sample indicating a complete loss of the intercalating property of the mutagen.

Novel modified poly vinyl chloride blend membranes for removal of heavy metals from mixed ion feed sample

Herein, an attempt has been made to prepare a novel membrane with good efficiency for removal of heavy metal ions namely lead (Pb), cadmium (Cd) and chromium (Cr). 4-amino benzoic acid (ABA) was covalently grafted onto the poly vinyl chloride (PVC) backbone by CN bond to enhance the hydrophilicity. 1H NMR and ATR-IR spectroscopy analysis confirmed the chemical modification of PVC. Further the modified polymer was blended in different compositions with polysulfone (PSf) for optimization. Morphological changes that occurred in blend membranes, due to the incorporation of modified PVC was studied by AFM and SEM techniques. The effect on hydrophilicity and performance of blends owing to incorporation of modified PVC was evaluated by water uptake, contact angle and flux studies. The density of functional groups in blends was analyzed by its ion-exchange capacity. Batch wise filtration of metal ions was carried out and the effect of pressure, feed pH and interference of ions was thoroughly investigated. Essentially, 100% rejection was obtained for all the metal ions in acidic pH with a productivity of 2.56l/m2h. The results were correlated with the results of commercially available NF 270 membrane under the same operating conditions.

Synthesis and characterization of novel sulfanilic acid–polyvinyl chloride–polysulfone blend membranes for metal ion rejection

Near-complete removal of heavy metals, namely Cd(II), Cr(VI) and Pb(II), has been attempted by a membrane purification process using a blend of modified polyvinyl chloride (PVC) and polysulfone (PSf), prepared by the diffusion induced phase separation (DIPS) method. The prepared novel material was characterized by NMR, ATR-IR spectroscopy and DSC. The sulphonyl groups incorporated into PVC enhance the hydrophilicity and are substantiated by water uptake, contact angle (CA) and flux studies. The obtained properties of the blend membrane like increased surface roughness and porosity are observed from AFM and SEM analysis. An enhanced rejection of ∼95% which is about 1.15, 1.41 and 1.37 times better than the commercially available NF 270 membrane was observed, for Cd(II), Cr(VI) and Pb(II) respectively. The work was further extended to study the antifouling property and the interference of other existing metal ions on the performance. An improved antifouling property with 98.5% rejection for bovine serum albumin (BSA) and a 75.6% flux recovery ratio (FRR) was achieved. The study gains significance in exploring the incorporation of sulphonyl groups in to polymers, to enhance membrane performance.