Kamalika Sen

Poly(ethylene glycol) vesicles: self-assembled site for luminescence generation.

Fluorescence in poly(ethylene glycol) (PEGs 400-12000) solutions is reported here for the first time. PEG solutions form a vesicular organization with the hydrophilic groups attached at both ends which arrange themselves beyond a particular concentration and offer electron-dense regions at the center of the vesicle. These vesicles provide an inherent site for fluorescence generation in PEG solutions. Fluorescence emission was observed at ~380 nm with an excitation wavelength of 300 nm. PEG of molecular weight 6000 was found to show maximum emission intensity at a particular concentration. The formation of PEG vesicles (~1 nm size) was confirmed by dynamic light scattering (DLS) and confocal laser microscopy. On addition of metal ions the polymeric vesicle breaks up to monomeric PEG, and hence, the fluorescence intensity decreases with a red shift. Fluorescence lifetime measurements indicate the nature of complexation of the metals with PEG. Since PEGs are used as one of the phases in aqueous biphasic systems (ABS) of liquid-liquid extractions, the nature of the fluorescence emission spectrum of the PEG phase after extraction was studied. Metal extraction in the PEG-rich phase of an ABS leads to quenching of fluorescence in PEG.

Impact of pH and temperature on phase diagrams of different aqueous biphasic systems

The phase diagrams of aqueous biphasic systems impart a distinct idea regarding the feasibility of biphase formation by different water soluble substances at their optimum concentrations. Depending on nature of the components viz., the water soluble polymers, surfactants, salts, amino acids or ionic liquids, a general trend of the biphase formation with varying temperature, pH and concentration has been studied over the recent years. This critical review is an endeavor to assess the general trends of these phase forming components to form biphasic systems with varying conditions of temperature and pH in light of the reported phase diagrams. Suitable explanations for the mechanisms of such behavior have been sorted out. The avenue yet to be explored has been addressed as these systems have a tremendous potential to be the future platform to solve different analytical issues.

Studies on stabilities of some human chorionic gonadotropin complexes with β-emitting radionuclides.

Human chorionic gonadotropin (hCG) is a peptide hormone, whose one of the structural subunits is identical to that of thyroid-stimulating hormone (TSH). As a consequence, the receptors of TSH also act as receptor for hCG hormone. Keeping in mind this interesting property of hCG we have studied the complex formation ability of various no-carrier-added β-emitting isotopes of (61)Cu (3.3 h), (62)Zn (9.2 h), (90)Nb (14.60 h) and (99)Mo (66.02 h) with hCG molecule. Stability of the hCG-M (M=metal ions) complexes was investigated by dialysis with respect to triple distilled water and ringer lactate solution, which has the same composition as extracellular fluid.

Aromatic amino acids in high selectivity bismuth(III) recognition

The three aromatic amino acids, tyrosine, tryptophan and phenylalanine, play different physiological roles in life processes. Metal ions capable of binding these amino acids may aid in the reduction of effective concentration of these amino acids in any physiological system. Here we have studied the efficacy of some heavy metals for their complexation with these three amino acids. Bismuth has been found to bind selectively with these aromatic amino acids and this was confirmed using spectrofluorimetric, spectrophotometric and cyclic voltammetric studies. The series of heavy metals has been chosen because each of these metals remains associated with the others at very low concentration levels and Bi(III) is the least toxic amongst the other elements. So, selective recognition for Bi(III) would also mean no response for the other heavy elements if contaminants are present even at low concentration levels. The affinity towards these amino acids has been found to be in the order tryptophan < phenylalanine < tyrosine. The association constants of these amino acids have been calculated using Benesi-Hildebrand equations and the corresponding free energy change has also been calculated. The values of the association constants obtained from BH equations using absorbance values corroborate with the Stern-Volmer constants obtained from fluorimetric studies. The evidence for complexation is also supported by the results of cyclic voltammetry.

Phase separation in aqueous systems for realizing virtually significant extractions

Polyvinylpyrrolidone (PVP) forms aqueous biphasic systems with tri-block co-polymers, surfactants and salts. The phase diagrams of PVP–salt and PVP–surfactant systems were constructed by a turbidometric titration method at 296 K. Density measurements of the phase forming solutions at this temperature also led to an attractive outcome of the formation of two tri-phasic systems among the components of our study (Na-tartrate + PVP + Triton-X-100 and Na-tartrate + PVP + PPG–PEG–PPG). We also constructed a spreadsheet reflecting the relationship between miscibility and the possibility of phase separation between the components, consisting of the seven phase forming solutions to open up different possibilities of ABS formation. Some completely new biphasic systems were obtained as well as the process of gel formation of a PVA solution in the presence of salt and polymer solutions was also observed. The applications of some of the developed ABSs are described for the recovery of an antibiotic drug, amoxicillin and a catalyst, molybdenum disulphide.

Detoxification of Hg(II) from aqueous and enzyme media: Pristine vs. tailored calcium alginate hydrogels.

Calcium alginate (CA) hydrogels were tailored using phenolic compounds (PC) like, thymol, morin, catechin, hesperidin, during their preparation. The PC incorporated gels show modified surface features as indicated by scanning electron microscopic images (SEM). The rheological studies show that excepting the hesperidin incorporated gels all the other kinds including calcium alginate pristine have similar mechanical strength. The hesperidine incorporated CA gels had the maximum capacity to adsorb Hg. The Freundlich adsorption isotherms show higher values of adsorption capacity for all PC incorporated CA beads than the pristine CA (PCA). The hesperidin incorporated CA gels were found to show the best adsorption condition at neutral pH and an optimum contact time of 2.5h at 25°C. Considering the possibility of ingested Hg detoxification from human alimentary tract, the hesperidin and morin incorporated CA beads were further modified through incorporation of cod liver oil as the digestion time of fat in stomach is higher. In vitro uptake capacities of Hg in pepsin and pancreatin containing enzyme media were studied with hesperidin and morin incorporated beads and their corresponding fat incorporated beads also. In the pepsin medium, there was no uptake by hesperidin and fat-hesperidin incorporated beads, which is possibly due to the higher acidity of the medium. But in pancreatin medium Hg was taken up by both kinds of beads. Morin and morin-fat incorporated beads were efficient to uptake Hg from both the pepsin and pancreatin medium. The tailored CA beads may therefore serve as efficient scaffolds to rescue Hg ingested individuals.

Unexplored analytics of some novel 3d–4f heterometallic Schiff base complexes

Three heterometallic Schiff-base complexes of Cu having Pr, Nd and Sm as the heteroatoms have been synthesized. The compounds have also been characterized by their IR spectra and CHN analysis. The single crystal structures of these compounds have been studied from the X-ray crystallographic data. To the best of our knowledge the article describes the possibility of application of these compounds in the field of species dependent anion sensing for the first time. Amongst a number of anionic species, certain sulphur species were found to have greater reactivity towards a Schiff-base complex as they can incur probable changes in the molecular complexity. The S2O82−and S2O32− species could modify the spectral features of the Schiff-base complex containing Nd as the heteroatom. This particular complex was found to exhibit changes in its absorbance and fluorescence spectral features upon interaction with the anionic species S2O82−and S2O32−. The results give a strong platform for the Schiff base complexes for their analytical applications.

Enhanced anion sensing by γ-irradiated polyphenol capped iron oxide nanoparticles

Abstract A novel method was designed for the synthesis of polyphenol capped amorphous iron oxide nanoparticles (ION) using an agro waste (peanut skin). The synthesized nanoparticles were characterized by absorption spectroscopy, TEM, SEM, IR, Raman and XRD. An increased rate of formation of the nanoparticles is observed upon low dose gamma irradiation. ION shows specific spectral features with perchlorate anion even in presence of other anions selected for the anion sensing study. The nanoparticles formed in presence of irradiation was found even more sensitive to lower concentration of perchlorate owing to its finely dispersed nature and increased surface area.

Block copolymer as a novel functional phase in an aqueous biphasic system for species selective iodine extraction

This article describes a newly designed block copolymer based aqueous biphasic system (ABS, composed of two immiscible aqueous phases) which is further utilized to study extraction behavior of three iodine species viz., I2, I−, and IO4−. Phase diagram and tie line data reveals the potential working range of this new biphasic system. Fluorescence, dynamic light scattering, transmission electron microscopy (TEM) and conductance data establish the micellar arrangement in solutions of this particular block copolymer. Elemental iodine is easily soluble in copolymer solution due to charge transfer complexation. Polymer phase of the ABS is found to have species dependent selectivity of extraction for the three different iodine species. Two non toxic, non flammable dyes 3,6-diamino-10-phenylphenazinium chloride (DPC) and haematoxylin are introduced for the first time to detect iodide and periodate species respectively in the copolymer medium.

On the design of Ag–morin nanocomposite to modify calcium alginate gel: framing out a novel sodium ion trap

The present work describes the design of a Ag–morin nanocomposite and its subsequent incorporation in calcium alginate gels which have the unique property to uptake and release sodium ions. The nanocomposite reported here is the first of its kind and is capable of modifying the calcium alginate gels both physically and chemically. The corrugated surface morphology of calcium alginate becomes modified and becomes smoother upon incorporation of the nanocomposite. Rheological studies reveal an increased viscoelastic nature upon modification of calcium alginate gels which are developing as wound dressing materials. The modified gel will be supposedly a better dressing material as it can also handle saline solution which in turn is a prerequisite for wound healing treatment.