Kalpana Chauhan

Synthesis and characterization of novel guar gum hydrogels and their use as Cu2+ sorbents

To prepare novel hydrogels for use in water technologies, guar gum was subjected to acid hydrolysis. The depolymerized guar gum obtained there from and the native guar gum were oxidized to their respective polycarboxylic forms using NO(x) as oxidant. All these polymers were crosslinked with N,N-methylenebisacrylamide, and were used as Cu(2+) sorbents. The candidate hydrogel exhibiting the highest uptake was used further to investigate the effect of external stimuli on sorption. The sorption on hydrogels was fast as the highest sorption was observed after 2 h at 40 degrees C and 20 ppm of Cu(2+) ions. The hydrogel prepared from the oxidized guar gum afforded the maximum sorption capacity of 125.893 mg g(-1). Langmuir and Freundlich isotherms, and pseudo second order kinetics matches the experimental data. The evidence of sorption was obtained by characterizing Cu(2+)-loaded hydrogels by FTIR spectroscopy.

Preparation and characterization of pH-responsive guar gum microspheres.

Guar gum, being the natural polymer is renewable, nontoxic, biocompatible and biodegradable. Therefore, it is the perfect material to formulate particulates or microspheres for potential applications in pharmaceutical. The formulation of material in nano/microsphere scale offers new rich in application potential. In view of that, novel biodegradable and pH-sensitive hydrogels composed of pH-sensitive methacrylic acid (MAc) and a biodegradable guar gum were synthesized by grafting reactions. Water-in-oil (w/o) emulsion method was used to direct the pH-sensitive material in microspheres shape using bi-functional glutaraldehyde (GA) as crosslinker. The synthesized microspheres were characterized by FTIR and SEM (different magnification). The swelling ratios of hydrogels in buffer solutions showed a pH-dependent profile at physiological pH. In vitro release data was analyzed using Ficks law, which indicated swelling controlled super case II transport of BSA through the synthesized microspheres. Therefore, in conclusion, as ascertained from the results the introduction of -COOH moieties along the guar gum chain drastically increases the end-use performance due to pH-sensitivity.

Modified chitosan microspheres in non-aggregated amylase immobilization

Immobilized enzymes are useful as reusable catalysts in industrial processes. In this study, α-amylase was used as a model enzyme to evaluate the propensity of synthesized porous chitosan microspheres as immobilization matrix. Chitosan microspheres were synthesized by grafting and covalent gelation technique using acrylamide (AAm) and glutaraldehyde (GA) as chemical agents, respectively. The synthesized chitosan-cl-poly(AAm) demonstrated amylase immobilization capacity of 350 mg/g. Furthermore, SEM results supported the porous microsphere structure for chitosan-cl-poly(AAm) with non-aggregated amylase immobilization, which accounts for comparable activity of immobilized amylase (3.28 μmol/ml/min) in contrast to free amylase (3.46 μmol/ml/min). The immobilized α-amylase was characterized for optimal pH and temperature activity and showed better resistance to temperature and pH inactivation in contrast to free amylase. The immobilized amylase retained more than 60% of its initial activity when stored at 4°C for 30 days and retained 50% of its initial activity after seven successive repeated-use cycles. In conclusion, the study can be used as base for the immobilization of competent industrial biocatalysts in non-aggregated active structure.

A green and highly efficient sulfur functionalization of starch

In this study, sulfur functionalized starch has been successfully prepared, via an iso-thiouronium salt intermediate, from the reaction of thiourea with chloroacetylated starch. The later was synthesized by a chloroacetylation reaction. Thiolation via an iso-thiouronium ion intermediate is an innovative green approach to achieve thiol functionalization of starch with an innocuous low cost thiourea reagent. The thiol products are amenable for further derivatization and were modified to a sulfide and a sulphonium salt. The sulphonium structure was accomplished by exhaustive alkylation with iodoethane as an alkylating agent, which resulted in permanent charge generation on the starch backbone. The above-mentioned reactions were also carried out using microwave heating to achieve maximum yet uniform modification of starch. The extent of the derivatization processes was confirmed by iodine titration and precipitation titration and also by characterization of the synthesized samples by FTIR spectroscopy, 1H-NMR, 13C-NMR, SEM-EDX, XRD, zeta potential measurements and elemental analysis (CHNS) to confirm the reaction output at every synthetic stage. Evidence that the degree of substitution of the thiol groups was ≥ 2 was obtained from titrimetry, SEM-EDX and elemental (CHNS) characterization results. Additionally, the generation of the permanent charge on the sulphonium structure was confirmed using zeta potential measurements.

New Chitosan-Thiomer: An Efficient Colorimetric Sensor and Effective Sorbent for Mercury at Ultralow Concentration.

This paper describes an innovative procedure for the fabrication of a facile colorimetric sensor in one step with thiol functional group for Hg(2+) detection at trace level. The sensor was successfully synthesized via chitosan isothiouronium salt intermediate with innocuous low cost thiourea reagent under microwave irradiation. It is an innovative green approach to achieve thiol functionalization with a high degree of substitution. Thiomer was characterized by titrimetry, FTIR, (1)H NMR, elemental analysis (CHNS), and EDX for extent of modification with detail structure. The synthesized and well characterized thiomer was screened for sensor application. The sensing solution of thiomer resulted in an instantaneous sharp color change from colorless, yellow, to brown with increase in Hg(2+) concentration. Chitosan thiomer also exhibited high sensitivity and selectivity for Hg(2+) over other possible interfering ions in aqueous media. The sensing responses were visualized quantitatively with quick response, good selectivity, high sensitivity, and a low detection limit of ∼0.465 ppb by the naked eye. The same was tested with a paper strip method for technological applications. Furthermore, the as-prepared sensors also exhibited exceptional sorption potential for Hg(2+) even from ultralow concentration aqueous solution and reduced the Hg(2+) concentration from 10 ppb to the extremely low level of ∼0.04 ppb as studied by cyclic voltammetry. Thus, the proposed method is simple, promising, and rapid without any complicated modifying step and is an economical alternative to traditional Hg(2+) sensors for rapid sensor application in environmental water samples at ppb levels.

Separation of Uranyl Ions on Starch-Based Functional Hydrogels: Mechanism and Kinetics

In this article, we report the mechanism and kinetics of adsorption of uranyl ions on starch-based functional hydrogels. The hydrogels were prepared from starch in native or hydrolyzed/oxidized form by crosslinking with N,N-methylenebisacrylamide. The hydrogels synthesized from the oxidized starch have carboxylic groups at C-6 position. The effect of the structure and external environmental factors, i.e., contact time, temperature, ion strength, and simulated seawater (0.55 M NaCl and 3 mM NaHCO3), was investigated on the uranyl adsorption behavior of hydrogels. The adsorption of uranyl ions was rapid as the highest adsorption was observed after 6 h and at 40°C. The sorbents also exhibited appreciable ion uptake even from the simulated seawater. The equilibrium data was analyzed using Langmuir and Freundlich adsorption isotherms and pseudo-first order and pseudo-second order kinetic models. Evidence of adsorption was obtained by characterization of the uranyl ions-loaded hydrogels by FTIR spectroscopy and also by elution with 0.1 N HCl.

Synthesis of new benzothiazole Schiff base as selective and sensitive colorimetric sensor for arsenic on-site detection at ppb level

The exposure of millions of people to unsafe levels of geogenic pollutant arsenic in drinking waters has sounded alarm bells for the development of low-cost methods for on-site continuous monitoring of arsenic in waters. Therefore, herein a new benzothiazole Schiff base colour probe is proposed to detect arsenic selectively in aqueous media. The arsenic probe was developed by simple condensation reaction via microwave method. The well-characterized sensing probe resulted in an instantaneous sharp colour change from light yellow to brown orange with an increase in arsenic concentration. With the colorimetric probe, the limit of detection for arsenic with naked eye speciation test is reported below the World Health Organization guideline of 10 μg L−1 within 10 s. The common coexisting ions in water samples were also scanned for colour response, confirming insignificant interference in arsenic detection. Therefore, this method is efficient for on-site detection of arsenic combined with a high tolerance to common coexisting ions.

Chitosan-thiomer stabilized silver nano-composites for antimicrobial and antioxidant applications

The present study involves a microwave assisted, greener synthesis of chitosan thiomer silver nanocomposites via an innocuous thiourea reagent for antimicrobial applications. The as-synthesized chitosan thiomer acts as a stabilizer, emulsifier, capping agent and reducing agent for chitosan silver nano-composite synthesis. The synthesized thiomers and nano-composites were characterized by various spectroscopic and microscopic techniques. The characterization results demonstrated monodispersed spherical silver nanoparticles (AgNPs) with an average size of ∼3 nm by TEM characterization. The derivatives and composites were screened for antioxidant activity and antimicrobial activity against bacteria [E. coli Gram (−) and S. aureus Gram (+)] and fungus (Candida albicans). The antimicrobial results indicated a highest inhibition zone of 35 mm and lowest MIC value of 3.7 μg mL−1 against E. coli with silver composites. Furthermore, the nanocomposites exhibited greater potential in biological applications as compared to the precursor thiomer, which can be attributed to the high effective surface area of the nanoparticles and plenty of –SH groups in the thiomer structure. Thiomers also exhibited distinguished antioxidant properties ranging from 58–82% even at 100 ppm, while cyclic voltammetric studies revealed comparable results at 50 ppm. The results indicated that the content of –SH group played an important role in antioxidant and antimicrobial activity. The synthesized nano-composites provide a promising potential to explore their use as a cost-effective and green solution for microbial infection.

A greener approach for impressive removal of As(III)/As(V) from an ultra-low concentration using a highly efficient chitosan thiomer as a new adsorbent

Contamination of ground water with arsenic is a serious problem all over the world. An urgent needs is being felt to develop a highly effective and extremely capable sorbent material for the removal of arsenic simultaneously in both species, i.e. As(III) and As(V) from the contaminated water. But in natural water As(III) is present in a non-ionic form which causes a great challenge to remove As(III) as compared to As(V) especially at a relatively low concentration. In this context the green chitosan thiomers with a high density of strong arsenic chelating (–SH) groups have been developed via thiourea reagent under conventional and microwave conditions and have been employed for the removal of As(III) and As(V). The sorption study supported almost identical sorption amounts of 17.0 and 17.6 mg g−1 at 50 ppb for As(III) and As(V) via the thiomer, respectively. The synthesized chitosan thiomer even proved efficient in sorption of As(III) and As(V) at 10 ppb and purified water below the WHO prescribed detection limit. Moreover, the thiomer can be used for arsenic removal without any pH adjustment in the pH range of 6.0 to 9.0, which is in accordance with the pH of natural water. The As(III) and As(V) sorption mechanism on the surface of chitosan thiomer has also been confirmed by FTIR, Raman, XPS and cyclic voltammetry. Isotherm studies indicated that the Freundlich model is successful in describing the adsorption process to a better extent than the Langmuir model for the As(III) and As(V) adsorption on the chitosan thiomer. In the kinetic studies the pseudo second-order kinetic model supported the kinetic data best. The intraparticle diffusion study suggested that both external mass transfer and intraparticle diffusion steps contribute to the rate controlling step. Thus, the proposed solution for arsenic removal is simple, promising and economical which needs no pre and post treatment in natural water samples even at the ppb level.

Efficient method of starch functionalization to bis-quaternary structure unit.

This paper presents the synthesis of bis-quaternary starch by innocuous reagents. For this, starch was functionalized to di-aldehyde structure by periodate oxidation. Aldehyde is reactive and amenable to further derivatization to amine structure. It was functionalized to amine via the modified Leuckart-Wallach reaction. Then, the aminated starch was modified to the quaternary form by the exhaustive methylation. The structural characterization of synthesized compounds was performed using titrimetric analytical estimation, FTIR, (1)H NMR, (13)C NMR, and SEM-EDX. Analytical results showed 58.8% aldehyde content in di-aldehyde starch. The synthesized quaternary derivatives with gemini like structure showed high degree of quaternization 62%. In conclusion, the applied protocol is efficient and revealed high extent of modification with almost good uniformity from the characterization studies.