Sustainable Catalytic Activity of Ag-Coated Chitosan-Capped γ-Fe2O3 Superparamagnetic Binary Nanohybrids (Ag-γ-Fe2O3@CS) for the Reduction of Environmentally Hazardous Dyes-A Kinetic Study of the Operating Mechanism Analyzing Methyl Orange Reduction.

The formation of binary nanohybrids consisting of environmentally benign components, γ-Fe2O3, chitosan (CS), and Ag (Ag-γ-Fe2O3@CS) (CSIOAg), containing very low concentration of Ag NPs (≤1.2 µM), has been reported. In the as-synthesized nanohybrids, the presence of γ-Fe2O3 (8.5 ± 0.8 nm) and Ag (5.9 ± 0.5 nm) are revealed by optical, XRD, TEM, and XPS analyses, and their presence in cubic phase is determined by XRD and SAED measurements. The catalytic activity of CSIOAg has been analyzed by performing the reduction of certain toxic dyes. Under all kinetic conditions, the reaction is attended by an induction period, which is reduced upon increasing [Ag] and [Dye] in a specific concentration range, as well as temperature, suggesting restructuring of the surface prior to reduction. In case of methyl orange (MO), the reduction results in its cleavage to produce N,N-dimethyl-1,4-phenylenediamine and sodium sulfanilate in a significantly higher (>97%) yield in a bimolecular reaction between MO and BH4 -. The duration of induction period is regularly decreased and the rate of reduction (k app) increases linearly with increasing Ag in the wide concentration range (0.03-2.4 µM). The reduction takes place with a second-order rate constant of 2.7 × 104 dm3 mol-1 s-1, which is >3.5-fold higher than that in the absence of chitosan (IOAg) under identical experimental conditions. The kinetics of reduction of MO is controlled by the nature and extent of its adsorption on the catalyst surface. The weaker binding between MO and Ag catalyst only allows its effective reduction. The XPS analysis of CSIOAg and IOAg containing the same amount of Ag (1.2 µM) showed its higher amount on the surface of CSIOAg (0.12%) as compared to that of IOAg (0.09%). Detailed kinetic analysis of MO reduction, performed under pseudo-kinetic conditions for both the nanohybrids revealed them to follow Langmuir-Hinshelwood kinetic model and exhibited the recyclability up to 10 cycles with fairly high reaction efficiency and TOF, suggesting it to be a sustainable green nanosystem.

Correction to "Sustainable Catalytic Activity of Ag-Coated Chitosan-Capped γ-Fe2O3 Superparamagnetic Binary Nanohybrids (Ag-γ-Fe2O3@CS) for the Reduction of Environmentally Hazardous Dyes-A Kinetic Study of the Operating Mechanism Analyzing Methyl Orange Reduction".

[This corrects the article DOI: 10.1021/acsomega.7b01498.].

Nanomaterials as matrices for enzyme immobilization.

Nanomaterials constitute novel and interesting matrices for enzyme immobilization. While their high surface to volume ratio is an obvious advantage, their Brownian motion can impact the behavior of enzymes immobilized on these matrices. Carbon nanotubes, superparamagnetic nanoparticles, and mesoporous materials constitute some important classes of matrices. Such immobilized enzyme systems have been used in both aqueous and low water media for biocatalysis and resolution of racemates. This overview examines the behavior of enzymes immobilized on nanomaterials and discusses the results reported with such biocatalyst preparations.

Rheological properties of binary and ternary protein-polysaccharide co-hydrogels and comparative release kinetics of salbutamol sulphate from their matrices.

Rheological properties of binary (AgarGelA and AgarGelB) and ternary (AgarGelAB and GelABAgar) co-hydrogels of agar (polysaccharide) with gelatin A and gelatin B (proteins) were studied to investigate their differential viscoelastic behavior. Two sets of rheological experiments, isochronal temperature and isothermal frequency sweep, were performed and the storage modulii, G' was measured which could be correlated to the gel strengths. Two separate peaks at 70°C and 35°C, corresponding to melting temperatures of agar and gelatin gels respectively, were obtained when derivative of G' with respect to temperature, dG'/dT was plotted against temperature which clearly showed the presence of two separate networks of gelatin and agar interconnected to each other. The results revealed that AgarGelAB was the strongest and AgarGelA was the weakest gel among all the gels studied. In order to see the effect of gel microstructure on drug encapsulation and release behavior, a model drug salbutamol was encapsulated in various gel matrices and the release of the same was seen in phosphate buffer pH 7.4, in simulated gastric fluid pH 1.2 (SGF) and in simulated intestinal fluid pH 6.8 (SIF) media. The drug release behavior universally followed sigmoidal kinetics invariant of gel composition. It is concluded that the hydrogel microstructure influenced the release behavior and best release, in all the three media, could be found with binary gel, AgarGelB, and ternary gel, AgarGelAB. Finally, microstructure of these gels is proposed.

Effect of agar-gelatin compositions on the release of salbutamol tablets.

The study was designed for the development of salbutamol-modified release tablet using various polymer composition of agar, gelatin A and gelatin B. The purpose is to observe the role of polymer composition on the modified dissolution rate of salbutamol. Pre-formulation trials were initiated by comprising different ratios of polymer blend in the tablets. Formulations were optimized based on their invitro release performed in enzyme free simulated gastric fluid (0.1 N HCl, pH 1.2). Dissolution profiles of tablets were compared among the tablets made of agar, gelatin A, gelatin B and their blends agar-gelatin A, agar-gelatin B, gelatin A-gelatin B and agar-gelatin A-gelatin B in 1:1 ratio. Polymer compositions were fixed based on our desired sustaining activity of the tablet which showed a biphasic release profile with immediate release followed by sustained release. Polymer blends were more effective in controlling drug release. The better controlling behavior of polymer blends was explained by specific interaction between polymer components, their network structure and polymer-drug interaction.

Kinetics of coacervation transition versus nanoparticle formation in chitosan-sodium tripolyphosphate solutions.

Chitosan (deacetylation=75-85%) and sodium tripolyphosphate (TPP) solutions were observed to undergo spontaneous coacervation transition or nanoparticle formation depending on the chitosan concentration and the volumetric mixing ratio [chitosan/TPP]. Three distinct conditions have been identified: (i) [chitosan]or=2 and 3.5