Enhancement of Stress Tolerance in the Polyhydroxyalkanoate Producers without Mobilization of the Accumulated Granules

Poly(3-hydroxybutyrate) [P(3HB)], a polymer belonging to the polyhydroxyalkanoate (PHA) family, is accumulated by numerous bacteria as carbon and energy storage material. The mobilization of accumulated P(3HB) is associated with increased stress and starvation tolerance. However, the potential function of accumulated copolymer such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] remained unknown. In this study, Delftia acidovorans DS 17 was used to evaluate the contributions of P(3HB) and P(3HB-co-3HV) granules during simulated exogenous carbon deprivation on cell survival by transferring cells with PHAs to carbon-free mineral salt medium supplemented with 1 % (w/v) nitrogen source. By mobilizing the intracellular P(3HB) and P(3HB-co-3HV) at 11 and 40 mol% 3HV compositions, the cells survived starvation. Surprisingly, D. acidovorans containing P(3HB-co-94 mol% 3HV) also survived although the mobilization was not as effective. Similarly, recombinant Escherichia coli pGEM-T::phbCAB _Cn (harboring the PHA biosynthesis genes of Cupriavidus necator) containing P(3HB) granules had a higher viable cell counts compared to those without P(3HB) granules but without any P(3HB) mobilization when exposed to oxidative stress by photoactivated titanium dioxide. This study provided strong evidence that enhancement of stress tolerance in PHA producers can be achieved without mobilization of the previously accumulated granules. Instead, PHA biosynthesis may improve bacterial survival via multiple mechanisms.     

Identification of Folding Intermediates of Streblin,The Most Stable Serine Protease: Biophysical Analysis

Streblin, a serine proteinase from plant Streblus asper, has been used to investigate the conformational changes induced by pH, temperature, and chaotropes. The near/far UV circular dichroism activities under fluorescence emission spectroscopy and 8-aniline-1-naphthalene sulfonate (ANS) binding have been carried out to understand the unfolding of the protein in the presence of denaturants. Spectroscopic studies reveal that streblin belongs to the α+β class of proteins and exhibits stability towards chemical denaturants, guanidine hydrochloride (GuHCl). The pH-induced transition of this protein is noncooperative for transition phases between pH 0.5 and 2.5 (midpoint, 1.5) and pH 2.5 and 10.0 (midpoint, 6.5). At pH 1.0 or lower, the protein unfolds to form acid-unfolded state, and for pH 7.5 and above, protein turns into an alkaline denatured state characterized by the absence of ANS binding. At pH 2.0 (1 M GuHCl), streblin exists in a partially unfolded state with characteristics of a molten globule state. The protein is found to exhibit strong and predominant ANS binding. In total, six different intermediate states has been identified to show protein folding pathways.     

Probing the Binding of Syzygium-Derived α-Glucosidase Inhibitors with N- and C-Terminal Human Maltase Glucoamylase by Docking and Molecular Dynamics Simulation

Human maltase glucoamylase (MGAM) is a potent molecular target for controlling post prandial glucose surplus in type 2 diabetes. Binding of small molecules from Syzygium sp. with α-glucosidase inhibitory potential in MGAM has been investigated in silico. Our results suggest that myricetin was the most potent inhibitor with high binding affinity for both N- and C-terminals of MGAM. Molecular dynamics revealed that myricetin interacts in its stretched conformation through water-mediated interactions with C-terminal of MGAM and by normal hydrogen bonding with the N-terminal. W1369 of the extended 21 amino acid residue helical loop of C-terminal plays a major role in myricetin binding. Owing to its additional sugar sites, overall binding of small molecules favours C-terminal MGAM.     

Dye sensitization of a large band gap semiconductor by an iron(III) complex

The Fe(III) complex, [Fe^III(HQS)₃] (HQS = 8-hydroxyquinoline-5-sulfonic acid), is found to effect sensitization of the large band gap semiconductor, TiO₂. The role of interfacial electron transfer in sensitization of TiO₂ nanoparticles by surface adsorbed [Fe^III(HQS)₃] was studied using femtosecond time scale transient absorption spectroscopy. Electron injection has been confirmed by direct detection of the electron in the conduction band. A TiO₂-based dye-sensitized solar cell (DSSC) was fabricated using [Fe^III(HQS)₃] as a sensitizer, and the resulting DSSC exhibited an open-circuit voltage value of 425 mV. The value of the short-circuit photocurrent was found to be 2.5 mA/cm². The solar to electric power conversion efficiency of the [Fe^III(HQS)₃] sensitized TiO₂-based DSSC device was 0.75 %. The results are discussed in the context of sensitization of TiO₂ by other Fe(II)-dye complexes.     

Magnetic polymer nanocomposites for environmental and biomedical applications

Hybrid nanomaterials have received voluminous interest due to the combination of unique properties of organic and inorganic component in one material. In this class, magnetic polymer nanocomposites are of particular interest because of the combination of excellent magnetic properties, stability, and good biocompatibility. Organic–inorganic magnetic nanocomposites can be prepared by in situ, ex situ, microwave reflux, co-precipitation, melt blending, and ceramic–glass processing and plasma polymerization techniques. These nanocomposites have been exploited for in vivo imaging, as superparamagnetic or negative contrast agents, drug carriers, heavy metal adsorbents, and magnetically recoverable photocatalysts for degradation of organic pollutants. This review article is mainly focused on fabrication of magnetic polymer nanocomposites and their applications. Different types of magnetic nanoparticles, methods of their synthesis, properties, and applications have also been reviewed briefly. The review also provides detailed insight into various types of magnetic nanocomposites and their synthesis. Diverse applications of magnetic nanocomposites including environmental and biomedical uses have been discussed.     

Mechanistic aspects for the oxidation of brilliant green dye by chloramine-T in the presence of perchloric acid: a spectrophotometric kinetic approach

The kinetics of a triarylmethane dye, brilliant green (BG), by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) was studied spectrophotometrically in HClO₄ media at 303 K. Under identical experimental conditions, the rate law was ?d [BG]/dt = k [BG] [H⁺]. Variations in ionic strength (μ) of the medium had no effect on the oxidation velocity. Addition of p-toluenesulfonamide, the reduction product of CAT and Cl^?, had no significant effect on the rate of reaction. The values of rate constants observed at five different temperatures (298, 303, 308, 313, and 318 K) were utilized to calculate the activation parameters. The observed results have been explained by a general mechanism and the related rate law has been obtained. The process demonstrated in this study is cost effective, which holds great promise in potential application for pollutant control.     

Studies on α-, β-, and γ-cyclodextrin inclusion complexes of isoquinoline alkaloids berberine, palmatine and coralyne

The complexation of three isoquinoline alkaloids berberine, palmatine and coralyne with α-, β-, and γ-CDs were studied by absorption, fluorescence, circular dichroism, NMR spectroscopy and microcalorimetric assay techniques. Their binding constant (K _BH) values were determined by Benesi–Hildebrand equation. All the alkaloids formed 1:1 stoichiometry complexes with the cyclodextrins (CDs). The binding affinity is largest in β-CD followed by γ-, and α-CD for coralyne, followed by berberine and then palmatine. The thermodynamic parameters of the complexation were determined by calorimetry. The stoichiometry of complex formation and the variation of the apparent binding constant from spectroscopic studies were confirmed by calorimetry. The formation of the inclusion complexes was entropy driven in almost all the systems. Coralyne formed the strongest complex with all the CDs, followed by berberine and palmatine in that order. Coralyne-β-CD complex was studied through NMR, indicating more than one interaction mode.     

Supramolecular self-assembly and nanoencapsulation of [60]fullerene by bis-β-cyclodextrin

Bis-β-cyclodextrin connected via ethylene diamine on the primary side of the β-cyclodextrin was synthesized and used for the supramolecular non-covalent inclusion complex with C₆₀ in a mixed solvent system at room temperature. The apparent association constant of the 2:2 inclusion complex determined by combination of UV–Vis absorbance and Benesi–Hildebrand equation was found to be 1.78 × 10⁶ M^?1. The product obtained was highly water-soluble and superior in stability in aqueous medium as compared to previously known β-cyclodextrin/C₆₀ complex. The non-covalent self-assembly of bis-β-cyclodextrin and C₆₀ was characterized and confirmed from FT-IR, UV–Vis, XRD and TGA. The supramolecular aggregation behavior and particle size of the inclusion complex was found from transmission electron microscope and static light scattering measurements. The size of the inclusion complex was found to be ~30 ± 5 nm.     

Microwave sintering of nickel ferrite nanoparticles processed via sol–gel method

Magnetic nickel ferrite (NiFe₂O₄) was prepared by sol–gel process and calcined in the 2.45 GHz singlemode microwave furnace to synthesize nickel nanopowder. The sol–gel method was used for the processing of the NiFe₂O₄ powder because of its potential for making fine, pure and homogeneous powders. Sol–gel is a chemical method that has the possibility of synthesizing a reproducible material. Microwave energy is used for the calcining of this powder and the sintering of the NiFe₂O₄ samples. Its use for calcination has the advantage of reducing the total processing time and the soak temperature. In addition to the above combination of sol–gel and microwave processing yields to nanoscale particles and a more uniform distribution of their sizes. X-ray diffraction, energy dispersive X-ray spectroscopy, transmission electron microscopy and vibrating sample magnetometer were carried out to investigate structural, elemental, morphological and magnetic aspects of NiFe₂O₄. The results showed that the mean size and the saturation magnetization of the NiFe₂O₄ nanoparticles are about 30 nm and 55.27 emu/g, respectively. This method could be used as an alternative to other chemical methods in order to obtain NiFe₂O₄ nanoparticles.     

Role of graphene in structural transformation of zirconium oxide

Fine powders of zirconium oxide (ZrO₂) were prepared using zirconium oxychloride by combustion method. The crystalline size of pure ZrO₂ was in range of 14–45 nm. Graphene was incorporated in ZrO₂ using graphene oxide as precursor and reducing it with hydrazine hydrate. X-Ray diffraction, Fourier transform infra-red spectroscopy, thermogravimetric analysis and Raman spectroscopy methods were used to characterize the samples. The role of graphene in structural transformation of ZrO₂ to monoclinic phase was clearly observed.