Interaction of Chromium with Resistant Strain <i>Aspergillus versicolor</i>: Investigation with Atomic Force Microscopy and Other Physical Studies

The interaction of chromium and a chromate resistant Aspergillus versicolor strain has been studied by atomic force (AFM) and transmission electron (TEM) microscopies. The nanomechanical properties such as cell wall rigidity and elasticity were measured by force spectroscopy and found to be 0.61 ± 0.08 N/m, and 20.5 ± 2.1 MPa, respectively. On chromium binding, ultrastuctural changes of the cell wall along with the formation of layered structures on the cell wall were observed. TEM and AFM micrographs demonstrate the accumulation of chromium on the cell wall, which were rough and irregular compared with the smooth pristine mycelia. The surface roughness, cell wall rigidity and elasticity increased to 35.5 ± 3.5 nm, 0.88 ± 0.05 N/m, and 62.5 ± 3.5 MPa, respectively, from the corresponding values of 5.2 ± 0.68 nm, 0.61 ± 0.02 N/m, and 20.5 ± 2.1 MPa for the pristine mycelia. X-ray photoelectron spectroscopy and Fourier transform infrared studies suggest that bound chromium was reduced to its trivalent state by the cell wall components. The reduced chromium species on the cell surface further electrostatically bind chromate ions forming layered structure on the cell wall

Copper(I) Hydroxyapatite Catalyzed Sonogashira Reaction of Alkynes with Styrenyl Bromides. Reaction of <i>cis</i>-Styrenyl Bromides Forming Unsymmetric Diynes

An efficient Sonogashira coupling of terminal alkynes and styrenyl bromides has been achieved under the catalysis of hydroxyapatite-supported copper­(I). The <i>trans</i>-styrenyl bromides produce the usual <i>trans</i>-enyne products, whereas the <i>cis</i>-styrenyl bromides lead to unsymmetric 1,3-diynes by the cross coupling of terminal alkyne and the alkyne generated from the <i>cis</i>-styrenyl bromide. A series of <i>trans</i>-enynes and unsymmetric 1,3-diynes have been synthesized by this protocol

Adsorption of nickel onto <i>Bacillus cereus</i> M¹₁₆: A mechanistic approach

<p>Adsorption characteristics of nickel on <i>Bacillus cereus</i> M¹₁₆ biomass have been studied under varied environmental conditions to explore the potentiality of the biomass for controlling water pollution due to nickel. The optimized parameters for adsorption process are as follows: pH: 7.0, temperature: 40°C, biomass dosage: 2 g L^–1. The process is best fitted to Redlich–Peterson isotherm model and follows pseudo-second order rate model. The combination of zeta potential measurement, SEM – EDXA, XRD, XPS, FTIR, TGA, and DSC studies allow a more comprehensive characterization of biomass to understand the mechanisms involved in nickel (II) adsorption in aqueous system.</p

Cerium Oxide Nanoparticles as Antioxidant or Pro-oxidant Agents

This study was initiated to resolve the ambiguity of contradictory pro-oxidant (toxic) and antioxidant (protective) effects of cerium oxide nanoparticles (CeONPs) taking zebrafish as a model system. To carry out the investigation, different CeONPs having different surface charges (+ve/–ve) with similar shapes and sizes were synthesized at different pH conditions (acidic/basic) using different capping agents (lysine/citrate). Our findings show that the alteration of the capping agent or pH had a profound effect on the biological activity of CeONPs. CeONPs synthesized at alkaline pH showed almost no toxic effect on zebrafish larvae; on the contrary, CeONPs synthesized at acidic pH were found to be toxic, leading to mortality, morphological changes, and abnormal swimming behavior of the larvae and altered levels of reactive oxygen species (ROS), mitochondrial membrane potential, and DNA degradation in larval cells. Moreover, the level of toxicity further increased on coating the NPs with positively charged capping agents. Thus, the study will be very useful in designing CeONPs for killing or protecting biological cells as needed

Interaction at the F₁₆CuPc/TiO₂ Interface: A Photoemission and X‑ray Absorption Study

The interfacial interaction and charge transfer dynamics between a F₁₆CuPc molecular thin film and rutile TiO₂(110) (1×1) surface have been studied by photoelectron spectroscopy (PES), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and resonant photoemission spectroscopy (RPES). The evolution of PES spectra as a function of F₁₆CuPc film thickness shows strong coupling between the molecules and the TiO₂ surface. Adsorbed molecules experience substrate mediated charge transfer. Electrons being pulled away from nitrogen atoms toward to carbon ring results in an opposite direction binding energy shift for C 1s and N 1s. Moreover, the molecule gets deformed due to their strong interaction with the TiO₂ surface. Ultrafast charge transfer from F₁₆CuPc molecules to the TiO₂ substrate takes place on the time scale of 10 fs due to their strong electronic coupling. The results pave the way for the design and realization of F₁₆CuPc based electronic devices

Concentration Mediated Structural Transition of Triblock Copolymer Ultrathin Films

X-ray reflectivity, atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle measurement techniques are used to study the structural changeover as a function of concentration of poly­(ethylene oxide)-poly­(propylene oxide)-poly­(ethylene oxide) (PEO-PPO-PEO) triblock copolymer diluted in toluene spin-coated as ultrathin films on hydrophilic Si substrate. A lamellar structure made of three alternating incomplete bilayers is observed until the concentration of copolymer solution attains a threshold value of about 3.6–4 g/L. Around this concentration and beyond, the entanglement of polymer chains takes place during drying and the growth of a homogeneous film made of complete bilayers on Si substrate is observed. The strong hydrophilic nature of the Si substrate dictates the growth of this amphiphilic copolymer. We evidence that the lower part of the films is made of hydrophilic PEO blocks attached to the substrate while the hydrophobic PPO blocks are directed toward air

Alumina-Supported Cu(II), A Versatile and Recyclable Catalyst for Regioselective Ring Opening of Aziridines and Epoxides and Subsequent Cyclization to Functionalized 1,4-Benzoxazines and 1,4-Benzodioxanes

An easily accessible catalyst, alumina-supported copper(II), efficiently catalyzes the ring opening of aziridines and epoxides followed by cyclization of the corresponding intermediate to produce a variety of functionalized 1,4-benzoxazines and 1,4-benzodioxanes, respectively, in one pot without any ligand in high yields. The ring cleavages of aziridines and epoxides are highly regioselective. The catalyst is inexpensive, non-air-sensitive, environmentally friendly, and recyclable. The function of the catalyst and the reaction pathway are postulated. This protocol is successfully utilized for the formation of three carbon−heteroatom bonds, namely, C−O, C−N, and C−S, in one pot

Alumina-Supported Cu(II), A Versatile and Recyclable Catalyst for Regioselective Ring Opening of Aziridines and Epoxides and Subsequent Cyclization to Functionalized 1,4-Benzoxazines and 1,4-Benzodioxanes

An easily accessible catalyst, alumina-supported copper(II), efficiently catalyzes the ring opening of aziridines and epoxides followed by cyclization of the corresponding intermediate to produce a variety of functionalized 1,4-benzoxazines and 1,4-benzodioxanes, respectively, in one pot without any ligand in high yields. The ring cleavages of aziridines and epoxides are highly regioselective. The catalyst is inexpensive, non-air-sensitive, environmentally friendly, and recyclable. The function of the catalyst and the reaction pathway are postulated. This protocol is successfully utilized for the formation of three carbon−heteroatom bonds, namely, C−O, C−N, and C−S, in one pot

Understanding the Biosynthesis and Catalytic Activity of Pd, Pt, and Ag Nanoparticles in Hydrogenation and Suzuki Coupling Reactions at the Nano–Bio Interface

Increasing demand of noble-metal nanoparticles (MNPs) in catalysis research urges the development of a nontoxic, clean, and environmentally friendly methodology for the production of MNPs on solid surface. Herein we have developed a facile approach for biosynthesis of MNPs (Pd, Pt, and Ag) on the surface of <i>Rhizopous oryzae</i> mycelia through in situ reduction process without using any toxic chemicals. The size and shape of the biosynthesized MNPs varied among the MNPs, and “flower”-like branched nanoparticles were obtained in case of Pd and Pt, while Ag produced spheroidal nanoparticles. The cell-surface proteins of the mycelia acted as protecting, reducing, and shape-directing agent to control the size and shape of the synthesized MNPs. Proteins of 78, 62, and 55 kDa were bound on the MNPs surfaces and played a significant role in determining the morphology of the MNPs. The catalytic efficiency varied among the MNPs, and Pd nanoflower exhibited superior catalytic activities in both hydrogenation and Suzuki coupling reactions. Surface composition, concentration, and intracellular localization of MNPs determine the catalytic activity of the biosynthesized MNPs. The nanocatalyst could be easily separated and reused multiple times without significant loss in activity (95% average conversion). Overall, the understanding of this complex biomineralization mechanism and catalytic behavior at the nano–bio interface has provided an alternative for the synthesis of supported metal nanocatalyst to improve the environmental sustainability

Crystalline Growth of Rubrene Film Enhanced by Vertical Ordering in Cadmium Arachidate Multilayer Substrate

The growth of highly crystalline rubrene thin films for organic field effect transistor (OFET) application remains a challenge. Here, we report on the vapor-deposited growth of rubrene films on the substrates made of cadmium arachidate (CdA) multilayers deposited onto SiO₂/Si­(100) via the Langmuir–Blodgett technique. The CdA films, containing 2<i>n</i>+1 layers, with integer <i>n</i> ranging from 0 to 4, are surface-terminated identically by the methyl group but exhibit the thickness-dependent morphology. The morphology and structure of both CdA and rubrene films are characterized by X-ray reflectivity (XRR), X-ray diffraction (XRD), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and atomic force microscopy (AFM). Crystalline rubrene films, evidenced by XRD and marked by platelet features in AFM images, become observable when grown onto the CdA layer thicker than 5L. XRD data show that vertical ordering, that is, ordering along surface normal, of CdA multilayer substrates exerts a strong influence in promoting the crystalline growth of rubrene films. This promoted growth is not due to the surface energy of CdA layer but derived from the additional interaction localized between rubrene and CdA island sidewall and presumably strengthened by a close dimensional match between the <i>a</i>-axis of rubrene lattice and the layer spacing of CdA multilayer. The best OFET mobility is recorded for 9L CdA substrate and reaches 6.7 × 10^–2 cm² V^–1 s^–1, presumably limited by the roughness of the interface between CdA and rubrene films