Synthesis of selenium nanowires morphologically directed by Shinorhizobial oligosaccharides

Shinorhizobial cyclosophoraose (cyclic β-(1→2)-glucan) or succinoglycan monomer (SGM 2), which has one acetyl, pyruvyl, and succinyl group, functions as a morphology-directing agent for the synthesis of pure trigonal selenium nanowires by using ascorbic acid (vitamin C) as the reducing agent. The synthesis was achieved in water at room temperature. Under these experimental conditions, the diameters of the as-prepared Se nanowires were varied in the range of 34-120 nm by cyclosophoraose and of 33-66 nm by SGM 2, in which the nanowires were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. Through this study, we propose that Shinorhizobial cyclic and linear oligosaccharides have morphologically directing functions for the synthesis of single-crystalline selenium nanowires by green chemical methods.     

Preparation and properties of partially oxidized N-methylisoquinolinium bis(oxalato)platinate nanowires

Electrochemical oxidation of [C₁₀H₁₀N]₂[Pt(ox)₂] · H₂O (1) (C₁₀H₁₀N = N-methylisoquinolinium, ox = oxalate) leads to the synthesis of new partially oxidized platinum nanowires of formula [C₁₀H₁₀N]_1.6[Pt(ox)₂] · 3H₂O (2). The nanowires were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Wires with diameters of less than 5 nm and lengths of over 1 μm were observed. Energy dispersive spectroscopy (EDS) and microanalysis confirmed the degree of partial oxidation of the nanowires. The bulk electrical properties including phase angle and real and imaginary impedance values were measured and a model of the electrical conduction circuit was proposed. The significance of this work is that the large N-methylisoquilolinium cation leads to nanostructures, possibly involving individual molecular wires which has not been previously observed in the bis(oxalato)platinate nanowire system.     

A laser light scattering study of gellan gels

A study of gellan has been made using the technique of photon correlation spectroscopy. It has been confirmed that gellan gels are largely stationary at a molecular level like other polysaccharide gels and quite unlike the gels of flexible polymers such as polyacrylamide. Solution-gel transitions of deacetylated gellan in 0.025MNaCl have been studied both as a function of concentration and temperature, and the results compared with those of a parallel investigation of agarose. The interstitial spaces within gellan gels have also been studied by measuring the diffusion coefficients of dextran fractions within the gels. Since all gels are nonergodic systems, the theory of dynamic light scattering from such systems is discussed insofar as it affects the present work. It has been shown that the gellan and agarose aqueous systems are fundamentally different, in that agarose does not from a solution at very low concentrations, but splits up into macroscopic gel particles. At very low concentrations, gellan forms a solution in the presence of both gelleing and nongelling ions, the molecules of which shows little change in hydrodynamic diameter with temperature in the range 20–80°C. At higher concentrations where gels are formed, both gellan and agarose exhibit hystersis in their tempertature transitions from gel to solution and solution to gel, the solution being of large molecular aggregates. The transitions are sharp, but in both cases ther is a continous rearrangement in the structural morphology over the entire temperature range on heating, rendering the system more homogeneous prior to dissociation. In the case of gellan, however, there are two distincit phases in these structural changes—this is not true of agarose. The mean mass per unit length of the gellan fibre in the presence of 0.025M NaCl is 19 k daltons/nm at 0.7% concentration and varies with concentration to the power 0.15. The mass per unit length of the agarose fibre is much larger (ca. 110 k Daltons/nm), this difference being consistent with the difference in properties at very low concentrations. © 1994 John Wiley & Sons, Inc.     

DNA assisted fragmentation of nickel nanoparticle clusters and their spectral properties

Nickel nanoparticle (NiNP) clusters in the range of 60-70 nm size on interaction with herring-sperm DNA (B-DNA) form a self-assembled duplex helix DNA structure with fragmented NiNPs as small as 5-15 nm, as evident from atomic force microscopic studies. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images also corroborate the findings. The properties of these self-assembled NiNPs-DNA structures have been further investigated by UV-visible, emission and circular dichroic (CD) spectral studies.     

Facile synthesis of fluorescent polysaccharides: Cytosine grafted agarose and κ-carrageenan

New fluorescent polymeric materials were synthesized by grafting the nucleobase cytosine on to the backbone of agarose and κ-carrageenan, employing a rapid water based method under microwave irradiation using potassium persulphate (KPS) as an initiator. The emission spectrum of the modified agarose and κ-carrageenan recorded in aqueous solution (5 × 10⁻⁵ M) exhibited emission maxima (λ_em,max) at 348 nm by excitation at 266 nm. The emission intensity was enhanced by ca. 104% and 60% compared to that of pure cytosine solution of the same concentration. When the concentration of the pure cytosine solution is made equivalent to the concentration of the cytosine molar component (3.09 × 10⁻⁵) and (3.5 × 10⁻⁵) present in 5 × 10⁻⁵ M solution of modified agarose and κ-carrageenan, respectively, then ca. 143% and 81% enhancement in emission intensity was observed. The remarkable fluorescent activity of the agarose-cytosine derivative may have potential uses as sensor in various applications.     

Morphology and antibacterial activity of carbohydrate-stabilized silver nanoparticles

Silver nanoparticles were prepared by a simple hydrothermal route and chemical reduction using carbohydrates (sucrose, soluble and waxy corn starch) as reducing as well as stabilizing agents. The crystallite size of these nanoparticles was evaluated from X-ray diffraction (XRD) and transmission electron microscopy (TEM) and was found to be 25 nm. The effect of carbohydrates on the morphology of the silver nanocomposites was studied using scanning EM (SEM). The nanocomposites exhibited interesting inhibitory as well as bactericidal activity against both Gram positive and Gram negative bacteria. Incorporation of silver also increased the thermal stability of the carbohydrates.     

Biochemical and biophysical characterization of collagens of marine sponge, Ircinia fusca (Porifera: Demospongiae: Irciniidae)

Collagens were isolated and partially characterized from the marine demosponge, Ircinia fusca from Gulf of Mannar (GoM), India, with an aim to develop potentially applicable collagens from unused and under-used resources. The yield of insoluble, salt soluble and acid soluble forms of collagens was 31.71 ± 1.59, 20.69 ± 1.03, and 17.38 ± 0.87 mg/g dry weight, respectively. Trichrome staining, Scanning & Transmission Electron microscopic (SEM & TEM) studies confirmed the presence of collagen in the isolated, terminally globular irciniid filaments. The partially purified (gel filtration chromatography), non-fibrillar collagens appeared as basement type collagenous sheets under light microscopy whereas the purified fibrillar collagens appeared as fibrils with a repeated band periodicity of 67 nm under Atomic Force Microscope (AFM). The non-fibrillar and fibrillar collagens were seen to have affinity for anti-collagen type IV and type I antibodies raised against human collagens, respectively. The macromolecules, i.e., total protein, carbohydrate and lipid contents within the tissues were also quantified. The present information on the three characteristic irciniid collagens (filamentous, fibrillar and non-fibrillar) could assist the future attempts to unravel the therapeutically important, safer collagens from marine sponges for their use in pharmaceutical and cosmeceutical industries.     

Green synthesis of silver nanoparticles using cellulose extracted from an aquatic weed; water hyacinth

As part of the desire to save the environment through “green” chemistry practices, we herein report an environmentally benign synthesis of silver nanoparticles (Ag-NPs) using cellulose extracted from an environmentally problematic aquatic weed, water hyacinth (WH), as both reducing and capping agent in an aqueous medium. By varying the pH of the solution and reaction time, the temporal evolutions of the optical and morphological properties of the as-synthesised Ag-NPs were investigated. The as-synthesised cellulose capped silver nanoparticles (C–Ag-NPs) were characterised using Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–vis), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The maximum surface plasmon resonance (SPR) peak decreased as the pH increased indicating that an increase in the pH of the solution favoured the formation of smaller particles. In addition, instantaneous change in the colour of the solution from colourless to brown within 5 min at pH 11 showed that the rate of reduction is faster at this pH compared to those at lower pH. The TEM micrographs showed that the materials are small, highly monodispersed and spherical in shape. The average particle mean diameters were calculated to be 5.69 ± 5.89 nm, 4.53 ± 1.36 nm and 2.68 ± 0.69 nm nm at pH 4, 8 and 11 respectively. The HRTEM confirmed the crystallinity of the material while the FTIR spectra confirmed the capping of the as-synthesised Ag-NPs by the cellulose. It has been shown therefore that based on this synthetic method, this aquatic plant can be used to the advantage of mankind.     

Synthesis, self-assembly and characterization of a new glucoside-type hydrogel having a Schiff base on the aglycon

A new hydrogel based on a substituted phenyl glucoside with a Schiff base in the aglycon was synthesized, and the self-assembling characteristics was studied. FTIR spectra, UV-vis absorption spectra and X-ray diffraction (XRD) revealed that π-π interactions between the Schiff base moieties, hydrogen bonds, and the interdigitated interactions between hydrophobic chains had effects on the formation of the self-assembling hydrogel. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) observation showed that the three-dimensional hydrogel network was constructed from nanotubes with inner diameters of ca. 75 nm and wall of ca. 20 nm.     

The single source preparation of rod-like mercury sulfide nanostructures via hydrothermal method

High-quality and high-yield rod-like HgS dendrites with cubic structure was synthesized by a wet chemical route, without using any surfactant and organic solvents at 180 °C for 5 h, by using Hg(NO₃)₂·H₂O and thioglycolic acid (TGA) as starting reagents. The obtained HgS with different morphologies and sized were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), and X-ray diffraction (XRD). The effects of reaction parameters, such as temperature, precursor concentration and reaction time on the morphology and particle size of products were investigated. Our experimental results showed that temperature reaction played key role in the final morphology of HgS. The morphology of HgS nanostructures could be changed from rod-like dendrites to nanoparticles by only decreased temperature reaction to 110 °C. In the present study the possible mechanism of HgS nanoparticles growth to dendrites in the aqueous solution was also discussed and the optical properties rod-like HgS dendrites were investigated by ultraviolet-visible (UV-Vis) spectroscopy.     

Nanostructural zinc oxide hollow spheres: A facile synthesis and catalytic properties

The development of reproducible procedures for the synthesis and organization of nanostructured metal oxides is important in order to exploit the unique properties of these materials for practical applications. The present work describes the transformation of Zn(NH₃)₄]²⁺ into hollow structured ZnO materials through solvothermal decomposition. An increase in ammonia concentration in the reaction medium, significantly changes the morphology of ZnO from spheres made of nanoparticles (20-30 nm) to hollow spheres composed of nanorods (200-350 nm) or to free microrods as evidenced from scanning and transmission electron micrographs (SEM/TEM). The powder X-ray diffraction (XRD) pattern of ZnO confirms formation of the wurtzite structure. Raman and Energy-dispersive spectroscopic (EDS) studies indicate the presence of oxygen deficiency in ZnO. The investigation on the catalytic behavior of ZnO in the synthesis of (4-methoxyphenyl)(phenyl) methanone (MPPM) by Friedel-Crafts acylation of anisole with benzoyl chloride has also been carried out. The results reveal that the prepared ZnO could produce ∼98% of yield compared to 41% produced by commercial ZnO.     

High performance edible nanocomposite films containing bacterial cellulose nanocrystals

Bacterial cellulose obtained from Gluconacetobacter xylinus in the form of long fibers were acid hydrolyzed under controlled conditions to obtain cellulose nanocrystals. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) confirmed the formation of rod like cellulose nanocrystals having an average diameter and length of 20 ± 5 nm and 290 ± 130 nm respectively. These nanocrystals were used to prepare gelatin nanocomposite films and characterized for elucidating its performance. The formation of percolated networks of cellulose nanocrystals within gelatin matrix resulted in improving the mechanical properties of nanocomposites. The moisture sorption and water vapor permeability (WVP) studies revealed that the addition of cellulose nanocrystals reduced the moisture affinity of gelatin, which is very favorable for edible packaging applications. Results of this study demonstrated the use of bacterial cellulose nanocrystals (BCNCs) in the fabrication of edible, biodegradable and high-performance nanocomposite films for food packaging applications at relatively low cost.     

Hydrothermal synthesis and characterization of bismuth selenide nanorods via a co-reduction route

Bi₂Se₃ nanorods have been synthesized through a simple hydrothermal reduction approach. The nanorods formed were ≈50 nm in average diameter and ≈4 μm nm in length. XRD characterization suggested that the product consisted of the rhombohedral phase of pure Bi₂Se₃. The products were also characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermo gravimetric analysis. The synthesis procedure is simple and uses less toxic reagents than the previously reported methods. The results showed that the capping agent CTAB plays a crucial role in the process. Other factors, such as the reaction time, the different capping agent and the sort of reductant also have influence on the morphology of the final products to some extent.     

Self-assembly of 6-O- and 6'-O-hexadecylsucroses mixture under aqueous conditions

In this paper, we report the self-assembly of 6-O- and 6′-O-hexadecylsucroses mixture under aqueous conditions. The mixture was synthesized by a five-step sequence from sucrose. The SEM image of a sample prepared by drying a dispersion of the mixture in water showed nanoparticles with the diameter of ∼50 nm and aggregates that were formed by further assembly of them. The XRD measurement of the sample exhibited the diffraction pattern assignable to face-centered cubic (FCC) structure and the diameter of a sphere, which took part in the FCC structure, was calculated to be 5.1 nm. This value was relatively close to that observed in the DLS measurement of a dispersion of the mixture in water and estimated for a spherical micelle based on the molecular sizes of the two sucrose ethers. On the basis of the above findings, the following self-assembly process of the mixture under aqueous conditions was proposed. The mixture formed the spherical micelles with the diameter of ∼5-7 nm in water. The micelles regularly organized according to the FCC structure during the drying process from the aqueous dispersion to construct the nanoparticles with the diameter of ∼50 nm. Several numbers of the nanoparticles further assembled to form the aggregates.     

Interactions between κ-carrageenan and chitosan in nanolayered coatings—Structural and transport properties

The interactions between κ-carrageenan and chitosan, two oppositely charged polysaccharides, have been investigated through microcalorimetric and quartz crystal microbalance measurements. Microcalorimetric measurements show that κ-carrageenan/chitosan interaction is an exothermic process and that the alternate deposition of κ-carrageenan and chitosan results in the formation of a nanolayered coating mainly due to the electrostatic interactions existing between the two polyelectrolytes (though other types of interactions may also be involved). Quartz crystal microbalance measurements confirmed that the alternating deposition of κ-carrageenan and chitosan resulted in the formation of a stable multilayer structure. The κ-carrageenan/chitosan nanolayered coating, assembled on a polyethylene terephthalate (PET) support, was characterized in terms of its surface (contact angle measurements) and gas barrier properties (water vapor and O₂ permeabilities) and analyzed by scanning electron microscopy (SEM). The water vapor permeability (WVP) and the oxygen permeability (O₂P) of the κ-carrageenan/chitosan nanolayers were found to be 0.020 ± 0.002 × 10⁻¹¹ and 0.043 ± 0.027 × 10⁻¹⁴ g m⁻¹ s⁻¹ Pa⁻¹, respectively. These results contribute to a better understanding of the type of interactions that play role during the construction of this type of nanostructures. This knowledge can be used in the establishment of an approach to produce edible, biodegradable multilayered nanostructures with improved mechanical and barrier properties for application in, e.g. food and biomedical industries.     

Synthesis and characterization of guar gum templated hybrid nano silica

The objective of the present study was the fabrication of green adsorbent hybrids for which native guar gum was used as template to polymerize tetraethoxysilane. The properties and performances of the hybrids could be tailored by using varying molecular sizes of the partially depolymerized guar gum templates of various molecular sizes as control. Zn(II) uptake from aqueous solution was used as a criterion for evaluating the adsorbent efficiency. The optimum material (H4) in terms of maximum Zn(II) uptake, was obtained when the template size used was 375 kDa at a calcination temperature of 700 °C. H4 was also evaluated for Ca(II), Mg(II), Cd(II) and Hg(II) adsorption. To explore the other applicability areas, the hybrids have been extensively characterized using FTIR, XRD, TGA-DTA, PL, SEM, TEM and BET analyses. H4 was found to be as efficient as previously reported vinyl modified-silica nanohybrids. It had a high surface area (264 m²/g) with silica nanoparticles in the size range of 90-140 nm. Being thermally very stable and photoluminescent, the material can be potentially used for many biological, medical and environmental applications.     

An integrated system of pyrene and rhodamine-6G for selective colorimetric and fluorometric sensing of mercury(II)

A pyrene and rhodamine-6G functionalized simple chemosensor L is studied toward sensing of metal ions in solution extensively. L shows selective color change from colorless to pink in the presence of Hg²⁺ in acetonitrile and the UV-Vis study shows peak at 525 nm with a ε value of 5.2 × 10⁴ M⁻¹ cm⁻¹ due to selective ring opening of rhodamine spirolactam moiety. The selective sensing of Hg²⁺ by L in the presence of other metal ions and reversible nature of “OFF-ON-OFF” functionality of L by Hg²⁺ and EDTA, respectively, are also established. The fluorescence study of L in the presence of Hg²⁺ shows emission at 550 nm when excited at 525 nm (ring opened rhodamine wavelength) or 340 nm (pyrene wavelength) in dry CH₃CN. Thus L acts as a selective colorimetric and fluorometric probe (dual probe) for the Hg²⁺ in solution. Metal ion sensing ability of L is also carried out in water as well as in aqueous Hepes buffer. These studies suggest that the fluorescence output of L in presence of Hg²⁺ in aqueous environment is apparently due to the generation of acid upon addition of Hg²⁺ salt in water.     

Biodegradable and biocompatible polyampholyte microgels derived from chitosan, carboxymethyl cellulose and modified methyl cellulose

Two biocompatible and biodegradable polyampholyte microgels, namely chitosan-carboxymethyl cellulose (CS-CMC) and chitosan-modified methyl cellulose (CS-ModMC) were synthesized by an inverse microemulsion technique. The CS-CMC microgel system was pH-responsive while the CS-ModMC system possessed both pH and thermo-responsive properties. For CS-CMC system, the number of -OCH₂COOH and -NH₂ groups was determined to be 1.5 and 1.1 meq/g of microgel, respectively. In the pH range of 4-9, the zeta potential values varied from +10 to −40 mV, while the hydrodynamic radius varied from 160 nm in the swollen state (acidic and basic pH) to 110 nm in the “collapse” state (neutral pH). Furthermore, TEM micrographs confirmed the swelling/deswelling behaviour of CS-CMC microgel particles at acidic, neutral and basic conditions. For CS-ModMC system, the number of -OCH₂COOH and -NH₂ groups was determined to be 0.8 and 0.6 meq/g microgel, respectively. In the pH range of 4-9, the surface charge on the microgels varied from +25 to −60 mV and the hydrodynamic radii were 190 nm at low pH, 80 nm at neutral pH, to 120 nm at a high pH. In vitro drug release studies confirmed that CS-CMC microgels could encapsulate and release a model drug, thus they could potentially be used as biocompatible and biodegradable drug carriers.     

Preparation and characterization of cellulose nanocrystals from rice straw

Pure cellulose have been isolated from rice straw at 36% yield and hydrolyzed (64% H₂SO₄, 8.75 mL/g, 45 °C) for 30 and 45 min to cellulose nanocrystals (CNCs), i.e., CNC30 and CNC45, respectively. CNC45 was smaller (11.2 nm wide, 5.06 nm thick and 117 nm long) than CNC30 (30.7 nm wide, 5.95 nm thick and 270 nm long). Freeze-drying of diluted CNC suspensions showed both assembled into long fibrous structures: ultra-fine fibers (∼400 nm wide) from CNC45 and 1-2 μm wide broad ribbons interspersed with CNC clusters from CNC30. The self-assembled fibers from CNC30 and CNC45 were more highly crystalline (86.0% and 91.2%, respectively) and contained larger crystallites (7.36 nm and 8.33 nm, respectively) than rice straw cellulose (61.8%, 4.42 nm). These self-assembled fibers had essentially nonporous or macroporous structures with the CNCs well aligned along the fiber axis. Furthermore, the self-assembled ultra-fine fibers showed extraordinary structural stability, withstanding vigorous shaking and prolong stirring in water.     

Influence of gelling agents on culture medium gel strength, water availability, tissue water potential, and maturation response in embryogenic cultures of Pinus strobus L.

Summary Maturation of somatic embryos of Pinus strobus L. was evaluated on media containing various types (agars and gellan gum), brands and concentrations of gelling agents in the presence of 80 μM ABA and 0.09 M sucrose. The media were characterized with respect to gel strength, water potential and water availability. Embryogenic tissue and somatic embryos cultured on medium with various concentrations of gellan gum were used to determine their water potential (Ψ). Regardless of the type of gelling agent used, gel strength increased with gelling agent concentration and was critical to the maturation response. High gel strength was associated with reduced water availability from the medium to the cultures. The water potential of gelled maturation medium remained constant between 0.4 and 1.0% gellan gum. It is concluded that the embryogenic tissue was exposed to varying amounts of water at the onset of and during the culture period, and that the amount of water in the culture environment in turn influenced the maturation response. Cotyledonary somatic embryos derived from gellan gum medium of high gel strength had a lower Ψ than somatic embryos matured on medium of lower gel strength. Once somatic embryos developed to the cotyledonary stage on the maturation medium, they were transferred to the germination medium. The germination frequency and the number of morphologically normal germinants were higher for somatic embryos matured on medium of high gel strength. Raising the concentration of the gelling agent in the maturation medium may be an alternative to the use of solutes to restrict water available to the embryogenic cultures.