Fabrication and characterization of cellulose nanoparticles from maize stalk pith via ultrasonic-mediated cationic etherification

In this study, parenchyma cellulose, which was extracted from maize stalk pith as an abundant source of agricultural residues, was applied for preparing cellulose nanoparticles (CNPs) via an ultrasound-assisted etherification and a subsequent sonication process. The ultrasonic-assisted treatment greatly improved the modification of the pith cellulose with glycidyltrimethylammonium chloride, leading to a partial increase in the dissolubility of the as-obtained product and thus disintegration of sheet-like cellulose into nanoparticles. While the formation of CNPs by ultrasonication was largely dependent on the cellulose consistency in the cationic-modified system. Under the condition of 25% cellulose consistency, the longer sono-treated duration yielded a more stable and dispersible suspension of CNP due to its higher zeta potential. Degree of substitution and FT-IR analyses indicated that quaternary ammonium salts were grafted onto hydroxyl groups of cellulose chain. SEM and TEM images exhibited the CNP to have spherical morphology with an average dimeter from 15 to 55 nm. XRD investigation revealed that CNPs consisted mainly of a crystalline cellulose Ι structure, and they had a lower crystallinity than the starting cellulose. Moreover, thermogravimetric results illustrated the thermal resistance of the CNPs was lower than the pith cellulose. The optimal CNP with highly cationic charges, good stability and acceptable thermostability might be considered as one of the alternatively renewable reinforcement additives for nanocomposite production.     

Facile synthesis of linear–hyperbranched polyphosphoesters via one‐pot tandem ROMP and ADMET polymerization and their transformation to architecturally defined nanoparticles

A convenient one‐pot synthesis of linear–hyperbranched polyphosphoesters (l–HBPPEs) was accomplished by a tandem ring‐opening metathesis polymerization (ROMP) and acyclic diene metathesis (ADMET) polymerization procedure. A linear monotelechelic poly(norbornene) with a terminal acrylate and many pendent thiol groups is first prepared through adding an internal cis‐olefin terminating agent to the reaction mixture immediately after the completion of the living ROMP, and then utilized as a macromolecular chain stopper in subsequent ADMET polymerization of a phosphoester functional AB₂ monomer, yielding l–HBPPEs as the reaction time prolonged. These l–HBPPEs bearing lots of pendent thiol groups in linear poly(norbornene) and peripheral acrylate groups in HBPPE could be self‐crosslinked in ultradilute solution through thiol‐Michael addition click reaction between acrylate and thiol to give single‐molecule nanoparticles with comparatively uniform size. This facile approach can be extended toward the fabrication of novel nanomaterials with sophisticated structures and tunable multifunctionalities. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 964–972     

Synthesis of Small‐Sized,Porous, and Low‐Toxic Magnetite Nanoparticles by Thin POSS Silica Coating

In this communication, we report the synthesis of small‐sized (<10 nm), water‐soluble, magnetic nanoparticles (MNPs) coated with polyhedral oligomeric silsesquioxanes (POSS), which contain either polyethylene glycol (PEG) or octa(tetramethylammonium) (OctaTMA) as functional groups. The POSS‐coated MNPs exhibit superparamagnetic behavior with saturation magnetic moments (51–53 emu g^?1) comparable to silica‐coated MNPs. They also provide good colloidal stability at different pH and salt concentrations, and low cytotoxicity to MCF‐7 human breast epithelial cells. The relaxivity data and magnetic resonance (MR) phantom images demonstrate the potential application of these MNPs in bioimaging.     

Surface modification of magnetic nanoparticles in biomedicine

Progress in surface modification of magnetic nanoparticles(MNPs)is summarized with regard to organic molecules,macromolecules and inorganic materials.Many researchers are now devoted to synthesizing new types of multi-functional MNPs,which show great application potential in both diagnosis and treatment of disease.By employing an ever-greater variety of surface modification techniques,MNPs can satisfy more and more of the demands of medical practice in areas like magnetic resonance imaging(MRI),fluorescent marking,cell targeting,and drug delivery.     

Nano palladium supported on high‐surface‐area metal–organic framework MIL‐101: an efficient catalyst for Sonogashira coupling of aryl and heteroaryl bromides with alkynes

Palladium nanoparticle‐incorporated metal–organic framework MIL‐101 (Pd/MIL‐101) was successfully synthesized and characterized using X‐ray diffraction, nitrogen physisorption, X‐ray photoelectron, UV–visible and infrared spectroscopies, and transmission electron microscopy. The characterization techniques confirmed high porosity and high surface area of MIL‐101 and high stability of nano‐size palladium particles. Pd/MIL‐101 nanocomposite was investigated for the Sonogashira cross‐coupling reaction of aryl and heteroaryl bromides with various alkynes under copper‐free conditions. The reusability of the catalyst was tested for up to four cycles without any significant loss in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Thermal Conversion of Methane to Formaldehyde Promoted by Gold in AuNbO3+ Cluster Cations

In addition to generation of a methyl radical, formation of a formaldehyde molecule was observed in the thermal reaction of methane with AuNbO₃⁺ heteronuclear oxide cluster cations. The clusters were prepared by laser ablation and mass‐selected to react with CH₄ in an ion‐trap reactor under thermal collision conditions. The reaction was studied by mass spectrometry and DFT calculations. The latter indicated that the gold atom promotes formaldehyde formation through transformation of an Au?O bond into an Au?Nb bond during the reaction.     

A gold-based nanobeacon probe for fluorescence sensing of organophosphorus pesticides

A nanomaterials-based novel molecular beacon has attracted growing attentions in fluorescent assays as many nanomaterials possess excellent quenching efficiency. In this work, a gold-based nanobeacon probe was established to detect organophosphorus pesticides for the first time. The constructed gold-based nanobeacon acted as a signal indicator and could display the decreasing of the intensity in the presence of targets, which competitively bound to single strand DNA. To achieve a high sensitive probe, some parameters including solution pH, temperature and reaction time were investigated and optimized. The gold-based nanobeacon probe assay was proved to be rapid and sensitive to achieve a detection limit of 0.035 μM for isocarbophos, 0.134 μM for profenofos, 0.384 μM for phorate and 2.35 μM for omethoate, respectively. The prepared nanobeacon effectively reduced the background and improved the detection sensitivity and selectivity. The probe is stable, easy to operate and does not need sophisticated instruments. These features makes the probe feasible for screening trace organophosphorus pesticides in real samples.     

Facile preparation of boronic acid‐functionalized magnetic nanoparticles with a high capacity and their use in the enrichment of cis‐diol‐containing compounds from plasma

The use of bronate affinity adsorbents is a new separation method that appeared recently with great potential for specific extraction of cis‐diol‐containing compounds. In this work,a new strategy for the facile construction of boronic acid‐functionalized Fe₃O₄ magnetic nanoparticles (Fe₃O₄@FPBA MNPs) with a high capacity was described. The extraction capacity of the Fe₃O₄@FPBA MNPs was determined to be 66.0 ± 2.7 µmol/g for catechol and 80.6 ± 2.0 µmol/g for dopamine, being higher than that for the reported methods. The Fe₃O₄@FPBA MNPs were used to extract four cis‐diol drugs: caffeic acid isopropyl ester, caffic acid bornyl ester, isopropyl 3‐(3,4‐dihydroxyphenyl)‐2‐hydroxypropanoate and 3‐(3, 4‐dihydroxyphenyl)‐2‐hydroxylpropionic acid – from the spiked rabbit plasma, and the recoveries of four drugs were between 87.29 and104.37% with relative standard deviations ranging from 1.34 to 8.81%. Under the most favorable conditions, the solid‐phase extraction combined with HPLC‐UV for the analysis of four drugs in plasma could eliminate interferences from endogenous components of the biological fluids and exhibited sufficient precision and accuracy. These results showed that the prepared Fe₃O₄@FPBA MNPs were qualified for efficiently enriching and determining the trace cis‐diol substances from biological samples. Copyright © 2014 John Wiley & Sons, Ltd.     

Partial Oxidation as a Rational Approach to Kinetic Control in Bioinspired Magnetite Synthesis

Biological systems show impressive control over the shape, size and organization of mineral structures, which often leads to advanced physical properties that are tuned to the function of these materials. Such control is also found in magnetotactic bacteria, which produce—in aqueous medium and at room temperature—magnetite nanoparticles with precisely controlled morphologies and sizes that are generally only accessible in synthetic systems with the use of organic solvents and/or the use of high‐temperature methods. The synthesis of magnetite under biomimetic conditions, that is, in water and at room temperature and using polymeric additives as control agents, is of interest as a green production method for magnetic nanoparticles. Inspired by the process of magnetite biomineralization, a rational approach is taken by the use of a solid precursor for the synthesis of magnetite nanoparticles. The conversion of a ferrous hydroxide precursor, which we demonstrate with cryo‐TEM and low‐dose electron diffraction, is used to achieve control over the solution supersaturation such that crystal growth can be regulated through the interaction with poly‐(α,β)‐dl ‐aspartic acid, a soluble, negatively charged polymer. In this way, stable suspensions of nanocrystals are achieved that show remanence and coercivity at the size limit of superparamagnetism, and which are able to align their magnetic moments forming strings in solution as is demonstrated by cryo‐electron tomography.     

From Spherical to Leaf‐Like Morphologies: Tunable Supramolecular Assembly of Alkynylgold(I) Complexes through Variations of the Alkyl Chain Length

A series of luminescent polynuclear alkynylgold(I) complexes with different lengths of alkyl chains attached at the N‐heterocyclic carbene moieties has been synthesised and demonstrated to display intriguing self‐assembly behaviours through a cooperative growth mechanism. Variation of the alkyl chain length was found to cause drastic morphological differences in the aggregates and to strongly affect the thermodynamic parameters as revealed by the nucleation–elongation model.