Facile formation of stimuli-responsive,fluorescent and magnetic nanoparticles based on cellulose stearoyl ester via nanoprecipitation

In comparison to stimuli-responsive, multi-functional nanoparticles (NPs) from synthetic polymers, such NPs based on sustainable, naturally occurring polysaccharides are still scarce. In the present study, stable stimuli-responsive, fluorescent and magnetic NPs were fabricated using cellulose stearoyl esters (CSEs) consisting of cellulose and stearoyl groups. The multifunctional NPs with the average diameters between 80 and 250 nm were obtained after facile nanoprecipitation using CSE solutions containing Fe₃O₄-NPs. Using the aqueous solution of fluorescent rhodamine B as precipitant, NPs with rhodamine B on NP surface were obtained. Rhodamine B could be released depending on the temperature. In comparison, stearoylaminoethyl rhodamine B can be encapsulated in CSE-NPs, which renders obtained NPs reversible fluorescence in response to UV illumination and heat treatment.     

Impact of PS/SiO2 morphologies on the SERS activity of PS/SiO2/Ag nanocomposite particles

To understand the relationship between the morphology of carboxyl-functionalized polystyrene/silica (PS/SiO₂) nanocomposite microspheres and the surface-enhanced Raman scattering (SERS) performance of PS/SiO₂/Ag nanocomposite particles, core-shell and raspberry-like PS/SiO₂ composite microspheres were used as templates to prepare PS/SiO₂/Ag nanocomposite particles. The core-shell and raspberry-like structured PS/SiO₂ templates were prepared via in situ sol-gel reaction by hydrolysis tetraethyl orthosilicate (TEOS) in alkali solution. Silver nanoparticles (10–50 nm) were loaded on the PS/SiO₂ templates’ surface by chemical reduction. The morphology and structure of the PS/SiO₂/Ag particles were characterized by TEM, SEM, X-ray diffraction (XRD), and ultraviolet-visible (UV-vis) spectroscopy. Rhodamine 6G (R6G) was selected as a model chemical to study the enhancement performance of substrate constructed by PS/SiO₂/Ag nanocomposite. Results indicated that the PS/SiO₂/Ag nanocomposite prepared based on the core-shell templates showed higher SERS activity. The beneficial effect was associated with a lower specific area of core-shell structure and the larger average diameter of nanosilvers than that of the raspberry-like templates.     

A photoionization study of the van der Waals molecule C2H4 · HCl

The dissociation energy of the C₂H₄ · HCl van der Waals complex was determined to be 3.18±0.73 kcal mol^?1 by a dissociative photoionization technique. C₂H₄ · HCl was produced by free expansion of a 1:4 mixture of C₂H₄ in HCl and the clusters were ionized with tunable synchrotron radiation. The photoionization efficiency function of (C₂H₄ · HCl)⁺ from C₂H₄ · HCl was determined between 600 and 1,300 Å and the onset for (C₂H₄ · HCl)⁺ was established as 1,163±2 Å = 10.66±0.02 eV; these values give ΔH _f ⁰ (C₂H₄ · HCl) = ?10.7±0.7 kcal mol^?1 and ΔH _f ⁰ (C₂H₄·HCl⁺)=235.1±0.9 kcal mol^?1. A complex ion dissociation energyD ₀(C₂H₄ · HCl⁺) = ?0.3±0.9 kcal mol^?1 was calculated from the results. The major features on the PIE curve for C₂H₄ · HCl⁺ can be analyzed in terms of the known energetic features of C₂H ₄ ⁺ and HCl. An extended energy diagram for the C₂H₄ + HCl system is presented.     

Polyoxotungstate nanoclusters supported on silica as an efficient solid-phase microextraction fiber of polycyclic aromatic hydrocarbons

A highly porous silica-supported tungstophosphoric acid (PW) nanocluster was prepared for use in solid-phase microextraction (SPME) of polycyclic aromatic hydrocarbons (PAHs). The PWs represent a class of discrete transition metal-oxide nanoclusters and their structures resemble discrete fragments of metal-oxide structures of definite size and shape. Transition metal-oxide nanoclusters display large structural diversity, and their monodisperse sizes can be tuned from several Ångstroms up to 10 nm. The highly porous silica-supported tungstophosphoric acid nanocluster material is found to be capable of efficiently extracting PAHs from aqueous sample solutions. The nanomaterial was immobilized on a stainless steel wire for fabrication of the SPME fiber. Following thermal desorption, the PAHs were quantified by GC-MS. Analytical merits include limits of detection that range from 0.02 to 0.1 pg mL^?1 and a dynamic range as wide as from 0.001 to 100 ng mL^?1. Under optimum conditions, the repeatability for one fiber (n?=?3), expressed as the relative standard deviation, is between 4.3 % and 8.6 %. The method is simple, rapid, and inexpensive. The thermal stability of the fiber and the high relative recovery make this method superior to conventional methods of extraction.

The highly porous silica-supported tungstophosphoric acid nanocluster material is found to be capable of efficiently extracting PAHs from aqueous sample solutions. The prepared nanomaterial was immobilized onto a stainless steel wire for fabrication of the SPME fiber. Following thermal desorption, the PAHs were quantified by GC-MS.     

On the determination of HCl+ (A,v′) vibrational populations from HCl+ (A→X) fluorescence spectra: direct comparison between photoionization and penning ionization

Using a beam apparatus, we have measured the HCl⁺ (A,v′→X,v″) fluorescence spectra of HCl⁺ (A,v′) ions formed in HeI (58.4 nm), and NeI (73.6 nm) photoionization and, for the first time, in He (2³ S) Penning ionization under single collision conditions with a wavelength bandwidth around 1 nm. In addition, we have studied Ne (3s ³ P _{2, 0}) Penning ionization of HCl at three different collision energies. The procedure and the problems in extracting HCl⁺ (A,v′) vibrational populations from the data are discussed in some detail. Thedirect comparison of photoionization and Penning ionization data allows definitive conclusions to be drawn on the question whether final state interactions in the Penning reaction change the “nascent” vibrational population (determined by electron spectrometry); for He (2³ S)+HCl, such changes are shown to be absent within the experimental uncertainty (<±10%). For Ne (3s ³ P _{2, 0})+HCl, the HCl⁺ (A,v′=0, 1) populations are also found to be close to those measured by electron spectrometry and essentially independent of collision energy in the range 34–96 meV. From measurements of the fluorescence intensity as a function of HCl density, we have evidence for a fast loss of HCl⁺ (A,v′) ions in collisions with HCl (rate constant around 5·10^?9 cm³s^?1).     

Heat of reaction and curing of epoxy resin

The heat of reaction and kinetics of curing of diglycidyl ether of bisphenol-A (DGEBA) type of epoxy resin with catalytic amounts of ethylmethylimidazole (EMI) have been studied by differential power-compensated calorimetry as a part of the program for the study of process monitoring for composite materials. The results were compared with those from 1∶1 and 1∶2 molar mixtures of DGEBA and EMI. A method of determination of heat of reaction from dynamic thermoanalytical instruments was given according to basic thermodynamic principles. The complicated mechanism, possibly involving initial ionic formation, has also been observed in other measurements, such as by time-domain dielectric spectroscopy. The behavior of commercially available DGEBA resin versus purified monomeric DGEBA were compared. The melting point of purified monomeric DGEBA crystals is 41.4 °C with a heat of fusion of 81 J/g. The melt of DGEBA is difficult to crystallize upon cooling. The glass transition of purified DGEBA monomer occurs around ?22 °C with aΔC _p of 0.60 J/K/g.     

Structural and thermal properties of HDPE/n-AlN polymer nanocomposites

High-density polyethylene (HDPE) containing various volume fractions (0–20 vol%) of aluminum nitride nanoparticles (n-AlN) is prepared by melt mixing. Structural and morphological characterizations of the prepared composites are carried out by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), and atomic force microscopy (AFM). Thermal stability and degradation kinetics of HDPE/AlN (nano) composites are investigated by Thermogravimetric analysis (TG). HR-TEM micrographs confirm fairly uniform dispersion of AlN nanoparticles, as well as the existence of long interconnected chain-like aggregates. AFM images also confirm homogeneous dispersion of n-AlN in the polymer matrix. Roughness analysis from the AFM data indicates the presence of substantial undulation from the mean surface level. Thermogravimetric data indicate small improvement in the thermal stability of the composites. Kinetic parameters, viz., the activation energy (E _a), frequency factor (A), and reaction order (n) are estimated using the isoconversional methods of Kissinger, Flynn–Wall–Ozawa (FWO), KAS, and Friedman. Activation energies (E _a) calculated by the above four models display nearly similar features and are enhanced by the presence of AlN nanoparticles. Kinetics of degradation of HDPE-AlN (nano) composites follows a first-order reaction.     

Thermal decomposition of polymethylmethacrylate synthesized with anionic catalysts

TG and DTA data are used to show that the thermal decomposition of polymethylmethacrylate (PMMA) synthesized with anionic catalysts depends on the nature of the catalyst. It is found that the thermal stability of PMMA obtained by using anionic amide catalysts is higher than that of radical PMMA and of PMMA obtained with other anionic catalysts, and depends on the temperature of polymerization and on the molecular weight of the polymer.     

Effect of Cl substituent in the aromatic tetracycline ring on its reactivity with solvated electrons

Decomposition yields of tetracycline hydrochloride /TC.HCl/ and chlorotetracycline hydrochloride /ClTC?HCl/ in methanol solution saturated with Ar or N₂O were determined. Rate constants of the reaction e_s with some antibiotics were obtained: $$\begin{gathered} k/e_s^ - + ClTC \cdot HCl/ = 2 \cdot 49 \times 10^8 dm^3 \cdot mole^{ - 1} \cdot s^{ - 1} ; \hfill \\ k/e_s^ - + TC \cdot HCl/ = 2 \cdot 86 \times 10^8 dm^3 \cdot mole^{ - 1} \cdot s^{ - 1} \cdot \hfill \\ \end{gathered} $$ On the basis of the diffence between decomposition yields: ΔG=G_?TC.HCl^?G?ClTC.HCl′ 7-C?Cl group decomposition yield and the rate constant $$k/e_s^ - + Cl - C - 7/ = 7 \cdot 94 \times 10^8 dm^3 \cdot mole^{ - 1} \cdot s^{ - 1} $$ were determined. It was demonstrated by¹H NMR that the radical formed by degradation of 7-C?Cl group is recombined with the H atoms leading to ClTC.HCl being converted into tetracycline hydrochloride /TC.HCl/.     

Kinetics and possible mechanism of hydrogen chloride oxidation over supported copper-containing salt catalysts: II. Kinetics of HCl oxidation in the deacon and methane oxychlorination reactions over the CuCl2-KCl-LaCl3 catalyst

The kinetics of HCl oxidation at 350–425°C over the supported CuCl₂-KCl-LaCl₃ catalyst has been investigated using a gradientless technique. The HCl oxidation kinetics in the Deacon and methane oxychlorination reactions has been studied in order to substantially extend the \(Cl_2 \left( {P_{Cl_2 } } \right)\) partial pressure variation range. When the reaction rate is independent of P _HCl, HCl oxidation on the copper-potassium catalysts is described by the same rate equation, irrespective of whether the catalyst contains lanthanum or not. The introduction of lanthanum chloride increases the HCl oxidation rate by one order of magnitude. The rate equation obtained has significant advantages over the equation corresponding to the Kenney-Slama equation. The kinetic features of HCl oxidation over the lanthanum-containing catalyst, whether the process depends on P _HCl or not, can be explained in terms of the superposition of the Kenney-Slama dissociative mechanism and the catalytic mechanism suggested here. The role of lanthanum chloride in both HCl oxidation pathways is considered.     

Organelle sensor: amperometric determination of nadh by immobilized mitochondrial electron transport particles

A new sensor for NADH was developed by making use of an immobilized subcellular organelle. Mitochondria was used as a model system for assembling an organelle sensor. Mitochondrial electron transport particles (ETP) were prepared from beef heart muscle and entrapped in the membrane formed of agar gel. The membrane-bound ETP was found capable of NADH oxidation: $$NADH + \tfrac{1}{2}O_2 + H^ + \xrightarrow{{ETP}}NAD^ - + H_2 O$$ The membrane was tightly attached to the surface of an oxygen electrode capable of amperometric detection of O2. The sensor responded to NADH in solution with a resulting electric output. The response was enhanced by the addition of 2,4-dinitrophenol (DNP). NADH was determined in the concentration range 1–300 µM. NADH was alternatively determined for 2 weeks without replacing the ETP-bound membrane.     

Largely enhanced molecular orientation and mechanical property of injection-molded high-density polyethylene parts via the synergistic effect of polyamide 6 in situ microfibrillar and intense shear flow

The high-density polyethylene (HDPE)/polyamide 6 (PA6) in situ microfibrillar composites (HAM-C) were fabricated by the “extrusion-hot stretch-quenching” technique, in which PA6 microfibrillar had diameters lying in the range 0.55 to 1.05 μm. Then the HAM-C and pure HDPE were processed by multi-melt multi-injection molding (MMMIM). The effect of PA6 in situ microfibrillar and secondary melt penetration on the crystalline morphologies and mechanical properties was investigated using a variety of characterization techniques including differential scanning calorimetry (DSC), rheological experiments, scanning electron microscopy (SEM), synchrotron two-dimensional small-angle X-ray scattering (SAXS), and tensile testing. It was found that PA6 microfibrillar not only acted as a heterogeneous nucleation agent, but also prolonged the relaxation time of HDPE matrix by suppressing the mobility of HDPE molecular chains. It was revealed, from observing the morphologies, that the presence of PA6 microfibrillar not only facilitated the formation of transcrystalline superstructures on its surface, but also induced much more oriented crystals nearby as a result of the amplified local shear field. Furthermore, SAXS results confirmed that the degree of orientation of the injection-molded HAM-C part (HAM-M) was largely enhanced. Finally, the tensile testing showed that the tensile strength and Young’s modulus of the HAM-M sample were enhanced by 38.8 and 54.6 %, respectively, when compared with pure HDPE parts. This work provides a promising way to tailor the crystalline structure of the injection-molded parts.     

Penning ionization electron spectrometry of hydrogen chloride

An electron spectrometric study has been performed on HCl using metastable helium and neon atoms as well as neon resonance photons. High resolution electron spectra were obtained with two different beam apparatuses for a mixed He(2¹ S, 2³ S) beam, a pure He(2³ S) beam, and, for the first time, state-selected pure Ne(3s ³ P ₂) and pure Ne(3s ³ P ₀) beams, and for NeI resonance photons. For the system He(2³ S)+HCl the vibrational populationsP(υ′) of the formed HCl⁺ (X ²∏ _i , υ′) and HCl⁺ (A ²Ω⁺, υ′) ions are found to differ from the Franck-Condon factors for unperturbed potentials, indicating slight bond stretching in HCl upon He(2³ S) approach. For He(2¹ S)+HCl the vibrational peak shapes and vibrational populations are substantially different from the He(2³ S) case, pointing to an additional, charge exchanged interaction (He⁺+HCl^?) in the entrance channel of the former system. For the first time, we have detected the electrons in both the He(2¹ S)+HCl and He(2³ S)+HCl spectra associated with the major mechanism for the formation of Cl⁺ ions: energy transfer to repulsive HCl** Rydberg states, dissociating toH(1s) and autoionizing Cl**(¹ D ₂ nl) atoms. For both Ne(³ P ₂)+HCl and Ne(³ P ₀)+HCl, the populationsP(υ′) of both final molecular states HCl⁺ (X, A) agree closely with the Franck-Condon factors at the average relative collision energyē _coll=55 meV and, for HCl⁺ (A ²Ω⁺), also atē _coll=130 meV.     

Mechanism and improvement of complex formation between LPS and polymyxin B that is immobilized on an ion exchanger

Polymyxin B was immobilized on the ion exchanger, Amberlite IRC-50. The modified support was used as an adsorbent for lipopolysaccharide ofE. coli from a phosphate buffer at pH = 7.0 and T = 20°C. The insertion of a spacer, 6-amino hexanoic acid, improved the adsorption capacity of the modified carrier significantly. Upon partial acetylation (25%) of primary amino groups of immobilized Polymyxin B, the adsorption capacity of the support was halved. From our results, it is concluded that the complex formation between lipopolysaccharide and immobilized Polymyxin B is based on both lipophilic, as well as electrostatic, interactions. Convenient procedures for the immobilization of the ligands and the characterization of the ion exchanger are described.     

On synthesis of Fe2SiO4/SiO2 and Fe2O3/SiO2 composites through sol–gel and solid-state reactions

Major processing factors in forming Fe₂SiO₄/SiO₂ and Fe₂O₃/SiO₂ powders via sol–gel synthesis followed by solid-state reactions are investigated. The results clearly indicate that the chemical compositions of the precursors, the ratio of the precursors, the nature of the catalyst used, and the gas atmosphere during solid-state reactions can all affect the outcome of the reaction product(s). The formation of Fe₂SiO₄/SiO₂ is enhanced by using the precursor iron(III) acetylacetonate as the Fe source with the precursor ratio of iron(III) acetylacetonate to tetraethyl orthosilicate being 1:1 and the addition of formic acid. Otherwise, crystalline Fe and Fe₃C are formed in place of Fe₂SiO₄. By altering the gas atmosphere during solid-state reactions from argon to oxygen, the reaction products change from Fe₂SiO₄/SiO₂ to Fe₂O₃/SiO₂. All of the observed phenomena can be rationalized via the degree of mixing of the Fe–O and Si–O domains at the molecular level in the gel network during sol–gel reactions and the presence of a reducing or oxidizing atmosphere during the solid-state reaction.     

Visual detection of arginine,histidine and lysine using quercetin-functionalized gold nanoparticles

We report on the use of quercetin-functionalized gold nanoparticles (QC-AuNPs) as a colorimetric probe for the amino acids arginine (Arg), histidine (His) and lysine (Lys). The method is based on the aggregation of the QC-AuNPs that is caused by these amino acids and leads to a visually detectable color change from red to blue. The absorption maxima shift from 525 nm to 702, 693, and 745 nm, respectively. Aggregations are confirmed by dynamic light scattering (DLS) and transmission electron microscopic techniques (TEM). The effects of the QC concentration, temperature and reaction time for the preparation of QC-Au NPs were tested. Other amino acids do not interfere. Under the optimal conditions, linear relationships exist between the absorption ratios at 702/525 nm (for Arg), 693/525 nm (for His), and 745/525 nm (for Lys) over the concentrations ranges from 2.5–1,250 μM (Arg) and 1–1,000 μM (His and Lys), respectively. The respective limits of detection are 0.04, 0.03, and 0.02 μM. The method provides a useful tool for the rapid visual and instrumental determination of the three amino acids. Figure

We report the use of quercetin as novel reagent for preparation and functionalization of gold nanoparticles to colorimetric sensing of three aminoacids (arginine, histidine and lysine). This is based on the aggregation of QC-AuNPs induced by three aminoacids.     

Solute-solvent interactions in acid-base dissociation: nine protonated nitrogen bases in water-DMSO solvents

A titration method utilizing glass electrodes and silver-silver chloride electrodes in a cell without liquid junction has been used to determine the acidic dissociation constants at 15, 25, and 35°C of nine protonated nitrogen bases in mixtures of water and dimethyl sulfoxide (DMSO). The mole fraction of DMSO in the mixed solvents was 0.2, 0.4, 0.6, and 0.8. The cell was calibrated with HCl (molality=0.01 mole-kg^?1) in the mixed solvents, and the ionic strength and chloride molality remained substantially unchanged during the titration with added base. This method minimizes the errors resulting from the formation of AgCl ₂ ^? in the media rich in DMSO. The pK _a of all the protonated bases passes through a minimum at a solvent composition close to that at which H₂O-DMSO mixtures display a maximum solvent structure. The results are discussed in terms of the preferential solvation of ions by the two types of solvent molecules. They are consistent with the hypothesis that increased solvent structure is accompanied by increased desolvation of the cation acids.     

In Situ Characterization of Proteins Using Laserspray Ionization on a High-Performance MALDI-LTQ-Orbitrap Mass Spectrometer

The MALDI-LTQ-Orbitrap XL mass spectrometer is a high performance instrument capable of high resolution and accurate mass (HRAM) measurements. The maximum m/z of 4000 precludes the MALDI analysis of proteins without generating multiply charged ions. Herein, we present the study of HRAM laserspray ionization mass spectrometry (MS) with MS/MS and MS imaging capabilities using 2-nitrophloroglucinol (2-NPG) as matrix on a MALDI-LTQ-Orbitrap XL mass spectrometer. The optimized conditions for multiply charged ion production have been determined and applied to tissue profiling and imaging. Biomolecules as large as 15 kDa have been detected with up to five positive charges at 100 K mass resolution (at m/z 400). More importantly, MS/MS and protein identification on multiply charged precursor ions from both standards and tissue samples have been achieved for the first time with an intermediate-pressure source. The initial results reported in this study highlight potential utilities of laserspray ionization MS analysis for simultaneous in situ protein identification, visualization, and characterization from complex tissue samples on a commercially available HRAM MALDI MS system. Graphical Abstract

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Toward mechanized peptide synthesis via polymeric reagents approach

Simultaneous application of high-molecular-weight active esters and polyvinylN,N- diethylbenzylamine was used as a basis for a continuous peptide synthesis via the polymeric reagents approach. Using the synthetic procedure developed, the hexapeptide Boc-L-Pro-L-Val-L-Lys[Z(p-NO₂)]-L-Val-L-Tyr(Dnp)-L-Pro-OBzr¹ and the tetrapeptide Boc-l-Lys[Z(p-NO₂)]-L-Lys[Z(p-NO₂)]-L-Arg(NO₂)-L-Arg(NO₂)-OBzr, corresponding to residues 19–24 and 15–18 of human ACTH, were synthesized in 63 and 70% overall yields, respectively.