Mechanochemical and microwave treatment of precipitated zirconium dioxide and study of its physical–chemical,thermal and photocatalytic properties

Journal of Thermal Analysis and Calorimetry - The effects of the microwave treatment (MWT) and mechanochemical treatment (MChT) on the structure and physicochemical properties of precipitated...     

The physical properties and unusual pyrolysis behaviour of a supramolecular complex of β-cyclodextrin and potassium ferrioxalate

The thermal pyrolysis behaviour of a complex of β-cyclodextrin (CD) and potassium ferrioxalate (PF) was analyzed using gas chromatography coupled to time-of-flight mass spectrometry. Two rare inorganic ions: CO(2)(2+) and O(4)(+), neither of which was found in the cases of free β-CD and PF, were synchronously observed during the decomposition of the complex. Our observations led to proposed formation mechanisms of the ions, in which the structural transformation of a metastable intermediate ion (C(2)H(4)O(3)(+)) was employed to qualitatively explain our data. Besides this, the formation, structure and magnetic properties of the complex were evaluated carefully. First, XPS analysis indicates a decrease of electron densities of Fe(III) ions in the presence of β-CD. We think that this is due to an effect of the noncovalent complexation between PF and β-CD. This gives an indication on the effect of second sphere coordination of β-CD on the electronic structure of the Fe(III) in the first coordination sphere. Second, structural changes in stacking modes and morphologies provide further support for the noncovalent complexation. For example, the surface feature of the complex gives us an impression that both β-CD and PF are evenly dispersed with each other. Also, the complex presents a uniform sponge-like porous nanostructure with diameters of less than 50 nm. This seems to be an important reason for those changes that occurred in the thermal analysis. Finally, the result of magnetic experiments implies that the coordination compound PF upon complexation with β-CD will experience a gradual decrease in magnetization with the increase of magnetic fields. These observations have significant implications for a better understanding of the importance of the construction and deconstruction of a second sphere coordination in modifying the physical properties of an σ-coordination compound.     

Structural characterization and physicochemical properties of quercetin–Pb complex

Flavonoids are a large group of ubiquitous molecules synthesized by plants. These molecules possess antioxidant activities which prevent free radical damage to biological molecules and can also be metal chelators. This article describes the synthesis of a Pb(II)–quercetin complex and characterization by UV–visible, infrared, ¹H nuclear magnetic resonance spectroscopy, thermogravimetric analysis, and differential thermal analysis. The formation of quercetin and Pb(II) complex ratio 1?:?1 was confirmed by UV–visible spectroscopy. The composition of the complex does not change with pH. Antimicrobial activities were evaluated by using Gram-positive and Gram-negative bacteria. The antioxidant properties of quercetin and the complex was evaluated by using 2,2′-diphenyl-1-picrylhydrazyl radical scavenging method. The quercetin–Pb complex was less effective than quercetin in antimicrobial and antioxidant activity.     

Selective soluble polymer–assisted electrochemical delamination of chemical vapor deposition graphene

Journal of Solid State Electrochemistry - We have explored an optimized electrochemical delamination technique to transfer large area graphene grown by chemical vapor deposition (CVD) technique. A...     

DFT study of chemical mechanism of pre-SERS spectra in Pyrazine–metal complex and metal–Pyrazine–metal junction

The chemical mechanism of Normal Raman Scattering (NRS) and pre-surface enhanced Raman scattering (pre-SERS) spectra for Pyrazine–Ag₂ complex, Ag₂–Pyrazine–Ag₂ junction and Ag₂–Pyrazine–Au₂ junction were investigated with density functional theory (DFT) and charge difference densities (CDDs) for the first time. The NRS intensities of the above three structures enhanced obviously relative to isolated Pyrazine and the enhancement mechanism was confirmed to be static chemical enhancement. The pre-SERS intensities of the above three structures enhanced evidently compared to corresponding NRS intensities, and the enhancement mechanism was confirmed to charge transfer (CT) resonance Raman enhancement. The largest enhanced orders of NRS and pre-SERS intensities among the three structures were up to 10³ and 10⁵, respectively. Compared the intensity of pre-SERS with corresponding intensity of NRS spectra, the enhancement effect of Pyrazine–Ag₂ complex was larger than the others. Intramolecular and intermolecular CT on resonant electronic transition were described by CDDs.     

Physical–chemical characterization of new anti-inflammatory agent (LPSF/GQ-130) and evaluation of its thermal compatibility with pharmaceutical excipients

LPSF/GQ-130 is a drug candidate, according to reports about its significant anti-inflammatory activity and non-toxicity demonstrated in an acute preclinical study. Despite this, knowledge of its physical–chemical properties is insufficient for the development of medicines. Thus, this work aimed to characterize the raw material at its molecular, particle, and agglomerate level as well as evaluate its thermal compatibility to pharmaceutical excipients. Through spectrometric techniques the molecular structure of the substance was confirmed. For thermal analysis its melting (171.3–176.5 °C) and degradation (238.3–297.4 °C) ranges, besides its purity (99.37 %), were determined. The kinetic non-isothermal degradation supplied the order of thermal reaction (0), the activation energy (96.14 kJ mol^?1) and the frequency factor (3.130 × 10^?7 min^?1). The diffraction of X-rays presented well defined signs in the angles 5.5°, 16.3°, and 44.18° 2θ, suggesting crystalline structure. Scanning electronic microscopy exhibited needle morphology. LPSF/GQ-130 presented Type-III isotherm adsorption/desorption, with a superficial area of 81.3529 m² g^?1 and water content calculated at 1 % using the Karl Fisher method. Laser granulometry calculated its granulometry between 11.65 and 13.10 μm, thus it was characterized as a very fine powder. The prototype was classified as insoluble in water (<0.0187 μg mL^?1) and soluble in acetone and acetonitrile, and exhibits instability in basic pH (100 %) and oxidative conditions (30–70 %). In thermal compatibility the excipients PVP K-30, Compritol^® 888 ATO, and MYRJ^® 59 seem to exercise a protective thermal activity for the prototype.     

An approach to core–shell nanostructured materials with high colloidal and chemical stability: synthesis, characterization and mechanistic evaluation

Silver–polypyrrole (PPy) core–shell nanoparticles have been fabricated by a facile one-step “green” synthesis using silver nitrate as an oxidant and soluble starch as an environmentally benign stabilizer and co-reducing agent. The morphology and optical properties of the particles were significantly affected by the reaction temperature, soluble starch concentration, and ratio of pyrrole monomer to AgNO₃ oxidant. The core–shell nanoparticles exhibited outstanding dispersive properties in deionized water due to residual starch, as compared with PPy nanoparticles in which starch was absent. The mechanism of core–shell nanoparticle formation was elucidated through TEM imaging vs. reaction time. The colloidal and chemical stability of the nanoparticles was demonstrated in a variety of solvents, including acids, bases, and ionic and organic solvents, through monitoring the localized surface plasmon resonance of the nanoparticles. Furthermore, the catalytic properties of these silver–PPy core–shell nanoparticles were also demonstrated.

In situ electrochemical evaluation of anticancer drug temozolomide and its metabolites–DNA interaction

Temozolomide (TMZ) is an antineoplastic alkylating agent with activity against serious and aggressive types of brain tumours. It has been postulated that TMZ exerts its antitumor activity via its spontaneous degradation at physiological pH. The in vitro evaluation of the interaction of TMZ and its final metabolites, 5-aminoimidazole-4-carboxamide (AIC) and methyldiazonium ion, with double-stranded DNA (dsDNA) was studied using differential pulse voltammetry at a glassy carbon electrode. The DNA damage was electrochemically detected following the changes in the oxidation peaks of guanosine and adenosine residues. The results obtained revealed the decrease of the dsDNA oxidation peaks with incubation time, showing that TMZ and AIC/methyldiazonium ion interact with dsDNA causing its condensation. Furthermore, the experiments of the in situ TMZ and AIC/methyldiazonium ion–dsDNA interaction using the multilayer dsDNA-electrochemical biosensor confirmed the condensation of dsDNA caused by these species and showed evidence for a specific interaction between the guanosine residues and TMZ metabolites, since free guanine oxidation peak was detected. The oxidative damage caused to DNA bases by TMZ metabolites was also detected electrochemically by monitoring the appearance of the 8-oxoguanine/2,8-dyhydroxyadenine oxidation peaks. Nondenaturing agarose gel electrophoresis of AIC/methyldiazonium ion–dsDNA samples confirmed the occurrence of dsDNA condensation and oxidative damage observed in the electrochemical results. The importance of the dsDNA-electrochemical biosensor in the in situ evaluation of TMZ–dsDNA interactions is clearly demonstrated.     

Effects of growth behaviors on chemical and physical properties of sol–gel derived ZnO:Ga films

In this study, we investigated the effects of different heating processes on the structural, electrical and chemical properties of ZnO:Ga (GZO) films from the viewpoint of nucleation and growth behaviors. An infrared heating furnace and a traditional tube furnace were employed for the homogeneous and heterogeneous nucleation of GZO films. XRD patterns demonstrated that the preferential growth orientation of both kinds of GZO films is still the (002) direction. XPS data implied that the infrared heating process enables more uniform distribution of the dopant material and retards the oxidization of gallium in grain boundary areas. At the same time, the textured crystallite might provide a free tunnel for oxygen diffusion. Thus, the activation of free charge carriers could be more efficient when the GZO films were annealed under vacuum. As a result, the samples annealed by the infrared heating furnace had a noticeably high carrier concentration. Although the mobility was slightly smaller than that of the samples annealed by the tube furnace, film resistivity dropped obviously in general.     

Investigation into the physical–chemical properties of chemically pretreated sugarcane bagasse

Journal of Thermal Analysis and Calorimetry - Enzymatic hydrolysis is one of the major steps involved in the conversion of sugarcane bagasse into ethanol. Pretreatments break down macrostructures...     

Synthesis of a mixed carboxylate–phosphinate AAZTA-like ligand and relaxometric characterization of its Gd complex

The synthesis of the new polydentate ligand AAZ2A2P^Et derived from the heptadentate polyaminocarboxylic ligand AAZTA (6-amino-6-methylperhydro-1,4-diazepine-N,N′,N″,N″-tetraacetic acid) in which two acetate groups were replaced by methyleneethylphosphinic pendant arms is reported. The relaxometric behavior of the corresponding mono-aquo Gd^III complex was also investigated.     

Synthesis and characterization of a novel organic–inorganic hybrid supramolecular recognition material and its selective adsorption for cesium

To separate Cs(I) from highly active liquid waste, a macroporous silica-based 25, 27-bis(iso-propyloxy)calix[4]arene-26,28-crown-6 (BiPCalix[4]C6) supramolecular recognition material, BiPCalix[4]C6/SiO₂–P, was synthesized and characterized by SEM, FT-IR, and TG-DSC. The adsorption properties of BiPCalix[4]C6/SiO₂–P and a macroporous polymer-based supramolecular recognition composite, BiPCalix[4]C6/XAD-7, were compared. It was found that BiPCalix[4]C6/SiO₂–P exhibited better adsorption ability and faster adsorption dynamics than BiPCalix[4]C6/XAD-7. The adsorption isotherm of Cs(I) onto BiPCalix[4]C6/SiO₂–P was studied at 298 K and it was well described by Langmuir isotherm model. The complex composition between BiPCalix[4]C6/SiO₂–P and Cs(I) was determined as 1:1 type by investigating the effect of the concentrations of BiPCalix[4]C6, Cs(I), and H⁺ on the adsorption. Meanwhile, the selectivity of BiPCalix[4]C6/SiO₂–P towards Na(I), K(I), Rb(I), Cs(I), Sr(II), Ba(II), Ru(III), Mo(VI), La(III), and Y(III) was investigated.     

Crystal structure and thermal decomposition mechanism of the supramolecular complex of barium chloride with inositol

The single crystal of [Ba(H2O)2(C6H12O6)2Cl2] was obtained based on the phase equilibrium results. Its structure was determined by X-ray crystallographic analysis. The crystals are monoclinic and in space group C2/c with a=1.901 7(2) nm, b = 0.682 13(8) nm, c = 0.162 60(2) nm,β=96.593(2)°and V= 2.095 3(4) nm3, Z= 4, DC=1.917 g·cm-3. In its solid state, this supramolecular complex is a three-dimensional network with double layers connected by hydrogen bondings. The molecule structure of [Ba(H2O)2(C6H12O6)2Cl2] has a central barium ion that is coordinated to two water molecules, two chlorides, and four hydroxyls from the two inosi-tols. Losing the coordinating water is controlled by random nucleation and growth mechanism (n = 2/3) and 3-dimensional diffusion mechanism (n=2).     

Traceability and uncertainty – A comparison of their application in chemical and physical measurement

 Establishment of the traceability and the evaluation of the uncertainty of the result of a measurement are essential in order to establish its comparability and fitness for purpose. There are both similarities and differences in the way that the concepts of traceability and uncertainty have been utilised in physical and chemical measurement. The International Committee of Weights and Measures (CIPM) have only in the last decade set up programmes in chemical metrology similar to those that have been in existence for physical metrology for over a century. However, analytical chemists over that same period have also developed techniques, based on the concepts of traceability and uncertainty, to ensure that their results are comparable and fit for purpose. This paper contrasts these developments in physical and chemical metrology and identifies areas where these two disciplines can learn from each other.     

Analytical evaluation of zero-pressure Joule–Thomson coefficient using second virial coefficient and its application

In this paper, we present an analytical procedure to evaluate the zero-pressure Joule–Thomson coefficient using the second virial coefficient over the Lennard-Jones (12-6) potential. The analytical expressions are derived for the first and second derivatives of the second virial coefficient. The proposed formulae guarantee the accurate and fast calculation of the Joule–Thomson coefficient. As an example of application, the analytical expression obtained is used to calculate results for the molecules He, Xe, \(N_2 \), \(H_2 \), \(O_2 \), \({\textit{CO}}\), \(C_2 H_4 \), \(C_3 H_8 \) and \(C_5 H_{12} \). The results obtained by the present analytical expression are found to be in good agreement with the data in the literature. The calculation of results will help to estimate the Joule–Thomson coefficient with sufficient reliability and to determine the interaction potentials.     

The total synthesis and biological evaluation of nafuredin-γ and its analogues

Nafuredin (1) is converted to nafuredin-γ (2) under mild basic conditions and both compounds exhibit the same inhibitory activity and selectivity against NADH-fumarate reductase (complex I). The total synthesis of 2 was achieved by a convergent approach using Stille coupling. The structural elements required for inhibitory activity against NADH-fumarate reductase (complex I) were then investigated by evaluation of nafuredin-γ (2) and its structural analogues.     

Enhanced physical and chemical adsorption of carbon dioxide using bimetallic copper–magnesium oxide/carbon nanocomposite

Mixed Cu and Mg oxides on nitrogen-rich activated carbon (AC) from Nypha fruticans biomass were characterized and their CO₂ adsorption performance was measured. Highly dispersed CuO and MgO nanoparticles on AC was obtained using an ultrasonic-assisted impregnation method. The optimum adsorbent is 5%CuO–25%MgO/AC having good surface properties of high surface area, pores volume and low particles agglomeration. The higher content of MgO of 5%CuO–25%MgO/AC adsorbent contributes to less metal carbide formation which increases their porosity, surface area and surface basicity. XPS analysis showed some amount of nitrogen content on the surface of the adsorbent which increased their surface basicity towards selective CO₂ adsorption. The presence of moisture accelerated the CO₂ chemisorption to form a hydroxyl layer on the surfaces. The 5%CuO–25%MgO/AC adsorbent successfully adsorbed CO₂ via physisorption and chemisorption of 14.8 and 36.2 wt%, respectively. It was significantly higher than fresh AC with better selectivity to CO₂.     

Total synthesis of (−)-synrotolide and the evaluation of its antiproliferative activity

The stereoselective synthesis of (−)-synrotolide was achieved in high overall yield from d-(−)-ribose and 3-butyn-1-ol. The pivotal step in this approach is the selective deprotection of the acetonide group in the presence of acetate groups using TiCl₄. Moreover, the biological activity of (−)-synrotolide was evaluated on HeLa, PANC 1, HepG2, and SK-N-SH cancer cell lines. The (−)-synrotolide selectively and potently inhibited the growth of PANC 1 cell line.     

Structural and spectroscopic properties of the peroxodiferric intermediate of Ricinus communis soluble Δ9 desaturase

Large-scale quantum and molecular mechanical methods (QM/MM) and QM calculations were carried out on the soluble Δ(9) desaturase (Δ(9)D) to investigate various structural models of the spectroscopically defined peroxodiferric (P) intermediate. This allowed us to formulate a consistent mechanistic picture for the initial stages of the reaction mechanism of Δ(9)D, an important diferrous nonheme iron enzyme that cleaves the C-H bonds in alkane chains resulting in the highly specific insertion of double bonds. The methods (density functional theory (DFT), time-dependent DFT (TD-DFT), QM(DFT)/MM, and TD-DFT with electrostatic embedding) were benchmarked by demonstrating that the known spectroscopic effects and structural perturbation caused by substrate binding to diferrous Δ(9)D can be qualitatively reproduced. We show that structural models whose spectroscopic (absorption, circular dichroism (CD), vibrational and M?ssbauer) characteristics correlate best with experimental data for the P intermediate correspond to the μ-1,2-O(2)(2-) binding mode. Coordination of Glu196 to one of the iron centers (Fe(B)) is demonstrated to be flexible, with the monodentate binding providing better agreement with spectroscopic data, and the bidentate structure being slightly favored energetically (1-10 kJ mol(-1)). Further possible structures, containing an additional proton or water molecule are also evaluated in connection with the possible activation of the P intermediate. Specifically, we suggest that protonation of the peroxide moiety, possibly preceded by water binding in the Fe(A) coordination sphere, could be responsible for the conversion of the P intermediate in Δ(9)D into a form capable of hydrogen abstraction. Finally, results are compared with recent findings on the related ribonucleotide reductase and toluene/methane monooxygenase enzymes.