Synthesis and characterization of (hydroxypropyl)cellulose/TiO2 nanocomposite films

A new method of synthesis of TiO₂ nanoparticles as well as preparation of the organic–inorganic hybrid nanocomposite films of (hydroxypropyl)cellulose (HPC)/TiO₂ is presented. At the first stage, the oxotitanium hydrogel phase was obtained by the mineralization of (tetra‐isopropyl)orthotitanate (TIPT) modified by the methacrylic acid (MAA) in 15 wt% solution of H₂O₂ at room temperature and subsequent annealing at the temperature of 85°C. The crystallization of the nanoparticles of TiO₂ was conducted at the oxotitanium hydrogel phase at temperatures around 120°C in the closed vessel. Nanocomposite hybrid films were prepared by the casting method from a solution of HPC and TiO₂ nanoparticles in the water. The films of nanocomposite with 10 µm thickness are transparent to visible light and have a lower glass transition temperature compared with HPC in the bulk. This shift of the glass transition is interpreted in terms of packing density of HPC in the interface of HPC nanocomposite with TiO₂. The X‐ray diffraction pattern of the nanocomposite film suggests a lower amount of mesomorphic phase of HPC in the composite compared with HPC in the bulk. Copyright © 2007 John Wiley & Sons, Ltd.     

DFT calculations, DRIFT spectroscopy and kinetic studies on the hydrolysis of isocyanic acid on the TiO2-anatase (1 0 1) surface

The co-adsorption of isocyanic acid (HNCO) and water (H₂O) and their reaction to ammonia and carbon dioxide on the anatase phase of TiO₂ were studied with ab initio density functional theory (DFT) calculations using a cluster model as well as with in situ DRIFTS investigations and kinetic experiments. We found that isocyanic acid can in principle adsorb both molecularly and dissociatively on the TiO₂(1 0 1) surface, but the moment at which water gets involved in the process, is vital for determining the further course of the surface reaction. In the absence of water, it was found that HNCO can adsorb in molecular form on the TiO₂ surface. Assuming this case to be the first step of the HNCO hydrolysis, the surface HNCO rearranges into an intermediate complex with a modified NCO skeleton. After decarboxylation water attacks the complex from the gas phase and ammonia is finally formed.

However, when water is present at the beginning of the hydrolysis reaction, it immediately attacks the NCO group present at the surface, yielding a carbamic acid complex, which is further transformed into a carbamate complex. After decarboxylation an NH₂ group remains at the surface. Finally, NH₃ is formed by hydrogen transfer from molecularly adsorbed water at a neighboring titanium center and the hydrolysis reaction is completed.

Since water is always present in diesel exhaust gas, only the second mechanism is relevant under practical conditions. Moreover, the calculated energy barrier is lower for the second mechanism compared to the first reaction pathway. The comparison between the sum of the theoretical vibrational spectra of the reaction intermediates with the in situ DRIFT spectra also strongly supports the accuracy of the second reaction pathway. The experimental investigation of the kinetics of the HNCO hydrolysis on TiO₂-anatase revealed a second order reaction—first order with respect to HNCO and first order with respect to water, which can only be reconciled with the second mechanism.     

Complexation of metal ions in Langmuir films formed with two amphiphilic dioxadithia crown ethers

The two new crown ethers presented in this study were synthesized in order to investigate two important features of ionophores, namely metal cation complexation and interfacial properties, and the way in which they interrelate. The two derivatives were conceived as analogs of membrane phospholipids with respect to their amphiphilicity and geometry. They contain a hydrophilic 1,1'-dioxo-3,3'-dithio-14-crown ether headgroup and bear two myristoyl or stearoyl lateral chains. The length of the myristoyl and stearoyl derivatives in an extended conformation is comparable with the thickness of the individual leaflets of cell membranes. The membrane-related and complexation properties of the two crown ether derivatives were studied in monomolecular films spread on pure water and on aqueous solutions of mono-, di-, and trivalent metal salts. The properties of the monolayers are described quantitatively using thermodynamic models. The compression isotherms of the monolayers formed on different subphases show a clear-cut differentiation of the monovalent and di- or trivalent cations with both ligands. This differentiation was interpreted in terms of conformational changes occurring in the crown ether derivatives upon complexation. Molecular modeling indicates that the mono- and divalent cations are coordinated differently by the ligands, yielding complexes with different conformations. The differences of the conformations of the mono- and di- or trivalent cation complexes may be important from the point of view of the interactions with lipid membranes and the biological activity of these potential ionophores.     

Gel Polymer Electrolytes with Talc as a Natural Mineral Filler and a Biodegradable Polymer Matrix in Sodium-Ion Batteries

A gel polymer electrolyte based on poly(vinyl alcohol) (PVA) is used in sodium-ion batteries (SIBs). The use of biodegradable and water-soluble polymer potentially reduces the negative environmental impact. The other components include sodium salt (NaPF₆), sulfolane (TMS) as a plasticizer and talc. For the first time, natural and abundant talc has been used as an inert filler in a gel polymer electrolyte. The best results were obtained for moderate amounts of filler (1 and 3 wt%). Then, an increase in the conductivity, transference numbers, and thermal stability of the membranes was observed. Moreover, the presence of talc had a positive effect on the cyclability of the hard carbon electrode. The discharge capacity after 50 cycles of HC|1 % T_TMS|Na and HC|3 % T_TMS|Na was 243 and 225 mAh g⁻¹, respectively. The use of talc in gel polymer electrolytes containing sodium ions improves the safety and efficiency of SIBs.     

Synthesis,structure, ADME and biological activity of three 2,6-disubstituted thiosemicarbazone derivatives

Three new 2,6-disubstituted thiosemicarbazone derivatives of pyridine, namely, 2-{amino[6-(pyrrolidin-1-yl)pyridin-2-yl]methylidene}-N,N-dimethylhydrazine-1-carbothioamide, C₁₃H₂₀N₆S, 2-{amino[6-(piperidin-1-yl)pyridin-2-yl]methylidene}-N,N-dimethylhydrazine-1-carbothioamide, C₁₄H₂₂N₆S, and 2-[amino(6-phenoxypyridin-2-yl)methylidene]-N,N-dimethylhydrazine-1-carbothioamide monohydrate, C₁₅H₁₇N₅OS·H₂O, have been synthesized and characterized by NMR spectroscopy and low-temperature single-crystal X-ray diffraction. In addition, their antibacterial and anti-yeast activities have been determined. The ability of the tested compounds to inhibit bacterial growth was comparable to vancomycin as a reference drug. Compared to isoniazid (MIC 0.125 and 8 µg ml⁻¹), the compounds showed the ability to inhibit the growth of Mycobacterium tuberculosis to a moderate degree for the standard strain and at the same level or higher (MIC 4–8 µg ml⁻¹) for the resistant strain. All three compounds adopt the zwitterionic form in the crystal structure regardless of the presence or absence of solvent molecules.     

Interfacial behavior of a series of amphiphilic block co-dendrimers

Amphiphiles with a dendritic structure are attractive materials as they combine the features of dendrimers with the self-assembling properties and interfacial behavior of amphiphiles. We have designed and synthesized three series of segmented amphiphilic block co-dendrimers (Janus-type) and studied their interfacial properties on the Langmuir trough. Various behaviors are observed with, as a rule, the lowest generation dendrimers behaving more or less like traditional amphiphiles while the larger molecules tend to exhibit more complicated isotherms, with a non-straightforward temperature dependence, one particular molecule seemingly forming supramolecular assemblies spontaneously. The results presented here, obtained on a series of molecules where many parameters have been varied systematically, show the limits that should be kept in mind when designing amphiphilic dendrimers.     

Lipid Nanoparticles Loaded with Iridoid Glycosides: Development and Optimization Using Experimental Factorial Design

Lipid nanoparticles based on multiple emulsion (W/O/W) systems are suitable for incorporating hydrophilic active substances, including iridoid glycosides. This study involved optimization of composition of lipid nanoparticles, incorporation of active compounds (aucubin and catalpol), evaluation of stability of the resulting nanocarriers, and characterization of their lipid matrix. Based on 3² factorial design, an optimized dispersion of lipid nanoparticles (solid lipid:surfactant—4.5:1.0 wt.%) was developed, predisposed for the incorporation of iridoid glycosides by emulsification-sonication method. The encapsulation efficiency of the active substances was determined at nearly 90% (aucubin) and 77% (catalpol). Regarding the stability study, room temperature was found to be the most suitable for maintaining the expected physicochemical parameter values (particle size < 100 nm; polydispersity index < 0.3; zeta potential > |± 30 mV|). Characterization of the lipid matrix confirmed the nanometer size range of the resulting carriers (below 100 nm), as well as the presence of the lipid in the stable β’ form.     

Supersonic jet studies of solvation effects on the spectroscopy and photophysics of 4-diethylaminopyridine

We present the results of spectroscopic and photophysical investigations of 4-diethylaminopyridine (DEAP) and its 1 : 1 complexes with a number of protic solvents such as water and various alcohols of different acidity isolated under supersonic jet conditions. While a double resonance vibrational spectroscopic method was employed to investigate the size and geometrical structure of jet-cooled clusters, laser-induced fluorescence spectroscopy was used to examine the changes of photophysics induced by complexation of DEAP with solvent molecule(s). The results obtained from ab initio calculations enable the assignment of geometries and of the vibrational spectra of the clusters in the OH-stretch region. The comparison of the experimental and calculated vibrational spectra indicates that the solvent molecule is hydrogen-bonded to the pyridine nitrogen atom. Dual luminescence is observed only for the complexes with alcohols of relatively strong acidity.     

A new recyclable Pd catalyst supported on vertically aligned carbon nanotubes for microwaves-assisted Heck reactions

Palladium supported on vertically aligned multi-walled carbon nanotubes (Pd/VA-CNTs) is used as catalyst for the C-C coupling reactions of p-iodonitrobenzene with styrene and ethyl acrylate under microwaves irradiation. Pd/VA-CNTs catalyst exhibits higher activity compared to Pd supported on activated charcoal, under the same reaction conditions. Due to the microwaves irradiation, the kinetics of the reaction is strongly accelerated compared to that obtained with a traditional heating mode. The macroscopic form of aligned CNTs support allows an easy recovery of the catalyst, avoiding a costly post-reaction filtration. In addition, the interaction between the active phase and the support leads to the negligible leaching of palladium during recycling tests. The observed results indicate that Pd/CNTs is a recyclable and stable heterogeneous catalytic system.