Attila Domján

Evaluation of surface and microstructure of differently plasticized chitosan films

Surface and structural investigations of natural biopolymer (chitosan) films containing various conventionally applied hydrophilic plasticizers (glycerol and poly(ethylene glycol) 400) were performed and the results were compared, with the aim of acquiring new information concerning the formation of these plasticized films. The surface tests revealed that the water uptake, the water-binding properties (moisture content) and the polarity were higher for the film containing glycerol as plasticizer. Positronium lifetime measurements and NMR studies performed to evaluate the effects of the plasticizer on the polymer structure demonstrated relevant differences in the effects of the plasticizers. The influence of glycerol on the structure of the film formed was more intensive than that of PEG 400. It can be concluded that the surface properties of the films, which are very important for their storage and application, cannot be established exactly by means of structural tests. Both surface and structural tests must be performed before the formulation of this type of plasticized mucoadhesive films.

Expanding the Boundaries of Water-Tolerant Frustrated Lewis Pair Hydrogenation: Enhanced Back Strain in the Lewis Acid Enables the Reductive Amination of Carbonyls

The development of a boron/nitrogen-centered frustrated Lewis pair (FLP) with remarkably high water tolerance is presented. As systematic steric tuning of the boron-based Lewis acid (LA) component revealed, the enhanced back-strain makes water binding increasingly reversible in the presence of relatively strong base. This advance allows the limits of FLPs hydrogenation to be expanded, as demonstrated by the FLP reductive amination of carbonyls. This metal-free catalytic variant displays a notably broad chemoselectivity and generality.

Phenol–polymer proximity in a thermoresponsive gel determined by solid-state 1H–1H CRAMPS NMR spectroscopy

Proximity was determined in a thermoresponsive host–guest gel system and the polymer–phenol distance was calculated using solid-state 1H–1H CRAMPS NMR spectroscopy and rate matrix analysis.

Water absorption in a polymeric network

Positron lifetime measurements were performed to study the swelling dynamics of an amphiphilic polymer network (APN). Lifetime spectroscopy proved to be suitable to investigate APNs. Very quick structural changes were indicated by lifetime parameters at very low swelling ratios. On the basis of the results a possible mechanism is proposed for the hydration of the investigated materials.

Multivariate calibration of the degree of crystallinity in intact pellets by X-ray powder diffraction.

XRPD is the method of choice to determine crystalline content in an amorphous environment. While several studies describe its use on powders, little information is available on its performance on finished products. The methods use may be limited not only by the need of sample pretreatment and its validation but also by the propensity of some materials to recrystallize when exposed to heat or mechanical stress. In this work the authors describe an attempt at constructing a model based on the XRPD measurement of intact layered pellets using univariate methods based on peak heights and PLS regression. Results indicate that neither the goodness-of-fit (below 0.9 for all tested variables), nor the RMSEC values (above 5 for all tested variables) of any model based on peak height were good enough to consider them for everyday use. PLS regression however provided a model with improved characteristics (R(2)=0.9581, RMSEC=3.04) despite the low API content and individual loading characteristics also reflected the validity of the model. PLS analysis also indicated that a specific sample may be different in some formulation characteristic that did not register on other examinations. This further indicates the methods usefulness in the analysis of intact dosage forms.

Non-symmetrical bent-shaped compounds containing a chiral moiety

The synthesis and mesomorphic properties of new non-symmetrical bent-shaped compounds containing a chiral moiety are reported. These materials were built up from 3-hydroxybenzoic acid as a central unit with a chiral terminal group derived from lactic acid. A columnar phase of the B1REV type with tilted molecules was observed in a wide temperature range down to room temperature. The ferroelectric-like character of switching with one peak in a half-period of the triangular electric field was observed and supported by texture observations and electro-optical changes. A longer terminal group ending with a double bond makes the compounds ready for polymerisation.

POSITRON LIFETIME STUDY OF SEVERAL CHIRAL MATERIALS IN AQUEOUS SOLUTION

The most obvious symmetry breaking in Nature is the left-right asymmetry of living beings: sugars and amino acids are almost exclusively represented by one of their stereoisomers (D-isomer for sugars and L-isomer for amino acids) at the expense of other possible isomers. In our experiment we studied the aqueous solutions of tartaric acid, alanine, and cysteine in the function of temperature by positron lifetime spectroscopy. The results were compared with those obtained in pure water under similar conditions. We always observed a sharp minimum of the positron lifetime at around 41 °C in water and in the solutions of the natural stereo-isomers. On the other hand, the same minimum occurred at considerably lower temperatures in the solutions of the “unnatural” isomers.

Positron lifetime study of the ferroelectric BaTiO3 in electric field

BaTiO3, was studied by positron lifetime spectroscopy in static electric fioeld. The strength of the field was varied from 0 up to 104 V/cm. Two characteristic points were found at 4500 V/cm and at 8500 V/cm. These field strengths were related to subsequent ordering processes of the crystal. Additional temperaturee dependent measurements were perforrmed in the 70–310 range to confirn the interopretaion of the two positron lifetimes. The two expected phase transitions were observed and these measurements showd that positron are trapped by Ba vacancies.

WO3–EDA hybrid nanoplates and nanowires: synthesis, characterization, formation mechanism and thermal decomposition

Previously the WO3–EDA hybrid material was obtained only from solvothermal reactions. In this study this hybrid was prepared by two novel methods: a solid–gas phase heterogeneous reaction, and a wet chemical process. In the case of the solid–gas phase reaction the effects of the composition, crystal structure, and the particle size of the WO3 powder and the presence of H2O vapor were studied, while in the case of the wet chemical process the effect of the solvent was investigated. The structure, composition, morphology and thermal decomposition of the as-prepared WO3–EDA hybrid were investigated by XRD, FTIR, solid-state NMR, elemental analysis, SEM, TEM and TG/DTA-MS measurements. In addition, its catalytic activity was tested in a Knoevenagel condensation model reaction. Based on the results the WO3–EDA empiric formula was proposed to replace the current WOx–EDA formula. From the solid–gas phase reaction WO3–EDA nanoplates were obtained for the first time. Furthermore, a new formation mechanism was proposed for the solid–gas phase formation of this hybrid material. The thermal decomposition of the hybrid resulted m-WO3 in air, and an amorphous tungsten oxide phase in nitrogen. During annealing, the evolved EDA transformed into a series of heterocyclic aromatic compounds in both atmospheres. The as-prepared hybrids had the same catalytic properties as the hybrids obtained previously from the solvothermal reactions.

Graphite Oxide-TiO2 Nanocomposite Type Photocatalyst for Methanol Photocatalytic Reforming Reaction

Graphite-oxide/TiO2 (GO/TiO2) composite materials were prepared by heterocoagulation method from Brodie’s graphite-oxide (GO) in order to test them as catalysts in the methanol photocatalytic reforming reaction in liquid phase. The preparation of the composite itself resulted in only little changes in the structure of GO as it was indicated by attenuated total reflection infrared (ATR-IR) and 13C magic-angle spinning nuclear magnetic resonance (13C MAS NMR) spectroscopic measurements. However, during the photocatalytic reaction, all of the GO/TiO2 samples darkened strongly indicating structural changes of GO. X-ray photoelectron spectroscopy along with NMR confirmed the loss of oxygen functionalities and emergence of graphitic species in the samples recovered from the photocatalytic reaction. Model experiments were designed to identify the key factors determining the activity of the GO/TiO2 derived photocatalysts. It was found that the emergence of a pronounced coupling between TiO2 and the graphite-like carbonaceous material is the most important contribution to get active and stable photocatalysts.