Csaba Novák

Thermal analysis of cyclodextrins and their inclusion compounds

This review examines the literature concerning the thermal properties of natural and semisynthetic cyclodextrins and their inclusion compounds. Particular emphasis is given to recent results of investigations by thermal methods of the hydrated forms of cyclodextrins. The limitations and advantages of the applications of thermal analyses concerning water- and drug-cyclodextrin interactions are also discussed.

Tracking the physical aging of poly(ethylene oxide): A technical note

Summary and ConclusionsPhysical aging of 2 types of PEO could be tracked by the combination of PALS, DSC, and SEM methods. After storing the samples at 40°C±2°C and 75%±5% RH, a decrease in the o-Ps lifetime values and an increase in the melting enthalpies as a function of storage time indicated a reorientation of the polymer chains. The limitations of monitoring enthalpy relaxation confirm the importance of methods that track volume relaxation, such as PALS. Structural changes could be observed even after a short storage time (4 weeks), which highlights the effect of further investigations of the influence of physical aging on the properties of PEO-containing dosage forms.

Investigation of tenoxicam and γ-cyclodextrin binary and ternary complexes

Tenoxicam is a widely used non-steroidal anti-inflammatory drug (NSAID). Itscomplexation with cyclodextrin was studied in order to improve its aqueoussolubility and to decrease its side-effects. Two- and three-component systems inseveral mole-ratios were prepared by means of two different methods. The drugliberation profile, the in vitro membrane diffusion and the n-octanol/water partitioncoefficient were investigated. The presence of complexes was detected via thermoanalyticaland X-ray diffractometric studies. On the basis of these data, several compositionswere selected for incorporation into topical dosage forms.

Code sectoring methods in CDMA-based broadband point-to-multipoint networks

Code sectoring methods in broadband wireless point-to-multipoint (PMP) networks applying code-division multiple access (CDMA) are discussed in this paper. Interference reduction is the key factor in PMP network design, therefore antenna- and frequency-sectoring solutions are commonly applied. CDMA allows code sectoring strategies, moreover advanced interference suppression techniques (e.g., multiuser detection) can be utilized. The combination of different sectoring schemes and multiuser receivers in a CDMA-based PMP network provides the effective control of interference. In this study different CDMA code sectoring approaches are proposed and downlink interference analyses of a PMP network sector are presented.

Investigation of Ethacrynic Acid and Random-methyl-β-cyclodextrin Binary Complexes

Cyclodextrin complexation was applied to achieve better aqueous solubility of the drug and to formulate suppositories. Binary products were prepared in several mole ratios by two different methods. The dissolution profiles and in vitro membrane diffusion behaviour of the compositions were investigated. Thermoanalytical studies were performed in order to confirm inclusion complex formation. Compositions were selected for further detailed investigations and for incorporation into suppository dosage form.

Changes in the thermotropic and the structural behaviour of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine/water liposomes effected by 2,4-dichlorphenol

Toxic 2,4-dichlorophenol (DCP) molecules, originating from the environment, drastically affect the main functions of organic cell membranes. To yield some information on the destroyed membrane structures, 1,2-dipalmitoyl-snglycero-3-phosphatidylcholine (DPPC)/water liposome systems containing different amounts of DCP were studied by differential scanning calorimetry and small-angle X-ray scattering (SAXS) methods. The transition points of the main transition and its enthalpy are changed only in a relatively narrow range of about 0–2.5%, while the enthalpy of the pretransition is affected by DCP more strongly. The disappearance of the pretransition occurs in a range of about 3 orders of magnitude of the DCP/DPPC ratio (from 10−5 to 10−2). The changes in the first Bragg profiles of the SAXS curves depend not only on the temperature but also very strongly on the DCP/DPPC molar ratios. Especially, at higher concentrations DCP causes a strong broadening in the Bragg profiles and a difference from the profiles of the nonrippled phase. The general destruction in the layer arrangements and the reductions in the transition enthalpies between them indicate defect structures consisting of domains with nonlayer structure which are formed simultaneously by DCP molecules.

Study of the mechanism of optical resolutions via diastereoisomeric salt formation: V. Thermoanalytical investigation of the optical resolution of the N-methylamphetamine by tartaric acid

The products obtained in the optical resolution of the N-methylamphetamine by the Pope-Peachy method, using half equivalent R, R-tartaric acid and half equivalent hydrochloric acid in absolute ethanol were investigated by thermoanalytical methods. The DSC measurements of the precipitated salts provide sufficient information for following the progress of the resolution. In this way, the results of the resolution can be estimated with the precision of about 5% optical purity.

Uplink interference analysis of LMDS networks applying CDMA with interference cancellation

Local multipoint distribution service (LMDS) is an emerging technology among broadband point-to-multipoint (PMP) wireless networks. The most critical point in designing LMDS networks is interference. Dominant access methods are FDMA and TDMA in LMDS, whereas CDMA has received less attention. Our aim is to demonstrate the feasibility of applying CDMA in LMDS networks by exploiting the results of research activities in CDMA interference suppression (e.g. multiuser detection). The uplink is the bottleneck of cellular PMP networks in terms of interference. Therefore, we analyze uplink interference in CDMA-based LMDS networks. Frequency-sectorized TDMA uplink interference scenarios are compared to those of CDMA using single user detector (matched filter) and multiuser detection algorithms, i.e. parallel interference cancellation (PIC) and successive interference cancellation (SIC). Uplink investigations of an LMDS sector are presented by carrier-to-interference ratio (C/I) maps and BER versus SNR simulations.

The Effect of Ionic Environment on the Adsorption of Phenol

The effect of the ionic environment on the adsorption of phenol from aqueous solutions was investigated in a predominantly microporous carbon and in a commercial carbon designed for wastewater treatment. It was found that not only the pH of the solution but also the method of its setting affects the adsorption capacity. Setting the pH with a buffer solution instead of HCl/NaOH results in a reduced adsorption capacity, owing to the increased number of competing species for adsorption sites, and also to pore blocking. The latter is less critical for the commercial carbon with wider pores. Thermal desorption of phenol exhibits an even stronger dependence on pH setting than adsorption. Upon heating, a mass equivalent to 10–35% of the adsorbed phenol is retained by the surface as a carbon-rich residue, which may modify not only the chemistry but also the pore volume and the pore size distribution of the carbon.

Coverage Enhancement by CDMA Code Sectoring in Hybrid Terrestrial/Satellite Point-to-Multipoint Networks

Interference reduction techniques in wireless point-to-multipoint (PIMP) networks are considered in this paper, utilizing code-division multiple access (CDMA) and hybrid terrestrial/satellite access. Downlink code sectoring approaches are introduced combined with multiuser detection. Full network coverage is achieved by assigning satellite access to critical interference zones. The aim of our proposed network architecture is providing the largest possible terrestrial coverage so that satellite access can be focused only on the most critical zones. Interference zone analyses are obtained by bit error rate (BER) simulations