Viorica Meltzer

Inclusion complexes of cyclodextrins with biradicals linked by a polyether chain—an EPR study

Complexation of beta-cyclodextrin with flexible nitroxide biradicals linked by a polyethylene glycol chain was monitored by EPR spectroscopy. The EPR spectra of the uncomplexed biradicals show an exchange interaction due to the flexibility of the polyethylene glycol chain. Complexation with cyclodextrin leads to the disappearance of the exchange interaction in the EPR spectra. The complexation can be reversed by the addition of competing guests (e.g., adamantane derivatives). At high concentration, the inclusion complexes precipitate, and differential scanning calorimetry (DSC) of the precipitates proved the formation of complexes. Elemental analysis data revealed that the complexes contain several cyclodextrin units per biradical but that the composition was not stoichiometric.

Kinetics of tartrazine photodegradation by UV/H2O2 in aqueous solution

In the present work, kinetics of tartrazine decay by UV irradiation and H2O2 photolysis, and the removal of total organic carbon (TOC) under specific experimental conditions was explored. Irradiation experiments were carried out using a photoreactor of original design with a low-pressure Hg vapour lamp. The photodegradation rate of tartrazine was optimised with respect to the H2O2 concentration and temperature for the constant dye concentration of 1.035 × 10−5 M. Tartrazine degradation and the removal of TOC followed the pseudo-first-order kinetics. The much higher kobs value for tartrazine degradation (7.91 × 10−4 s−1) as compared with the TOC removal (2.3 × 10−4 s−1) confirmed the presence of reaction intermediates in the solution.

Thermodynamic study of binary mixture of citric acid and tartaric acid

AbstractThe solid — liquid phase equilibria for binary mixture of citric acid with tartaric acid were measured using differential scanning calorimetry. The phase diagram showed the existence a simple eutectic behavior. The thermal properties of this system as heat of mixing, entropy of fusion and excess thermodynamic functions were computed using enthalpy of fusion values. The composition of eutectic was determined using a Tammann diagram.

Modulation of dansyl moiety fluorescence in systems containing cyclodextrins

The present study reports on the changes in dansyl moiety fluorescence due to the interactions with the β-cyclodextrin cavity observed by steady-state fluorescence spectroscopy. First, the interaction of a guest molecule, dansyl-TEMPO (DT), which has in its structure a dansyl group as a fluorescent moiety and a paramagnetic fragment (TEMPO), with β-cyclodextrin was studied. Analysis of the EPR spectral parameters provided additional information on the host–guest interaction, suggesting that the cyclodextrin cavity accommodates dansyl rather than a TEMPO moiety. Second, the affinity between 1-adamantol or adamantane end-capped polyethylene glycols – A2Pnn – (as guests) and dansyl-β-cyclodextrin (D-β-CD, as a host) was investigated. In the presence of adamantol, the intensity of fluorescence of D-β-CD decreases and a hypsochromic effect was noticed. The same behaviour was observed in the presence of A2Pnn. Using Benesi–Hildebrand and Stern–Volmer equations and also the sensitivity factor made possible to obtain quantitative data on the interaction between the dansyl moiety and the cyclodextrin cavity. The formation of inclusion complexes in the solid state between D-β-CD and A2Pnn was evidenced analysing the DSC curves of the pure solids, physical mixture and prepared solid complexes. In addition, the use of D-β-CD for fluorescent labeling of a covalently based network hydrogel and diffusion of dansyl derivatives into a gel are shown as possible further application of this study.

DSC and oxygen uptake studies of γ-irradiated ethylene–propylene elastomers

Abstract The specific heat capacity of irradiated ethylene–propylene copolymer was examined by differential scanning calorimetry. Additional measurements on oxidative stability of γ-exposed EPR were performed by isothermal and isobaric oxygen uptake. The c p differences between vacuum – and air – radiolysis of polymers are pointed out. The oxidative irradiation environment generates peroxy radicals that are involved in the air-degraded samples. The c p dependencies on temperature determined for the two manners of irradiation are not alike. The assessment of the thermal behavior by DSC and oxygen uptake confirms the key role of RO 2 . in the radiolytic and thermal degradation of these polymers.

Solid-state study of Captopril and Metoprolol Tartrate binary system

The structural and thermal characterization of Captopril (CA) and Metoprolol Tartrate (MT) pure compounds and binary system have been obtained. Solid–liquid equilibrium for binary mixture CA–MT was investigated using differential scanning calorimetry. Simple eutectic behavior for this system was observed. The experimental solid–liquid phase temperatures were compared with predictions obtained from available eutectic equilibrium models. The results indicate non-ideality in this mixture. The negative value of the mixing enthalpy indicates the presence of clusters with hydrogen bonds formation in the melt, as confirmed by FT-IR measurements. The preparation of ground mixtures demonstrated that the application of mechanical energy can result in the partial melting of the sample because of the eutectic behavior. Trans–cis iso-merization of CA was observed for the samples annealed at high temperature, anticipated due to the presence of MT in the system.

Characterization of Electron Beam Irradiated Polyvinylpyrrolidone-Dextran (PVP/DEX) Blends

In the past years an increased interest to create new polymeric blends with application in the medical area for development of new types of biomaterials has appeared. Electron beam irradiation is well known as a method of producing important changes in polymer structure, being an alternative to chemical synthesis of biomaterials based on polymeric materials. The aim of the present study was to investigate the behaviour of some polyvinylpyrrolidone-dextran (PVP/DEX) blends under electron beam irradiation. Aqueous solutions of PVP with molecular weights of 360 000 Da (PVP 360), 40 000 Da (PVP 40), and DEX with molecular weight of 500 000 Da (DEX), were mixed as to obtain 50:50 blends of PVP40/DEX and PVP360/DEX. The obtained blends were irradiated with electron beam at different radiation doses and after irradiation treatment were processed by freeze-drying. PVP/DEX blends were characterized by infrared spectroscopy (FT-IR) and thermal analysis. The analyses were conducted in order to establish the relation between radiation dose and changes of structural and thermal properties.

Thermodynamic study of binary system Propafenone Hydrocloride with Metoprolol Tartrate: solid-liquid equilibrium and compatibility with α-lactose monohydrate and corn starch.

Solid-liquid equilibrium (SLE) for binary mixture of Propafenone Hydrocloride (PP) with Metoprolol Tartrate (MT) was investigated using differential scanning calorimetry (DSC) and corresponding activity coefficients were calculated. Simple eutectic behavior for this system was observed. The excess thermodynamic functions: G(E) and S(E) for the pre-, post-, and eutectic composition have been obtained using the computed activity coefficients data of the eutectic phase with their excess chemical potentials μi(E) (i=1, 2). The experimental solid-liquid phase temperatures were compared with predictions obtained from available eutectic equilibrium models. The results indicate non-ideality in this mixture. Also, the compatibility of each component and their eutectic mixture with usual excipients was investigated, and the DSC experiments indicate possible weak interactions with α-lactose monohydrate and compatibility with corn starch. The results obtained were confirmed by FT-IR measurements.

Thermal analysis of binary liquid crystals eutectic system cholesteril p-phenoxi phenyl carbamate–cholesteril p-biphenyl carbamate

For a binary mixture of two liquid crystals, cholesteril p-phenoxi phenyl carbamate and cholesteril p-biphenyl carbamate, the solidus–liquidus equilibrium was investigated using differential scanning calorimetry (DSC) and the thermodynamic parameters were obtained. Simple eutectic point was observed for this system, situated approximately at the same temperature for all the studied compositions. This behavior is favored by grinding and is more evident in the composition 50:50. The excess functions GE and SE for the pre-, post-, and eutectic composition have been calculated using the phase diagram data. Comparing the experimental data with the existing theoretical data, the system deviation from the ideal behavior is observed. The structure of pure compounds was elucidated using FT-IR and hot-stage polarizing microscopy.

E-beam radiation synthesis of xanthan-gum/carboxymethylcellulose superabsorbent hydrogels with incorporated graphene oxide

ABSTRACT In this study the electron beam (e-beam) radiation synthesis in “paste-like condition” and characterization of the network structure of acrylic acid (AA) sodium salt/xanthan gum (XG)/carboxymethylcellulose (CMC) superabsorbent hydrogels incorporating graphene oxide (GO) was investigated. The effects of the AA concentration on gel fraction, sol-gel analysis, swelling degree and network parameters, as well as the relationship between these parameters and radiation dose was also established. Gel fraction exceeds 90%, and the p0/q0 ratio shows a moderate degradation process. The swelling kinetic data were used to determine, first the swelling degree, second the diffusion characteristics, and third the average molecular weight between crosslinks (Mc), as well as. The diffusion data revealed a Fickian mechanism transport, for each hydrogel compositions. The network parameters (Mc and ξ) increased with absorbed dose, while cross-linking density and the radiation-chemical yields were decreased.