Elena Pincu

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.

HPLC Separation of Acetaminophen and its Impurities Using A Mixed-mode Reversed-Phase/Cation Exchange Stationary Phase

Determination of acetaminophen and its main impurities: 4-nitrophenol, 4-chloroacetanilide, as well as 4-aminophenol and its degradation products, p-benzoquinone and hydroquinone has been developed and validated by a new high-performance liquid chromatography method. Chromatographic separation has been obtained on a Hypersil Duet C18/SCX column, using gradient elution, with a mixture of phosphate buffer (pH = 4.88) and methanol as a mobile phase. Analysis time did not exceed 14.5 min and good resolutions, peak shapes and asymmetries have resulted. The linearity of the method has been tested in the range of 5.0-60 µg/mL for acetaminophen and 0.5-6 µg/mL for the other compounds. The limits of detection and quantification have been also established to be lower than 0.1 µg/mL and 0.5 µg/mL, respectively. The method has been successfully applied for the analysis of commercial acetaminophen preparations.

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.n

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.

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.

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.

Physico-chemical study of norfloxacin and metronidazole binary mixtures

The physico-chemical characterization of norfloxacin commercial sample (NF), norfloxacin anhydrous form A (NFanhA), norfloxacin pentahydrate (NF·5H2O) and metronidazole (MZ) has been carried out. It was determined that the commercial sample is a mixture of 74% anhydrous NF form A and 26% hemipentahydrate NF. From XRPD analysis, it was observed that after the water loss, NF·5H2O undergoes a solid–solid transition and is converting to NFanhA. Solid–liquid equilibrium for NFanhA–MZ and NF·5H2O–MZ binary systems has been investigated using differential scanning calorimetry, and simple eutectic point was observed, in good approximation, at 419xa0K for all the mixtures studied. The experimental solid–liquid phase diagram was compared with predictions obtained from available eutectic equilibrium models. The results indicate non-ideality for the mixture. The mixing enthalpy was determined at the eutectic composition and the negative value obtained, ΔMHxa0=xa0−xa013.28xa0kJxa0mol−1, indicates that molecules of the two components form clusters in the eutectic melt.

New polymeric composites for heat transfer

The aim of this study was the obtaining of a modified textile material capable of absorbing the body heat resulting from intense activities and maintaining the optimum human body temperature (36–37xa0°C). Thus, temperature-sensitive reactive polymer particles were obtained through the use of suspension polymerization of glycidyl methacrylate and paraffin and subsequent grafting on textile material was realized. The materials were characterized in order to determine their morphological, thermal, and comfort parameters.

Inclusion complexes of steroidal heterocyclic compounds with cyclodextrins in aqueous solution and in the solid state

The complex formation of five steroidal heterocyclic compounds (1-5) with β-cyclodextrin and hydroxypropyl-β-cyclodextrin was investigated in aqueous solution and in solid state in order to find the strenght of interaction. The complex formation of these steroidic compounds with CDs in aqueous solution was studied by solubility analysis and ultraviolet absorption methods. For the study of solid state interaction, solid complexes were prepared by the solvent evaporation method and complexes obtained were analysed by thermal analysis. Also, synthesis, NMR and IR data of the new steroidic compounds 1,2, and 3are presented.