Structural Elucidation of Poloxamer 237 and Poloxamer 237/Praziquantel Solid Dispersions: Impact of Poly(Vinylpyrrolidone) over Drug Recrystallization and Dissolution.

Praziquantel (PZQ) is the recommended, effective, and safe treatment against all forms of schistosomiasis. Solid dispersions (SDs) in water-soluble polymers have been reported to increase solubility and bioavailability of poorly water-soluble drugs like PZQ, generally due to the amorphous form stabilization. In this work, poloxamer (PLX) 237 and poly(vinylpyrrolidone) (PVP) K30 were evaluated as potential carriers to revert PZQ crystallization.

Unexpected solvent impact in the crystallinity of praziquantel/poly(vinylpyrrolidone) formulations. A solubility, DSC and solid-state NMR study.

The saturation solubility of PVP:PZQ physical mixtures (PMs) and solid dispersions (SDs) prepared from ethanol (E/E) or ethanol/water (E/W) by the solvent evaporation method at 1:1, 2:1 and 3:1 ratio (w/w) was determined. The presence of PVP improves the solubility of PZQ (0.31±0.

Elucidating the guest-host interactions and complex formation of praziquantel and cyclodextrin derivatives by (13)C and (15)N solid-state NMR spectroscopy.

Praziquantel is the drug of choice to treat several parasitic infections including the neglected tropical disease schistosomiasis. Due to its low aqueous solubility, cyclodextrins have been tested as potential host candidates to prepare praziquantel inclusion complexes with improved solubility. For the first time, the interactions of praziquantel with β-cyclodextrin and β-cyclodextrin derivatives (methyl-β-cyclodextrin and hydroxypropyl-β-cyclodextrin) were investigated using high resolution solid-state NMR spectroscopy.

First solid-state NMR spectroscopy evaluation of complexes of benznidazole with cyclodextrin derivatives.

Complexation of benznidazole (BZL), a drug of choice for the treatment of Chagas'neglected disease, with cyclodextrin (CD) derivatives was analyzed by solid-state NMR. (13)C cross polarization/magic angle spinning spectra were recorded from BZL and from BZL:β-CD, BZL:methyl β-CD and BZL:hydroxypropyl β-CD complexes, which were obtained by the solvent evaporation technique. No significant evidence was obtained on BZL inclusion complexes involving either β-CD or hydroxypropyl β-CD.

(13)C and (15)N solid-state NMR studies on albendazole and cyclodextrin albendazole complexes.

(13)C and (15)N solid-state nuclear magnetic resonance (NMR) spectra were recorded from albendazole (ABZ) and from ABZ:β-cyclodextrin, ABZ:methyl-β-cyclodextrin, ABZ:hydroxypropyl-β-cyclodextrin and ABZ:citrate-β-cyclodextrin, which were prepared by the spray-drying technique. ABZ signals were typical of a crystalline solid for the pure drug and of an amorphous compound obtained from ABZ:cyclodextrin samples. Relevant spectral differences were correlated with chemical interaction between ABZ and cyclodextrins.

New thermoresistant polymorph from CO2 recrystallization of minocycline hydrochloride.

Purpose: To prepare and thoroughly characterize a new polymorph of the broad-spectrum antibiotic minocycline from its hydrochloride dehydrate salts.

Methods: The new minocycline hydrochloride polymorph was prepared by means of the antisolvent effect caused by carbon dioxide. Minocycline recrystallized as a red crystalline hydrochloride salt, starting from solutions or suspensions containing CO2 and ethanol under defined conditions of temperature, pressure and composition.

A stable amorphous statin: solid-state NMR and dielectric studies on dynamic heterogeneity of simvastatin.

Statins have been widely used as cholesterol-lowering agents. However, low aqueous solubility of crystalline statins and, consequently, reduced biovailability require seeking for alternative forms and formulations to ensure an accurate therapeutic window. The objective of the present study was to evaluate the stability of amorphous simvastatin by probing molecular dynamics using two nondestructive techniques: solid-state NMR and dielectric relaxation spectroscopy.

Molecular dynamics of amorphous gentiobiose studied by solid-state NMR.

A solid-state NMR (SSNMR) study is reported on the effect of temperature on the molecular mobility of amorphous gentiobiose, which is complemented with data obtained from crystalline samples. (13)C cross-polarization/magic-angle-spinning (CPMAS) spectra and (1)H MAS spectra were obtained for gentiobiose at natural abundance, in the amorphous state, from 293 K up to the glass transformation region (T(g) = 359 K). Two well-defined molecular mobility regimes were observed, corresponding to different motional modes.

Molecular mobility studies on the amorphous state of disaccharides. I-thermally stimulated currents and differential scanning calorimetry.

The relaxational processes in amorphous solid gentiobiose and cellobiose are studied by thermally stimulated depolarization currents (TSDC) in the temperature region from 108K up to 423K. The slow molecular mobility was characterized in the crystal and in the glassy state. The features of different motional components of the secondary relaxation have been monitored as a function of time as the glass structurally relaxes on aging.

Effect of curing protocol on the polymerization of dual-cured resin cements.

Objectives: The purpose of this study was to evaluate how curing protocol affects the extent of polymerization of dual-cured resin cements.

Methods: Four commercial resin cements were used (DuoLink, Panavia F 2.0, Variolink II and Enforce).

Sodium complexes containing 2-iminopyrrolyl ligands: the influence of steric hindrance in the formation of coordination polymers.

Iminopyrrolyl complexes of sodium were prepared from the reaction of 2-arylformiminopyrrole ligand precursors (aryl = C(6)H(5) (I); 2,6-Me(2)C(6)H(3) (II); 2,4,6-Me(3)C(6)H(2) (III); 2,6-(i)Pr(2)C(6)H(3) (IV)) with one equivalent of sodium hydride. The resulting corresponding compounds 1-4, [{Na(mu(2):kappa(2)N,N'-iminopyrrolyl)}(2n)(OEt(2))(2x)] (n > or = 1; x = 0 or 1), were obtained in moderate to high yields and were characterised by NMR spectroscopy, high resolution mass spectrometry and X-ray diffraction, when suitable crystals were obtained. The X-ray structure of compound 1 (n >> 1; x = 0) reveals the formation of a coordination polymer with repeating units consisting of dimers that contain two iminopyrrolyl ligands chelating two sodium atoms, where both pyrrolyl rings exhibit bridging sigma + sigma coordination to the Na atoms within the dimer; the self-assembling of the polymer is established by additional pi-bonds (eta(5)-coordination) of each of the pyrrolyl rings to the sodium atoms of the adjacent dimer units.

One-step self-etching adhesive polymerization: influence of a self-curing activator.

Objectives: The objectives of this work were to study the spatially resolved extent of photopolymerization and the final volumetric contraction of the self-etching adhesive Xeno IV (Dentsply/Caulk, Milford, DE, USA) in association with the self-curing agent Aurora (Dentsply/Caulk, Milford, DE, USA), using (1)H Stray-Field magnetic resonance imaging ((1)H STRAFI-MRI).

Methods: One-dimensional (1)H STRAFI-MRI images (projections along an axis, profiles) were acquired from the adhesive with and without Aurora, before and after solvent removal. Specimens were observed after the irradiation period recommended by the manufacturers and new profiles were recorded.

The role of aluminium and silicon in the setting chemistry of glass ionomer cements.

A model of the setting chemistry of glass-ionomer cements (GICs) is proposed based on 27Al and 29Si solid state nuclear magnetic resonance spectroscopy data on three GICs. All the precursor glasses are found to contain three aluminium species viz.: four, five and six-coordinate aluminium environments as well as four-bridging silicate tetrahedra.

Multinuclear magnetic resonance studies on the chemical interaction of a self-etching adhesive with radicular and coronal human dentin.

This study presents evidence at molecular level for the chemical interaction between human dentin from different tooth regions and a monomer with phosphate groups, incorporated in the formulation of a simplified adhesive system. Because dentin was observed as a powder, previous verification was obtained for an eventual collagen denaturation due to the grinding process. The presence of chemical bonds involving coronal (CD) or radicular dentin (RD) was investigated using multinuclear magnetic resonance (MR) techniques.

Structural and spatially resolved studies on the hardening of a commercial resin-modified glass-ionomer cement.

A commercial photopolymerizable resin-modified glass-ionomer (Fuji II LC) was studied using a variety of nuclear magnetic resonance (NMR) techniques. (1)H and (19)F stray-field imaging (STRAFI) enabled to follow the acid-base reaction kinetics in self-cured (SC) samples. Gelation and maturation processes with 25 min and 40 h average time constants, respectively, were distinguished.

Novel light-cured resins and composites with improved physicochemical properties.

Objectives: The aim of this study was to determine the effect of two new diluent agents (Bis-GMA analogues), at different dilution levels and filler contents on relevant physicochemical properties of several novel resins and composites containing Bis-GMA as matrix. Composites using TEGDMA as diluent were used as control.

Methods: Twenty formulations were prepared combining three monomer mixtures (Bis-GMA/TEGDMA, Bis-GMA/CH(3) Bis-GMA and Bis-GMA/CF(3) Bis-GMA), at three dilution levels (85/15, 10/90, 0/100) and two percentages of filler loading (silanated barium aluminosilicate glass): 0%, 10%, 35%.

Evaluation of two Bis-GMA analogues as potential monomer diluents to improve the mechanical properties of light-cured composite resins.

Objectives: The aim of this study was to investigate the influence of new diluent agents, diluent ratio and filler content, on relevant mechanical properties of several novel composite resins containing Bis-GMA as resin matrices, and to compare these with the properties of composites based on TEGDMA, a conventionally used diluent.

Methods: Two Bis-GMA analogues were synthesized and 20 experimental composite resins were prepared combining three monomer mixtures (Bis-GMA/TEGDMA, Bis-GMA/CH3 Bis-GMA and Bis-GMA/CF3 Bis-GMA), at three dilution rates (85/15, 10/90, 0/100) and three levels of hybrid filler content (barium aluminosilicate glass): 0, 10 and 35%. Flexural strength (FS), modulus of elasticity (ME) and microhardness (VHN) of the composites were evaluated.

Spatially resolved photopolymerization kinetics and oxygen inhibition in dental adhesives.

A comparative study of three commercial dental adhesives was performed by (1)H nuclear magnetic resonance spectroscopy and Stray-Field magnetic resonance imaging. Spectroscopic evidence was found for the presence of solvent and unreacted methacrylate groups in photopolymerized adhesives. Spatially resolved photopolymerization kinetics and volumetric contraction (solvent evaporation and polymerization shrinkage) were obtained without solvent removal and in the presence of oxygen from the atmosphere.

Stray-field imaging and multinuclear magnetic resonance spectroscopy studies on the setting of a commercial glass-ionomer cement.

A commercial glass-ionomer (Fuji II) was studied using different NMR techniques. 1H and 19F stray-field imaging (STRAFI) were used to monitor the curing kinetics of the cement and two processes were distinguished: the gelation and maturation phases. Characterization of the aluminium and silicon species present in the glass component and cement was performed by conventional 27Al and 29Si MAS and two-dimensional 27Al triple quantum MAS NMR (MQMAS) techniques.

Low viscosity dimethacrylate comonomer compositions [Bis-GMA and CH3Bis-GMA] for novel dental composites; analysis of the network by stray-field MRI, solid-state NMR and DSC & FTIR.

The effect of dilution of 2,2-bis (4-(2-hydroxy-3-methacryloxyprop-1-oxy) phenyl) propane (Bis-GMA) with 2,2-bis(4-(2-methacryloxyprop-1-oxy)phenyl) propane (CH3Bis-GMA) on extent of polymerization (Ep) was investigated by FTIR and NMR. The results correlate well with Ep values of the system and its flexibility probed by Tg (obtained by DSC). Spatially resolved photopolymerization kinetics and polymerization shrinkage (PS, i.