Attila Gácsi

The solubility of Ca(OH) 2 in extremely concentrated NaOH solutions at 25°C

AbstractThe solubility of Ca(OH)2 in aqueous NaOH solutions up to 12.50 M at 25°C has been determined. The solubility data obtained for NaOH concentrations lower than 3 M was compared with those published in the literature. The solubility of Ca(OH)2 steadily decreases with the increasing NaOH concentration. The solubility data obtained at a constant ionic strength (I = 1 M Na(Cl,OH)) enabled the determination of the conditional solubility product of Ca(OH)2(s) (lgLCa(OH)2 = − 4.10 ± 0.02). Formation of the hydroxo complex CaOH+(aq) was invoked to describe the variation of [Ca2+]T with [OH−]T. Its conditional stability constant was found to be lgKCaOH+ = 0.97 ± 0.02. The experimental protocol employed was proven to be suitable for accurate solubility determinations in rapidly equilibrating systems comprising of highly concentrated, alkaline solutions and containing analytes in the ppm range.

Sebum lipids influence macrophage polarization and activation

As lipids are known to regulate macrophage functions, it is reasonable to suppose that a sebocyte–macrophage axis mediated by sebum lipids may exist.

A comprehensive study on the dominant formation of the dissolved Ca(OH)2(aq) in strongly alkaline solutions saturated by Ca(II)

The solubility of calcium hydroxide and the aqueous speciation of Ca(II) in alkaline medium at various temperatures and background electrolyte concentrations were characterized by solubility measurements applying ICP-OES and potentiometric detection methods. Contrary to suggestions from previous literature, the (dissolved) Ca(OH)2(aq) was found to be the dominant solution species above pH ∼ 13, although the well-known CaOH+(aq) is also formed to a much smaller extent. The solubility product, as well as the formation constants for the species CaOH+ and Ca(OH)2 were found to be (8.8 ± 0.2) × 10−5 M3, (1.5 ± 0.1) M−1 and (4.7 ± 0.1) M−2, respectively, at 25 °C, at 1 M ionic strength and expressed in terms of concentrations. The most important implication of this model is that the total concentration of the dissolved calcium(II) cannot be decreased below ca. 2 × 10−4 M at any base concentration, even if this is increased to the solubility limit of the caustic. This statement was further validated via precipitation titrations. The standard enthalpies and entropies of the reactions were also calculated from temperature-dependent solubility measurements.

Calcium L-tartrate complex formation in neutral and in hyperalkaline aqueous solutions

The complex formation reaction between the l-tartrate (Tar2-) and calcium ions taking place in neutral and in hyperalkaline (pH > 13) aqueous solutions has been investigated. It was demonstrated that upon NaOH addition the solubility of the CaTar(s) precipitate significantly increases. Conductometric and freezing point depression measurements further confirmed that in this process water soluble species are formed as a result of a reaction between the CaTar(s) and the hydroxide ion (or, conversely, between Ca(OH)2(s) and the Tar2- ion). 13C NMR spectroscopic measurements yielded the value of pK3 = 15.4 ± 0.2 for the proton dissociation of one of the alcoholic OH groups of Tar2- (at 25.0 °C and 4 M Na(Cl) ionic strength). Upon addition of calcium ions to an alkaline Tar2- solution, the 1H NMR signal gradually broadened and the 13C-satellite peaks split to two components, which also indicate complexation. From H2/Pt potentiometric titrations performed with solutions in the 13.6 ≤ pH ≤ 14.4 range, it was observed, that this complex formation is accompanied by a hydroxide ion consuming process. The titration curves can be best described via assuming the formation of the CaTarH-1-(aq) (lg β11-1 = -11.2 ± 0.1) and CaTarH-22-(aq) (lg β11-2 = -25.3 ± 0.1) complexes. In hyperalkaline solutions, these two species account for more than 90-99% of the calcium ions present and the contribution of the other reasonable and well-established calcium-containing solution species is rather small. The possible structures of the above complexes have been modeled via ab initio calculations. The stoichiometries are consistent both with species containing coordinated alcoholate group(s) and with mixed Ca(ii)-hydroxo-tartrato complexes. From the data available at present, both types of structures can be considered as chemically reasonable.

Stratum corneum lipid liposomes for investigating skin penetration enhancer effects

Knowledge of the mechanism of action of skin penetration enhancers is essential to formulators for optimizing formulations and to maximize the efficacy of enhancers. To obtain information about the effects of penetration enhancers as a fast initial screening, investigations have been performed to identify possible correlations of the biological effectiveness of penetration enhancers with their interaction with a well-defined model system consisting of skin mimic lipid bilayers, as determined by calcein release experiments using stratum corneum lipid liposomes (SCLLs). We aimed to investigate the enhancing effects of different concentrations of two chemical penetration enhancers, Kolliphor RH40 and Transcutol on SCLLs. The results obtained by SCLL-based techniques were compared with conventional ex vivo penetration studies in case of Kolliphor RH40 to evaluate the potential of SCLLs as an alternative tool for screening various types and concentrations of penetration enhancers. As a result, calcein leakage assay performed with SCLL was considered to be a good model for the skin penetration enhancing effect. This method could be used as a time-saving and sensitive alternative in vitro screening technique in the early stage of the development of dermal formulations.

Following-up skin penetration of lidocaine from different vehicles by Raman spectroscopic mapping

HIGHLIGHTSThe incorporation of lidocaine in different nanocarrier systems was accomplished.The skin penetration of novel delivery systems as lyotropic liquid crystals and nanostructured lipid carriers was followed‐up.The applicability of Raman spectroscopy for monitoring skin penetration pathways ex vivo was confirmed. ABSTRACT The application of local anesthetics, usually administered by subcutaneous injection, is common in the course of diagnostic, therapeutic, and cosmetic dermatology procedures. The effective dermal delivery of lidocaine could offer a solution to many adverse effects caused by needle insertion, such as pain, local reactions or toxicity, and additionally, it avoids the disruption of anatomical landmarks. Therefore, novel dermal formulations of local anesthetics are needed to overcome the barrier function of the skin and provide sufficient and prolonged anesthesia. In our study, we aimed to investigate and compare the penetration profiles of four different lidocaine containing formulations (hydrogel, oleogel, lyotropic liquid crystal and nanostructured lipid carrier) by Raman microscopic mapping of the drug. The application of Raman spectroscopy provided information about the spatial distribution of lidocaine in the skin ex vivo. The penetration of lidocaine from lyotropic liquid crystal and nanostructured carrier reached deeper skin layers and a higher amount of the drug was diffused into the skin, compared with hydrogel and oleogel. This study confirmed that nanostructured carriers can improve skin penetration properties of lidocaine and proved the applicability of Raman spectroscopy in the research of dermatological preparations ex vivo as a nondestructive, relatively easy and fast technique.