Maria Tomoaia-Cotisel

Insoluble mixed monolayers. III: The ionization characteristics of some fatty acids at the air/water interface

Abstract The surface pressure versus molecular area isotherms of stearic, oleic, and linoleic acids spread at aqueous solution/air interfaces have been recorded within a wide range of pH (1 to 10.7). The dissolution process of the surfactant from the monolayer into the alkaline subphases is investigated. Collapse pressure and equilibrium spreading pressure are determined. The relationship between them is discussed by presuming that the freshly collapsed bulk phase is in a metastable mesomorphous state. Molecular model studies show the limiting molecular area and the collapse one of the studied acids to be determined by the space necessities of the hydrocarbon chain in its most extended conformation. Apparent surface acidity constants (Ka) are derived from the dependence of the collapse pressure on pH. For stearic, oleic, and linoleic acidspKa, values of 5.63, 6.22, and 5.94 were obtained, respectively. Correlation between the apparent surface acidity constants and the acidity constants of fatty acids in aqueous solutions is discussed.

Xanthophyll films: I. Single-component monolayers at the air/water interface

Abstract Surface pressure versus area data for monolayers of some all-trans xanthophylls and their derivatives: β-cryptoxanthin, β-cryptoxanthin acetate, β-cryptoxanthin palmitate, zeaxanthin, zeaxanthin monoacetate, zeaxanthin diacetate, zeaxanthin monopalmitate, lutein and lutein diacetate at the air/water interface, are presented. The monolayer properties: limiting molecular area, collapse area, collapse pressure, and surface compressional modulus are discussed and interpreted in terms of the rotating rigid plate model of carotenoid molecules previously proposed by us. An attempt is made to describe the surface pressure-area curves of the monolayers in the liquid expanded state by means of a two-dimensional van der Waals-type equation. The van der Waals attractive constant values are discussed in terms of the molecular structure of the above mentioned carotenoids.

Protein binding to gold colloids

Gold nanoparticles (size from 10 to 50 nm) were synthesized by three different methods and were characterized by UV-Vis spectroscopy and transmission electron microscopy (TEM). The shape and size distribution of gold nanoparticles were determined. The interaction of major storage protein extracted and purified from aleurone cells of barley with the gold colloids has been examined using absorption UV-Vis spectroscopy and TEM observations. These investigations evidence the binding of aleurone protein to gold nanoparticles. This binding might occur by electrostatic forces between the negatively charged citrate capped gold particles and the positively charged groups of the protein (e.g., arginine and lysine residues).

Silicon effect on the composition and structure of nanocalcium phosphates: In vitro biocompatibility to human osteoblasts

Nanostructured calcium phosphates, such as nanohydroxyapatite (HAP) and HAP with silicon content (HAP-Si) of 0.47wt.% (1% SiO2), 2.34wt.% (5% SiO2) and 4.67wt.% (10% SiO2) in the final product, were synthesized by aqueous precipitation, freeze dried and then calcined at 650, 950 and 1150°C. The obtained materials were investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrometry, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) imaging. From the analysis of the XRD patterns, the HAP and β-tricalcium phosphate (β-TCP) phases were identified and their amounts in the samples were estimated. The size of HAP and β-TCP crystallites was estimated to be in the nanocrystalline domain. FTIR spectra showed the presence of characteristic vibrations for P-O, H-O and Si-O groups and their modification with Si content and calcination temperature. TEM, SEM and AFM images also revealed the morphology of the particles and of their aggregates. These materials have been used to manufacture scaffolds which were tested for their influence on adhesion and proliferation of cells, in human osteoblast culture, considering their further use in bone reconstruction. It was found that an appropriate addition of silicon in nanocalcium phosphate scaffolds leads to an enhanced adhesion and proliferation of cells in osteoblasts in vitro.

Xanthophyll films: II. Two-component monolayers of some xanthophylls and egg lecithin at the air/water interface

Abstract The surface pressure of the binary monolayers of some all-trans xanthophylls (β-cryptoxanthin, zeaxanthin, or lutein) with egg lecithin has been measured by the Wilhelmy method, as a function of the mean area at various compositions. The surface properties of the mixed films at the air/water interface, obtained by compression isotherms, are interpreted in terms of both the additivity rule of the molecular areas and the two-dimensional phase rule applied to the collapse pressures taking into account the excess free energies of mixing of the two components. The findings indicate that each of the xanthophylls under consideration is miscible with egg lecithin in monolayers at all the molar ratios considered. The results are discussed both in terms of the packing of the two components in two-dimensional solutions and according to the molecular structures of the three xanthophylls studied.

Biogenic Syntheses of Gold Nanoparticles Using Plant Extracts

A biogenic approach for the synthesis of gold nanoparticles (GNPs) by reducing chloroauric acid (HAuCl4) with three different plant extracts (from Angelica, Hypericum, and Hamamelis) is described. The content of reducing compounds (polyphenols) in each plant extract was determined by photometric dosing. The formation of GNPs was tracked by ultraviolet-visible spectroscopy and their characterization was performed using transmission electron microscopy (TEM) and atomic force microscopy (AFM) imaging and FTIR spectra. GNPs, with diameters ranging from about 4 nm to 8 nm, were obtained at room temperature and pH value about 8. They present various shapes from spherical, to ovals, heart or polyhedral forms. Generally, the GNPs colloidal dispersions are rather stable in time, and the self assembly of GNPs is sparsely observed. However, at lower concentration of the plant extract the tendency to self aggregation of the GNPs increased. The plant extracts contain reducing agents, compounds with stabilizing effect on the GNPs, but also components which mediate their self assembly. The GNPs obtained by these biogenic syntheses have potential biological and medical applications, taking into account at least two characteristics, their size and aqueous stability.

Insoluble mixed monolayers. I. Phase equilibria at the collapse of binary monolayers at gas/liquid interfaces

Abstract Based on the two-dimensional phase rule, 13 fundamental types of phase diagrams are given for binary systems of surfactants spread at the gas-liquid interface, by taking into account the possibility of total miscibility, partial miscibility, or immiscibility of the components both in the monolayer and in the collapsed bulk phase (4 of them are known in the literature and 9 are new ones). A thermodynamic model of the monolayer is proposed, by considering the molecules of the two surfactants together with their solvation shell, the “free” subphase liquid molecules to be the third component of the monolayer and by presuming the molar fraction of the latter to become practically equal to zero at the equilibrium collapse surface pressure. The definition of the surface chemical potentials and the physical meaning of the standard state are discussed. The equations of the equilibrium curves are derived. The approximations of perfect solutions and of the regular ones are applied to the systems with total miscibility. The conditions necessary for the appearance of surface azeotropes are discussed. The state parameters of surface azeotropes are derived from the surface characteristics of the surfactants and of the interaction parameters. Several relations, reported by other authors, are obtained as particular cases. Experimental collapse pressure versus composition curves are reported and discussed by using the relations derived. Examples are given for the applicability of the approximation of perfect solutions and of regular solutions, as well as for a system with nonregular behavior. Some results are discussed in terms of the molecular structure.

Effects of doxorubicin mediated by gold nanoparticles and resveratrol in two human cervical tumor cell lines

Green synthesis of gold nanoparticles capped with resveratrol (GNPs) and their physical and chemical characterization by UV-vis spectra, FTIR, DLS, XRD, TEM and AFM are reported. The GNPs are highly stable, with average diameter of about 20 nm. Then, supramolecular nanoassemblies of GNPs and doxorubicin (Dox), Dox-GNPs complexes, were prepared and morphologically characterized. The stability of these Dox nanocomplexes is high in phosphate buffer saline as estimated by UV-vis spectra, TEM and AFM analysis. Effects of resveratrol (Resv), Resv-Dox mixtures, GNPs and Dox-GNPs complexes on HeLa and CaSki cells, after 24h drug incubation, were assessed using MTT cell viability assay. Results showed strong anticancer activity for Resv-Dox mixtures and Dox-GNPs complexes in the two human cervical carcinoma cell lines. Clearly, both Resv and GNPs can mediate the anticancer activity of Dox at its very low concentration of 0.1 μg/mL, reaching the cytotoxicity of Dox alone, at its concentration up to 20 times higher. Cytotoxic effects of Resv-Dox mixtures and Dox-GNPs complexes have been found for the first time in HeLa and CaSki cells. Furthermore, the apoptosis induction in HeLa and CaSki cells was evidenced for Resv-Dox mixtures and Dox-GNPs complexes by flow cytometry using Annexin V-FITC/propidium iodide cellular staining. For CaSki cells, the apoptosis was also demonstrated, mainly for the treatment with Dox-GNPs complexes, by MTT formazan cellular staining visualized in phase contrast microscopy. Our results provide strong evidence that novel drug delivery vehicles developed on Dox-GNPs nanocomplexes and Resv could have wide applications in cancer diagnosis and treatment.

Inclusion of α-lipoic acid in β-cyclodextrin. Physical–chemical and structural characterization

The inclusion of α-lipoic acid (LA) in β-cyclodextrin (β-CD) by increasing the aqueous solubility and photostability can enhance its medicinal use in the oral administration. Different preparation methods were employed to obtain an α-lipoic acid-β-cyclodextrin (LA-β-CD) inclusion complex and to determine the physical–chemical characteristics and the interactions present in this compound. The formation of the solid inclusion compound was confirmed by X-ray powder diffraction, differential scanning calorimetry (DSC) and infrared spectroscopy (FTIR). FTIR and DSC data confirm the new obtained compound. The crystalline structure of this compound belongs to the monoclinic system with four molecules in the unit cell. 1H NMR spectroscopic method was employed to study the inclusion process in aqueous solution. Job plots derived from the 1H NMR spectral data demonstrated an 1:1 stoichiometry of the inclusion complex in liquid state. 2D NMR data suggest the orientation of LA with the carboxyl group near to narrower rim of the β-CD.

Insoluble mixed monolayers: II. Protolytic equilibria and the influence of the pH on the collapse pressure

Abstract A general thermodynamic treatment is given for the protolytic equilibria in an insoluble monolayer, containing surfactant molecules with n ionizable protons and able to accept m more protons, and being spread at the liquid/gas interface. The correlation between the pH of the subphase liquid and the collapse pressure of the monolayer is discussed. By using the approximation of perfect solutions and of binary surface systems (protonated and deprotonated molecular species of the surfactant) several methods are proposed for deriving apparent surface acidity constants from experimental collapse pressure vs pH curves, in the case of both miscible in monolayer miscible in collapsed bulk phase and miscible in monolayer immiscible in collapsed bulk phase, type systems. Some of these methods are based on a complete perfect solution approximation (CA) taking into account the molar fraction of the subphase liquid in the monolayer and the others use “surfactant” approximation (SA), neglecting this molar fraction. The methods proposed are tested on monolayers of carotenoid pigments spread at aqueous solution/air interfaces. Results obtained by the different methods are rather close to each other, but the approximation CA is better than SA. The apparent surface acidity constants of different carotenoids are compared with each other and discussed in terms of molecular structure and electronic effects.