Adsorption of chlorhexidine on synthetic hydroxyapatite and in vitro biological activity

The kinetic of chlorhexidine digluconate (CHXDG) uptake from aqueous solution by hydroxyapatite (HA) was investigated by ultraviolet (UV) analysis performed in HA powder (UV-solid) after the CHX adsorption. Adsorption isotherm of chlorhexidine (CHX) uptake was modeled by a combination of Languimir and Langmuir-Freundlich mechanisms. Strong molecule-molecule interactions and positive cooperativity predominated in the surface when CHX concentration was above 8.6 μg(CHX)/mg(HA). UV-solid spectra (shape, intensity and band position) of CHX bound to HA revealed that long-range molecular structures, such as aggregates or micelles, started to be formed at low CHX concentrations (1.52 μg(CHX)/mg(HA)) and predominated at high concentrations. Grazing-incidence X-ray diffraction (GIXRD) analysis from synchrotron radiation discarded the formation of crystalline structures on HA surface or precipitation of CHX crystalline salts, as suggested in previous works. The effect of the HA/CHX association on HA in vitro bioactivity, cytotoxicity and CHX antimicrobial activity was evaluated. It was shown that CHX did not inhibit the precipitation of a poorly crystalline apatite at HA/CHX surface after soaking in simulating body fluid (SBF). Cell viability studies after exposure to extracts of HA and HA/CHX showed that both biomaterials did not present significant in vitro toxicity. Moreover, HA/CHX inhibited Enterococcus faecalis growth for up to 6 days, revealing that binding to HA did not affect antimicrobial activity of CHX and reduced bacterial adhesion. These results suggested that HA/CHX association could result in a potential adjuvant antimicrobial system for clinical use.     

Surface miscibility of EPC/DOTAP/DOPE in binary and ternary mixed monolayers

Surface pressure (π)-molecular area (A) curves were used to characterize the packing of pseudo-ternary mixed Langmuir monolayers of egg phosphatidylcholine (EPC), 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) and L-α-dioleoyl phosphatidylethanolamine (DOPE). This pseudo-ternary mixture EPC/DOPE/DOTAP has been successfully employed in liposome formulations designed for DNA non-viral vectors. Pseudo-binary mixtures were also studied as a control. Miscibility behavior was inferred from π-A curves applying the additivity rule by calculating the excess free energy of mixture (ΔG(Exc)). The interaction between the lipids was also deduced from the surface compressional modulus (C(s)(-1)). The deviation from ideality shows dependence on the lipid polar head type and monolayer composition. For lower DOPE concentrations, the forces are predominantly attractive. However, if the monolayer is DOPE rich, the DOTAP presence disturbs the PE-PE intermolecular interaction and the net interaction is then repulsive. The ternary monolayer EPC/DOPE/DOTAP presented itself in two configurations, modulated by the DOPE content, in a similar behavior to the DOPE/DOTAP monolayers. These results contribute to the understanding of the lipid interactions and packing in self-assembled systems associated with the in vitro and in vivo stability of liposomes.     

Ruthenium-catalyzed asymmetric transfer hydrogenation of ketones in ethanol

A ruthenium catalyst formed in situ by combining [Ru(p-cymene)Cl₂]₂ and an amino acid hydroxy-amide was found to catalyze efficiently the asymmetric reduction of aryl alkyl ketones under transfer hydrogenation conditions using ethanol as the hydrogen donor. The secondary alcohol products were obtained in moderate to good yields and with good to excellent enantioselectivity (up to 97% ee).     

Multi-stage solvers optimized for damping and propagation

Explicit multi-stage solvers are routinely used to solve the semi-discretized equations that arise in Computational Fluid Dynamics (CFD) problems. Often they are used in combination with multi-grid methods. In that case, the role of the multi-stage solver is to efficiently reduce the high frequency modes on the current grid and is called a smoother. In the past, when optimizing the coefficients of the scheme, only the damping characteristics of the smoother were taken into account and the interaction with the remainder of the multi-grid cycle was neglected. Recently it had been found that coefficients that result in less damping, but allow for a higher Courant-Friedrichs-Lewy (CFL) number are often superior to schemes that try to optimize damping alone. While this is certainly true for multi-stage schemes used as a stand-alone solver, we investigate in this paper if using higher CFL numbers also yields better results in a multi-grid setting. We compare the results with a previous study we conducted and where a more accurate model of the multi-grid cycle was used to optimize the various parameters of the solver.We show that the use of the more accurate model results in better coefficients and that in a multi-grid setting propagation is of little importance.We also look into the gains to be made when we allow the parameters to be different for the pre- and post-smoother and show that even better coefficients can be found in this way.     

Existence of a Weak Solution in L p to the Vortex-Wave System

The vortex-wave system is a coupling of the two-dimensional vorticity equation with the point-vortex system. It is a model for the motion of a finite number of concentrated vortices moving in a distributed vorticity background. In this article, we prove existence of a weak solution to this system with an initial background vorticity in L ^p , p>2, up to the time of first collision of point vortices.     

Indications of field-directing and self-templating effects on the formation of organic lines on silicon

It has previously been shown that multimolecular organic nanostructures form on H-Si(100)-2×1 via a radical mediated growth process. In this mechanism, growth begins through the addition of a molecule to a silicon surface dangling bond, followed by the abstraction of a neighboring H atom and generation of a new dangling bond on the neighboring site. Nanostructures formed by this mechanism grow along one edge of a dimer row. Here, we explored the possibility of using lithographically prepared, biased metal contacts on the silicon surface to generate an electric field that orients molecules during the growth process to achieve growth in the perpendicular-to-row direction. The formation of some nanostructures in a direction that was nearly perpendicular to the dimer rows was achieved, whereas such features were not formed in the absence of the field. Analysis of the scanning tunneling microscopy images suggests that the formation of these nanostructures may involve self-templating effects in addition to dangling bond diffusion rather than a straightforward addition∕abstraction mechanism. These initial results offer some indication that a molecular pattern writer can be achieved.     

Balancing binding strength and charge transfer lifetime in supramolecular associates of fullerenes

A macrocyclic exTTF host for fullerenes offers control over the electronic coupling between an electron donor and an acceptor, and stabilizes the charge separated state lifetimes into the range of 500 ps.     

A simple and green analytical method for determination of glyphosate in commercial formulations and water by diffuse reflectance spectroscopy

This article describes a simple, inexpensive, and environmentally friendly method for the monitoring of glyphosate using diffuse reflectance spectroscopy. The proposed method is based on reflectance measurements of the colored compound produced from the spot test reaction between glyphosate and p-dimethylaminocinnamaldehyde (p-DAC) in acid medium, using a filter paper as solid support. Experimental designs were used to optimize the analytical conditions. All reflectance measurements were carried out at 495 nm. Under optimal conditions, the glyphosate calibration graphs obtained by plotting the optical density of the reflectance signal (AR) against the concentration were linear in the range 50-500 μg mL(-1), with a correlation coefficient of 0.9987. The limit of detection (LOD) for glyphosate was 7.28 μg mL(-1). The technique was successfully applied to the direct determination of glyphosate in commercial formulations, as well as in water samples (river water, pure water and mineral drinking water) after a previous clean-up or pre-concentration step. Recoveries were in the ranges 93.2-102.6% and 91.3-102.9% for the commercial formulations and water samples, respectively.     

The effect of composition of solid silver amalgam electrodes on their electrochemical response

The main purpose of this work was to evaluate the effect of the silver to mercury ratio on the voltammetric responses of silver solid amalgam electrodes (AgSAE’s). For this, the AgSAE were prepared by mechanical mixing the metals in the following mass ratios of silver to mercury: 30/70, 40/60, 50/50, 60/40, and 70/30. The resulting AgSAE’s were physically characterized by energy dispersive X-ray analysis, X-ray diffraction and scanning electron microscopy, confirming the mass percentages of the silver and mercury, the total absence of liquid mercury and a globular structure of all AgSAE’s. Furthermore, it was observed that the AgSAE 30/70 contained only one single phase (Ag₂Hg₃), and no metallic silver or mercury oxides. Additionally, the resulting AgSAE’s were chemically characterized with respect to the influence of the electrode composition on the reproducibility and electrochemical signals of a hexamine-ruthenium (III) chloride solution by use of electrochemical impedance spectroscopy and cyclic voltammetry. The separation between anodic and cathodic peaks, and consequently, the charge transfer resistance across the electrode/solution interface, and the electroactive area were calculated demonstrating that the 30/70 composition is the best surface for practical applications. Finally, square-wave voltammetry experiments were performed in 4-nitrophenol solution, with a previous optimization of the experimental and voltammetric parameters. The calculated detection limit shows that the AgSAE 30/70 is suitable for determining any contamination by p-nitrophenol, minimizing the toxic residues in case of using liquid mercury electrodes.     

Characterization of γ-carboxylated tryptic peptides by collision-induced dissociation and electron transfer dissociation mass spectrometry

Vitamin K-dependent carboxylation of glutamic acid (Glu) residues into γ-carboxyglutamic acid (Gla) is a post-translational modification essential for normal protein activity of, for example, proteins involved in the blood coagulation system. These proteins may contain as many as 12 sites for γ-carboxylation within a protein sequence of 45 amino acid residues. In the biopharmaceutical industry, powerful analytical techniques are required for identification and localization of modified sites. We here present comparatively easy and rapid methods for studies of Gla-containing proteins using recent technology. The performances of two mass spectrometric fragmentation techniques, collision-induced dissociation (CID) and electron transfer dissociation (ETD), were evaluated with respect to γ-carboxylated peptides, applying on-line LC-ion trap MS. ETD MS has so far not been reported for Gla-containing peptides and the applicability of CID for heavily γ-carboxylated proteins has not been evaluated. The anticoagulant protein, protein C, containing nine Gla-sites, was chosen as a model protein. After tryptic digestion, three peptides containing Gla-residues were detected by MS; a 1.2 kDa fragment containing two Gla-residues, a 4.5 kDa peptide containing seven residues and also the 5.6 kDa tryptic peptides containing all nine Gla-residues. Regarding the shortest peptide, both CID and ETD provided extensive peptide sequencing. For the larger peptides, fragmentation by CID resulted in loss of the 44 Da CO(2)-group, while little additional fragmentation of the peptide chain was observed. In contrast, ETD resulted in comprehensive fragmentation of the peptide backbone. The study demonstrates that the combination of both techniques would be beneficial and complementary for investigation of γ-carboxylated proteins and peptides.