Bioactivity Performance of Pure Mg after Plasma Electrolytic Oxidation in Silicate-Based Solutions

The biodegradable metals, including magnesium (Mg), are a convenient alternative to permanent metals but fast uncontrolled corrosion limited wide clinical application. Formation of a barrier coating on Mg alloys could be a successful strategy for the production of a stable external layer that prevents fast corrosion. Our research was aimed to develop an Mg stable oxide coating using plasma electrolytic oxidation (PEO) in silicate-based solutions. 99.9% pure Mg alloy was anodized in electrolytes contained mixtures of sodium silicate and sodium fluoride, calcium hydroxide and sodium hydroxide. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), contact angle (CA), Photoluminescence analysis and immersion tests were performed to assess structural and long-term corrosion properties of the new coating. Biocompatibility and antibacterial potential of the new coating were evaluated using U2OS cell culture and the gram-positive Staphylococcus aureus (S. aureus, strain B 918). PEO provided the formation of a porous oxide layer with relatively high roughness. It was shown that Ca(OH)₂ was a crucial compound for oxidation and surface modification of Mg implants, treated with the PEO method. The addition of Ca²⁺ ions resulted in more intense oxidation of the Mg surface and growth of the oxide layer with a higher active surface area. Cell culture experiments demonstrated appropriate cell adhesion to all investigated coatings with a significantly better proliferation rate for the samples treated in Ca(OH)₂-containing electrolyte. In contrast, NaOH-based electrolyte provided more relevant antibacterial effects but did not support cell proliferation. In conclusion, it should be noted that PEO of Mg alloy in silicate baths containing Ca(OH)₂ provided the formation of stable biocompatible oxide coatings that could be used in the development of commercial degradable implants.     

Intramolecular Hydrogen Bonding Restricts Gd–Aqua-Ligand Dynamics

Aqua ligands can undergo rapid internal rotation about the M−O bond. For magnetic resonance contrast agents, this rotation results in diminished relaxivity. Herein, we show that an intramolecular hydrogen bond to the aqua ligand can reduce this internal rotation and increase relaxivity. Molecular modeling was used to design a series of four Gd complexes capable of forming an intramolecular H-bond to the coordinated water ligand, and these complexes had anomalously high relaxivities compared to similar complexes lacking a H-bond acceptor. Molecular dynamics simulations supported the formation of a stable intramolecular H-bond, while alternative hypotheses that could explain the higher relaxivity were systematically ruled out. Intramolecular H-bonding represents a useful strategy to limit internal water rotational motion and increase relaxivity of Gd complexes.     

Chemical Equilibrium for the Reacting System Acetic Acid–Ethanol–Ethyl Acetate–Water at 303.15 K, 313.15 K and 323.15 K

The chemical equilibrium (CE) for the quaternary reacting system ethanol–acetic acid–ethyl acetate–water was studied at 303.15, 313.15 and 323.15 K and atmospheric pressure. The CE compositions were determined by gas chromatography and nuclear magnetic resonance analytical methods. The thermodynamic constants of CE at 303.15, 313.15 and 323.15 K were calculated based on the obtained experimental data with the use of the NRTL model.     

Synthesis and X-ray structure of methyl esters of the dicarboxyphenylsulfide iron(II) clathrochelates

All six constitutional isomers of the dimethoxy-terminated clathrochelate FeBd₂((CH₃OOCC₆H₄S)₂Gm)(BF)₂ (where Bd^2? is α-benzildioxime dianion, Gm is glyoxime residue, and BF is fluoroboron capping group) were obtained under mild reaction conditions by nucleophilic substitution of their dichloroclathrochelate precursor with the corresponding methyl ester of carboxyphenylthiolate anion generated in situ in the presence of triethylamine. In the case of homodifunctionalized cage complexes with equivalent ortho-, meta-, or para-substituted arylsulfide groups, 1.5-fold excess of methyl ester of the corresponding mercaptobenzoic acid was added. In the case of their heterodifunctionalized macrobicyclic analogs, subsequent addition of one equivalent of the first nucleophilic agent and one equivalent of the second nucleophile was used. The complexes were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV–vis, ¹H and ¹³C{¹H} NMR spectra, and by single-crystal X-ray diffraction. In all these molecules, the encapsulated iron(II) is situated in the center of FeN₆-coordination polyhedron, the geometry of which is intermediate between a trigonal prism and a trigonal antiprism with the average distortion angles φ from 24.7 to 25.2°. The absence of strong intermolecular interactions and the substantial sterical clashes hampering a rotation around the single C–S bonds, resulted in different orientations of the functionalizing arylsulfide substituents at a cage framework.     

A Dual Active-Set Algorithm for Regularized Monotonic Regression

Monotonic (isotonic) regression is a powerful tool used for solving a wide range of important applied problems. One of its features, which poses a limitation on its use in some areas, is that it produces a piecewise constant fitted response. For smoothing the fitted response, we introduce a regularization term in the monotonic regression, formulated as a least distance problem with monotonicity constraints. The resulting smoothed monotonic regression is a convex quadratic optimization problem. We focus on the case, where the set of observations is completely (linearly) ordered. Our smoothed pool-adjacent-violators algorithm is designed for solving the regularized problem. It belongs to the class of dual active-set algorithms. We prove that it converges to the optimal solution in a finite number of iterations that does not exceed the problem size. One of its advantages is that the active set is progressively enlarging by including one or, typically, more constraints per iteration. This resulted in solving large-scale test problems in a few iterations, whereas the size of that problems was prohibitively too large for the conventional quadratic optimization solvers. Although the complexity of our algorithm grows quadratically with the problem size, we found its running time to grow almost linearly in our computational experiments.     

A simple proof of the Lyapunov finite-time stability theorem

We offer a simple proof of the Lyapunov finite-time stability theorem for Filippov systems which does not use any generalized derivatives to differentiate the composition of the Lyapunov function with absolutely continuous solutions.     

Forensic Identification of Dyes in Ballpoint Pen Inks Using LC–ESI–MS

The aim of this work was to develop a new technique using flow injection analysis combined with LC–ESI–MS which allows identification of dyes in ballpoint pen inks. A sample preparation procedure for the extraction of dyes from ballpoint pen strokes has been developed. The characteristic group of ions for each sample of 21 studied ballpoint pen inks corresponding to the present dyes has been determined using flow injection method. LC separation conditions for identified dyes have been optimized on reversed-phase sorbent based on silica gel. The best composition of the mobile phase for the dyes mixture LC separation was 0.1% aqueous formic acid and acetonitrile. Detection of dyes was carried out using mass spectrometry with electrospray ionization in positive and negative modes after reversed-phase liquid chromatography separation. Dye composition of ink was additionally confirmed comparing the data obtained from the literature. Flow injection analysis allows obtaining intensive ions of unknown strokes. It is difficult to get this information using only chromatographic methods, because dyes peak intensity can be low and noise of basic line high. Flow injection method allows distinguishing the analyzed 21 ballpoint pens by determining a characteristic set of dyes. The developed flow injection technique is very simple and quick. As a result, a novel approach for the identification of dyes in the ballpoint pen inks by flow injection analysis with LC–ESI–MS and UV detection without using standard dye samples has been established. It can be an effective alternative to the existing LC–DAD–MS and IR spectroscopy methods.     

The unsubstituted <Emphasis Type="Italic">ortho</Emphasis>-amidino benzoic acid: crystal structure,characterization and p<Emphasis Type="Italic">K</Emphasis><Subscript>a</Subscript> determination

The simplest o-amidino benzoic acid—2-(amino(imino)methyl)benzoic acid—has been isolated in 23 % yield as a side product of the reaction of phthalonitrile and ammonia along with desired 1-imino-1H-isoindol-3-amine. This amidino acid was fully characterized by nuclear magnetic resonance, IR spectroscopy, mass spectrometry; pK_a values were also determined. X-ray diffraction study and quantum chemical calculations revealed that in the solid state it exists as a zwitterion that is stabilized by intermolecular hydrogen bonds.     

Constant flux relation for driven dissipative systems

Conservation laws constrain the stationary state statistics of driven dissipative systems because the average flux of a conserved quantity between driving and dissipation scales should be constant. This requirement leads to a universal scaling law for flux-measuring correlation functions, which generalizes the 4/5th law of Navier-Stokes turbulence. We demonstrate the utility of this simple idea by deriving new exact scaling relations for models of aggregating particle systems in the fluctuation-dominated regime and for energy and wave action cascades in models of strong wave turbulence.     

Structure determination of medium-sized sodium clusters

Sodium cluster anions Na(n)(-) with n = 39-350 have been studied by low temperature photoelectron spectroscopy and density functional theory (DFT). The highly structured experimental spectra are in excellent agreement with the electronic density of states (DOS) of the DFT lowest energy structures. Even for the largest sizes, a pronounced sensitivity of the DOS on fine geometric details could be observed, allowing for a reliable identification of a specific icosahedral growth motif. The intermediate sizes between the closed-shell Mackay clusters with 55, 147, and 309 atoms form by growth of overlayers, which often exhibit a twist deformation with respect to regular (Mackay-type) ones.