Corneal topography measurement by means of radial shearing interference: Part III – measurement errors

This work contains results of computer simulation researches, which define requirements for measurement conditions, which should be fulfilled so that measurement results ensure allowable errors. They define: allowable measurement errors (interferogram's scanning) and conditions, which should fulfill computer programs, so that errors introduced by mathematical operations and computer are the smallest.     

Effect of medium pH on chemical selectivity of oxalic acid biosynthesis by <Emphasis Type="Italic">Aspergillus niger</Emphasis> W78C in submerged batch cultures with sucrose as a carbon source

The pH of the medium is the key environmental parameter of chemical selectivity of oxalic acid biosynthesis by Aspergillus niger. The activity of the enzyme oxaloacetate hydrolase, which is responsible for decomposition of oxaloacetate to oxalate and acetate inside the cell of the fungus, is highest at pH 6. In the present study, the influence of pH in the range of 3–7 on oxalic acid secretion by A. niger W78C from sucrose was investigated. The highest oxalic acid concentration, 64.3 g dm^?3, was reached in the medium with pH 6. The chemical selectivity of the process was 58.6% because of the presence of citric and gluconic acids in the cultivation broth in the amount of 15.3 and 30.2 g dm^?3, respectively. Both an increase and a decrease of medium pH caused a decrease of oxalic acid concentration. The obtained results confirm that pH 6 of the carbohydrate medium is appropriate for oxalic acid synthesis by A. niger, but the chemical selectivity of the process described in this paper was high in comparison to values reported previously in the literature.     

Analysis of supramolecular interactions in alendroniate alkali metal salts: synthesis,structure, and properties of novel sodium alendronate polymorph

A new polymorph of anhydrous sodium alendronate, C₄H₁₂NO₇P₂Na, has been synthesized and characterized by single crystal X-ray diffraction as well as infrared spectroscopy and thermal analysis. The title compound crystallizes in the monoclinic P2₁/c space group. Asymmetric unit consists of one alendronic anion and one sodium cation. An interplay of classical strong O-H^…O, N-H^…O and non-classical weak C-H^…O hydrogen bonds creates 3D framework in the crystal. Contrary to previously reported sodium alendronate salts, in which Na⁺ cation is surrounded by six-coordinated sphere, in compound (1), the Na⁺ cation is five-coordinated in a distorted trigonal-bipyramidal geometry. In order to provide a detailed investigation of the molecular arrangement in view of intermolecular interactions, the title compound was compared with alendronic acid and other known alkali metal alendronate salts, retrieved from the Cambridge Crystal Structure Database. The intercontacts were qualitatively and quantitatively compared using Hirshfeld surface analysis. It highlights that strong O^…H/H^…O and subtle H^…H contacts play an influential role in the total surface area. The Me^+…H/H^…Me⁺ and Me^+…O/O^…Me⁺ contacts are meaningful as well. These evidently simple systems show a diverse complexity. Moreover, the powder X-ray diffraction, DSC, thermogravimetry/derivative thermogravimetry, and FT-IR results are also reported.

     

Thermoanalytical studies of the ceramic-metal composites obtained by gel-centrifugal casting

Journal of Thermal Analysis and Calorimetry - Composite material with a gradient concentration of the metallic phase was prepared by the novel gel-centrifugal casting method. This method combines...     

Design,synthesis, structure elucidation and in vitro antiviral and antimicrobial evaluation

In this study, we described the synthesis of the derivatives of thiosemicarbazide, dicarboximide, 1,2,4-triazole-5-thione and 4-oxo-1,3-thiazolidine. Two different dicarboxylic acid anhydrides reacted with 4-substituted-3-thiosemicarbazide, and derivatives of thiosemicarbazide and dicarboximide were obtained. Next, cyclization reaction of dicarboximide derivatives in alkaline media was used to prepare 1,2,4-triazole-5-thione. The 4-oxo-1,3-thiazolidine was synthesized by the reaction of dicarboximide with ethyl bromoacetate. All obtained derivatives were analysed by ¹H and ¹³C NMR spectra, and for one compound, the X-ray crystallography was done. Antimicrobial, antiviral and in vitro evaluations of cytotoxicity were examined. According to the preliminary antiviral screening, compounds 3 and 4 presented the antiviral activity against HSV-1 and CVB3. Additionally, compound 3 shows selective in vitro toxic effect against human epithelial cells FaDu, without affecting normal animal cell line (Vero). The same derivatives 3 and 4 also displayed a wide spectrum of antimicrobial activity against reference microorganisms and indicated both antibacterial and antifungal potential activities.     

A survey of acid catalysis and oxidation conditions in the two-step, one-flask synthesis of meso-substituted corroles via dipyrromethanedicarbinols and pyrrole

The reaction of dipyrromethanedicarbinols with pyrrole leading to meso-substituted corroles was investigated to determine whether mild acid catalysts [Dy(OTf)(3), Yb(OTf)(3), Sc(OTf)(3), and InCl(3)] known to provide porphyrins from dipyrromethanecarbinol species while suppressing undesired reversibility (resulting in scrambling) are applicable to reactions affording corrole, and to explore the requirements of the oxidation step. We examined a model reaction leading to meso-triphenylcorrole (TPC) to survey the effect of acid catalyst, acid concentration, ratio of pyrrole to dipyrromethanedicarbinol, oxidant, oxidant quantity, and reaction time on the yield of TPC (by UV-vis) in reactions performed at room temperature in CH(2)Cl(2). Key to this survey was a modification of the well-known spectrophotometric method for monitoring reactions leading to porphyrin. The survey revealed that TPC could be prepared via a subset of the mild acid catalysts [Dy(OTf)(3) and Yb(OTf)(3)], and a preparative-scale reaction afforded an isolated yield of TPC of 49%, devoid of porphyrin. Suppression of reversible processes was further demonstrated by the synthesis of three corroles bearing different meso substituents in defined locations in isolated yields ranging from 50% to 80%. The reaction conditions were applicable to a dipyrromethanedicarbinol bearing electron-withdrawing pentafluorophenyl substituents-provided that the reaction time of the condensation step was increased. We identified circumstances under which DDQ can cause severe interference with the detection and isolation of some corroles, we found that the yield and purity of the corrole depend on judicious selection of oxidation conditions, and we assessed the sensitivity toward light of dilute solutions of the corroles prepared in this study.     

Vacuum flash pyrolysis (VFP) of malonyl peroxides: decarboxylation versus decarbonylation of the intermediary α-lactones

Vacuum Flash Pyrolysis (VFP) at ca. 450–500°C and ca. 0.1–0.3 Torr of the spirocyclic malonyl peroxides ($\text{2a,b}$) affords high yields of allenes ($\text{5a,b}$), while the simple malonyl peroxide ($\text{2c}$) leads to ketone ($\text{4}$), derived respectively from decarboxylation and decarbonylation of the intermediary α-lactones ($\text{3}$).     

Influence of styrene on the oxidative dehydrogenation of ethylbenzene

The influence of styrene and by-products of side reactions on the oxidative dehydrogenation of ethylbenzene into styrene with use of the vanadia-magnesia catalyst has been investigated. Notable slowing-down influence of styrene contained in the substrates on the process has been ascertained, whereas the contamination with other products has not caused such an effect. The apparent activation energy and pre-exponential factor for the investigated reactions were calculated.     

Solvent effect on the rate of metal deposition reactions: Investigations of the kinetics of Ni(II) discharge at the mercury in mixed water methanol solvents

The kinetics of Ni²⁺ deposition at the mercury electrode, from non-complexing electrolytes in mixed water methanol solvents has been investigated. The rate of this reaction, in the whole composition range, at large overpotentials is controlled by a limiting “chemical” process. The rate constants of the limiting process when plotted as a function of the solvent composition display a relationship similar to those observed for the large organic, bidendate ligands substitution reactions, believed to the controlled by the Ni(II)-solvent bond rupture. Hence, the limiting “chemical” process in Ni²⁺ discharge can be identified as the slow solvent dissociation step. These results confirm the mechanism of Ni²⁺ dischrage already proposed by Gierst and Dandoy on the basis of investigations performed in aqueous solutions.