A simple and selective kinetic spectrophotometric method for the determination of kanamycin using acetylacetone-formaldehyde reagent in N,N′-dimethylformamide medium

A simple, sensitive, and selective kinetic spectrophotometric method for the determination of kanamycin in pure form and pharmaceutical formulations is described. The method is based on the measurement of the intensity of the yellow chromogen formed by the reaction between kanamycin and acetylacetone-formaldehyde reagent in a N,N′-dimethyl formamide medium. The variable-time method was used to evaluate the rate of reaction of the colored chromogen formed at 410 nm. The reaction conditions were optimized and the calibration graph was found to be linear in the range 60–160 μg/mL. The results obtained by the developed and reference methods are in good agreement. Various statistical parameters were evaluated to establish the precision, accuracy, repeatability, and reproducibility of the proposed method. The text was submitted by the authors in English.     

EFFECT OF COMPOSITION AND PROCESSING CONDITION ON MICROSTRUCTURAL PROPERTIES AND DURABILITY OF FLUOROPOLYMER/ACRYLIC BLENDS

Fluoropolymer blends have been widely used as binders for exterior coatings because of their excellent resistance to ultra-violet (UV) radiation as well as to many corrosive chemical agents.It is known that the fluorinated component usually has a lower glass transition temperature and easily crystallizes in the final structure depending upon the blend composition and sample annealing condition.We investigated the effect of blend composition and annealing process (slow and fast cooling) on the surface mor...     

Topotactic oxidation pathway of ScTiO3 and high-temperature structure evolution of ScTiO3.5 and Sc4Ti3O12-type phases

The novel oxide defect fluorite phase ScTiO(3.5) is formed during the topotactic oxidation of ScTiO(3) bixbyite. We report the oxidation pathway of ScTiO(3) and structure evolution of ScTiO(3.5), Sc(4)Ti(3)O(12), and related scandium-deficient phases as well as high-temperature phase transitions between room temperature and 1300 °Cusing in-situ X-ray diffraction. We provide the first detailed powder neutron diffraction study for ScTiO(3). ScTiO(3) crystallizes in the cubic bixbyite structure in space group Ia3 (206) with a = 9.7099(4) ?. The topotactic oxidation product ScTiO(3.5) crystallizes in an oxide defect fluorite structure in space group Fm3m (225) with a = 4.89199(5) ?. Thermogravimetric and differential thermal analysis experiments combined with in-situ X-ray powder diffraction studies illustrate a complex sequence of a topotactic oxidation pathway, phase segregation, and ion ordering at high temperatures. The optimized bulk synthesis for phase pure ScTiO(3.5) is presented. In contrast to the vanadium-based defect fluorite phases AVO(3.5+x) (A = Sc, In) the novel titanium analogue ScTiO(3.5) is stable over a wide temperature range. Above 950 °C ScTiO(3.5) undergoes decomposition with the final products being Sc(4)Ti(3)O(12) and TiO(2). Simultaneous Rietveld refinements against powder X-ray and neutron diffraction data showed that Sc(4)Ti(3)O(12) also exists in the defect fluorite structure in space group Fm3m (225) with a = 4.90077(4) ?. Sc(4)Ti(3)O(12) undergoes partial reduction in CO/Ar atmosphere to form Sc(4)Ti(3)O(11.69(2)).     

Characterization of nucleobase-amino acid stacking interactions utilized by a DNA repair enzyme

The present work characterizes the gas-phase stacking interactions between four aromatic amino acid residues (histidine, phenylalanine, tyrosine, and tryptophan) and adenine or 3-methyladenine due to the proposed utilization of these interactions by enzymes that repair DNA alkylation damage. The MP2 potential energy surfaces of the stacked dimers are considered as a function of four variables (vertical displacement, angle of rotation, horizontal displacement, and tilt angle) using a variety of basis sets. It is found that the maximum stacking interaction energy decreases with the amino acid according to TRP > TYR approximately HIS > PHE for both nucleobases. However, the magnitude of the stacking interaction significantly increases upon alkylation (by 50-115%). Comparison of the stacking energies calculated using our surface scans to those estimated from experimental crystal structures indicates that the stacking interactions within the active site of 3-methyladenine DNA glycosylase can account for 65-75% of the maximum possible stacking interaction between the relevant molecules. The decrease in stacking in the crystal structure arises due to significant differences in the relative orientations of the nucleobase and amino acid. Nevertheless, alkylation is found to significantly increase the stacking energy when the crystal structure geometries are considered. Our calculations provide computational support for suggestions that alkylation enhances the stacking interactions within the active site of DNA repair enzymes, and they give a measure of the magnitude of this enhancement. Our results suggest that alkylation likely plays a more important role in substrate identification and removal than the nature of the aromatic amino acid that interacts with the substrate via stacking interactions.     

Scanning electrochemical cell microscopy: High-resolution structure−property studies of mono- and polycrystalline electrode materials

Scanning electrochemical cell microscopy (SECCM) is a nanopipette-based scanning electrochemical probe microscopy technique that utilises a mobile droplet cell to measure and visualise electrode activity with high spatiotemporal resolution. This article spotlights the use of SECCM for studying the electrochemistry of crystalline electrode materials, ranging from well-defined monocrystals (e.g., transition metal dichalcogenides: MoS₂, WS₂ and WSe₂) to structurally/compositionally heterogeneous polycrystals (e.g., polycrystalline Pt, Au, Pd, Cu, Zn, low carbon steel, boron-doped diamond) and covering the diverse areas of (photo)electrocatalysis, corrosion science, surface science and electroanalysis. In particular, it is emphasised how nanoscale-resolved information from SECCM is readily related to electrode structure and properties, collected at a commensurate scale with complementary, co-located microscopy/spectroscopy techniques, to allow structure–property relationships to be assigned directly and unambiguously.     

Measurement of isomeric yield ratios for 93Nb(??,4n)89m,gNb and natMo(??,xn1p)95m,gNb reactions with 50-, 60-, and 70-MeV bremsstrahlung

We measured the isomeric yield ratios for the photonuclear reactions of ⁹³Nb(??,4n)^89m,gNb and ^natMo(??,xnp)^95m,gNb by using the activation method. The high-purity ⁹³Nb and ^natMo metallic foils in disc shape were irradiated with uncollimated bremsstrahlung beams of 50-, 60-, and 70-MeV generated from an electron linear accelerator in Pohang Accelerator Laboratory. The induced activities in the irradiated foils were measured by the high-resolution ??-ray spectrometry with a calibrated high-purity Germanium (HPGe) detector coupled to a PC-based 4?K multichannel analyzer. The reaction ⁹³Nb(??,4n)^89m,gNb was studied for the first time which has no comparable literature data. The result of ^95m,gNb isomeric pair was measured based on (??,p), (??,np), and (??,2np) reactions which is the first measurement at the intermediate energy region of 50?C70-MeV with a ^natMo target.     

The Role of the Pars Recta and Pars Oblique of Cricothyroid Muscle in Speech Production

To evaluate the functional difference of the pars recta and pars oblique during speech production, the electromyographic activities of these muscles were measured in thyroidectomized patients. The hooked wire electrodes were inserted into the normal side of the bellies of the pars recta and pars oblique bundles. Two kinds of sentences were used to obtain pitch changes, a simple interrogative sentence and a complex sentence with stress contrasts. The pars recta and pars oblique were simultaneously activated for initial lengthening and tensing of vocal folds to produce speech. The pars oblique might be initially more active than the pars recta at the initial task of speech and the pars recta might be more active at the pitch elevation in the interrogative sentence and the stress contrast of the complex sentence. The maximum electromyographic activity range of the pars recta and pars oblique seemed to be nearly equal. These results demonstrated that the patterns of electrical activities of the two bellies are different during speech and the combined activities of the pars recta and pars oblique are important in the adjustment of the vocal fold length during speech.     

Structural investigation of mM Ni(II) complex isomers using transmission XAFS: the significance of model development

High‐accuracy transmission XAFS determined using the hybrid technique has been used to refine the geometries of bis(N‐n‐propyl‐salicylaldiminato) nickel(II) (n‐pr Ni) and bis(N‐i‐propyl‐salicylaldiminato) nickel(II) (i‐pr Ni) complexes which have approximately square planar and tetrahedral metal coordination. Multiple‐scattering formalisms embedded in FEFF were used for XAFS modelling of the complexes. Here it is shown that an IFEFFIT‐like package using weighting from experimental uncertainty converges to a well defined XAFS model. Structural refinement of (i‐pr Ni) was found to yield a distorted tetrahedral geometry providing an excellent fit, χ_r² = 2.94. The structure of (n‐pr Ni) is best modelled with a distorted square planar geometry, χ_r² = 3.27. This study demonstrates the insight that can be obtained from the propagation of uncertainty in XAFS analysis and the consequent confidence which can be obtained in hypothesis testing and in analysis of alternate structures ab initio. It also demonstrates the limitations of this (or any other) data set by defining the point at which signal becomes embedded in noise or amplified uncertainty, and hence can justify the use of a particular k‐range for one data set or a different range for another. It is demonstrated that, with careful attention to data collection, including the correction of systematic errors with statistical analysis of uncertainty (the hybrid method), it is possible to obtain reliable structural information from dilute solutions using transmission XAFS data.     

Functional model of oxomolybdoenzymes: Synthesis and characterization of a molybdenum complex with sulphur and pterin ligands exhibiting saturation kinetics with pyridine N-oxide

Redox reaction between 6-acetonylisoxanthopterin (H₂pte) and [Mo^VIO₂ (ssp)] [ssp = anion of 2-(salicylideneamino) benzenethiol] in CH₃OH-C₂H₅OH medium produces a new mixed ligand compound [Mo^IV (ssp) (Hpte) (OCH₃)] (1). It has been characterized by elemental analysis, ESMS data, UV-Vis, IR,¹HNMR (1D and 2D) spectroscopy and cyclic voltammetry. Kinetics of formation of this compound as well as that of its reaction with pyridine N-oxide have been followed spectrophotometrically. Both the reactions follow substrate saturation kinetics and involve metal-centred oxygen atom transfer process. Large negative values of entropy of activation indicate the operation of associative mechanism.