Simultaneous determination of vitamin B12 and its derivatives using some of multivariate calibration 1 (MVC1) techniques

Resolution of binary mixtures of vitamin B12, methylcobalamin and B12 coenzyme with minimum sample pre-treatment and without analyte separation has been successfully achieved by methods of partial least squares algorithm with one dependent variable (PLS1), orthogonal signal correction/partial least squares (OSC/PLS), principal component regression (PCR) and hybrid linear analysis (HLA). Data of analysis were obtained from UV-vis spectra. The UV-vis spectra of the vitamin B12, methylcobalamin and B12 coenzyme were recorded in the same spectral conditions. The method of central composite design was used in the ranges of 10-80mgL(-1) for vitamin B12 and methylcobalamin and 20-130mgL(-1) for B12 coenzyme. The models refinement procedure and validation were performed by cross-validation. The minimum root mean square error of prediction (RMSEP) was 2.26mgL(-1) for vitamin B12 with PLS1, 1.33mgL(-1) for methylcobalamin with OSC/PLS and 3.24mgL(-1) for B12 coenzyme with HLA techniques. Figures of merit such as selectivity, sensitivity, analytical sensitivity and LOD were determined for three compounds. The procedure was successfully applied to simultaneous determination of three compounds in synthetic mixtures and in a pharmaceutical formulation.     

Investigating the effects of nanoparticles mean diameter on laminar mixed convection of a nanofluid through an inclined tube with circumferentially nonuniform heat flux

In this study, laminar mixed convection of a water-based nanofluid containing Al₂O₃ nanoparticles in an inclined copper tube, which is heated at the top half surface, is investigated numerically. A heat conduction mechanism through the tube wall was implemented. Three-dimensional equations using a two-phase mixture model were solved to investigate the hydrodynamic and thermal behaviors of the nanofluid over a wide range of nanoparticle volume fractions. To verify the model, the results were compared with previous works and a good agreement between the results was observed. The effect of nanoparticles diameter on the hydrodynamic and thermal parameters over a wide range of Grashof numbers is presented and discussed for a particle volume fraction and Reynolds number. It is shown that the diameter of nanoparticles affects the particle distribution in the cross section perpendicular to the tube axis, heat transfer coefficient, and shear stress.     

A stoichiometric imprinted chelating resin for selective recognition of copper(II) ions in aqueous media

This work reports the preparation of a new copper(II) ion-imprinted polymer (IIP) material, using 5,6;14,15-dibenzo-1,4-dioxa-8,12-diazacyclopentadecane-5,14-diene (DBDA15C4) and 2-vinylpyridine (VP) as a non-vinylated chelating agent and a functional vinyl monomer, respectively. The Cu²⁺ ion can form stable complexes with DBDA15C4 and VP. The stoichiometries of Cu²⁺-DBDA15C4 and ternary Cu²⁺-DBDA15C4-VP complexes were elucidated using conductometric and spectrophotometric methods, and found to be Cu²⁺(DBDA15C4), Cu²⁺(DBDA15C4)₂ and Cu²⁺(DBDA15C4)(VP)₂. The results obtained from solution studies were also supported by ab initio theoretical calculations. The resulting ternary complex Cu²⁺(DBDA15C4)(VP)₂ was copolymerized with ethyleneglycoldimethacrylate, as a cross-linking monomer, via bulk polymerization method. The imprinted copper ion was removed from the polymeric matrix by 0.1 M HNO₃. The Cu²⁺-imprinted polymer particles were characterized by IR spectroscopy and elemental analysis. Optimum pH range for rebinding of Cu²⁺ on the IIP and equilibrium binding time were 7.0-7.5 and 45 min, respectively. Sorbent capacity and enrichment factor for Cu²⁺ were obtained as 75.3 ± 1.9 μmol g⁻¹ and 100, respectively. In selectivity study, it was found that imprinting results in increased affinity of the material toward Cu²⁺ ion over other competitor metal ions with the same charge and close ionic radius. The prepared IIPs were repeatedly used and regenerated for five times without a significant decrease in polymer binding affinities.     

Fe3O4–SiO2–Bi2O3-catalyzed One-Pot Synthesis of Tetrahydrobenzo[b]pyran Derivatives Under Solvent-Free Conditions

Russian Journal of Organic Chemistry - A Fe3O4–SiO2–Bi2O3 magnetic nanocatalyst was used to synthesize tetrahydrobenzo[b]pyran derivatives from malononitrile, cyclohexane-1,3-dione, and...     

Guiding in the visible with "colorful" solid-core Bragg fibers

We report on the fabrication and characterization of solid-core all-polymer Bragg fibers consisting of a large-diameter polymethyl methylacrylate (PMMA) core surrounded by 50 alternating PMMA/Polystyrene (PS) polymer layers. By modifying the reflector layer thickness we illustrate that bandgap position can be adjusted at will in the visible. Moreover, such fibers are intensely colored in both the transmission and the outside reflection modes. Potential applications of such fibers are discussed.     

Chemoselective synthesis of 4‐oxo‐2‐aryl‐4,10‐dihydropyrimido [1,2‐a][1,3]benzimidazol‐3‐yl cyanides via [3+3] atom combination of 2‐aminobenzimidazole with ethyl‐α‐cyanocinnamoates

Chemoselective synthesis of 4‐oxo‐2‐aryl‐4,10‐dihydropyrimido[1,2‐a][1,3]benzimidazol‐3‐yl cyanides from three‐component reactions of 2‐aminobenzimidazole, aldehydes, and ethyl cyanoacetate via [3+3] atom combination is reported. The effect of different base catalysts such as sodium acetate, triethylamine, and magnesium oxide MgO on the product yield has also been investigated under conventional heating. J. Heterocyclic Chem., (2011).     

27Al and 31P NMR Investigations of Soluble Aluminophosphate Species in Alcohol–Water Mixtures

In this work, phosphorus-31 and aluminum-27 nuclear magnetic resonance techniques were used to characterize the distribution of soluble aluminophosphate species in methanol + water and ethanol + water mixtures. The assignment of the peaks to aluminate species was attempted, clarifying earlier work and producing information on the different aluminophosphate complexes. Nine peaks were observed at ?0.41, ?6.4, ?7.5, ?7.9, ?13.1, ?13.9, ?16.6, ?18.1 and ?20.6 ppm. Four new peaks appeared in the ³¹P NMR spectra of the alcoholic aluminophosphate solutions and their intensities changed with changes of the alcohol:water volume ratio. These new peaks were observed in the presence of methanol or ethanol but not in aqueous solutions.     

Effect of gender, season, and vitamin D status on bone biochemical markers in Saudi diabetes patients

Biochemical bone turnover markers (BTMs) provide important information on the diagnosis, therapy and monitoring of metabolic bone diseases. They are evident before measurable changes in bone mineral density (BMD) take place. A total of 35 adult Saudi patients (23 males; 12 females) with type 2 diabetes and diagnosed to be vitamin D deficient were recruited in this prospective study. Here we investigated the effects of gender, season, and vitamin D status on bone biochemical markers of bone remodeling. Anthropometry and blood samples were collected at different intervals. Metabolic parameters and bone biomarkers were measured routinely and by ELISA. Both males and females had a significant increase in their vitamin D status over time, but no significant changes in the bone biomarkers were observed in females. In males there was a significant increase in circulating levels of corrected calcium and OPN (p = 0.004 and 0.01 respectively) and a significant decrease in crosslaps (p = 0.005). In all subjects there was a modest but significant positive relationship between vitamin D status and OC (R = 0.34; p = 0.04). In conclusion, our study demonstrates that changes in bone remodeling markers are affected by season, gender, and possibly vitamin D status. This gender difference may well reflect the physiologic pathway responsible for the higher peak bone mass achieved in males compared to females.     

On an inequality of Ramanujan concerning the prime counting function

We discuss on the sign of $\mathcal{R}_{\alpha }(x):=\pi(x)^{2}-\frac{\alpha x}{\log x}\pi(\frac{x}{\alpha })$ for x sufficiently large, and for various values of ??>0. The case ??=e refers to a result due to Ramanujan asserting that $\mathcal{R}_{e}(x)<0$ . Related by this inequality, we obtain a conditional result that gives the number N>530.2 such that $\mathcal{R}_{e}(x)<0$ is valid for x>e ^N . Moreover, we show that under assumption of validity of the Riemann hypothesis, the inequality $\mathcal{R}_{e}(x)<0$ holds for x>138,766,146,692,471,228. Then, in various cases for ??, we find numerical values of x _?? in which $\mathcal{R}_{\alpha }(x)$ is strictly positive or negative for x??x _?? .     

Generation of mid-infrared radiation by self-difference frequency mixing in chromium-doped zinc selenide

We report what we believe to be the first demonstration of mid-infrared generation (approximately 9 microm) by self-difference frequency generation in Fresnel birefringence quasi-phase-matched Cr:ZnSe laser slabs.