Design,preparation, and characterization of Fe3O4 nanoparticles encapsulating β-cyclodextrin-bearing guanidine as a highly efficient and reusable heterogeneous base catalyst for synthesis of 3,4-dihydropyrano[3,2-c]chromenes

Chromene substructure is an important structural motif present in a variety of medicines, natural products, and materials showing biological activities. Here, a simple and convenient procedure for the synthesis of 3,4-dihydropyrano[3,2-c]chromene derivatives is described. For this purpose, Fe₃O₄ nanoparticles supported on β-cyclodextrin-guanidine were successfully prepared and used as catalyst. The structure of this catalyst was assigned by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, thermal gravimetric analysis, and vibrating sample magnetometer techniques. The prepared nanocomposites were used as a highly active, heterogeneous, and reusable nanocatalyst for the one-pot, three-component reaction of 4-hydroxycoumarin, aromatic aldehydes, and ethyl cyanoacetate. This method has advantages such as mild conditions, high yields, easy workup and simple purification of products, little catalyst loading, cost efficiency, and reusability of the catalyst.     

Quantum chemical calculations based on ONIOM and the DFT methods in the inclusion complex: doxycycline/2-O-Me-β-cyclodextrin

A computational study of inclusion complexes of 2-methyl-βCD with Doxycycline tautomeric (enol and keto form) has been performed with several combinations of ONIOM hybrid calculations. The reliability of the ONIOM2 calculations at the integrated level, ONIOM2 (M05-2X/6-31G(d): M05-2X/3-21G*), ONIOM2 (M05-2X/6-31G(d):HF/3-21G*), ONIOM2 (B3LYP/6-31G(d):HF/3-21G*), ONIOM2 (B3LYP/6-31G(d):B3LYP/3-21G*) and ONIOM2 (B3PW91/6-31G(d):B3PW91/3-21G*) was examined. Their complexation, binding, deformation and stabilization energies, and geometrical data were compared with those of the target geometry structure optimized at the M05-2X/6-31G(d) level of theory. Mixed combinations ONIOM2 (M05-2X 6-31G(d):HF 3-21G*) and ONIOM2 (B3LYP 6-31G(d):HF 3-21G*) reproduces nearly the target geometry structure and provides realistic energetic results at a relatively low computational cost.     

Entropy analysis for viscoelastic magnetohydrodynamic flow over a stretching surface

This paper presents the application of the second law analysis of thermodynamics to viscoelastic magnetohydrodynamic flow over a stretching surface. The velocity and temperature profiles are obtained analytically using the Kummer's functions and used to compute the entropy generation number. The effects of the magnetic parameter, the Prandtl number, the heat source/heat sink parameter and the surface temperature parameter on velocity and temperature profiles are presented. The influences of the same parameters, the Hartmann number, the dimensionless group parameter and the Reynolds number on the entropy generation are also discussed.     

C-20 ketone reduction of hydrocortisone by rice field microalga <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> MCCS 013

A unicellular microalga, Chlorella vulgaris, was isolated from rice field and applied in the biotransformation experiment of hydrocortisone (1). This strain has not been previously tested for hydrocortisone bioconversion. Fermentation was carried out in BG-11 medium supplemented with 0.05% substrate at 25°C for 14 days incubation. The products obtained were chromatographically purified followed by their characterization using spectroscopic methods. 11β,17α,20β,21-Tetrahydroxypregn-4-en-3-one (2), 11β,17β-dihydroxyandrost-4-en-3-one (3), and 11β-hydroxyandrost-4-ene-3,17-dione (4) were the main bioproducts in the hydrocortisone bioconversion. Bioreaction characteristics observed were 20-ketone reduction for accumulation of compound 2 and side chain degradation of the substrate to prepare compounds 3 and 4. Time course study showed the accumulation of the product 2 from the second day of the fermentation and 3 as well as 4 from the third day. All the metabolites reached their maximum concentration in seven days. Microalgal 18S rRNA gene was also amplified by PCR. PCR products were sequenced to confirm their authenticity as 18S rRNA gene of microalgae. The result of PCR blasted with other sequenced microalgae in NCBI showed 100% homology to the 18S small subunit rRNA of six strains of Chlorella vulgaris.     

Metrological traceability is not always a straight line

The two most important concepts in metrology are certainly “traceability to standards” and “measurement uncertainty evaluation”. So far the questions related to these concepts have been reasonably solved in the metrology of “classical quantities”, but for the introduction of metrological concepts in new fields, such as chemistry and biology, a lot of problems remain and must be solved in order to support international arrangements. In this presentation, the authors want to develop the strategy implemented at Laboratoire national de métrologie et d’essais (LNE) in metrology in chemistry and biology. The strategy is based on: (1) pure solutions for calibration of analytical instruments, (2) use of certified reference materials (matrix reference materials), and (3) participation to proficiency testing schemes. Examples will be presented in organic and inorganic chemistry. For laboratory medicine, proficiency testing providers play an important role in the organization of External Quality Assessment Schemes. For the time being, the reference value or the assigned value of the comparison is calculated with the results obtained by the participants. This assigned value is not often traceable to SI units. One of the methods suggested by LNE is to ensure the metrological traceability to SI units of the assigned value for the more critical quantities carried on analytes by implementing the Joint committee for traceability in laboratory medicine reference methods.     

Approaches to uncertainty evaluation based on proficiency testing schemes in chemical measurements

Since the advent of the Guide to the Expression of Uncertainty in Measurement (GUM) founding the principles of uncertainty evaluation, numerous projects have been carried out to develop alternative practical methods when it is impossible to model technical or economical aspects of the measurement process. These methods can use all the experimental data available to the laboratories, such as repeatability, reproducibility, quality-control charts, etc. The studies presented in this paper compare the results obtained by the modelling method from GUM with the uncertainties found by applying alternative methods. They show two examples, one in the field of environmental monitoring, the other in the biomedical field, based on the exploitation of PT schemes results. Presented at BERM-11, October 2007, Tsukuba, Japan.     

Measurement of wire diameter by optical diffraction

A combined interference and diffraction pattern, in the form of equidistant interference fringes, resulting from illuminating a vertical metallic wire by a laser beam is analyzed to measure the diameter of four standard wires. The diameters range from 170 to 450 μm. It is found that the error in the diameter measurements increases for small metallic wires and for small distances between the wire and the screen due to scattering effects. The intensity of the incident laser beam was controlled by a pair of sheet polaroids to minimize the scattered radiation. The used technique is highly sensitive, but requires controlled environmental conditions and absence of vibration effects. The expanded uncertainty for k=2 is calculated and found to decrease from U(D)=±1.45 μm for the wire of nominal diameter 170 μm to ±0.57 μm for the diameter 450 μm.