Synthesis of α-Metoylene-γ-Lactones in Furanosidic Systems

Abstract

Synthesis of stereoisomeric α-methylene-γ-lactones in furanose-and furanuronoamide derivatives was easily accomplished by Reformatsky Reaction with ethyl bromcmethylacrylic ester and zinc. Pyridinium chlorochromate/3Å molecular sieve powder showed to be an excellent reagent for the oxidation of secondary hydroxyl groups of a furanose system and of α-hydroxy amides.     

Inkjet-printed electrochemical sensors

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The aggregation of the sodium dodecyl sulfate –n - octanol–water system at low concentration

Micelle formation in sodium dodecyl sulfate (SDS)–n-octanol mixtures was studied by several techniques and the results were interpreted using regular solution theory for mixed-micelle formation. Octanol was considered as a nonionic surfactant. The composition of micelles at the critical micelle concentration (cmc) was computed together with the interaction parameter and the activity coefficient of the components of the micelles. The fluorescence quenching technique with pyrene was employed to obtain the SDS and octanol aggregation numbers at the cmc. The results were in agreement with similar studies on other alcohol–SDS systems. At the cmc spherical, almost fully ionized micelles formed, while at a higher concentration there was a transition to anisometric (probably rodlike) micelles which pushed sodium counterions into their Stern double layer. Mixed anisometric micelles were more ionized than pure SDS micelles. When the octanol:SDS total ratio exceeded 0.85:1, an emulsion of octanol appeared in equilibrium with the micelles. Received: 23 December 1998 Accepted in revised form: 3 March 1999     

Stabilization of superparamagnetic nickel nanoparticles in a sepiolite matrix

Superparamagnetic nickel-rich nanoparticles at room temperature have been obtained in a silicate matrix (sepiolite) by a chemical route. During the synthesis process, the control of the acid treatment of the matrix allows nickel cations being incorporated in different locations, into the octahedral site of the structural channels or being deposited onto the sepiolite surface. Thus, two different types of nickel nanoparticles have been obtained depending on the nature of the acid attack: small (~7 nm) and embedded superparamagnetic, or large (~27 nm) deposited single domain nickel nanoparticles for strong or weak acid attack, respectively. Moreover, the embedded nanoparticles have been revealed to possess a remarkable stability against complete oxidation. According to the usage of characterization techniques (transmission electron microscopy, X-ray diffraction and magnetic measurements), embedded nanoparticles seem to be coated with a non-ferromagnetic coating that hinders the oxygen diffusion.     

Optical characterization and composition of abdominal wall muscle from rat

Complete optical characterization of biological tissue is desirable to develop clinical methods using optical technologies. Particularly, to develop optical clearing methods in biological tissues, it is necessary to know the composition of the tissue, the percentage of each constituent and corresponding refractive indexes. To obtain such information for rat muscle, we used a simple method to characterize tissue constituents for both content percentage and refractive index. The study consisted on measuring mass with a precision weighting scale and the refractive index with an Abbe refractometer during tissue dehydration. With the collected data, we used a theoretical model to calculate the refractive index and percentage for both interstitial fluid and solid part of the rat muscle. The results obtained are in good agreement with data published by other authors, and were considered of vital information for the optical clearing studies that we planned to perform.     

Generation of NOON States in Waveguide Arrays

A method to generate NOON states with three photons by injecting photons in an array of three waveguides is presented. Conditional measurements project the wave function in a given (desired) state. In passing, it is shown how the array of three waveguides, that effectively reproduces the interaction of three fields, may be reduced to the interaction of two fields.     

Dielectric behavior of hexaferrites BaCo2−xZnxFe16O27

The dielectric constant (′) and dielectric loss (tan δ) for hexaferrites BaCo_2−xZn_xFe₁₆O₂₇ have been studied as a function of frequency (f), temperature (T) and composition (x). The experimental results indicate that ′ and tan δ above the relaxation frequency only decrease as the frequency increases and as the temperature decreases. Tan δ shows the dielectric relaxation at certain critical frequencies which rise as temperature increases. The activation energy for the dielectric relaxation (E_D), ′, and tan δ are found to be minimum for x = 0.8.     

Determination of the Mechanical Properties of Powdered Agricultural Products and Sugar

Grain, forage cereals and different types of flour are commonly stored in silos. Their behavior within these structures is mainly governed by their mechanical properties. Since their advent, numerical methods have increasingly been used in silo design. However, the results obtained using these methods strongly depend on the variables employed to define the materials stored. Since the literature provides little information on the variables required for modeling the behavior of agricultural powdered materials, the goals of the present work were to: i) provide values for the different variables that are needed when designing silos using numerical methods (e.g., the Poisson ratio, the dilatancy angle and the modulus of elasticity, etc.), and ii) investigate the suitability of tests used in soil mechanics for powdered materials (e.g., the direct shear and the oedometric and triaxial test). Recommended values for these variables are proposed.     

Novel acid-catalyzed rearrangement of tetrahydro-1,2,3,4-tetrazines: unexpected formation of glycosazones

The present contribution discloses a simple and unexpected acid-catalyzed cleavage of tetrahydrotetrazines leading to 1,2-bis(hydrazones). Incorporation of a chiral fragment derived from carbohydrates enables the rapid preparation of glycosazones, a family of compounds employed by Emil Fischer to elucidate the configuration of sugars. In addition, a mechanistic proposal accounts for experimental observations.