Exploring the Chemistry of Non-sticky Sugars: Synthesis of Polyfluorinated Carbohydrate Analogues of d-Allopyranose

There is a growing interest in the preparation of polyfluorinated carbohydrates. A limited number of fluorohexopyranosides have been used in biological investigations because of the synthetic challenge they present. Hence, we report the synthesis of fluorinated homodimer, fluorodisaccharides, C-terminal fluoroglycopeptides, lipoic acid fluoroglycoconjugate and trifluoroallopyranoside derivatives functionalized at C-6. Our strategy uses levoglucosan as inexpensive starting material and facilitates an approach to complex carbohydrate analogues with multiple C−F bonds. The challenge of our synthetic route centered around an efficient preparation of crucial 1,6-anhydro-2,4-dideoxy-difluoroglucopyranose and focused on achieving a difficult glycosylation of the trifluoroallopyranose donor. The results clearly highlight challenges related to the preparation of polyhalogenated complex organic molecules and pave the way to access novel medically relevant tools.     

Simulating the Shroud of Turin: A Laboratory Experiment

The Shroud of Turin, a piece of linen cloth bearing an anatomically correct image of a crucified human being, which resembles Jesus of Nazareth, has been an enigma to scientists. While recent studies including radiocarbon dating suggest the cloth is a medieval relic, few if any proposals have been put forward that satisfactorily explain how the image was generated. In combination with a lecture on the scientific method and the problem of bias, a laboratory experiment has been developed that allows science students to attempt to simulate the image on the Shroud. The experiment involves an active-learning experience in which students discover which techniques do not work to generate the image and which begin to suggest how such an image could have been generated.     

Fractionation of ethylene/1‐pentene copolymers using a combination of SEC‐FTIR and SEC‐HPer DSC

The short chain branching distribution (SCBD) and thermal properties of ethylene/1‐pentene copolymers were studied using SEC‐FTIR and SEC‐HPer DSC. The copolymers, synthesized with Cp₂ZrCl₂/MAO, were fractionated using size exclusion chromatography (SEC). The infrared analysis of the fractions showed that the copolymers had—on average—higher 1‐pentene concentration in the low molecular weight range. Furthermore, the thermal properties of the SEC deposits of these copolymers on a Germanium disc were studied using high performance differential scanning calorimetry (HPer DSC). Single SEC separations were used to accumulate fractions in the microgram range that were directly analyzed with regard to their thermal properties, thus allowing us to study SCBD as well as thermal behavior simultaneously. When these fractions (with masses ranging from 10–80 μg) were analyzed using HPer DSC, good melting and crystallization temperature distributions were obtained, proving that HPer DSC can be used as a complementary method to SEC‐FTIR. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2956–2965, 2007     

Rapid cooling of lipid in a prilling tower Theoretical considerations and consequences on the structure of the microspheres

Two lipid binders, glyceryl behenate and paraffin wax, were examined regarding their ability to be used in a prilling process. Prilling has the advantage to produce microgranules very reproducible in size and shape but involves ultrafast cooling of liquid droplets. The different steps to produce solid micropheres from the molten state were successfully modelled to predict crystallisation time as a function of the binder used. Bulk versus microgranules characterization by differential scanning calorimetry, X-ray diffraction and microscopies showed the peculiar suitability of the 50/50 mixture of the two lipid binders for prilling, in agreement with the theoretical approach.     

Use of coated capillaries for the electrophoretic separation of stereoisomers of a growth hormone secretagogue

The diastereoisomeric separation of peptidomimetics of hexarelin, a strong growth hormone secretagogue, in CE has been studied. Highly sulfated‐γ‐CD was found to be an appropriate selector for the separation of the stereoisomers. However, non‐repeatable analyses were obtained on bare fused silica capillary due to the progressive adsorption of the analytes on the capillary wall. Two types of polyelectrolyte coating agents were tested to prevent this phenomenon. Coating with neutral polyethylene oxide was found to be efficient but resulted in a very long analysis time (about 40 min). Coating with cationic poly(diallyldimethylammonium) chloride was found both to prevent analyte adsorption, reduce analysis time and alter separation selectivity. EOF measurement revealed that the highly sulfated‐γ‐CDs were strongly adsorbed on the poly(diallyldimethylammonium) chloride coating surface yielding a stable strong cathodic EOF, which considerably reduced analysis time (about 12 min). Very good repeatability of analysis was obtained (RSD_{migration time}<1%).     

Free charge carrier repartition over the surface of photosensitive materials: Why and how to manage?

The free charge carrier repartition over the surface of the photosensitive solids can be efficiently managed by selective elimination of the “parasite” free charge carriers (FCCs) from the exited body. This makes it possible to “correct” the natural FCC repartition law represented by the well-known fifty-fifty ratio (1 generated electron in conduction band versus 1 hole formed in valence band) and to better protect the FCCs against recombination. The chemical design principles of the FCC selective photo-generators (FCCP-Ss) were formulated. The functioning mechanism of the hole selective nanocomposite photo-generators (Sh⁺-FCCPs) was examined. This type of active materials generating mainly the most powerful oxidation agents (OH⁰ radicals) is suitable for application in oxidation photocatalysis, microbiological object sterilization, and self-cleaning surface development.     

57Fe Mössbauer spectra and magnetic data from the kagomé antiferromagnet H3O-jarosite

⁵⁷Fe Mössbauer spectra are presented from (H₃O)Fe₃(SO₄)₂(OH)₆ (or H₃O-jarosite), which is a model kagomé antiferromagnet which features geometrical frustration and spin-glass-like behaviour. Dynamic scaling of the freezing temperature as a function of frequency is observed over a large frequency range, which indicates the presence of a spin-glass transition. A fast relaxation model between “up” and “down” states, separated by an energy gap, is presented to account for the shape of the Mössbauer spectra below the freezing temperature. From a calculation of the Electric Field Gradient tensor, it is suggested that H₃O-jarosite is an XY-Heisenberg antiferromagnet, where the Fe³⁺ moments lie in the kagomé planes.