Low-loss subwavelength metal C-aperture waveguide

We present a design of a linear optical waveguide that utilizes a C-shaped metallic nano-aperture that efficiently transports light while maintaining a spot size of lambda/10. The performance of a C-aperture waveguide is superior to both a regular ridge waveguide and other surface plasmon based metal nano-optical waveguides. The energy transport mechanisms are explained by the coupling of an aperture surface resonance and the thickness resonances inside the guide channel. Finite-difference time-domain simulations of gold C-aperture waveguides are performed for a 1.5 microm wavelength incident plane wave. The 1/e decay length in power transmission is predicted to be approximately 2.5 microm. The total power throughput is 1.66 for the 2.55 microm long guide, with an intensity 6 times that of the incident wave at a distance 120 nm from the exit plane, having a spot size of 150 nm.     

Thermoresponsive Poly(2‐oxazine)s

The monomers 2‐methyl‐2‐oxazine (MeOZI), 2‐ethyl‐2‐oxazine (EtOZI), and 2‐n‐propyl‐2‐oxazine (nPropOZI) were synthesized and polymerized via the living cationic ring‐opening polymerization (CROP) under microwave‐assisted conditions. pEtOZI and pnPropOZI were found to be thermoresponsive, exhibiting LCST behavior in water and their cloud point temperatures (T_CP) are lower than for poly(2‐oxazoline)s with similar side chains. However, comparison of poly(2‐oxazine) and poly(2‐oxazoline)s isomers reveals that poly(2‐oxazine)s are more water soluble, indicating that the side chain has a stronger impact on polymer solubility than the main chain. In conclusion, variations of both the side chains and the main chains of the poly(cyclic imino ether)s resulted in a series of distinct homopolymers with tunable T_CP.     

Large time behaviour of solutions of the Swift–Hohenberg equation

We study the limiting profiles v of solutions of the Swift–Hohenberg equation on a one-dimensional domain (0,L) for different values of L. We identify those values of L for which v=0, and discuss the size and the shape of v when it is nontrivial and a global minimiser of an associated energy functional. To cite this article: L.A. Peletier, V. Rottschäfer, C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

Straightforward sustainability assessment of sugar-derived molecules from first-generation biomass

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Crystal and molecular structure of (2E,4S,10R)-4-hydroxy-2-undecen-10-olide (nor-patulolide C), C11H18O3

The stereogeometry and absolute configuration of the title compound has been proved by an X-ray diffraction analysis. Crystal data: monoclinic, P2₁,a=7.7976(2),b=7.8288(2),c=8.9791(4) Å, =90.331(4)^o, Z=2. The crystal structure has been solved by vector search methods and refined toR=0.042 for 1798 observed reflections.     

Enantio-controlled synthesis of the crocyclic C14-C23 subunit of cytochalasin b

The synthesis of the C₁₄-C₂₃ macrocyclic subunit of cytochalasin B from pulegone is described. The key feature of this synthesis is the photo-induced rearrangement of epoxy diazomethyl ketone E to a γ-hydroxy alkenoic ester (Scheme 2). The intermediate epoxy alcohol F was prepared using the asymmetric Sharpless epoxidation. Considerable attention was given to the preparation of allylic alcohol 14, having a t-butyldimethylsilyloxy protecting function, as starting material for the asymmetric epoxidation, however, several unforeseen difficulties were encountered (Schemes 3 and 4). Satisfactory results were obtained using the methoxy group as protecting function (Scheme 5). The allylic alcohol 22 was prepared from bromide 20 by chain lengthening with propargyl alcohol. The Sharpless epoxidation of 22 took place with high induction. Conversion to epoxy ester 24, to diazo ketone 25 and photo-rearrangement to 26 and deprotection to give 28, completes the sequence.     

Rubrenolide, total synthesis and revision of its reported stereochemical structure

In this paper the synthesis of the natural product rubrenolide is presented. Due to an error in the original proposed stereochemical structure of rubrenolide, the synthesis was not straightforward. Application of the photo-induced rearrangement of an appropriate epoxy diazomethyl ketone gave access to the precursor lactone with an ee of 91%. Coupling of this lactone with (4S)-2,2-dimethyl-[1,3]-dioxolane-4-carbaldehyde gave, after some additional steps, the final product that was identical with an authentic sample of the natural product.     

Excited States and Charge Separation in Membranes of the Green Sulfur Bacterium Prosthecochloris aestuarii

Time-resolved absorbance changes were measured in isolated membranes, depleted of chlorosomes, and in the Fenna-Matthews-Olson (FMO) complex of the green sulfur bacterium Prosthecochloris aestuarri. The isolated FMO complex showed a biphasic decay of excited bacteriochlorophyll a (BChl a) with time constants of about 80 and 1400 ps. Approximately the same time constants were observed upon excitation of isolated membranes together with a component of about 30 ps. It is concluded that the efficiency of energy transfer from the FMO to the core complex is very low, in agreement with earlier measurements of the efficiency of charge separation. The 30 ps decay component is ascribed to trapping of the excitation energy from the core BChl a by the reaction center.     

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