Sucrose analogs: an attractive (bio)source for glycodiversification

Covering: up to April 2012Sucrose is a widespread carbohydrate in nature and is involved in many biological processes. Its natural abundance makes it a very appealing renewable raw material for the synthetic production of high-valued molecules. To further diversify the structure and the inherent properties of these molecules, the access to sucrose analogs is of utmost interest and has historically been widely explored through chemical means. Nature also offers a large panel of sucrose-scaffold derivatives, including phosphorylated or highly substituted phenylpropanoid esters amenable to transformation. Additionally, the use of microorganisms or enzymes could provide an alternative ecologically-compatible manner to diversify sucrose-scaffold derivatives to enable the synthesis of oligo- or polysaccharides, glycoconjugates or polymers that could exhibit original properties for biotechnological applications. This review covers the main biological routes to sucrose derivatives or analogs that are prevalent in nature, that can be obtained via enzymatic processes and the potential applications of such sucrose derivatives in sugar bioconversion, in particular through the engineering of substrates, enzymes or microorganisms.     

Chemical details on nucleolipid supramolecular architecture: molecular modeling and physicochemical studies

Nucleolipids are currently under investigation as vectors for oligonucleotides (ON) delivery thanks to their supramolecular organization properties and their ability to develop specific interactions (i.e., stacking and potential Watson and Crick hydrogen bonds) for lipoplexes formation. To investigate the factors that govern the interaction events at a molecular level and optimize nucleolipid chemical structures, physicochemical experiments (tensiometry, AFM, BAM, and ellipsometry) combined with molecular dynamics simulation were performed on a series of zwitterionic nucleolipids (PUPC, DPUPC, PAPC) featuring a phosphocholine chain (PC). After construction and initial equilibration, simulations of pure nucleolipid bilayers were run for 100 ns at constant temperature and pressure, and their properties were compared to experimental data and to natural dipalmitoylphosphatidylcholine (DPPC) bilayers. Nucleolipid-based membranes are significantly more ordered and compact than DPPC bilayers mainly due to the presence of many intermolecular interactions between nucleoside polar heads. The hydrophilic phosphocholine moieties connected to the 5' hydroxyls are located above the bilayers, penalizing nucleic bases accessibility for further interactions with ON. Hence, a neutral nucleolipid (PUOH) without hydrophilic phosphocholine was inserted in the membranes. Simulations and experimental analysis of nucleolipid membranes in interaction with a single strand RNA structure indicate that PUOH interacts with ON in the subphase. This study demonstrates that molecular modeling can be used to determine the interactions between oligonucleotide and nucleolipids.     

A Fast‐Initiating Ionically Tagged Ruthenium Complex: A Robust Supported Pre‐catalyst for Batch‐Process and Continuous‐Flow Olefin Metathesis

In this study, a new pyridinium‐tagged Ru complex was designed and anchored onto sulfonated silica, thereby forming a robust and highly active supported olefin‐metathesis pre‐catalyst for applications under batch and continuous‐flow conditions. The involvement of an oxazine–benzylidene ligand allowed the reactivity of the formed Ru pre‐catalyst to be efficiently controlled through both steric and electronic activation. The oxazine scaffold facilitated the introduction of the pyridinium tag, thereby affording the corresponding cationic pre‐catalyst in good yield. Excellent activities in ring‐closing (RCM), cross (CM), and enyne metathesis were observed with only 0.5 mol % loading of the pre‐catalyst. When this powerful pre‐catalyst was immobilized onto a silica‐based cationic‐exchange resin, a versatile catalytically active material for batch reactions was generated that also served as fixed‐bed material for flow reactors. This system could be reused at 1 mol % loading to afford metathesis products in high purity with very low ruthenium contamination under batch conditions (below 5 ppm). Scavenging procedures for both batch and flow processes were conducted, which led to a lowering of the ruthenium content to as little as one tenth of the original values.     

A continuous/discrete fractional Noether’s theorem

We prove a fractional Noether’s theorem for fractional Lagrangian systems invariant under a symmetry group both in the continuous and discrete cases. This provides an explicit conservation law (first integral) given by a closed formula which can be algorithmically implemented. In the discrete case, the conservation law is moreover computable in a finite number of steps.     

Optimal piezoelectric actuator and sensor location for active vibration control, using genetic algorithm

This paper deals with the optimization of piezoelectric actuators and sensors locations for active vibration control. Two modified optimization criteria are used, ensuring good observability or controllability of the structure, and considering residual modes to limit the spillover effect. Two optimization variables are considered for each piezoelectric device: the location of its center and its orientation. Genetic algorithms are used to find the optimal configurations. Several simulations are presented for a simply supported plate.     

Nash constructible functions

Nash constructible functions on a real algebraic set V are defined as linear combinations, with integer coefficients, of Euler characteristic of fibres of proper regular morphisms restricted to connected components of algebraic sets. We prove that if V is compact, these functions are sums of signs of semialgebraic arc-analytic functions (i.e. functions which become analytic when composed with any analytic arc). We also give a sharp upper bound to the number of semialgebraic arc-analytic functions which are necessary to define any given Nash constructible functions.     

Band-edge-induced Bragg diffraction in two-dimensional photonic crystals

Two-dimensional photonic crystals composed of two orthogonal volume diffraction gratings have been photogenerated in photopolymers. When the read beam is set at the Bragg angle, the diffraction efficiency of the transmission grating is strongly enhanced at the band edge of the reflection grating recorded in the material. Such a device provides Bragg operation and enhancement of the diffraction efficiency of the thin diffraction grating together with good wavelength selectivity. Such advantages could be interesting for optical signal processing.