Rotational polymorphism in 2-naphthalenethiol SAMs on Au(111)

We evidence by STM that 2-naphthalenethiol self-assembled monolayers formed at the n-tetradecane/Au(111) interface coexist as two structural phases which both possess molecules into two different orientations (standing and lying). Such a rotational polymorphism is observed and understood at the molecular level for the first time.     

Relating structural and thermodynamic effects of the Pb(II) lone pair: a new picolinate ligand designed to accommodate the Pb(II) lone pair leads to high stability and selectivity

The crystal and molecular structure and the stability of lead and calcium complexes of two chelates containing picolinate chelating groups in different geometries have been investigated in order to relate the ligand affinity and selectivity for lead over calcium with the ability of the ligand to accommodate a stereochemically active lone pair. The crystal structures of the lead complexes of the diprotonated and monoprotonated tripodal ligand tpaa2- show that the three picolinate arms of the tripodal ligand coordinate the lead in an asymmetric way leaving a gap in the coordination sphere to accommodate the lead lone pair. As a consequence of this binding mode, one picolinate arm is very weakly bound and therefore can be expected to contribute very little to the complex stability. Conversely, the geometry of the dipodal ligand H2dpaea is designed to accommodate the lead lone pair; in the structure of the [Pb(dpaea)] complex the donor atoms of the ligand occupy only a quarter of the coordination sphere, reducing the sterical interaction between the lead lone pair with respect to the H3tpaa complexes. As a result, in the lead structures of H2dpaea all the ligand donor atoms are strongly bound to the metal ion leading to increased stability. The high value of the formation constant measured for the lead complex of the dipodal dpaea2- (log beta11(Pb)=12.1(3)) compared to the lower value found for the one of the tripodal tpaa3- (log beta11(Pb)=10.0(1)) provides direct evidence of the influence of the stereochemically active lead lone pair on complex stability. As a result, since the ligand geometry has little effect on the stability of the calcium complex, a remarkable increase in the Pb/Ca selectivity is observed for dpaea-(10(6.6)) compared to tpaa3- (10(1.5)), making the dipodal ligand a good candidate for application as extracting agent for the lead removal from contaminated water.     

Membrane Deformation by Neolectins with Engineered Glycolipid Binding Sites

Lectins are glycan‐binding proteins that are involved in the recognition of glycoconjugates at the cell surface. When binding to glycolipids, multivalent lectins can affect their distribution and alter membrane shapes. Neolectins have now been designed with controlled number and position of binding sites to decipher the role of multivalency on avidity to a glycosylated surface and on membrane dynamics of glycolipids. A monomeric hexavalent neolectin has been first engineered from a trimeric hexavalent bacterial lectin, From this neolectin template, 13 different neolectins with a valency ranging from 0 to 6 were designed, produced, and analyzed for their ability to bind fucose in solution, to attach to a glycosylated surface and to invaginate glycolipid‐containing giant liposomes. Whereas the avidity only depends on the presence of at least two binding sites, the ability to bend and invaginate membranes critically depends on the distance between two adjacent binding sites.     

Survey and unification of local search techniques in metaheuristics for multi-objective combinatorial optimisation

Metaheuristics are algorithms that have proven their efficiency on multi-objective combinatorial optimisation problems. They often use local search techniques, either at their core or as intensification mechanisms, to obtain a well-converged and diversified final result. This paper surveys the use of local search techniques in multi-objective metaheuristics and proposes a general structure to describe and unify their underlying components. This structure can instantiate most of the multi-objective local search techniques and algorithms in literature.     

Numerical analysis of flame shape bifurcation in a two-stage swirled liquid burner using Large Eddy Simulation

A flame shape bifurcation in the liquid-fueled two-stage swirled BIMER combustor is studied using Large Eddy Simulations. This combustor, developed at the EM2C Laboratory to study Lean Premixed Prevaporized (LPP) burners, is composed of a two-stage injection system: a central swirled pilot stage fueled with a pressure-swirl atomizer, to sustain a piloting flame, and an outer swirled stage fed with a multi-point injection, to generate the LPP regime. After ignition in the pilot-only operating condition, a V flame is stabilized near the Inner Shear Layer (ISL). When switching to multipoint-only injection, a flame shape transition is observed and the flame bifurcates into a M-shape. In this work, we identify the mechanisms that lead to this bifurcation, and we show that the transition is driven by a complex coupling between the flame, the chamber acoustics and the ISL vortices. By switching to a multipoint-only injection, the fuel is essentially given to the ISL flame, which is mainly premixed. Because of the increased heat release rate and thanks to positive Rayleigh criterion, the quarter wave mode of the chamber is promoted. The ISL vortices, locked to this mode, increase in size until they are large enough to merge the flame in the CRZ, the radial momentum budget forcing the flow topology to switch to a bubble-like structure. Therefore, these results show that it is the existence of two possible flow topologies that renders this flame shape transition possible, the instability being responsible for transferring sufficient energy to the flow to enable the transitioning and the flame then changing its shape simply to adapt to the new topology.     

Cinnamide Derivatives of d‐Mannose as Inhibitors of the Bacterial Virulence Factor LecB from Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic Gram‐negative pathogen with high antibiotic resistance. Its lectin LecB was identified as a virulence factor and is relevant in bacterial adhesion and biofilm formation. Inhibition of LecB with carbohydrate‐based ligands results in a decrease in toxicity and biofilm formation. We recently discovered two classes of potent drug‐like glycomimetic inhibitors, that is, sulfonamides and cinnamides of d‐mannose. Here, we describe the chemical synthesis and biochemical evaluation of more than 20 derivatives with increased potency compared to the unsubstituted cinnamide. The structure–activity relationship (SAR) obtained and the extended biophysical characterization allowed the experimental determination of the binding mode of these cinnamides with LecB. The established surface binding mode now allows future rational structure‐based drug design. Importantly, all glycomimetics tested showed extended receptor residence times with half‐lives in the 5–20 min range, a prerequisite for therapeutic application. Thus, the glycomimetics described here provide an excellent basis for future development of anti‐infectives against this multidrug‐resistant pathogen.