Exploring k and ? with R–Equation Model Using Elliptic Relaxation Function

An extended version of the isotropic R?Cequation model accompanied by an elliptic relaxation approach to account for the distinct effects of low-Reynolds number (LRN) and wall proximity is proposed. The turbulent kinetic energy k and the dissipation rate ? are evaluated using the R ( $=k^2/\tilde{\epsilon}$ ) transport equation together with some empirical relations. The eddy viscosity formulation maintains the positivity of normal Reynolds stresses and the Schwarz?? inequality for turbulent shear stresses. The model coefficients/functions preserve the anisotropic characteristics of turbulence in the sense that they are sensitized to rotational and nonequilibrium flows. The model is validated against a few well-documented flow cases, yielding predictions in good agreement with the direct numerical simulation (DNS) and experimental data. Comparisons indicate that the present model offers some improvement over the Spalart?CAllmaras one?Cequation model and competitiveness with the SST k?C?? model.     

A Novel Rearrangement Reaction of N‐Acyliminium Ions Leading to Heterobicycles Arylated at Bridgehead Atom

Starting with thiazolines, an important class of heterocyclic imines, a novel rearrangement reaction of corresponding N‐acyliminium ions is described. Furthermore, a new class of heterobicyclic compounds arylated at a single bridgehead atom is obtained diastereospecifically.     

Generation of candidate ligands for nicotinic acetylcholine receptors via in situ click chemistry with a soluble acetylcholine binding protein template

Nicotinic acetylcholine receptors (nAChRs), which are responsible for mediating key physiological functions, are ubiquitous in the central and peripheral nervous systems. As members of the Cys loop ligand-gated ion channel family, neuronal nAChRs are pentameric, composed of various permutations of α (α2 to α10) and β (β2 to β4) subunits forming functional heteromeric or homomeric receptors. Diversity in nAChR subunit composition complicates the development of selective ligands for specific subtypes, since the five binding sites reside at the subunit interfaces. The acetylcholine binding protein (AChBP), a soluble extracellular domain homologue secreted by mollusks, serves as a general structural surrogate for the nAChRs. In this work, homomeric AChBPs from Lymnaea and Aplysia snails were used as in situ templates for the generation of novel and potent ligands that selectively bind to these proteins. The cycloaddition reaction between building-block azides and alkynes to form stable 1,2,3-triazoles was used to generate the leads. The extent of triazole formation on the AChBP template correlated with the affinity of the triazole product for the nicotinic ligand binding site. Instead of the in situ protein-templated azide-alkyne cycloaddition reaction occurring at a localized, sequestered enzyme active center as previously shown, we demonstrate that the in situ reaction can take place at the subunit interfaces of an oligomeric protein and can thus be used as a tool for identifying novel candidate nAChR ligands. The crystal structure of one of the in situ-formed triazole-AChBP complexes shows binding poses and molecular determinants of interactions predicted from structures of known agonists and antagonists. Hence, the click chemistry approach with an in situ template of a receptor provides a novel synthetic avenue for generating candidate agonists and antagonists for ligand-gated ion channels.     

Effect of the orientation of the optic axis on simulated scattering matrix elements of small birefringent particles

We study how the orientation of the optic axis affects single-scattering properties for small, birefringent calcite particles simulated using DDSCAT 7.1.1. We consider two irregular model particles, a flake and a rhomboid, in either a (i)?fixed or (ii)?random orientation. Simulations are performed for three volume-equivalent radii of 0.1, 0.45, and 1.0?μm. For each target, we repeat the computations for three sets of orientations of the optic axis. When a fixed spatial orientation of the target is considered, the simulations are significantly affected by the orientation of the optic axis. However, the effect is considerably weaker when assuming the same targets in random spatial orientation.     

Unexpected thermal decomposition of the "Alder carbene" (iPr(2)N)(2)C

The "Alder carbene" (iPr(2)N)(2)C undergoes a β-fragmentation in solution already at room temperature, affording propene and N,N,N'-triisopropylformamidine. This stands in sharp contrast to the indefinite stability previously claimed for this iconic compound.     

Alkynyl-functionalised and linked bicyclo[1.1.1]pentanes of group 14

We report the synthesis and properties of alkynyl-functionalised and -bridged bicyclo[1.1.1]pentane derivatives consisting of the heavier group 14 elements silicon and tin.     

Improving the carboxyamidomethyl ester for subtilisin A-catalysed peptide synthesis

A series of novel glycine esters was evaluated for efficiency in subtilisin A-CLEA-catalysed peptide synthesis. The reactivity of the easily accessible carboxyamidomethyl (Cam) ester was further enhanced by elongating it with an amino acid residue, thereby creating more recognition space for subtilisin A.     

A Manifold Three‐Step Synthetic Route to Polycyclic Annulated Hydantoins via Cyclic Imines

A new three‐step synthetic pathway to generate polycyclic annulated hydantoins via rarely investigated heterocyclic imines is described. This procedure includes a one‐pot reaction forming imines as precursor structures (e.g., Asinger reaction), followed by an Ugi reaction to build up a bisamide structure that allows a ring‐closing reaction to the targeted hydantoins via substitution. This pathway leads to a multiplicity of substances with a potential pharmacological activity.     

Investigation of sediment transport at the interface of a porous and a free flow domain

Sediment transport involves fluid flow in two different regions. In the free flow domain, the flow is governed by the viscous Newtonian fluid; sediment only occurs as suspended particles. In the porous domain however, the flow is governed by the pore geometry of the porous skeleton consisting of sedimented grains. In nature, the interface between these two domains is not a no-slip boundary for the free flow. In this study, we quantify how sediment transport is affected by the interaction of the two different flows. We do this by comparing fluid flow in no-slip bounded flow channels to fluid flow in channels containing both a free and a porous domain. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)