Encapsulation of Halocarbons in a Tetrahedral Anion Cage

Caged supramolecular systems are promising hosts for guest inclusion, separation, and stabilization. Well‐studied examples are mainly metal‐coordination‐based or covalent architectures. An anion‐coordination‐based cage that is capable of encapsulating halocarbon guests is reported for the first time. This A₄L₄‐type (A=anion) tetrahedral cage, [(PO₄)₄ L ₄]^12?, assembled from a C₃‐symmetric tris(bisurea) ligand ( L ) and phosphate ion (PO₄^3?), readily accommodates a series of quasi‐tetrahedral halocarbons, such as the Freon components CFCl₃, CF₂Cl₂, CHFCl₂, and C(CH₃)F₃, and chlorocarbons CH₂Cl₂, CHCl₃, CCl₄, C(CH₃)Cl₃, C(CH₃)₂Cl₂, and C(CH₃)₃Cl. The guest encapsulation in the solid state is confirmed by crystal structures, while the host–guest interactions in solution were demonstrated by NMR techniques.     

Modulating membrane properties: the effect of trehalose and cholesterol on a phospholipid bilayer

The protective properties of trehalose on cholesterol-containing lipid dipalmitoylphosphatidylcholine (DPPC) bilayers are studied through molecular simulations. The ability of the disaccharide to interact with the phospholipid headgroups and stabilize the membrane persists even at high cholesterol concentrations and restricts some of the changes to the structure that would otherwise be imposed by cholesterol molecules. Predictions of bilayer properties such as area per lipid, tail ordering, and chain conformation support the notion that the disaccharide decreases the main melting transition in these multicomponent model membranes, which correspond more closely to common biological systems than pure bilayers. Molecular simulations indicate that the membrane dynamics are slowed considerably by the presence of trehalose, indicating that high sugar concentrations would serve to avert possible phase separations that could arise in mixed phospholipid systems. Various time correlation functions suggest that the character of the modifications in lipid dynamics induced by trehalose and cholesterol is different in the hydrophilic and hydrophobic regions of the membrane.     

Regio- and stereoselective synthesis of aminoinositols and 1,2-diaminoinositols from conduritol B epoxide

[Chemical reaction: See text] A systematic approach to the regio- and stereoselective synthesis of aminoinositols and 1,2-diaminoinositols arising from tetra-O-benzylconduritol B epoxide (9) and its aziridine analogue 22, respectively, is described. In all cases, the synthetic methodologies rely on the regio- and stereocontrolled azidolysis of the starting precursors to give the corresponding trans regioadducts. Subsequent functional group manipulation under strict configurational control affords the isomeric cis adducts. Chemoselective functionalization of the diamine moiety in 1,2-diaminoinositol derivatives can be achieved by the proper design of the reaction sequence and choice of reagents. The described protocols allow efficient access to each of the eight possible configurations of the 1,2-diamino and 1,2-amino alcohol moieties from chemical modifications of the epoxide moiety on the common precursor 9.     

An unexpected chelation-controlled Yb(OTf)(3)-catalyzed aminolysis and azidolysis of cyclitol epoxides

A chelation-controlled aminolysis and azidolysis of cyclitol epoxides with Yb(OTf)(3) has been disclosed. The presence of a free OH group able to direct the coordination with the lanthanide seems essential for an efficient regiocontrol of the process.     

Interfacial mechanisms governing cyclopentane clathrate hydrate adhesion/cohesion

The present work uses a micromechanical force apparatus to directly measure cyclopentane clathrate hydrate cohesive force and hydrate-steel adhesive force, as a function of contact time, contact force and temperature. We present a hydrate interparticle force model, which includes capillary and sintering contributions and is based on fundamental interparticle force theories. In this process, we estimate the cyclopentane hydrate tensile strength to be approximately 0.91 MPa. This hydrate interparticle force model also predicts the effect of temperature on hydrate particle cohesion force. Finally, we present the first direct measurements of hydrate cohesive force in the gas phase to be 9.1 ± 2.1 mN/m at approximately 3 °C (as opposed to 4.3 ± 0.4 mN/m in liquid cyclopentane).     

Molecular dynamics study on the stabilization of dehydrated lipid bilayers with glucose and trehalose

In this study, we use molecular dynamics simulations to investigate and compare the interactions of DPPC bilayers with and without saccharides (glucose or trehalose) under dehydrated conditions. Results from the simulations indicate that unilamellar bilayers lose their structural integrity under dehydrated conditions in the absence of saccharides; however, in the presence of either glucose or trehalose, the bilayers maintain their stability. Hydrogen bond analysis shows that the saccharide molecules displace a significant amount of water surrounding the lipid headgroups. At the same time, the additional hydrogen bonds formed between water and saccharide molecules help to maintain a hydration layer on the lipid bilayer interface. On the basis of the hydrogen bond distributions, trehalose forms more hydrogen bonds with the lipids than glucose, and it is less likely to interact with neighboring saccharide molecules. These results suggest that the interaction between the saccharide and lipid molecules through hydrogen bonds is an essential component of the mechanism for the stabilization of lipid bilayers.     

Barbier-type diastereoselective allylation of alpha-amino aldehydes with an enantiopure 2-sulfinylallyl building block.

An optimized procedure for the diastereoselective allylation under aqueous Barbier conditions of a series of alpha-amino aldehydes with our new chiral building block (S(s))-3-chloro-2-(p-tolylsulfinyl)-1-propene [(S(s))-1a] to afford enantiomerically pure sulfinylamino alcohols in good yields and diastereoselectivites is reported. High levels of diastereoinduction can be achieved from alpha-amino aldehydes configurationally related to natural alpha-amino acids.