Reversible Re‐programing of Cell–Cell Interactions

The ability to engineer and re‐program the surfaces of cells would provide an enabling synthetic biological method for the design of cell‐ and tissue‐based therapies. A new cell surface‐engineering strategy is described that uses lipid‐chemically self‐assembled nanorings (lipid‐CSANs) that can be used for the stable and reversible modification of any cell surface with a molecular reporter or targeting ligand. In the presence of a non‐toxic FDA‐approved drug, the nanorings were quickly disassembled and the cell–cell interactions reversed. Similar to T‐cells genetically engineered to express chimeric antigen receptors (CARS), when activated peripheral blood mononuclear cells (PBMCs) were functionalized with the anti‐EpCAM‐lipid‐CSANs, they were shown to selectively kill antigen‐positive cancer cells. Taken together, these results demonstrate that lipid‐CSANs have the potential to be a rapid, stable, and general method for the reversible engineering of cell surfaces and cell–cell interactions.     

Asymmetric synthesis of (4S,5S)-2-oxo-4-phenyloxazolidine-5-carboxylic acid using a 1,2-addition of PhMgBr to an N-sulfinimine derived from (R)-glyceraldehyde acetonide and (S)-t-BSA

We report an asymmetric synthesis of (4S,5S)-2-oxo-4-phenyloxazolidine-5-carboxylic acid via stereoselective addition of phenylmagnesium bromide (PhMgBr) to an N-sulfinimine derived from (R)-glyceraldehyde acetonide. (S)- and (R)-Glyceraldehyde acetonides, important chiral synthons in synthetic organic chemistry, are prepared from the corresponding epichlorohydrin using an identical synthetic methodology.     

An enaminone-directed benzannulation/macrocyclization approach to cyclophane ring systems

A straightforward and modular preparative approach to 1,3,5-triaroylbenzene-based functionalized cyclophane ring systems has been developed. The key cyclophane-forming macrocyclization reaction was accomplished during the course of a regioselective cross-benzannulation between bis(aryl ethynyl) ketone and enaminone reactants. Macrocyclic products with ring sizes ranging from 18- to 22-membered were successfully constructed. The composition of the tether connecting the two aryl ethynyl ketone fragments can be easily varied; consequently, this method is suitable for construction of a diverse range of structurally distinct cyclophane products. To illustrate this feature, cyclophanes possessing xylyl, alkyl, di(ethylene triamine), and di(ethylene oxy) bridging units were synthesized in isolated yields of 11-46%. Three new cyclophanes (calixarene-like macrocyles 8 and 9, as well as crownophane 18) were structurally characterized by X-ray diffractometry.     

A CAN-induced cyclodimerization-Ritter trapping strategy for the one-pot synthesis of 1-amino-4-aryltetralins from styrenes

[reaction: see text]. A facile one-pot synthesis of 1-amino-4-aryl-tetralin derivatives by the CAN-induced cyclodimerization of various styrenes in acetonitrile and acrylonitrile is described.     

Functionalized spiro- and fused-ring heterocycles via oxidative demetalation of cyclohexadienyl ruthenium complexes

Electron-rich alkoxy- and chloro-substituted azaspirocyclic cyclohexadienyl Ru(II) complexes have been converted to either azaspiro[4.5]decane derivatives or functionalized tetrahydroisoquinolines by treatment with suitable oxidizing agents. Copper(II) chloride was found to provide demetalated products in high yield relative to the other oxidants examined (FeCl(3), DDQ, CAN, [Cp(2)Fe][PF(6)], phenyliodine diacetate, IBX). In certain instances, the efficiency of oxidative demetalation was enhanced by the inclusion of chloride ion additives in the reaction. Pyridinium dichromate (PDC) was also found to effect the demetalation of a wide range of cyclohexadienyl Ru complexes; however, isolated yields of metal-free products were exceedingly low. The cyclohexadienyl ruthenium complexes used in this study were prepared from (arene)Ru(II) precursors; thus, the isolation of alicyclic cyclohexadienone derivatives upon demetalation constitutes completion of a Ru-mediated dearomatization process.     

Magnetic behaviour of the orthochromite La0.5Gd0.5CrO3

Magnetic behaviour of the perovskite La_0.5Gd_0.5CrO₃ has been studied. The orthochromite orders canted antiferromagnetically below Neel temperature T_N of ～225 K. Reversal of magnetization is observed in temperature dependence of magnetization measured in field cooled mode under external fields upto 500 Oe. In the field dependence of magnetization below T_N, a small hysteresis is observed with the magnetic anisotropy continuously increasing with lowering of temperature. Estimated values of Cr³⁺ moments, internal field due to sub-lattice of canted ordered Cr³⁺ and the paramagnetic Curie temperature of Gd³⁺ sub-lattice are found to be smaller than reported for GdCrO₃. Compared with Pr substituted analogue La_0.5Pr_0.5CrO₃, Cr³⁺ moment is about the same but the internal field at the Gd³⁺ sub-lattice is much smaller.     

Growth pattern of Ag(n) (n = 1-8) clusters on the α-Al2O3(0001) surface: a first principles study

We report an extensive first-principles study of the structure and electronic properties of Ag(n) (n = 1-8) clusters isolated in gas phase and deposited on the α-Al(2)O(3) surface. We have used the plane wave based pseudopotential method within the framework of density functional theory. The electron ion interaction has been described using projector augmented wave (PAW), and the spin-polarized GGA scheme was used for the exchange correlation energy. The results reveal that, albeit interacting with support alumina, the Ag atoms prefers to remain bonded together suggesting an island growth motif is preferred over wetting the surface. When compared the equilibrium structures of Ag clusters between free and on alumina substrate, a significant difference was observed starting from n = 7 onward. While Ag(7) forms a three-dimensional (3D) pentagonal bipyramid in the isolated gas phase, on alumina support it forms a planar hexagonal structure parallel to the surface plane. Moreover, the spin moment of the Ag(7) cluster was found to be fully quenched. This has been attributed to higher delocalization of electron density as the size of the cluster increases. Furthermore, a comparison of chemical bonding analysis through electronic density of state (EDOS) shows that the EDOS of the deposited Ag(n) cluster is significantly broader, which has been ascribed to the enhanced spd hybridization. On the basis of the energetics, it is found that the adsorption energy of Ag clusters on the α-Al(2)O(3) surface decreases with cluster size.