In situ visualization of Braun's lipoprotein on E. coli sacculi.

Braun's lipoprotein (Lpp) plays a major role in stabilizing the integrity of the cell envelope in Escherichia coli, as it provides a covalent cross-link between the outer membrane and the peptidoglycan layer. An important challenge in elucidating the physiological role of Lpp lies in attaining a detailed understanding of its distribution on the peptidoglycan layer. Here, using atomic force microscopy, we visualized Lpp directly on peptidoglycan sacculi. Lpp is homogeneously distributed over the outer surface of the sacculus at a high density. However, it is absent at the constriction site during cell division, revealing its role in the cell division process with Pal, another cell envelope-associated protein. Collectively, we have established a framework to elucidate the distribution of Lpp and other peptidoglycan-bound proteins via a direct imaging modality.

Bifunctional Phosphonium Salt Directed Enantioselective Formal [4 + 1] Annulation of Hydroxyl-Substituted para-Quinone Methides with α-Halogenated Ketones.

A highly diastereo- and enantioselective [4 + 1] cycloaddition of para-quinone methides to α-halogenated ketones was realized by bifunctional phosphonium salt catalysis, furnishing functionalized 2,3-dihydrobenzofurans in high yields and excellent stereoselectivities (>20:1 dr and up to >99.9% ee). Mechanistic observations suggested that the reaction underwent a cascade intermolecular substitution/intramolecular 1,6-addition process. DFT calculations revealed the presence of multiple H-bonding interactions between the catalyst and the enolate intermediate in the stereodetermining transition states.

Highly Enantioselective Synthesis of Fused Tri- and Tetrasubstituted Aziridines: aza-Darzens Reaction of Cyclic Imines with α-Halogenated Ketones Catalyzed by Bifunctional Phosphonium Salt.

The first enantioselective aza-Darzens reaction of cyclic imines with α-halogenated ketones was realized under mild reaction conditions by using amino-acid-derived bifunctional phosphonium salts as phase-transfer promoters. A variety of structurally dense tri- and tetrasubstituted aziridine derivatives, containing benzofused heterocycles as well as spiro-structures, were readily synthesized in high yields with excellent diastereo- and enantioselectivities (up to >20:1 d.r. and >99.9 % ee). The highly functionalized aziridine products could be easily transformed into different classes of biologically active compounds.

Preparation of thermosensitive polymer magnetic particles and their application in protein separations.

This paper presents a kind of thermoresponsive polymeric magnetic particles for protein separations. The magnetofluids were directly encapsulated in hollow particles constructed by self-assembly of rod-coil poly(ethylene glycol)-poly(N-isopropylacrylamide)/α-cyclodextrin (PEG-PNIPAM/α-CD) complexes. The resulting particles showed reversible protein absorption/desorption capacity because the reversible thermo-sensitivity of PNIPAM. Above the lower critical solution temperature (LCST) of PNIPAM, these particles showed high absorptive capacities and adsorption was done at lower temperature. The protein-laden particles are readily removed from the feed solution in a magnetic field.