A polyrotaxane gel using boronic acid-appended γ-cyclodextrin as a hybrid cross-linker

A boronic acid-appended γ-cyclodextrin (BA-CyD) was synthesized as a hybrid cross-linker of polyvinyl alcohol (PVA) to form a new type of hydrogel. The CyD moiety of BA-CyD forms an inclusion complex with the PVA chain to produce a mechanically interlocking structure. At the same time, the BA moiety of BA-CyD forms covalent bonds with the 1,3-diol moieties of PVA. On the basis of these two modes of interaction, the hybrid cross-linker connects two PVA chains, thus resulting in the formation of a hydrogel. To investigate the possibility of this hydrogel becoming the basis for an intelligent material for drug delivery, sugar-responsive drug release from the hydrogel was demonstrated.     

Construction of quaternary carbon centers by a base-catalyzed enantioselective aldol reaction and related reactions of trimethoxysilyl enol ethers

The aldol reactions of trimethoxysilyl enol ethers catalyzed by lithium binaphtholate were found to be powerful tools for the construction of quaternary asymmetric carbon centers. The stereoselectivities were greatly affected by the presence of water. Trimethoxysilyl enol ether derived from a cyclic ketone, such as cyclohexanone, was used as a substrate to obtain the anti-adduct preferentially under anhydrous conditions; by contrast, the syn-adduct was preferentially obtained under aqueous conditions with high stereoselectivity. The aldol-Tishchenko reaction of a trimethoxysilyl enol ether derived from acyclic ketones proceeded to give monoacyl 1,3-diol derivatives in high enantioselectivities.     

(E)‐,(Z)‐Parallel Preparative Methods for Stereodefined β,β‐Diaryl‐ and α,β‐Diaryl‐α,β‐unsaturated Esters: Application to the Stereocomplementary Concise Synthesis of Zimelidine

Parallel and practical methods for the preparation of both (E)‐ and (Z)‐β‐aryl¹‐β‐aryl²‐α,β‐unsaturated esters 1 and (E)‐ and (Z)‐α‐aryl¹‐β‐aryl²‐α,β‐unsaturated esters 2 are described. These methods involve accessible, robust, stereocomplementary N‐methylimidazole (NMI)‐mediated enol tosylations (14 examples, 70–99 % yield), as well as stereoretentive Suzuki–Miyaura cross‐couplings (36 examples, 64–99 % yield). The highlighted feature of the present protocol is the use of parallel and stereocomplementary approaches to obtain highly (E)‐ and (Z)‐pure products 1 and 2 by utilizing sequential enol tosylations and cross‐coupling reactions. An expeditious and parallel synthesis of (E)‐ and (Z)‐zimelidine ( 3 ), which is a highly representative selective serotonin reuptake inhibitor (SSRI), was performed by utilizing the present methods.     

X‐ray irradiation induces local rearrangement of silica particles in swollen rubber

X‐ray photon correlation spectroscopy (XPCS) of swollen rubber containing spherical silica nanoparticles is reported. It is shown that irradiation by intense X‐rays leads to the breakdown of cross‐links, thereby inducing the local rearrangement of silica nanoparticles. This rearrangement process depends on the cross‐link density and is characterized by a compressed exponential relaxation with aging behaviour, which resembles a common feature of complex fluids observed with XPCS.     

Liquid‐Crystalline Biomacromolecular Templates for the Formation of Oriented Thin‐Film Hybrids Composed of Ordered Chitin and Alkaline‐Earth Carbonate

Macroscopically ordered inorganic thin films have been formed on unidirectionally oriented, liquid‐crystalline chitin matrices. In the presence of poly(acrylic acid) (PAA), unidirectionally oriented chitin films act as templates for the formation of oriented thin‐film crystals of alkaline‐earth carbonates such as SrCO₃ and BaCO₃. The morphology and orientation of crystals are dependent on the metal ion concentration. For SrCO₃ crystallization, unidirectional thin films and hexagonal‐shaped thin films have been deposited from 200 and 25 mm concentration strontium solutions, respectively.     

A Flow Microreactor System Enables Organolithium Reactions without Protecting Alkoxycarbonyl Groups

A flow microreactor system consisting of micromixers and microtube reactors provides an effective tool for the generation and reactions of aryllithiums bearing an alkoxycarbonyl group at para‐, meta‐, and ortho‐positions. Alkyl p‐ and m‐lithiobenzoates were generated by the I/Li exchange reaction with PhLi. The Br/Li exchange reactions with sBuLi were unsuccessful. Subsequent reactions of the resulting aryllithiums with electrophiles gave the desired products in good yields. On the other hand, alkyl o‐lithiobenzoates were successfully generated by the Br/Li exchange reaction with sBuLi. Subsequent reactions with electrophiles gave the desired products in good yields.     

Atomic and nanostructures of monolayer c(2 × 2)NiN on Cu(0 0 1)

Structures of monolayer nickel nitride (NiN) on Cu(0 0 1) surface are studied by X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Formations of Ni–N chemical bonds and NiN monolayer at the surface are confirmed by XPS on the N-adsorbed Cu(0 0 1) surfaces after Ni deposition and subsequent annealing to 670 K. A c(2 × 2) structure is always observed in the LEED patterns, which is a quite contrast to the (2 × 2)p4g structure observed usually at the N-adsorbed Ni(0 0 1) surface. Atomic images by STM indicate the mixture of Ni–N and Cu–N structures at the surface. Density of the trenches on the N-saturated surface decreases and the grid pattern on partially N-covered surfaces becomes disordered with increasing the Ni coverage. These results are attributed to the decrease of the surface compressive stress at the N-adsorbed Cu surface by mixing Ni atoms.     

On the reversible O2 binding of the Fe-porphyrin complex

Electronic mechanism of the reversible O(2) binding by heme was studied by using Density Functional Theory calculations. The ground state of oxyheme was calculated to be open singlet state [Fe(S =1/2) + O(2)(S = 1/2)]. The potential energy surface for singlet state is associative, while that for triplet state is dissociative. Because the ground state of the O(2)+ deoxyheme system is triplet in the dissociation limit [Fe(S = 2) + O(2)(S = 1)], the O(2) binding process requires relativistic spin-orbit interaction to accomplish the intersystem crossing from triplet to singlet states. Owing to the singlet-triplet crossing, the activation energies for both O(2) binding and dissociation become moderate, and hence reversible. We also found that the deviation of the Fe atom from the porphyrin plane is also important reaction coordinate for O(2) binding. The potential surface is associative/dissociative when the Fe atom locates in-plane/out-of-plane.