A general approach to mechanism in multiproduct reactions: product-specific intermolecular kinetic isotope effects.

Here we report a general method for the measurement of (13)C kinetic isotope effects at natural abundance for reactions that yield two or more products concurrently. We use, as an example, a recently reported Co-catalyzed reaction between cyclopentene and 1-phenyl-1-propyne. High-precision intermolecular (13)C isotope effects are reported for both the formal [2+2] cycloaddition (major) and Alder-ene (minor) reaction products. Mechanistic possibilities that are in accord with observed isotope effect measurements are discussed.

Water-Based Dual-Cross-Linked Polymer Binders for High-Energy-Density Lithium-Sulfur Batteries.

High-mass-loading electrodes with long-term stability have long been a great challenge for lithium-sulfur batteries (LSBs), since the conventional binders are unable to cope with the shuttling of lithium polysulfides and the structural damage in an electrode. Here, a novel water-based polymer, polyphosphate acid cross-linked chitosan ethylamide carbamide (PACEC), is developed as a binder to construct high-energy-density sulfur cathode and flexible LSBs. With a dual-cross-linked network, the PACEC shows excellent affinity with lithium polysulfides to relieve the shuttle effect and robust mechanical properties to stabilize the electrode. The sulfur cathode based on PACEC demonstrates a high sulfur loading of 14.8 mg cm-2, the areal initial capacity of 17.5 mAh cm-2, and Coulombic efficiency of 99.3%, while the amount of electrolyte is strictly limited to 6 µL mg-1. More importantly, a robust pouch cell with an area of 6 cm2 and only 177% oversized lithium can successfully integrate the energy density of 6.5 mAh cm-2 with the cycling retention per cycle of 99.74% during 270 cycles and flexibility at a curvature of 3 mm. This study provides inspirations for the design of eco-friendly polymer binders and paving new ways for the development of LSBs.

Carbon nanotubes promote neuron differentiation from human embryonic stem cells.

Human embryonic stem cells (hESCs) hold great promise for regenerative medicine and transplantation therapy due to their self-renewal and pluripotent properties. We report that 2D thin film scaffolds composed of biocompatible polymer grafted carbon nanotubes (CNTs), can selectively differentiate human embryonic stem cells into neuron cells while maintaining excellent cell viability. According to fluorescence image analysis, neuron differentiation efficiency of poly(acrylic acid) grafted CNT thin films is significant greater than that on poly(acrylic acid) thin films. When compared with the conventional poly-L-ornithine surfaces, a standard substratum commonly used for neuron culture, this new type thin film scaffold shows enhanced neuron differentiation. No noticeable cytotoxic effect difference has been detected between these two surfaces. The surface analysis and cell adhesion study have suggested that CNT-based surfaces can enhance protein adsorption and cell attachment. This finding indicates that CNT-based materials are excellent candidates for hESCs' neuron differentiation.

A near-infrared mechano responsive polymer system.

A new type of crosslinked polyarylamide based film with a fibrillar morphology that is photomechanically responsive has been created. Without any additive or need of pre-alignment, these films can actuate under NIR stimulation. By constructing the photoresponsive film on top of a piezoelectric poly(vinylidene difluoride) film, electrical energy can be generated under NIR excitation. This is the first polymer system that exhibits NIR response without any conventional photosensitive moieties.