Investigation of the Stereochemical Mechanism of the Nucleophilic Substitution Reaction at Pentacoordinate Phosphorus of Spirophosphorane.

The stereochemical mechanism of the nucleophilic substitution reaction at pentacoordinate phosphorus (P-V) atom is rarely studied. Here, we report the Atherton-Todd-type reaction of pentacoordinate hydrospirophosphorane with phenolic compounds in detail. The stereochemical mechanism of nucleophilic substitution at P-V atom was proposed by 31P NMR tracing experiment, X-ray diffraction analysis, and density functional theory calculations. The first step of the Atherton-Todd-type reaction is the formation of halogenated spirophosphorane intermediate with retention of configuration at phosphorus definitely. The second step is a nucleophilic substitution reaction at P-V atom of halogenated spirophosphorane. When using CCl4 as a halogenating agent, the reaction of chlorinated spirophosphorane proceeds via SN2(P-V) mechanism, and the backside attack of P-Cl bond is the main pathway. For chlorinated spirophosphorane with ΔP configuration, the completely P-inverted product is normally obtained. As for chlorinated spirophosphorane with ΛP configuration, which has larger steric hindrance behind P-Cl bond, the proportion of P-retained products apparently increases and a pair of diastereoisomers is acquired. Furthermore, if CBr4 is used as a halogenating agent, the nucleophilic substitution reaction of brominated spirophosphorane may go through a SN1(P-V) mechanism to afford a pair of diastereoisomers.

Tremella-like NiO microspheres embedded with fish-scale-like polypyrrole for high-performance asymmetric supercapacitor.

Tremella-like NiO microspheres embedded with fish-scale-like polypyrrole (PPy) were synthesized by polymerizing pyrrole (Py) onto uniform NiO nanosheets. PPy has a fish-scale-like appearance with a thickness of approximately 10 nm, and is connected to the NiO nanosheet surface. NiO/PPy microspheres (diameter of ∼4 µm) were applied as the electrode material in a supercapacitor. The NiO/PPy-6 obtained under a NiO : Py molar ratio of 6 shows a high specific capacitance of 3648.6 F g-1 at 3 A g-1 and good rate capability (1783 F g-1 at a high current density of 30 A g-1). An asymmetric supercapacitor (ASC) was fabricated using NiO/PPy-6 and activated carbon (AC) as the positive electrode and the negative electrode, respectively. NiO/PPy-6//AC can achieve a high specific capacitance of 937.5 F g-1 at 3 A g-1 and a high energy density of 333.3 W h kg-1 at a power density of 2399.99 W kg-1. The excellent supercapacitor performance is assigned to the combined contribution of both components and the unique heterostructure in NiO/PPy-6.

Controllable synthesis of AgNWs@PDA@AgNPs core-shell nanocobs based on a mussel-inspired polydopamine for highly sensitive SERS detection.

In this work, a series of AgNWs@PDA@AgNPs core-shell nanocobs based on a mussel-inspired polydopamine (PDA) were controllably synthesized and achieve highly sensitive SERS detection. Owing to the existence of abundant catechol and amine functional groups, PDA molecules could assemble a functional layer on the surface of silver nanowires (AgNWs) and exhibit exceptional adhesion performance. More importantly, silver nanoparticles (AgNPs) with controlled coverage and size were achieved on the surface of the PDA layer by in situ reduction of silver ions into AgNPs with catechol functional groups, forming AgNWs@PDA@AgNPs core-shell nanocobs. By regulating synergistical effect between the AgNWs and AgNPs, the AgNWs@PDA@AgNPs core-shell nanocobs demonstrated a highly sensitive and stable SERS response to Rhodamine 6G (R6G) molecules, and a low limit of detection down to 10-12 M. Furthermore, the AgNWs@PDA@AgNPs core-shell nanocobs showed an excellent reproducibility and superior stability as a SERS substrate to achieve trace detection. This strategy would have great potential to fabricate multifarious SERS-active substrates that make it possible to detect single molecules and singles cell in chemical and biological fields.