Preparation of Graphite Intercalation Compounds Containing Crown Ethers

Crown ethers are well established as cointercalates in many layered hosts, but there are no reports of crown ethers incorporated into graphite. Here, we describe the preparation of the first graphite intercalation compounds (GICs) containing crown ethers. These GICs are obtained either by reductive intercalation of an alkali metal-amine complex followed by cointercalate exchange or by the direct reaction of graphite with a crown ether, alkali metal, and an electrocatalyst. Structural and compositional characterization of these new GICs using powder X-ray diffraction, thermal analysis, and GC/MS indicates the formation of well-ordered, stage-1 bilayer galleries

RETRACTED ARTICLE: Degradable poly-L-lysine-modified PLGA cell microcarriers with excellent antibacterial and osteogenic activity

We, the Editors, Authors and Publisher of the journal Artificial Cells, Nanomedicine, and Biotechnology, have retracted the following article: Hanyang Zhang, Jianhang Jiao & Hui Jin (2019) Degradable poly-L-lysine-modified PLGA cell microcarriers with excellent antibacterial and osteogenic activity. Artificial Cells, Nanomedicine, and Biotechnology, 47:1, 2391–2404, DOI: 10.1080/21691401.2019.1623230 Since publication, the authors continued their study and found that the original experimental results were unverifiable. The authors checked their data and confirmed there are fundamental errors present. Therefore, they have agreed to the retraction of this article. The authors apologise for this oversight. We have been informed in our decision-making by our policy on publishing ethics and integrity and the COPE guidelines on retractions. The retracted article will remain online to maintain the scholarly record, but it will be digitally watermarked on each page as ‘Retracted’.</p

Preparation, Characterization, and Structure Trends for Graphite Intercalation Compounds Containing Pyrrolidinium Cations

New graphite intercalation compounds (GICs) containing <i>N</i>,<i>N</i>-<i>n</i>-alkyl substituted pyrrolidinium cation intercalates (Py_{<i>n</i>.<i>m</i>}, <i>n</i>, <i>m</i> = alkyl chain lengths) are obtained via cationic exchange from stage-1 donor-type GIC [Na­(ethylene­diamine)_1.0]­C₁₅. Powder X-ray diffraction and thermogravimetric analyses are used to determine the GIC structures and compositions. [Py_4.8]­C₄₇·0.71DMSO and [Py_8.8]­C₄₈ with intercalate monolayers are obtained as stage-1 GICs with gallery expansions of 0.48 nm, whereas [Py_1.18]­C₄₇ and [Py_12.12]­C₈₀·0.25DMSO form stage-1 GICs with intercalate bilayers and gallery expansions of 0.81 nm. The gallery dimensions require that alkyl chain substituents orient parallel to the encasing graphene sheets. Smaller intercalate cations such as Py_1.4, Py_4.4, and Py_1.8 either form high-stage GICs or do not form stable intercalation compounds. These results, along with those reported for graphite intercalation of other quaternary ammonium cations, indicate trends in graphite chemistry where larger intercalates form more stable and lower-stage GICs, and the graphene sheet charge densities can be correlated to the intercalate footprint areas

Structure and Dynamic Behavior of the Na–Crown Ether Complex in the Graphite Layers Studied by DFT and ¹H NMR

Diffusion of alkali metals in graphite layers is significant for the chemical and electrochemical properties of graphite intercalation compounds (GICs). Crown ethers co-intercalate into graphite with alkali metal (Na and K) cations and form ternary GICs. The structures and molecular dynamics of 15-crown-5 and 18-crown-6 ether coordinating to Na⁺ or K⁺ in GICs were investigated by DFT calculations and ¹H solid state NMR analyses. DFT calculations suggest a stacked structure of crown ether–metal complex with some offset. ¹H NMR shows two kinds of molecular motions at room temperature: isotropic rotation with molecular diffusion and axial rotation with fluctuation of the axis. The structure and dynamics of crown ether molecules in GIC galleries are strongly affected by the geometry of the crown ether molecules and the strength of the interaction between alkali metal and ligand molecules