Solid-State NMR Structural Studies of Multifunctional Carbon-Based Materials

This dissertation focuses on elucidating the structures of five important carbon-based materials using solid-state nuclear magnetic resonance (SSNMR) as well as other analytical methods. All of these materials originate from or are associated with rather unremarkable naturally-occurring graphite, yet possess exceptional properties leading to important applications. Three of these materials are derivatives of graphene oxide (GO) – a product of the oxidation of graphite. Structural investigation of GO-derivatives to better understand graphene chemistry has evolved into a pivotal issue in an era of rapid development of two-dimensional (2D) materials. The fourth material is an activated form of graphene, named activated microwave-expanded graphite oxide (a-MEGO). a-MEGO’s unique electronic properties, such as its capacitance and energy density due to its ultra-high surface area, make it an ideal supercapacitor electrode material. Despite great interest in its use, a structural representation of a-MEGO is lacking. Additionally, the adsorption mechanism of electrolytes to a-MEGO has not been investigated. The last material examined in this thesis, graphitic carbon nitride (g-C3N4), is a semiconducting polymer. It can be synthesized from different precursors and is widely known for its unique electronic properties for artificial photosynthesis, e.g., water splitting. Recent studies have demonstrated a novel synthetic approach for 2D g-C3N4 using the small-molecular precursor urea. However, the effectiveness of such a synthetic approach and the resultant polymeric forms of g-C3N4 remain unknown. The overarching goal of this dissertation research is to investigate the structures of these five materials and address the aforementioned issues using SSNMR. Successful completion of these investigations contributes greatly to understanding the electronic properties of these carbon-based materials and extending their applications to new territories

Effect of arylnaphthalene lignans on SOD activity in K562 cells.

<p>K562 cells were treated with of the indicated concentrations of HJA, HJB, JB, CME, TEME and POD for 48± SD of five independent experiments; **<i>P</i><0.01 compared with control group.</p

Effect of arylnaphthalene lignans on apoptosis in K562 cells.

<p>(A) The apoptosis rate and changes in the cell cycle of K562 cells treated with arylnaphthalene lignans at the indicated doses for 24 h were analyzed by PI staining and subsequent flow cytometry. Representative data are shown. (B) Apoptosis was further analyzed by annexin V/PI staining and flow cytometry of K562 cells treated with the indicated concentrations of HJA, HJB, JB, CME and ETO for 48 h. Representative FACS scatter-grams are shown. All results are representative of three independent experiments.</p

Chemical structures of 6′-hydroxy justicidin B (HJB), 6′-hydroxy justicidin A (HJA), justicidin B (JB), chinensinaphthol methyl ether (CME), Taiwanin E methyl ether (TEME), etoposide (ETO), paclitaxel (TAX) and podophyllotoxin (POD).

<p>Chemical structures of 6′-hydroxy justicidin B (HJB), 6′-hydroxy justicidin A (HJA), justicidin B (JB), chinensinaphthol methyl ether (CME), Taiwanin E methyl ether (TEME), etoposide (ETO), paclitaxel (TAX) and podophyllotoxin (POD).</p

Effects of arylnaphthalene lignans on caspase-3 activity in K562 cells.

<p>Active caspase-3 expression was detected by flow cytometry in K562 cells after treatment with the indicated concentrations of HJA, HJB, JB, CME, TEME, ETO and TAX for 48 h. The results are representative of three independent experiments.</p

Effect of HJB, HJA, JB, CME, TEME, POD and ETO on K562 cell proliferation.

<p>Cells were exposed to the indicated concentrations of arylnaphthalene lignans and incubated for 48± SD of three independent experiments, where each sample was tested in at least triplicate.</p

Synthesis of ¹³C‑,¹⁵N‑Labeled Graphitic Carbon Nitrides and NMR-Based Evidence of Hydrogen-Bonding Assisted Two-Dimensional Assembly

Graphitic carbon nitride (g-C₃N₄) has gained great attention as a material of promise for artificial photosynthesis. In place of synthesis of traditional three-dimensional g-C₃N₄ via polymerization of melamine or melem, recent studies seek to establish an alternative synthetic approach for two-dimensional g-C₃N₄ using a smaller precursor such as urea. However, the effectiveness of such a synthetic approach and resultant polymeric forms of g-C₃N₄ in this approach are still largely unknown. In this study, we present that solid-state NMR (SSNMR) analysis for ¹³C- and ¹⁵N-labeled g-C₃N₄ prepared from urea offers an unparalleled structural view for the heterogeneous in-plane structure of g-C₃N₄ and most likely for its moieties. We revealed that urea was successfully assembled in melem oligomers, which include extended oligomers involving six or more melem subunits. SSNMR, transmission electron micrograph, and <i>ab initio</i> calculation data suggested that the melem oligomer units were further extended into graphene-like layered materials via widespread NH–N hydrogen bonds between oligomers

Four organic–inorganic compounds based on polyoxometalates: crystal structures and catalytic epoxidation of styrene

<div><p>Four compounds based on polyoxometalates, [Cu(4-bpo)(H₂O)][Cu₂(<i>μ</i>₂-Cl)(4-bpo)₂(H₂O)][SiW₁₂O₄₀][N(CH₃)₄]₂·H₂O (<b>1</b>), [Cu(4-bpo)]₄[P₂W₁₈O₆₂][N(CH₃)₄]₂·6H₂O (<b>2</b>), [Cu₂(<i>μ</i>₂-OH)(4-bpo)₂(Hina)(H₂O)₂]₂[P₂W₁₈O₆₂]·4H₂O (<b>3</b>), and [Cu₂(Hina)₄(H₂O)₂][H₂P₂W₁₈O₆₂](Hina)·11H₂O (<b>4</b>) (4-bpo=2,5-bis(4-pyridyl)-1,3,4-oxadiazole, ina=isonicotinic acid), have been hydrothermally synthesized and characterized by elemental analysis, IR, and single-crystal X-ray diffraction. The 3-D framework of <b>1</b> is composed by Keggin-type polyoxoanions {SiW₁₂} and two types of infinite chains, {Cu(4-bpo)(H₂O)}_<i>n</i> and {Cu₂(<i>μ</i>₂-Cl)(4-bpo)₂(H₂O)}_<i>n</i>, through hydrogen bonds. Compound <b>2</b> has a 3-D rigid framework which is fabricated by Wells–Dawson type polyoxoanions {P₂W₁₈} and Cu-(4-bpo) chains through covalent bonds. Compound <b>3</b> contains an infinite {Cu₂(<i>μ</i>₂-OH)(4-bpo)₂(Hina)(H₂O)₂}_<i>n</i> double-chain and {P₂W₁₈} polyoxoanions immobilized in the voids between the chains. Compound <b>4</b> exhibits a 3-D supramolecular network directed by hydrogen bonds between {P₂W₁₈} polyoxoanions and the double paddle-wheel {Cu₂(Hina)₄(H₂O)₂}. Compounds <b>1–4</b> were tested as heterogeneous catalysts for the epoxidation of styrene using <i>tert-</i>butyl hydroperoxide (TBHP) as oxidant. The compounds show catalytic activity with <b>2</b> giving the highest yield of styrene oxide.</p></div

Lipid–Polymer Hybrid Nanoparticles for Oral Delivery of Tartary Buckwheat Flavonoids

Flavonoids rich in Tartary buckwheat (TBFs) are the acknowledged health-promoting substances, even with the low oral bioavailability due to its chemical instability in gastrointestinal tract and poor intestinal absorption. To obtain the enhanced oral delivery, TBFs, obtained by an environmentally friendly extraction strategy in advance with the amount of 7.66 ± 0.47 mg rutin/g, was incorporated in biocompatible lipid-polymer hybrid nanoparticles (LPNs). Its high encapsulation efficiency of 96.4% ± 1.1%, narrow size distribution of 61.25 ± 1.83 nm with spherical shape, and good storage stability were observed. Compared to free TBFs, TBFs/LPNs exhibited higher antioxidant activity and significant suppression on the pro-inflammatory cytokine secretion in RAW 264.7 macrophage. Moreover, the enhanced delivery of TBFs/LPNs was also embodied in the improved transmembrane transport in Caco-2 monolayer, suggesting its better intestinal absorption, and significantly immune-enhancing efficacy in immunosuppressed mice. These results demonstrated the new perspectives of Tartary buckwheat flavonoids-loaded nanosystem for pharmaceutical and nutraceutical applications