Evaluation of the supramolecular interaction of Congo red with cucurbiturils using mass spectrometry and spectroscopic methods

The ability of cucurbit[n]urils (CB[n]) to decolourise aqueous solutions of the azo dye Congo red (CR) was described more than a century ago alongside the first synthesis of CB[n]. No subsequent studies of the nature of the physical interactions have been reported despite the interest in using CB[n] as adsorbents for the removal of CR and related organic dyes from wastewaters. In the present work the supramolecular interaction between CB[n] (n = 7, 8) and CR was studied by electrospray ionisation mass spectrometry (ESI-MS), 1H NMR, and solid-state characterisation of isolated complexes. Under positive ESI, the formation of host–guest complexes in the gas phase was not observed, suggesting that CR anions do not interact with the portals and the nonpolar inner cavity of the CB[n] molecules. Conversely, under negative ESI, 1 : 1 and higher order (1 : 2, 2 : 1, 3 : 1 and 2 : 2) CR: CB[7] and CR: CB[8] adducts were detected, which is attributed to interaction between CR and the outer surface hydrogens of CB[n]. Solid-state supramolecular adducts between CB[n] and CR were isolated from aqueous media under either ambient conditions, giving structures denoted as CR@CB[n](RT), or hydrothermal (100 ºC) conditions, giving structures denoted as CR@CB[n](100). The adducts were characterised by elemental and thermogravimetric analyses (TGA), powder X-ray diffraction (PXRD), and spectroscopic methods (FT-IR, FT-Raman, 13C{1H} CP MAS NMR, UV/vis and near-IR absorption, fluorescence excitation and emission). The interaction conditions and acid content of the starting CB[n] influenced the protonation state of CR molecules. CR@CB[7](RT) contained only unprotonated CR, while CR@CB[8](100) contained exclusively protonated CR (ammonium and azonium/quinoid structures). Other adducts contained mixtures of protonated/unprotonated forms.publishe

Separability and entanglement in 2x3xN composite quantum systems

The separability and entanglement of quantum mixed states in \Cb^2 \otimes \Cb^3 \otimes \Cb^N composite quantum systems are investigated. It is shown that all quantum states $\rho$ with positive partial transposes and rank $r(\rho)\leq N$ are separable.Comment: Latex, 15 page

Acyclic Congeners of Cucurbit[n]uril and a Related Mechanistic Study on the Cucurbit[n]uril Forming Reaction.

Supramolecular chemistry has been a very important research area in the past several decades. In this research field, molecular containers, such as cyclodextrin, attracts special attention due to their wide applications both in academia and industry. Cucurbit[n]uril (CB[n]), as a new generation molecular container, has selective and tight binding towards lots of cations and neutral molecules. A homologous family of CB[n] has been discovered including CB[5]-CB[8], CB[10], iCB[n], ns-CB[10] and ns-CB[6]. CB[n] analogues and derivatives have also been developed. CB[n] still has several issues, such as low solubility in water, difficulty to be functionalized, and slow association and dissociation kinetics. This thesis describes efforts to address these issues by developing new CB[n] type molecular containers and carrying out mechanistic investigations. Three chapters are included in this thesis. Chapter 1 is a literature review of molecular encapsulation and molecular container chemistry. We first introduced general concepts of molecular encapsulation and present examples of molecular container, such as cyclodextrin. This is followed by an introduction to CB[n] molecular containers and their supramolecular chemistry. Chapter 2 introduces new acyclic CB[n] congeners II-5a and II-5b. II-5a and II-5b are obtained from step-wise synthesis with reasonable yields. This step-wise synthetic route avoids difficult separation process. We measured the binding constants of II-5a towards a number of guests and found the binding affinity is usually comparable to CB[7]. The recognition property of II-5a is investigated in depth. We found that the length and functional groups of the guests greatly influence the binding affinity. Nevertheless, the charge and size of the guests do not have as a big influence on the binding constants as CB[7]. We discovered that the ionic strength of the buffer is critical for the binding constant. By comparing the recognition property of II-5a and II-6, it is discovered that the substituted o-xylyene walls are important for the tight binding compounds. II-5a and II-5b are new examples of CB[n] type molecular containers. They retain most of the good recognition property of CB[n] and have advantages compared to CB[n], including 1) aromatic walls that makes further functionalization possible; 2) acyclic structure that enables fast association and dissociation kinetics. Chapter 3 describes the mechanistic study of CB[n] forming reactions. Another possible way to synthesize CB[n] molecular container is to use aldehydes instead of paraformaldehyde. But neither previous researchers nor our work has succeeded to make the aldehydes participating CB[n] forming reactions happen. Mechanistic investigation was carried out to explain why this reaction simply does not occur. We used III-7 instead of glycoluril to avoid cyclization reactions. Several reasons are discovered: 1) side products are formed, such as III-SP1 and III-SP2; 2) S-shape intermediates are yielded, such as III-15S, III-16S, III-17S and III-18S, which are not able to continue the reaction to form macrocycles; 3) a small equilibrium constant for the chain grouth reaction. This study explains why aldehydes usually do not participate in CB[n] forming reactions. This work could also lead to the discovery of certain aldehydes that can form CB[n] type macrocycles

Equivalence of Tripartite Quantum States under Local Unitary Transformations

The equivalence of tripartite pure states under local unitary transformations is investigated. The nonlocal properties for a class of tripartite quantum states in \Cb^K \otimes \Cb^M \otimes \Cb^N composite systems are investigated and a complete set of invariants under local unitary transformations for these states is presented. It is shown that two of these states are locally equivalent if and only if all these invariants have the same values.Comment: 7 page

Fine structure of the zeros of orthogonal polynomials, I. A tale of two pictures

Mhaskar-Saff found a kind of universal behavior for the bulk structure of the zeros of orthogonal polynomials for large n. Motivated by two plots, we look at the finer structure for the case of the Verblunsky coefficients and for what we call the BLS condition: αn = Cb^n + O ((bΔ)^n). In the former case, we describe the results of Stoiciu. In the latter case, we prove asymptotically equal spacing for the bulk of zeros

Templated Synthesis of Glycoluril Oligomers and Monofunctionalized Cucurbit[6]uril Derivatives

The molecular recognition properties exhibited by molecular containers have inspired supramolecular chemists to generate diverse and specialized macrocycles. The family of hosts known as cucurbiturils (CB[n]) have become a popular platform for molecular recognition due to their high binding affinities and selectivity in water. As CB[n] branch into increasingly complex applications it becomes important to find efficient pathways to prepare monofunctionalized CB[n] derivatives bearing reactive functional groups. Chapter 1 presents a literature review of the synthesis, properties, mechanism of formation, and applications of the CB[n] family. We use this background information to explain our key hypothesis, that templated reactions offer potential routes to obtain glycoluril oligomer building blocks that allow the preparation of monofunctionalized CB[n] compounds. Chapter 2 describes the templated synthesis of glycoluril hexamer (6C) in a one step synthetic procedure on the gram scale using the p-xylylenediammonium ion (II-11). Hexamer 6C undergos cyclization with (substituted) phthalaldehdyes II-12, II-14, II-15, II-18 under acidic conditions at room temperature to deliver monofunctionalized CB[6] derivatives II-13, II-15, II-16, and II-19. Furthermore, the reaction kinetics for CB[6] cyclization between hexamer and formaldehyde or phthalaldehyde is influenced by the size and shape of ammonium ion templates. The larger size of the p- xylylenediammonium ion (II-11) allows it to act as a negative template by discouraging transformation of hexamer and paraformaldehyde to form CB[6]. However, II-11 and hexanediammonium ion (II-20) act as positive templates during the reaction of 6C and phthalaldehyde II-12 by giving (±)-II-21 as an intermediate along the mechanistic pathway to CB[6] derivative II-13. Finally, a fluorescence turn-on assay was investigated using the fluorophore and metal-ion binding (e.g., Eu3+) of naphthalene- CB[6] derivative II-19. The synthesis of monofunctionalized CB[6] derivatives in high yields has broad implications toward tailor-made approaches to CB[n] derived functional systems in the future. Chapter 3 describes the high yield synthesis of glycoluril pentamer (5C) by the 3,5- dimethylphenol induced fragmentation of bis-ns-CB[10] under acid conditions. The access to large quantities of 5C and 6C and previously reported tetramer III-4 allowed for a comparison of host-guest recognition properties of acyclic CB[n]-type receptors toward alkaneammonium ions in water

Dynamic Interfacial Adhesion through Cucurbit[n]uril Molecular Recognition.

Supramolecular building blocks, such as cucurbit[n]uril (CB[n])-based host-guest complexes, have been extensively studied at the nano- and microscale as adhesion promoters. Herein, we exploit a new class of CB[n]-threaded highly branched polyrotaxanes (HBP-CB[n]) as aqueous adhesives to macroscopically bond two wet surfaces, including biological tissue, through the formation of CB[8] heteroternary complexes. The dynamic nature of these complexes gives rise to adhesion with remarkable toughness, displaying recovery and reversible adhesion upon mechanical failure at the interface. Incorporation of functional guests, such as azobenzene moieties, allows for stimuli-activated on-demand adhesion/de-adhesion. Macroscopic interfacial adhesion through dynamic host-guest molecular recognition represents an innovative strategy for designing the next generation of functional interfaces, biomedical devices, tissue adhesives, and wound dressings