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Cucurbit[8]uril Assisted Supramolecular Architectures of Carbon Materials for Hydrogels, Photocatalysis and Sensing

Periodic Reporting for period 1 - CASACAMAhyps (Cucurbit[8]uril Assisted Supramolecular Architectures of Carbon Materials for Hydrogels, Photocatalysis and Sensing)

Reporting period: 2018-05-15 to 2020-05-14

The project has addressed a long-standing problem of how to obtain low-cost production uniformly distributed carbon materials (Graphene and carbon dots etc.) into composite systems in aqueous conditions. For instance, graphene-polymer nanocomposites can be obtained on a mass scale, but the homogeneity of the graphene sheets (or carbon nanofibers) in the matrix is extremely difficult to control, often causing uncontrollable aggregates. We will address these issues to obtain hybrid supramolecular hydrogels and fibers for bioengineering and sensing applications. Cucurbit[8]uril macrocycles will be used as host molecules for host-guest complexations.
Carbon materials have been incorporated into polymers to produce various composite materials for applications including optoelectronics, medical accessories, aerospace and sports equipment, etc. Owing to its high electrical and mechanical properties, graphene is a perfect 2-D material that can form a self-assembled network on its own or interact with other polymers via electrostatic and/or chemical bonds. C-dots are particularly attractive for bioimaging and diagnostics applications. Their fluorescence allows for non-invasive monitoring of drug release kinetics as well as local and systematic drug distribution. Thus, the hydrogels and fibers obtained herein can be useful for various applications including stretchable/wearable electronic devices, microactuators, tissue engineering, implanted biocompatible sensors, etc.

Objectives:
- Synthesis of cucurbit[8]uril macrocycle as well as its 1st and 2nd guest-molecules.
- Synthesis of carbon quantum dots (C-dots).
- Surface functionalization of carbon materials, i.e. graphene and C-dots.
- Synthesis of polymers and polymers bearing 2nd-guest molecules. CB[8] is a special macrocycle, which can simultaneously accommodate two guest moieties (1st & 2nd ).
- Development of dynamic hybrid-supramolecular hydrogels.
- Development of hybrid fluorescent hydrogels and fibers.
- Synthesis of supraparticles using the combination of C-dots and nanocrystals. We also synthesized indium phosphide/zinc selenide (InP/ZnS) nanocrystals (NCs) using expertise developed in the host laboratory.
- New knowledge was acquired to synthesize monodisperse colloidal particles with smooth and rough surfaces. We will be exploring these colloids for similar applications.
In the beginning, we synthesized cucurbit[8]uril (CB[8]) macrocycles and various guest molecules. This was done using expertise developed in the host laboratory.

First, we report exfoliated graphene (GR) sheets in water. This was achieved when silane-terminated dicationic-viologen (MV2+) molecules and graphite were mixed together in the water. After 9 h of sonication, a stable graphene solution (GR-MV2+) was obtained. Characterization techniques confirmed the covalent tethering of viologen molecules on the surface of the graphene sheets. The electrostatic repulsion originating from hydrophilic dicationic viologens present on the surface of the GR sheets dramatically improves their solubility in aqueous solutions. Meanwhile, dibenzofuran (DBF), a second guest for CB[8], was grafted onto hydroxyethyl cellulose (HEC). CB[8]-mediated host−guest chemistry was used to obtain supramolecular hydrogels consisting of uniformly distributed GR and guest-functionalized macromolecules (HEC-DBF). The formation of a supramolecular hydrogel (G′ > G′′) was observed when CB[8] was present in the system with 1.25 wt % HEC-DBF and 0.0125 wt % GR-MV2+ whereas the solution formed a viscous liquid (G′ < G′′) with the smaller macrocycle CB[7] or without any CB. Importantly, the obtained GR hydrogels show superior bioelectrical properties over identical systems produced without CB[8].

Second, we aimed to obtain carbon quantum dot (C-dot)-based fluorescent hydrogels and fibers without C-dot aggregation in the matrix. This is an unpublished work. We cannot provide more details here.

Currently, we are working on the interaction of core-shell indium phosphide/zinc selenide (InP/ZnS) nanocrystals (NCs) and carbon quantum dots to develop supraparticles. InP/ZnS NCs were synthesized using expertise developed in the host laboratory.
Beyond the state of the art of the project, we have synthesized various monodisperse rough-surfaced (raspberry) colloids with a positive surface charge. We have studied the importance of the ratio between ethanol and water to produce these colloids with extreme uniformity. Several surface functional groups including hydroxyls, amines, and azides were also produced on the surface of raspberry colloids, which will be used to obtain polymer grafted colloids.

During the project, several public engagement opportunities arose, namely the Cambridge Science Festival as well as the Japan-UK Young Scientists Workshop. I participated in both of these events representing the Marie Curie Fellowship. The Cambridge Science Festival was held in March 2019, where I demonstrated experiments on polymer cross-linking to children aged 5-12. The Japan-UK Young Scientists Workshop, coordinated by the Clifton Scientific Trust, was held in July 2019. I devised and carried out a hands-on week-long immersive project on the synthesis of supramolecular hydrogels for six high school students (three British and three Japanese), in which the students learned about synthetic techniques, working in a laboratory and the life of a scientist.

During the fellowship, I had an opportunity to improve my knowledge on the synthesis of CB[n], hydrogels, fibers, polymers, C-dots, and colloids through working alongside world-leading chemists in the Melville Laboratory, UCAM. During the progress of the project, I had the opportunity to work, collaborate, and use the instrumental facilities of other laboratories within UCAM. This helped me develop new collaboration within the departments and to manage interlaboratory professional relations. In the long-term, this experience will result in my scientific maturity and serve to strengthen my background expertise. All the benefits derived from this fellowship will place me in a privileged situation to begin my independent career in the near future.

I had a confirmed oral presentation about the work that I carried out during my fellowship at the ACS Spring National Meeting and Exposition, March 22-26, 2020, in Philadelphia, PA. However, due to the COVID-19 outbreak, the meeting was unfortunately cancelled.