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1. Positively Charged Additives Facilitate Incorporation in Inorganic Single Crystals

Author

Nahi, Ouassef, Broad, Alexander, Kulak, Alexander N., Freeman, Helen M., Zhang, Shuheng, Turner, Thomas D., Roach, Lucien, Darkins, Robert, Ford, Ian J., and Meldrum, Fiona C.

Subjects
Condensed Matter - Materials Science, Physics - Applied Physics
Abstract

Incorporation of guest additives within inorganic single crystals offers a unique strategy for creating nanocomposites with tailored properties. While anionic additives have been widely used to control the properties of crystals, their effective incorporation remains a key challenge. Here, we show that cationic additives are an excellent alterative for the synthesis of nanocomposites, where they are shown to deliver exceptional levels of incorporation of up to 70 wt% of positively charged amino acids, polymer particles, gold nanoparticles, and silver nanoclusters within inorganic single crystals. This high additive loading endows the nanocomposites with new functional properties including plasmon coupling, bright fluorescence, and surface-enhanced Raman scattering (SERS). Cationic additives are also shown to outperform their acidic counterparts, where they are highly active in a wider range of crystal systems, owing to their outstanding colloidal stability in the crystallization media and strong affinity for the crystal surfaces. This work demonstrates that although often overlooked, cationic additives can make valuable crystallization additives to create composite materials with tailored composition-structure-property relationships. This versatile and straightforward approach advances the field of single-crystal composites and provides exciting prospects for the design and fabrication of new hybrid materials with tunable functional properties.

Published
2022
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2. Synthesis and structure-property relationships of single crystal nanocomposites

Author

Nahi, Ouassef, Meldrum, Fiona, and Cayre, Olivier

Abstract

The work in this thesis explores the ability of cationic additives to direct the crystallization of calcium carbonate. Although considered less potent than their acidic counterparts, cationic additives are shown to enable exceptional control over the size, morphology, composition, structure and polymorph of the mineral. In particular, functionalization of polymer and metal nanoparticles with polycations enables their incorporation at exceptional levels within calcite (CaCO3) and alternative carbonate, sulfate and oxide single crystals. These nanocomposites are endowed with new optical properties including bright fluorescence and surface-enhanced Raman scattering. Computation simulations provide crucial insights into the molecular interactions between these cationic additives and host crystals, and structural analyses using synchrotron powder XRD reveal high lattice strains. The internal structures of the nanocomposites can also be controlled by annealing, providing a straightforward strategy for engineering the thermal and optical properties. Cationic polyamines can additionally direct the formation of all three anhydrous polymorphs of calcium carbonate, where aragonite (metastable phase of CaCO3) was observed to form via a particle attachment mechanism reminiscent of the growth of biogenic aragonite. Alternative hybrid single crystals are also explored, where protein nanogels impregnated with diverse (bio)-active compounds are incorporated within calcite. The host crystal effectively protects the payloads, and controlled release can be achieved by dissolution of the mineral in acidic solutions. Finally, while most bio-inspired strategies used to synthesize nanocomposites are carried out in pure aqueous solutions, the introduction of small amounts of organic co-solvents in the crystallization medium is shown to significantly enhance incorporation of various additives within inorganic crystals. This constitutes a significant step-change in methodology, which can find applications in a wide range of industrial fields. This work therefore delivers new insights into the structure-composition-property relationships of composite crystals and offers new straightforward synthetic routes for generating nanocomposites with advanced functional properties.

Published
2022

6. Polyamines Promote Aragonite Nucleation and Generate Biomimetic Structures.

Author

Nahi, Ouassef, Kulak, Alexander N., Zhang, Shuheng, He, Xuefeng, Aslam, Zabeada, Ilett, Martha A., Ford, Ian J., Darkins, Robert, and Meldrum, Fiona C.

Subjects
*CALCIUM carbonate, *CALCITE, *ARAGONITE, *SMALL molecules, *POLYAMINES, *MAGNESIUM ions, *VATERITE
Abstract

Calcium carbonate biomineralization is remarkable for the ability of organisms to produce calcite or aragonite with perfect fidelity, where this is commonly attributed to specific anionic biomacromolecules. However, it is proven difficult to mimic this behavior using synthetic or biogenic anionic organic molecules. Here, it is shown that cationic polyamines ranging from small molecules to large polyelectrolytes can exert exceptional control over calcium carbonate polymorph, promoting aragonite nucleation at extremely low concentrations but suppressing its growth at high concentrations, such that calcite or vaterite form. The aragonite crystals form via particle assembly, giving nanoparticulate structures analogous to biogenic aragonite, and subsequent growth yields stacked aragonite platelets comparable to structures seen in developing nacre. This mechanism of polymorph selectivity is captured in a theoretical model based on these competing nucleation and growth effects and is completely distinct from the activity of magnesium ions, which generate aragonite by inhibiting calcite. Profiting from these contrasting mechanisms, it is then demonstrated that polyamines and magnesium ions can be combined to give unprecedented control over aragonite formation. These results give insight into calcite/aragonite polymorphism and raise the possibility that organisms may exploit both amine‐rich organic molecules and magnesium ions in controlling calcium carbonate polymorph. [ABSTRACT FROM AUTHOR]

Published
2023
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9. Incorporation of nanogels within calcite single crystals for the storage, protection and controlled release of active compounds†

Author

Thomas Kress, Alexander N. Kulak, Ola G. Grendal, Yi-Yeoun Kim, Melinda J. Duer, Fiona C. Meldrum, Ouassef Nahi, Olivier J. Cayre, Nahi, Ouassef [0000-0002-5752-4329], Kress, Thomas [0000-0001-9133-4310], Kim, Yi-Yeoun [0000-0002-8503-4554], Grendal, Ola G [0000-0002-4589-8737], Meldrum, Fiona C [0000-0001-9243-8517], and Apollo - University of Cambridge Repository

Subjects
chemistry.chemical_classification, Calcite, FOS: Nanotechnology, 34 Chemical Sciences, Chemistry, Bioengineering, 02 engineering and technology, General Chemistry, Polymer, 010402 general chemistry, 021001 nanoscience & nanotechnology, 01 natural sciences, Controlled release, Amorphous calcium carbonate, 0104 chemical sciences, 3402 Inorganic Chemistry, chemistry.chemical_compound, Chemical engineering, Vaterite, Nanotechnology, Nanocarriers, 0210 nano-technology, Mesoporous material, Nanogel
Abstract

Nanocarriers have tremendous potential for the encapsulation, storage and delivery of active compounds. However, current formulations often employ open structures that achieve efficient loading of active agents, but that suffer undesired leakage and instability of the payloads over time. Here, a straightforward strategy that overcomes these issues is presented, in which protein nanogels are encapsulated within single crystals of calcite (CaCO3). Demonstrating our approach with bovine serum albumin (BSA) nanogels loaded with (bio)active compounds, including doxorubicin (a chemotherapeutic drug) and lysozyme (an antibacterial enzyme), we show that these nanogels can be occluded within calcite host crystals at levels of up to 45 vol%. Encapsulated within the dense mineral, the active compounds are stable against harsh conditions such as high temperature and pH, and controlled release can be triggered by a simple reduction of the pH. Comparisons with analogous systems – amorphous calcium carbonate, mesoporous vaterite (CaCO3) polycrystals, and calcite crystals containing polymer vesicles – demonstrate the superior encapsulation performance of the nanogel/calcite system. This opens the door to encapsulating a broad range of existing nanocarrier systems within single crystal hosts for the efficient storage, transport and controlled release of various active guest species., Nanocarriers have tremendous potential for the encapsulation, storage and delivery of active compounds.

Published
2021

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