Revealing the early stages of carbamazepine crystallization by cryoTEM and 3D electron diffraction

Time-resolved carbamazepine crystallization from wet ethanol has been monitored using a combination of cryoTEM and 3D electron diffraction. Carbamazepine is shown to crystallize exclusively as a dihydrate after 180 s. When the timescale was reduced to 30 s, three further polymorphs could be identified. At 20 s, the development of early stage carbamazepine dihydrate was observed through phase separation. This work reveals two possible crystallization pathways present in this active pharmaceutical ingredient

β-Chitin nano-Fibrils Self-Assembly in Aqueous Environments

Chitin is one of the most studied biopolymers but the understanding of how it assembles from molecules to microfibers is still limited. Organisms are able to assemble chitin with precise control over polymorphism, texture, and final morphology. The produced hierarchical structure leads to materials with outstanding mechanical properties. In this study, the self-assembly in aqueous solutions of \u3b2-chitin nanofibrils, as far as possible similar to their native state, is investigated. These nanofibrils increase their tendency to self-assemble in fibers, up to millimetric length and 4810 \u3bcm thickness, with the pH increasing from 3 to 8, forming loosely organized bundles as observed using cryo-transmission electron microscopy. The knowledge from this study contributes to the understanding of the self-assembly process that follows chitin once extruded from cells in living organisms. Moreover, it describes a model system which can be used to investigate how other biomolecules can affect the self-assembly of chitin nanofibrils

Micron-sized biogenic and synthetic hollow mineral spheres occlude additives within single crystals

Incorporating additives within host single crystals is an effective strategy for producing composite materials with tunable mechanical, magnetic and optical properties. The type of guest materials that can be occluded can be limited, however, as incorporation is a complex process depending on many factors including binding of the additive to the crystal surface, the rate of crystal growth and the stability of the additives in the crystallisation solution. In particular, the size of occluded guests has been restricted to a few angstroms – as for single molecules – to a few hundred nanometers – as for polymer vesicles and particles. Here, we present a synthetic approach for occluding micrometer-scale objects, including high-complexity unicellular organisms and synthetic hollow calcite spheres within calcite single crystals. Both of these objects can transport functional additives, including organic molecules and nanoparticles that would not otherwise occlude within calcite. Therefore, this method constitutes a generic approach using calcite as a delivery system for active compounds, while providing them with effective protection against environmental factors that could cause degradation

Forming nacreous layer of the shells of the bivalves Atrina rigida and Pinctada margaritifera: An environmental- and cryo-scanning electron microscopy study

International audienceA key to understanding control over mineral formation in mollusk shells is the microenvironment inside the pre-formed 3-dimensional organic matrix framework where mineral forms. Much of what is known about nacre formation is from observations of the mature tissue. Although these studies have elucidated several important aspects of this process, the structure of the organic matrix and the microenvironment where the crystal nucleates and grows are very difficult to infer from observations of the mature nacre. Here, we use environmental- and cryo-scanning electron microscopy to investigate the organic matrix structure at the onset of mineralization in the nacre of two mollusk species: the bivalves Atrina rigida and Pinctada margaritifera. These two techniques allow the visualization of hydrated biological materials coupled with the preservation of the organic matrix close to physiological conditions. We identified a hydrated gel-like protein phase filling the space between two interlamellar sheets prior to mineral formation. The results are consistent with this phase being the silk-like proteins, and show that mineral formation does not occur in an aqueous solution, but in a hydrated gel-like medium. As the tablets grow, the silk-fibroin is pushed aside and becomes sandwiched between the mineral and the chitin layer

Self-assembly of collagen molecules into fibrils in solution

Type I collagen is a major constituent of many biological tissues, including skin, bone, tendon and cartilages. Its main functions are to shape extracellular matrices, promote cell attachment and provide tissues with strength, flexibility and elasticity. At the core these functions is its remarkable ability of collagen to form highly organized fibrils through the self-assembly of the molecules. The fibrilogenesis involves the lateral association of collagen triple helices into staggered parallel arrays that give rise to the characteristic D-band periodicity of 67 nm. Currently, the mechanisms of collagen self-assembly are poorly understood. Here, we combine the nanometer-scale resolution of cryo-transmission electron microscopy (cryoTEM) with molecular dynamics to investigate the self-assembly of collagen molecules into fibrils in solution

Polymeric Frustrated Lewis Pairs

Frustrated Lewis Pair (FLP) chemistry is a significant and growing field since it offers a novel non-metal catalyst for hydrogenation and small molecule activation. Once it was discovered, different FLPs with varying reactivity towards small molecules have been extensively investigated. Its research has mainly focused on small molecule-based FLPs, however, especially in the aspect of hydrogenation reactions. In the field of polymer chemistry, several examples of conventional Lewis pair adduct containing polymers have been reported but there has yet been no exploration of FLPs incorporated into polymers up to the date of this project. Dynamic crosslinked polymeric networks have attracted more attention in recent years as their shape can be post-modified after polymerisation due to their exchangeable crosslinks. This dynamic crosslinking also makes the material stimuli-responsive and provides self-healing properties. This thesis introduces the synthesis of a polymeric network with combined features of frustrated Lewis pairs and dynamic crosslinking. New monomers containing Lewis acid or Lewis base centres were designed and synthesised successfully. For the pair 4- styryl-diphenylborane and 4-styryl-diphenylphosphine, the two monomers were found to be able to bind together at high concentration in toluene so as to form a weak conventional Lewis pair (CLP) adduct. An FLP can be obtained when the phosphine monomer was replaced to its more hindered analogue, 4-styryl-dimesitylphosphine, which is reactive enough to form a complex with diethyl azodicarboxylate (DEAD), where the DEAD bridges the boron and phosphorous centres. The monomers obtained were copolymerised with styrene by RAFT polymerisations. It was also found to be possible to control both the molecular weight and the dispersity. The FLP polymers synthesised in this way were characterised by NMR spectroscopy and gel permission chromatography. The Lewis acidity of both the monomer and resultant polymer were tested using the Gutmann-Beckett Method, and a decrease in Lewis acidity was observed when the boron monomer was polymerised. The network was synthesised by addition of DEAD into the solution containing both Lewis acid and Lewis base polymers. A gel was quickly generated (in 10 seconds). The mechanical properties of the network formed were determined by rheology. The gel was responsive to heat, in that it would break and return to a polymer solution at high temperatures. The gel formed also shows the ability to self-heal with the assistance of a solvent after physical cracking. The synthesis of the next generation of polymeric FLPs was also examined. A much more Lewis acidic boron monomer, (2,3,5,6-tetrafluorostyryl)- bis(pentafluorophenyl)borane was synthesised. This boron monomer was paired with 4-styryl-dimesitylphosphine to form a reactive FLP that was able to activate small molecules, including dihydrogen molecules and carbon dioxide. The catalysis reactivity of the hydrogenation reactions of this FLP was also explored. The copolymers made from these reactions readily formed a supramolecular gel upon mixing, which also proved temperature responsive. These early-stage results proved that this new boron-monomer is capable of generating a novel stimuli-responsive smart polymer for carbon capture and hydrogenation catalysis. Except for the polymeric FLP, some early-stage research about polymeric CLP and novel synthetic methods for boron-monomers were also introduced and discussed

Controlling Internal Pore Sizes in Bicontinuous Polymeric Nanospheres

Complex polymeric nanospheres were formed in water from comb-like amphiphilic block copolymers. Their internal morphology was determined by three-dimensional cryo-electron tomographic analysis. Varying the polymer molecular weight (MW) and the hydrophilic block weight content allowed for fine control over the internal structure. Construction of a partial phase diagram allowed us to determine the criteria for the formation of bicontinuous polymer nanosphere (BPN), namely for copolymers with MW of up to 17?kDa and hydrophilic weight fractions of ?0.25; and varying the organic solvent to water ratio used in their preparation allowed for control over nanosphere diameters from 70 to 460?nm. Significantly, altering the block copolymer hydrophilic–hydrophobic balance enabled control of the internal pore diameter of the BPNs from 10 to 19?nm