Nanoscale mosaicity revealed in peptide microcrystals by scanning electron nanodiffraction.

Changes in lattice structure across sub-regions of protein crystals are challenging to assess when relying on whole crystal measurements. Because of this difficulty, macromolecular structure determination from protein micro and nanocrystals requires assumptions of bulk crystallinity and domain block substructure. Here we map lattice structure across micron size areas of cryogenically preserved three-dimensional peptide crystals using a nano-focused electron beam. This approach produces diffraction from as few as 1500 molecules in a crystal, is sensitive to crystal thickness and three-dimensional lattice orientation. Real-space maps reconstructed from unsupervised classification of diffraction patterns across a crystal reveal regions of crystal order/disorder and three-dimensional lattice tilts on the sub-100nm scale. The nanoscale lattice reorientation observed in the micron-sized peptide crystal lattices studied here provides a direct view of their plasticity. Knowledge of these features facilitates an improved understanding of peptide assemblies that could aid in the determination of structures from nano- and microcrystals by single or serial crystal electron diffraction

Bespoke library docking for 5-HT2A receptor agonists with antidepressant activity

There is considerable interest in screening ultralarge chemical libraries for ligand discovery, both empirically and computationally1-4. Efforts have focused on readily synthesizable molecules, inevitably leaving many chemotypes unexplored. Here we investigate structure-based docking of a bespoke virtual library of tetrahydropyridines-a scaffold that is poorly sampled by a general billion-molecule virtual library but is well suited to many aminergic G-protein-coupled receptors. Using three inputs, each with diverse available derivatives, a one pot C-H alkenylation, electrocyclization and reduction provides the tetrahydropyridine core with up to six sites of derivatization5-7. Docking a virtual library of 75 million tetrahydropyridines against a model of the serotonin 5-HT2A receptor (5-HT2AR) led to the synthesis and testing of 17 initial molecules. Four of these molecules had low-micromolar activities against either the 5-HT2A or the 5-HT2B receptors. Structure-based optimization led to the 5-HT2AR agonists (R)-69 and (R)-70, with half-maximal effective concentration values of 41 nM and 110 nM, respectively, and unusual signalling kinetics that differ from psychedelic 5-HT2AR agonists. Cryo-electron microscopy structural analysis confirmed the predicted binding mode to 5-HT2AR. The favourable physical properties of these new agonists conferred high brain permeability, enabling mouse behavioural assays. Notably, neither had psychedelic activity, in contrast to classic 5-HT2AR agonists, whereas both had potent antidepressant activity in mouse models and had the same efficacy as antidepressants such as fluoxetine at as low as 1/40th of the dose. Prospects for using bespoke virtual libraries to sample pharmacologically relevant chemical space will be considered

Resolving Soft Material Crystallinity through Scanning Transmission Electron Nanodiffraction

A method for imaging the semi-crystalline structure of organic, electrically conduct- ing molecular thin films using scanning nanodiffraction transmission electron microscopy (4D-STEM) is developed, with a maximum achieved resolution of 5-10 nm, depending on the material analyzed. The changes in local nanocrystalline structure of the polymer thin films under study - regioregular Poly(3-hexyl-thiophene-2,5-diyl), the small molecule 7,7’- (4,4 - bis(2 - ethylhexyl) - 4H - silolo[3,2-b:4, 5-b’] dithiophene - 2,6 - diyl) bis(6 - flu- oro - 4 - (5’- hexyl[2,2’-bithiophen] - 5 - yl)benzo[c][1,2,5] - thiadiazole), abbreviated as p- DTS(FBTTh2 )2 or T1, and Poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b ]thiophene], abbreviated as PBTTT - with processing conditions, such as solvent addition and annealing, are characterized and visualized. The methods presented show spatially resolved features such as overlapping grains and nematic liquid crystal character that have not been directly imaged before, and help remove ambiguities in X-ray and other techniques that have been thus far used to characterize these materials.The method is first applied to polyethylene and P3HT samples to demonstrate the via- bility of the electron transmission technique on soft materials and determine its limitations. A resolution of 5 nm is achieved on P3HT. The method is subsequently used to visualize the changes in crystal structure of T1 when treated with 1,8-diiodooctane (DIO), and then on PBTTT to characterize morphological changes upon annealing. It is found that for T1, while the untreated samples exhibited a liquid-crystal-like structure with crystalline orientations varying smoothly over all possible rotations, the addition of a co-solvent induces partial segmentation of the structure characterized by the emergence of sharp grain boundaries and overlapping domains with unrelated orientations. In the case of PBTTT, the crystalline character of the nematic liquid crystal phase increases upon annealing. These results demon- strate how scanning electron nanobeam diffraction can provide a new level of insight into the structure of functional organic solids, and show how structure-property relationships can be visualized in organic systems using nanoscale electron microscopy techniques previously only available for hard materials such as metals and ceramics

Resolving Soft Material Crystallinity through Scanning Transmission Electron Nanodiffraction

A method for imaging the semi-crystalline structure of organic, electrically conduct- ing molecular thin films using scanning nanodiffraction transmission electron microscopy (4D-STEM) is developed, with a maximum achieved resolution of 5-10 nm, depending on the material analyzed. The changes in local nanocrystalline structure of the polymer thin films under study - regioregular Poly(3-hexyl-thiophene-2,5-diyl), the small molecule 7,7’- (4,4 - bis(2 - ethylhexyl) - 4H - silolo[3,2-b:4, 5-b’] dithiophene - 2,6 - diyl) bis(6 - flu- oro - 4 - (5’- hexyl[2,2’-bithiophen] - 5 - yl)benzo[c][1,2,5] - thiadiazole), abbreviated as p- DTS(FBTTh2 )2 or T1, and Poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b ]thiophene], abbreviated as PBTTT - with processing conditions, such as solvent addition and annealing, are characterized and visualized. The methods presented show spatially resolved features such as overlapping grains and nematic liquid crystal character that have not been directly imaged before, and help remove ambiguities in X-ray and other techniques that have been thus far used to characterize these materials.The method is first applied to polyethylene and P3HT samples to demonstrate the via- bility of the electron transmission technique on soft materials and determine its limitations. A resolution of 5 nm is achieved on P3HT. The method is subsequently used to visualize the changes in crystal structure of T1 when treated with 1,8-diiodooctane (DIO), and then on PBTTT to characterize morphological changes upon annealing. It is found that for T1, while the untreated samples exhibited a liquid-crystal-like structure with crystalline orientations varying smoothly over all possible rotations, the addition of a co-solvent induces partial segmentation of the structure characterized by the emergence of sharp grain boundaries and overlapping domains with unrelated orientations. In the case of PBTTT, the crystalline character of the nematic liquid crystal phase increases upon annealing. These results demon- strate how scanning electron nanobeam diffraction can provide a new level of insight into the structure of functional organic solids, and show how structure-property relationships can be visualized in organic systems using nanoscale electron microscopy techniques previously only available for hard materials such as metals and ceramics

Diffraction imaging of nanocrystalline structures in organic semiconductor molecular thin films

The properties of organic solids depend on their structure and morphology, yet direct imaging using conventional electron microscopy methods is hampered by the complex internal structure of these materials and their sensitivity to electron beams. Here, we manage to observe the nanocrystalline structure of two organic molecular thin-film systems using transmission electron microscopy by employing a scanning nanodiffraction method that allows for full access to reciprocal space over the size of a spatially localized probe (~2 nm). The morphologies revealed by this technique vary from grains with pronounced segmentation of the structure-characterized by sharp grain boundaries and overlapping domains-to liquid-crystal structures with crystalline orientations varying smoothly over all possible rotations that contain disclinations representing singularities in the director field. The results show how structure-property relationships can be visualized in organic systems using techniques previously only available for hard materials such as metals and ceramics

Orientation mapping of semicrystalline polymers using scanning electron nanobeam diffraction.

We demonstrate a scanning electron nanobeam diffraction technique that can be used for mapping the size and distribution of nanoscale crystalline regions in a polymer blend. In addition, it can map the relative orientation of crystallites and the degree of crystallinity of the material. The model polymer blend is a 50:50w/w mixture of semicrystalline poly(3-hexylthiophene-2,5-diyl) (P3HT) and amorphous polystyrene (PS). The technique uses a scanning electron beam to raster across the sample and acquires a diffraction image at each probe position. Through image alignment and filtering, the diffraction image dataset enables mapping of the crystalline regions within the scanned area and construction of an orientation map

Orientation mapping of semicrystalline polymers using scanning electron nanobeam diffraction.

We demonstrate a scanning electron nanobeam diffraction technique that can be used for mapping the size and distribution of nanoscale crystalline regions in a polymer blend. In addition, it can map the relative orientation of crystallites and the degree of crystallinity of the material. The model polymer blend is a 50:50w/w mixture of semicrystalline poly(3-hexylthiophene-2,5-diyl) (P3HT) and amorphous polystyrene (PS). The technique uses a scanning electron beam to raster across the sample and acquires a diffraction image at each probe position. Through image alignment and filtering, the diffraction image dataset enables mapping of the crystalline regions within the scanned area and construction of an orientation map