Andrew J. Surman

Exploring the Symmetry, Structure, and Self‐Assembly Mechanism of a Gigantic Seven‐Fold Symmetric {Pd84} Wheel

The symmetry, structure and formation mechanism of the structurally self-complementary {Pd84} = [Pd84O42(PO4)42(CH3CO2)28](70-) wheel is explored. Not only does the symmetry give rise to a non-closest packed structure, the mechanism of the wheel formation is proposed to depend on the delicate balance between reaction conditions. We achieve the resolution of gigantic polyoxopalladate species through electrophoresis and size-exclusion chromatography, the latter has been used in conjunction with electrospray mass spectrometry to probe the formation of the ring, which was found to proceed by the stepwise aggregation of {Pd6}(-) = [Pd6O4(CH3CO2)2(PO4)3Na(6-n)H(n)](-) building blocks. Furthermore, the higher-order assembly of these clusters into hollow blackberry structures of around 50 nm has been observed using dynamic and static light scattering.

Controlling the ring curvature, solution assembly, and reactivity of gigantic molybdenum blue wheels.

We describe the synthesis, structure, self-assembly, solution chemistry, and mass spectrometry of two new gigantic decameric molybdenum blue wheels, {Mo200Ce12} (1) and {Mo100Ce6} (2), by building block rearrangement of the tetradecameric {Mo154} framework archetype and control of the architectures curvature in solution from the addition of Ce(III). The assembly of 1 and 2 could be directed accordingly by adjusting the ionic strength and acidity of the reaction mixture. Alternatively, the dimeric cluster {Mo200Ce12} could be transformed directly to the monomeric species {Mo100Ce6} upon addition of a potassium salt. ESI-ion mobility mass spectra were successfully obtained for both {Mo200Ce12} and {Mo100Ce6}, which is the first report in molybdenum blue chemistry thereby confirming that the gigantic clusters are stable in solution and that ion mobility measurements can be used to characterize nanoscale inorganic molecules.

Sizing and Discovery of Nanosized Polyoxometalate Clusters by Mass Spectrometry

Ion mobility-mass spectrometry (IM-MS) is a powerful technique for structural characterization, e.g., sizing and conformation, particularly when combined with quantitative modeling and comparison to theoretical values. Traveling wave IM-MS (TW-IM-MS) has recently become commercially available to nonspecialist groups and has been exploited in the structural study of large biomolecules, however reliable calibrants for large anions have not been available. Polyoxometalate (POM) species—nanoscale inorganic anions—share many of the facets of large biomolecules, however, the full potential of IM-MS in their study has yet to be realized due to a lack of suitable calibration data or validated theoretical models. Herein we address these limitations by reporting DT-IM (drift tube) data for a set of POM clusters {M12} Keggin 1, {M18} Dawson 2, and two {M7} Anderson derivatives 3 and 4 which demonstrate their use as a TW-IM-MS calibrant set to facilitate characterization of very large (ca. 1–4 nm) anionic species. The data was also used to assess the validity of standard techniques to model the collision cross sections of large inorganic anions using the nanoscale family of compounds based upon the {Se2W29} unit including the trimer, {Se8W86O299} A, tetramer, {Se8W116O408} B, and hexamer {Se12W174O612} C, including their relative sizing in solution. Furthermore, using this data set, we demonstrated how IM-MS can be used to conveniently characterize and identify the synthesis of two new, i.e., previously unreported POM species, {P8W116}, unknown D, and {Te8W116}, unknown E, which are not amenable to analysis by other means with the approximate formulation of [H34W118X8M2O416]44–, where X = P and M = Co for D and X = Te and M = Mn for E. This work establishes a new type of inorganic calibrant for IM-MS allowing sizing, structural analysis, and discovery of molecular nanostructures directly from solution.

Targeting of anionic membrane species by lanthanide(III) complexes: towards improved MRI contrast agents for apoptosis

In most healthy mammalian cells an uneven distribution of the mixture of the phospholipid species that make up the bilayer cell membrane is maintained between inner and outer layers: anionic species (principally phosphatidylserine, PS) are arranged largely on the inner layer. 1 In some abnormal cells this is not the case and a considerable amount of anionic lipids are displayed on the outer membrane surface; this is known in cells undergoing the early/intermediate stages of apoptosis (programmed cell death), 2 tumour vasculature, 3 bacteria and viruses. 4 Detection and imaging of apoptotic cells in vivo is desirable, as a clinical and research tool: the extent and speed of onset of apoptosis in tumours following a treatment has shown to be a good prognostic indicator of treatment outcome. 5 In vitro, apoptotic cells are typically detected using biomolecules known to bind phosphatidylserine, conjugated with fluorescent moieties; the most extensively used in this context has been Annexin V. 6 For in vivo imaging, Annexin V and others have been modified with various functionalities for imaging, for

Self‐Templating and In Situ Assembly of a Cubic Cluster‐of‐Clusters Architecture Based on a {Mo24Fe12} Inorganic Macrocycle

Abstract Engineering self‐templating inorganic architectures is critical for the development of bottom‐up approaches to nanoscience, but systems with a hierarchy of templates are elusive. Herein we describe that the cluster‐anion‐templated (CAT) assembly of a {CAT}⊂{Mo24Fe12} macrocycle forms a giant ca. 220 nm3 unit cell containing 16 macrocycles clustered into eight face‐shared tetrahedral cluster‐of‐clusters assemblies. We show that {CAT}⊂{Mo24Fe12} with different CATs gives the compounds 1–4 for CAT=Anderson {FeMo6} (1), Keggin {PMo12} (2), Dawson {P2W18} (3), and {Mo12O36(HPO3)2} (4) polyoxometalates. “Template‐free” assembly can be achieved, whereby the macrocycle components can also form a template in situ allowing template to macrocycle to superstructure formation and the ability to exchange the templates. Furthermore, the transformation of template clusters within the inorganic macrocycle {Mo24Fe12} allows the self‐generation of an uncapped {Mo12O36(HPO3)2} in compound 4.

Spontaneous Assembly of an Organic–Inorganic Nucleic Acid Z-DNA Double-Helix Structure

Abstract Herein, we report a hybrid polyoxometalate organic–inorganic compound, Na2[(HGMP)2Mo5O15]⋅7 H2O (1; where GMP=guanosine monophosphate), which spontaneously assembles into a structure with dimensions that are strikingly similar to those of the naturally occurring left‐handed Z‐form of DNA. The helical parameters in the crystal structure of the new compound, such as rise per turn and helical twist per dimer, are nearly identical to this DNA conformation, allowing a close comparison of the two structures. Solution circular dichroism studies show that compound 1 also forms extended secondary structures in solution. Gel electrophoresis studies demonstrate the formation of non‐covalent adducts with natural plasmids. Thus we show a route by which simple hybrid inorganic–organic monomers, such as compound 1, can spontaneously assemble into a double helix without the need for a covalently connected linear sequence of nucleic acid base pairs.

Overcoming the Crystallization Bottleneck: A Family of Gigantic Inorganic {Pdx}L (x=84, 72) Palladium Macrocycles Discovered using Solution Techniques

Abstract The {Pd84}Ac wheel, initially discovered serendipitously, is the only reported giant palladium macrocycle—a unique structure that spontaneously assembles from small building blocks. Analogues of this structure are elusive. A new modular route to {Pd84}Ac is described, allowing incorporation of other ligands, and a new screening approach to cluster discovery. Structural assignments were made of new species from solution experiments, overcoming the need for crystallographic analysis. As a result, two new palladium macrocycles were discovered: a structural analogue of the existing {Pd84}Ac wheel with glycolate ligands, {Pd84}Gly, and the next in a magic number series for this cluster family—a new {Pd72}Prop wheel decorated with propionate ligands. These findings confirm predictions of a magic number rule for the family of {Pdx} macrocycles. Furthermore, structures with variable fractions of functional ligands were obtained. Together these discoveries establish palladium clusters as a new class of tunable nanostructures. In facilitating the discovery of species that would not have been discovered by orthodox crystallization approaches, this work also demonstrates the value of solution‐based screening and characterization in cluster chemistry, as a means to decouple cluster formation, discovery, and isolation.

Miller–Urey Spark-Discharge Experiments in the Deuterium World

Abstract We designed and conducted a series of primordial‐soup Miller‐Urey style experiments with deuterated gases and reagents to compare the spark‐discharge products of a “deuterated world” with the standard reaction in the “hydrogenated world”. While the deuteration of the system has little effect on the distribution of amino acid products, significant differences are seen in other regions of the product‐space. Not only do we observe about 120 new species, we also see significant differences in their distribution if the two hydrogen isotope worlds are compared. Several isotopologue matches can be identified in both, but a large proportion of products have no equivalent in the corresponding isotope world with ca. 43 new species in the D world and ca. 39 new species in the H world. This shows that isotopic exchange (the addition of only one neutron) may lead to significant additional complexity in chemical space under otherwise identical reaction conditions.