Complementary cyclisation reactions of hex-2-ene-1,6-diamine derivatives were exploited in the synthesis of alternative molecular scaffolds. The value of the synthetic approach was analysed using LLAMA, an open-access computational tool for assessing the lead-likeness and novelty of molecular scaffolds.
Combinatorial chemical evolution is used to select oil-water droplet interfaces that drive inorganic nanoparticle synthesis.
Soluble additives are widely used to control crystallization, leading to definition of properties including size, morphology, polymorph and composition. However, due to the number of potential variables in these experiments, it is typically extremely difficult to identify reaction conditions -as defined by solution compositions, temperatures and combinations of additives -that give the desired product. This article introduces a high throughput methodology which addresses this challenge and enables the streamlined preparation and characterization of crystalline materials. Using calcium carbonate precipitated in the presence of selected amino acids as a model system, we use well plates as micro volume crystallizers, and an accurate liquid handling pipetting workstation for sample preparation. Following changes in the solution turbidity using a plate reader delivers information about the reaction kinetics, while semi automated scanning electron microscopy, powder XRD and Raman microscopy provide structural information about the library of crystalline products. Of particular interest for the CaCO3 system is the development of fluorescence based protocols which rapidly evaluate the amounts of the additives occluded within the crystals. Together, these methods provide a strategy for efficiently screening a broad reaction space, where this can both accelerate the ability to generate crystalline materials with target properties, and develop our understanding of additive directed crystallization.
The syntheses of configurationally restricted mono- and bis-macrocyclic copper(II) perchlorate complexes (copper(II) 5-benzyl-1,5,8,12-tetraazabicyclo[10.2.2]hexadecane and dicopper(II) 5,5'-[1,4-phenylenebis(methylene)]-bis(1,5,8,12-tetraazabicyclo[10.2.2]hexadecane)) are reported and the X-ray structure of the copper(II) mono-macrocyclic complex has been determined. EXAFS studies on the bis-macrocyclic species in aqueous solution show that the copper coordination spheres are essentially identical to the solid state structure, and do not vary in the presence of 20 equivalents of sodium acetate per metal centre. DFT calculations were carried out at the BP86/TZP level to determine the nature of potential binding interactions with CXCR4 aspartate residues. The alkylated single macrocyclic compound was modelled with an acetate included to represent the aspartate residue, demonstrating that the predicted macrocycle configuration has the lowest energy and the acetate interaction is effectively monodentate giving a distorted trigonal bipyramidal geometry at the copper centre. In vitro anti-HIV infection assays show that the configurationally restricted dicopper(II) complex is more active (average EC(50) = 0.026 microM against HIV-1) than the non-constrained dicopper(II) 1,1'-[1,4-phenylenebis(methylene)]-bis(1,4,8,11-tetraazacyclotetradecane) (average EC(50) = 0.047 microM against HIV-1) although it is an order of magnitude less active than the configurationally restricted dizinc(II) complex.
On entering the Earth’s atmosphere, micrometeoroids partially or completely ablate, leaving behind layers of metallic atoms and ions. The relative concentration of the various metal layers is not well explained by current models of ablation. Furthermore, estimates of the total flux of cosmic dust and meteoroids entering the Earth’s atmosphere vary over two orders of magnitude. To better constrain these estimates and to better model the metal layers in the mesosphere, an experimental Meteoric Ablation Simulator (MASI) has been developed. Interplanetary Dust Particle (IDP) analogs are subjected to temperature profiles simulating realistic entry heating, to ascertain the differential ablation of relevant metal species. MASI is the first ablation experiment capable of simulating detailed mass, velocity, and entry angle-specific temperature profiles whilst simultaneously tracking the resulting gas-phase ablation products in a time resolved manner. This enables the determination of elemental atmospheric entry yields which consider the mass and size distribution of IDPs. The instrument has also enabled the first direct measurements of differential ablation in a laboratory setting.
these techniques are limited by the requirement for complex enzymatic reactions. As an alternative strategy that bypasses the need for genetic engineering, combinatorial methods can be employed. These can be used to explore tens to hundreds of reaction conditions, where the most promising or "lead" conditions may be selected based on the structures or properties of the resultant material. [ 17,18 ] Lead conditions can then be used to narrow the reaction landscape in successive screening rounds. Surprisingly, although combinatorial methods are often used in solid-state chemistry to explore, for example, different reagent compositions, [ 18 ] we are not aware of their use in identifying soluble additives capable of directing mineralization.In this article we demonstrate how combinatorial methods can be used in conjunction with effi cient screening processes to rapidly identify combinations of small organic molecules that are capable of directing the formation of photoluminescent quantum dot minerals in aqueous solution and at room temperature. Indeed, a key feature of biomineralization processes is that control over mineral formation is achieved using many soluble additives that operate in concert. That this feature has seldom been addressed in bioinspired methods is almost certainly due to the vast number of potential variables, which renders a full, systematic exploration intractable. As a solution to this challenge, we here utilize a genetic algorithm as a bioinspired heuristic that mimics natural evolution. Genetic algorithms use selection, recombination, and mutation strategies to rapidly identify and optimize the combination of conditions (here, soluble additives), which gives rise to materials with target properties. [ 19 ] Using a pipetting robot to prepare reaction sets and a UV-light table to rapidly assess the reactions for the formation of photoluminescent minerals, we are able to rapidly identify the key additives that promote the formation of quantum dot superstructures from one-pot aqueous reactions.Our initial library of organic mediators included 23 components, of which 17 were amino acids and 6 were surfactants. Stock solutions of the amino acids were prepared to initial concentrations of 100 × 10 −3 M , and explored at concentrations ranging from 0.01 to 50 × 10 −3 M , while surfactants were prepared to near their solubility limits in water. Surfactants were included as potential structure-directing agents to drive hierarchical assembly in aqueous solution. The overall screening approach used to identify the key additive set is summarized in Figure 1 . First, library amino acids and surfactants were randomly mixed in 48 wells of a multi-well plate, such that each well contained between 1-6 amino acids and 1-3 surfactants (Figure 1 A). Cadmium chloride and thioacetic acid (as a sulfur source) [ 20 ] were then added to a concentration of 1 × 10 −3 M in all wells, as precursors for CdS. After 3 d the plate was viewed under UV illumination (Figure 1 A) and with a fl uorimetric Biomineralization, whi...
An unusual copper(ii) complex of a highly rigid and bulky ligand (a macrocycle-glyoxal condensate) has been synthesized and investigated via DFT calculations and structural characterisation.
As the bonding in many compounds can be adequately described using localized, two-centre twoelectron bonds, the electronic structure of molecules where such a description is inadequate is often chemically very interesting. Three-centre bond orders provide a useful tool for detecting the presence and analyzing the importance of multicentre and hypervalent effects. To depict the resulting chemical structures, a graphical device is introduced which constructs the chemical connections ab initio from the electronic structure. The three-centre, two-electron bonding in a set of electron-deficient boranes and the three-centre, four-electron bonding in a set of electron-rich xenon fluorides has been analyzed and the approach has been used to test for the occurrence and importance of pseudo-aromatic, closed-loops in polyoxometalates.Scheme 1 Transformation of delocalized molecular orbitals into C-H bond orbitals in methane.
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