Self Assembly Flashcards
What is self-assembly?
Reversible formation of a number of cooperative interactions based on the intrinsic information contained in the components themselves.
Why is self-assembly preferred over conventional organic synthesis?
Inefficient methods via conventional kinetic methods. Self-assembly under thermodynamic control, based on intrinsic stability of the species, and subject to automatic error-checking process.
How does DNA self-assemble?
Self-assembly via formation of hydrogen bonding between residues, recognition occurs via number of H bonds available on each nucleotide: A-T 2 x H bonds, C-G 3 x H bonds.
Entropy destabilising initially but levels off once a sufficient number of degrees of freedom have already been restricted. Enthalpy favourable for each interaction formed. This means that once the first few base pairs have hydrogen bonded, the free energy is negative for subsequent binding and it is now favourable to continue binding - runaway system.
How can fullerene self-assemble?
Fullerence synthesis in a carbon arc furnace - conditions where C-C bond formation is reversible. Isolated pentagons in C60 with closed structure makes C60 particularly stable.
How does insulin self-assemble?
Example of self-assembly with covalent modification. Preproinsulin self-assembles using non-covalent forces placing polypeptide chains A and B adjacent to each other in correct orientation for insulin. They form disulphide bridges to link together and give proinsulin. The excess polypeptide is then removed to give insulin.
What design features need to be inbuilt for abiotic self-assembly?
Supermolecular interactions, example: two C-shaped molecules come together like parts of a tennis ball, linked by 8 hydrogen bonds.
How do you prove that these molecules self-assemble?
Prove that proton NMR signals are down to self-assembly by comparing against analogous species which are unable to self-assemble. Depending on rate of proton exchange, may see two signals or just one shifted cf. reference compounds.
Find the Mr of the compound, e.g. by vapour pressure osmometry or DOSY spectroscopy
X-ray crystallography
Encapsulation in solution - proof by change in chemical shift for guest. Easy example of guest to try is methane as small.
What is the supramolecular cube?
Use of ruthenium complexes to form the corners and pyridine to give edges. Supramolecular cube most thermodynamically stable product as no dangling bonds and relatively unstrained.
What are the platonic and archimedean solids and why are they relevant to self-assembly?
Set of 3D solids that can be generated by attaching one type of face and two types of face respectively. These can be used to generate larger capsules than the cube, with these forming the most stable structures.
What can impact edge-and-node self-assembled Archimedean solids?
Use of bent ligands can enable access to a wider range of solids. By changing the bite angle and length of the attachments, further design can be chosen.
Predicted product will generally be the thermodynamic one, and this can take a long time to form. Smaller assemblies may be formed as kinetic traps.
