Supramolecular Chemistry CH30211 Flashcards
Which nucleotide bases join more strongly?
Guanosine and Cytosine, 3 hydrogen bonds
Guanosine forms a tetraplex through which interactions?
Hydrogen bonding, then pi stacking in a parallel and antiparallel manner
How can a cation be separated from solution?
With a crown ether, binding constant for substrates varies with ring size (e.g. [18]crown-6 strong for potassium)
What is supramolecular chemistry? Why is it important?
The chemistry of intramolecular bonds, important for describing the behaviour and properties of a system
How can a supramolecular system develop?
Host-guest complex or Self assembled aggregates (solid/solution) or latticed complexes (solid)
What is a host-guest interaction?
The binding of a small molecule to a larger molecules binding pocket
What is the lock and key concept?
That guest is geometrically, interactionally and has shape complementarity to the host, allows discrimination between interactions
How is the lock and key argument flawed?
It is misleadingly rigid, underestimating the effects of entropy
What is the induced fit theory?
Guest triggers change in host. Allows host to interact with different (similar) guest
What are the key features to an ion-ion interaction?
Very Strong Attractive or repulsive Non-directional Long range Highly dependent on dielectric constant of the medium
What are the key features to an ion-dipole interaction?
Weak Attractive or repulsive Directional Medium range Highly dependent on dielectric constant of the medium
What are the key feature to a dipole-dipole interaction?
Weak
Directional
Highly dependent on the dielectric constant of the medium
Has been observed in solid-state carbonyls
What are the key features to a cation-pi interaction?
A special subset of dipole-dipole interactions, with a diverse energetic landscape
What are the key features to an anion-pi/anion-pi* interaction?
Very weak
Only in electron-deficient aromatic systems
What are the key features to an pi-pi interaction?
Weak
Directional
Heavily dependent on the dielectric constant of the medium
Heavily influenced by the nature of the pi-system
What are the key features to van der Waals interactions?
Very weak
Non-directional
Dependent on polarizability of the molecule
Minimises void spaces in crystals
What are the key features to closed shell interactions?
Very weak Heavy metal-metal interactions Halogen bonds (polarisable halogens and electronegative atoms)
What are the key features to a hydrogen bond interaction?
Direction interactions with a diverse energy landscape
Attractive and repulsive
Primary and secondary
A special subset of dipole interactions
Ubiquitous in nature, highly dependent on the dielectric constant of the medium
What are the different geometries of hydrogen bonding which may occur?
Linear Bent Donating bifurcated (two acceptors) Accepting bifurcated (two H on donor) Trifurcated (three acceptors) Three centre bifurcated (two H on donor, to three acceptors)
What are strong and weak hydrogen bonds similar to?
Strong hydrogen bonds have near covalent character
Weak hydrogen bonds have near van der Waals character
What is the solvophobic effect?
The tendency of solute particles to cluster as the attractive interaction between solvent particles is strengthened
What are the key features to the solvophobic effect?
Very weak
Ubiquitous
All molecules are solvated at all times
Has enthalpic and entropic factors
What is the effect of the solvophobic effect?
Has enthalpic and entropic factors:
For guest and host to interact, solvation must be overcome
What is enthalpically (un)favourable in guest-host interaction
Unfavoured: Desolvation of host/guest and host rearrangement
Favoured: Complexation and solvation of host
What is entropically (un)favourable in the guest-host interaction?
Unfavoured: solvation of complex
Favoured: desolvation of host/guest
Why is choosing the correct solvent desirable?
In some solvents, different solutes will interact favourable: in other solutes the solvent-solute interaction will dominate preventing the reaction
Give an example of an ion-ion interaction
Negative to positive ion
Give an example of an ion-dipole interaction
Carbonyl to positive ion
Give an example of a dipole-dipole interaction
Carbonyl oxygen, to carbonyl carbon
Give an example of a cation-pi interaction
Positive ion to an aromatic ring, e.g. artificial ion channels
Give an example of an anion-pi interaction
e.g. artificial ion channels
Give an example of a pi-pi interaction
Face-to-face and edge-to-face aromatics.
Repulsion will occur if stacked directly on top
Give an example of hydrogen bonding
Water to water.
AAA opposite DDD will give primary and secondary attractive hydrogen bonding
ADA to DAD will give primary attractive and secondary repulsive hydrogen bonding
