Lecture 2 Flashcards
What are Macrocyclic ligand/ prosthetic ligands?
- additional non-amino acid components of proteins which are essential for their biological function
- all partially unsaturated
- tetradentate
- tetrapyrroles
- bind strongly to specific metal ions in their deprotonated forms
Characteristics of macrocyclic ligands
aromatic systems (18 pi electrons) very rigid and planar/close to planar intensely coloured compounds
What is a nucleic acid?
A protein made of nucleotide segments e.g. ATP, RNA, DNA
What are the potential binding sites for metal on a nucleic acid?
1) Phosphate oxygen atoms
2) Sugar hydroxyl groups
3) The nucleobase (A G T or C) from oxygen or nitrogen
What is hard/soft acid-base theory:
- Lewis acids and bases can be defined as hard or soft
- Hard/hard and soft/soft interactions are favoured
- Hard refers to strongly basic groups with high proton affinity, with anything else being classed as soft
- Hard is charge dominated, soft is orbital dominated
What is the macrocyclic effect?
- Although Metal- Amino acid bonding is thermodynamically stable it is kinetically labile
- macrocycles are used to make exchange reactions kinetically stable
- all 4 bonds to the macrocycle must be broken simultaneously for a reaction to occur which is unlikely due to the rigidity of tetrapyrroles
What ions are macrocyclic ligands selective towards?
Spherical ions with a radius of 0.6-0.7 amstrong, larger ions can sometimes bind out of plane, with smaller ions can’t bind to all 4 nitrogens at once so are leached out of the complex
What is the primary structure of a protein?
The sequence of amino acids that make up the protien
What is secondary structure? What are the two main types of secondary structure?
- secondary structure is ‘the local conformation extended over groups of a few adjacent amino acids.
- hydrogen bonding between NH and C=O regions of the proteins lead to alpha help or beta sheet regions
Which groups favour the alpha helix?
Lysine and aniline
What are properties of the alpha helix?
- mobility like sprigs/screws
- convert processes happening at metal site to biological changes
- one small change can affect the structure of the whole enzyme
What are the properties of a beta sheet?
- confermational rigidity
- can provide strain to modify the properties of a metal ion
What is tertiary structure? Give some examples.
- the overall structure of the biopolymer
- K+ channels in cell membranes, flexible with channel expanding and contracting to allow ion movement
- plastocyanin the e- carrier in chloroplasts. More rigid, coordinatively unsaturated with distorted ligand sites
Describe metal centres in metalloprotiens
- often coordinatively unsaturated with an open site for binding during catalysis
- environment is often unsymmetrical causing distorted coordination geometries
What are enzymes?
- natural catalysts which lower Ea and cause a reaction to be up to 10^20 times faster
- Can be specific to a certain stereoisomer and reaction or carry out a series of similar reactions
