Co-ordination chemistry Flashcards
Ligand
Species that donates one or more pairs of electrons to form a co-ordinate bond to a metal ion
Chelate ligand
A ligand that can bind to a metal ion through more than one donor atom to form a ring
Bidentate
Ligand that can form 2 bonds to a metal ion
Complex ion
A charged co-ordination complex (metal plus its ligands)
What are the 2 types of structural isomers
- co-ordination isomers
* linkage isomers
What is a co-ordination isomer
- when a co-ordination compound contains 2 complex ions
* ie. for [Cr(NH3)][CoF6] the isomer can be [Co(NH3)][CrF6]
What are linkage isomers
Structural isomers that differ in how one or more ligands are attached to the transition metal
• ie. NO2 can bind with N atom or the O atom
What geometric isomers are possible?
• cis/trans
• mer/fac
mer: when on the same plane
fac: different planes
What are siderophores? Give an example
- chelating molecules secreted by micro-organisms that are able to bind Fe ions very strongly
- enterobactin is an example
- lipophilic so can cross cell membranes
- transfers Fe into cells
What are the 2 main sources of iron?
- anaerobic bacteria - in the form Fe2+
2. Aerobic bacteria in surface environments - as Fe3+
What are the 2 forms of iron obtained in human nutrition?
- haem - from meat (blood)
2. non-haem - absorbed 5-10 time slower which is a potential problem for many vegetarians
what form of amino acids are favoured in basic and acidic conditions?
Acidic: cation form
Basic: anion form
What are the two terminals of a protein chain?
N terminus - ammonium
C-terminus - carboxylate
• all have charged termini at pH 7
What are the bonds present is secondary structures and their properties?
- alpha helix - intra-chain H-bonds
- gives elasticity to proteins
- beta pleated sheets
- gives the structure rigidity
What is transferrin?
- Following digestion the absorbed iron is taken up by the ptoein transferring
- transferring is an iron transport protein in blood
- introduces Fe into the iron metabolic processes in the blood
What is the co-ordination environment of Transferrin?
- 2 tyrosines - uninegative
- 1 histidine - neutral ligand
- 1 aspartic acid - uninegative
- completed by an anion such as carbonate which is a buffer found in the blood
Describe how trasnferrin works at a cellular level
- transferrin docks to transferrin receptors on cell surfaces
- metal containing transferrin is taken into the cell where a drop in pH causes release of the Fe3+
- demetalled protein is returned to the outside to look for more iron
Biological roles of transferrin
- iron transport via blood
- bactericidal (significant component of egg whites) - deprives bacteria of Fs, so cannot grow
- these proteins are present in their iron free forms
What is ferritin?
Iron storage protein
• iron is passed form transferrin to ferritin
3 structural features of ferritin
- protein coat or shell
- rust core
- core-protein interface
What is ferritin composed of?
Predominantly FeO(OH) with phosphate
What is the size of the ferritin core and structure?
Core: 70-75Å
Entire structure - 120 Å
How do Fe ions enter ferritin?
through the channels at corners
