Co-ordination chemistry

Question 1

Ligand

Answer 1

Species that donates one or more pairs of electrons to form a co-ordinate bond to a metal ion

Question 2

Chelate ligand

Answer 2

A ligand that can bind to a metal ion through more than one donor atom to form a ring

Question 3

Bidentate

Answer 3

Ligand that can form 2 bonds to a metal ion

Question 4

Complex ion

Answer 4

A charged co-ordination complex (metal plus its ligands)

Question 5

What are the 2 types of structural isomers

Answer 5

• co-ordination isomers

* linkage isomers

Question 6

What is a co-ordination isomer

Answer 6

• when a co-ordination compound contains 2 complex ions

* ie. for [Cr(NH3)][CoF6] the isomer can be [Co(NH3)][CrF6]

Question 7

What are linkage isomers

Answer 7

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

Question 8

What geometric isomers are possible?

Answer 8

• cis/trans
• mer/fac
mer: when on the same plane
fac: different planes

Question 9

What are siderophores? Give an example

Answer 9

• 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

Question 10

What are the 2 main sources of iron?

Answer 10

1. anaerobic bacteria - in the form Fe2+

2. Aerobic bacteria in surface environments - as Fe3+

Question 11

What are the 2 forms of iron obtained in human nutrition?

Answer 11

1. haem - from meat (blood)

2. non-haem - absorbed 5-10 time slower which is a potential problem for many vegetarians

Question 12

what form of amino acids are favoured in basic and acidic conditions?

Answer 12

Acidic: cation form
Basic: anion form

Question 13

What are the two terminals of a protein chain?

Answer 13

N terminus - ammonium

C-terminus - carboxylate

• all have charged termini at pH 7

Question 14

What are the bonds present is secondary structures and their properties?

Answer 14

• alpha helix - intra-chain H-bonds
• gives elasticity to proteins
• beta pleated sheets
• gives the structure rigidity

Question 15

What is transferrin?

Answer 15

• 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

Question 16

What is the co-ordination environment of Transferrin?

Answer 16

• 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

Question 17

Describe how trasnferrin works at a cellular level

Answer 17

• 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

Question 18

Biological roles of transferrin

Answer 18

• 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

Question 19

What is ferritin?

Answer 19

Iron storage protein

• iron is passed form transferrin to ferritin

Question 20

3 structural features of ferritin

Answer 20

• protein coat or shell
• rust core
• core-protein interface

Question 21

What is ferritin composed of?

Answer 21

Predominantly FeO(OH) with phosphate

Question 22

What is the size of the ferritin core and structure?

Answer 22

Core: 70-75Å

Entire structure - 120 Å

Question 23

How do Fe ions enter ferritin?

Answer 23

through the channels at corners