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Applications of Organic and Bioinorganic Chemistry > Metal ions in Biochemistry & Coordination Chemistry > Flashcards

Metal ions in Biochemistry & Coordination Chemistry Flashcards

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1
Q

What are the roles of metal ions ?

A
  • Charge carrier
  • Osmotic balance
  • Triggers (nerve signalling and muscle contraction)
  • Structural (bones and proteins)
  • Catalysts
  • Transport and storage (i.e. O2)
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2
Q

Bulk metals used by nature ?

A
  • Make up 1% of the human body weight

- Na+, Mg2+, K+ and Ca2+

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3
Q

Trace metals used by nature?

A

V, Cr, Mn, Fe, Co, Ni, Cu, ZN, Mo an W

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4
Q

Specific role of Na and K ?

A
  • Charge carrier

- Osmotic balance

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5
Q

Specific role of Mg ?

A
  • Structural role

- Hydrolytic cleavage

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6
Q

Specific role of Ca ?

A
  • Structural role
  • Trigger
  • Charge carrier
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7
Q

Specific role of Zn ?

A
  • Structural role

- Hydrolytic cleavage

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8
Q

Specific role of Fe and Cu ?

A
  • O2 transport, storage and/or activation
  • Electron transport
  • Superoxide (O3-) breakdown
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9
Q

Specific role of Mo ?

A
  • Oxo (O) transfer

- N2 activation

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10
Q

Specific role of Ni ?

A
  • Methane (CH4) production
  • H2 activation
  • Hydrolysis
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11
Q

Specific role of Mn ?

A
  • O2 evolution
  • Peroxide breakdown
  • Superoxide breakdown
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12
Q

Specific role of Co ?

A
  • Free radical reactions

- Nucleophilic metal ion

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13
Q

What is the job of P and S ?

A

PO3R2- and SO3R- make organic (CHNO) compounds soluble in water as anions

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14
Q

What is the job of Na+ and K+?

A
  • Counterions and electrical carriers – can’t use Ca2+ or Al3+ as these would precipitate organic anions
  • Also serve as messengers, activating Na+ or K+ specific ATPases
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15
Q

What is the job of Mg2+ ?

A

Used as a weak Lewis acid inside cell and binds to anionic surfaces such as RNA and ribosomes

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16
Q

What is the job of Ca2+ ?

A

Kept out of cell and is used as a temporary reflux trigger (i.e. nerve impulses)

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17
Q

What does the number of available oxidation states help predict ?

A

Some of the roles of the metal

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18
Q

Irving-Williams Series ?

A
  • Relative stability of metal complexes
  • Mn(II) < Fe(II) < Co(II) < Ni(II) < Cu(II) > Zn(II)
  • The ionic radius is expected to decrease regularly for Mn2+ to Zn2+
  • Stability increases in this order
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19
Q

Metal ions do not freely exist in nature, they are always surrounded by ?

A

Ligands, from simple like H20 to more complex haems

20
Q

For instance, whenever metals dissolve in water, they are hydrated (coordinated) by ? to form ?

A

For instance, whenever metals dissolve in water, they are hydrated (coordinated) by water molecules to form a charged complex

21
Q

What does the water ‘complex’ contain ?

A

The water ‘complex’ has a positive charge (n+) and requires anions for charge
balance

22
Q

What is a Lewis acid and a Lewis base ?

A
  • Lewis acid = Electron pair acceptor
    i. e. metal ions
  • Lewis base = electron pair donor
    i. e. ligands
23
Q

What are Soft acids and bases?

A

Large species that are easily polarisable (think of a bean bag)

24
Q

What are Hard acids and bases?

A

Small species that are not easily polarised (think of a marble)

25
Q

L (Lewis base) must have electrons to ‘donate’ to ?

A

M (Lewis acid)

26
Q

What can a Lewis base either be ?

A

Neutral (uncharged) or charged (usually negative, e.g. CN-)

27
Q

In water, what is the most common ligand ?

A

Water

28
Q

What is a complex ion ?

A

When the coordination complex carries a charge

29
Q

In regards to the periodic table, where is the electronegativity the highest?

A
  • Electronegativity is higher on the right side of the periodic table
  • Electronegativity is higher on the top of the periodic table
30
Q

Explain electronegativity in ionic bonds ?

A

Large electronegativity difference

31
Q

Explain electronegativity in covalent bonds ?

A

Small electronegativity difference

32
Q

What is meant by the coordination number and oxidation ?

A
  • Coordination number: the number of ligands bound to the metal
  • Oxidation state: the charge of the ‘free’ metal ion
33
Q

What is the most common coordination environment ?

A

Octahedral (Coordination number: 6)

34
Q

What is important to note in regards to the octahedral geometry and it’s ligands ?

A

In octahedral geometry, the ligands lie on the axis. Thus, the orbitals that are on the axis (dz2 and dx2-y2) are higher in energy than the ones that lie in-between the axis (dzx, dyz, and dxy). In a sense, the orbitals on the axis are essentially ‘repelled’ by the electrons of the ligand

35
Q

What is meant by Δo ?

A
  • The energy difference between the two levels (ligand-field splitting)
  • The magnitude of Δo is ligand dependent
36
Q

What does the size of Δ depend on ?

A

Depends on L (Lewis base)

37
Q

What are ligands causing a small Δ called ?

A

Low field ligands (H20)

38
Q

What are ligands causing a large Δ called ?

A

High field ligands (CN-), forces electrons into lower levels

39
Q

What gives metal complexes magnetic properties ?

A

Unpaired electrons

40
Q

Addition of a cyanide solution to a colourless [Fe(H2O)6]2+ aquo solution results in ?

A

The appearance of a blue colour (technically this may be spin forbidden)

41
Q

The excitation of an electron in [Fe(CN)6]4- is responsible for ?

A

The blue colour of this complex

42
Q

What are colours in solution sometimes caused by ?

A

Excitation of lower energy to higher energy d orbitals

43
Q

The ability of ligands to spit the d orbitals varies according to ?

A

The spectrochemical series (ligands based on the strength of their interaction with metal ions)

44
Q

What is meant by weak field ligands ?

A

Ligands that cause a transition metal to have a small crystal field splitting, which leads to high spin

45
Q

What is meant by strong field ligands ?

A

Ligands that produce a large crystal field splitting, which leads to low spin

46
Q

What is the Chelate effect ?

A

Entropy favours multi-dentate ligands over monodentate ligands

Applications of Organic and Bioinorganic Chemistry (6 decks)

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