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Porphyrins & Related complexes. 200901106 김현지. How do inorganic compounds and ions help cause biochemical reaction?. Promotion of reactions by providing appropriate geometry for breaking of forming bonds tetrahedral, octahedral, square-planar Changes in acid-base activity

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how do inorganic compounds and ions help cause biochemical reaction
How do inorganic compounds and ionshelp cause biochemical reaction?
  • Promotion of reactions by providing appropriate geometry for breaking of forming bonds

tetrahedral, octahedral, square-planar

  • Changes in acid-base activity

water bound to metal ion – more acidic than free water

  • Changes in redox potentials

coordination by different ligands changes redox potentials

4. Some ions(Na+,K+,Ca2+,Cl-) act as specific charge carriers, with concentration gradients maintained and modified by membrane ion pumps and trigger mechanisms

how do inorganic compounds and ions help cause biochemical reaction1
How do inorganic compounds and ionshelp cause biochemical reaction?
  • Organometallic reactions can create species that are otherwise not attainable.
  • Inorganic ions, both cationic and anionic, are sued as structural units to form bone and other hard structures

7. A few small molecules have specific effects that do not fit easily in to any of the categories above

porph ine c 20 h 14 n 4
Porphine , C20H14N4
  • The unsubstituted porphyrin
  • Aromaticity
  • 1. Heterocyclic
  • 2. Planar geometry
  • all the atoms lie in a single plane
  • 3. Completely conjugated
  • Sp2 hybridized carbon atoms
  • 4. 4n+2 pi electrons
porphy rins

Metal ion :

surrounded by the four nitrogens of

a porphine ring in a square-planar

  • Axial sites :
  • available for other ligands


1. side chains

2. Metal ions

3. Surrounding species

result in very different reactions

and roles for these compounds

porphy rins1

① O2 storage and transport

: myoglobinand hemoglobin

② electron transport

: cytochromesb and c

③ O2 activation and utilization

: cytochromeP450 and


porphy rins2


can be substituted 12 Position

8 Position : β position

pyrrolic ring

4 Position : meso position

methine bridge

Symmetry : D2h

green elements known to form complexes with porphyrins red metals found in nature
Green : Elements known to form complexes with porphyrinsRed : Metals found in Nature
iron porphyrins
Iron Porphyrins

Hemoglobin and Myoglobin

: oxygen transfer and storage agents in the blood and muscle tissue.



iron porphyrins1
Iron Porphyrins



(= 4 Heme protein)


(= 1 Heme protein)

iron porphyrins2
Iron Porphyrins

1. Hemoglobin

  • 4Irons can each carry 1O2

One iron binds an oxygen molecule,

  • the molecular shape changes

to make binding of additional oxygen molecules easier

- K4 many time larger than the K1

iron porphyrins3
Iron Porphyrins

1. Hemoglobin

initial removal of oxygen,

the entire load of oxygen is delivered

at the required site.

  • favored by pH changes - Bohr effect
  • ① The concentration CO2 increases,
  • ② Formation of bicarbonate
  • ③ pH to decrease
  • ④ Increased acidity

⑤ Favors release of O2

from the oxyhemoglobin

iron porphyrins4
Iron Porphyrins

2. Myoglobin

similar to a single subunit of hemoglobin

iron porphyrins5
Iron Porphyrins


Myoglobin & Hemoglobin Binding Curves

Myglobin binds O2

more strongly than

the first O2 of Hemoglobin

But fourth equilibrium constant of hemoglobin is larger than that

for myoglobin by a factor of about 50

iron porphyrins6
Iron Porphyrins

1-1. Carboxyhemoglobin

Hemoglobin Fe(II)

: 70pm out of the plane,

typical high-spin d6 ion

  • CarboxyHemoglobin Fe(II)
  • : oxygen or carbon monoxide
  • bond to the sixth position,
  • - the iron becomes coplanar
  • with the porphyrin,
  • - the resulting compound is
  • diamagnetic

CO : strong enough ligand to force spin pairing

resulting pi back-bonding stabilizes the complex.

iron porphyrins7
Iron Porphyrins

1-2. Oxyhemoglobin

Bonding as nearly that of


Metal-to-ligand electron transfer to result in

a simple double bond between the oxygens.

iron porphyrins8
Iron Porphyrins

1-2. Oxyhemoglobin

Molecular Orbital


Strong σ interaction

: dz2 & πgz

Weak πinteraction

  • : dxz & πgx
  • Increased ligand field results
  • In pairing of the electrons & Weakened O-O bond
iron porphyrins9
Iron Porphyrins
  • Cytochromes & Peroxidases & Catalases

Cytochrome P450 catalyzes

: oxidation reactions in the liver - adrenal cortex,

Helping to detoxify some substances by adding hydroxyl groups

- Make the compounds more water soluble

& more susceptible to further reactions

Peroxidases & Catalases

: Fe(III)-hemecompunds

that decompose hydrogen peroxide and organic peroxides

iron porphyrins10
Iron Porphyrins

Hydrogen peroxide made from Fe(III) &triethylenetetramine(trien)

Mechanism of the [Fe(trien)]3+ - H2O2

Tracer studies using

18O-labeled water :

oxygengas from peroxide

Result :

O2 must involve

removal of hydrogen from H2O2

similar ring compounds
Similar Ring Compounds

1. Chlorophylls

  • Chlorin:Porphine ring + one double bond reduced
  • ex )chlorophylls
  • Chlorophylls : green pigments found in plants,
  • containMagnesium
  • and start the process of photosynthesis
  • 2 H2O O2 + 4H+ + 4e-
  • CO2 + 4H+ + 4e- [CH2O] + H2O
  • [CH2O] ; sugars, carbohydrates, cellulose
similar ring compounds1
Similar Ring Compounds

Other compounds containing metal ions

  • ion-sulfur proteins with active sites
  • Involving iron, sulfur, and sulfur-containing amino acids
  • Fe(II) & Fe(III) in tetrahedralsitesbridged by sulfide ions
  • Bound into the protein by Fe-S bonds to the amino acid.
  • Ferredoxins
similar ring compounds2
Similar Ring Compounds

Other compounds containing metal ions

  • Ferredoxins
  • Clostridialferredoxin:
  • two identical Fe-S complexes
  • Cubane structure :
  • 4S, 4Fe in a distorted cube
similar ring compounds3
Similar Ring Compounds

2. Coenzyme B12

(= Vitamin B12 , cyanocobalamin)

Cobaltinto a corrin ring structure

One less =CH- bridge between

the pyrrole rings than the porphyrins

Co(III) ,

4 corrinnitrogens

  • : contribute electrons , charge 2-

the benzimidazole nitrogen

: contributes 2e-

cyanide or adenosine in the sixth position

; contributes 2e- , charge 1-

without sixth ligand : cobalamin

similar ring compounds4
Similar Ring Compounds

2. Coenzyme B12

(= Vitamin B12 , cyanocobalamin)

ex) Alkylcobalamins

depend on cleavage of the alkyl-cobalt bond

  • Co(I) & alkyl cation
  • Co(II) & alkyl radical
  • Co(III) & alkyl anion
  • With the radical mechanism – most common
similar ring compounds5
Similar Ring Compounds

2. Coenzyme B12

(= Vitamin B12 , cyanocabalamin)

alkyl products











Molecular symmetry, David J. Wilock, Wiley p17~18

Biochemistry, Stryer 7ed, P752~755

Inorganic chemistry, Gary L miessler, pearson, p 631~640