Structure of Chlorophyll & Haemoglobin

Structure of Chlorophyll

• Chlorophyll is a green color pigment in green plants and algae.

• It is a magnesium- porphyrin complex.

• It is a square planar complex with Mg2+ the center .

• The magnesium is at the centre of the modified ring septeon (corrin).

• The modified porphyrin acts as the ligand.

• It is a naturally occurring chelate complex of Mg.

Structure Of Hemoglobin

• Blood contains red blood corpuscles or cells .

• About 95% of the dry weight of the red blood cells is composed of hemoglobin ( or haemoglobin)

• 100mL of the blood of a normal male contains approximately 15g of hemoglobin all of which is within the red blood cells.

• Haemoglobin contains about 0.35% of iron and thus there are 50mg of Fe per 100mL blood and 2.5g of iron in the total blood volume of 5000ml in an adult man.

• Haemoglobin is a conjugated protein having molecular weight of 64,500.

• It is a tetramer in and contains four identical units which are arranged roughly in a tetrahedron .

• Each unit contains FOUR identical heme groups.

• Each hemoglobin molecule has four heme groups bound to the globin (a protein) on its surface.

• Fe(II) in hemoglobin is in the high spin state (Fe2+ = 3d6 =t4

2g e2g)

• Thus Fe (II) has four unpaired electrons in hemeglobin molecule.

• The structure of haemoglobin is an octahedral complex of Fe(II).

• The centre of haemoglobin is occupied by Fe(II) and the four corners of the square base are occupied by the four N- atoms of the heme group.

• One axial position is occupied by N-atom of histidine while the other axial positions is occupied by the H2O molecule.

Role of hemoglobin in biological living

systems

• Hemoglobin is very sensitive to O2 and hence readily combines with it

• Thus when we breathe in oxygen, hemoglobin (Hb) present in our body combines reversibly with the oxygen in the lungs to form oxy-hemoglobin (HbO2 )

Haemoglobin + O2 Oxy- hemoglobin ↔ + H2 O

(or) Hb + O2 HbO↔ 2 + H2 O

• The formation of HbO2, is called oxy-genation of hemoglobin.

• In HbO2, Fe is in +3 oxidation state.

• In the formation of HbO2, H2o molecules present at one of the axial positions in hemoglobin are reversibly replaced by O2 molecules.

• As the blood runs through the arteries to the tissues, the oxygen pressure decreases and oxygen gets bound with the hemoglobin is set free.

• This free oxygen diffuses into the body cells where it combines with glucose(food) and oxidizes it into Carbon di oxide and water.

• Thus oxygen is used in the combustion of food.

C6H12O6 + 6O2 6CO→ 2 + 6H20 + 38 ATP

(energy)

• The oxidation of glucose to carbon di oxide is an energy releasing process in which energy in the form of ATP molecules is produced.

• This energy is utilized by the living organisms to perform their various metabolic activities, and for maintaining their body temperature.

• Water produced in the above reaction is retained in the body while decomposes to give carbon di oxide and hemoglobin.

• Carbon di oxide is exhaled out and the haemglobin goes to the lungs for reuse.

• The above discussion makes it evident that the functions of hemoglobin in our body is to supply oxygen to various parts of the body.

• Thus hemoglobin is an oxygen – carrier.

• In the oxygenation of a hemoglobin molecule, a proton, (H+ ) is also produced.

• This proton reacts with bicarbonate dissolved in the blood to liberate carbon di oxide.

HCO-3 + H+ ↔ H2 CO3 H↔ 2O + CO2

CO2 liberated as above is exhausted out.

References1.Advanced Inorganic Chemistry, Vol II , Satya

Prakash ,G.D.Tuli, S.K.Basu, R.D.Madan.

2.Advanced Inorganic Chemistry, Gurudeep Raj