Bio-inorganic chemistry of Iron, Copper and Chrominiuma and difference between first row and other rows of transition metal.

Primary valency.

Primary valence corresponds to an oxidation state of the metal ion. This is also referred as ionizable valency.

For example, in the complex [Co(NH₃)₆]Cl₃, the six NH₃ molecules are attached to the central metal ion (CO³⁺) and acts as secondary valency.The primary valency I,e oxidations state of +3 is satisfied by three cl^- ions.

Secondary valency.

It is also termed as coordination number of the central metal ion. It is non- ionizable .It is more or less fixed depending upon the central metal atom.

Bio-inorganic chemistry of Iron Fe.

Iron is essential in the small amount of both plants and animals life but it is toxic in large quantity. Biologically iron is most important transition metal It involves several different processes.

1. Haemoglobin

Haemoglobin contains iron.It acts as the oxygen carrier in the blood of mammals, birds and fishes.

2. Myoglobin

Myoglobin also contains iron which acts as oxygen storage in muscle tissue.

3. Cytochrome and ferredoxins.

Also, contain iron.Cytochrome act as an electron carries in plants, animals, and bacteria.Similarily ferredoxins act as the electron carrier in plants and animals.

4. Ferritin and transferrin.

Transferrin serves as storage and scavenging of iron in mammals.

5. As nitrogenase.

As nitrogenase, the enzyme used in nitrogen fixation found in bacteria.

6. It also acts as a number of other enzymes such as aldehyde oxidase (oxidation of aldehyde), catalase, and peroxidase(decomposition of H₂O₂, Succinic dehydrogenase, aerobic oxidation of carbohydrate, ribonucleotide reductase (reduces ribose to deoxyribose, DNA biosynthesis etc.

7. Iron is also the metal used at the active side of many important redox enzymes dealing with cellular respiration and oxidation-reduction in many plants and animals.

Bio-inorganic chemistry of chromium.

A trace amount of chromium is necessary for the diet of mammals. Chromium III and insulin are both involve in maintaining the correct level of glucose in the blood. In a case of Chromium deficiency glucose is only removed from the blood.Half as fast as normally.Some cases of diabetes may reflect faulty metabolism of chromium. The most important medical aspect of chromium salt like K₂Cr₂O₇ Potassium chromate is that larger amount either ingested or in the toxic on the skin are carcinogenic.Some of the biological importance of chromium are listed as below.

1. A trace amount of chromium is necessary for the daily diet of mammals.
2. Chromium interacts with the thyroid metabolism in human.
3. Bonding of chromium Cr III with nucleic acid has been found to stimulate the DNA-dependent RNA synthesis.
4. The chromium III acts with insulin in the first step of metabolism of sugar entry into the cell and facilitates the interaction of insulin with its receptors on the cell surface.Hence, chromium III and insulin are involved in maintaining the correct level of sugar or glucose in the blood.
5. A Large amount of Cr (VI) is carcinogenic to skin.

Bio-inorganic chemistry of copper.

Copper is essential to life. Biologically copper is considered as the most important essentially metal which is present about 100mg in an adult in a human body.It’s present in small amount is essential whereas the larger amount is toxic. Deficiency of copper in animals results in the inability to use. Iron store in the liver and the animals suffer from anaemia. Copper is bonded to protein in the body either as metalloprotein or as enzymes.

For example include as amine oxidase, cytochrome oxidase etc.

Some of the important biological function of a copper are given as below.

1. About 4-5 mg of copper is required in a daily diet which deficiency causes anaemia like symptoms, neutropenia, bone abnormalities etc.
2. Copper is a key constituent of the respiration enzymes complex, cytochrome c, oxidase.
3. Copper is a constituent of blood pigments haemocyanin in fish and other vertebrates.
4. The copper is bonded to proteins in the body either as metalloenzyme or as metalloproteins such as amine oxidase oxidation of amine, Ascorbate oxidase (oxidation of ascorbic acid).
5. It is also important in lysine oxidase to affect the elasticity of aortic wall, dopamine hydroxylase (affect the brain function), Tyrosine (affect the skin pigmentation) etc.
6. Copper containing proteins and several blue copper proteins act as electron transfer agents and several living beings.
7. Ceruloplasmin which plays a role in iron metabolism.

Comparison between the 3d, 4d and 5d series transition element.

The several properties among 3d, 4d and 5d series transition element differ with each other due to the total charge on their size and other several periodic properties Some of the properties are as discussed as below.

a. Electronic configuration.

Most of the first-row transition element have regular electronic configuration I,e (n-1) d ^{1to 10} ns² but two elements namely chromium (3d⁵4s¹) and copper (3d¹⁰ 4s⁴) differ from a regular configuration.

In the second transition series, some elements like Nb(Niobium) Mo, Ru, Rh, Pd and Ag have irregular electronic configuration and platinum (pt) and Au in 3^rd series also shows irregular configuration.These irregularities are due to special stability associated with half filled and fulfilled (n-1) d orbitals.

b. Reactivity of element.

The reactivity among the transition series element generally decreased in the group from 1^st transition series to 3^rd transition series due to the increased charge density.

c. Stability of oxidation state.

Since the transition metal element shows the variable oxidation state however the lower oxidation state becomes progressively less stable and higher ones more stable on moving from 1^st transition series to 3^rd transition series.

The maximum oxidation state in 3d transition series is exhibited by Mn^+7. Whereas the Ruthenium Ru in 4d and Osmium in 5d series shows maximum oxidation state of (+8) in their tetraoxides (MO)₄.

d. Stability of complex.

Elements of 1^st transition series form more stable complexes with oxygen , nitrogen and fluorine donors while those of the 2^nd,and 3^rd series form more stable complexes with P, S, and heavier halogens donors.

e. Metal-Metal bonding and cluster compounds.

The metal-metal bonding to form the cluster compounds is more prominent in 4d and 5d series element than in 3d series element, however, some carbonyl compounds of 3d series with M-N bonding are common such as Mn₂(CO)_1o, Fe₂(CO)₉ etc.

Reference.

F.A.Cotton and Wilkinson G. Basic inorganic Chemistry. John,Wiley and Sons (Asia), 2007.

Lee., J.D. Concise Inorganic Chemistry. fifth edition. New Delhi: Oxford University Press., 2008.

Sharma, M.L and P.N Chaudhary. A textbook of B.S.C chemistry. Kathmandu Nepal: Ekta Books Thapathali Kathmandu, 2011.