Metal ion catalysis involves the use of metal ions like Fe2+, Cu2+, Zn2+, Mn2+, Co3+, Ni3+, and Mo6+ to enhance the reactivity of chemical reactions. About 1/3 of all known enzymes use metal ion catalysis. Metal ions act as Lewis acids and form complexes with reactants to facilitate catalysis. Examples include hemoglobin which uses iron to bind oxygen, and carbonic anhydrase which uses zinc to catalyze the hydration of carbon dioxide. Platinum ions can catalyze hydrosilylation reactions but also have disadvantages like side reactions and requiring harsh conditions.

2. METALION CATALYSIS
By SAMEEN FATIMA
ROLL NO. 908529

3. CONTENT
METAL ION CATALYSIS (A bit introduction)
EXAMPLE
CLASSES
METAL ION OR ELECTROSTATIC CATALYSIS -
STABILIZATION OF ITS CHARGE
 METALION CATALYSIS WTH COMPLETE
ORIENTATION
 METAL ION CATALYSIS -
DECREASING pKa OF WATER
 DISADVANTAGES
EXAMPLE OF PLATINUIM ION CATALYST

4. METAL ION CATALYSIS
• Metal ion catalysis is also called electrostatic catalysis. It is a
specific process or reaction in which metal ions are used to
enhance the reactivity of a reaction. In this process some
metalloenzymes are used to go on a catalytic pathway in this
reaction same metal ions i.e.: Fe2+, Cu2+, Zn2+, Mn2+, Co3+,
Ni3+, Mo6+ etc. are used. [1]
Almost 1/3 enzymes from the known percentage of enzymes
are worked on the metal ion catalysis process. [2]
• Metal ions always act as a complex system with the reactant
while doing the catalytic process. And also called the Lewis
acids.

5. Examples
• Here the metal ion act as the electrophilic catalyst.
• Hemoglobin is an honorary enzyme. Oxygen binds to the iron in
the heme, forming an octahedral iron complex. This form is called
oxyhemoglobin; the form without the bound oxygen is called
deoxyhemoglobin.
[3]
d+
means
partial
positive

6. [4]
• Here the metal ion act as the metal ion acted as the catalyst and
formed complex system. The catalyst is Lewis acids.
[5]

7. METAL ION CATALYSIS -
DECREASINGpKaOFWATER
[6]
For instance, the water molecule in the pentammineaquacobalt(III)
ion has a pKa of 6.6, compared to pure water, with a pKa of 15.7.
(To calculate the latter, write the equilibrium expression for water:
H2O + H2O <==> H3O+ + OH- . Then write the Ka expression, as
for a generic acid, which is [H3O+][ OH-]/ [H2O] = 10-14/55.5.
The pKa is 15.7). The complexed hydroxide is a better
nucleophile than bulk water.

8. Classes
There are two classes of metal ion_ requiring enzymes that can
be distinguished on the basis of their working strength:
METALLOENYMES: Contain tightly bound metal ions
(Fe2+, Cu2+, Zn2+, Mn2+, Co3+ etc.).
METALACTIVATED ENZYMES: Loosely binds metal ions
from solution (Na+, K+, Mg2+, Ca2+).
Here are some ways through which a metal ion acts as catalyst:
• By binding to substrate to orient them properly for reaction.
• By mediating oxidation- reduction reaction through reversible
changes in the metal ions oxidation state.
• By electro-stating stabilizing and shielding negative charges.
• Often the metal ion act as similar to proton or polarizes water
to generate OH. [7]

9. METAL ION OR ELECTROSTATIC
CATALYSIS - STABILIZATION OF ITS
CHARGE
• The decarboxylation of dimethyl oxaloacetate can be catalyzed
by either Cu2+/Al3+.
This happens when the metal ion complexes with the two oxygen
atom of reactant, the decarboxylation of the reaction increases
by the presences of catalyst hence it formed the carbonyl group.
[8]

10. METALION CATALYSIS WTH
COMPLETE ORIENTATION
Carbonic anhydrase is a zinc-containing enzyme that catalyzes the
reversible hydration of carbon dioxide. [9]

11. EXAMPLE OF PLATINUIM ION CATALYST:
Hydrosilylation reactions, the (commonly) anti-Markovnikov
additions of silanes to unsaturated bonds present in compounds such
as alkenes and alkynes, offer numerous unique and advantageous
properties for the preparation of polymeric materials, such as high
yields and stereoselectivity. These reactions require to be catalyzed,
for which platinum compounds were used
in the initial stages.
[10]

12. In spite of the high utility in industry, however, it is known that the
platinum catalysts still suffer from a number of drawbacks. For
example, platinum-catalysed hydrosilylation of olefins is often
accompanied by side reactions, such as dehydrogenative silylation,
hydrogenation of olefins, isomerization of olefins, olefin
oligomerization and redistribution of hydrosilanes.
[11]

13. The reaction conditions are often harsh, using
high temperatures and elevated pressures, with
hurdles related to catalyst leeching, reactor
corrosion and by-product formation.
DISADVANTAGES:

14. REFERENCE
https://www.studocu.com/row/document/jamia-millia-islamia/biochemistry/metal-
ion-catalysis/19168471 [1]
https://www.slideshare.net/nourtamim/catalysis-mechanisms [2]
https://onlinelibrary.wiley.com/doi/abs/10.1002/med.21301 [3]
https://chem.libretexts.org/Bookshelves/General_Chemistry/Book%3A_Structure_and
_Reactivity_in_Organic_Biological_and_Inorganic_Chemistry_%28Schaller%29/V%3A__
Reactivity_in_Organic_Biological_and_Inorganic_Chemistry_3/04%3A_Oxygen_Binding
_and_Reduction/4.02%3A_Oxygen_Binding [4]
https://www.studocu.com/row/document/jamia-millia-islamia/biochemistry/metal-
ion-catalysis/19168471 [5]
https://chem.libretexts.org/Courses/CSU_Chico/CSU_Chico%3A_CHEM_451__Biochem
istry_I/CHEM_451_Test/09%3A_Catalysis/9.1%3A_A._Methods_of_Catalysis/A2.__Met
al_Ion_or_Electrostatic_Catalysis [6]
https://www.slideshare.net/nourtamim/catalysis-mechanisms [7]
https://www.studocu.com/row/document/jamia-millia-islamia/biochemistry/metal-
ion-catalysis/19168471 [8]
PPT - Chapter 15 Enzymatic Catalysis PowerPoint Presentation, free download -
ID:484310 (slideserve.com) [9]
https://www.researchgate.net/publication/320562283_Fifty_Years_of_Hydrosilylation_
in_Polymer_Science_A_Review_of_Current_Trends_of_Low-Cost_Transition-
Metal_and_MetalFree_Catalysts_NonThermally_Triggered_Hydrosilylation_Reactions_
and_Industrial_Appl [10]
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