1. The document discusses electrochemistry and its application to proteins. It examines how electrochemical parameters like pH, potential difference, and electrode material can be varied to selectively modify amino acids in proteins. 2. It also discusses electron transfer reactions in proteins, noting that proteins contain redox-active groups that facilitate intramolecular charge transport and electron exchange. Special orientations of the protein on electrode surfaces and use of mediators are often required. 3. The kinetics of electron transfer in proteins is slow due to diffusion limitations and the need to overcome reorganization energy for electron transfer to occur. Marcus theory provides an explanation for electron transfer rates.

1. Mr.Halavath Ramesh
16-MCH-001
Department of Chemistry
Loyola College, Chennai.

2. The majority of electrochemical studies of biomolecules have been analytical in nature, usually
involving electron transfer by redox protein. Synthetic applications of electrochemistry to proteins,
leading to the production of recoverable products, has been far less widely studied. However, the
use of proteins in electro synthesis, exemplified by hen egg-white Lysozyme, demonstrates that the
reaction parameters of pH, potential difference, electrodematerial etc., can be varied in order to
target different individual amino acid residues including tyrosine, tryptophan and methionine. This
methodology provides a novel route to quantities of selectively-modified proteins.
WALTON AND HEPTINSTALL Electrochemistry is the study of systems that involve
an electron-transfer step at an electrode as part of the process. There may be chemical reactions
that accompany electron transfer, or sometimes precede it, as well as associated phenomena such as
adsorption or other effects at the heterogeneous interface between the electrolyte and electrode.
Moreover, there may also be more than one electron-transfer step in any particular electrochemical
mechanism.
Proteins have evolved over billions of years into structures capable of precise
reactions, including highly specific substrate recognition, analyte binding , and facile and
directional electron tunneling. In addition, proteins are essential to many chemical processes
essential to life, such as photosynthesis, respiration, water oxidation , Molecular oxygen
reducation,and Nitrogen fixation. One application is in Bio-catalysis in synthetic organic
chemistry. The high chemo,regio and stereo-selectivity of enzymes negates the need for protecting
groups, and thus reduces synthetic steps and simplifies work flow.

3. Electrochemistry: Electrochemistry deals with the interaction between electrical energy and
Chemical change.
Bioelectrochemistry: Bioelectrochemistry is a branch of electrochemistry and biophysical
chemistry concerned with electrophysiological topics like cell electron protons transport , cell
membrane potentials and electrode reactions of redox enzymes.
1. Redox active proteins contain redox active groups(e.g.FAD,FMN or Heme groups) as part of a
coenzyme .These coenzyme are surround by the major non-redox active part of the protein the
so called Apoenzyme.
2. Coenzyme and apoenzyme can be covalently linked in some proteins but they don’t have to.
3. Therefore one irreversible process in protein electrochemistry could be the loss of a co factor.
Slow rate of electron transfer to or within proteins.
A special orientation protein –electrode has to be achieved(e.g. modification of the of the
electrode surface is necessary)
Adsorption at the electrode surface
Therefore protein samples should be purified very carefully. Special modified electrode surface
have to be applied.
Slow diffusion of the protein
Some redox active electron carriers i.e, mediators have to be used. Also modification of the
electrode surface is helpful.
ET reactions often are couple with proton transfer
The redox potential are strongly PH dependant .

4. Electron Transfer (ET) and Electron Transport(ETp) in Proteins
Electron flow through a protein molecules involves intra molecular charge transport
and electron exchange with the surroundings. These two distinct and widely studied
processes can not be unambiguously separated sinces the interface of a molecules with
an adjacent electrode or ionic solution can have a profound influence on the molecular
properties and hence on the molecules electrical conductance.
The process of directed electron motion or electron flow through molecular
structure is termed electron transport or electron transfer , depending on the
environment in which it occurs. In the discussion below , we donates as electron
transfer (ET) the electron flow process with all or part of the protein in direct contact
with an electrolyte , which is ionically conducting and which can function as an
electron sink or source via redox process. The electrolyte also provides charges, which
screen the change in electrical potential due to the electron flow. Electron flow in
which an electrolyte is absent or does not participate in the electron flow process, with
electrodes that are not ion conductors , is termed electron transport(ETp). Etp is
usually measured in a solid state configuration. In Etp normally there is no possibility
for charge balance via ions from an electrolyte while ET involves a surrounding
medium with mobile ions which can provide such charge balance.

5. Electrode Materials
Common electrode materials are mercury ,Gold, Platin,Silver,Nickel,Metaloxides(e.g.ito)
Carbon materials.
In 1977 a well defined one electron reduction Fe(III)/Fe(II) in Cytochrome C was
observed at a gold electrode modified by 4,4-bipyridyl serving as a promoter at the
electrode surface.
Modified Electrodes
1. Adsorption of Thiols/Disulphides on Au/Pt.
2. Coating with lipid biolayers containing immobilized proteins.
3. Electro polymerization
4. Covalent attachment.
Electrochemical Reaction
Transfer of electron-Electricity
Zn(s) + Cu+2(aq) = Zn+2(aq) + Cu(s)
Anode: Oxidation-Donation of electron-half cell reaction
Zn(s) -2e- = Zn+2 (aq)
Cathode: Reduction-gaining of electrons-half cell reaction.
Cu+2(aq) + 2e- = Cu(s)
Electrolytic medium:
Elimination of migration current.

6. Electrochemical Cell
1.Electrolytic cell:
Electrical energy ------> chemical energy
2. Voltaic Cell:
Chemical energy……..> Electrical energy
Electrochemical Cell –Current
1.Diffusion Current: Concentration gradient
2. Migration Current: Moment of charged particles along an electric field.
3.Convection Current: Physical movement-stirring.
Theory-Nernst Equation
Ecell = Eo cell-RT log Q

7. Cell Potential: The cell potential is the way in which we can measure how much
voltage exists between the two half cells of a battery.

13. Marcus Theory
Marcus theory is a theory originally developed by Rudolph A. Marcus, starting in 1956,
to explain the rate of electron transfer reactions – the rate at which an electron can
move or jump from one chemical species (called the electron donor to another (called
electron acceptor).