electrochemical potential:
a measure of the energy change upon transfer of
electrons in an oxidation reduction reaction; the measured voltage of
an electrochemical cell; the tendency to drive a redox reaction forward.
This potential can be measured with a voltmeter and a salt bridge between
half cells.
electron spin:
the magnetic field associated with a single electron. Covalent
bonds are composed of two electrons each. The pair must be of opposite
spin to be allowed in the same molecular orbital. Free radicals have one
or more unpaired electrons and are therefore also paramagnetic.
electron transfer:
the movement of electron(s) from one molecule to the other;
an oxidation reduction reaction in which the reductant donates electron(s)
to the oxidant which accepts them.
electron transport chain:
a series or cascade of electron transfers;
a sequential movement of electron(s) from an some primary donor to
some final acceptor; a shuttle system for electrons.
electrophile:
a reactive molecule or group which is attracted towards and
tends to react with the more electron rich portion of another molecule.
Electrophiles can be cations, oxidants, free radicals, or the positive
side of a dipole.
emodin:
an anthroquinone found in cascara, senna, and other medicinal herbs.
It has antiinfective and possibly antineoplastic effects. The glycoside
of emodin is known for its cathartic effects.
endoperoxide:
an organic molecule having two oxygen atoms bound in series as
part of a ring structure, the remaining ring members being carbon atoms.
enediol (R-COH=COH-R):
a reactive group composed of two carbon atoms
connected by a double bond and having a hydroxyl group bound to each
carbon atom. This structure often behaves as a medium strength reductant
which can give up one or two hydrogen atoms. Losing two hydrogen atoms
produces an alpha-dicarbonyl compound (R-CO-CO-R). This can usually be
reduced again and converted back into an enediol.
ene reaction:
the reaction of singlet oxygen with an olefin so as to produce
a hydroperoxide.
enol (C=COH-):
a molecular configuration composed of two carbon atoms
connected by a double bond with a hydroxyl group at one of the carbon
atoms. This structure can tautomerize to become a ketone (CH-C=O).
enzyme:
a naturally occurring catalyst in living things; a protein which
catalyses biochemical reactions. Enzymes require substrates which are
the reactants upon which they act. Many require cofactors to become
active. Many can be modulated by ambient conditions such as pH, redox
potential, or the presence of specific inhibitors.
epoxide:
a heterocyclic three element ring consisting of two carbon atoms and
one oxygen atom. The sigma bonds of the oxygen atom resemble an ether
linkage, except that they are under considerably more angular strain
and are less stable. Epoxides can be cleaved by acidic or alkaline
solutions and can form various addition products. They can be produced
by the addition of one atom of oxygen to an olefin, either from
chlorine dioxide or occassionally from ozone. Epoxides are also
produced in vivo by action of the cytochrome P450 enzyme complex,
which adds one atom of oxygen to the carbon carbon double bond of an
aromatic xenobiotic. The resultant epoxide usually rapidly and
spontaneously rearranges to form a phenolic compound.
ethylene bridge:
a link between two parts of an organic molecule composed
of two carbon atoms bound in between by a double bond.
ethylene diamine tetraacetic acid (EDTA):
a chelating agent possessing two
tertiary amino groups and four carboxyl groups. Together these provide
six ligands which bind numerous metal cations.
