Organic Chemicals in the
Environment
Where are they found?
What are the effects do they have?
Surface effects
Membranes
Waxes
Foams
Soil - Humus
The air-water interface
The surface tension of water is 0.073 N/m. Ions can increase
this value somewhat to 0.075 N/m. However, organic
compounds Tend to lower the value. The surface tension of
organic liquids (e.g. octane, benzene etc.) range from
0.020 to 0.050 N/m.
There are two types of surface adlayers on water.
1. Organic thin films such as oil spills (prior to oxidative
weathering). These compounds are both insoluble and
less dense than water.
2. Surfactants are amphipathic molecules. There are dry
surfactants such as detergents (mostly hydrophobic) and
wet surfactants such as proteins (mostly hydrophilic).
Surface tension
Liquids tend to adopt shapes that minimize their surface area.
This places the maximum number of molecules in the bulk.
Droplets of liquids tend to be spherical because a sphere is
the shape with the smallest surface-to-volume ratio. The work
needed to change the area by dσ is:
dw = γdσ
The coefficient γ is called the surface tension. It has
dimensions of energy per unit area (J/m

groups indicated.
The fluid mosaic model of membranes
Biochemistry of Lipids, Lipoproteins
and Membranes, Vance & Vance, Elsevier 1996
Plasma membrane
Cytosol
Membrane asymmetry
The inner and outer leaflets of membrane bilayers have
different compositions. Erythrocytes are the most studied.
The cytosolic side is composed of PE and PS. The PE
distribution is ca. 80% in the inner membrane and 20% in
the outer membrane. PS is negatively charged and PE is
moderately negative in charge. The inner membrane is
thus largely negative.
The outer membrane consists of PC, sphingomyelin, and
glycolipids. Cholesterol is also important and associates
with the membrane to provide added fluidity. Plasma
membranes have equimolar quantities of cholesterol. By
contrast, the endoplasmic reticulum and mitchondrial
membranes have small amounts of cholesterol.
Detergents and
Lysophospholipids
Detergents are amphipathic
molecules that can have charged
or uncharged head groups and
single hydrophobic tails. If one
of the acyl chains is cleaved from
a lipid then a lysophospholipid is
created.
Other associating molecules

) and the unit is
also the volt.
The Nernst equation
The Nernst equation describes the potential for each half-reaction
a(Ox) + ne
-
b(Red)
The standard potential (i.e. potential at 1 molar concentration) is E
o
.
The electrode potential is given by:
where R is the gas constant and F is the Faraday (96,450 J/volt).
In an electrochemical cell where two half-reactions are combined
to make a redox reaction, the electromotive force is:
emf = E(+) - E(-)
The free energy is G = -nFE. Therefore, the standard free energy
change for a redox process is ∆G
o
= -nF(E
o
ox
-E
o
red
) = -nF∆E
o
.
E = E
o
–

so that
the trans-membrane potential is obtained as follows.
∆
G
volt
=
∆
G
conc
– F∆E =–RT ln
C
o
C
i
∆E =
RT
F
ln
C
o
C
i
Natural foams from wax
Natural foams can occur from tree sap, fallen leaves and
zooplankton. For example, zooplankton are composed of
wax esters. Sometimes as much as 75% of the organism
is attributable these compounds. An example of a wax
ester is bee’s wax, which is Palmitic acid (C16:0) esterified
by a C30 chain, known as triacontanol (or melissyl alcohol).
The word "wax" is derived from the old english "weax" for

loss. When moving plants from sun
to shade the amount of cutin required
changes due to the amount of water
generated by photosynthesis.
The formation of a polymeric
layer of molecules to for
cutin is shown on the right.
The cutin polymer is a crosslinked
set of esters of long α,ω-alcohol
carboxylic acids or dicarboxylic acids.
Monomer composition in cutin
Biochemistry of wax synthesis
Acetyl co-A
1. Acetyl group
2. Coenzyme A
•Beta-mercaptoethylamine
•Pantothenic acid
•Phosphate
•3', 5'-adenosine diphosphate
Acetyl-CoA is an important molecule in metabolism. Its
main use is to convey the carbon atoms within the acetyl
group to the Krebs Cycle to be oxidized for energy production.
In chemical structure, acetyl-CoA is the thioester between
coenzyme A (a thiol) and acetic acid (an acyl group carrier).
It is also a carrier of two carbon units in fatty acid synthesis.
Suberin is found in bark
Waxes are also found in suberin, which is a lipidic polyester
present in tree barks, tuber skins and abscisic tissue of
falling leaves. It is also formed in plant after wounding. Upon
depolymerization, cork suberin releases a mixture of

2
(OH)
2
(O=)PO
O
O
OP(=O)(OH)
2
OP(=O)(OH)
2
OP(OH)
2
OP(OH)
2
OP(OH)
2
(OH)
2
(O=)PO
O
O
O
IP5
IP6
Inositol hexaphosphate
Phytic acid (inositol hexaphosphate
(IP6), or phytate) is the principal
storage form of phosphorus in
many plant tissues, especially in
the grass family (wheat, rice, rye,

4-alkylcatechol
Breakdown of lignin
Lignin is a biopolymer composed of 4-alkylcatechol units.
The breakdown of lignin in the soil leads to five common
phenolic acids.
(1) (2) (3) (4) (5)
1. para-coumaric acid
2. Syringic acid
3. para-hydroxybenzoic acid
4. Vanillic acid
5. Ferulic acid
CO
2
H
O
H
CO
2
H
OCH
3
OH
CHO
2
H
OH
CHO
2
H
OH