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Teacher Outline
Part I. The Hydrophobic Effect
Key words to go over: electronegativity, covalent bonds, partial positive and negative charges,
hydrogen bonds, hydrophobic effect, Second Law of Thermodynamics
1. Engage: Salad dressing experiment
a. Shake oil and colored (balsamic/red wine) vinegar together and watch the two settle
out into two layers.
2. Explain Critical Concept #1: Polarity affects the hydrophobicity or hydrophilicity of a
molecule due to weak interactions called hydrogen bonds.
a. Polar molecules are formed when atoms with different electronegativities, or
attraction of electrons, are covalently bonded. This results in an uneven distribution
of electrons across the molecule, creating partial positive and negative charges
called dipoles. Electrons tend to localize around more electronegative atoms,
creating a partial negative charge.
i. Exploration and Application of Knowledge: Water contains two hydrogen
atoms and one oxygen atom. The oxygen is very electronegative and
therefore has a partial positive charge.
b. This polarity affects the way the molecule interacts with other molecules, such as
water. The hydrogen in water has a partial positive charge and interact weakly with
other electronegative atoms (commonly oxygen and nitrogen), through a bond
known as the hydrogen bond. Molecules that participate in hydrogen bonds are
called hydrophilic, and those that do not are called hydrophobic.
i. To remember: -philic = love, -phobic = fear. So hydrophilic molecules are
water loving.
c. Non-polar molecules are hydrophobic because they have equally distributed charge
and thus cannot form hydrogen bonds.
i. Evaluation/application of knowledge: Looking at the structure of vinegar and
oil, which is polar and which is non-polar? Vinegar is polar and oil is nonpolar.
3. Explain Critical Concept #2: The Second Law of Thermodynamics states that a system in
order will spontaneous return to disorder. This law guides the hydrophobic effect.
a. The hydrophobic effect describes the tendency for hydrophobic molecules to
aggregate together, away from hydrophilic molecules.
b. Exploration and Application of Knowledge: Which state is more ordered in the salad
dressing experiment?
i. The system is at its most ordered state when it is fully shaken, since the
vinegar is evenly distributed as droplets among the oil. Then the distinct
layers form, the system is at a greater disorder. This may sound counterintuitive, but by creating that single interface between the oil and vinegar,
more vinegar molecules are made available to the disordered system,
forming hydrogen bond within themselves. When dispersed within the oil,
there is a greater overall surface area that makes up the interface between
the oil and vinegar, disrupting more hydrogen bonds between the vinegar
molecules.
Part 2. Bridging the gap by using surfactants
Key words to go over: amphipathic molecules, surfactant, emulsion, surface tension
1. Engage: Salad dressing experiment with addition of detergent
a. Shake with the addition of egg yolk (mustard or lecithin should work too) and
compare to mixture without.
2. Explain Critical Concept #1: Amphipathic molecules are molecules that have both polar and
non-polar properties. They can span across the interface of hydrophilic and hydrophobic
layers, where the polar regions form hydrogen bonds with the hydrophilic layer. By
supplementing hydrogen bonds at the hydrophilic interface, they reduce the surface
tension thereby stabilizing the mixture.
a. Exploration and Application of Knowledge: In an amphipathic molecule, which region
is hydrophilic and which region is hydrophobic? The polar region is hydrophilic and
the non-polar region is hydrophobic.
Oil phase
non-polar tail
polar head
Aqueous phase
Amphipathic
molecule
b. The salad dressing mixture settles out until a surfactant (for example, egg yolk) is
added, creating a type of solution called an emulsion, seen below in the diagram.
3. This lesson plan can be expanded to explain the ability of soap to clean grease!
Part 3. Elaborate: Biological examples of the hydrophobic effect and amphipathic molecules
in action!
Key words to go over: hydrocarbons, macromolecules, lipids, phospholipids, membrane
1. Example #1: The cell membrane is composed of phospholipids, which are amphipathic
molecules.
a. A phospholipid is a type of lipid, which is a molecule that is largely composed of
hydrocarbons. Hydrocarbons are just molecules that only contains carbon and
hydrogen. Lipids are one of the four classes macromolecules that are the basis for
cellular life. The other three are carbohydrates, nucleic acids, and proteins.
b. Exploration and Application of Knowledge: What are some of the requirements of
the cell membrane? Keeping organelles, nutrients, solutes inside to help maintain
homeostasis of the cell.
c. Exploration and Application of Knowledge: How may phospholipids arrange
themselves to form the cell membrane (figure of a phospholipid structure is in
handout)?
i. They align side by side, forming a row and the two rows come together to
form a lipid bilayer. The hydrophobic regions face inward and the polar
regions face intracellular and extracellular water-filled fluid.
2. Example #2: Some types of nanoparticles are made by creating emulsions
a. Recall the emulsion made in Part 2: The is the same way some nanoparticles are
made in the lab! Instead of just shaking the mixture by hand, they add even more
energy to the system by using two different machines, called homogenizers and
sonicators. A homogenizer rapidly and vigorously blends the mixture and the
sonicator uses sound energy to disturb the system. The high level of energy and the
presence of surfactants allow the particles to get very small.
3. Example #3: Intro into drug delivery systems and pharmaceutics: Loading lipid-based
nanoparticles with small molecule drugs allows for previously hydrophobic drugs to be
given to patients intravenously.
a. Engage: Insoluble molecule experiment
i. Compare adding sugar and cotton balls to water.
ii. Things that can form intermolecular interactions with water easily, are said
to be soluble in water.
iii. Disclaimer: This is a nuance to the ideas we learned in hydrophilicity
segment, since the structure of cellulose shows that is is hydrophilic.
1. However, since cellulose exists in chains as a polymer, is forms an
amorphous structure that wants to interact more with itself than
water.
b. Background: Many drugs are not very hydrophilic and thus insoluble in the blood,
making them hard to give intravenously. Oral forms of drugs are difficult to make
since the stomach is a very harsh, acidic environment that can break them down
before they can be absorbed into the blood stream. Other issues include that they
also can be very irritating to the gastrointestinal lining. Many cancer drugs and
antibiotics need to be given intravenously.
i. Exploration and Application of Knowledge: Many drugs that have been
discovered are very hydrophobic. How may this be an issue when giving a
drug intravenously?
c. Lipids can assemble so that their hydrophobic tails aggregate around the
hydrophobic drug, shielding it from the aqueous solution in the form of a particle.
Recall: The Second Law of Thermodynamics is responsible for this assembly. These
particles can be made very small, and are called nanoparticles. Nano- refers to
nanometer. For reference, a human hair is about 7 micrometers, which is 1000x
larger than 70 nanometers. There are two different basic types of lipid-based
nanoparticles commonly made: micelles and liposomes.
i. Engage: Watch this video from the NIH on nanotechnology and the relative
scales of biology. https://www.nih.gov/research-training/nanotechnologynih.
d. Exploration and Application of Knowledge: If you had a hydrophobic small molecule
drug, where would you find them in the two nanoparticles in the figures below
(handout has figures)?
i. The hydrophobic drug would be found in the hydrophobic region of the
nanoparticle, represented by the chains. These chains represent
hydrocarbons that are very non-polar. Hydrophilic drugs can be either
covalently bonded to the outer facing polar head groups of the liposome or
micelle, or enveloped by the polar heads inside the liposome.
(Optional) Part 4. Communicating with the public and other scientists.
 Create a class Instagram account where each group makes a series of posts to
communicate what they learned during this class.
 Follow up each post with the following hashtags/tags:
o #sciencecommunication –This allows students to see the other types of science
people are communicating about on Instagram.
o #instascienceclass – This hashtag currently has only 1 post listed on Instagram,
and will allow students to see other classes in the area participating in this
unique Insta-science classroom experience.
o Tag my science outreach Instagram account in the description,
@insta.sciencegrammar
 Encourage students to make posts such as:
o Write a short summary of the most interesting thing that you’ve learned in class
today.
o Make a post about one of the explore or application questions.
o Include images from the different experiments done throughout the lesson.
o Propose other applications where you see these concepts at play in daily life.
o Asking questions about the activities or content (that I will field and answer in
the comments!)- make sure to tag @insta.sciencegrammar!
 A few weeks past the SciREN networking event, I will post a series of videos a
nanoparticles being made, microscopic images of them after and their relevance in
biomedical science!
References:
1. Tymoczko, John L., Jeremy M. Berg, and Lubert Stryer. Biochemistry: a short course.
Macmillan, 2011.
2. Whitten, K. W., Davis, R. E., Peck, M. L., and Stanley, G. G. Chemistry, 9 th edition. Cole
Publishing, 2009.
3. Boundless. “Phospholipids.” Boundless Biology. Boundless, 30 Aug. 2016. Retrieved 09 Sep.
2016 from https://www.boundless.com/biology/textbooks/boundless-biologytextbook/biological-macromolecules-3/lipids-55/phospholipids-300-11433/.
 All other images found open source on Wikipedia or made by me.