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Oil and Water Don’t Mix Model 1. When chemists think of fats they think of a large class of molecules called lipids. The word lipids comes from the Greek “ lipos†for fat. Natural fats and oils are made mostly of molecules called triglycerides. Fats are solid triglycerides, while oils are liquid triglycerides.

A triglyceride is made from the combination of fatty acids and glycerol; it has the basic structure shown in Figure 4.1. Fatty acids can be from 4 to 35 carbons long, but 14-20 carbon fatty acids are most common in food. O C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 CH 3 O O C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 CH 3 O O C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 CH 3 O H 2 C HC H 2 C O O O H 2 C HC H 2 C HO C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 CH 3 O HO C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 CH 3 O HO C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 CH 3 O + 3H 2 O Glycerol Fatty Acids Triglyceride H C H really looks like...

H H H Figure 9.1 . Glycerol and fatty acids combine to make a triglyceride. When fatty acids and glycerol combine, bonds are broken and formed in a chemical reaction to produce a triglyceride and 3 molecules of water. In that process, a new group of atoms is formed called an ester . The properties of a given triglyceride depend upon the chemical structure of the three fatty acids it contains, and the properties of a lipid depend upon the particular mixture of triglycerides it contains.

Table 9.1 . The composition of mono-, di- and triglycerides Monoglyceride = Glycerol + One fatty acid Diglyceride = Glycerol + Two fatty acids Triglyceride = Glycerol + Three fatty acids RO C R O anesterfunctional group R = the "rest" of the molecule Figure 9.2 . An ester functional group By definition, Lipids are insoluble in water, so that means triglycerides are insoluble in water. To be soluble means that two molecules will dissolve in one another to form a homogeneous mixture. When compounds are insoluble , the combination forms a heterogenous mixture.

When a lipid (e.g. oil) is mixed with water, you will see boundaries form between the two phases – literally, the two cannot mix. Key Concept The polarity of a molecule is determined by the separation of charge between its atoms. In polar molecules most atoms are connected polar bonds. In non- polar molecules most atoms are connected by non-polar bonds. OH NH CO ï¤- ï¤- ï¤- ï¤+ ï¤+ ï¤+ CH CC CC Polarbonds Non-polarbonds Figure 9.3 .

Non-polar versus polar bonds Polar compounds can mix with or dissolve /are soluble in water ( hydrophilic ) to form homogeneous mixtures (i.e. sugar dissolving in water, lemon juice dissolving in water, vinegar dissolving in water). Non-polar compounds can mix with or dissolve /are soluble in oils ( hydrophobic ) to form homogenous mixtures (e.g. vanilla extract dissolving in oil, melted butter mixing with olive oil). These facts are described by the principle like dissolves like . BUT oil (non-polar, hydrophobic) and water (polar, hydrophilic) don’t mix or dissolve in one another. 1.

Why is a fatty acid called a fatty acid ? 2. How many ester bonds are formed when a triglyceride is made? 3. On Figure 9.1, use the Draw tool or insert a shape to box the atoms that become the water molecule.

4. How many water molecules are produced when a monoglyceride is made? 5. A triglyceride has some polar and some non-polar bonds – and yet the molecule as a whole is very hydrophobic (i.e. water hating). a. Why is the tryiglyceride – as a whole – water hating? b.

Explain why the non-polar carbon chain is unable to interact with water. 6. Define the phrase non-polar bond . Use the word charge in your answer. 7.

The words hydrophobic and hydrophilic are derived from the Greek: hydro = water, phobos = fear, and phileo = love. Explain why these words are consistent with the chemical properties of a triglyceride. Saturated and Unsaturated Fats Model 2. Fatty acids come in different forms. HO C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 CH 3 O HO C C H 2 C C H 2 C CH 2 H 2 C CH 2 H 2 C CH 2 H 2 C CH 2 CH 3 OH H HO C C H 2 C C H 2 C CH 2 H 2 C C C H 2 C CH 2 H 2 C CH 3 OH H H H saturatedfattyacidchain monounsaturatedfattyacidchain polyunsaturatedfattyacidchain makingthedoublebond requiredthelossof2H atoms.TwoHatoms=a singleunitofunsaturation Figure 9.4 .

Saturated, Unsaturated and polyunsaturated Fatty Acids Saturated, monounsaturated and polyunsaturated fatty acids can all be used to make triglycerides. A single triglyceride can be made of fatty acid chains of all of one type (e.g. all saturated) or a mixture of types, for example one saturated, one monounsaturated and one polyunsaturated fatty acid chain. C O C C C O O O C O C O C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C CH 3 C H 2 H 2 C C H 2 H 2 C C H 2 C C H 2 C C H 2 H 2 C C H 2 H 2 C CH 3 H H C H 2 H 2 C C H 2 H 2 C C H 2 C C C C H 2 C C H 2 H 2 C H 3 C H H H H H H H H H Figure 9.5 . A triglyceride made with different types of fatty acids The properties of a given triglyceride molecule depend on the structure (i.e. type) of the three fatty acids that make up the triglyceride, and their relative position on the glycerol backbone.

C O OH C H 2 H 2 C C H 2 H 2 C C H 2 C C H 2 C C H 2 H 2 C C H 2 H 2 C CH 3 H H C O OH C H 2 H 2 C C H 2 H 2 C C H 2 C C H 2 C C H 2 H 2 C C H 2 H 2 C CH 3 H H type 1 type 2 Figure. 9.7 . On a nutrition label, Total fat includes Saturated, Polyunsaturated and Monounsaturated fats. Figure 9.6 . Different types of double bonds.

Fatty acids can have double bonds between carbon atoms. Double bonds come in two main types, as shown in Figure 9.6. The double bond between the carbons “fixes†all the atoms in place – in effect, the 4 atoms attached to the doubly bonded carbons (shown in boldface in figure 9.6) are “stuck thereâ€. Since these atoms are fixed in space, we can think of the double bond as having two “sidesâ€. This is in contrast to singly bonded atoms, which are able to rotate freely.

The generic food term “fat†refers largely to triglycerides. Therefore, for example, saturated fat is referring to the composition of the fatty acid chains that make up the triglycerides. 8. Using the information in Figure 9.4, a. What does it mean when a fatty acid is unsaturated ? b.

What do the prefixes mono- and poly- tell you about the unsaturation? c. If some fatty acids are saturated , what are they saturated with? 9. Looking at Figure 9.6, a. What is the difference between the two types of double bonds? b.

Chemists refer to these two types of double bonds as cis and trans . Considering that trans is Latin for “on the opposite side†and cis is Latin for “on the same sideâ€, which type of double bond (Figure 9.6, type 1 or 2) is trans and which type is cis ? Putting it all together : 10. It is possible to cook garlic in olive oil and transfer the flavors of the garlic to the oil. Since the flavors of garlic can all be attributed to molecules, what does this process tell you about the polarity of the garlic flavor molecules?

11. Many salad dressings are a mixture of oil and vinegar, like the image shown below. Photo by Bill Keller Please explain why the mixture on the left is apparently separated into two phases. 12. Some vitamins like vitamins A and D are fat soluble .

What does that tell you about their structure? _.cdx _.cdx _.cdx _.cdx _.cdx _.cdx _.cdx Model 1 . What we perceive as the taste of “sour†is actually our tongues detecting the presence of H+ cations. H+ cations are special cations called protons. When they are released by molecules into water they make the solution acidic, and that acidity is what we taste as “sourâ€. The term acid comes from the Latin acidus, meaning “sour or tart.†And it is that same Latin word that is the origin for the word acetus – more commonly known as vinegar.

What is it in vinegar that creates acidity and conveys the taste of sour? H O C O C and aproton aspecialCATion theanion O CH 3 CH 3 O H aspecialgroupofatoms calledacarboxylicacid aceticacid(i.e.vinegar) inwater thisparticularanioncalled acetateisquitestable thepKaisameasureofhowwellthisreactionoccurs.Strong acids(withlowpKa's)generateH + ions(andthe correspondinganion)easily. Figure 8.1. Acetic acid dissociating into ions If acetic acid (the “sour taste†of vinegar) is added to water, then the carboxylic acid group will give up a proton , leaving behind an anion. Why don’t the proton and the anion just immediately recombine to make acetic acid again?

Because the anion is quite stable. When the anion is stable, the acid is more acidic. To put this another way, the more stable the anion produced, the more likely the acid is to release a proton. Chemists measure how readily an acid releases a proton using a number called the pKa; the lower the pKa, the more acidic the acid and the more stable the anion produced. Table 8.1.

Acids found in typical foods. Acid Structure pKa of acid Food source Acetic Acid H O C O CH .75 Vinegar Citric Acid C H 2 C C H 2 C C CO OO O O O O H H H H 3.15, 4.77, 5.19 Lemon juice Malic Acid H O C O C H 2 CH O O O H H 3.40, 5.11 Apple juice Lactic Acid H 3 C CH C O O O H H 3.88 Yogurt H O C O C CHO O O H H O C O C CHO O O H 2H + and HH pKa~40 pKa~14 pKa3.4 pKa5.1 HH (a) (b) (c) (d) Figure 8.2. The dissociation of malic acid into ions. Hydrogens (a) and (d) are lost as protons. De-protonation (i.e. loss of a proton) does not occur for hydrogens (b) and (c).

Questions 1. What is the significance of the red bond on the left of Figure 8.1 and the two red electrons on the oxygen (on the right side of the figure)? 2. As shown in Table 8.1., citric, malic and lactic acids all have hydrogen atoms that are not part of carboxylic acids. Considering the information provided for malic acid in Figure 8.2, why do you think that de-protonation (i.e. removal of a proton) does not occur at positions (b) and (c)?

3. In Table 8.1, why does citric acid have three pKa measurements listed, while malic acid has two and lactic and acetic acids each have one? 4. Vitamin C is a molecule with a pKa of 4.1. Is Vitamin C an acid or base?

Explain. Model 2 . Some molecules are the opposite of acidic ; these molecules don’t release protons, instead they take protons from other molecules. Taking a proton from water creates an anion with a special name – hydroxide . Molecules that produce hydroxide ions when mixed with water are alkaline, they are also called bases or basic molecules.

H N H O H thehydroxideANion H H O H H N H HH ammonia (i.e.householdbleach)ammonium H N H HH releaseofaprotonbyammonium isnotafavorablereaction... verysmall concentrationof protons basesproducemany hydroxideionswhen mixedwithwater instead,theNH 3 base consumesanyprotons Basescanalso reactwith(and therefore decreasethe concentrationof) protons Figure 8.3 . The base ammonia takes a proton from water to make the hydroxide anion. Table 8.2. Relative concentrations of protons and hydroxide ions in acidic, neutral and basic solutions Concentration H+ (protons) Concentration of –OH (hydroxide) Acidic pH High Low H+ > –OH Neutral pH Equal Equal H+ = –OH Basic pH (Alkaline) Low High H+ < –OH The pH is a different number used to measure the concentration or the amount of H+ ions in solution.

The more protons (H+) there are, the lower the pH. Alkaline or basic molecules produce very few H+ ions, and they can also consume H+ ions – both effects lower the H+ concentration and raise the pH. IncreasingAcidity Neutral Decreasingacidity (increasingalkalinity) humangastricjuice(pH1.3-3.0) lemonjuice(pH2.1) distilledwhitevinegar(pH2.4) orangejuice(pH3.0) yogurt(pH4.5) blackcoffee(pH5.0) milk(pH6.9) eggwhite(pH7.6-9.5) Bakingsodainwater(pH8.4) householdammonia(pH11.9) Figure 8.4 . pH values of common foods. H O H OH and aproton aspecialCATion thehydroxideANion H equalamounts Figure 8.5 . The dissociation of water.

Water has a neutral pH - so the amounts of H+ and –OH ions produced are equal. Questions: 1. Based on the pH of milk in Figure 8.4, what would you predict about the relative concentration of H+ and –OH ? 2. Water has a neutral pH.

If you squirt some lemon juice into water, the pH changes. a) What do you expect will happen to the pH of the mixture of water and lemon juice? Will the number increase or decrease? b) What do you expect about the relative concentrations of H+ and –OH in the lemon juice and water mixture? 3. If you measure carefully, it is possible to take some vinegar (acidic) and mix it with baking soda dissolved in water (basic/alkaline)- the mixture will get warm (evidence of a chemical reaction occurring), but the final mixture has a neutral pH. How can this be?

Talk about the relative concentration of H+ and –OH ions. 4. Natural unsweetened cocoa powder has a pH of about 5 (slightly acidic). Dutch processed cocoa is made by treating natural unsweetened cocoa powder with a base (an alkaline substance). The resulting Dutch processed cocoa is darker in color and milder in flavor.

Should the pH of Dutch processed cocoa be lower or higher than natural unsweetened cocoa powder? Explain. _.cdx _.cdx _.cdx _.cdx _.cdx _.cdx _.cdx _.cdx _.cdx

Paper for above instructions

Oil and Water Don't Mix: An Exploration of Lipids and Their Properties

Introduction

The phenomenon of oil and water not mixing is a classic observation in chemistry that serves to illustrate the fundamental principles of molecular structure and interactions, notably the role of polarity. The interactions between fatty acids, triglycerides, and water molecules demonstrate the intricate balance of hydrophobic and hydrophilic interactions in biological systems. This paper aims to dissect the structural composition of triglycerides, elucidate their hydrophobic nature, and explore the implications for health and nutrition.

The Composition of Fats: Triglycerides

Fats primarily comprise triglycerides, which result from the combination of glycerol and three fatty acids. Each fatty acid contains a hydrocarbon tail that can vary in length and saturation (Berg et al., 2002). The glycerol backbone is a three-carbon molecule where each carbon is attached to an ester bond formed through the reaction with fatty acids, yielding water as a byproduct (McKee & McKee, 2013). This structure not only defines triglycerides but also illustrates why they are non-polar and hydrophobic due to the long carbon chains that dominate their overall polarity (Goldberg, 2012).
The length and saturation of fatty acids within triglycerides impact their physical properties, notably their state at room temperature; saturated fats are typically solid, while unsaturated fats are liquid (Richardson, 2000). Saturated fatty acids possess no double bonds between carbon atoms, leading to a straight structure that allows for tight packing, hence solidifying at room temperature. In contrast, unsaturated fatty acids possess one or more double bonds, creating bends in the carbon chain, which prevents tight packing and allows for a liquid state (Lipid Research Clinics Program, 1980).

Why Are Fatty Acids Called Fatty Acids?

Fatty acids derive their name from their long hydrocarbon tails, which are lipid-based, combined with the presence of a carboxylic acid functional group (-COOH). This structure exhibits acidic properties due to the potential for the molecule to release a proton (H+) (Stryer, 2012). The hydrophilic nature arises from the polar carboxylic group, allowing fatty acids to interact with polar solvents under certain conditions, while their long non-polar tails contribute to their hydrophobic properties overall.

The Formation of Ester Bonds

The formation of a triglyceride involves the synthesis of three ester bonds (one for each fatty acid molecule). As fatty acids attach to the glycerol backbone, a dehydration reaction occurs, combining the hydroxyl group of glycerol with the carboxyl group of the fatty acid, releasing three molecules of water in the process (Choe & Min, 2006). This bonding mechanism is fundamental in establishing the properties of lipids, directly linking their structure to functionality.

Solubility and Polarity

A key aspect of why triglycerides are hydrophobic lies in their polarity. Polar molecules, such as water, can interact with other polar molecules, while non-polar molecules do not mix well with polar solvents (Vollhardt & Neuhaus, 2014). Triglycerides, due to their long hydrocarbon tails predominantly composed of non-polar bonds, exhibit hydrophobic characteristics, leading to their separation from water when mixed (Relationships between structure and properties of lipids, 2020). This concept hinges on the principle that “like dissolves like,” meaning polar solvents will dissolve polar substances, whereas non-polar substances will only dissolve other non-polar substances.

The Nature of Soaps and Emulsifiers

Interestingly, the hydrophobic nature of triglycerides forms the basis for many household products like soaps that act as emulsifiers. Soaps contain a hydrophilic head and a hydrophobic tail, allowing them to interact with both water and fat, which can help to disperse grease and oil in water (Miller & Spinks, 2011). Emulsifiers enable the mixing of otherwise immiscible substances, serving significant applications in food science and cosmetics.

Saturated vs. Unsaturated Fats

The distinctions between saturated and unsaturated fats present several implications for health. Diets high in saturated fats are linked to increased cholesterol levels and heart disease, whereas unsaturated fats, particularly polyunsaturated ones, are often associated with protective cardiovascular effects (Mozaffarian et al., 2010). Understanding the structure-function relationships in fats is critical for those in the health and nutrition fields.

The Role of Lipids in the Body

Lipids play crucial roles in biological organisms beyond mere energy storage; they are fundamental components of cellular membranes, acting as barriers and sites for cell signaling (Friedman et al., 2010). The phospholipid bilayer, comprised of phospholipids that have hydrophilic heads and hydrophobic tails, perfectly exemplifies the importance of lipid polarity in biological functions. Additionally, fat-soluble vitamins such as A, D, E, and K showcase how lipid compounds are necessary for biological processes (Kratz et al., 2013).

Conclusion

In summary, the behavior of triglycerides exemplifies the profound implications of structural chemistry. Their hydrophobic nature stems from their molecular composition, defining their role in biological systems and dietary health. Understanding lipid chemistry equips individuals with the necessary knowledge to navigate health, nutrition, and bioenergetics effectively, emphasizing the biological importance of these crucial macromolecules.

References:

1. Berg, J. M., Tymoczko, J. L., & Stryer, L. (2002). "Biochemistry". W.H. Freeman.
2. Choe, E., & Min, D. B. (2006). "Mechanisms and factors influencing the shelf life of edible oils". Comprehensive Reviews in Food Science and Food Safety, 5(3), 169-180.
3. Friedman, M., et al. (2010). "Functional Foods and Nutraceuticals: from Numbers to Reality". Functional Foods in Health and Disease, 4(8), 240-275.
4. Goldberg, I. (2012). "Food Science and Technology". Oxford Press.
5. Kratz, M., et al. (2013). "Fat-soluble vitamins: An overview of the health benefits". Journal of Nutritional Science, 2, e25.
6. Lipid Research Clinics Program. (1980). "The lipid research clinics coronary primary prevention trial results". Journal of the American Medical Association, 243(21), 2078-2086.
7. Miller, J. D., & Spinks, J. (2011). "Soaps and Detergents: Principles of Green Chemistry". Academic Press.
8. Mozaffarian, D., et al. (2010). "Trans-fatty acids and cardiovascular disease". New England Journal of Medicine, 362(21), 206-2073.
9. Richardson, C. R. (2000). "Health effects of polyunsaturated fatty acids". American Journal of Clinical Nutrition, 71(6), 525S-526S.
10. Vollhardt, K. P. C., & Neuhaus, R. (2014). "Organic Chemistry". W.H. Freeman.