Lipids room incredible. Defined based on the physical property of (in)solubility, lipids room naturally emerging compounds that room quintessential because that life. In our cells, for example, lipids administer physical barriers, act as messengers, provide energy, and even help administer a mechanism for intracellular and extracellular transport. In addition, lipids deserve to be fairly tasty! 


As alluded come above, lipids room a class of naturally occurring molecules that space soluble in nonpolar essential solvents, and are not soluble in water. However what space the properties that define lipid solubility? let’s explore. Once talking about solubility, we are basically talking about how a molecule interacts v a solvent—this properties is mainly dictated by the polarity of the molecule.

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To do this point, let’s start with things that are not lipids. For polar compounds, such as water, the visibility of a partial fee on either finish of the molecule opens up up opportunity for dipole-dipole interactions, or even hydrogen bonding. When polar molecule or ions are placed into a polar solvent, dipole-dipole interaction (or technically ion-dipole interactions because that the latter) occur between the solute and also the solvent, permitting the link to dissolve.

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Due to water’s polarity, it can “dissolve” various other polar substances, such together table salt (NaCl)


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for nonpolar compounds, choose lipids, they exhibition dispersion forces with each other, and also with your solvents. It is unfavorable for polar molecules favor water to connect with nonpolar molecules prefer lipids because the transient fee interactions from the lipid molecules are not enough to stabilize the solid separation of charges uncovered on the water molecules.

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Dispersion pressures are specifically apparent in hydrocarbon chains, and also get stronger as the variety of carbon atom in the hydrocarbon chain increases. This is reflected by the boiling point of hydrocarbons — the much longer the chain, the higher the boiling point. This is due to the fact that with raised chain length, over there is rise in surface locations that have the right to accommodate raised intermolecular interactions.


Lipid Classification


Because lipids are greatly defined based on solubility in necessary solvents, there are a huge variety of molecules the are thought about to be lipids. Therefore it is valuable to sub-categorize lipids. Indigenous an necessary chemistry perspective, complicated lipids space lipid molecule that can be hydrolyzed into smaller, functional fragments (a carboxylic acid and an alcohol). On the various other hand, an easy lipids are not maybe to it is in hydrolyzed into these sensible fragments. However, it is essential to keep in mind that the category of “simple” and also “complex” can be misleading since “simple” lipids deserve to be fairly elaborate in their structure.

Complex Lipids

Complex lipids room considered thus because lock contain one or an ext ester groups — if a solid base (or, in part cases, a solid acid) is added, this ester teams can it is in hydrolyzed to create a carboxylic acid and an alcohol. Vice versa, the involvement of a carboxylic acid to an alcohol through an ester link is dubbed esterification. For complex lipids, the “carboxylic acid” ingredient is frequently a fatty mountain (which will certainly be debated in much more detail below).

Examples of complicated lipids include triglycerides, waxes, and also phospholipids. These are all naturally occurring molecules through important biological functions and are very regulated in the body. The following schematic is an instance of how these molecules can be broken down into their individual parts.

Simple Lipids

As formerly mentioned, basic lipids do not readily undergo hydrolytic cleavage due to the absence of a reactive carbonyl or carboxyl group. However, the ax “simple” can be a bit of a misnomer. Because that example, lipid molecule such as steroids execute not have a reactive carbonyl or carboxyl group, and thus space not easily hydrolyzed (compared come a triglyceride, for example). However, steroid molecule are fairly intricate, consist of of a tetracyclic ring mechanism with a strictly geometry. In enhancement to steroids, the other significant classes of simple lipids room prostaglandins and terpenes. All 3 of these simple lipid classes play an essential roles in the human body.


To affix these molecules to foods students are acquainted with, the significant lipid ingredient in several fatty foodstuffs comes in the type of triglycerides – a complex lipid whereby 3 fatty acid molecules (carboxylic acid) are esterified come a molecule of glycerol (alcohol). Triglycerides space a kind of “neutral lipid” because they are relatively inert, storing volatile fatty mountain molecules in a method that is an ext energetically favorable because that cells.

While the glycerol section of the triglyceride continues to be constant, the fatty acid portion of the triglyceride can vary widely. As mentioned above, fat acids are carboxylic acids that contain long, unbranched hydrocarbon chains. This chains have the right to vary in length, frequently containing in between 12 and also 20 carbon atoms. Furthermore, fat acids can be saturated (ie no carbon-carbon bonds) or unsaturated (contains at the very least 1 carbon-carbon bond). Instances of a saturated and also unsaturated fatty acid are presented below.

As you deserve to see indigenous the structure schematics above, the visibility of a double bond in the palmitoleic mountain dramatically alters the structure of the fat acid, which, in turn, dramatically transforms its melt point. Due to the fact that of the straight nature of the saturated fat acid, these molecules deserve to pack an ext tightly in the solid phase, resulting in an increased variety of dispersion interaction (and for this reason the requirement of more energy to break them). Alternatively, the kink result from the twin bond in unsaturated fatty acids prevents efficient packing, to decrease the overall strength that the dispersion pressures holding the fat molecule together.

The general ascendancy of thumb is the saturated fatty acids have actually a higher melting allude than unsaturated fat acids. Triglycerides containing unsaturated fatty acids are liquid at room temperature whereas triglycerides containing saturated fat acids are solid at room temperature. This is the difference in between an oil and a fat.

Also influence the melting point is the size of the hydrocarbon chain — longer chains have a greater melting point than shorter chains. This is again pertained to the stamin of the dispersion pressures that much longer chains afford.

Naturally occurring oils and also fats space usually made up of a mixture that triglycerides, definition that every glycerol backbone have the right to contain up to 3 different fatty mountain molecules. However, there space trends. For instance, triglycerides from pet fats commonly have a higher percentage that saturated fat acids compared to triglycerides extracted from plants oils. As such, they likewise have different impacts on person health.

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Trans Fats

When speak of the double bonds in naturally developing unsaturated fat acids, we room usually introduce to a cis dual bond formation. Cis binding are developed in nature (as protest to infectious diseases world fashion bonds) because the enzyme responsible because that desaturation reactions — reactions the transform a saturation carbon-carbon bond into an unsaturated carbon-carbon shortcut — operate in a means that only results in cis bond formation.

While unsaturated fatty acids space generally thought about to be “heart healthy,” the presence of one or more double bonds in the hydrocarbon chain renders these molecules an ext susceptible come autooxidation (reaction of oxygen through the double bonds). If sufficient autooxidation occurs, the oil will certainly go rancid — this is why food oils have tendency to have actually a much shorter shelf life 보다 fats (saturated fatty acids are an ext stable).

To resolve this issue, and prevent food waste, food scientists enforced a technique to partially hydrogenate unsaturated oil mixtures till a preferred texture was obtained. By reduce the dual bonds in an unsaturated fatty acid mixture, the melting suggest can also be altered. This change in the fatty acid physical building favors some cooking applications. For instance, Crisco, which was widely offered for baking, is actually comprised of partially-hydrogenated cottonseed oil. Before hydrogenation, cottonseed oil is fluid at room temperature; after ~ hydrogenation, that is a solid in ~ room temperature, yet it melts top top cooking. Margarine is make in a similar fashion. This is a great demonstration the the role of intermolecular pressures in identify the physics properties the a substance.

Hydrogenation is in reality a really energetically high value reaction. However, by making use of a metal catalyst (usually Nickel), the activation energy is significantly lowered, making the reaction scalable. Furthermore, partially-hydrogenated vegetables oils are much cheaper 보다 animal-derived fats, therefore this process also benefits the pocketbooks the consumers.

While partial-hydrogenation sounds like a an excellent idea top top paper, the metal catalyst can likewise induce isomerization the the cis twin bond in a fatty acid, converting it to a trans twin bond. That is approximated that the hydrogenation procedure used in food production produces a mixture comprise 10 – 15% trans saturated fat acids. It was recently found that trans fats can influence our cardiovascular equipment by increasing the lot of LDL (low density lipoprotein, aka “bad cholesterol”), and increase the hazard of heart disease. As a result, the lot of trans fats in food should be included on the food label, together per FDA requirements.