Hydrophobic Effect

in this video, we're going to begin our discussion on the hydrophobic effect. So the hydrophobic effect is this phenomenon of the exclusion of hydrophobic substances by water. And so we've mentioned the hydrophobic effect several times in our previous lesson videos. So we already know that hydrophobic molecules are water fearing molecules that are insoluble or not soluble because they do not dissolve well with water. And actually, when you try to mix hydrophobic substances with water, they will actually form a completely separate phase. Now the hydrophobic effect is actually super important for life, and that's why your professors want you guys to know about it now. The reason that the hydrophobic effect is so important for life is because it's critical for both protein folding and for the formation of membranes, which are two processes that will talk more about in a different video later in our course now down below. In our example, we have an experiment that you guys can actually try at your homes, and that's taking a cup of water and pouring in oil into it. And which will notice is that the oil does not dissolve with the water, and that's because the oil is hydrophobic. And so no matter how much you try to stir that oil and dissolve the oil with water, the oil will not dissolve with water. And eventually all of these oil bubbles that you create are going to clump together to create a completely separate oil phase that's separate from the water. And so you might think that these oil bubbles are clumping together because hydrophobic substances must have a strong attraction for each other. Right? Well, that's what it appears to be. So in water hydrophobic non polar substances appear toe have a strong net attraction or strong net affinity for each other. But that is not the case. And so, other than the super weak Vander Waals forces that exists between all molecules, hydrophobic substances do not have a strong attraction for one another. And so, if hydrophobic substances don't have a strong attraction for one another, then why is it that they're clumping up like what we're seeing over here? Well, we'll explain that in our next lesson video. So I'll see you guys there

So we already said in our previous video that the hydrophobic effect is not explained by the strong net affinity of hydrophobic substances for each other. But the hydrophobic effect can be explained by looking at the water molecules that surround a non polar substance. And so when we take a non polar substance and we added in tow water, it becomes a hydrated, non polar substance. And all that means is that there's a cage like shell or layer of water molecules surrounding the non polar substance. And this layer of water molecules is referred to as the hydration shell. And we already talked about hydration shells a little bit when we talked about water soluble ity and our previous videos. And really, there's three things to note about the water molecules and hydration shell surrounding a non polar substance, and the first thing to note is that water molecules in the hydration show cannot participate in normal hydrogen bonding. Now, the second thing to note is that water molecules in the hydration shell they move slower than normal. They formed fewer but stronger hydrogen bonds, and because they form stronger hydrogen bonds, they have mawr energy and more energy means that they are less stable. And then the third thing to note about water molecules in the hydration shell is that they have fewer options for orientations in three D space. And this has to do with the stronger hydrogen bonds. So when they form these strong hydrogen bonds, they're harder to break. And because they're harder to break, it's harder for them to take on different orientations, and so fewer orientations means that they're gonna be mawr ordered. And we know that more order is associated with less entropy from our thermodynamic videos, but recalled that the universe is moving towards a state of increased entropy, and so because water molecules in the hydration shell around a non polar substance are decreasing the entropy, this means that the formation of a hydration shell around a non polar substance is not thermo dynamically favorable. But it actually is thermo dynamically favorable for hydration shells to merge together when non polar substances clump and reduce their surface area. And so even though the entropy is decreased when non polar substances clump, this decrease in local entropy is largely offset by an overall increase in the entropy of the surroundings or of the universe when water molecules that used to be part of the hydration shell break free from the hydration shell and increase the universal entropy. And so all we're saying here is that when non polar substances clump and water, this is actually a thermo, dynamically favorable process and a spontaneous process. So let's take a look at our example below to help clear this up a little bit. So, down here, what we have is water, and we're taking a non polar molecule and adding it to the water, which means that it's going to become a hydrated, non polar substance. And hydrated. Non polar substances have a hydration shell around them, and we know that water molecules in the hydration, shell arm or ordered and Maura order again is associated with lowered entropy. And so here we have a hydration shell of water molecules surrounding the non polar molecule, and that means that there's going to be a decrease in the entropy of the system. Now, over here we're adding a second non polar molecule, which means that we're getting a formation of another hydro hydration shell. And so if the first hydration shell decrease the entropy of the system. The formation of a second hydration shell is gonna further decrease the entropy of the system. And so when non polar substances clumped together, there's actually a decrease in three different things. The first is that there's a decrease in the surface area of the non polar molecules. The second is that there's a decrease in the number of molecules that are part of the hydration shell. And so notice. Over here we have a total of seven water molecules, part of this hydration shell and another seven water molecules, part of this hydration shell. So there is a total of 14 water molecules part of the hydration shells. Now, when the non polar molecules clump together, they reduce their surface area, and they reduce the number of water molecules that are part of the hydration show. So here in this hydration shell, notice that there's Onley, a total of nine water molecules, part of the hydration shell, not 14. And so the other water molecules that used to be part of the hydration shells. They broke free, and so they broke free from the hydration shell on their circled in red, And this image here And so the last thing that's decreased when non polar substances clumped together is that there's a decreased in local entropy, So two things combining in tow one decreases the local entropy. But this decrease in local entropy is largely offset by an increase in the entropy of the surroundings, or of the universe, when water molecules that used to be part of the hydration shell break free. So these water molecules that break free, they end up increasing the overall entropy of the universe, which means that when non polar molecules clump together, ultimately they end up increasing the entropy of the universe. And that means that the clumping of non polar molecules is thermo, dynamically favorable. And so this concludes our lesson on the hydrophobic effect explanation. And if you have any questions, leave them in the comments below. And in our next video, we're gonna talk about the role of the hydrophobic effect in protein folding and membrane formation. So I'll see you guys in that video

So we already said in our previous videos that the hydrophobic effect is important toe life because it's critical for protein folding as well as the formation of membranes. And so, in our example below, we have protein folding on the left and membrane formation on the right, and so when we take a protein that's an unorganized protein that's unfolded and we fold it very nicely into a nice organized structure that decreases local entropy because we're going from unorganized and spread out, spread out all over the place to a nice, neat organized formation of the protein. And so whenever there's a decrease in entropy or local entropy, we know that it needs to be accompanied by an increase in the universal entropy or the entropy of the surroundings. And so that's where the hydrophobic effect comes into play. And so here we have a protein represented by this green line. Here, this is an unfolded protein and extending off of the protein we have. These yellow are groups which are non polar, are groups, and around these non polar are groups. We have our hydration shells with these water molecules, and so you can see that the water molecules are surrounding the, uh, the are groups. The non polar are groups here, so they create a hydration shell. And we know that the water molecules in the hydration shell they decrease entropy. And so this is not thermo dynamically favorable. Now, when these non polar substances clump what'll happen, is the water molecules will break free from the hydration shell and increase the universal entropy. So even though there's a decrease in local entropy, where the, uh, non polar, our group's heir, clumping together to decrease entropy, it's offset by the water molecules that break free and increase the universal entropy. So here you can see we have our folded protein on the water molecules, uh, here have broken free from the hydration shell, and that allows our protein to fold. So the hydrophobic effect is very important for the proper folding of a protein, and we'll talk more about this later on in our course when we talk about proteins. Now, over here we have membrane formation, and we've seen this image a few times in our previous videos. And so we've got a phosphor, a lipid here which of course has a polar head and to non polar tales and the non polar tales. They're gonna be hydrated, non polar tales. So they're gonna have water molecules in a hydration shell surrounding these non polar tales. And so these water molecules that are surrounding the non polar tales they can begin to break free. And when these fossil lipids, they clump together so you can see here we're clumping and we're reducing the surface area, and we're reducing the amount of water molecules that air in the hydration shells surrounding these non polar substances. And so the fossil lipids are gonna continue to accumulate. Continue to, uh, reduce the surface area and reduce the hydration shells and continue to increase the universal entropy by releasing water molecules from the hydration shells. And so that allows for the formation of a fossil lipid bi layer. And this is incredibly important to the formation of life, just like we talked about in our a b O Genesis videos. And so this concludes our lesson on the hydrophobic effect, and I'll see you guys in a practice videos

Which of the following best explains the hydrophobic effect?

• A. Hydrophobic substances have a strong net affinity for each other.
• B. Hydrophilic substances increase local entropy upon clumping.
• C. Hydrophobic substances clump due to their strong intermolecular forces.
• D. Hydrophobic substances increase universal entropy when they clump.

Which of the following is false concerning H₂O molecules in the hydration shell around nonpolar substances?

• A. Cannot participate in normal hydrogen bonding.
• B. Form stronger hydrogen bonds than free H₂O
• C. Less ordered & higher entropy than free H₂O
• D. Less options for orientations in 3D space than free H₂O