Phosopholipids in Salty solutions

  • Thread starter Krazer101
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In summary, the problem involves a phospholipid bilayer membrane with a mixture of 90% uncharged lipid and 10% singly charged acid lipid. The membrane is in contact with a 100mM NaCl solution at 25 degrees Celsius. The task is to calculate the areal charge density and surface potential of the membrane. The membrane is modeled as concentric spheres and the equations for electric field and potential are used. The percentage of charged lipid heads is used to determine the charge density.
  • #1
Krazer101
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Homework Statement


Consider a phospholipid bilayer membrane consisting of a mixture of 90% uncharged lipid and 10% singly charged acid lipid. Assume 68 Angstroms surface area per lipid head groups, and assume further that the charged lipids are uniformly distributed and immobile. The membrane is in contact with an aqueous solution of NaCl at 25 degrees celcius. The salt concentration is 100mM.

a.) Calculate the areal charge density of the membrane

b.) Calculate the surface potential of the membrane


Homework Equations


area density = derivative of charge?
Electric field and potential equations

The Attempt at a Solution



I am totally stuck and have no idea where to begin. I was first wondering what to model the membrane as? Should I model the bilayer as concentric spheres? I believe if I use concentric spheres, I can find the potential. I am unsure about the charge density; I don't quite understand how to use percentage of heads that are charged/not for this.
 
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  • #2
Anyone know where to start?
 

1. What are phospholipids?

Phospholipids are a type of lipid molecule that make up the cell membrane. They have a hydrophilic (water-loving) head and a hydrophobic (water-repellent) tail, which allows them to form a bilayer in aqueous solutions.

2. How do phospholipids behave in salty solutions?

In salty solutions, phospholipids tend to form micelles, which are small spherical structures with the hydrophilic heads facing outwards and the hydrophobic tails facing inwards towards the center of the micelle.

3. What is the effect of salt concentration on phospholipid behavior?

As the salt concentration increases, the stability of the micelles increases as well. This is because the salt ions interact with the hydrophilic heads of the phospholipids, making them less likely to break apart.

4. How do phospholipids interact with ions in salty solutions?

Phospholipids have a negative charge on their hydrophilic heads, so they can interact with positively charged ions in salty solutions. This interaction can affect the overall structure and stability of the phospholipids.

5. Can phospholipids form bilayers in high salt concentrations?

Yes, phospholipids can still form bilayers in high salt concentrations, but they may be more loosely packed and less stable compared to bilayers in lower salt concentrations. In extreme cases, the high salt concentration may cause the phospholipids to form inverted micelles, with the hydrophobic tails facing outwards and the hydrophilic heads facing inwards.

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