Calculating Diffusion Constant for Phosphatidylcholine in Water

In summary, phosphatidylcholine is a lipid found in egg yolk that forms spherical particles called micelles when mixed with water. The molecular weight of these particles is 97,000 g/mol and their density is 1.018 g/cm3 at a temperature of 25°C. Assuming the particles are not hydrated, their radius is 3.35 nm and their diffusion coefficient in water is 7.24E-11.
  • #1
kasse
384
1
Phosphatidylcholine is a lipid that can be found in egg yolk. When phosphatidylcholine is mixed with water it will form micelles – spherical particles.

Molecular weight (Mw) for the particles is 97*000 g/mole
Density for the particles is 1.018 g/cm3
The temperature is 25°C

a) What is the radius for the particles?


Assume that the particles are not hydrated.
The viscosity of water (eta) at the given temperature is 0,9 mPa·s (milliPascal second)
Boltzmann constant: 1,38 ´ 10-23 J/K
(Pa=kg/ms2 and J=kgm2/s2)

b) What is the diffusion coefficient (D) for the particles in water?

a) One particle has the mass m = (97 000 g/mol)/6.02E23 = 1.61E-19 g.

This gives V = 1.58E-25 m3, and since the volume of a sphere is given by (4/3)*pi*r^3, the radius for the particles is 3.35 nm.

b) Stokes-Einstein: [tex]D = \frac{k_B T}{6 \pi \eta R_s} = \frac{1.38E-23 \cdot 298}{6 \pi \cdot 0.9E-3 \cdot 3.35E-9} = 7.24E-11[/tex]

What's wrong here?
 
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  • #2
V = 1.58E-25 m3 is correct

3.35 nm is wrong... u key the values wrongly.
 
  • #3


There are a few potential issues with this calculation. First, the given molecular weight is extremely high for a single particle, which may indicate a mistake in the data. Additionally, the assumption that the particles are not hydrated may not be accurate, as phosphatidylcholine is a lipid that is often found in hydrated form in biological systems. This could affect the calculation of the diffusion coefficient. Also, the given density may not be accurate for the particles in water, as the presence of water could affect their density. Finally, the Stokes-Einstein equation is an approximation and may not accurately reflect the diffusion behavior of these particles in water. More precise experimental measurements would be necessary to accurately determine the diffusion constant for phosphatidylcholine in water.
 

FAQ: Calculating Diffusion Constant for Phosphatidylcholine in Water

What is the purpose of calculating the diffusion constant for phosphatidylcholine in water?

The diffusion constant for phosphatidylcholine in water is a measure of how quickly the phosphatidylcholine molecules move and spread in water. This information is important for understanding the behavior and properties of phosphatidylcholine, a common lipid found in cell membranes. It can also provide insight into the diffusion of other similar molecules in water.

How is the diffusion constant for phosphatidylcholine in water calculated?

The diffusion constant for phosphatidylcholine in water can be calculated using the Stokes-Einstein equation, which takes into account the size of the molecule, the temperature, and the viscosity of the solvent. Alternatively, it can be measured experimentally using techniques such as fluorescence correlation spectroscopy or dynamic light scattering.

What factors can affect the diffusion constant for phosphatidylcholine in water?

The diffusion constant for phosphatidylcholine in water can be affected by temperature, concentration of the lipid, presence of other solutes, and the type of water (e.g. pure water vs. salt water). It can also be influenced by the properties of the membrane, such as thickness and lipid composition.

Is there a standard or expected value for the diffusion constant of phosphatidylcholine in water?

The diffusion constant for phosphatidylcholine in water can vary depending on the specific conditions and methods used for measurement. However, in general, it falls within the range of 1-10 x 10^-10 m^2/s, with higher values indicating faster diffusion. It is important to note that this value can also vary among different types of phosphatidylcholine and under different experimental conditions.

What are the practical applications of calculating the diffusion constant for phosphatidylcholine in water?

Understanding the diffusion behavior of phosphatidylcholine in water has various practical applications. For example, it can provide insight into the stability and functionality of lipid-based drug delivery systems. It can also help in predicting the behavior of phosphatidylcholine-containing products, such as cosmetics and food emulsions. Additionally, this information can be useful in biotechnology and biomedical research, particularly in understanding the diffusion of lipids in biological systems.

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