Calculating Diffusion Constant for Phosphatidylcholine in Water

Click For Summary
SUMMARY

The discussion focuses on calculating the diffusion constant for phosphatidylcholine in water, specifically addressing the radius of the particles and the diffusion coefficient. The molecular weight of phosphatidylcholine is established at 97,000 g/mol, with a density of 1.018 g/cm³ at 25°C. The radius of the particles was incorrectly calculated as 3.35 nm, while the volume was correctly determined as 1.58E-25 m³. The diffusion coefficient (D) was calculated using the Stokes-Einstein equation, yielding a value of 7.24E-11 m²/s.

PREREQUISITES
  • Understanding of Stokes-Einstein equation for diffusion calculations
  • Knowledge of molecular weight and density calculations
  • Familiarity with basic principles of micelle formation in lipids
  • Proficiency in unit conversions between grams, moles, and cubic meters
NEXT STEPS
  • Research the Stokes-Einstein equation in detail for diffusion analysis
  • Learn about micelle formation and its implications in biochemistry
  • Explore the effects of temperature on viscosity and diffusion coefficients
  • Investigate advanced lipid properties and their applications in drug delivery systems
USEFUL FOR

Researchers in biochemistry, molecular biologists, and professionals involved in lipid studies or drug formulation will benefit from this discussion.

kasse
Messages
383
Reaction score
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: 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

What's wrong here?
 
Physics news on Phys.org
V = 1.58E-25 m3 is correct

3.35 nm is wrong... u key the values wrongly.