Yingtai: Molecular Mass And Sedimentation Coefficient During Ultracentrifugation

Yingtai: Molecular mass and sedimentation coefficient during ultracentrifugation

In the process of ultracentrifugation, the molecular mass and sedimentation coefficient can be determined using the following methods:

1. Sedimentation Velocity Method:

In an ultracentrifuge, the sedimentation velocity method can be used to determine the sedimentation coefficient of molecules. The sedimentation coefficient reflects the size and shape of the molecule and can be determined by observing the rate at which the molecule moves in the solution under the influence of centrifugal force. Specifically, the sedimentation coefficient (S) can be calculated using the formula:

\[ S = \frac{r}{t} \]

where \( r \) is the distance the molecule moves in a given time \( t \). By monitoring the position of the molecule in real-time, the sedimentation coefficient can be calculated.

2. Sedimentation Equilibrium Method:

Another method is the sedimentation equilibrium method, which involves measuring when equilibrium is reached during centrifugation. At this point, the sedimentation rate of the molecule equals its diffusion rate. By measuring the concentration distribution of the molecule at different centrifugal forces and time points, the relationship between molecular mass and sedimentation coefficient can be established. The molecular mass (M) can be calculated using the formula:

\[ M = \frac{RT}{N_A} \cdot \frac{d^2}{dr^2} \cdot \frac{1}{C} \]

where \( R \) is the gas constant, \( T \) is the absolute temperature, \( N_A \) is Avogadro's number, \( C \) is the concentration of the molecule, and \( \frac{d^2}{dr^2} \) is the second derivative of the concentration gradient.

3. Optical Systems:

Ultracentrifuges equipped with various optical systems (such as absorbance, interference, and fluorescence) can monitor the sedimentation process in real-time. These optical systems allow precise tracking of molecular position and concentration changes, thereby enabling the calculation of sedimentation coefficients and molecular masses.

In summary, using analytical ultracentrifuges along with their optical systems and data analysis methods, it is possible to effectively determine the molecular mass and sedimentation coefficient.