Mixtures of amino acids can be analyzed by first separating...

Mixtures of amino acids can be analyzed by first separating the mixture into its components through ionexchange chromatography. Amino acids placed on a cationexchange resin (see Fig. $3-17$ a) containing sulfonate $\left(-\mathrm{SO}_{3}^{-}\right)$ groups flow down the column at different rates because of two factors that influence their movement: (1) ionic attraction between the sulfonate residues on the column and positively charged functional groups on the amino acids, and (2) hydro- phobic interactions between amino acid side chains and the strongly hydrophobic backbone of the polystyrene resin. For each pair of amino acids listed, determine which will be eluted first from the cation-exchange column by a pH 7.0 buffer. (a) Asp and Lys (b) Arg and Met (c) Glu and Val (d) Gly and Leu (e) Ser and Ala

Mixtures of amino acids can be analyzed by first separating the mixture into its components through ionexchange chromatography. Amino acids placed on a cationexchange resin (see Fig. $3-17$ a) containing sulfonate $\left(-\mathrm{SO}_{3}^{-}\right)$ groups flow down the column at different rates because of two factors that influence their movement: (1) ionic attraction between the sulfonate residues on the column and positively
charged functional groups on the amino acids, and (2) hydro-
phobic interactions between amino acid side chains and the strongly hydrophobic backbone of the polystyrene resin. For each pair of amino acids listed, determine which will be eluted first from the cation-exchange column by a pH 7.0 buffer.
(a) Asp and Lys
(b) Arg and Met
(c) Glu and Val
(d) Gly and Leu
(e) Ser and Ala

Key Concepts

Hydrophobic Interactions in Chromatography

In addition to ionic interactions, the stationary phase may exhibit hydrophobic character. This characteristic causes additional retention of molecules based on the hydrophobicity of their side chains. Consequently, both electrostatic and hydrophobic interactions can influence the separation and elution behavior of analytes.

Amino Acid Ionization and pH Effects

Amino acids possess ionizable groups—the amino and carboxyl groups, along with any charged side chains. At a given pH, such as 7.0, the ionization state of these groups will determine the net charge and thus the degree of interaction with the ion-exchange resin. Understanding how pH affects these charges is critical to predicting elution order.

Cation-Exchange Chromatography

A subtype of ion-exchange chromatography where the stationary phase is negatively charged, allowing it to bind positively charged molecules. In such systems, molecules with higher positive charges are more strongly retained, and elution is often achieved by modifying the pH or ionic strength of the mobile phase.

Ion-Exchange Chromatography

This technique separates charged molecules based on their differential interactions with a charged stationary phase. Compounds are retained or eluted by their affinity for the oppositely charged groups on the resin, making it a powerful method for separating complex mixtures based on charge differences.

Transcript

00:01 Hello there.

00:02 So i'm going to be discussing the catayon exchange chromatography and specifically we'll look at how it's, how it's moderning, is using separating amino acids and which amino acid will be separated first, i mean which will be looked at first from pairs of amino acids.

00:21 Okay.

00:22 So what we know is that the cation exchange resin has solved on its groups and then has polystyrene material.

00:39 So polystyrene material will form hydrophobic interactions with our amino acids that have hydrophobic side chains, which are represented as hp.

00:50 Then the softened groups will bind to the amino acids with positively charged side chains.

00:57 So you ask you, so what happened to the amino acids with negatively charged side chains? since they are negatively charged side chains and the softening groups are negative recharge they are basically going to be repelled by the reason.

01:13 So you are going to have them actually being eluded first, then our hydrophobic amino assets, then our positively charged amino assets.

01:24 So our positively charged amina is basically going to be last.

01:27 So just keep that principle in mind.

01:28 The negatively charged wants to be eluded first, then the hydrophobic ones, then the positively charged ones.

01:33 So let's look at some pairs and see how this plays out.

01:37 So we have aspartite and lysine.

01:40 Now let's know that aspartite is a negative -charged and minus a while licein has a positively charged side chain.

01:47 So basically, aspartate is going to come out first in despair...