Titration Curve of Glycine: The zwitter ionic changes

Do you remember seeing those graphs in high school chemistry class? They show the change in concentration over time during chemical reactions. For example, the graph below shows how much sodium hydroxide is needed to convert potassium chloride into potassium hydroxide (KOH).

A titration curve is often used to determine the amount of something required to achieve a specific reaction. The shape of the curve depends on the type of reaction. For example, a titration curve of glycine would look very different from sodium carbonate.

Chemistry teachers always taught us that a titration curve has a sigmoid shape. But recent studies have revealed that some titration curves don’t fit this standard pattern, and they can even have multiple shapes. The usual rules for interpreting these curves aren’t always applicable.

titration curve of Glycine notes

Glycine is optically inactive, simplest amino acid because it has no asymmetric carbon atom. Acid-Base titration involves the gradual addition (or) removal of protons. It has three different stages when the Glycine undergoes acid-base titration.

What is Glycine?

Glycine is a nonessential amino acid found in both plants and animals. Some foods contain glycine naturally, such as soybeans and chicken broth. Others include supplements or medications. Glycine is also known as L-proline because it has similar chemical properties as proline. The human body cannot produce glycine, so it must be obtained from food sources or through supplementation. Glycine helps the body heal wounds and build connective tissue.

Steps of Titration curve of Glycine

Stage 1: At low pH

titration curve of Glycine

At very low pH, the predominant ionic species of Glycine is the fully protonated form, +H3N-CH2-COOH. For Glycine, the pH at the midpoint is 2.34, thus it’s Carboxyl group (–COOH) has pKa of 2.34.

Stage 2: Reaching middle pH

As the titration proceeds, another important point is reached at pH 5.97. Here there is another point of infection, at which removal of the first proton is essentially complete and removal of the second proton has just begun.

Stage 3: Releasing Proton

the third stage of the titration corresponds to the removal of a proton from the –NH3+ group of Glycine. The pH at the midpoint of this stage is 9.60, equal to the pKa for the –NH3+ group.

From this titration curve of glycine, we can derive several important pieces of information.

effect of chemical environment of pka
  • It gives a quantitative measure of the pKa of each of the two ionic groups; 2.34 for the Carboxyl group (–COOH) and 9.60 for the Amino group (–NH3+).
  • The perturbed pKa of Glycine is caused by repulsion between the departing proton and the nearby positively charged amino group on the α-carbon atom.
  • The titration curve of Glycine has two regions of buffering power. At pKa 2.34, glycine is a good buffer near this pH. The other buffering zone is centered on a pH of 9.60.
  • Glycine is not a good buffer at the pH of intracellular fluid (or) blood, about 7.4. To calculate the buffering ranges, we can use the Handerson-Hasselbalch equation.

What is the titration curve?

The titration curve plots the concentration versus pH value of a solution. The graph reveals the acidity or basicity of the solution being tested. The titration curve shows how much They must add a base (or acid) to the solution until a certain point is reached. For example, if you want to know whether a mixture of water and vinegar is acidic enough to cause damage to human skin, the titration curve would tell you.

It is a graphical representation of a ligand’s dissociation constant (Kd) bound to its target molecule. In other words, the titration curve shows how much ligand or drug concentration is required to displace 50% of the free receptor from bound complexes.

The concept behind titration curves is simple. If a ligand binds strongly to a protein, then less ligand should be needed to displace the bound complex from the receptor. Conversely, if the ligand does not bind strongly to the protein, higher ligand concentrations should be needed.

  1. Titration curves measure the affinity between two molecules, allowing us to compare one compound against another. It helps us determine which compounds might bind well to their targets of interest.
  2. There are several ways to generate titration curves. One way involves plotting the ligand concentration versus the percentage of unbound receptors. Another method uses a graph where the amount of ligand present is plotted along the x-axis and the fraction of bound receptors along the y-axis.
  3. Researchers can predict whether certain drugs would likely bind to a particular protein and affect its function using the calculated Kd values. Such information provides insight into the potential therapeutic efficacy of these drugs.

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