Question

An undergraduate researcher you know is confused. They were told to measure the amount of helix in poly-L-Glutamate in 0.1 M phosphate. When they made the solution using H3PO4 and KH2PO4 they saw a nice CD signal indicative of alpha helix. The next week they tried again using identical reagents except that they were out of the potassium salt and had to substitute Na2HPO4. When they made a CD measurement they saw a large negative signal at 195 nm indicating random coil conformation. How would you explain the behavior of poly-Glu to the confused student so that it made sense? What simple step did the student likely forget while making up the solution?

Answer 1

Answer:-

     Many chemical reactions are affected by the acidity of the solution in which they occur. In order for a particular reaction to occur or to occur at an appropriate rate, the pH of the reaction medium must be controlled. Such control is provided by buffer solutions, which are solutions that maintain a particular pH. Biochemical reactions are especially sensitive to pH. Most biological molecules contain groups of atoms that may be charged or neutral depending on pH, and whether these groups are charged or neutral has a significant effect on the biological activity of the molecule.

The helical structure will be distorted in pH change hence It is clearly mentioned about the helical structure.

The simple step the student forgot while making the solution was both of the solution are monohydrogen phosphtes while there should be combination of mono and dihydrogen phoshphates.

This buffer system consists of dihydrogen phosphate ions (H₂PO₄^-) as hydrogen-ion donor (acid) and hydrogen phosphate ions (HPO₄^2-) as hydrogen-ion acceptor (base).Hence here hydrogen-ion donar is missing and will directly effect the pH and that will be reduced.