What is the net charge of phosphatidylethanolamine at pH 7?

The net charge of phosphatidylethanolamine at pH 7 is indeed zero. To understand why, it is important to consider the structure and the ionization states of the functional groups present in this phospholipid.

Phosphatidylethanolamine contains an ethanolamine head group that has an amine (-NH2) functional group. At physiological pH (around pH 7), the amine group can accept a proton, becoming -NH3+. However, the presence of the phosphate group carries a negative charge at this pH due to its deprotonated nature.

In this case, when balancing positive and negative charges, the positive charge from the protonated ethanolamine head group (+1) is countered by the negative charge from the phosphate (-1). Therefore, when you combine these charges, the overall net charge of phosphatidylethanolamine in a biological context at pH 7 is neutral, which is why it is considered to have a net charge of zero.

This reasoning aligns with the behavior of similar phospholipids, where the pH noticeably influences the charge states of polar head groups. In summary, at pH 7, the balance between the positively charged amino group and