Final answer:
At physiologic pH, PS and PI are negatively charged due to their acidic head groups while PC and PE are polar and uncharged, as they do not possess acidic or basic groups that would impact their charge at this pH.
Step-by-step explanation:
At physiologic pH, the head groups of phosphatidylserine (PS) and phosphatidylinositol (PI) have an overall negative charge while phosphatidylcholine (PC) and phosphatidylethanolamine (PE) are polar and uncharged. This is because PS and PI contain acidic functional groups that can lose protons to become negatively charged at neutral pH. On the other hand, PC and PE lack these acidic groups and therefore remain uncharged at physiologic pH.
The overall charge of a molecule at a given pH is determined by the ionization state of its functional groups. Acidic functional groups like the carboxylate group (-COO-) in PS will lose protons and carry a negative charge. Basic functional groups such as amino groups (-NH3+) found in amino acids can gain protons and be positively charged; however, PC and PE do not have these basic groups in their head structures at a level to confer an overall positive charge at physiological pH.