Where would glycine have a positive charge?

In an acidic environment, glycine, which is the simplest amino acid, would exist predominantly in its positively charged form. This occurs because at low pH levels, the amino group (-NH2) of glycine can accept a proton (H+), resulting in a positively charged ion known as a cation.

The structure of glycine consists of an amino group, a carboxyl group, and a side chain that is simply a hydrogen atom. In an acidic environment, the carboxyl group (-COOH) remains protonated, and the amino group becomes protonated, forming the zwitterionic form (-NH3+ and -COO-). The net effect in a very acidic environment leads to the predominance of the positively charged species.

In contrast, at neutral pH, glycine exists mainly in its zwitterionic form, where it has no net charge overall, and in a basic environment, it would predominantly carry a negative charge as the proton from the amino group would be lost, resulting in the amino group being in its deprotonated form (-NH2). A highly saline solution does not directly affect the overall charge of glycine but may influence its solubility and interactions rather than its protonation state