This work builds on existing knowledge by focusing on self-assembly under physiological buffer conditions (pH, ionic strength). We investigate the effects of altering two different design variables on the relationship between molecular scale and macroscale properties: 1) the overall peptide charge; 2) the hydrogen bonding interactions, achieved through changing the terminal amino acids from glutamine (Q) to serine (S). The former is a mechanism to tune repulsive interactions between peptides and the latter modulates attractive intermolecular interactions. We demonstrate that controlling the balance between these attractive and repulsive interactions is critical in controlling the self-assembly of P11 peptides and determining conditions under which peptide hydrogels can form.