At pH 6.0 the N-terminus of His-His-His-His would have a (positive/ negative) charge. The C-terminus would have a (positive/ negative) charge. Since the pKa for His is 6.0, essentially half of the residues would carry a (negative/ positive) charge on their side chains, so that the charge per residue could be considered to be (+2.0/ +0.5 / +1.0/ +1.5). The result would be a net charge on the tetrapeptide of (+2.0/ -1.0/ +1.0/ -2.0). The tetrapeptide would be (more/ less) soluble in water than Histidine itself. When the bonds are formed between the carboxylate and amino groups to form the tetrapeptide, the groups that would interact with water are lost.