What is the physiological pH at which charged amino acids are specifically charged?

Which of the following amino acids is NOT a positively charged basic amino acid?

Which structural feature allows aspartic acid to donate a hydrogen ion and become negatively charged?

How does the structure of glutamic acid differ from aspartic acid, and how does this affect its ability to donate a hydrogen ion?

How does histidine's R group structure allow it to accept a hydrogen ion?

Which of the following is a negatively charged acidic amino acid?

What is the role of the carboxyl group in aspartic acid's ability to become negatively charged?