Properties of Amino Acid Base The neutral forms of amino acids are zwitter ions67. Amino acid have both amine and carboxyl active groups as the acid-base properties. At isoelectric point in certain pH it has the amino acid becomes positively charged (protonated, –NH3+) while the carboxyl group becomes negatively charged (deprotonated, –COO- ) so that the amino acid is amphoteric68. This isoelectric point is specific depending on the type of amino acid. The isoelectric point or isoelectric pH is the pH at which molecules have no electrical charge or the charge is zero69. Based on the circumstances it can be concluded that the amino acid is in the form of a zwitter-ion. To get zwitter-ions it can be extracted from amino acid solution as hite crystalline structures that have a high melting point due to their dipolar nature. Amino acid that free and exist in zwitter-ion form at neutral or nearneutral physiological pH, this condition caused by their negative and positive charges. Amphoteric is the ability of a substance to change its acidity from acidic to basic but this happen depends on the conditions or environment in which the substance reacts. The substance is in a strong acidic environment then the substance is basic and on the contrary if the substance is in an acidic environment then the substance It is alkaline. One example of the amphoteric substances that we usually encounter around us is water (H20). In amino acids the carboxyl group (-COOH) is acidic and the amine group (-NH) is basic. So, amino acids can be acidic and basic, and this property is termed amphoteric . Molecules that are amphoteric can be neutral or have no charge, but can also be dipolar as written in the structure above. In this dipolar form, amino acids act as "Zwitter Ions". In hard acid solutions (acid pH) most of the amino acids are in the form of cations (positive charge), in hard base solutions (alkaline pH) the amino acids are in the form of anions (negative charge). At a certain pH, each amino acid can be in the isoelectric point, which is the point or pH of an amino acid that has a neutral electrical charge. and the pH value at which the amino acid is in a neutral state is known as the isoelectric point of the amino acid. The isoelectric point of acidic amino acids is at pH 3, a more acidic solution is needed for this group of amino acids to add protons to the second carboxylic group. The isoelectric point of basic amino acids is around pH 9-10, a more basic solution is needed to remove the proton from the second ammonium group. Amino acids have both amine and carboxyl active groups, so they can be considered both acids and bases (although their natural pH is usually influenced by the R-group they have). At a certain pH, called the isoelectric point, the amine group in amino acids becomes positively charged (protonated, –NH3+), while the carboxyl group becomes negatively charged (deprotonated, –COO –). This isoelectric point is specific depending on the type of amino acid. In such circumstances, the amino acid is said to be in the form of a zwitter-ion.