An ion is an atom or molecule with a positive or negative charge. A zwitterion is a molecule with both charges but a net charge of zero. Amino acids are a classic example of zwitterions. They are highly soluble in water and useful in buffers, cleaners, and medications.
An ion is an atom or molecule with a positive or negative electrical charge. A zwitterion is a molecule with both positive and negative charges, but with a net charge of zero. Atoms are composed of positively charged subatomic particles called protons, negatively charged electrons and neutral particles called neutrons. When the number of protons is not equal to the number of electrons, an atom will have a positive or negative charge. The negatively charged atoms or molecules are called anions, while the positively charged atoms and molecules are known as cations.
Acids and bases can exist as ions or as uncharged molecules, but at neutral pH levels they are ions. Most zwitterions are ampholytes, molecules that contain both acidic and basic groups. Amino acids are a classic example; have both groups in a single molecule, but since both are charged at neutral pH, the net charge of the amino acid will be zero.
Due to its electrical charges, a zwitterion will be highly soluble in water and fairly insoluble in organic solvents. Water molecules are polar due to electrical differences between hydrogen and oxygen molecules; that is, the oxygen atoms in water are attracted to cations and the hydrogen atoms in water are attracted to anions. When a zwitterion is dissolved in water, the hydrogen atoms in the water immediately surround the negatively charged group, and the oxygen atoms in the water immediately surround the positively charged group, thus dissolving it completely.
Besides amino acids, some other common types of these molecules are buffers, cleaners, and medications. The fact that they are water soluble is what makes them so useful. When a zwitterion is stored in a dry, solid form, such as in a pill, it will be in the form of a neutral molecule or salt. When eaten or placed in water, it takes on its ionic form, or charge, and dissolves.
While it is true that most amino acids have a neutral charge, it is important to note that some have a third charged group, which gives them an overall positive or negative charge. For this reason proteins, which are composed of amino acids, generally have a net negative or net positive charge.
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