foreign here from chemistrystudent.com in this video we're going to look at amino acids and how they form zwitter ions well we're going to talk about what amino acids are they're acidic and basic properties look at how they form zweta ions and why they're optically active amines and proteins have been covered in separate videos check the links in the description below before we talk in detail about amino acids there are a few essential ideas you need to be comfortable with amines are a group of organic compounds that derive or come from ammonia NH3 they have a nitrogen in with a lone pair of electrons that can act as a base and accept h plus ions carboxylic acids are a class of organic compounds that contain a carbonar group C double Bondo and a hydroxy oh group on the same carbon atom they are able to act as weak acids and partially dissociate in solution forming carboxylate ions according to the bronsted Larry definition acids are proton donors and bases are proton acceptors pH is a scale used to represent the concentration of h plus ions in a solution and can be considered a measure of acidity and alkalinity a solution with a pH below 7 is acidic and the concentration of h plus ions or protons in the solution is greater than the concentration of hydroxide ions a solution with a pH above 7 is considered alkaline and a concentration of hydroxide ions in the solution is greater than the concentration of h plus ions recap done let's go amino acids are a class of organic compounds that all have an nh2 amine group and a carboxylic acid cooh group there are naturally occurring amino acids that all have the same basic structure with the amine and carboxylic acid groups at each end with a different R Group bondage to the central carbon this Central carbon is sometimes called the alpha carbon the simplest amino acid is glycine and has only a hydrogen as the R Group in its General structure the amine and carboxylic acid groups enable amino acids to join together in condensation reactions forming dipeptides when two amino acids join together and polypeptides when lots of amino acids join together forming a long chain in nature this enables the formation of proteins essential macromolecules in all living organisms as aiming groups are basic amino acids can accept h plus ions and as carboxylic acids are acidic amino acids can also donate h plus ions meaning amino acids have something of a split personality and can both accept and donate h plus ions because of this they exist in solid state and in neutral Solutions as something called a zwitter ion a zwitter ion is a compound that has a full negative and positive charge somewhere in its structure and yet has no overall charge to form a zwitter ion there is an internal acid-base reaction in an amino acid the carboxylic acid group will lose a h plus ion and the amine group will accept a h plus ion as a result the carboxylic acid group will end up with a negative charge a carboxylate ion group and the amine group will end up with a positive charge a positively charged NH3 plus ammonium group both of these groups now have a full ionic charge however as they are both one plus and one minus they cancel each other out and the molecule has no overall charge and so can be referred to as a zwitter ion if placed into a solution that contains hydroxide ions so an alkaline solution the NH3 plus part of the zwitter ion will lose a h plus ion and act as an acid reacting with the oh minus ions to form water most importantly though the amino acid will no longer be a zwitter ion as the ammonium group will have lost its positive charge and becomes nh2 again meaning the molecule now has an overall negative charge from the carboxylate group if however the zwitter ion is placed in an acidic solution so one that contains h plus ions the carboxylate COO minus part of the Twitter ion will accept a h plus ion and act as a base reforming a carboxylic acid group cooh again the molecule is no longer a zwitter ion as it has lost that negative charge in its structure and now has an overall charge of one plus from the NH3 plus ammonium group this shows us that amino acids can exist in free forms all dependent on the pH of the solution they are in for example in an acidic solution with a low PH the amino acid alanine exists as a positively charged ion in a neutral solution it exists as a sweater ion and in an alkaline solution with a high pH it exists as a negatively charged ion the exact pH at which either the carboxylate group of isrita ion accepts a h plus ion or the NH3 plus group releases a h plus ion is different for different amino acids this is all because different R groups affect the acidity of the carboxylic acid group and the basicity of the amine group differently the more acidic the acid group is the lower the ph solution needs to be for the carboxylate ion to accept a h plus ion back again and reform the acid group the weaker the acid group however the less acidic the solution needs to be meaning it can accept a h plus Ion at a slightly higher pH this kind of makes sense a stronger carboxylic acid group doesn't really want to take the h plus ion back meaning a high concentration of h plus ions and low ph is needed to force it to take a h plus ion and reform the acid equally a weaker carboxylic acid group can easily be forced to take a h plus ion back meaning it can happen with a lower concentration of h plus ions and a slightly higher pH it's the same story for the aiming group if the amine group has a high basicity that means it easily accepts h plus ions and if it does easily accept one it isn't going to want to let it go either meaning it takes a high concentration of oh minus ions to force the ammonium group in a zwitter ion to give up a h plus ion and reform the nh2 group compared to an amine group with a low basicity this is why different zwitter ions will release h plus sounds from the NH3 plus groups at different PHS in alkaline Solutions this also means that zwitter ions form at different PHS for different amino acids the pH at which the amino acid forms a zwitter ion and exists with no overall charge is sometimes referred to as its isoelectric Point as a final note naturally occur in amino acids have a chiral Center and can rotate monochromatic plane polarized light this is because the central carbon in an amino acid often referred to as the alpha carbon has four different groups bonded to it with the exception of glycine this means there are two possible ways of arranging the groups bonded to it each being an enantiomer that will rotate plane polarized light in opposite directions as a result naturally occurrent amino acids are optically active Optical isomerism has been covered in more detail at chemistrystudent.com check the links in the description below so to summarize amino acids are a group of compounds that all have the same general structure with a carboxylic acid group and an amine group in a neutral solution and in solid state amino acids exist as zwitter ions with a negatively charged carboxylate group and positively charged ammonium ion group there is no overall charge in alkaline Solutions amino acids exist as negatively charged ions because the ammonium group from its Twitter ion loses its extra H plus ion to reactive oh minus ions leave in behind the negatively charged carboxylate ion and now a neutral nh2 amine group in acidic Solutions amino acids exist as positively charged ions as the carboxylate ion is forced to accept a h plus ion if the pH is low enough the carboxylic acid group becomes neutral and the ammonium NH3 plus group is still positively charged the exact pH at which a zitter ion forms in solution is different for different amino acids as the strength of the acid group changes depending on the R Group in the amino acid and when this point is reached it's called the isoelectric point this means it takes a different pH to force the carboxylate group to gain a h plus ion the basicity of the aiming group also changes based on the R Group at just for right pH for carboxylic acid group will lose a h plus ion in solution and the amine group will hold a h plus ion and a zwitter ion will form a parchment glycine for Central Alpha carbon atom in an amino acid has four different groups bonded to it meaning it is a chiral Center this means amino acids can have Optical isomers and each isomer rotates plane polarized light in opposite directions I hope you found this video useful please check out other relevant videos in the links given in the description below and visit chemistrystudent.com for free notes and revision materials foreign