Aspartame is an artificial sweetener that was first introduced in the US in the 1980's.  It is sold in the US under the brand name NutraSweet.  It is 200 times sweeter than sucrose (table sugar).  It is water soluble, but it has limitations on its stability at high temperatures and basic pH's.  This means it is not good for cooking or for an extended shelf life in certain foods.  But it does work well in diet sodas and drinks. 

In terms of structure, I am not able to draw the structure here but it is basically a dipeptide of two different amino acids: aspartic acid and phenylalanine.  Each amino acid contains an amine and a carboxylic acid.  Aspartic acid also contains an extra carboxylic acid, and phenylalanine contains a benzene ring.  Also, the C-terminus acid is in the form of a methyl ester.  You can see the structure in the first link below.