What I am wondering, are aspartic acid and glutamic acid at physiological pH present in zwitterion form. In my textbook it says that all aminoacids are at pH 7,4 or 7 in zwitterion form. I wonder how if pKa values of side chains of aspartic acid is 3,65. There are also arginine, lysine, cysteine and tyrosine that will not have overall neutral charge at pH = 7.
The IUPAC goldbook defines a zwitterion as being overall neutral. Any other definition is thus contrary to the standard definition.