and the like preferred acylating agents include benzoyl chloride hippuryl chloride acetyl chloride cyclohexanoyl chloride cyclopentanoyl chloride and cycloheptanoyl chloride the amine groups can also be modified by the reaction of a carboxylic acid with coupling agents such as the carbodiimide derivatives of amino acids particularly hydrophilic amino acids such as phenylalanine tryptophan and tyrosine further examples include dicyclohexylcarbodiimide and the like if the amino acid is multifunctional i e has more than one oh nh 2 or sh group then it may optionally be acylated at one or more functional groups to form for example an ester amide or thioester linkage in acylated poly amino acids one or more of the amino acids may be modified acylated modified poly amino acids may include one or more acylated amino acid s although linear modified poly amino acids will generally include only one acylated amino acid other poly amino acid configurations can include more than one acylated amino acid poly amino acids can be polymerized with the acylated amino acid s or can be acylated after polymerization sulfonated amino acids and poly amino acids are modified by sulfonating at least one free amine group with a sulfonating agent which reacts with at least one of the free amine groups present wherein ar 3 is a substituted or unsubstituted phenyl or naphthyl y is so 2 r 18 has the formula str9 wherein r 19 is c 1 to c 24 alkyl c 1 to c 24 alkenyl phenyl naphthyl c 1 to c 10.