the present invention is directed to novel disulfides and thiols that are of up to about eighteen amino acids . one example , is a compound of the formula : a - b - c - s - s - d - e - f , wherein : a and f are selected from the group consisting of hydrogen , an amino acid , a dipeptide , a tripeptide , a modified polypeptide up to three amino acids long , and a carbobenzoxy group , b and e are selected from the group consisting of an amino acid , a dipeptide , a tripeptide , and a modified polypeptide comprising up to and including three amino acids , c and d are selected from the group consisting of a modified polypeptide and a polypeptide comprising up to and including three amino acids , and s is the sulfur atom in the modified polypeptide and the polypeptide in c and d .