The present invention provites a compound having the following structure: ##STR00001## wherein, in the formula: X is selected from the group consisting of hydroxy, substituted hydroxy, halogen, thiol, and substituted thiol; one of Y.sup.1 and Y.sup.2 is hydrogen or alkyl, and the other is Z-W, wherein Z is a single bond, or a divalent group having alkane or substituted alkane having two hydrogen atoms removed, and W is hydroxy, substituted hydroxy, aldehyde, carboxyl, or substituted carboxyl; and R.sup.1-R.sup.24 are independently selected from the group of hydrogen, alkyl, and substituted alkyl.