| http://www.w3.org/ns/prov#value | - This invention also provides a compound having structure: ##STR12## wherein each of R1, R2, R3 or R4 is independently hydrogen, or a lower alkyl; or wherein one but only one of R1, R2 or R3 is a lower alkyl azide group, a lower alkyl amine, a group comprising a lower alkyl group linked to a lower alkyl carboxylic acid or derivative, with each of the remaining two of R1, R2 or R3 is independently h
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