| http://www.w3.org/ns/prov#value | - Each of R1, R2 and R3 is an independent group selected from the group consisting of carbocyclic groups preferably containing from 3-10 carbon atoms including aryl, aralkyl and cycloalkyl such as benzyl, phenyl, p-methylbenzyl, cyclohexyl, cyclopentyl and the like, and alkyl groups preferably containing from 1-20 carbon atoms, such as methyl, ethyl, propyl, isobutyl, pentyl, hexyl, heptyl, decyl an
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