| http://www.w3.org/ns/prov#value | - ##STR00029## where R.sub.1, R.sub.2 and Z.sub.1 to Z.sub.4 are independently chosen from hydrogen and organic moieties having about 1-60 carbon atoms, such as about 1-20, about 1-12, or about 1-6 carbon atoms. Suitable organic moieties can be
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