prov:value
| - om; Xa1 and Xa4 independently represent a SH group or OH group; na1, na2, na3 and ma1 independently represent an integer ranging from 0 to 500, whereby at least one of na1, na2 and na3 is an integer greater than 0; additionally, at least one of Xa1, Xa2, Xa3, and Xa4 is a sulfur atom; ##STR190## wherein Ra1 and Ra2 independently represent a hydrogen atom, or an alkyl group such as a methyl group,
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