| http://www.w3.org/ns/prov#value | - In the most preferred embodiments of the present invention, Y is a radical of formula (Ib), X is O, R3 is phosphono, R4 is H, and R1, R2 and R5 are selected from (C12-C24)acyl with the proviso that the total number of carbon atoms in R1, R2 and R5 is from about 46 to about 52.
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