R1, R2, R3, R4, R5, and R6 are the same or different and each represents one member selected from {HEAD ~ the group} consisting of {TAIL ~ hydrogen}, a hydroxyl group, a substituted or unsubstituted aliphatic hydrocarbon group, and a substituted or unsubstituted aromatic hydrocarbon group, provided that at least one of R1 to R6 is a hydroxyl group; and 
consisting of
R1 , R2 , R3 , R4 , R5 , and R6 are the same or different and each represents one member selected from { HEAD ~ the group } consisting of { TAIL ~ hydrogen } , a hydroxyl group , a substituted or unsubstituted aliphatic hydrocarbon group , and a substituted or unsubstituted aromatic hydrocarbon group , provided that at least one of R1 to R6 is a hydroxyl group ; and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH