6,9-Bis(carboxymethyl)-3-(2,14-dioxo-18,21,24,27,30,33,36-heptaoxa-3,15-diazaheptatriacontanyl)-11,23-dioxo-27,30,33,36,39,42,45-heptaoxa-3,6,9,12,24-pentaazahexatetracontanoic acid