2,7-Naphthalenedisulfonic acid,5-(acetylamino)-3-[[4-[2-[[2-[5-[[[(4-cyanophenyl)amino]carbonyl]amino]-2-[[2-[3-(1,1-dimethylethyl)-4-hydroxyphenoxy]-1-oxotetradecyl]amino]-4-hydroxyphenoxy]ethyl]sulfonyl]ethoxy]phenyl]azo]-4-hydroxy-,dipotassium salt