Delcourt, R. published the artcileElectrophoretic behavior of phthaleins alone and in the presence of proteins, Quality Control of 596-01-0, the publication is Protides of the Biological Fluids (1959), 119-26, database is CAplus.
cf. C.A. 53, 5370g. The mobility of 16 phthalein dyes and their binding of human serum albumin was studied by paper electrophoresis at pH 8.6. By considering phenolphthalein as the simplest member of the series, mobility is diminished by methylation of the phenol moiety; sulfonation augments mobility without suppressing the effect of methylation, while halogenation suppresses the influence of methylation. For the formation of complexes with albumin, the presence of a halogen atom in the phthalein is essential. Affinity of halogenated phthaleins for proteins depends on the nature of the halogen (Cl < Br < I). Thus, iodophthalein is more firmly attached to the protein and is able to displace bromo- and chloro-phthalein from their protein complexes. It was not possible to determine which free groups on the protein are involved in this binding.
Protides of the Biological Fluids published new progress about 596-01-0. 596-01-0 belongs to benzofurans, auxiliary class Benzofuran,Naphthalene,Alcohol,Ester, name is 3,3-Bis(4-hydroxynaphthalen-1-yl)isobenzofuran-1(3H)-one, and the molecular formula is C28H18O4, Quality Control of 596-01-0.
Referemce:
https://en.wikipedia.org/wiki/Benzofuran,
Benzofuran | C8H6O – PubChem