Polymer bound pyrrole compounds, VIII. Water-soluble pyrrole pigments carrying polyether side chains

Fontich, M.; Fors, Pere; Sese, Maria L.; Trull, Francesc R.

doi:10.1016/0014-3057(94)90251-8

Cited by 3 publications

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“…We were attracted to poly(ethylene glycol) (PEG) as a water-solubilizing group because it could be attached covalently in a position remote from the carboxylic acid groups of the pigment. Borrowing from earlier work ( , ), we converted molecular weight ∼1900 poly(ethylene glycol) monomethyl ether (MPEG-OH) into its terminal thiol and regioselectively added (thiol addition) the reagent to bilirubin to produce 1 , which is soluble in water. To compare the behavior of water-soluble 1 to water-solubilized fatty acids, we also converted a series of dicarboxylic acids (C 4 to C 20 ) to their monoesters ( 2 − 6 ) with MPEG-OH.…”

Section: Discussionmentioning

confidence: 99%

“…MPEG-S-Bilirubin (1). MPEG-S-bilirubin (1) was prepared according to Fontich et al (27), by synthesis and addition of MPEG-SH to the exo-vinyl group of bilirubin. Thus, MPEG-OH was converted to its p-toluenesulfonate ester MPEG-OTs (29) in 89% yield by reaction with freshly purified p-toluenesulfonyl chloride in dichloromethane in the presence of triethylamine.…”

Section: Methodsmentioning

confidence: 99%

“…We now describe studies on the solution structure and acid dissociation constants of a water-soluble derivative of bilirubin (1) bearing a poly(ethylene glycol) (PEG) side chain (27) and of a series of fatty-acid model compounds (2)(3)(4)(5)(6) solubilized in a similar way. These compounds dissolve readily in water without the need for a cosolvent such as DMSO, and their pK a 's can be readily measured titrimetrically.…”

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pK_a and Aggregation of Bilirubin: Titrimetric and Ultracentrifugation Studies on Water-Soluble Pegylated Conjugates of Bilirubin and Fatty Acids

et al. 2004

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A water-soluble conjugate (1) with intact carboxyl groups was prepared by addition of poly(ethylene glycol) thiol (MPEG-SH) regiospecifically to the exo vinyl group of bilirubin. (1)H and (13)C NMR and absorbance spectroscopy in CDCl(3) and DMSO-d(6) confirmed the assigned structure and showed that pegylation did not disrupt the hydrogen-bonded ridge-tile conformation of the pigment moiety. Aqueous solutions of 1 were optically clear, but NMR signals were seen only from the MPEG portion and none from the tetrapyrrole, consistent with dissolved assemblies containing aggregated bilirubin cores within mobile polyether chains. On alkalinization (pH >12), signals from the pigment moiety reappeared. Titrimetric measurements on 1 in water showed the pK(a)'s of the two carboxyl groups to be similar (average 6.42). Control studies with pegylated half-esters of succinic, suberic, brassylic, thapsic, and 1,20-eicosanedioic acid showed that pegylation per se has little, if any, effect on carboxyl ionization. However, aggregation increases the apparent pK(a) by approximately 1-2 units. The molecularity of bilirubin in solution was further characterized by ultracentrifugation. Over the pH range 8.5-10 in buffer, bilirubin formed multimers with aggregation numbers ranging from approximately 2-7. Bilirubin is monomeric in DMSO or CHCl(3) at approximately 2 x 10(-)(5) M, but aggregation occurred when the CHCl(3) was contaminated with trace adventitious (perhaps lipoidal) impurities. These observations show that aggregation increases the pK(a)'s of aliphatic carboxylic acids relative to their monomer values in water. They are consistent with earlier (13)C NMR-based estimates of approximately 4.2 and approximately 4.9 for the aqueous pK(a)'s of bilirubin and similar studies of bilirubin in micellar bile-salt solutions. Together with earlier work, they confirm that the pK(a)'s of bilirubin are about normal for aliphatic carboxyls and suggest that the high (>7.5) values occasionally reported, including those based on CHCl(3) partitioning, are artifacts of aggregation or technique.

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Section: Methodsmentioning

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pK_a and Aggregation of Bilirubin: Titrimetric and Ultracentrifugation Studies on Water-Soluble Pegylated Conjugates of Bilirubin and Fatty Acids

et al. 2004

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Strategies toward the synthesis of amphiphilic porphyrins

2014

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Conformational folding induced by π–π interaction in a series of flexible dyads consisting of isomeric mesoporphyrin nitrobenzyl esters

Colominas¹,

Eixarch²,

Fors³

et al. 1996

J. Chem. Soc., Perkin Trans. 2

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Polymer bound pyrrole compounds, VIII. Water-soluble pyrrole pigments carrying polyether side chains

Cited by 3 publications

References 56 publications

pK_a and Aggregation of Bilirubin: Titrimetric and Ultracentrifugation Studies on Water-Soluble Pegylated Conjugates of Bilirubin and Fatty Acids

pK_a and Aggregation of Bilirubin: Titrimetric and Ultracentrifugation Studies on Water-Soluble Pegylated Conjugates of Bilirubin and Fatty Acids

Strategies toward the synthesis of amphiphilic porphyrins

Conformational folding induced by π–π interaction in a series of flexible dyads consisting of isomeric mesoporphyrin nitrobenzyl esters

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Polymer bound pyrrole compounds, VIII. Water-soluble pyrrole pigments carrying polyether side chains

Cited by 3 publications

References 56 publications

pKa and Aggregation of Bilirubin: Titrimetric and Ultracentrifugation Studies on Water-Soluble Pegylated Conjugates of Bilirubin and Fatty Acids

pKa and Aggregation of Bilirubin: Titrimetric and Ultracentrifugation Studies on Water-Soluble Pegylated Conjugates of Bilirubin and Fatty Acids

Strategies toward the synthesis of amphiphilic porphyrins

Conformational folding induced by π–π interaction in a series of flexible dyads consisting of isomeric mesoporphyrin nitrobenzyl esters

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Product

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pK_a and Aggregation of Bilirubin: Titrimetric and Ultracentrifugation Studies on Water-Soluble Pegylated Conjugates of Bilirubin and Fatty Acids

pK_a and Aggregation of Bilirubin: Titrimetric and Ultracentrifugation Studies on Water-Soluble Pegylated Conjugates of Bilirubin and Fatty Acids