Capillary electrophoretic separation of cationic porphyrins

Area of Science:

• Analytical Chemistry
• Separation Science
• Supramolecular Chemistry

Background:

• Cationic porphyrins possess diverse applications, including nucleic acid interactions, pharmacology, and electron transfer processes.
• Traditional chromatographic methods often struggle to effectively separate these complex cationic porphyrin molecules.
• Developing efficient separation techniques is crucial for advancing the study and application of cationic porphyrins.

Purpose of the Study:

• To report the successful separation of various cationic porphyrins using capillary electrophoresis (CE).
• To investigate the efficacy of centrifugal partition chromatography (CPC) for preparative-scale separation of porphyrin derivatives.
• To explore factors influencing the separation of cationic porphyrins under CE conditions.

Main Methods:

• Synthesis of cationic porphyrins via alkylation of tetrapyridylporphyrin (TPyP).
• Capillary electrophoresis (CE) using fused silica capillaries in phosphate buffer (pH 2-5).
• Preparative-scale separation using centrifugal partition chromatography (CPC).

Main Results:

• CE successfully separated mixtures of mono-, di-, tri-, and tetramethylated pyridinium porphyrins (e.g., TMPyP(4)).
• CE also resolved conformational isomers (atropisomers) of TMPyP(2) and separated metallo-TMPyP(4) complexes.
• CPC enabled preparative separation of cis-di- and trimethylated TMPyP derivatives.

Conclusions:

• Capillary electrophoresis and centrifugal partition chromatography offer powerful and novel separation techniques for cationic porphyrins.
• Net charge, molecular mass, and shape are key factors in CE separation of these compounds.
• Aggregation and protonation significantly influence porphyrin separation, requiring careful control of solution conditions.