Ferric heme b (= ferric protoporphyrin IX = hemin) is an important prosthetic group of different types of enzymes, including the intensively investigated and widely applied horseradish peroxidase (HRP). In HRP, hemin is present in monomeric form in a hydrophobic pocket containing among other amino acid side chains the two imidazoyl groups of His170 and His42. Both amino acids are important for the peroxidase activity of HRP as an axial ligand of hemin (proximal His170) and as an acid/base catalyst (distal His42). A key feature of the peroxidase mechanism of HRP is the initial formation of compound I under heterolytic cleavage of added hydrogen peroxide as a terminal oxidant. Investigations of free hemin dispersed in aqueous solution showed that different types of hemin dimers can form, depending on the experimental conditions, possibly resulting in hemin crystallization. Although it has been recognized already in the 1970s that hemin aggregation can be prevented in aqueous solution by using micelle-forming amphiphiles, it remains a challenge to prepare hemin-containing micellar and vesicular systems with peroxidase-like activities. Such systems are of interest as cheap HRP-mimicking catalysts for analytical and synthetic applications. Some of the key concepts on which research in this fascinating and interdisciplinary field is based are summarized, along with major accomplishments and possible directions for further improvement. A systematic analysis of the physico-chemical properties of hemin in aqueous micellar solutions and vesicular dispersions must be combined with a reliable evaluation of its catalytic activity. Future studies should show how well the molecular complexity around hemin in HRP can be mimicked by using micelles or vesicles. Because of the importance of heme b in virtually all biological systems and the fact that porphyrins and hemes can be obtained under potentially prebiotic conditions, ideas exist about the possible role of heme-containing micellar and vesicular systems in prebiotic times. Table of contents Ferric heme b in aqueous micellar and vesicular systems 17 Micellar systems 17 Vesicular systems 27 The possible presence of hemes in prebiotic times 35 Conclusions and outlook 36Fig. 2. Chemical structures of δ-aminolevulinic acid, uroporphyrinogen III, heme a, heme b (= iron protoporphyrin IX), and heme c. For the three known pathways of the biosynthesis of heme b (Kořený et al., 2022), δ-aminolevulinic acid and uroporphyrinogen III are the common intermediates. Biosynthetically, heme a and heme c are related to heme b (see Layer et al.

Polyaniline emeraldine salt-type products were synthesized under mild, environmentally friendly conditions using hemin as a cost-effective catalyst, p-aminodiphenylamine (PADPA) as a monomer, and micelles formed from SDBS as templates.

Multivesicular vesicles, i. e. vesicles containing internal, non‐concentrically arranged smaller vesicles, are artificial, polymolecular compartment systems, which can be prepared from naturally occurring or fully synthetic bilayer‐forming amphiphiles in aqueous solution through various guided assembly procedures. The general concepts for the preparation of such “vesicles‐inside‐vesicles” systems (also called “vesosomes”) are summarized, and the different methods used are compared. Selected applications of multivesicular vesicles in the field of drug delivery, cell‐mimicking model systems, and as versatile compartments for the investigation of confined reactions are discussed.

Multivesicular vesicles, i. e. vesicles containing internal, nonconcentrically arranged smaller vesicles, are artificial, polymolecular compartment systems, which can be prepared from naturally occurring or fully synthetic bilayer-forming amphiphiles in aqueous solution through various guided assembly procedures. The general concepts for the preparation of such "vesicles-inside-vesicles" systems (also called "vesosomes") are summarized, and the different methods used are compared. Selected applications of multivesicular vesicles in the field of drug delivery, cell-mimicking model systems, and as versatile compartments for the investigation of confined reactions are discussed.

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