Abstract
Porphyrinic compounds are widespread in nature and play key roles in biological processes such as oxygen transport in blood, enzymatic redox reactions or photosynthesis. In addition, both naturally derived as well as synthetic porphyrinic compounds are extensively explored for biomedical and technical applications such as photodynamic therapy (PDT) or photovoltaic systems, respectively. Their unique electronic structures and photophysical properties make this class of compounds so interesting for the multiple functions encountered. It is therefore not surprising that optical methods are typically the prevalent analytical tool applied in characterization and processes involving porphyrinic compounds. However, a wealth of complementary information can be obtained from NMR spectroscopic techniques. Based on the advantage of providing structural and dynamic information with atomic resolution simultaneously, NMR spectroscopy is a powerful method for studying molecular interactions between porphyrinic compounds and macromolecules. Such interactions are of special interest in medical applications of porphyrinic photosensitizers that are mostly combined with macromolecular carrier systems. The macromolecular surrounding typically stabilizes the encapsulated drug and may also modify its physical properties. Moreover, the interaction with macromolecular physiological components needs to be explored to understand and control mechanisms of action and therapeutic efficacy. This review focuses on such non-covalent interactions of porphyrinic drugs with synthetic polymers as well as with biomolecules such as phospholipids or proteins. A brief introduction into various NMR spectroscopic techniques is given including chemical shift perturbation methods, NOE enhancement spectroscopy, relaxation time measurements and diffusion-ordered spectroscopy. How these NMR tools are used to address porphyrin–macromolecule interactions with respect to their function in biomedical applications is the central point of the current review.
Highlights
Porphyrinic compounds stand out among the organic molecules found in nature due to their unique properties associated with their common scaffold, a planar macrocycle consisting of four pyrrole rings linked by methine bridges [1]
nuclear magnetic resonance (NMR) spectroscopy to address the interactions of biomedical-relevant porphyrinic compounds with macromolecules in solution
We have shown that NMR spectroscopy can offer a wealth of complementary information, thanks to its versatility, its accessibility to a vast range of dynamic properties, and its possibility to measure interactions with atomic resolution
Summary
Porphyrinic compounds stand out among the organic molecules found in nature due to their unique properties associated with their common scaffold, a planar macrocycle consisting of four pyrrole rings linked by methine bridges [1]. Heme forms the iron complex of protoporphyrin IX (PPIX) and its protein complex hemoglobin is the major constituent of red blood cells, imparting them. Heme functions as cofactor or an important role in oxygen transport and storage in living systems. Are partly reduced dihydro-porphyrins and their magnesium complexes form the core the green color to plants [4]. TheThe chlorophylls areare part of ture of chlorophylls, rendering structure of chlorophylls, rendering the green color to plants chlorophylls part the light‐harvesting complexes of all organisms andand thusthus fulfill one one of the of the light-harvesting complexes of photosynthetic all photosynthetic organisms fulfill of most important functions in life with their ability to use solar energy and transferring it the most important functions in life with their ability to use solar energy and transferring to reaction centers so that molecular oxygen can be formed [9,10].
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