Magnetic resonance imaginG Contrast agents exEmplified by iron complexes

Nuclear magnetic resonance is already a broadly exploited phenomenon both in chemistry and medicine. Magnetic resonance imaging is a routine technique in medical diagnosis readily applied for soft tissues like brain, cardiovascular system or gastrointestinal tract. Contrast agents stepped into the field and enabled better recognition of a lesion in the early stage of a disease. The authors present an introductory description of a fascinating history, classification of contrast agents followed by the mechanisms of their action. Classes of positive and negative contrast agents are described. Further discussion is focused on the T1 (positive) molecular species. The mechanism was divided into (1) inner sphere, where both direct coordination of water molecule and its presence in second sphere is considered (Fig. 1) [1] and (2) an outer sphere mechanism which is assumed for the water molecules diffusing into the surrounding of the paramagnet [21, 28]. Further, the most important requirements for medical applications are given. Those are: high relaxivity, charge-osmolality, stability, toxicity via potential transmetallation of redox activity [42]. Molecular examples are quoted based on previously investigated iron complexes. Majority of them are iron(III) species [68], however, some iron(II) compounds like activable, self-immolative or ParaCEST systems have recently appeared [86, 89]. Iron compounds as positive contrast agents may soon accompany classic gadolinium complexes

Amalgamation of complex iron(III) ions and iron nanoclusters with MWCNTs as a route to potential T2 MRI contrast agents

Nikodem Kuźnik,1 Mateusz M Tomczyk,1 Marzena Wyskocka,1 Łukasz Przypis,1 Artur P Herman,1 Rafał Jędrysiak,1 Krzysztof K Koziol,2 Slawomir Boncel11Department of Organic Chemistry, Bioorganic Chemistry and Biotechnology, Faculty of Chemistry, Silesian University of Technology, Gliwice, Poland; 2Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UKAbstract: Iron-filled multiwall carbon nanotubes (Fe@MWCNTs) were functionalized toward a variety of potential magnetic resonance imaging contrast agents. Oxidized Fe@MWNCTs were covered with PEG5000 via direct esterification or using acyl chloride derivatives. Alternatively, the latter were functionalized with an aminophenol ligand (Fe@O-MWCNT-L). Moreover, pristine Fe@MWCNTs were functionalized with N-phenylaziridine groups (Fe@f-MWCNT) via [2+1] cycloaddition of nitrene. All of these chemically modified nanotubes served as a vehicle for anchoring Fe3+ ions. The new hybrids – Fe(III)/Fe@(f-/O-)MWCNTs – containing 6%–14% of the “tethered” Fe3+ ions were studied in terms of the acceleration of relaxation of water protons in nuclear magnetic resonance. The highest transverse relaxivity r2=63.9±0.9 mL mg-1 s-1 was recorded for Fe(III)/Fe@O-MWCNT-L, while for Fe(III)/Fe@f-MWCNT, with r2=57.9±2.9 mL mg-1 s-1, the highest impact of the anchored Fe(III) ions was observed. The T1/T2 ratio of 30–100 found for all of the nanotube hybrids presented in this work is a very important factor for their potential application as T2 contrast agents. Increased stability of the hybrids was confirmed by ultraviolet–visible spectrophotometry.Keywords: multiwall carbon nanotubes, Fe3+, transverse relaxation time T2, MRI contrast agen