Photodynamic therapy(PDT) has recently emerged as a promising new non-invasive treatment modality for a large number of neoplastic and non-neoplastic lesions. Photoexcitation of a photosensitizing drug in the tumor tissue causes generation of reactive oxygen species which results in cell death. The current porphyrinic photosensitizers suffer a wide range of drawbacks leading to the development of the chemistry of alternative photosensitizing agents in PDT. Among them, the 4d and 5d transition metal-based photosensitizers have been explored extensively with the exception of the 3d metal complexes. The objective of this thesis work is to design and synthesize photoactive iron(III) abd cobalt(III) complexes and evalutate their photonuclease and photocytotoxic potential. Bioessential 3d metal ions provide an excellent platform for metal-based PDT drug designing as because of its varied spectral, magnetic and redox properties, with its complexes possessing rich photochemical behavior in aqueous and non-aqueous media. We have synthesized binary iron(III) complexes as netropsin mimics using amino acid Schiff bases derived from salicylaldehyde/napthaldehyde and arginine/lysine. The complexes were found to be good AT selective DNA binders and exhibited significant DNA photocleavage activity. To enhance the photodynamic potential, we further synthesized iron(III) complexes of phenolate-based ligand and planar phenanthroline bases. The DNA photocleavage activity of these complexes and their photocytotoxic potential in cancer models were studied. ROS generated by these complexes were found to induce apoptotic cell death. Ternary cobalt(III) complexes were synthesized to study the effect of the central metal atom. The diamagnetic cobalt(III) complexes were structurally dissimilar to their iron(III) analogues. Although the Co(III)/Co(II) redox couple is chemically and photochemically accessible but the Co(III)-dppz complex, unlike its iron(III)-dppz analogue, exhibited selective damage to hTSHR expressing cells but not in HeLa cells. A structure-activity relationship study on iron(III) phenolates having modified dppz ligands was carried out and it was found that electron donating group on the phenazine unit and an increase of the aromatic surface area largely improved the PDT efficiency. Finally, SMVT targeted iron(III) complexes with biotin as targeting moiety were synthesized and the in vitro efficacy of the complexes was tested in HepG2 cells over-expressing SMVTs and compared to HeLa amd HEK293 cells. The complexes exhibited higher phytocytotoxicity in HepG2 than in HeLa and cells and HEK293 cells. An endocytotic mode of uptake took place in HepG2 cells whereas in HEK293 cells, uptake is purely by diffusion. This is expected to reduce the side-effects and have less effect on cells with relatively less SMVTs. In summary, the present research work opens up novel strategies for the design and development of primarily iron-based photosensitizers for their potential applications in PDT with various targeting moieties.

Σε αυτή την εργασία περιγράφονται οι αντιδράσεις αλάτων του κοβαλτίου(ΙΙ) [Co(O2CMe)2•4H2O, Co(ClO4)2•6H2O και Co(O2CPh)2] με την Ν-σαλικυλιδενο-4- μεθυλο-ο-αμινοφαινόλη (saphΗ2-4Me), την Ν-σαλικυλιδενο-4-χλωρο-ο-αμινοφαινόλη (saphΗ2-4Cl) και την Ν-σαλικυλιδενο-ο-αμινοφαινόλη (saphΗ2). Από τo σύστημα αντίδρασης Co(O2CMe)2•4H2O/saphΗ2-4Me/ΝaΟΗ σε διαλύτη MeOH απομονώθηκε ένα οκταεδρικό σύμπλοκο με τύπο (Η5Ο2)[CoΙΙΙ(saph-4Me)2]•H2O (1). Χρησιμοποιώντας την Εt3N ως βάση, από ένα ανάλογο σύστημα αντίδρασης, απομονώθηκε ένα οκταεδρικό σύμπλοκο με τύπο (Εt3NH)[CoΙΙΙ(saph-4Me)2]•ΜeCΟ2Η•MeOH (2). Από το σύστημα αντίδρασηςfCo(O2CMe)2•4H2O/ saphΗ2-4Cl/Εt3N σε διαλύτη MeOH απομονώθηκε το ισοδομικό του συμπλόκου 2, δηλαδή το σύμπλοκο (Εt3NH)[CoΙΙΙ(saph-4Cl)2]•ΜeCΟ2Η•MeOH (3). Οι τρεις σύμπλοκες ενώσεις χαρακτηρίστηκαν με IR φασματοσκοπία, ενώ για τα σύμπλοκα 1 και 2 πραγματοποιήθηκαν και μετρήσεις 1Η ΝΜR φασματοσκοπίας. Οι κρυσταλλικές δομές των συμπλόκων 1, 2 και 3 επιλύθηκαν με κρυσταλλογραφία ακτίνων Χ μονοκρυστάλλου. Βάσει των πειραματικών δεδομένων και τα τρία σύμπλοκα είναι ανιοντικά μονοπυρηνικά με το ιόν του κοβαλτίου(ΙΙΙ) να περιβάλλεται από δύο τριδοντικούς, πλήρως αποπρωτονιωμένους, υποκαταστάτες, οι οποίοι ενώνονται με αυτό μέσω των δύο αποπρωτονιομένων φαινολικών οξυγόνων και με το άτομο του ιμινικού αζώτου. Τα κατιόντα είναι το Η5Ο2+ για το σύμπλοκο 1 και το Εt3NH+ για τα 2 και 3. / In this work the reactions of cobalt(II) salts [Co(O2CMe)2•4H2O, Co(ClO4)2•6H2O and Co(O2CPh)2] with N-salicylidene-4-methyl-o-aminophenol (saphH2-4Me), N-salicylidene-4-chloro-o-aminophenol (saphH2-4Cl) and N-salicylidene-o-aminophenol (saphH2) Schiff bases are described. From the Co(O2CMe)2•4H2O/ saphH2-4Me/NaOH reaction system in MeOH we have isolated a six-coordinated complex with the formula (H5O2)[CoΙΙΙ(saph-4Me)2]•H2O (1). From a similar reaction system with Et3N as a base, we isolated a six-coordinated complex with the formula (Et3NH)[CoΙΙΙ(saph-4Me)2]•MeCO2H•MeOH (2). The Co(O2CMe)2•4H2O/saphH2-4Cl/Et3N reaction system in MeOH has led to the complex (Et3NH)[CoΙΙΙ(saph-4Cl)2]•MeCO2H•MeOH (3), which is isostructural to 2. The three complexes have been characterized by IR spectroscopy, while the complexes 1 and 2 have been also studied by 1H NMR spectroscopy. The crystal structures of 1, 2 and 3 have been determined by single-crystal X-ray crystallography. Based on experimental results, all the three complexes are anionic mononuclear with the CoIII ion being surrounded by two tridentate dianionic Schiff-base ligands, which chelate the metal ion through the deprotonated phenolic oxygen atoms and the nitrogen atom of the azomethine group. The cation for the complex 1 is H5O2+, while for the complexes 2 and 3 the cation is Et3NH+.