A series of mixed-metal bimetallic complexes [(TL)2M(dpp)RhCl2(TL)]3 (M = Ru and Os, terminal ligands (TL) = phen, Ph2phen, Me2phen and bpy, terminal ligands (TL) = phen, bpy and Me2bpy ), which couple one Ru or Os polyazine light absorber (LA) to a cis-RhIIICl2 center through a dpp bridging ligand (BL), were synthesized using a building block method. These are related to previously studied trimetallic systems [{(TL)2M(dpp)2RhCl2]5+, but the bimetallics are synthetically more complex to prepare due to the tendency of RhIII halide starting materials to react with diimine ligands to form cis-[Rh(NN)2Cl2]+ motifs. The bimetallic complexes, [(phen)2Ru(dpp)RhCl2(bpy)]3+, [(phen)2Ru(dpp)RhCl2(phen)]3+, [(Ph2phen)2Ru(dpp)RhCl2(phen)]3+, [(Me2phen)2Ru(dpp)RhCl2(phen)]3+, [(bpy)2Ru(dpp)RhCl2(bpy)]3+, [(bpy)2Ru(dpp)RhCl2(Me2bpy)]3+ and [(bpy)2Os(dpp)RhCl2(phen)]3+, were characterized and studied by electrochemistry, electronic absorption spectroscopy, ESI-mass spectrometry, steady-state and time-resolved emission spectroscopy. Ï¿" ï¿" The electrochemical properties of bimetallic complexes with polyazine ligands exhibit a reversible one-electron metal-based oxidation, a quasi-reversible RhIII/IICl2 overlapped with a small amount of RhII/ICl and an irreversible RhII/ICl2 �reductions prior to the reversible bridging ligand dpp0/- �reduction. ï¿" ï¿" The title bimetallic complexes are efficient light absorbers due to the [(TL)2MII(dpp)] light absorber subunit. The bimetallics display ligand-based ï¿"'ï¿"* transitions in the UV region and metal-to-ligand charge transfer (MLCT) transitions in the visible region of the spectrum with approximately half the absorption extinction coefficient values relative to the trimetallics in the spectrum. The Os,Rh bimetallic complex, [(bpy)2Os(dpp)RhCl2(phen)]3+, displays Os(dï¿")'dpp(ï¿"*) CT transition at 521 nm and a low energy absorption band at 750 nm in the near-infrared region representing direct 1GS'3MLCT excitation due to the high degree of spin orbital coupling in Os complexes. The bimetallic complexes [(phen)2Ru(dpp)RhCl2(bpy)]3+, [(phen)2Ru(dpp)RhCl2(phen)]3+, [(Ph2phen)2Ru(dpp)RhCl2(phen)]3+, [(Me2phen)2Ru(dpp)RhCl2(phen)]3+, [(bpy)2Ru(dpp)RhCl2(bpy)]3+ and [(bpy)2Ru(dpp)RhCl2(Me2bpy)]3+ display Ru(dï¿")'dpp(ï¿"*) MLCT transitions centered at 505, 508, 515, 516, 510 and 506 nm, respectively. The bimetallic complex [(Ph2phen)2Ru(dpp)RhCl2(phen)]3+ displays enhanced absorption. Ï¿" ï¿" The photophysical properties of Ru,Rh bimetallic complexes are close to those of trimetallic analogues. In room temperature acetonitrile, both bimetallic and trimetallic complexes display a weak and short-lived emission from the Ru(dï¿")'dpp(ï¿"*) 3MLCT excited state. For example, the bimetallic complex [(phen)2Ru(dpp)RhCl2(bpy)]3+ emits at 766 nm and the trimetallic complex [{(phen)2Ru(dpp)}2RhCl2]5+ emits at 760 nm. At 77 K in 4:1 ethanol/methanol glass, the bimetallics, as well as trimetallics, exhibit a more intense blue-shifted emission with a longer lifetime, which is from the same 3MLCT excited state. At 77 K, the low temperature emission from the same 3MLCT state of [{(phen)2Ru(dpp)}2RhCl2]5+ blue-shifts to 706 nm with the emission lifetime of 1.8 ms and the bimetallic [(phen)2Ru(dpp)RhCl2(bpy)]3+ emits at 706 nm (t = 1.8 ms). The Ru,Rh complexes 3MLCT excited states can populate Ru(dï¿")'Rh(ds*) triplet metal-to-metal charge transfer (3MMCT) excited states through intramolecular electron transfer at room temperature, which is impeded in the rigid matrice at 77 K due to the large reorganizational energy and restricted molecular motion. The emission of Os,Rh bimetallic complex [(bpy)2Os(dpp)RhCl2(phen)]3+ could not be detected by our instruments likely due to its expected red-shifted emission which lies outside our detector window. ï¿" ï¿" �The Ru,Rh bimetallics display interesting and efficient photo-reactivity with DNA activated by visible light. The DNA gel shift assay, selective precipitation, ESI-mass spectrometry and polymerase chain reaction (PCR) studies suggest that Ru,Rh bimetallic complexes photobind to DNA following visible light excitation. This reactivity is not observed for analogous Ru,Rh,Ru trimetallics due to the steric protection of the Rh site in that motif. The bimetallic [(TL)2Ru(dpp)RhCl2(TL)]3+ systems can photobind and photocleave DNA through low-lying 3MMCT excited states when excited by the low energy visible light, with or without molecular oxygen. This is unusual but desirable reactivity for photodynamic therapy (PDT) drug development. The Os,Rh bimetallic complex [(bpy)2Os(dpp)RhCl2(phen)]3+ photobinds and photocleaves DNA under red therapeutic light excitation without molecular oxygen, an unprecedented result. Polymerase chain reaction experiments were used to evaluate the impact on DNA amplification of the DNA photo-modification and photo-damage induced by [(bpy)2Os(dpp)RhCl2(phen)]3+ under red light irradiation. Either photobinding or photocleavage induced by red light excitation of [(bpy)2Os(dpp)RhCl2(phen)]3+ on DNA inhibits amplification via PCR methods, a model for in vivo replication. Moreover, significant thermal stability of DNA photo-modification over 90 "C is required for PCR. A red light-activated drug that acts in an oxygen-independent mechanism to impede DNA amplification is unique in this field and desirable for study as a new class of PDT drugs. / Ph. D.

Photodynamic therapy (PDT) is a promising approach used in the treatment of cancer, age related macular degeneration, psoriasis, and other diseases. Our research is focused on the discovery of new photonucleases for use in PDT. This study evaluates the photo-induced DNA cleaving abilities of a series of acridine and phenazine-based chromophores. The extended, aromatic ring systems of these compounds are expected to intercalate between adjoining base pairs in the DNA double-helix. Once irradiated, strand breakage, or nicking of plasmid DNA is achieved at micromolar concentrations of compound (pH 7.0 and 22 °C). Our scavenger experiments show that this process occurs as a result of direct electron transfer to oxygen and/or by means of energy transfer which results in the production of singlet oxygen. Three of the photonucleases being examined were designed to chelate metal. These exhibited increased levels of DNA photocleavage in the presence of copper(II).

Photosensitizing molecules and/or metal complexes that interact with DNA via intercalation and groove binding have potential applications as molecular structural probes, as footprinting reagents and in photodynamic therapeutics. To this regard, small molecules that bind to DNA and the energetics involved in these interactions, acridine-based therapeutics, photosensitization, photodynamic therapy, phenothiazine-mediated photosensitization, DNA photocleavage reaction mechanisms and photosensitizing metal complexes are introduced in Chapter I. Next, in Chapter II, the synthesis of a photonuclease consisting of a 3,6-acridinediamine chromophore attached to four metal-coordinating imidazole rings is described. The DNA photocleavage yields, emission quantum yields, and thermal denaturation studies by this acridine-imadazole conjugate in the presence of 16 metal salts are also reported. In Chapter III is the synthesis of a bisacridine covalently tethered to a copper(II)-binding pyridine linker. Additionally, DNA photocleavage studies as well as DNA binding affinity and binding mode(s) of this bisacridine incorporating the copper(II)-binding pyridine linker are examined. The syntheses, characterization, DNA photocleavage studies, DNA thermal denaturation, and viscometric measurements of three new phenothiazinium photosensitizers are described in Chapters IV and V. Collectively, markedly enhanced DNA photocleavage yields are observed in the presence of metals (Chapters II-III) or in comparison to a parent molecule, Chapters II and IV. DNA melting isotherms show higher levels of duplex stabilization with the acridines, specifically in the presence of several metals (Chapter II-III) as well as with the phenothiazine-based ligands (Chapters IV-V). Moreover, different DNA binding modes were observed depending on metal complexation (Chapter III) and nucleic acid structure (Chapter IV). Finally, Chapter VI describes a small project implemented as a National Science Foundation pedagogical laboratory exercise in which a non-invasive procedure for DNA isolation from human cheek cells was utilized with the polymerase chain reaction to amplify alleles encoding a single nucleotide polymorphism involved in normal human color vision.

Cyanine dyes are attractive photosensitizers for photodynamic therapy due to their ease of structure modification and intense absorption in the near-infrared range. Photosensitizers that can bind to DNA and absorb at long enough wavelengths of light to deeply penetrate biological tissue are in high demand for treatment of cancer and other diseases. The following study analyzes the DNA interactions of three pentamethine cyanine dyes with very similar structures, all of which absorb light at wavelengths longer than 800 nm. The work described involves an extensive study of the photocleavage abilities and DNA binding characteristics of these dyes. Our lead compound was a bromophenyl meso substituted symmetrical quinoline cyanine dye. Spectroscopic data, gel electrophoresis experiments and other studies were used to provide evidence of DNA binding mode, ROS production, and of dye-sensitized DNA photocleavage at the unprecedented wavelength of 850 nm.

<p dir="ltr">A study on the impact of the position of the attachment of the photolabile, backbone amide linker, 4-formyl-3-hydroxy-5-nitrobenzoic acid, on the synthesis of a model cyclic pentapeptide was conducted. The peptide was synthesized on a solid support and cleaved photolytically. The crude product was analyzed for the effect of changing position by LC/MS, 1HNMR, and yield. The target peptide could not be identified convincingly by LC/MS or NMR. It was observed that attachment of the backbone amide linker to the N alpha of tyrosine provided the highest crude product yield.</p>

No description available.

The present thesis deals with different aspects of the chemistry of iron complexes, their interaction with DNA and photo-induced cleavage of double-stranded DNA. Chapter I presents a general introduction on metal-based drugs in cancer therapy and the evolution of the transition metal complexes capable of targeting DNA leading to DNA strand scission, emphasizing particularly the photo-induced DNA cleavage activities for their potential utility in PDT. The mechanistic pathways associated with the DNA cleavage are discussed citing selected examples of compounds that are known to be efficient DNA photo-cleavers on irradiation with light of different wavelengths. Objective of the present investigation is dealt in this chapter. Chapter II deals with the synthesis, crystal structure, DNA binding and oxidative DNA cleavage activity of ternary iron(II) complexes of phenanthroline bases to explore the chemistry of iron(II) complexes towards the metal-assisted photo-induced DNA cleavage activity. Chapter III presents the synthesis and characterization of a cationic imidazo[1,5-a]pyridine derivative to explore the role of imidazopyridine moiety in the photo-induced DNA cleavage activity of the compound. Its cytotoxic effect to the HeLa cancer cell has also been studied using UV-A light of 365 nm. Chapter IV presents the synthesis and characterization of dipyridoquinoxaline (dpq) complexes of bivalent 3d-metal ions such as d6-iron(II), d7-cobalt(II), d8-nickel(II), d9-copper(II) and d10-zinc(II) to explore any specific role that is played by the transition-metal ions in exhibiting visible light-induced DNA cleavage activity. Chapter V deals with the synthesis, characterization of oxo-bridged diiron(III) complexes of phenanthrolne bases having a structural motif found in many iron-containing metalloproteins with a diiron core in the active site. DNA binding and photo-induced DNA cleavage activity of the complexes is studied. Finally, Chapter VI deals with the synthesis and characterization of oxo-bridged diiron(III) complexes having L-histidine (L-his) and N,N-donor heterocyclic bases. This chapter describes the double-strand DNA cleavage activity of [{Fe(L-his)(dpq)}2(μ-O)](ClO4)2. Rationalization of the DNA double strand break (dsb) has been made using molecular docking calculations. This chapter also deals with the site-specific protein (bovine serum albumin, BSA) cleavage activity of the complexes on UV-A light irradiation. The references have been compiled at the end of each chapter and indicated as superscript numbers in the text. The complexes presented in this thesis are represented by bold-faced numbers. Crystallographic data of the complexes, characterized structurally by single crystal X-ray crystallography, are given in CIF format in the enclosed CD (Appendix-I). Due acknowledgements have been made wherever the work described is based on the findings of other investigators. Any omission that might have happened due to oversight or mistake is regretted.

Research efforts to determine the causes, effects and locations of mutations within the human genome have been widely pursued due to their role in the development of various diseases. The main cause of mutations in vivo is oxidative damage to DNA via oxidants and free radical species. Numerous studies have been performed in vitro to determine how oxidative damage is induced in DNA. Most of these in vitro studies require photosensitizers to initiate the oxidative damage through various mechanisms. For the purposes of this research, all the photosensitizers that were used initiated oxidative damage in DNA through the electron transfer mechanism. In the charge transport studies, an anthraquinone photosensitizer was covalently linked to the 5 end of DNA by a short carbon tether in order to determine the pattern of damage induced along the length of the DNA. Anthraquinone preferentially damages guanine bases. Our first work sought to determine the effects of charge transport through guanine rich quadruplex DNA dimers. The dimers were formed by the combination of two hairpins with duplex overhangs extending beyond the quadruplex region. This enabled the optimal comparison of the effects of charge transport between duplex and quadruplex DNA structures. Another area of research we pursued in this area was to determine the effects of charge transport in M-DNA (a novel DNA conformation that was reported to form in the presence of zinc ions at a pH above 8). Earlier work on M-DNA suggested that it behaved like a molecular wire. Our research attempted to determine the effects of charge transport on this structure in order to show the behavior of a DNA molecular wire as compared to the standard studies performed in this area on normal B-DNA structures. Lastly, in collaboration with Dr. Ramaiah and colleagues we designed some viologen linked acridine photosensitizers which were tested for any ability to cleave GGG bulges. In preliminary studies, these viologen linked acridine derivatives showed preferential cleavage for guanine bases. They were not covalently bound to DNA, although they could potentially form non covalent interactions with DNA such as intercalation and/or groove binding. Our overall research goal was to determine the extent and overall effect of oxidative damage (using different photosensitizers) on the various DNA structures mentioned above.

The present thesis deals with different aspects of the chemistry and photo-biology of various ferrocene-conjugates, their interaction with double helical DNA, DNA photocleavage and photo-enhanced cytotoxicity in visible light, localization and cellular uptake to study the mechanism of cell death. Phenyl analogues of the active complexes have been synthesized and used for comparison in biological assays. Chapter I presents an overview of cancer and its types, various treatments for cancer. A general overview on the Photodynamic Therapy, a new modality of light activated cancer treatment and its various possible mechanism of action, has been made. The promise of photoactivated chemotherapy is discussed with recently developed metal based antitumor agents. Biological applications of few ferrocene conjugates as anticancer and anti-malarial agents are discussed. The objective of the present investigation is also presented in this chapter. Chapter II presents the synthesis, characterization, structure, DNA binding, DNA photocleavage, photocytotoxicity and cellular localization of ferrocene-conjugated dipicolylamine oxovanadium(IV) complexes of curcumin. To explore the role of the ferrocenyl moiety the phenyl analogue of the ferrocenyl complexes is synthesized and used as a control for comparison purpose. Chapter III deals with the photo-induced DNA cleavage and photo-enhanced cytotoxicity of ferrocene-conjugated oxovanadium(IV) complexes of heterocyclic bases. The synthesis, characterization, structural comparisons, DNA binding, DNA photocleavage and photocytotoxic activity in visible light are discussed in detail. Chapter IV describes the synthesis, characterization and structure of ferrocene-conjugated oxovanadium(IV) complexes of acetylacetonate derivatives. The complexes are evaluated for DNA binding, DNA photocleavage and photocytotoxic activity in HeLa, MCF-7, 3T3 cells in visible light. The fluorescent nature of the complexes is used to study the cellular localization of the complexes and the mechanism of cell death induced by the complexes is also discussed. Chapter V presents the photocytotoxic effect of ferrocene-conjugated oxovanadium(IV) complexes of different curcuminoids in HeLa , HepG2 and 3T3 cells. Curcumin based fluorescence has been successfully used to study the cellular uptake and localization behavior of the complexes. The positive role of the ferrocenyl complex is evident from the ~4 fold increase in its photocytotoxicity compared to the phenyl analogue. The apoptotic mode of cell death is evident from nuclear co-staining using Hoechst dye. Chapter VI describes the synthesis, characterization and photochemotherapeutic efficacy of ferrocene conjugates of N-alkyl pyridinium salts. Mitochondria targeting property of ferrocene compound having n-butyltriphenylphosphonium group has been studied by JC-1 assay. FACS analysis showed significant sub G1/G0 phase cell-cycle arrest in cancer cells on visible light treatment. Finally, the summary of the dissertation and conclusions drawn from the present investigations are presented. The references in the text have been indicated as superscript numbers and compiled at the end of each chapter. The complexes presented in this thesis are represented by bold-faced numbers. Crystallographic data of the structurally characterized complexes are given in CIF format in the enclosed CD (Appendix-I). Due acknowledgements have been made wherever the work described is based on the findings of other investigators. Any unintentional omission that might have happened due to oversight or mistake is regretted. INDEX WORDS: Ferrocene conjugates Crystal structure DNA binding DNA photocleavage Photocytotoxicity Vanadium Cellular Imaging

Photodynamic therapy (PDT) is a non-invasive treatment of cancer with an advantage of having localized photo-activation of the drug at the targeted tumor cells leaving the healthy cells unaffected by the photo-toxicity of the PDT agent. Organic molecules and 4d/5d metal complexes have been extensively studied for their DNA cleavage activity and photo-cytotoxicity in UV and/or visible light. The photoactivity of the current PDT drugs is due to reactive singlet oxygen species. To address the hypoxic nature within neoplasia and to get a realistic scenario to build model and potent PDT agents, attempts have been made in this thesis work to design and synthesize new cobalt and copper complexes having a variety of ancillary ligands and planar phenanthroline bases showing efficient visible light-induced anaerobic plasmid DNA cleavage activity. The disulfide and thiol compounds are known to generate thyil radical in anaerobic medium in presence of some electron donating solvent. To exploit this chemistry of the sulfur anion radical as a reactive species damaging DNA under light irradiation, we have prepared copper(II) complexes of bis(2-hydroxybenzylamino-ethyl)disulfide and D-penicillaminedisulfide and characterized. The complexes are moderate binders to calf thymus DNA and exhibit plasmid DNA cleavage activity in red light. Near-IR light-induced double-strand DNA cleavage activity is observed for the complexes having 3,3' -dithiodipropionic acid and phenanthroline bases. These complexes show lethal double strand breaks in SC DNA responsible for the inhibition in DNA repair mechanism in the cells thus becoming potent candidates as transcription inhibitors. The work has been extended to achieve better visible light-induced plasmid DNA cleavage activity and UV light-induced photocytotoxicity using a more bio-compatible metal ion, viz. cobalt(II) with the same ligand system and enhancement in the photocytotoxicity is observed. To investigate the role of the disulfide ancillary ligands, complexes of salicylideneaminothiophenol bound to the copper(II) are prepared and the complexes show significant plasmid DNA cleavage activity in red light. Finally, ternary cobalt(III) phenanthroline base complexes are prepared to study their DNA cleavage activity in red light and photo-cytotoxicity in UV light. The complexes show efficient plasmid DNA cleavage activity in red light, significant cytotoxicity in UV light, low dark cytotoxicity, and protein (BSA, lysozyme) cleavage activity in UV light. The mechanistic aspects of the photo-induced DNA and protein cleavage activity of the complexes have been studied. A dual involvement of the charge transfer and d-d band is observed in the photosensitization process leading to generation of reactive oxygen species. In summary, the thesis work presents cobalt and copper complexes having thiolate and disulfide moieties that are designed and synthesized as new photodynamic therapeutic agents showing anaerobic DNA cleavage activity in red light and photocytotoxicity. The present study opens up new strategies for designing and developing cobalt and copper based photosensitizers for their potential photochemotherapeutic applications under hypoxic reaction conditions. References: Lahiri, D. et al., J Chern. Sci, 2010, 122, 321-333; Inorg. Chern., 2009, 48, 339-349; Dalton Trans. 2010,39,1807-1816; Polyhedron, 2010, 29, 2417-2425.