Le développement de l’hydrogène en tant que nouveau vecteur d’énergie demande de pouvoir le stocker à grande échelle, dans des conditions d’encombrement, de coût énergétique et de sécurité acceptables. Le stockage sous forme solide dans des hydrures métalliques réversibles, constitue une solution particulièrement sûre et intéressante pour des applications dans le secteur des transports. Parmi de nombreux matériaux possibles, le système Mg/MgH2, constitue l’un des meilleurs candidats : abondant, bon marché, capacité de stockage réversible et élevée (7,6 % H2 en masse). Son utilisation à l’échelle industrielle est néanmoins limitée par les cinétiques de sorption très lentes et la stabilité thermodynamique importante (enthalpie de formation élevée) nécessitant des températures de fonctionnement supérieure à 300 °C. Ce projet vise au développement de composites à base de MgH2 et d’additifs avec des propriétés de stockage améliorées. L’originalité des travaux menés repose sur le type d’additifs choisi, les complexes de métaux de transition (centre métallique : Ni et Ru, ligands organiques : phosphines). En effet, ces derniers ne sont pour le moment que très peu utilisés dans la littérature. L’objectif de ce travail de thèse est donc d’explorer leur potentiel et leur efficacité pour améliorer les propriétés de stockage du système Mg/MgH2. Différents composites "MgH2 + complexe" ont été préparés par broyage et imprégnation et les cinétiques de sorption des systèmes obtenus ainsi que leurs paramètres thermodynamiques ont été déterminés par analyse thermique (DTP, DSC, PCT). Enfin, de nombreuses techniques de caractérisation physico-chimiques (DRX, RMN, XPS, MEB, MET) ont été utilisées afin de comprendre les phénomènes se déroulant lors de l’hydrogénation et la déshydrogénation des composites préparés. Le meilleur système « MgH2 + complexe » préparé durant ce travail (MgH2 dopé avec 20 % du complexe NiHCl(PCy3)2) est capable d’absorber 6 % en masse d’H2 à 100 °C en 30 min et de libérer son hydrogène sous vide à 200 °C. Les énergies d’activation apparentes et enthalpies de formation de ce composite sont respectivement de 22 et –65 kJ/mol H2 pour l’hydrogénation (contre 200 et –74,7 kJ/mol H2 pour du Mg commercial) et de 127 et 63 kJ/mol H2 pour la déshydrogénation (contre 239 et 74,7 kJ/mol H2 pour du MgH2 commercial) / Although hydrogen is widely recognized as a promising energy carrier, its widespread adoption as alternative to fossil fuels depends critically on the ability to store hydrogen at adequate densities, cost and security. Application devices are far from a valuable technology, and fundamental research is still required. In this regard, solid-state systems present the advantage of denser and safer hydrogen storage. Among them, Mg/MgH2 is considered as a highly promising material in terms of reversibility, cost, gravimetric and volumetric capacity. However, high thermodynamic stability (high formation enthalpy) and slow hydrogen sorption kinetics limits its practical applications.This project aims to develop Mg/MgH2-based systems with improved hydrogen storage properties thanks to the use of additives. The originality of this work is brought by the kind of additive chosen, transition metal complexes (Ni and Ru based, with phosphine ligands). Indeed, they are, for now, only very little used in the literature. The objective of this work is therefore to study their potential and their efficiency to improve the hydrogen storage properties of the Mg/MgH2 system. Different “MgH2 + complex” composites were prepared by ball milling and impregnation method and the sorption kinetics and thermodynamic parameters of the formed systems were studied by TPD, DSC and PCT analyses. Finally, XRD, NMR, XPS, SEM and TEM techniques were used to understand the phenomena taking place during the hydrogenation and the dehydrogenation of the prepared composites.The best “MgH2 + complex” system prepared during this work (MgH2 doped with 20 wt% of NiHCl(PCy3)2 complex) is able to absorb 6 wt% of H2 at 100 °C in 30 min, and to release the stored hydrogen at 200 °C under vacuum. The apparent activation energies and the formation enthalpies of the composite are respectively of 22 and –65 kJ/mol H2 for the hydrogenation reaction (against 200 and –74,7 kJ/mol H2 for commercial Mg) and of 127 and 63 kJ/mol H2 for dehydrogenation (against 239 and 74,7 kJ/mol H2 for commercial MgH2).

No description available.

<p dir="ltr">Interfaces play an important role in a broad range of physical, chemical, and biochemical processes. For example, nutrient transport from and to cells happens at the cellular membrane interface, the corrosion of metals occurs due to chemical reactions at the solid/air interface, and the development of waterproof clothing relies on the modification of the clothing surface with hydrophobic species. The importance and complexity of interfaces make a detailed understanding of the interfacial physicochemical processes central to both the fundamental science and the development of new technologies. Specifically in the fields of energy storage/production and heterogeneous catalysis, understanding the transformations of the active species on surfaces leads to the development of high-performance, stable interfaces. In the thesis presented herein, ion soft landing was used as a preparative technique to understand the chemical changes that ions undergo on surfaces. Ion soft landing is a mass spectrometry technique in which polyatomic ions are deposited onto surfaces while preserving their chemical structure and charge state. The advantage of using ion soft landing to study interfaces is that it enables the preparation of well-defined ionic interfaces by the deposition of mass-selected ions on a defined surface area with high control over the amount of deposited material. Because ion soft landing uses purified ion beams formed in the gas phase, it also allows to study the chemical properties of the analytes in the absence of counterions or solvent molecules. Collectively, these capabilities make ion soft landing a powerful approach for preparing ionic interfaces and studying their chemical properties. A new direction in ion soft landing research takes advantage of gas phase ion chemistry techniques, such as collision-induced dissociation, to generate well-defined reactive fragment ions as unique building blocks for studying chemistry at interfaces. <b>Chapter 2 </b>of this thesis discusses the development of an ion soft landing instrument that enables high transmission of fragment ions for their deposition onto surfaces. Ion soft landing of reactive fragment ions opens up possibilities for studying their stability and reactivity on surfaces providing a path to the controlled preparation of unique ionic interfaces. <b>Chapters 3 </b>and <b>4 </b>describe an unusual spontaneous ligand loss observed for soft landed [Ni(bpy)₃]²⁺⁰, an ion of interest in the field of catalysis, and its stabilization by codeposition with anions. We compared the reactivity of [Ni(bpy)₃]²⁺on surfaces against that of [Ni(bpy)₂]²⁺and [Ni(bpy)]⁺species (both formed by ligand removal in the gas phase). This comparison indicates that the dissociation of [Ni(bpy)₃]²⁺ occurs both due to its reorganization on a surface and by charge-reduction. Both processes substantially reduce ligand binding energy and facilitate ligand loss from the complex.</p><p dir="ltr"><b>Chapter 5 </b>diverges from ion soft landing and instead presents a gas-phase ion chemistry study on the stability of cucurbituril-viologen host-guest complexes to better understand the intrinsic properties that influence the strength of their interaction. We found that there is a “perfect fit” size of the host that maximizes interactions with the guest thus increasing its stability. In addition, guests of smaller sizes that are better incorporated into the host have a substantial stability compared to those that have functional groups extending outside of the protecting cavity of the host. The results of this work reveal a strategy to stabilize viologens in the gas phase for the preparation of functional interfaces using ion soft landing.</p><p dir="ltr">Finally, <b>Chapter 6 </b>shows the results of a work at the teaching/learning interface, specifically regarding an undergraduate research project developed for the Analytical Chemistry I course (CHM323) at Purdue University. The goal of this project was to further develop students’ scientific skills on planning, problem-solving, and critical thinking to assess the performance of two analytical techniques. Specifically, the project described in <b>Chapter 6 </b>was designed in such a way that students had to do research on appropriate analytical techniques to quantify ascorbic acid in an unknown sample, propose an experimental protocol, perform it in the laboratory, and concisely summarize the results of their work in a lab report.</p><p dir="ltr">In summary, the work presented in this thesis encompasses three areas. First, it shows the advantages of using fragment ions produced in the gas phase to study the complex physicochemical processes occurring at interfaces. Second, it presents a study on the gas-phase stability of viologen-based host-guest complexes with the prospect of making viologens accessible for the preparation of functional interfaces using ion soft landing. Finally, it describes an undergraduate laboratory project aimed at developing the scientific skills of students in an analytical chemistry course.</p>

Quantum chemical calculations at BP86/TZVPP//BP86/SVP have been carried out for the Nheterocylic carbene and analogues complexes (tetrylene) [(CO)4W-NHE] (W4-NHE) with E = C – Pb. The tetrylene complexes W4-NHE possess end-on-bonded NHE ligands (E = C, Si), while for E = Ge and Sn, they possess slightly side-on-bonded ligands. The strongest side-on-bonded ligand when E = Pb has a bending angle of 102.9°. The trend of the bond dissociations energies (BDEs) for the W-E bond is W4-NHC > W4-NHSi > W4-NHGe > W4-NHSn > W4-NHPb. Analysis of the bonding situation suggests that the NHE ligands in W4-NHE are strong σ-donors and weak π-donors. This is because the tetrylenes have only one lone-pair orbital available for donation. The polarization of the W-E bond and the hybridization at atom E explain the trend in the bond strength of the tetrylene complexes W4-NHE. The W-E bonds of the heavier systems W4-NHE are strongly polarized toward atom E giving rise to rather weak electrostatic attraction with the tungsten atom which is the main source for the decreasing trend of the bond energies. The theoretical calculations suggest that transition-metal complexes tetrylenes [(CO)4W-{NHE}] (E = C – Pb) should be synthetically accessible compounds with tetrylenes NHE act as two-electron-donor ligands in complexes. / Phân tích cấu trúc và bản chất liên kết hóa học của hợp chất với kim loại chuyển tiếp chứa phối tử N-heterocyclic carbene và các đồng đẳng (tetrylene) [(CO)4W–NHE] (W4-NHE) với E = C – Pb sử dụng tính toán hóa lượng tử ở mức BP86/TZVPP//BP86/SVP. Cấu trúc của phức W4-NHE cho thấy các phối tử NHE với E = C, Si tạo với phân tử W(CO)4 một góc thẳng α = 180,0°, trong khi đó các phức W4-NHE thì phối tử NHE với E = Ge – Pb tạo liên kết với nhóm W(CO)4 một góc cong α < 180,0° và góc cong càng trở nên nhọn hơn khi E = Pb (α = 102.9°). Năng lượng phân ly liên kết của liên kết W-E giảm dần: W4-NHC > W4-NHSi > W4-NHGe > W4-NHSn > W4-NHPb. Tính toán hóa lượng tử trong phức [(CO)4W-{NHE}] (E = C – Pb) cho thấy phối tử tetrylene là chất cho electron. Điều này có thể do phối tử tetrylene chỉ giữ lại một cặp electron tại nguyên tử E để đóng vai trò là chất cho điện tử. Độ bền liên kết của phức W4-NHE được giải thích nhờ vào độ phân cực của liên kết W-E và sự lai hóa của nguyên tử trung tâm E. Nguyên nhân chính làm giảm dần năng lượng liên kết là do liên kết W-E của các phức nặng hơn W4-NHE bị phân cực mạnh về phía nguyên tử E dẫn đến lực hút tĩnh điện với nguyên tử W yếu dần. Hệ phức nghiên cứu được coi là hợp chất điển hình cho các nghiên cứu thực nghiệm.

Iron-mediated oxidative cyclisation provides an efficient approach to pyrano[3,2-a]carbazole alkaloids. Thus, improved routes to girinimbine and murrayacine as well as the first total syntheses of O-methylmurrayamine A and 7-methoxymurrayacine are reported. Asymmetric epoxidation of girinimbine led to (−)-trans-dihydroxygirinimbine and the assignment of its absolute configuration. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Ce travail de thèse s'inscrit dans le contexte général des solutions envisageables pour répondre aux problèmes du réchauffement climatique global et de la diminution des ressources fossiles. Il a été en majeure partie consacré à l'étude et au développement d'électrocatalyseurs moléculaires pour la réduction du dioxyde de carbone. Un tel procédé pourrait permettre de transformer et valoriser le CO2 en l'exploitant comme une matière première carbonée disponible en quantité non limitée, bon marché et peu toxique. Dans une première partie, un métallocavitand, dont la structure est basée sur un calix[4]arène fonctionnalisé par quatre complexes phénanthroline tris-carbonyl de rhénium(I), a été étudié en solution et sur déposé sur surface transparente conductrice. Le but de cette étude était de contrôler par un stimulus électrochimique la fermeture et l'ouverture du bord large du cavitand. La complexité des processus rédox de ces métallo-macrocycles nous a conduits à étudier en détails les propriétés électrochimiques de complexes de rhénium(I) modèles. Ces propriétés avaient précédemment été rapportées dans la littérature mais étaient sujettes à désaccords entre les différents auteurs. Finalement l'ensemble de cette étude nous a conduits à préciser et à mieux comprendre le mécanisme de la catalyse de réduction du CO2 par ce type de complexes. Dans une deuxième partie, qui représente la partie la plus conséquente de cette thèse, la synthèse, la caractérisation physico-chimique et l'étude spectro-électrochimique de complexes bipyridine tris-carbonyle de manganèse, analogues des complexes de rhénium évoqués ci-dessus, ont été entreprises. Le but était de développer un catalyseur innovant pour la réduction électrochimique du dioxyde de carbone, du type complexe métallique, en substituant les métaux rares utilisés actuellement par un métal non-noble et abondant : le manganèse. Les propriétés électrochimiques des nouveaux complexes de Mn synthétisés ont été caractérisées en détail. La simulation des voltammétries cycliques, associée à des études mécanistiques par spectro-électrochimie UV-vis, a permis d'accéder aux données cinétiques et thermodynamiques des différentes réactions chimiques associées aux réactions de transferts d'électron irréversibles. Ces complexes de manganèse se sont révélés être des électrocatalyseurs de la réduction du CO2 au moins aussi efficaces que les complexes analogues de rhénium, décrits jusque-là comme étant les meilleurs systèmes pour cette application. Les complexes de Mn ainsi préparés montrent une excellente sélectivité (rendements faradiques élevés et peu ou pas de H2) et une bonne efficacité pour l'électro-réduction du CO2 en CO en milieu hydro-organique. Les catalyses à l'échelle préparatrice fonctionnent avec des surtensions modérées. Les mécanismes mis en jeu lors de la catalyse ont été étudiés par spectro-électrochimie UV-vis et RPE (en onde continue et pulsée) associées à des caculs théoriques DFT. Un intermédiaire-clé a ainsi pu être mis en évidence et caractérisé. Enfin, l'étude des réactions de décarbonylation photo-induites dans ces complexes est rapportée. / This PhD takes place in the general context of possible solutions to global warming and peak oil issues. It mostly deals with the study and development of molecular electrocatalysts for carbon dioxide reduction. This process may open the way to the use and valorization of CO2 as a raw material. In the first part, a metallocavitand, which structure is based on a calix[4]arene modified by four phenanthroline tris-carbonyl rhenium(I) complexes, was studied in solution and deposited on a conductive transparent surface. The aim of this study was to control through an electrochemical stimulus the closing and opening of the wide rim of the cavitand. Complexity of the redox properties of the metallocavitand led us to investigate in detail the electrochemical properties of simpler examples of these rhenium(I) complexes. These properties were previously described in the literature ; however, there was disagreement in the interpretation of the results. Finally this study led us to a more precise and better understanding of the mechanism of the reduction of CO2 by a complex of this kind. In the second part, which is the main part of this PhD, synthesis, physico-chemical characterization and spectro-electrochemical study of bipyridine tris-carbonyl manganese complexes, analogues of the rhenium complexes mentioned above, were undertaken. The aim was to develop an innovative catalyst for the electrochemical reduction of carbon dioxide, based on a metallic complex, by substituting rare and noble metals currently used by a non-noble and abundant metal: manganese. Electrochemical properties of newly synthesized manganese complexes were investigated in detail. Simulations of cyclic voltammetry, associated with mechanism studies by UV-vis spectro-electrochemistry, allowed us to determine kinetic and thermodynamic properties of the different chemical reactions coupled with the irreversible electron transfers. These manganese complexes proved to electrocatalyse the reduction of carbon dioxide at least as efficiently as the analog rhenium complexes which were, until now, the best system for this application. These manganese electrocatalysts exhibit a very good selectivity (high faradic yields and no or very little H2) and a good efficiency for reduction of CO2 to CO in aqueous-organic media. Preparative scale electrolysis operates at low overpotential. Mechanisms of the different catalytic pathways were studied using UV-vis and EPR (continuous wave or pulsed) spectro-electrochemistry associated with DFT calculations. A key-intermediate was evinced and investigated. Finally the study of photo-induced decarbonylation reactions of these complexes is also described.

Photo sensitizers showing visible light induced DNA cleavage activity are of current importance for medicinal applications related to photodynamic therapy (PTD) considering greater skin penetration of light near 700 nm. While organic molecules and complexes of 4d-5d metal ions are extensively studied for their DNA photo-damage properties in UV and visible light, the chemistry of 3D metal complexes showing visible light-induced DNA cleavage activity is relatively unexplored efforts have been made in this thesis work to design new ternary copper (II) complexes having a-amino acids Such copper (II) complexes with tunable coordination geometry could find potential applications in PDT. Ternary Copper (II) complexes containing L-methionine, S-methy1-L-cysteine and phenanthroline bases are prepared and characterized. They display DNA binding and visible light induced DNA cleavage activity. An enhancement of the DNA cleavage activity is observed for analogous ternary copper (II) complexes contained L-lysine with a pendant cationic amine moiety as a photo-induced DNA Cleavage activity using binary and ternary copper (II) complexes of L-arginine and phenanthroline bases. We have observed AT selective DNA binding and visible light –induced DNA cleavage activity. The crescent-shaped bis-arginine Copper (II) complex mimics the natural antiviral antibiotic netropsin. T o investigate the role of the pendant groups of the amino acids, we have explored the DNA binding and DNA cleavage activity of analogues L-glutamine and L-asparagine complexes. We have prepared ternary copper (II) complexes containing two photosensitizers, viz., L-tryptophan (L-trp) and dipyridoquininoxaline/dipyridophenazine to achieve double strand breaks forming linear DNA. Complex [Cu(L-trp)(dppz)(H2O)+ shows a stacking arrangement of the indole and dppz rings giving a separation that fits with the base pair separation of ds-DNA. Photosensitizes in these complexes approach two different complementary stands of the ds-DNA, leading to double strand breaks and formation of linear DNA. Mechanistic studies on the DNA photocleavage reactions reveal the formation of singlet oxygen(1O2)species by a type-II pathway in preference to the hydroxyl radical generation. A process leading to an efficient DNA cleavage activity on visible light irradiation. The observation of sequence selectivity and double strand DNA cleavage on red light exposure by national design of the complexes is significant considering importance of the results in the chemistry of photodynamic therapy of cancer. The results of this dissertation open up new avenues for designing and developing 3d metal-based photosensitizers with potential utility in nulcleic acid chemistry.

Introduction The chemistry of transitional metal complexes bearing σ-bonded H−X (X = H, Si, C) species/fragments, the so called σ-complexes, are key intermediates in catalytic processes such as hydrogenation, hydrosilylation, alkane functionalization etc. Particularly, the σ-H2 complexes form the best-known group of σ-complexes in which H2 is bound to the metal center in η2-fashion. Several well characterized examples of η2-silane and η2-borane complexes have also been reported. Moreover, in recent years, the carbon analogues of these complexes in which alkanes are coordinated through η2-C-H bonds to the metal center have been attracting the attention of organometallic chemists. An approach towards direct functionalization of σ-bonds in simple alkanes is the heterolytic activation of the C−H bond using highly electrophilic complexes. After all, for fine catalyst design and the selective functionalization of H−H, silanes or simple alkanes, it is necessary to understand the bonding nature of these σ-complexes in depth. Objectives The objectives of this work are as follows a) An attempt to stabilize and gain insights into the bonding nature and reactivity behavior of various sigma ligands on ruthenium center [Ru(η2-HX)(Tpms)(PPh3)2][OTf], (X = H, SiR (R = Me3 or Me2Ph) and CH3). b) Synthesis, characterization and reactivity studies of electrophilic ruthenium(II) complexes bearing (C6F5)2PCH2CH2P(C6F5)2 (dfppe) ligand towards heterolysis of H2. c) An approach towards preparation of insoluble molecular clusters from [Ru(P(OH)3)(dppe)2][OTf]2 complex and Zn, Cd and Cu acetates to realize σ-bond activation under heterogeneous conditions. Significant results In our attempts to gain insights into the bonding nature and reactivity behavior of σ-H2, silane and methane complexes, we followed two strategies to generate these complexes in solution. First, we synthesized and well characterized two new Ru(II)-complexes [RuH(Tpms)(PPh3)2] and [Ru(OTf)(Tpms)(PPh3)2], (OTf = trifluoromethane sulfonate) where Ru-H and Ru-OTf are the key reactive centers, followed by their subsequent reactions with electrophilic reagents such as HOTf, Me3SiOTf and CH3OTf and with H2, PhMe2SiH and CH4 at low temperature, respectively. These reactions finally resulted in the characterization of σ-H2 and σ-silane complexes, however, no σ-methane complex was observed even at low temperature (Scheme 1). Scheme 1 In order to realize highly eletrophilic metal complexes, a chelating fluorinated phosphine ligand 1,2-bis-(pentafluorophenylphosphino)ethane, (C6F5)2PCH2CH2P(C6F5)2 (dfppe) was employed and the synthesis and structural characterization of a series of new, Ru(II) hydride complexes [RuH(P(OMe)3)(bpy)(dfppe)][OTf], cis-[RuH2(dfppe)(PPh3)2] and [RuH(CO)Cl(PPh3)(dfppe)] were accomplished. Protonation reaction of the hydride complexes [RuH(P(OMe)3)(bpy)(dfppe)][OTf] (Scheme 2) and [RuH(CO)Cl(PPh3)(dfppe)] (Scheme 3) with HOTf at low temperature gave free H2 and five-coordinate species [Ru(P(OMe)3)(bpy)(dfppe)][OTf]2 and [Ru(CO)Cl(PPh3)(dfppe)][OTf], respectively. Surprisingly, in all these reactions, dihydrogen complexes are formed which were unobservable in which the H2 ligand was found to be highly labile. Reaction of is-[Ru(bpy)(dfppe)(OH2)(P(OMe)3)][OTf]2 with H2 however, resulted in the heterolytic activation of the H–H bond and concomitant protonation of H2O to give the corresponding hydride complex cis-[Ru(H)(bpy)(dfppe)(P(OMe)3)][OTf] and H3O+ (Scheme 2) . Scheme 2 Scheme 3 In an attempt to prepare insoluble molecular clusters in order to realize σ-bond activation under heterogeneous conditions, we studied the reactivity of highly electrophilic [Ru(P(OH)3)(dppe)2]2+ (dppe = (C6H5)2PCH2CH2P(C6H5)2) complex with various metal acetates. Usage of Zn(OAc)2.2H2O afforded a novel [Ru2(dppe)4P2(OH)2O4Zn2(OAc)(DMP)(OTf)][OTf]2 (Ru-Zn ) soluble bimetallic complex (Scheme 4) which was characterized in detail by NMR and single crystal X-ray crystallography. To achieve the expected insoluble molecular cluster further studies are required to tune the electronics and the sterics around the phosphorous acid moiety. Scheme 4

Scorpionate and terpyridine ligands are of importance in inorganic chemistry for their metal-binding properties. Tris-pyrazolylborate (Scorpionate) ligands that show facial binding mode and steric protection have been extensively used to synthesize complexes modeling the active site structure and biological function of various metalloproteins and as catalysts in C-H and NO activation and carbine transfer reactions. Terpyridine and modified terpyridine ligands showing meridional binding mode have been used in bioinorganic chemistry where Pt-terpyridine complexes are known to inhibit the activity of thiordoxin reductase (TrxR) besides showing interaction with G-quadruplex. The thesis work stems from our interest to use these ligand systems to design and prepare new 3-d metal-based photodynamic therapeutic (PDT) agents to explore their visible light-induced DNA cleavage activity and photocytotoxicity. Efforts have been made in this thesis work to design and synthesize Co(II) and Cu(II) complexes having scorpionate (Tpph) abd terpyridine (tpy) ligands. Ternary 3d-metal complexes having Tpph and planar phenanthroline bases have been synthesized and structurally characterized. The steric encumbrance of Tpph has led to the reduction in chemical nuclease activity along with enhanced photo-induced DNA cleavage activity, particularly of the Cu(II) and Co(II) complexes. The Co(II), Cu(II) and Zn(II) complexes of Tpph and a pyridyl ligand having a photoactive naphthalilmide moiety show molecular light-switch effect on binding to calf thymus DNA or BSA protein. The complexes do not show any chemical nuclease activity. The Cu(II) complex shows significant DNA cleavage activity in red light. The Co(II) complex displays significant photocytotoxicity in UV-A light. Ternary Cu(II) complexes of ph-tpy and heterocycylic bases are prepared and their DNA binding and cleavage activity studied. The complexes are avid binders to CT-DNA. The dipyridoquinoxaline (dpq) and dipyridophenazine (dppz) complexes are photocleavers of DNA in visible light. A significant enhancement in cytotoxicity in HeLa cancer cells is observed on exposure of the dppz complex to light. The binary Cu(II) complexes are also prepared to reduce the dark toxicity using phenyl and pyrenyl substituted terpyridine ligands. The pyrenyl substituted complex shows DNA cleavage activity in the visible light, low dark toxicity and unprecedented photocytotoxicity in visible light. The copper(II) complexes generally show dark cellular toxicity due to the presence of reducing thiols. The present terpyridine copper(II) complex having pendant pyrenyl moiety shows significant PDT effect that is similar to that of the PDT drug Photofrin. Binary Co(II) complexes show efficient DNA cleavage activity in visible light, significant photocytotoxicity in visible light and cytosolic uptake behaviour. Considering the bio-essential nature of the cobalt and copper ions, the present study opens up new strategies for designing and developing 3d-metal-based photosensitizers for their potential applications in PDT.

Iron-mediated oxidative cyclisation provides an efficient approach to pyrano[3,2-a]carbazole alkaloids. Thus, improved routes to girinimbine and murrayacine as well as the first total syntheses of O-methylmurrayamine A and 7-methoxymurrayacine are reported. Asymmetric epoxidation of girinimbine led to (−)-trans-dihydroxygirinimbine and the assignment of its absolute configuration. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.