No abstract

Strikingly different TRIR spectra are recorded for the complex in D2O or CD3CN or when DNA-bound.

The reactions of (η 6 -arene)Mo(CO) 2 (Sol) and M(CO) 5 (Sol) with CO have been studied in a range of alkane solvents (Sol), and the kinetic and activation parameters have been determined (M ) Cr, Mo, or W). For M ) Cr the ∆H q is constant (22 ( 2 kJ mol -1 ), while the ∆S q term becomes less negative as the alkane chain length increases. For the larger metals the variation in kinetic and activation parameters is less significant. Solvent displacement by CO involves an interchange mechanism for the Cr system, while for Mo or W complexes the mechanism is more associative in character. The photochemistry of (η 6 -arene)Mo(CO) 3 (arene ) benzene, mesitylene, p-xylene, or hexamethylbenzene) compounds was investigated by laser flash photolysis, supported by matrix isolation and time-resolved infrared spectroscopy (TRIR). In contrast to the behavior to the analogous (η 6 -arene)Cr-(CO) 3 , it is found that the efficiency for photochemical expulsion of CO from (η 6 -mesitylene)-Mo(CO) 3 is markedly wavelength dependent (Φ CO ) 0.587, 0.120, and 0.053 at 266, 313, and 334 nm, respectively).

A novel Near Infra-Red emitting BODIPY derivative is presented which exhibits the largest Stokes shift thus far reported for a BODIPY compound.

The photochemistry of (η6-C6H6)M(CO)3 (M = Cr or Mo) is described. Photolysis with λexc. > 300 nm of (η6-C6H6)Cr(CO)3 in low-temperature matrixes containing CO produced the CO-loss product, while lower energy photolysis (λexc. > 400 nm) produced Cr(CO)6. Pulsed photolysis (λexc. = 400 nm) of (η6-C6H6)Cr(CO)3 in n-heptane solution at room temperature produced an excited-state species (1966 and 1888 cm−1) that decays over 150 ps to (η6-C6H6)Cr(CO)2(n-heptane) (70%) and (η6-C6H6)Cr(CO)3 (30%). Pulsed photolysis (λexc. = 266 nm) of (η6-C6H6)Cr(CO)3 in n-heptane produced bands assigned to (η6-C6H6)Cr(CO)2(n-heptane) (1930 and 1870 cm−1) within 1 ps. These bands increase with a rate identical to the rate of decay of the excited-state species and the rate of recovery of (η6-C6H6)Cr(CO)3. Photolysis of (η6-C6H6)Mo(CO)3 at 400 nm produced an excited-state species (1996 and 1898 cm−1) and traces of (η6-C6H6)Mo(CO)2(n-heptane) within 1 ps. For the chromium system CO-loss can occur following excitation at both 400 and 266 nm via an avoided crossing of a MACT (metal-to-arene charge transfer) and MCCT/LF (metal-to-carbonyl charge transfer/ligand field) states. This leads to an unusually slow CO-loss following excitation with 400 nm light. Rapid CO-loss is observed following 266 nm excitation because of direct population of the MCCT/LF state. The quantum yield for CO-loss in the chromium system decreases with increasing excitation energy because of the competing population of a high-energy unreactive MACT state. For the molydenum system CO-loss is a minor process for 400 nm excitation, and an unreactive MACT state is evident from the TRIR spectra. A higher quantum yield for CO-loss is observed following 266 nm excitation through both direct population of the MCCT/LF state and production of a vibrationally excited reactive MACT state. This results in the quantum yield for CO-loss increasing with increasing excitation energy.

Free radical generation is an inevitable consequence of aerobic existence and is implicated in a wide variety of pathological conditions including cancer, cardiovascular disease, ageing and neurodegenerative disorder. Free radicals can, however, be used to our advantage since their production is catalysed by synthetic inorganic molecules—termed artificial metallonucleases—that cut DNA strands by oxidative cleavage reactions. Here, we report the rational design and DNA binding interactions of a novel di-Cu2+ artificial metallonuclease [Cu2(tetra-(2-pyridyl)-NMe-naphthalene)Cl4] (Cu2TPNap). Cu2TPNap is a high-affinity binder of duplex DNA with an apparent binding constant (Kapp) of 107 M(bp)−1. The agent binds non-intercalatively in the major groove causing condensation and G-C specific destabilization. Artificial metallonuclease activity occurs in the absence of exogenous reductant, is dependent on superoxide and hydrogen peroxide, and gives rise to single strand DNA breaks. Pre-associative molecular docking studies with the 8-mer d(GGGGCCCC)2, a model for poly[d(G-C)2], identified selective major groove incorporation of the complex with ancillary Cu2+-phosphate backbone binding. Molecular mechanics methods then showed the d(GGGGCCCC)2 adduct to relax about the complex and this interaction is supported by UV melting experiments where poly[d(G-C)2] is selectively destabilized.

In order to expand the current repertoire of cancer treatments and to help circumvent limitations associated with resistance, the identification of new metallodrugs with high potency and novel mechanisms of action is of significant importance. Here we present a class of di-copper(II) complex based on the synthetic chemical nuclease [Cu(Phen)2]+ (where Phen = 1,10-phenanthroline) that is selective against solid epithelial cancer cells from the National Cancer Institute’s 60 human cell line panel (NCI-60). Two metallodrug leads are studied and in each case two [Cu(Phen)2]+ units are bridged by a dicarboxylate linker but the length and rigidity of the linkers differ distinctly. Both agents catalyze intracellular superoxide (O2•−) and singlet oxygen (1O2) formation with radical species mediating oxidative damage within nuclear DNA in the form of double strand breaks and to the mitochondria in terms of membrane depolarization. The complexes are effective DNA binders and can discriminate AT/AT from TA/TA steps of duplex DNA through induction of distinctive Z-like DNA or by intercalative interactions.

propanone singlet excited state was detected on the reaction path to the metallaketene species. This metallacyclopropanone excited state species has a lifetime of less than 100 ps and a characteristic bridging carbonyl band at 1770 cm −1 . The tungsten ketene species was also detected but in contrast to the chromium system, this forms directly from a low-lying triplet excited state. The electrochemical release of CO showed a greater efficiency for the chromium complex when compared to the tungsten.