DNA binding of dinuclear iron(II) metallosupramolecular cylinders. DNA unwinding and sequence preference

[Fe2L3]4+ (L = C25H20N4) is a synthetic tetracationic supramolecular cylinder (with a triple helical architecture) that targets the major groove of DNA and can bind to DNA Y-shaped junctions. To explore the DNA-binding mode of [Fe2L3]4+, we examine herein the interactions of pure enantiomers of this cylinder with DNA by biochemical and molecular biology methods. The results have revealed that, in addition to the previously reported bending of DNA, the enantiomers extensively unwind DNA, with the M enantiomer being the more efficient at unwinding, and exhibit preferential binding to regular alternating purine–pyrimidine sequences, with the M enantiomer showing a greater preference. Also, interestingly, the DNA binding of bulky cylinders [Fe2(L-CF3)3]4+ and [Fe2(L-Ph)3]4+ results in no DNA unwinding and also no sequence preference of their DNA binding was observed. The observation of sequence-preference in the binding of these supramolecular cylinders suggests that a concept based on the use of metallosupramolecular cylinders might result in molecular designs that recognize the genetic code in a sequence-dependent manner with a potential ability to affect the processing of the genetic code

Disordered Carbon nanotube alloys in the Effect Medium Super Cell Approximation

We investigate a disordered single-walled carbon nanotube (SWCNT) in an effective medium super cell approximation (EMSCA). First type of disorder that we consider is the presence of vacancies. Our results show that the vacancies induce some bound states on their neighbor host sites, leading to the creation of a band around the Fermi energy in the SWCNT average density of states.Second type of disorder considered is a substitutional $B_{cb}N_{cn}C_{1-cb-cn}$ alloy due to it's applications in hetrojunctions. We found that for a fixed boron (nitrogen) concentration, by increasing the nitrogen (boron) concentration the averaged semiconducting gap, $E_{g}$, decreases and at a critical concentration it disappears. A consequence of our results for nano electronic devices is that by changing the boron(nitrogen) concentration, one can make a semiconductor SWCNT with a pre-determined energy gap.Comment: 4 page

Plasmon signatures in high harmonic generation

High harmonic generation in polarizable multi-electron systems is investigated in the framework of multi-configuration time-dependent Hartree-Fock. The harmonic spectra exhibit two cut offs. The first cut off is in agreement with the well established, single active electron cut off law. The second cut off presents a signature of multi-electron dynamics. The strong laser field excites non-linear plasmon oscillations. Electrons that are ionized from one of the multi-plasmon states and recombine to the ground state gain additional energy, thereby creating the second plateau.Comment: Major revision, 12 pages, 5 figures, submitted to J. Phys. B (2005), accepte

Climate and disease in historical urban space: evidence from 19th century Poznań, Poland

This study examines the relationship between temperature levels and precipitation amounts as explanatory variables for the probability of death due to waterborne and airborne diseases in historical urban space. To date, the literature has not focused on the climatological epidemiology of 19th century Polish urban areas. We used individual mortality data from Poznań parish death registers between 1850 and 1900. Each deceased individual was assigned average monthly temperature values and precipitation amounts in the month of death, LAG1 (1-month-lagged) temperature and LAG1 rainfall, and place of residence. We studied the relationship between weather conditions and mortality using formalized statistical models reflecting the discrete nature of the response data (via multinomial logistic regression). Lagged monthly average temperature levels and lagged monthly average precipitation amounts were better predictors of airborne and waterborne disease mortality than the concurrent (non-lagged) monthly averages. The lagged effects of temperature and precipitation on waterborne and airborne diseases were significant (except for the smooth lagged average monthly temperature effect for airborne diseases). There was also significant spatial heterogeneity (differences among city quarters) in the prevalence of deaths due to waterborne and airborne diseases.</p

Photoactivatable organometallic pyridyl ruthenium(II) arene complexes

The synthesis and characterization of a family of piano-stool RuII arene complexes of the type [(η6-arene)Ru(N,N′)(L)][PF6]2, where arene is p-cymene (p-cym), hexamethylbenzene (hmb), or indane (ind), N,N′ is 2,2′-bipyrimidine (bpm), 1,10-phenanthroline (phen), 1,10-phenanthroline-5,6-dione (phendio), or 4,7-diphenyl-1,10-phenanthroline (bathophen), and L is pyridine (Py), 4-methylpyridine (4-MePy), 4-methoxypyridine (4-MeOPy), 4,4′-bipyridine (4,4′-bpy), 4-phenylpyridine (4-PhPy), 4-benzylpyridine (4-BzPy), 1,2,4-triazole (trz), 3-acetylpyridine (3-AcPy), nicotinamide (NA), or methyl nicotinate (MN), are reported, including the X-ray crystal structures of [(η6-p-cym)Ru(bpm)(4-MePy)]2+ (2), [(η6-p-cym)Ru(bpm)(4-BzPy)]2+ (6), [(η6-p-cym)Ru(bpm)(trz)]2+ (7), [(η6-p-cym)Ru(phen)(Py)]2+ (10), and [(η6-ind)Ru(bpy)(Py)]2+ (13). These complexes can selectively photodissociate the monodentate ligand (L) when excited with UVA or white light, allowing strict control of the formation of the reactive aqua species [(η6-arene)Ru(N,N′)(OH2)]2+ that otherwise would not form in the dark. The photoproducts were characterized by UV–vis absorption and 1H NMR spectroscopy. DFT and TD-DFT calculations were employed to characterize the excited states and to obtain information on the photochemistry of the complexes. All the RuII pyridine complexes follow a relatively similar photochemical L-ligand dissociation mechanism, likely to occur from a series of 3MC triplet states with dissociative character. The photochemical process proved to be much more efficient when UVA-range irradiation was used. More strikingly, light activation was used to phototrigger binding of these potential anticancer agents with discriminating preference toward 9-ethylguanine (9-EtG) over 9-ethyladenine (9-EtA). Calf thymus (CT)-DNA binding studies showed that the irradiated complexes bind to CT-DNA, whereas the nonirradiated forms bind negligibly. Studies of CT-DNA interactions in cell-free media suggest combined weak monofunctional coordinative and intercalative binding modes. The RuII arene complexes [(η6-p-cym)Ru(bpm)(Py)]2+ (1), [(η6-p-cym)Ru(bpm)(4-MeOPy)]2+ (3), [(η6-p-cym)Ru(4,4′-bpy)]2+ (4), [(η6-hmb)Ru(bpm)(Py)]2+ (8), [(η6-ind)Ru(bpm)(Py)]2+ (9), [(η6-p-cym)Ru(phen)(Py)]2+ (10), [(η6-p-cym)Ru(bathophen)(Py)]2+ (12), [(η6-p-cym)Ru(bpm)(NA)]2+ (15), and [(η6-p-cym)Ru(bpm)(MN)]2+ (16) were cytotoxic toward A2780 human ovarian cancer cell line in the absence of photoirradiation (IC50 values in the range of 9.0–60 μM)

Bipyrimidine ruthenium(II) arene complexes : structure, reactivity and cytotoxicity

The synthesis and characterization of complexes [(η6-arene)Ru(N,N′)X][PF6], where arene is para-cymene (p-cym), biphenyl (bip), ethyl benzoate (etb), hexamethylbenzene (hmb), indane (ind) or 1,2,3,4-tetrahydronaphthalene (thn), N,N′ is 2,2′-bipyrimidine (bpm) and X is Cl, Br or I, are reported, including the X-ray crystal structures of [(η6-p-cym)Ru(bpm)I][PF6], [(η6-bip)Ru(bpm)Cl][PF6], [(η6-bip)Ru(bpm)I][PF6] and [(η6-etb)Ru(bpm)Cl][PF6]. Complexes in which N,N′ is 1,10-phenanthroline (phen), 1,10-phenanthroline-5,6-dione or 4,7-diphenyl-1,10-phenanthroline (bathophen) were studied for comparison. The RuII arene complexes undergo ligand-exchange reactions in aqueous solution at 310 K; their half-lives for hydrolysis range from 14 to 715 min. Density functional theory calculations on [(η6-p-cym)Ru(bpm)Cl][PF6], [(η6-p-cym)Ru(bpm)Br][PF6], [(η6-p-cym)Ru(bpm)I][PF6], [(η6-bip)Ru(bpm)Cl][PF6], [(η6-bip)Ru(bpm)Br][PF6] and [(η6-bip)Ru(bpm)I][PF6] suggest that aquation occurs via an associative pathway and that the reaction is thermodynamically favourable when the leaving ligand is I > Br ≈ Cl. pK a* values for the aqua adducts of the complexes range from 6.9 to 7.32. A binding preference for 9-ethylguanine (9-EtG) compared with 9-ethyladenine (9-EtA) was observed for [(η6-p-cym)Ru(bpm)Cl][PF6], [(η6-hmb)Ru(bpm)Cl]+, [(η6-ind)Ru(bpm)Cl]+, [(η6-thn)Ru(bpm)Cl]+, [(η6-p-cym)Ru(phen)Cl]+ and [(η6-p-cym)Ru(bathophen)Cl]+ in aqueous solution at 310 K. The X-ray crystal structure of the guanine complex [(η6-p-cym)Ru(bpm)(9-EtG-N7)][PF6]2 shows multiple hydrogen bonding. Density functional theory calculations show that the 9-EtG adducts of all complexes are thermodynamically preferred compared with those of 9-EtA. However, the bmp complexes are inactive towards A2780 human ovarian cancer cells. Calf thymus DNA interactions for [(η6-p-cym)Ru(bpm)Cl][PF6] and [(η6-p-cym)Ru(phen)Cl][PF6] consist of weak coordinative, intercalative and monofunctional coordination. Binding to biomolecules such as glutathione may play a role in deactivating the bpm complexes

Modulation Instability of Ultrashort Pulses in Quadratic Nonlinear Media beyond the Slowly Varying Envelope Approximation

We report a modulational instability (MI) analysis of a mathematical model appropriate for ultrashort pulses in cascaded quadratic-cubic nonlinear media beyond the so-called slowly varying envelope approximation. Theoretically predicted MI properties are found to be in good agreement with numerical simulation. The study shows the possibility of controlling the generation of MI and formation of solitons in a cascaded quadratic-cubic media in the few cycle regimes. We also find that stable propagation of soliton-like few-cycle pulses in the medium is subject to the fulfilment of the modulation instability criteria

Enhanced dissociation of charge-transfer states in narrow band gap polymer:fullerene solar cells processed with 1,8-octanedithiol

The improved photovoltaic performance of narrow band gap polymer:fullerene solar cells processed from solutions containing small amounts of 1,8-octanedithiol is analyzed by modeling of the experimental photocurrent. In contrast to devices that are spin coated from pristine chlorobenzene, these cells do not produce a recombination-limited photocurrent. Modeling of the experimental data reveals that a sixfold reduction in the decay rate of photogenerated bound electron–hole pairs can account for the marked increase in short-circuit current density and fill factor. At short-circuit conditions, the dissociation probability of bound pairs is found to increase from 48% to 70%.

In vitro effects of 10,10'-oxybisphenoxarsine on isolated rat liver mitochondria

10,10'-Oxybisphenoxarsine (OBPA), a trivalent, heterocyclic organoarsenical, is a potent, broad spectrum antimicrobial agent often incorporated into plasticized polyvinyl chlorides. Although highly toxic, the mechanism of OBPA toxicity is unknown. Since it is hepatotoxic, we investigated the in vitro effects of OBPA on rat liver mitochondria. Isolated mitochondria were incubated with 1 to 8 [mu] OBPA and oxygen consumption was monitored polarographically. State 3 respiration of [alpha]-ketoglutarate, pyruvate, isocitrate, and succinate was rapidly inhibited. OBPA also uncoupled oxidative phosphorylation, although this was masked, at higher concentrations, by progressive respiratory inhibition. The electron transport chain appeared unaffected by OBPA, as measured by NADH oxidation, but several tricarboxcylic acid cycle dehydrogenases were inhibited. This inhibition was prevented and, in some cases, reversed by glutathione. It is likely that OBPA, like other trivalent organoarsenicals, exerts its toxic effects by reacting with vital mitochondrial sulfhydryl groups.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24072/1/0000324.pd