1,474 research outputs found
Photoactivatable organometallic pyridyl ruthenium(II) arene complexes
The synthesis and characterization of a family of piano-stool RuII arene complexes of the type [(Ī·6-arene)Ru(N,Nā²)(L)][PF6]2, where arene is p-cymene (p-cym), hexamethylbenzene (hmb), or indane (ind), N,Nā² is 2,2ā²-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), 4,4ā²-bipyridine (4,4ā²-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 [(Ī·6-p-cym)Ru(bpm)(4-MePy)]2+ (2), [(Ī·6-p-cym)Ru(bpm)(4-BzPy)]2+ (6), [(Ī·6-p-cym)Ru(bpm)(trz)]2+ (7), [(Ī·6-p-cym)Ru(phen)(Py)]2+ (10), and [(Ī·6-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 [(Ī·6-arene)Ru(N,Nā²)(OH2)]2+ that otherwise would not form in the dark. The photoproducts were characterized by UVāvis 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 [(Ī·6-p-cym)Ru(bpm)(Py)]2+ (1), [(Ī·6-p-cym)Ru(bpm)(4-MeOPy)]2+ (3), [(Ī·6-p-cym)Ru(4,4ā²-bpy)]2+ (4), [(Ī·6-hmb)Ru(bpm)(Py)]2+ (8), [(Ī·6-ind)Ru(bpm)(Py)]2+ (9), [(Ī·6-p-cym)Ru(phen)(Py)]2+ (10), [(Ī·6-p-cym)Ru(bathophen)(Py)]2+ (12), [(Ī·6-p-cym)Ru(bpm)(NA)]2+ (15), and [(Ī·6-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 9.0ā60 Ī¼M)
High-order harmonic generation with a strong laser field and an attosecond-pulse train: the Dirac Delta comb and monochromatic limits
In recent publications, it has been shown that high-order harmonic generation
can be manipulated by employing a time-delayed attosecond pulse train
superposed to a strong, near-infrared laser field. It is an open question,
however, which is the most adequate way to approximate the attosecond pulse
train in a semi-analytic framework. Employing the Strong-Field Approximation
and saddle-point methods, we make a detailed assessment of the spectra obtained
by modeling the attosecond pulse train by either a monochromatic wave or a
Dirac-Delta comb. These are the two extreme limits of a real train, which is
composed by a finite set of harmonics. Specifically, in the monochromatic
limit, we find the downhill and uphill sets of orbits reported in the
literature, and analyze their influence on the high-harmonic spectra. We show
that, in principle, the downhill trajectories lead to stronger harmonics, and
pronounced enhancements in the low-plateau region. These features are analyzed
in terms of quantum interference effects between pairs of quantum orbits, and
compared to those obtained in the Dirac-Delta limit.Comment: 10 pages, 7 figures (eps files). To appear in Laser Physic
Climate and disease in historical urban space: evidence from 19th century PoznaÅ, 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 PoznaÅ 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
Bipyrimidine ruthenium(II) arene complexes : structure, reactivity and cytotoxicity
The synthesis and characterization of complexes [(Ī·6-arene)Ru(N,Nā²)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,Nā² is 2,2ā²-bipyrimidine (bpm) and X is Cl, Br or I, are reported, including the X-ray crystal structures of [(Ī·6-p-cym)Ru(bpm)I][PF6], [(Ī·6-bip)Ru(bpm)Cl][PF6], [(Ī·6-bip)Ru(bpm)I][PF6] and [(Ī·6-etb)Ru(bpm)Cl][PF6]. Complexes in which N,Nā² 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 [(Ī·6-p-cym)Ru(bpm)Cl][PF6], [(Ī·6-p-cym)Ru(bpm)Br][PF6], [(Ī·6-p-cym)Ru(bpm)I][PF6], [(Ī·6-bip)Ru(bpm)Cl][PF6], [(Ī·6-bip)Ru(bpm)Br][PF6] and [(Ī·6-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 ā 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 [(Ī·6-p-cym)Ru(bpm)Cl][PF6], [(Ī·6-hmb)Ru(bpm)Cl]+, [(Ī·6-ind)Ru(bpm)Cl]+, [(Ī·6-thn)Ru(bpm)Cl]+, [(Ī·6-p-cym)Ru(phen)Cl]+ and [(Ī·6-p-cym)Ru(bathophen)Cl]+ in aqueous solution at 310 K. The X-ray crystal structure of the guanine complex [(Ī·6-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 [(Ī·6-p-cym)Ru(bpm)Cl][PF6] and [(Ī·6-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
New PV system concept : inductive power transfer for PV modules
The proposed new PV system concept is based on several AC modules that are connected in series using inductive power transfer. These modules include a cell matrix that is connected to a module integrated DC/AC inverter. The high frequency AC current flows through the primary side planar coil generating a magnetic flux. Outside of the PV module, there is a clamp including ferromagnetic material for the magnetic circuit that caries the magnetic flux to the secondary winding. The magnetic flux induces an AC current in the secondary winding, which is formed by the common cable. An AC/AC converter is placed at the end of the PV module strings to generate the 50 Hz and to connect the PV power plant to the electricity grid. This new PV system concept is a fundamentally new approach of the electricity transmission in the field of PV system technology. It is not restricted to the replacement or optimisation of an individual system component, but it requires the continuing development of the PV module construction and the contactless connection technology to the common cable. The proposed inductive power transfer per each PV module opens up a complete new field for the PV system technology
Few-cycle soliton propagation
Soliton propagation is usually described in the ``slowly varying envelope
approximation'' (SVEA) regime, which is not applicable for ultrashort pulses.
We present theoretical results and numerical simulations for both NLS and
parametric () ultrashort solitons in the ``generalised few-cycle
envelope approximation'' (GFEA) regime, demonstrating their altered
propagation.Comment: 4 pages, 4 figure
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
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
Walking of antitumor bifunctional trinuclear PtII complex on double-helical DNA
The trinuclear BBR3464 ([{trans-PtCl(NH3)2}2Āµ-(trans-Pt(NH3)2(H2N(CH2)6NH2)2)]4+) belongs to the polynuclear class of platinum-based anticancer agents. DNA adducts of this complex differ significantly in structure and type from those of clinically used mononuclear platinum complexes, especially, long-range (Pt, Pt) intrastrand and interstrand cross-links are formed in both 5ā²ā5ā² and 3ā²ā3ā² orientations. We show employing short oligonucleotide duplexes containing single, site-specific cross-links of BBR3464 and gel electrophoresis that in contrast to major DNA adducts of clinically used platinum complexes, under physiological conditions the coordination bonds between platinum and N7 of G residues involved in the cross-links of BBR3464 can be cleaved. This cleavage may lead to the linkage isomerization reactions between this metallodrug and double-helical DNA. Differential scanning calorimetry of duplexes containing single, site-specific cross-links of BBR3464 reveals that one of the driving forces that leads to the lability of DNA cross-links of this metallodrug is a difference between the thermodynamic destabilization induced by the cross-link and by the adduct into which it could isomerize. The rearrangements may proceed in the way that cross-links originally formed in one strand of DNA can spontaneously translocate from one DNA strand to its complementary counterpart, which may evoke walking of the platinum complex on DNA molecule
Few cycle pulse propagation
We present a comprehensive framework for treating the nonlinear interaction
of few-cycle pulses using an envelope description that goes beyond the
traditional SVEA method. This is applied to a range of simulations that
demonstrate how the effect of a nonlinearity differs between the
many-cycle and few-cycle cases. Our approach, which includes diffraction,
dispersion, multiple fields, and a wide range of nonlinearities, builds upon
the work of Brabec and Krausz[1] and Porras[2]. No approximations are made
until the final stage when a particular problem is considered.
The original version (v1) of this arXiv paper is close to the published
Phys.Rev.A. version, and much smaller in size.Comment: 9 pages, 14 figure
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