1,195 research outputs found
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 purineāpyrimidine 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
Shape-selective recognition of DNA abasic sites by metallohelices : inhibition of human AP endonuclease 1
Loss of a base in DNA leading to creation of an abasic (AP) site leaving a deoxyribose residue in the strand, is a frequent lesion that may occur spontaneously or under the action of various physical and chemical agents. Progress in the understanding of the chemistry and enzymology of abasic DNA largely relies upon the study of AP sites in synthetic duplexes. We report here on interactions of diastereomerically pure metalloāhelical āflexicateā complexes, bimetallic triple-stranded ferro-helicates [Fe2(NN-NN)3]4+ incorporating the common NNāNN bis(bidentate) helicand, with short DNA duplexes containing AP sites in different sequence contexts. The results show that the flexicates bind to AP sites in DNA duplexes in a shape-selective manner. They preferentially bind to AP sites flanked by purines on both sides and their binding is enhanced when a pyrimidine is placed in opposite orientation to the lesion. Notably, the Ī-enantiomer binds to all tested AP sites with higher affinity than the Ī-enantiomer. In addition, the binding of the flexicates to AP sites inhibits the activity of human AP endonuclease 1, which is as a valid anticancer drug target. Hence, this finding indicates the potential of utilizing well-defined metalloāhelical complexes for cancer chemotherapy
The fundamental solution of the unidirectional pulse propagation equation
The fundamental solution of a variant of the three-dimensional wave equation
known as "unidirectional pulse propagation equation" (UPPE) and its paraxial
approximation is obtained. It is shown that the fundamental solution can be
presented as a projection of a fundamental solution of the wave equation to
some functional subspace. We discuss the degree of equivalence of the UPPE and
the wave equation in this respect. In particular, we show that the UPPE, in
contrast to the common belief, describes wave propagation in both longitudinal
and temporal directions, and, thereby, its fundamental solution possesses a
non-causal character.Comment: accepted to J. Math. Phy
Iron(II) supramolecular helicates interfere with the HIV-1 TatāTAR RNA interaction critical for viral replication
The interaction between the HIV-1 transactivator protein Tat and TAR (transactivation responsive region) RNA, plays a critical role in HIV-1 transcription. Iron(II) supramolecular helicates were evaluated for their in vitro activity to inhibit TatāTAR RNA interaction using UV melting studies, electrophoretic mobility shift assay, and RNase A footprinting. The results demonstrate that iron(II) supramolecular helicates inhibit Tat-TAR interaction at nanomolar concentrations by binding to TAR RNA. These studies provide a new insight into the biological potential of metallosupramolecular helicates
Sub two-cycle soliton-effect pulse compression at 800 nm in Photonic Crystal Fibers
The possibility of soliton self-compression of ultrashort laser pulses down
to the few-cycle regime in photonic crystal fibers is numerically investigated.
We show that efficient sub-two-cycle temporal compression of nanojoule-level
800 nm pulses can be achieved by employing short (typically 5-mm-long)
commercially available photonic crystal fibers and pulse durations of around
100 fs, regardless of initial linear chirp, and without the need of additional
dispersion compensation techniques. We envisage applications in a new
generation of compact and efficient sub-two cycle laser pulse sources.Comment: 16 pages, 6 figure
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)
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
Asymmetric emission of high energy electrons in the two-dimensional hydrodynamic expansion of large xenon clusters irradiated by intense laser fields
Energy spectra and angular distributions have been measured of electrons that
are emitted upon disassembly of following irradiation by intense
(10 W cm) laser pulses whose durations are varied over
the 100-2200 fs range. The cluster explosion dynamics occur in the hydrodynamic
regime. Electron emission is found to be unexpectedly asymmetric and exhibits a
resonance when the laser pulse duration is 1 ps. These results are
rationalized by extending the hydrodynamic model to also take into account the
force that the light field exerts on the polarization charge that is induced on
surface of the cluster. We show that the magnitude of this electrostrictive
force is comparable to those of Coulombic and the hydrodynamic forces, and it
exhibits resonance behavior. Contrary to earlier understanding, we find that
low-energy electrons are connected to the resonance in energy absorption by the
cluster. The high-energy electrons seem to be produced by a mechanism that is
not so strongly influenced by the resonance.Comment: 1 Revtex file, 8 figs. in eps forma
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