Red-light photosensitized cleavage of DNA by (l-lysine)(phenanthroline base)copper(II) complexes

Ternary copper(II) complexes [Cu(l-lys)B(ClO4)](ClO4)(1-4), where B is a heterocyclic base, viz. 2,2'-bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq, 3) and dipyrido[3,2-a:2',3'-c]phenazene (dppz, 4), are prepared and their DNA binding and photo-induced DNA cleavage activity studied (l-lys =l-lysine). Complex 2, structurally characterized by X-ray crystallography, shows a square-pyramidal (4 + 1) coordination geometry in which the N,O-donor l-lysine and N,N-donor heterocyclic base bind at the basal plane and the perchlorate ligand is bonded at the elongated axial site. The crystal structure shows the presence of a pendant cationic amine moiety -(CH2)4NH3+ of l-lysine. The one-electron paramagnetic complexes display a d-d band in the range of 598-762 nm in DMF and exhibit cyclic voltammetric response due to Cu(II)/Cu(I) couple in the range of 0.07 to -0.20 V vs. SCE in DMF-Tris-HCl buffer. The complexes having phenanthroline bases display good binding propensity to the calf thymus DNA giving an order: 4 (dppz) > 3 (dpq) > 2 (phen)> 1 (bpy). Control cleavage experiments using pUC19 supercoiled DNA and distamycin suggest major groove binding for the dppz and minor groove binding for the other complexes. Complexes 2-4 show efficient DNA cleavage activity on UV (365 nm) or visible light (694 nm ruby laser) irradiation via a mechanistic pathway involving formation of singlet oxygen as the reactive species. The amino acid l-lysine bound to the metal shows photosensitizing effect at red light, while the heterocyclic bases are primarily DNA groove binders. The dpq and dppz ligands display red light-induced photosensitizing effects in copper-bound form.     

Efficient visible light induced nuclease activity of a ternary mono-1,10-phenanthroline copper(II) complex containing 2-(methylthio)ethylsalicylaldimine

Ternary Schiff base copper(II) complex [CuL(phen)](ClO(4)), where HL is 2-(methylthio)ethylsalicylaldimine and phen is 1,10-phenanthroline, has been prepared and structurally characterized by X-ray crystallography. The complex shows a CuN(3)OS coordination in a square-pyramidal (4 + 1) geometry with the sulfur as an equatorial ligand. The complex is an avid binder to double-stranded DNA in the minor groove and exhibits both photonuclease and chemical nuclease activity. When exposed to UV light of 312 nm (96 W) or visible light of 532 nm (125 W) under aerobic conditions, the complex causes significant cleavage of supercoiled pUC19 DNA in the absence of any externally added reducing agent or H(2)O(2).     

Excellent electromagnetic interference shielding effectiveness of chemically reduced graphitic oxide paper at 101 GHz*

Graphitic oxide (GO) was synthesized by oxidation of graphite powder using Hummer’s method and the formed GO is solution processed into paper-like macroscopic form. Subsequently, chemically reduced graphitic oxide paper (CRGOP) is prepared by hydrazine vapours induced reduction of formed GO precursor based paper. The formation of GO and its successful reduction to RGO phase is confirmed by FTIR, Raman Spectroscopy and X-ray diffraction. It has been observed that due to high electrical conductivity ~200 micron thick CRGOP display excellent EMI shielding performance at very high frequency of 101 GHz frequency with total shielding effectiveness (SE) value of ?35.49 dB (i.e. >99.97% blocking of incident EM radiation) which is much higher compared to pristine GO paper (?1.55 dB) or comparable to expanded graphite (EG) sheet (?35.61 dB). Due to their lightweight nature, these freestanding CRGOPs display average specific SE value of ?221.8 dB cm³/g. Besides, their excellent flexibility and makes them potential candidate for lightweight EMI gasketing material compared to other forms of flexible carbons like EG.     

Multiple time scale behaviors and network dynamics in liquid methanol

Canonical ensemble molecular dynamics simulations of liquid methanol, modeled using a rigid-body, pair-additive potential, are used to compute static distributions and temporal correlations of tagged molecule potential energies as a means of characterizing the liquid state dynamics. The static distribution of tagged molecule potential energies shows a clear multimodal structure with three distinct peaks, similar to those observed previously in water and liquid silica. The multimodality is shown to originate from electrostatic effects, but not from local, hydrogen bond interactions. An interesting outcome of this study is the remarkable similarity in the tagged potential energy power spectra of methanol, water, and silica, despite the differences in the underlying interactions and the dimensionality of the network. All three liquids show a distinct multiple time scale (MTS) regime with a 1/ f (alpha) dependence with a clear positive correlation between the scaling exponent alpha and the diffusivity. The low-frequency limit of the MTS regime is determined by the frequency of crossover to white noise behavior which occurs at approximately 0.1 cm (-1) in the case of methanol under standard temperature and pressure conditions. The power spectral regime above 200 cm (-1) in all three systems is dominated by resonances due to localized vibrations, such as librations. The correlation between alpha and the diffusivity in all three liquids appears to be related to the strength of the coupling between the localized motions and the larger length/time scale network reorganizations. Thus, the time scales associated with network reorganization dynamics appear to be qualitatively similar in these systems, despite the fact that water and silica both display diffusional anomalies but methanol does not.     

Dissipation and criticality in the lowest Landau level of graphene

The lowest Landau level of graphene is studied numerically by considering a tight-binding Hamiltonian with disorder. The Hall conductance sigma_{xy} and the longitudinal conductance sigma_{xx} are computed. We demonstrate that bond disorder can produce a plateaulike feature centered at nu=0, while the longitudinal conductance is nonzero in the same region, reflecting a band of extended states between +/-E_{c}, whose magnitude depends on the disorder strength. The critical exponent corresponding to the localization length at the edges of this band is found to be 2.47+/-0.04. When both bond disorder and a finite mass term exist the localization length exponent varies continuously between approximately 1.0 and approximately 7/3.     

Rounding by disorder of first-order quantum phase transitions: emergence of quantum critical points

We give a heuristic argument for disorder rounding of a first-order quantum phase transition into a continuous phase transition. From both weak and strong disorder analysis of the N-color quantum Ashkin-Teller model in one spatial dimension, we find that, for N > or =3, the first-order transition is rounded to a continuous transition and the physical picture is the same as the random transverse field Ising model for a limited parameter regime. The results are strikingly different from the corresponding classical problem in two dimensions where the fate of the renormalization group flows is a fixed point corresponding to N-decoupled pure Ising models.     

Anisotropic cosmological models and generalized scalar tensor theory

In this paper generalized scalar tensor theory has been considered in the background of anisotropic cosmological models, namely, axially symmetric Bianchi-I, Bianchi-III and Kortowski-Sachs space-time. For bulk viscous fluid, both exponential and power-law solutions have been studied and some assumptions among the physical parameters and solutions have been discussed.     

Self-pulsing characteristics of a high-power single transverse mode Yb-doped CW fiber laser

We present an experimental study of self-pulsing characteristics of a high-power single transverse mode Yb-doped double-clad continuous wave (CW) fiber laser. The self-pulsing features under high-power single-end pumping and double-end pumping configurations have been shown to be distinct. Our experimental observation indicates that in single-end pumping configuration, self-pulsing is predominant due to saturable absorption effect, caused by the weakly pumped portion of the fiber at the farther end. However, in double-end pumping configuration, uniform pumping and hence gain uniformity along the fiber length avoids the onset of saturable absorption of signal along the fiber length and thereby reduces self-pulsing, which finally results in a much more stable output.     

Electrically injected quantum-dot photonic crystal microcavity light sources

The design, fabrication, and characterization of an electrically injected quantum-dot photonic crystal microcavity light source are described. The optical gain in the GaAs/AlGaAs-based device is provided by self-organized InGaAs quantum dots with ground-state room-temperature emission at 1.1 microm. The carriers are injected directly into the photonic crystal microcavity, which contains approximately 50 dots, avoiding surface state recombination in the photonic crystal pattern. The spectral characteristics of a single-defect photonic crystal microcavity show a single 2 nm broad microcavity resonance. The output power is of the order of a few tens of nanowatts.     

Separation of Clinical Grade 188Re from 188W Using Polymer Embedded Nanocrystalline Titania

Currently, ¹⁸⁸Re is obtained from ¹⁸⁸W/¹⁸⁸Re chromatographic generator containing alumina which has a limited capacity (~80 mg Wg^?1) for ¹⁸⁸W. This results in high bolus volumes of ¹⁸⁸Re, which often needs to be concentrated before radiolabeling. We have demonstrated the feasibility of using polymer embedded nano crystalline titania (TiP), a novel high capacity sorbent material (~300 mg Wg^?1), for developing a ¹⁸⁸W/¹⁸⁸Re chromatographic generator. A TiP based chromatographic ¹⁸⁸W/¹⁸⁸Re generator was developed in which ¹⁸⁸Re could be eluted with 0.9% saline solution. About 90% of the ¹⁸⁸Re could be recovered in the first 4–5 mL of total activity with more than 80% yield. The purity of ¹⁸⁸Re is adequate for clinical applications.