Investigation of dissociative electron attachment to 2'-deoxycytidine-3'-monophosphate using DFT method and time dependent wave packet approach

Effect of electron correlation on single strand breaks (SSBs) induced by low energy electron (LEE) has been investigated in a fragment excised from a DNA, viz., 2'-deoxycytidine-3'-monophosphate [3'-dCMPH] molecule in gas phase at DFT-B3LYP/6-31+G(d) accuracy level and using local complex potential based time dependent wave packet (LCP-TDWP) approach. The results obtained, in conjunction with our earlier investigation, show the possibility of SSB at very low energy (0.15 eV) where the LEE transfers from π? to σ? resonance state which resembles a S(N)2 type mechanism. In addition, for the first time, an indication of quantum mechanical tunneling in strand breaking is seen from the highest anionic bound vibrational state (χ(5)), which may have a substantial role during DNA damage.     

Efficacy of clay content and microstructure of curing agents on the structure–property relationship of new‐generation polyurethane nanocomposites

The physicomechanical properties of new polyurethanes (PUs) derived from toluene diisocyanate, poly(propylene glycol), and cured by third‐generation hyperbranched polyester polyol (HB3), trimethylolpropane (TMP), or glycerol and their nanocomposites have been investigated. An apparent microphase‐segregated morphology of PU nanocomposites cured by HB3 has been observed by transmission electron microscopy and atomic force microscopy. Morphological studies reveal regions of mostly exfoliated and some intercalated morphology in the case of the nanocomposites, which have been further ascertained by X‐ray diffraction analysis. The HB3‐cured PU nanocomposite containing 8 wt% of modified montmorillonite (Cloisite 30B) clay shows approximately 140% increase in tensile strength along with improvement in thermal and dynamic mechanical properties in comparison with the control hyperbranched PU. It has also been found from Fourier transform infrared spectroscopy analysis that the extent of tethering reactions between the polymer chains carrying residual –NCO groups and the reactive hydroxyl (?OH) groups of HB3 is significant, and the nanofiller has been found to preferentially react with the –NCO group of the prepolymer. Furthermore, the properties of HB3‐cured PU have been compared with the glycerol and TMP‐cured PUs and their nanocomposites. The physicomechanical and thermal properties for nanocomposites of HB3‐cured PUs are superior to those of the conventionally cured PUs. Copyright © 2011 John Wiley & Sons, Ltd.     

Cyanido-bridged one-dimensional systems assembled from [ReIVCl4(CN)2]2? and [MII(cyclam)]2+ (M = Ni, Cu) precursors

Three new cyanido-bridged heterometallic Re^IVNi^II and Re^IVCu^II one-dimensional systems were synthesized and extensively characterized both structurally and magnetically. Single-crystal X-ray diffraction analysis revealed that these compounds display a common topology, with chains composed of alternating [Re^IVCl₄(CN)₂]^2? and [M^II(cyclam)]²⁺ (M = Ni in 1, Cu in 2) or [Cu^II(N,N??-dimethylcyclam)]²⁺ (in 3) building units. Two different chain orientations with a tilt angle of ca. 51° to 55° are present in the crystal packing of these compounds. The magnetic susceptibility measurements suggest the presence of intrachain ferromagnetic interactions between the S = 3/2 Re^IV centers and the 3d metal ions: S = 1 Ni^II or S = 1/2 Cu^II. At low temperature, a three-dimensional ordered magnetic phase induced by interchain antiferromagnetic interactions (antiferromagnetic for 1 and 2; canted antiferromagnetic for 3) is detected for the three compounds.     

Quantum group of orientation-preserving Riemannian isometries

We formulate a quantum group analogue of the group of orientation-preserving Riemannian isometries of a compact Riemannian spin manifold, more generally, of a (possibly R-twisted and of compact type) spectral triple. The main advantage of this formulation, which is directly in terms of the Dirac operator, is that it does not need the existence of any ‘good’ Laplacian as in our previous works on quantum isometry groups. Several interesting examples, including those coming from Rieffel-type deformation as well as the equivariant spectral triples on SU_μ(2) and are discussed.     

Nonlocal Coulomb interaction in the two-dimensional spin-<Emphasis Type="Bold">1/2</Emphasis> Falicov–Kimball model

The two-dimensional (2D) extended Falicov–Kimball model has been studied to observe the role of nonlocal Coulomb interaction (U _nc) using an exact diagonalization technique. The f-state occupation (n ^f ), the f–d intersite correlation function (c _fd), the specific heat (C), entropy (S) and the specific heat coefficient (γ) have been examined. Nonlocal Coulomb interaction-induced discontinuous insulator-to-metal transition occurs at a critical f-level energy. More ordered state is obtained with the increase of U _nc. In the specific heat curves, two-peak structure as well as a single-peak structure appears. At low-temperature region, a sharp rise in the specific heat coefficient γ is observed. The peak value of γ shifts to the higher temperature region with U _nc.