Crystallization kinetics and morphology of poly(lactic acid) with polysaccharide as nucleating agent

Journal of Thermal Analysis and Calorimetry - An ever-increasing concern about environmental pollution has spearheaded research into alternative biodegradable polymers. Currently, poly(lactic acid)...     

Symmetry classes for elasticity tensors

Harmonic and Cartan decompositions are used to prove that there are eight symmetry classes of elasticity tensors. Recent results in apparent contradiction with this conclusion are discussed in a short history of the problem.Research supported by GNFM of CNR (Italy)     

Metal-phthalocyanine array on the moiré pattern of a graphene sheet

Iron-phthalocyanine (FePc) molecules have been adsorbed on a graphene sheet prepared on the Ir(111) surface. The FePc molecules are flat-lying on graphene, as determined by near-edge X-ray absorption fine-structure, constituting a sub-nanometer thick molecular array at the single-layer coverage. The flat FePc single-layer presents a weak interaction of the organic macrocycle with the graphene surface and Ir subsurface substrate. Further FePc deposition on top of the first flat single-layer determines a three-dimensional island growth with varying molecular orientation.     

MAD: practical implementation of MCAO concepts

The European Southern Observatory (ESO) together with external research institutes have built a Multi-Conjugate Adaptive Optics (MCAO) Demonstrator (MAD) to perform wide field-of-view adaptive optics correction (2′ in K band). The aim of MAD is to demonstrate the on-sky feasibility of the MCAO technique and to evaluate its critical aspects in the framework of both the 2nd generation instrumentation for the Very Large Telescope (VLT) and the Overwhelmingly Large Telescope (OWL). The MAD module will be installed on the VLT to perform on-sky observations. MAD comprises two deformable mirrors and two different multi-reference wavefront sensors with natural guide stars. In this article we present the MAD design, some aspects of the MAD calibration and the first closed-loop results in the laboratory in Single Conjugated Adaptive Optics (SCAO) and Ground Layer Adaptive Optics (GLAO) configurations. To cite this article: E. Marchetti et al., C. R. Physique 6 (2005).     

Tuning the activity of Zn(II) complexes in DNA cleavage: clues for design of new efficient metallo-hydrolases

The hydrolytic ability toward plasmid DNA of a mononuclear and a binuclear Zn(II) complex with two macrocyclic ligands, containing respectively a phenanthroline (L1) and a dipyridine moiety (L2), was analyzed at different pH values and compared with their activity in bis( p-nitrophenyl)phosphate (BNPP) cleavage. Only the most nucleophilic species [ZnL1(OH)]+ and [Zn2L2(OH)2]2+, present in solution at alkaline pH values, are active in BNPP cleavage, and the dinuclear L2 complex is remarkably more active than the mononuclear L1 one. Circular dichroism and unwinding experiments show that both complexes interact with DNA in a nonintercalative mode. Experiments with supercoiled plasmid DNA show that both complexes can cleave DNA at neutral pH, where the L1 and L2 complexes display a similar reactivity. Conversely, the pH-dependence of their cleavage ability is remarkably different. The reactivity of the mononuclear complex, in fact, decreases with pH while that of the dinuclear one is enhanced at alkaline pH values. The efficiency of the two complexes in DNA cleavage at different pH values was elucidated by means of a quantum mechanics/molecular mechanics (QM/MM) study on the adducts between DNA and the different complexed species present in solution.     

BN-Doped Metal–Organic Frameworks: Tailoring 2D and 3D Porous Architectures through Molecular Editing of Borazines

Building on the MOF approach to prepare porous materials, herein we report the engineering of porous BN-doped materials using tricarboxylic hexaarylborazine ligands, which are laterally decorated with functional groups at the full-carbon ‘inner shell’. Whilst an open porous 3D entangled structure could be obtained from the double interpenetration of two identical metal frameworks derived from the methyl substituted borazine, the chlorine-functionalised linker undergoes formation of a porous layered 2D honeycomb structure, as shown by single-crystal X-ray diffraction analysis. In this architecture, the borazine cores are rotated by 60° in alternating layers, thus generating large rhombohedral channels running perpendicular to the planes of the networks. An analogous unsubstituted full-carbon metal framework was synthesised for comparison. The resulting MOF revealed a crystalline 3D entangled porous structure, composed by three mutually interpenetrating networks, hence denser than those obtained from the borazine linkers. Their microporosity and CO₂ uptake were investigated, with the porous 3D BN-MOF entangled structure exhibiting a large apparent BET specific surface area (1091 m² g⁻¹) and significant CO₂ reversible adsorption (3.31 mmol g⁻¹) at 1 bar and 273 K.     

Electron density analysis of large (molecular and periodic) systems: A parallel implementation

A parallel implementation is presented of a series of algorithms for the evaluation of several one‐electron properties of large molecular and periodic (of any dimensionality) systems. The electron charge and momentum densities of the system, the electrostatic potential, X‐ray structure factors, directional Compton profiles can be effectively evaluated at low computational cost along with a full topological analysis of the electron charge density (ECD) of the system according to Bader's quantum theory of atoms in molecules. The speedup of the parallelization of the different algorithms is presented. The search of all symmetry‐irreducible critical points of the ECD of the crystallized crambin protein and the evaluation of all the corresponding bond paths, for instance, would require about 32 days if run in serial mode and reduces to less than 2 days when run in parallel mode over 32 processors. © 2015 Wiley Periodicals, Inc.