Spontaneous 2-dimensional carrier confinement at the n-type SrTiO3/LaAlO3 interface

We describe the intrinsic mechanism of 2-dimensional electron confinement at the n-type SrTiO3/LaAlO3 interface as a function of the sheet carrier density n(s) via advanced first-principles calculations. Electrons localize spontaneously in Ti 3d(xy) levels within a thin (?2 nm) interface-adjacent SrTiO3 region for n(s) lower than a threshold value n(c)～10(14) cm(-2). For n(s)>n(c) a portion of charge flows into Ti 3d(xz)-d(yz) levels extending farther from the interface. This intrinsic confinement can be attributed to the interface-induced symmetry breaking and localized nature of Ti 3d t(2g) states. The sheet carrier density directly controls the binding energy and the spatial extension of the conductive region. A direct, quantitative relation of these quantities with n(s) is provided.     

A green way to γ-lactams through a copper catalyzed ARGET-ATRC in ethanol and in the presence of ascorbic acid

A ‘green’ ARGET-ATRC, for the CuCl[PMDETA] catalysed cyclo-isomerization of N-allyl-α-polychloroamides to γ-lactams is described. The process works efficiently (yields 78-96%), uses a bio-solvent, as ethanol, and exploits the reducing feature of ascorbic acid to limit, at a low level (2-4%), the amount of catalyst. To preserve the efficacy of the catalytic cycle, addition of Na₂CO₃ is essential, which quenches the HCl released during the CuCl[PMDETA] regeneration step. Profitable features of the process are: mild reaction temperatures (25-37 °C), relatively short reaction times (usually 5 h) and low solvent volumes (2 mmol of substrate/mL of ethanol). The method, upon stoichiometric adjustment, was also used for the synthesis of α,β-unsaturated-γ-lactams from N-(2-chloroallyl)-α-polychloroamides, via a tandem process involving an ATRC and a reductive [1,2]-elimination.     

A heme-peptide metalloenzyme mimetic with natural peroxidase-like activity

Mimicking enzymes with alternative molecules represents an important objective in synthetic biology, aimed to obtain new chemical entities for specific applications. This objective is hampered by the large size and complexity of enzymes. The manipulation of their structures often leads to a reduction of enzyme activity. Herein, we describe the spectroscopic and functional characterization of Fe(III)-mimochrome VI, a 3.5 kDa synthetic heme-protein model, which displays a peroxidase-like catalytic activity. By the use of hydrogen peroxide, Fe(III)-mimochrome VI efficiently catalyzes the oxidation of several substrates, with a typical Michaelis-Menten mechanism and with several multiple turnovers. The catalytic efficiency of Fe(III)-mimochrome VI in the oxidation of 2,2'-azino-di(3-ethyl-benzothiazoline-6-sulfonic acid (ABTS) and guaiacol (k(cat)/K(m)=4417 and 870 mM(-1) s(-1), respectively) is comparable to that of native horseradish peroxidase (HRP, k(cat)/K(m)=5125 and 500 mM(-1) s(-1), respectively). Fe(III)-mimochrome VI also converts phenol to 4- and 2-nitrophenol in the presence of NO(2) (-) and H(2) O(2) in high yields. These results demonstrate that small synthetic peptides can impart high enzyme activities to metal cofactors, and anticipate the possibility of constructing new biocatalysts tailored to specific functions.     

Gradient integrability and rigidity results for two-phase conductivities in two dimensions

This paper deals with higher gradient integrability for σ-harmonic functions u with discontinuous coefficients σ  , i.e. weak solutions of div(σ∇u)=0$\mathrm{div}(\sigma \mathrm{\nabla }u)=0$ in dimension two. When σ is assumed to be symmetric, then the optimal integrability exponent of the gradient field is known thanks to the work of Astala and Leonetti and Nesi. When only the ellipticity is fixed and σ is otherwise unconstrained, the optimal exponent is established, in the strongest possible way of the existence of so-called exact solutions, via the exhibition of optimal microgeometries.     

Hypercentralizing generalized skew derivations on left ideals in prime rings

Let $\mathcal{R }$ be a prime ring of characteristic different from $2, \mathcal{Q }_r$ the right Martindale quotient ring of $\mathcal{R }, \mathcal{C }$ the extended centroid of $\mathcal{R }, \mathcal{I }$ a nonzero left ideal of $\mathcal{R }, F$ a nonzero generalized skew derivation of $\mathcal{R }$ with associated automorphism $\alpha $ , and $n,k \ge 1$ be fixed integers. If $[F(r^n),r^n]_k=0$ for all $r \in \mathcal{I }$ , then there exists $\lambda \in \mathcal{C }$ such that $F(x)=\lambda x$ , for all $x\in \mathcal{I }$ . More precisely one of the following holds: (1) $\alpha $ is an $X$ -inner automorphism of $\mathcal{R }$ and there exist $b,c \in \mathcal{Q }_r$ and $q$ invertible element of $\mathcal{Q }_r$ , such that $F(x)=bx-qxq^{-1}c$ , for all $x\in \mathcal{Q }_r$ . Moreover there exists $\gamma \in \mathcal{C }$ such that $\mathcal{I }(q^{-1}c-\gamma )=(0)$ and $b-\gamma q \in \mathcal{C }$ ; (2) $\alpha $ is an $X$ -outer automorphism of $\mathcal{R }$ and there exist $c \in \mathcal{Q }_r, \lambda \in \mathcal{C }$ , such that $F(x)=\lambda x-\alpha (x)c$ , for all $x\in \mathcal{Q }_r$ , with $\alpha (\mathcal{I })c=0$ .     

Simple and Dendritic Cyclam Derivatives. Photophysical Properties,Effect of Protonation and Zn2+ Coordination,Preliminary Screening as Inhibitors of Tumour Cell Growth

We have synthesized two novel dendrimers (BG1 and BG2) consisting of a 1,4,8,11-tetraazacyclotetradecane (cyclam, 1) core with appended four dimethoxybenzene and eight benzyl units (BG1) and twelve dimethoxybenzene and sixteen benzyl units (BG2). The absorption and luminescence spectra of these compounds and the changes taking place upon protonation and Zn²⁺ coordination of their cyclam core have been investigated in acetonitrile-dichloromethane 1:1 v/v solution. For comparison purposes, the absorption and luminescence spectra of 1,4,8,11-tetrabenzyl-cyclam (2), and dendrons BD1 and BD2, model compounds of the branches of BG1 and BG2 respectively, have also been studied. BD1, BD2, BG1, and BG2 exhibit the absorption and emission spectra of their 1,3-dimethoxybenzene unit, but in the two dendrimers the emission intensity is quenched by the cyclam amine groups and increases upon protonation and metal coordination. In order to test if these cyclam derivatives have an antitumour effect, we have studied their action on proliferation in the human neuroblastoma TS12 cell line. Screening experiments have shown that cell proliferation was (i) strongly reduced by the tetrabenzyl substituted cyclam 2, and (ii) unaffected by cyclam and the benzo dendrimers BG1 and BG2. Antitumour screening experiments have also been performed on the tetranaphthyl substituted cyclam 3 and the naphtho-dendrimer NG2, whose photophysical properties have been previously studied. Cell proliferation came out to be moderately reduced by 3, whereas dendrimer NG2 had no effect, similar to dendrimers BG1 and BG2.     

New nanohybrids of poly(ε‐caprolactone) and a modified Mg/Al hydrotalcite: Mechanical and thermal properties

Novel composites based on poly(ε‐caprolactone) (PCL) and an organically modified layer double hydroxide (LDH) obtained using the melt‐extrusion technique have been characterized through structural, thermal, and mechanical analyses. Although exfoliation has not been achieved and despite the very low content of filler (from 1 to 3% by weight), significant enhancements are obtained in the physical and mechanical properties of the composites with respect to neat PCL. As a consequence, LDHs can substitute other nanofillers, in particular, cationic clays for polymeric matrices. They can be modified by a large number of organic anions, generally more numerous than the cationic ones, and can be mixed in very simple ways with polymers. This makes such nanofillers suitable to obtain new hybrid materials for a series of applications, from active food packaging to intelligent materials for biomedical device, for example, controlled drug release. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 945–954, 2007     

Lithium hydroxide phase transition under high pressure: an ab initio molecular dynamics study.

The high-pressure phase transition in the deuterated lithium hydroxide crystalline state has been studied by Car-Parrinello molecular dynamics simulations, in the constant-pressure, constant-temperature ensemble. The recently developed metadynamics approach has been applied to encourage the system to transform into different phases in an affordable simulation time. A previously not completely characterized high-pressure phase has been obtained. The structural and spectroscopic properties have been studied and compared with the neutron scattering, infrared and Raman measurements. It has been found that the calculated structure differs slightly from the experimental hypothesis, and that the presence of strong hydrogen bonds is the source of the red shift and of the characteristic features of the OD-stretching bands in both IR and Raman spectra.