A new organogelator based on an enantiopure C2 symmetric pyrrolidine

The synthesis and the properties of a new chiral organogelator based on a C(2) symmetric pyrrolidine, are described together with its use for the synthesis of other functionalised organogelators.     

Reactivity of Ti(IV) species hosted in TS-1 towards H2O2-H2O solutions investigated by ab initio cluster and periodic approaches combined with experimental XANES and EXAFS data: a review and new highlights

This work is intended to underline how the most-advanced experimental and theoretical physical chemistry tools must be used synergistically to understand the reactivity of Ti-silicalite-1 (TS-1) in an important number of low-temperature oxidation reactions with aqueous H(2)O(2) as the oxidant. Literature results are carefully reviewed and accompanied with new, unpublished highlights of both experimental and computational origin. The first part of this work is devoted to a discussion of the defective nature of the material and to the synergic role played by Si vacancies and Ti insertion in the framework. A summary of the experimental Ti-K-edge EXAFS and XANES literature concerning the activated material in vacuo conditions is then presented and compared to the corresponding Ti geometries obtained by ab initio calculations. From such a comparison, the excellent agreement between experiment and theory is evident. A very good agreement is also obtained for the interaction with water and ammonia. For both H(2)O and NH(3), the agreement is due to the possibility to perform experiments in which the probe molecule is dosed from the gas phase, thus allowing to reach the 1 : 1 (or 1 : 2) ratio between the adsorbing Ti sites and the adsorbed molecule. Then, interaction with hydrogen peroxide is discussed, underlining the problems faced in reaching a common view between experimental and theoretical results, owing to the difficulties both in performing experiments where anhydrous H(2)O(2) is dosed on TS-1, and in taking into account the role played by the aqueous medium in the reactivity of Ti(iv) centres toward H(2)O(2) using ab initio calculations. Only once such difficulties have been overcome, by increasing the complexities of both experiments and ab initio models, is a joint-view finally obtained. Where needed, comparison with other experimental results (X-ray and neutron diffraction, NMR, IR, Raman, UV-vis and resonant Raman) is made.     

Study of immobilized metal affinity chromatography sorbents for the analysis of peptides by on‐line solid‐phase extraction capillary electrophoresis‐mass spectrometry

Several commercial immobilized metal affinity chromatography sorbents were evaluated in this study for the analysis of two small peptide fragments of the amyloid β‐protein (Aβ) (Aβ(1–15) and Aβ(10–20) peptides) by on‐line immobilized metal affinity SPE‐CE (IMA‐SPE‐CE). The performance of a nickel metal ion (Ni(II)) sorbent based on nitrilotriacetic acid as a chelating agent was significantly better than two copper metal ion (Cu(II)) sorbents based on iminodiacetic acid. A BGE of 25 mM phosphate (pH 7.4) and an eluent of 50 mM imidazole (in BGE) yielded a 25‐fold and 5‐fold decrease in the LODs by IMA‐SPE‐CE‐UV for Aβ(1–15) and Aβ(10–20) peptides (0.1 and 0.5 μg/mL, respectively) with regard to CE‐UV (2.5 μg/mL for both peptides). The phosphate BGE was also used in IMA‐SPE‐CE‐MS, but the eluent needed to be substituted by a 0.5% HAc v/v solution. Under optimum preconcentration and detection conditions, reproducibility of peak areas and migration times was acceptable (23.2 and 12.0%RSD, respectively). The method was more sensitive for Aβ(10–20) peptide, which could be detected until 0.25 μg/mL. Linearity for Aβ(10–20) peptide was good in a narrow concentration range (0.25–2.5 μg/mL, R² = 0.93). Lastly, the potential of the optimized Ni(II)‐IMA‐SPE‐CE‐MS method for the analysis of amyloid peptides in biological fluids was evaluated by analyzing spiked plasma and serum samples.     

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.     

Discrete Magnesium Hydride Aggregates: A Cationic Mg13H18 Cluster Stabilized by NNNN‐Type Macrocycles

Large magnesium hydride aggregates [Mg₁₃(Me₃TACD)₆(μ₂‐H₁₂)(μ₃‐H₆)][A]₂ ((Me₃TACD)H=1,4,7‐trimethyl‐1,4,7,10‐tetraazacyclododecane; A=AlEt₄, AlnBu₄, B{3,5‐(CF₃)₂C₆H₃}₄) were synthesized stepwise from alkyl complexes [Mg₂(Me₃TACD)R₃] (R=Et, nBu) and phenylsilane in the presence of additional Mg^II ions. The central magnesium atom is octahedrally coordinated by six hydrides as in solid α‐MgH₂ of the rutile type. Further coordination to six magnesium atoms leads to a substructure of seven edge‐sharing octahedra as found in the hexagonal layer of brucite (Mg(OH)₂). Upon protonolysis in the presence of 1,2‐dimethoxyethane (DME), this cluster was degraded into a tetranuclear dication [Mg₂(Me₃TACD)(μ‐H)₂(DME)]₂[A]₂.     

Crossed graphene: Stability and electronic structure

Carbon has always attracted attention due to its rich chemistry and the almost complementary properties of the natural phases graphite and diamond. While graphite is a highly anisotropic semi‐metal, diamond shows high hardness and thermal conductivity and is a wide‐gap insulator. With the discovery of graphene, fullerenes, and carbon nanotubes which resemble properties of the two crystalline phases, research on those and novel carbon materials emerged. Since carbon is forming different covalent bonds, there is a multitude of possibilities to create new structures by just combining sp, sp², and sp³ bonded carbon. Here we report on the discovery of a new sp² and sp³ bonded carbon structure which can be seen as a crossed graphene structure providing hybrid properties of graphene and diamond by means of an evolutionary algorithm.

     

Notes on projective normality of reducible curves

We give some results on quadratic normality of reducible curves canonically embedded and partially extend this study to their projective normality.