Molecular [(fe(3))-(fe(3))] and [(fe(4))-(fe(4))] coordination cluster pairs as single or composite arrays

The synthesis of molecular cluster pairs is a challenge for coordination chemists due to the potential applications of these species in molecular spintronics or quantum computing. The ligand H(4)L, 1,3-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-2-methoxybenzene, has been successfully used to obtain a series of such complexes using the basic Fe(III) trinuclear carboxylates as starting materials. Synthetic control has allowed the isolation of the two molecular cluster pairs that form the composite [Fe(4)O(2)(PhCO(2))(6)(H(2)L)(pz)](2)[Fe(3)O(PhCO(2))(5)(py)(H(2)L)](2) (1). The dimers of trinuclear units, [Fe(3)O(PhCO(2))(5)(H(2)O)(H(2)L)](2) (2) and [Fe(3)O(o-MePhCO(2))(5)(H(2)L)(py)](2) (3), and the dimers of tetranuclear units, [Fe(4)O(2)(PhCO(2))(6)(H(2)L)(pz)](2) (4) and [Fe(4)O(2)(o-MePhCO(2))(6)(H(2)L)(pz)](2) (5), are presented here. The magnetic properties of the reported aggregates show that they are pairs of semi-independent clusters weakly interacting magnetically as required for two-qubit quantum gates.     

Exploring the energy landscape of a molecular engineered analog of a tumor-homing peptide

Recently a new non-coded amino acid was designed as a replacement for Arg, to protect the tumor-homing pentapeptide CREKA (Cys-Arg-Glu-Lys-Ala) from proteases. This constrained Arg analog, denoted c(5)Arg, was engineered to also promote the stability of the CREKA bioactive conformation. The conformational profile of the CREKA analog obtained by replacing Arg by c(5)Arg has been extensively investigated in this work. Two molecular dynamics simulations-based strategies have been employed: a modified simulated annealing and replica exchange. Results obtained using both techniques show that the conformational features of the new analog fulfill the purpose of its design. The new CREKA analog not only preserves the main structural attributes found for the bioactive conformation of the parent peptide but also shows lower flexibility. Moreover, the conformational profile of the mutated peptide narrows towards the most stable structures previously observed for the parent CREKA peptide.     

Thermal behavior of copper(II) pseudohalide complexes containing bidentate amines

Pseudohalide complexes of copper(II) with aliphatic bidentate amines, [Cu(N₃)₂(N,N-diEten)]₂ 1, [Cu(NCO)₂(N,N-diEten)]₂ 2, [Cu(NCO)₂(N,N-diMeen)]₂ 3, [Cu(N₃)(NCS)(N,N'-diMeen)]₂ 4 and [Cu(N₃)(NCO)(N,N-diMeen)]₂ 5 (N,N-diEten=N,N-diethylethylenediamine; N,N-diMeen=N,N- dimethyl-ethylenediamine and N,N'-diMeen = N,N'-dimethylethylenediamine), were prepared, characterized and their thermal behavior was investigated by TG curves. According to thermal analysis and X-ray diffraction patterns all compounds decomposed giving copper(II) oxide as final product. The mechanisms of decomposition were proposed and an order of thermal stability was established.This revised version was published online in November 2005 with corrections to the Cover Date.     

Considerations about the226Ra gross alpha counting determination

Chemical elemental compositions of some silicate, magnetic and glass spherules were investigated with INAA. The elements determined include Os, Ir, Ni, Co, Fe, Cr, Au, La, Ce, Sm, Eu, Yb, Lu and Sc etc. The elemental correlation, as well as their enrichment (or depletion) factors relative to Cl chondrite were examined. The high concentrations of the refractory siderophile elements contained in these spherules support the proposal that they originate from extraterrestrial substances. Some useful chemical criteria for identifying the sources of silicate, magnetic and glass spherules are put forward.     

Neuro-genetic multioptimization of the determination of polychlorinated biphenyl congeners in human milk by headspace solid phase microextraction coupled to gas chromatography with electron capture detection

Polychlorinated biphenyls (PCB) can eventually contaminate breast milk, which is a serious issue to the newborn due to their high vulnerability. Solid phase microextraction (SPME) can be a very convenient technique for their isolation and pre-concentration prior chromatographic analysis. Here, a simultaneous multioptimization strategy based on a neuro-genetic approach was applied to a headspace SPME method for determination of 12 PCB in human milk. Gas chromatography with electron capture detection (ECD) was adopted for the separation and detection of the analytes. Experiments according to a Doehlert design were carried out with varied extraction time and temperature, media ionic strength and concentration of the methanol (co-solvent). To find the best model that simultaneously correlate all PCB peak areas and SPME extraction conditions, a multivariate calibration method based on a Bayesian Neural Network (BNN) was applied. The net output from the neural network was used as input in a genetic algorithm (GA) optimization operation (neuro-genetic approach). The GA pointed out that the best values of the overall SPME operational conditions were the saturation of the media with NaCl, extraction temperature of 95 °C, extraction time of 60 min and addition of 5% (v/v) methanol to the media. These optimized parameters resulted in the decrease of the detection limits and increase on the sensitivity for all tested analytes, showing that the use of neuro-genetic approach can be a promising way for optimization of SPME methods.     

Free-Standing,Flexible Nanofeatured Polymeric Films Prepared by Spin-Coating and Anodic Polymerization as Electrodes for Supercapacitors

Flexible and self-standing multilayered films made of nanoperforated poly(lactic acid) (PLA) layers separated by anodically polymerized poly(3,4-ethylenedioxythiophene) (PEDOT) conducting layers have been prepared and used as electrodes for supercapacitors. The influence of the external layer has been evaluated by comparing the charge storage capacity of four- and five-layered films in which the external layer is made of PEDOT (PLA/PEDOT/PLA/PEDOT) and nanoperforated PLA (PLA/PEDOT/PLA/PEDOT/PLA), respectively. In spite of the amount of conducting polymer is the same for both four- and five-layered films, they exhibit significant differences. The electrochemical response in terms of electroactivity, areal specific capacitance, stability, and coulombic efficiency was greater for the four-layered electrodes than for the five-layered ones. Furthermore, the response in terms of leakage current and self-discharge was significantly better for the former electrodes than for the latter ones.     

Coordination complexes exhibiting anion...pi interactions: synthesis, structure, and theoretical studies

The polydentate ligand 2,4,6-tris(dipyridin-2-ylamino)-1,3,5-triazine (dpyatriz) in combination with the Cu(ClO 4) 2/CuX 2 salt mixtures (X (-) = Cl (-), Br (-), or N 3 (-)) leads to the formation of molecular coordination aggregates with formulas [Cu 3Cl 3(dpyatriz) 2](ClO 4) 3 ( 2), [Cu 3Br 3(dpyatriz) 2](ClO 4) 3 ( 3), and [Cu 4(N 3) 4(dpyatriz) 2(DMF) 4(ClO 4) 2](ClO 4) 2 ( 4). These complexes consist of two dpyatriz ligands bridged via coordination to Cu (II) and disposed either face-to-face in an eclipsed manner ( 2 and 3) or parallel and mutually shifted in one direction. The copper ions complete their coordination positions with Cl (-) ( 2), Br (-) ( 3), or N 3 (-), ClO 4 (-), and N, N-dimethylformamide (DMF) ( 4) ligands. All complexes crystallize together with noncoordinate ClO 4 (-) groups that display anion...pi interactions with the triazine rings. These interactions have been studied by means of high level ab initio calculations and the MIPp partition scheme. These calculations have proven the ClO 4 (-)...[C 3N 3] interactions to be favorable and have revealed a synergistic effect from the combined occurrence of pi-pi stacking of triazine rings and the interaction of these moieties with perchlorate ions, as observed in the experimental systems.     

Navier–Stokes Equations on Weighted Graphs

Navier–Stokes equations arise in the study of incompressible fluid mechanics, star movement inside a galaxy, dynamics of airplane wings, etc. In the case of Newtonian incompressible fluids, we propose an adaptation of such equations to finite connected weighted graphs such that it produces an ordinary differential equation with solutions contained in a linear subspace, this subspace corresponding to the Newtonian conservation law. We discuss the particular case when the graph is the complete graph K _m , with constant weight, and provide a necessary and sufficient condition for it to have solutions.     

The type set for some measures on \mathbb{R}^{2n} with n-dimensional support

Let be realhomogeneous functions in ofdegree and let bethe Borel measure on given by