Design of dinuclear copper species with carboranylcarboxylate ligands: study of their steric and electronic effects

A series of new mononuclear and carboranylcarboxylate‐bridged dinuclear copper(II) compounds containing the 1‐CH₃‐2‐CO₂H‐1,2‐closo‐C₂B₁₀H₁₀ carborane ligand ( L H) has been synthesized. Reaction of different copper salts with L H at room temperature leads to dinuclear compounds of the general formula [Cu₂(μ‐ L )₄( L_t )₂] ( L_t =thf ( 1 ), L_t =H₂O ( 1′ )). The reaction of 1 and 1′ with different terminal pyridyl (py) ligands leads to the formation of a series of structurally analogous complexes by substitution of the terminal ligand thf or H₂O ( L_t =py ( 2 ), p‐CF₃‐py ( 3 ), p‐CH₃‐py ( 4 ), pz ( 6 ), and 4,4′‐bpy ( 7 )), which maintain the structural Cu₂(μ‐O₂CR)₄ core in the majority of the cases except for o‐(CH₃)₂‐py, where a mononuclear compound ( 5 ) is exclusively obtained. These compounds have been characterized through analytical, spectroscopic (NMR, IR, UV‐visible, ESI‐MS) and magnetic techniques. X‐ray structural analysis revealed a paddle‐wheel structure for the dinuclear compounds, with a square‐pyramidal geometry around each copper ion and the carboranylcarboxylate ions bridging two copper atoms in syn–syn mode. The mononuclear complex obtained with the o‐(CH₃)₂‐py ligand presents a square‐planar structure, in which the carboranylcarboxylate ligand adopts a monodentate coordination mode. The magnetic properties of the dinuclear compounds 1 , 3 , 4 , and 6 show a strong antiferromagnetic coupling in all cases (J=?261 ( 1 ), ?255 ( 3 ), ?241 ( 4 ), ?249 cm^?1 ( 6 )). Computational studies based on hybrid density functional methods have been used to study the magnetic properties of the complexes and also to evaluate their relative stability on the basis of the strength of the bond between each Cu^II and the terminal ligand.     

Comparison of 24-h volume and creatinine-corrected total urinary polyphenol as a biomarker of total dietary polyphenols in the Invecchiare InCHIANTI study

Polyphenols have beneficial effects on several chronic diseases but assessing polyphenols intake from self-reported dietary questionnaires tends to be inaccurate and not very reliable. A promising alternative is to use urinary excretion of polyphenols as a proxy measure of intake. The best method to assess urinary excretion is to collect 24-h urine. However, since collecting 24-h urine method is expensive, time consuming and may be difficult to implement in large population-based studies, measures obtained from spot urine normalized by creatinine are commonly used. The purpose of the study was to evaluate the correlation between polyphenols dietary intake and total urinary polyphenol excretion (TPE), expressed by both 24-h volume and urinary creatinine normalization in 928 participants from the InCHIANTI study. Dietary intake data were collected using a validated food frequency questionnaire. Urinary TPE was analyzed by Folin-Ciocalteau assay. Both urinary TPE expression models were statistically correlated (r=0.580), and the partial correlation coefficient improved (pr=0.722) after adjusting for the variables that modify the urinary creatinine excretion (i.e. gender, age, BMI, physical activity and renal function). In crude models, polyphenol intake was associated with TPE corrected by 24-h volume (r=0.211; P<0.001), but not with creatinine normalization (r=0.014; P=0.692). However, urinary TPE expressed by creatinine correction was significantly correlated with dietary polyphenols after adjusting for covariates (pr=0.113; P=0.002). We conclude that urinary TPE expressed by 24-h volume is a better biomarker of polyphenol dietary intake than by urinary creatinine normalization. After covariate adjustment, both can be used for studying the relationships between polyphenol intake and health in large-scale epidemiological studies.     

Tangent Fermions: Dirac or Majorana Fermions on a Lattice Without Fermion Doubling

Methods to discretize the Hamiltonian of a topological insulator or topological superconductor, without giving up on the topological protection of the massless excitations (respectively, Dirac fermions or Majorana fermions) are reviewed. The method of tangent fermions, pioneered by Richard Stacey, is singled out as being uniquely suited for this purpose. Tangent fermions propagate on a $2+1$ dimensional space-time lattice with a tangent dispersion: ${\tan }^2(\mathit{\epsilon }/2)={\tan }^2(k_x/2)+{\tan }^2(k_y/2)$ in dimensionless units. They avoid the fermion doubling lattice artefact that will spoil the topological protection, while preserving the fundamental symmetries of the Dirac Hamiltonian. Although the discretized Hamiltonian is nonlocal, as required by the fermion-doubling no-go theorem, it is possible to transform the wave equation into a generalized eigenproblem that is local in space and time. Applications that are discussed include Klein tunneling of Dirac fermions through a potential barrier, the absence of localization by disorder, the anomalous quantum Hall effect in a magnetic field, and the thermal metal of Majorana fermions.     

Phase separation in a poly(ether sulfone) modified epoxy-amine system studied by temperature modulated differential scanning calorimetry and dielectric relaxation spectroscopy

The phase separation induced by the curing reaction of an epoxy based on diglycidylether of bisphenol A (DGEBA) with methylene dianiline (MDA) modified with poly(ether sulfone) (PES) at a concentration of 20 wt% was studied by temperature modulated differential scanning calorimetry (TMDSC) and dielectric relaxation spectroscopy (DRS). The effect of phase separation on the curing kinetics and vitrification phenomena is analysed. The dependence of the log of the measuring frequency on the degree of conversion allows the correlation between the dipolar relaxation of each phase and the vitrification observed by TMDSC to be established.     

Effect of previous thermal history on physical aging of amorphous poly (ethylene terephthalate)

Physical aging of amorphous PET, at aging temperatures (T_a) of 40 and 60°C and different aging times (t_a), has been studied by DSC using two kinds of samples with different thermal history: Liquid-Nitrogen-Quenched samples (LNQ) and DSC cooled samples at a controlled cooling rate of 60 K/min (CC). At T_a = 40°C, a sub-T_g peak appears in LNQ samples but is not clearly observed in the CC samples. At T_g = 60°C, a superposed peak to T_g is observed in both kinds of samples. This different behaviour can be explained considering the distribution of relaxation times in the polymer.     

Site-selective multi-emitter gold-silver metallopolymers: A novel class of self-assembled materials

New luminescent heterometallopolymers [(Au-C₆F₅)_m(AgOSO₂CF₃)_n (PVP)] with different Au:Ag molar ratios were synthesized. The luminescent emissions of these polymers are strongly dependent on the temperature, excitation wavelengths, and the Au(I):Ag(I) molar ratio. The incorporation of a precise amount of Ag(I) atoms in the backbone of [(Au-C₆F₅)_m(PVP)] metallopolymer allows a controlled tuning of the emission energy in the green-blue range.