Density functional description of the early stages of the dioxygenation of [(MeC(CH2PPh2)3)M(catecholate)]+ complexes [M = Co(III), Ir(III)]: toward a rationalization of the catalytic mechanism of ring-opening dioxygenases

Density Functional Theory (DFT) has been applied to characterize the early stages of the reaction of dioxygenation of [(triphos)M(catecholate)]+ complexes [M = Co(III), Ir(III); triphos = MeC(CH2PPh2)3], which have been considered to be models of ring-opening dioxygenases. The structural features of the starting complexes and of the intermediate complexes formed by addition of O2 to the coordinated catecholato ion are well reproduced. The calculations showed that this preliminary stage can be obtained only when the oxygen molecule attacks the molecule on the catecholato site.     

Real bounds, ergodicity and negative Schwarzian for multimodal maps

We consider smooth multimodal maps which have finitely many non-flat critical points. We prove the existence of real bounds. From this we obtain a new proof for the non-existence of wandering intervals, derive extremely useful improved Koebe principles, show that high iterates have `negative Schwarzian derivative' and give results on ergodic properties of the map. One of the main complications in the proofs is that we allow to have inflection points.

     

Dielectric relaxation in single crystal NH4H2PO4 in the high-temperature regime

The dispersion curves of the dielectric response in single crystal NH₄H₂PO₄ were obtained in the radio frequency range and below the high-temperature transition at T_p−160 °C. The results reveal dielectric relaxation at low frequency, which is about 10⁵ Hz at 70 °C, and it shifts to higher frequencies (∼3×10⁶ Hz) as the temperature increases. The relaxation frequency was determined from the peak obtained in the imaginary part of the permittivity as well as from the derivative of the real part of the permittivity. The activation energy E_a=0.55 eV, obtained from the relaxation frequency is very close to that derived from the dc conductivity. We suggest that this dielectric relaxation could be due to the proton jump and phosphate reorientation that cause distortion and change the local lattice polarizability inducing dipoles like      

Instabilities of micellar systems under homogeneous and non-homogeneous flow conditions

The rheological behavior of a cetylpyridinium chloride 100 mmol l^–1/sodium salicylate 60 mmol l^–1 aqueous solution was studied in this work under homogeneous (cone and plate) and non-homogeneous flow conditions (vane-bob and capillary rheometers), respectively. Instabilities consistent with non-monotonic flow curves were observed in all cases and the solution exhibited similar behavior under the different flow conditions. Hysteresis and the sigmoidal flow curve suggested as characteristic of systems that show constitutive instabilities were observed when running cycles of increasing and decreasing stress or shear rate, respectively. This information, together with a detailed determination of steady states at shear stresses close to the onset of the instabilities, allowed one to show unequivocally that "top and bottom jumping" are the mechanisms to trigger the instabilities in this micellar system. It is shown in addition that there is not a true plateau region in between the "top and bottom jumping". Finally, the flow behavior beyond the upturn seemed to be unstable and was found accompanied by an apparent violation of the no-slip boundary condition.     

Randomised circular means of Fourier transforms of measures

We explore decay estimates for circular means of the Fourier transform of a measure on in terms of its -dimensional energy. We find new upper bounds for the decay exponent. We also prove sharp estimates for a certain family of randomised versions of this problem.

     

A Mechanical Model for Analyzing the Runaway Solutions in the Radiation Reaction Problem

In order to understand the rise of runaway solutions in the radiation reaction problem a mechanical model is used. An alternative demonstration of Daboul’s theorem, through Hurwitz’s criterion, is given. The origin of runaway solutions in electrodynamics is discussed. They arise when the particle has a negative mechanical mass or when approximations are used in the equation of motion. In the 1-dimensional mechanical model an exact and linear equation of motion for the particle is obtained, the corresponding exact solution is again runaway when the mechanical mass is negative. The exact solution is not runaway when the mechanical mass is positive. However, the use of approximations leads to an equation of motion which has runaway solutions. It is exhibited that the use of approximations in the 3-dimensional mechanical model is completely necessary because the general equation of motion for the particle is non-linear. The analysis of this case proceeds in a very similar way to the one carried out in electrodynamics. This means that the number of dimensions also plays an important role in the analysis.     

Silica nano-particles produced by worms through a bio-digestion process of rice husk

It is reported the production and characterization of silica nano-particles by Californian-red worms through a bio-digestion process of rice husk; the rice husk contains, naturally, high concentrations of silica (22%). The worms were fed gradually with rice husk and water during 5 months to clean the worm’s digestive system from other types of food. The humus was collected, dried at room temperature, pH neutralized and calcined at different temperatures (500, 600 and 700 °C) to remove the organic matter. The calcined humus was digested to remove traces of inorganic compounds. The size of the silica particles was in the range from 55 to 250 nm depending on calcination temperatures. The efficiency in the production of the particles was 88%. These results were compared with those obtained using other agro-industrial wastes that contain silica: coffee (12%) and cane (8%) husk. The samples were characterized by XRD, FTIR, EDS, DLS, SEM and TEM.     

Os(VIII)-catalysed oxidation of sulfides by sodium salt of N-chlorobenzenesulfonamide

Catalytic activity of Os(VIII) in the oxidation of some twenty organic sulfides with sodium salt of N-chlorobenzenesulfonamide (CAB) has been investigated in alkaline (pH8.7) t-butanol–water (1:1 v/v) medium. Significant retarding influence of [OH⁻] on the reactivity is exhibited. The catalysed reaction is strongly accelerated in the presence of Hg(II). Imperfections are observed in the linear Hammett relationship in the case of –NO₂ substituents.     

N‐(Tri­phenyl­methyl­sulfanyl)­phthal­imide

The title compound, C₂₇H₁₉NO₂S, contains chains of fused (19) rings formed by intermolecular C—H·O=C hydrogen bonds and running along the [011] and [01] directions. These chains are linked through short intermol­ecular C—H·π contacts, giving rise to sheets. The conformation of the title compound is dominated primarily by the nearly orthogonal lone‐pair orbitals on the N and S atoms.