Impact of water on the OH + HOCl reaction

The effect of a single water molecule on the OH + HOCl reaction has been investigated. The naked reaction, the reaction without water, has two elementary reaction paths, depending on how the hydroxyl radical approaches the HOCl molecule. In both cases, the reaction begins with the formation of prereactive hydrogen bond complexes before the abstraction of the hydrogen by the hydroxyl radical. When water is added, the products of the reaction do not change, and the reaction becomes quite complex yielding six different reaction paths. Interestingly, a geometrical rearrangement occurs in the prereactive hydrogen bonded region, which prepares the HOCl moiety to react with the hydroxyl radical. The rate constant for the reaction without water is computed to be 2.2 × 10(-13) cm(3) molecule(-1) s(-1) at room temperature, which is in good agreement with experimental values. The reaction between ClOH···H(2)O and OH is estimated to be slower than the naked reaction by 4-5 orders of magnitude. Although, the reaction between ClOH and the H(2)O···HO complex is also predicted to be slower, it is up to 2.2 times faster than the naked reaction at altitudes below 6 km. Another intriguing finding of this work is an interesting three-body interchange reaction that can occur, that is HOCl + HO···H(2)O → HOCl···H(2)O + OH.     

Synthesis of magnetic nanoparticles: effects of polyelectrolyte concentration and pH

This study refers to the effect of sodium polyacrylate concentration (1 to 5 mass %) and pH (10 to 12) on the synthesis of magnetic nanoparticles (magnetite?Cmaghemite) and their characterization by Mössbauer spectroscopy. The magnetic particles were obtained by coprecipitation method using iron chloride (II) and iron chloride (III) as precursor reagents and sodium polyacrylate as stabilizing agent. All samples showed Mössbauer broad resonance lines in typical doublet and sextets patterns of magnetite or maghemite with corresponding wide particle size distributions. The stability of magnetic particles was carried out by measuring particle sizes with dynamic light scattering (DLS). The z-average values for magnetic particles were in the range 24 to 590 nm and no significant change in size was observed on aging by leaving this material in air for 20 days. X-ray diffraction patterns showed characteristic peaks of the spinel structure and have an increase in their broadening as the pH decreases, effect that is dominated by the decrease in crystallite sizes. The nanoparticles showed to be magnetic at pH 12 and at room temperature.     

On the Binding of Congo Red to Amyloid Fibrils

Amyloids are characterized by their capacity to bind Congo red (CR), one of the most used amyloid‐specific dyes. The structural features of CR binding were unknown for years, mainly because of the lack of amyloid structures solved at high resolution. In the last few years, solid‐state NMR spectroscopy enabled the determination of the structural features of amyloids, such as the HET‐s prion forming domain (HET‐s PFD), which also has recently been used to determine the amyloid–CR interface at atomic resolution. Herein, we combine spectroscopic data with molecular docking, molecular dynamics, and excitonic quantum/molecular mechanics calculations to examine and rationalize CR binding to amyloids. In contrast to a previous assumption on the binding mode, our results suggest that CR binding to the HET‐s PFD involves a cooperative process entailing the formation of a complex with 1:1 stoichiometry. This provides a molecular basis to explain the bathochromic shift in the maximal absorbance wavelength when CR is bound to amyloids.     

In‐Situ Growth and Immobilization of CdS Nanoparticles onto Functionalized MoS2: Preparation,Characterization and Fabrication of Photoelectrochemical Cells

A facile strategy for the controllable growth of CdS nanoparticles at the periphery of MoS₂ en route the preparation of electron donor‐acceptor nanoensembles is developed. Precisely, the carboxylic group of α‐lipoic acid, as addend of the modified MoS₂ obtained upon 1,2‐dithiolane functionalization, was employed as anchor site for the in situ preparation and immobilization of the CdS nanoparticles in an one‐pot two‐step process. The newly prepared MoS₂/CdS hybrid material was characterized by complementary spectroscopic, thermal and microscopy imaging means. Absorption spectroscopy was employed to register the formation of MoS₂/CdS, by observing a broad shoulder centered at 420 nm due to CdS nanoparticles, while the excitonic bands of MoS₂ were also evident. Moreover, based on the efficient quenching of the characteristic fluorescence emission of CdS at 725 nm by the presence of MoS₂, strong electronic interactions at the excited state between the two species within the ensemble were identified. Photoelectrochemical assays of MoS₂/CdS thin‐film electrodes revealed a prompt, steady and reproducible anodic photoresponse during repeated on‐off cycles of illumination. A significant zero‐current photopotential of ?540 mV and an anodic photocurrent of 1 μA were observed, underlining improved charge‐separation and electron transport from CdS to MoS₂. The superior performance of the charge‐transfer processes in MoS₂/CdS is of direct interest for the fabrication of photoelectrochemical and optoelectronic devices.     

Ring Opening and Bidentate Coordination of Amidinate Germylenes and Silylenes on Carbonyl Dicobalt Complexes: The Importance of a Slight Difference in Ligand Volume

The reactions of [Co₂(CO)₈] with one equiv of the benzamidinate (R₂bzam) group‐14 tetrylenes [M(R₂bzam)(HMDS)] (HMDS=N(SiMe₃)₂; 1 : M=Ge, R=iPr; 2 : M=Si, R=tBu; 3 : M=Ge, R=tBu) at 20 °C led to the monosubstituted complexes [Co₂{κ¹M?M(R₂bzam)(HMDS)}(CO)₇] ( 4 : M=Ge, R=iPr; 5 : M=Si, R=tBu; 6 : M=Ge, R=tBu), which contain a terminal κ¹M–tetrylene ligand. Whereas the Co₂Si and Co₂Ge tert‐butyl derivatives 5 and 6 are stable at 20 °C, the Co₂Ge isopropyl derivative 4 evolved to the ligand‐bridged derivative [Co₂{μ‐κ²Ge,N‐Ge(iPr₂bzam)(HMDS)}(μ‐CO)(CO)₅] ( 7 ), in which the Ge atom spans the Co?Co bond and one arm of the amidinate fragment is attached to a Co atom. The mechanism of this reaction has been modeled with the help of DFT calculations, which have also demonstrated that the transformation of amidinate‐tetrylene ligands on the dicobalt framework is negligibly influenced by the nature of the group‐14 metal atom (Si or Ge) but is strongly dependent upon the volume of the amidinate N?R groups. The disubstituted derivatives [Co₂{κ¹M?M(R₂bzam)(HMDS)}₂(CO)₆] ( 8 : M=Ge, R=iPr; 9 : M=Si, R=tBu; 10 : M=Ge, R=tBu), which contain two terminal κ¹M–tetrylene ligands, have been prepared by treating [Co₂(CO)₈] with two equiv of 1 – 3 at 20 °C. The IR spectra of 8 – 10 have shown that the basicity of germylenes 1 and 3 is very high (comparable to that of trialkylphosphanes and 1,3‐diarylimidazol‐2‐ylidenes), whereas that of silylene 2 is even higher.     

Porous MII/Pyrimidine‐4,6‐Dicarboxylato Neutral Frameworks: Synthetic Influence on the Adsorption Capacity and Evaluation of CO2‐Adsorbent Interactions

The understanding of the factors that affect the real pore‐network structure for a given bulk material due to different synthetic procedures is essential to develop the material with the best adsorption properties. In this work, we have deeply studied the influence of the crystallinity degree over the adsorption capacity on three new isostructural MOFs with the formula {[CdM(μ₄‐pmdc)₂(H₂O)₂] ? solv}_n (in which, pmdc=pyrimidine‐4,6‐dicarboxylate; solv=corresponding solvent; M^II=Cd ( 1 ), Mn ( 2 ), Zn ( 3 )). Compared with other methods, the solvent‐free synthesis stands as the most effective route because, apart from enabling the preparation of the heterometallic compounds 2 and 3 , it also renders the adsorbents with the highest performance, which is indeed close to the expected one derived from Grand Canonical Monte Carlo (GCMC) calculations. The structural analysis of the as‐synthesised and evacuated frameworks reveals the existence of a metal atom exposed to the pore. The accessibility of this site is limited due to its atomic environment, which is why it is considered as a pseudo‐open‐metal site. The chemical and physical characterisation confirms that this site can be modified as the metal atom is replaced in compounds 2 and 3 . To assess the effect of the metal replacement on the adsorption behaviour, an exhaustive study of CO₂ experimental isotherms has been performed. The affinity of the pseudo‐open metal sites towards CO₂ and the distribution of the preferred adsorption sites are discussed on the basis of DFT and GCMC calculations.     

Random and stochastic disturbances on the input flow in chemostat models with wall growth

In this paper, we analyze a chemostat model with wall growth where the input flow is perturbed by two different stochastic processes: the well-known standard Wiener process, which leads into several drawbacks from the biological point of view, and a suitable Ornstein-Uhlenbeck process depending on some parameters which allow us to control the noise to be bounded inside some interval that can be fixed previously by practitioners. Thanks to this last approach, which has already proved to be very realistic when modeling other simplest chemostat models, it will be possible to prove the persistence and coexistence of the species in the model without needing the theory of random dynamical systems and pullback attractors needed when dealing with the Wiener process. This is an advantage since the theoretical framework in this paper is much less complicated and provides us much more information than the other.     

A compact rational Krylov method for large‐scale rational eigenvalue problems

In this work, we propose a new method, termed as R‐CORK, for the numerical solution of large‐scale rational eigenvalue problems, which is based on a linearization and on a compact decomposition of the rational Krylov subspaces corresponding to this linearization. R‐CORK is an extension of the compact rational Krylov method (CORK) introduced very recently in the literature to solve a family of nonlinear eigenvalue problems that can be expressed and linearized in certain particular ways and which include arbitrary polynomial eigenvalue problems, but not arbitrary rational eigenvalue problems. The R‐CORK method exploits the structure of the linearized problem by representing the Krylov vectors in a compact form in order to reduce the cost of storage, resulting in a method with two levels of orthogonalization. The first level of orthogonalization works with vectors of the same size as the original problem, and the second level works with vectors of size much smaller than the original problem. Since vectors of the size of the linearization are never stored or orthogonalized, R‐CORK is more efficient from the point of view of memory and orthogonalization than the classical rational Krylov method applied directly to the linearization. Taking into account that the R‐CORK method is based on a classical rational Krylov method, to implement implicit restarting is also possible, and we show how to do it in a memory‐efficient way. Finally, some numerical examples are included in order to show that the R‐CORK method performs satisfactorily in practice.