Half-sandwich Ni(II) complexes bearing enantiopure bidentate NHC-carboxylate ligands: efficient catalysts for the hydrosilylative reduction of acetophenones

Chiral nickel complexes containing NHC-carboxylate chelate ligands derived from the (S)-isomeric form of amino acids have been synthesised from the corresponding imidazolium salt and nickelocene. The presence of the carboxylate on the N-side arm of the heterocycle results in the competing formation of mixtures of mono- and bis-NHC complexes (i.e., [Ni(η5-Cp)(κ2-C,O-NHC)] and [Ni(κ2-C,O-NHC)2]), both of which retain the (S)-configuration of the stereogenic center and which can be separated by chromatography. Both the 18e- and 16e- complexes are found to be very stable and cannot be interconverted. The composition of the resulting mixtures depends mainly on the entity of the amino acid residue and, of more practical interest, on the reaction conditions. Thus, microwave heating and MeCN as a solvent favor the formation of the half-sandwich nickel complexes, rather than the bis-NHC compounds. Some of the [Ni(η5-Cp)(κ2-C,O-NHC)] complexes turn out to be among the best nickel catalysts for the hydrosilylative reduction of p-acetophenones described to date, although without chiral induction, in the absence of activating additives and under mild catalytic conditions.

Severe respiratory disease caused by human respiratory syncytial virus impairs language learning during early infancy

Human respiratory syncytial virus infection is a leading cause of pediatric morbidity and mortality. A previous murine study showed that during severe acute respiratory infections the virus invades the central nervous system, and that infected animals evolve with long-lasting learning difficulties associated with long-term potentiation impairment in their hippocampus. We hypothesized here that human infants who presented a severe episode of respiratory syncytial virus infection before 6 months of age would develop long-term learning difficulties. We measured the acquisition of the native phoneme repertoire during the first year, a milestone in early human development, comprising a reduction in the sensitivity to the irrelevant nonnative phonetic information and an increase in the sensitivity to the information relevant for the native one. We found that infants with a history of severe respiratory infection by the human respiratory syncytial virus presented poor distinction of native and nonnative phonetic contrasts at 6 months of age, and remained atypically sensitive to nonnative contrasts at 12 months, which associated with weak communicative abilities. Our results uncover previously unknown long-term language learning difficulties associated with a single episode of severe respiratory infection by the human respiratory syncytial virus, which could relate to memory impairments.

Water-soluble NHC-stabilized platinum nanoparticles as recoverable catalysts for hydrogenation in water

Aromatic compounds have been hydrogenated in water using recoverable catalysts based on water-soluble platinum nanoparticles capped with NHC ligands.

Monitoring of nanoparticle reactivity in solution: interaction of l-lysine and Ru nanoparticles probed by chemical shift perturbation parallels regioselective H/D exchange

Thanks to new water-soluble Ru nanoparticles (NPs) stabilized by sulfonated NHC ligands, we demonstrate that it is possible to monitor the catalyst/substrate interaction using NMR chemical shift perturbations (CSPs), under conditions that closely resemble those applied during the enantiospecific C-H deuteration of l-lysine. Correlating the pH dependence of the interaction of l-lysine with the surface of the RuNPs and its subsequent deuteration, our study underscores the importance of oriented binding to the surface as a critical factor for H/D exchange.

Water-soluble platinum nanoparticles stabilized by sulfonated N-heterocyclic carbenes: influence of the synthetic approach

On the surface: Pt nanoparticles with NHC ligands at the surface have been prepared in water using different organometallic approaches.

Mean-field crack networks on desiccated films and their applications: Girl with a Pearl Earring

Usual requirements for bulk and fissure energies are considered in obtaining the interdependence among external stress, thickness and area of crack polygons in desiccated films. The average area of crack polygons increases with thickness as a power-law of 4/3. The sequential fragmentation process is characterized by a topological factor related to a scaling finite procedure. Non-sequential overly tensioned (prompt) fragmentation is briefly discussed. Vermeer's painting, Girl with a Pearl Earring, is considered explicitly by using computational image tools and simple experiments and applying the proposed theoretical analysis. In particular, concerning the source of lightened effects on the girl's face, the left/right thickness layer ratio (≈1.34) and the stress ratio (≈1.102) are evaluated. Other master paintings are briefly considered.

Competitive Exclusion and Axiomatic Set-Theory: De Morgan's Laws, Ecological Virtual Processes, Symmetries and Frozen Diversity

This work applies the competitive exclusion principle and the concept of potential competitors as simple axiomatic tools to generalized situations in ecology. These tools enable apparent competition and its dual counterpart to be explicitly evaluated in poorly understood ecological systems. Within this set-theory framework we explore theoretical symmetries and invariances, De Morgan's laws, frozen evolutionary diversity and virtual processes. In particular, we find that the exclusion principle compromises the geometrical growth of the number of species. By theoretical extending this principle, we can describe interspecific depredation in the dual case. This study also briefly considers the debated situation of intraspecific competition. The ecological consequences of our findings are discussed; particularly, the use of our framework to reinterpret coupled mathematical differential equations describing certain ecological processes.

Magnetically recoverable catalysts based on mono- or bis-(NHC) complexes of palladium for the Suzuki–Miyaura reaction in aqueous media: two NHC–Pd linkages are better than one

Mono- and bis(NHC) Pd complexes grafted onto magnetic particles are compared as catalysts in the Suzuki–Miyaura reaction in aqueous media. The latter is found to be an outstanding recyclable catalyst.

[Higher risk for health care associated infections in hospitalized children with special health needs]

BACKGROUND

Nosocomial infections (NIs) represent an important public health issue, being associated with high morbidity, mortality and costs.

OBJECTIVES

To identify risk factors of NIs in a cohort of hospitalized pediatric patients, with emphasis in children with special health care needs (CSHCN).

PATIENTS AND METHODS

We studied patients hospitalized in Sótero del Río Pediatric Hospital at Santiago-Chile, between September and December, 2009. Relative Risk (RR) was calculated between CSHCN-3 (children attended by three or more health care professionals) versus non CSHCN-3, and between children with medical complexity (CMC) versus non CMC, using log-binomial models.

RESULTS

920 patients were included. Prevalence of NIs was 12.7%. The most frequent diagnoses were gastrointestinal and respiratory viral infections. Both crude and adjusted by confounders (age and sex), CSHCN-3 and CMC presented significantly higher risk of NIs compared to patients without these conditions (RR 2.91 and RR 2.16, respectively).

CONCLUSION

CSHCN-3 and CMC represent independent conditions associated to a 2-3 fold risk of NIs.

Synthesis and behavior of novel sulfonated water-soluble N-heterocyclic carbene (η4-diene) platinum(0) complexes

Novel water-soluble (NHC)Pt(0)(1,6-diene) complexes are presented, along with details of their preparation, stability, and use as catalysts for the hydrosilylation of acetylenes in water.

Intermittence for humans spreading 45,000 years ago: from Eurasia to the Americas

From northeastern Eurasia to the Americas, a three-stage spread of modern humans is considered through large-scale intermittence (exploitation/relocation). Conceptually, this work supports intermittence as a real strategy for colonization of new habitats. For the first stage, northeastern Eurasia travel, we adapt our model to archaeological dates determining the diffusion coefficient (exploitation phase) as D = 299.44 km2/yr and the velocity parameter (relocation phase) as vo = 4.8944 km/yr. The relative phase weight (✧0.46) between both kinds of motions is consistent with a moderate biological population rate (r΄ ✧ 0.0046/yr). The second stage is related to population fragmentation. The last stage, reaching Alaska, corresponds essentially to relocation (vo ✧ 0.75 km/yr).

Stability in air of silver and silver oxide nanoparticle shells deposited over silica spheres without using coupling agents

The deposition of silver nanoparticles on the surface of silica was carried out using our simple, robust and rapid chemical method without surface modification of silica or added coupling agents. The process was carried out at room temperature using water/methanol mixtures, tetraethyl orthosilicate as Si source and silver nanoparticles (NPs) in a single-pot reaction. Using EDS, XRD, HRTEM and High Angle Annular Dark Field (HAADF) STEM characterization techniques, we have found the coexistence of silver NPs and silver oxides NPs anchored to the surface of sub-micron silica spheres, with Ag NPs predominating sizes around 2-3 nm approximately, and Ag2O NPs sizes over 10 nm.

A mathematical model for the Andean Tiwanaku civilization collapse: climate variations

We propose a mathematical nonlinear model for the Tiwanaku civilization collapse based on the assumption, supported by archeological data, that a drought caused a lack of the main resource, water. We evaluate the parameter of our model using archaeological data. According to our numerical simulation the population core should have decreased from 45,000 to 2000 inhabitants due to lake surface contraction.

Deposition of silver nanoshell and reactivity of silver nanoparticles with surface silanols of submicrospherical silica

We describe in this report the production of a smooth and uniform silver outer nanoshell with thickness -15 nm on submicrospherical silica, using a rapid and simple one pot chemical route. The reaction mechanism proposed for the formation of the silver nanoshell is the reactivity of silver nanoparticles with surface silanols at high pH, without added coupling agent or surface modification of silica, leading to the formation of the continuous and homogeneous silver nanoshell on the silica spheres.

[Clinical guidelines on identification, management and complications of chronic kidney disease]

The key messages of these guidelines on chronic kidney disease are: Chronic kidney disease (CKD) is a public health problem due to its wide distribution, high rate of complications and cost. CKD is a common condition, its prevalence being about 10%, and is treatable if it is detected on time. A patient with CKD has a higher risk of cardiovascular mortality than of progression of its underlying renal disease. A new definition of CKD, based on estimated Glomerular Filtration Rate (eGFR) and kidney damage, facilitates its detection and management. CKD is detected with three simple tests: 1) Blood pressure measurement, 2) Detection of proteinuria or albuminuria in an isolated urine sample, and 3) Estimation of renal function (eGFR), based on serum creatinine, age, gender and race. The CKD risk groups are individuals with diabetes, hypertension and a family history of renal disease. The most cost-effective measures are to detect and treat diabetic and hypertensive patients in the community. Therapy must emphasize the maximal reduction of cardiovascular risk. The complications of CKD such as anemia and renal osteodystrophy can be identified and treated on time. Most patients with chronic kidney disease are detected in the community, therefore their initial care must be organized at the level of primary care, along with programs for hypertension and diabetes.

Late renal vein thrombosis associated with recurrence of membranous nephropathy in a renal allograft: a case report

Allograft renal vein thrombosis (RVT) is an uncommon but potentially catastrophic complication. Although it usually occurs in the early posttransplant period and is associated with surgical complications or vascular rejection, it may develop later, when it is generally related with a hypercoagulable state. Typical clinical presentation is sudden oligoanuric acute renal failure, and hematuria, with a painful and swollen renal allograft. Confirmation of the diagnosis requires Doppler ultrasound and computed tomography. Herein we have reported a successfully treated case of late RVT that developed in an allograft with recurrent membranous nephropathy associated with the nephrotic syndrome. The patient fully recovered renal graft function a few days after presentation, which was related to anticoagulant therapy. We demonstrated complete recanalization of the venous thrombosis.

Crystal Structures of Poly(aryl ether) Dendrons with Palladium Scorpionate Complexes at Their Focal Point

Novel palladium(II) complexes with bis(pyrazol-1-yl)methane ligands at the focal point of G0-G3 poly(aryl ether) Fréchet-type dendrons are reported. The molecular structures of the metallodendrimer series G0, G1, and G2 [(dend)CH(3,5-Me2pz)2(PdCl2)] have been determined by X-ray diffraction methods. The three structures show a similar three-dimensional organization of the metal complex, which is progressively engulfed by the branches with increasing dendrimer generation.

Synthesis and1H NMR studies of paramagnetic nickel(ii) complexes containing bis(pyrazolyl)methane ligands with dendritic substituents

The substituted bis(pyrazolyl)methane ligands RCH(3,5-Me2pz)2(R=SiMe3, CH2Ph, G1, G2, and G3; Gn=Fréchet-type dendritic wedges of generation n) have been prepared starting from H2C(3,5-Me2pz)2. Reaction of these didentate ligands with [NiBr2(DME)] is a straightforward procedure that allows the synthesis of the nickel(II) complexes [NiBr2{RCH(3,5-Me2pz)2}]. The molecular structure of compound (R=CH2Ph) has been determined by X-ray diffraction studies. The nickel centre coordinates two bromine and two nitrogen atoms in a tetrahedral environment, and the metallacycle Ni(NN)2C adopts a boat conformation with the benzyl group in an axial position. 1H NMR studies have been carried out to characterize these paramagnetic nickel compounds in solution. Valuable information about the disposition of the ligands and dendritic wedges in solution has been obtained thanks to the influence of the paramagnetic centre on the proton resonances.

Generation effects on the microstructure and product distribution in ethylene polymerization promoted by dendritic nickel catalysts

Carbosilane dendrimers Gn-[(ONNMe2)NiBr2]m, containing up to sixteen terminal pyridylimine nickel complexes, have been studied as catalysts for polymerization of ethylene; the microstructure and the oligomer/polymer distribution are significantly affected by the generation of the dendritic precursor.

A mathematical model for Neanderthal extinction

A simple mathematical homogeneous model of competition is used to describe Neanderthal extinction in Europe. It considers two interacting species, Neanderthals and Early Modern Men, in the same ecological niche. Using paleontological data we claim that the parameter of similarity, between both species, fluctuates between 0.992 and 0.997. An extension of the model including migration (diffusion) is also discussed; nevertheless, extinction of Neanderthal seems unavoidable. Numerical analysis of travelling wave solutions (fronts) confirms the extinction. The wave-front-velocity is estimated from linear analysis and numerical simulations confirm this estimation. We conjecture a mathematical formulation for the principle of exclusion between competitive interacting species (Gause).