Multilevel quantum mechanical calculations show the role of promoter molecules in the dehydration of methanol to dimethyl ether in H-ZSM-5.

Methyl carboxylate esters promote the formation of dimethyl ether (DME) from the dehydration of methanol in H-ZSM-5 zeolite. We employ a multilevel quantum method to explore the possible associative and dissociative mechanisms in the presence, and absence, of six methyl ester promoters. This hybrid method combines density functional theory, with dispersion corrections (DFT-D3), for the full periodic system, with second-order Møller-Plesset perturbation theory (MP2) for small clusters representing the reaction site, and coupled cluster with single, double, and perturbative triple substitution (CCSD(T)) for the reacting molecules. The calculated adsorption enthalpy of methanol, and reaction enthalpies of the dehydration of methanol to DME within H-ZSM-5, agree with experiment to within chemical accuracy (∼4 kJ mol-1). For the promoters, a reaction pathway via an associative mechanism gives lower overall reaction enthalpies and barriers compared to the reaction with methanol only. Each stage of this mechanism is explored and related to experimental data. We provide evidence that suggests the promoter's adsorption to the Brønsted acid site is the most important factor dictating its efficiency.

Corticosteroid exposure not associated with long-term bone mineral density in pediatric liver transplantation.

OBJECTIVES: The aim of the study was to examine the association of corticosteroid exposure and other skeletal risk factors with bone mineral density (BMD) and fractures following pediatric liver transplantation (LT) at a large single center. PATIENTS AND METHODS: Lumbar spine BMD, measured using dual-energy x-ray absorptiometry (DXA), was corrected for bone age in 52 ambulatory children ages 4 to 18 years, at least 1 year post-LT. Potential risk factors for skeletal health such as corticosteroid exposure, dietary and lifestyle factors, and growth and fracture occurrence, were related to BMD using univariate and multivariate regression analyses. RESULTS: The prevalence of low BMD (z score <-2) and post-LT fractures was 3 of 52 (5.8%) and 11 of 52 (21%), respectively. Univariate analysis revealed age >10 years at LT and body mass index (BMI) < 85th percentile at time of DXA were significantly associated with BMD (both P = 0.02). BMD did not correlate with corticosteroid dosage in the first year post-LT, the year before DXA or cumulative lifetime exposure. A cholestatic primary LT indication, acute rejection episodes, and fractures post-LT were not associated with BMD. Extracurricular physical activity, vitamin D, and calcium intake were not associated with BMD or fractures. Multivariate linear regression revealed increased time post-LT (P = 0.04) and higher BMI z score at time of DXA (P = 0.02) as the strongest independent variables associated with greater BMD. CONCLUSIONS: Neither corticosteroid exposure nor a cholestatic primary indication for LT influenced BMD, which was largely normal in this ambulatory group. Children and adolescents undergoing LT after the age of 10 years and those with low BMI post-LT may be at greatest risk of poor skeletal health later in life, and thus a potential target patient population to benefit from preventive interventions.

A family of diastereomeric dodecanuclear coordination cages based on inversion of chirality of individual triangular cyclic helicate faces.

The dodecanuclear coordination cage [Cd12(Lnaph)12(Lmes)4](BF4)24 consists of a set of four triangular, trinuclear helical panels {Cd3(µ-Lnaph)3}6+ (based on ditopic bridging ligands Lnaph), which are connected by four tritopic ligands Lmes. The result is that the four triangular helical panels and the four Lmes-capped triangular faces of the cuboctahedral core form two alternating subsets of the eight triangular faces of the cuboctahedron. Crystallographic investigations revealed that the triangular helicate faces can have 'clockwise' (C) or 'anticlockwise' (A) helicity, and that the helicity of each face can vary independently of the others as they are mechanically separated. This generates a set of three diastereoisomers in which all four cyclic helicate faces in the cuboctahedron have the same chirality (AAAA/CCCC enantiomers with T symmetry; AAAC/CCCA enantiomers with C 3 symmetry; and achiral AACC with S 4 symmetry). This mirrors the known behaviour of many simpler M4L6 tetrahedral cages which can likewise exist as T, C 3 or S 4 isomers according to the sense of tris-chelate chirality around each individual metal centre: but here it is translated onto a much larger scale by the four chiral units being entire trinuclear helicate faces rather than single metal centres. 1H NMR spectroscopy confirms the presence of the three diastereoisomers with their different molecular symmetries in a ratio slightly different from what is expected on purely statistical grounds; and 1H NMR measurements on a non-equilibrium sample (enriched by manual crystal-picking before preparing the solution) showed that the distribution does not change over several weeks in solution, indicating the kinetic inertness of the cage assemblies.

Surveys of vehicle colour frequency and the transfer of vehicle paints to stationary objects in Sydney, Australia.

The interpretation of vehicle paint traces in forensic casework hinges on a number of factors including the type of paint, colour, number of layers, and background information. Vehicle colour surveys are an important source of information for the forensic paint examiner when interpreting the level of significance of a paint transfer between vehicles involved in a collision, or smears of vehicle paint left at a scene. The two surveys that are presented here investigated (i) the frequency of the colour of vehicles observed on both a motorway and suburban roads in Western Sydney and (ii) the frequency of different vehicle paint colours transferred to car park pillars and walls from five different car parks within North West Sydney, Australia. In the first survey, the highest frequency of vehicle colours recorded was white, grey, black and blue. The second survey resulted in very similar findings with the four most commonly seen colours across the five car parks being blue, white, red, and silver. The results in the second survey take into account the potential for anomalies within the data due to the use of painted service vehicles used within the car parks, such as trolleys and trailers. The results from both surveys were very similar to previous vehicle colour surveys that have been conducted and also corresponded to the vehicle colour registration data obtained from the NSW Roads and Maritime Service website. The results from these two surveys provide up to date statistics that can assist the forensic paint examiner with valuable background data when assessing the significance of vehicle paint evidence in casework.

A survey of glass found on the headwear and head hair of a random population vs. people working with glass.

This study investigated the prevalence of glass particles on the headwear and head hair of two different population groups; the general public who do not work with glass, and glaziers from O'Brien(®) Glass Industries who work with glass and have regular contact with broken glass. The 232 samples collected from the head hair and headwear from the random population resulted in the recovery of 6 glass fragments in total on 6 individuals (i.e. one fragment each). All of these fragments were from head hair samples with no multiple fragments recovered. The two headwear samples that were taken revealed no fragments. These results were in contrast to the survey that was conducted on the head hair and headwear of 25 glaziers from O'Brien(®), in which 138 glass fragments were found in total on 24 of the 25 glaziers. The size and number of fragments found in each sample were also generally larger for the glaziers group. The results from this study indicate that the prevalence of glass on the head hair and head wear of the random population is very low in comparison to the head hair and headwear of those who have regular contact with breaking glass. The significance of this finding with respect to the interpretation of glass evidence is also discussed.