Tandem mass spectrometry of deprotonated iodothyronines

In order to assist with the development of more selective and sensitive methods for thyroid hormone analysis the [M-H]- anions of the iodothyronines T4, T3, rT3, (3,5)-T2 and the non-iodinated thyronine (T0) have been generated by negative ion electrospray mass spectrometry. Tandem mass spectra of these ions were recorded on a triple-quadrupole mass spectrometer and show a strong analogy with the fragmentation pathways of the parent compound, tyrosine. All iodothyronines also show significant abundances of the iodide anion in their tandem mass spectra, which represents an attractive target for multiple reaction monitoring (MRM) analysis, given that iodothyronines are the only iodine bearing endogenous molecules. Characteristic fragments are observed at m/z 359.7 and 604.5 for rT3 but are absent in the spectrum of T3, thus differentiating the two positional isomers. The striking difference in the fragmentation patterns of these regioisomeric species is attributed to the increased acidity of the phenol moiety in rT3 compared with T3.     

Substituent effects on thermal decolorization rates of bisbenzospiropyrans

[reaction: see text] A novel application of photochromic molecules is to mimic physiological oscillatory calcium signals by reversibly binding and releasing calcium ions in response to light. Substituent changes on the largely unexplored photochromic bisbenzospiropyran scaffold led to significant changes in thermal fading rates in several organic solvents. Excellent correlations have been found between fading rates and empirical Hammett constants as well as calculated ground-state energies. These correlations can be used to improve scaffold design.     

Evaluation of models for the low temperature combustion of alkanes through interpretation of pressure-temperature ignition diagrams

The purpose of this paper is to show the application of global uncertainty analysis to comprehensive and reduced kinetic models as a tool to identify important thermochemical and reaction rate parameters as determinants of the conditions leading to autoignition. Propane oxidation is taken as the test case. The simulation of experimental investigations of the cool flames and two-stage ignitions, via the pressure-temperature ignition diagram, show that existing kinetic models for the low temperature combustion of propane at sub-atmospheric pressures reflect a greater reactivity than seems to be appropriate. That is, the models lead to a prediction of two-stage ignition at pressures somewhat lower and with ignition delays shorter than is found experimentally. The inconsistency between experiment and numerical simulation seems not to be an inherent problem of the qualitative structure of the models, but may derive from uncertainties in the parameters within the mechanism. By use of "brute force", Morris-one-at-a-time and Monte-Carlo simulations, we show that uncertainties in only a small number of parameters, and falling well within the errors that may reasonably be assigned, can shift the response appropriately. Moreover, it appears that in the low temperature combustion regime, thermochemistry is at least as, if not more, important than the reaction rates, yet usually receives less attention within sensitivity studies. In the present case, the main factors controlling the temperature reached in the first stage of two-stage ignition and the time to ignition appear to be connected with the thermochemistry of three specific hydroperoxyalkyl radicals and their derivatives. Other factors, such as heat and mass transport are also addressed, and their effects are mitigated to some extent by evaluation of initial and revised models against experimental data for ignition delay obtained under microgravity. The results highlight more general issues that pertain to the numerical simulation of the combustion of higher hydrocarbons and contribute to the development of the protocol necessary for testing kinetic models before they are ready for use in a predictive capacity.     

Observation of a centrality-dependent dijet asymmetry in lead-lead collisions at sqrt[S(NN)] =2.76 TeV with the ATLAS detector at the LHC

By using the ATLAS detector, observations have been made of a centrality-dependent dijet asymmetry in the collisions of lead ions at the Large Hadron Collider. In a sample of lead-lead events with a per-nucleon center of mass energy of 2.76 TeV, selected with a minimum bias trigger, jets are reconstructed in fine-grained, longitudinally segmented electromagnetic and hadronic calorimeters. The transverse energies of dijets in opposite hemispheres are observed to become systematically more unbalanced with increasing event centrality leading to a large number of events which contain highly asymmetric dijets. This is the first observation of an enhancement of events with such large dijet asymmetries, not observed in proton-proton collisions, which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium.     

Characterising ontogenetic niche shifts in Nile crocodile using stable isotope (δ13C, δ15N) analyses of scute keratin

Nile crocodiles undergo a three to five order of magnitude increase in body size during their lifespan. This shift coincides with a change in resource and habitat use which influences the strength, type and symmetry of interactions with other species. Identifying size-specific crocodile groups displaying similar traits is important for conservation planning. Here, we illustrate how stable carbon (δ¹³ C) and nitrogen (δ¹⁵ N) isotope analysis of scute keratin, together with breakpoint modelling analysis can be used to characterise ontogenetic niche shifts. Using a sample set of 238 crocodiles from the Okavango Delta, Botswana (35–463 cm total length), we found prominent size-related changes in the scute keratin δ¹³ C and δ¹⁵ N profiles close to 40 and 119 cm snout-vent length. The first shift corroborated the findings of a traditional stomach-content study conducted on the same population at the same time, and the second conformed to known crocodile ecology. This approach can be used as a first approximation to identify size-specific groups within crocodile populations, and these can then be investigated further using isotopic or other methods.     

Integrating Algebra and Proof in High School: Students' Work with Multiple Variables and a Single Parameter in a Proof Context

In the United States, researchers argue that proof is largely concentrated in the domain of high school geometry, thus providing students a distorted image of what proof entails, which is at odds with the central role that proof plays in mathematics. Despite the centrality of proof, there is a lack of studies addressing how to integrate proof into other mathematical domains. In this article, we discuss a teaching experiment designed to integrate algebra and proof in the high school curriculum. Algebraic proof was envisioned as the vehicle that would provide high school students the opportunity to learn not only about proof in a context other than geometry but also about aspects of algebra. Results from the experiment indicate that students meaningfully learned about aspects of both algebra and proof in that they produced algebraic proofs involving multiple variables and a single parameter, based on conjectures they themselves generated.     

THE IMPACT OF THE NATIONAL NUMERACY STRATEGY IN YEAR 4 (II): TEACHING

The Nuffield Year 4 project set out to examine selected aspects of the impact of the National Numeracy Strategy (NNS) in primary schools by using comparable data on Year 4 pupil attainment and teaching collected in 1997/98 and 2001/02, two years before and two years after the introduction of the Numeracy Strategy. In this second paper we address the following questions:

• How and to what extent has numeracy teaching in Year 4 changed?

• Why have these changes occurred?

• How can we improve future implementation of reforms?

• How can we inform continuing professional development?

     

N-Heterocyclic carbene catalysed redox isomerisation of esters to functionalised benzaldehydes

N-Heterocyclic carbene catalysed redox isomerisation with reduction about the carbonyl has been developed in the transformation of trienyl esters to tetrasubstituted benzaldehydes. The reaction proceeds in good to excellent yield, and in cases that provide 2,2′-biaryls, enantioselectivity is observed. Mechanistic studies demonstrate the intermediacy of a cyclohexenyl β-lactone, while implicating formation of the homoenolate as turnover limiting.