Teaching the substitutive conception of the equals sign

A cumulative body of research has shown that children typically shift from an operational to a relational conception of the equals sign as they move through schooling. Jones (2008) argued that a truly relational conception of the equals sign comprises a substitutive component and a sameness component. Here we present two studies that build on this argument. The first investigated how the equals sign is typically presented to primary children in England, and we report that in the main an operational conception seems to be promoted. The second study measured the impact of a specially designed intervention on early secondary children's conceptions of the equals sign. Pre- and post-test data revealed that the intervention promoted substitutive and sameness components of symbolic equivalence. We consider the theoretical and pedagogical implications of the results.     

Synthesis and functionalization of 3-alkylidene-1,2-diazetidines using transition metal catalysis

An efficient two-step synthesis of a wide range of 3-methylene-1,2-diazetidines has been developed through application of a Cu(I)-catalyzed 4-exo ring closure. The double bond of this new class of strained heterocycle can be functionalized in a stereocontrolled manner by using palladium-catalyzed Heck reactions. Moreover, chemoselective reduction of 3-alkylidene-1,2-diazetidines gives access to saturated 1,2-diazetidines and vicinal diamines.     

Microfluidic device for label-free measurement of platelet activation

In this work we demonstrate a new microfluidic method for the rapid assessment of platelet size and morphology in whole blood. The device continuously fractionates particles according to size by displacing them perpendicularly to the fluid flow direction in a micro-fabricated post array. Whole blood, labeled with the fluorescent, platelet specific, antibody PE-anti-CD41, was run through the device and the positions of fluorescent objects noted as they exited the array. From this, histograms of platelet size were created which show marked increases in size after exposure to thrombin or a temperature of 4 degrees C. We infer that the well known morphological changes that occur during activation are causing the observed increase in size.     

Twisted molecular magnets

The use of derivatised salicylaldoximes in manganese chemistry has led to the synthesis of a family of approximately fifty hexanuclear ([Mn(III)(6)]) and thirty trinuclear ([Mn(III)(3)]) Single-Molecule Magnets (SMMs). Deliberate, targeted structural distortion of the metallic core afforded family members with increasingly puckered configurations, leading to a switch in the pairwise magnetic exchange from antiferromagnetic to ferromagnetic. Examination of both the structural and magnetic data revealed a semi-quantitative magneto-structural correlation, from which the factors governing the magnetic properties could be extracted and used for predicting the properties of new family members and even more complicated structures containing analogous building blocks. Herein we describe an overview of this extensive body of work and discuss its potential impact on similar systems.     

Ultra-fast tandem mass spectrometry scanning combined with monolithic column liquid chromatography increases throughput in proteomic analysis

Liquid chromatography combined with electrospray ionization mass spectrometry (LC/ESI-MS) has been used successfully for the characterization of biomolecules in proteomics in the last few years. This methodology relied largely on the use of reversed-phase chromatography, in particular C18-based resins, which are suitable for separation of peptides. Here we show that polymeric [polystyrene divinylbenzene] monolithic columns can be used to separate peptide mixtures faster and at a higher resolution. For 500 fmol bovine serum albumin, up to 68% sequence coverage and Mascot Mowse scores of >2000 were obtained using a 9 min gradient on a monolithic column coupled to an ion trap mass spectrometer with ultra-fast MS/MS scan rates. In order to achieve similar results using C18 columns, it was necessary to extend gradient times to 30 min. In addition, we demonstrate the utility of this approach for the analysis of whole Escherichia coli cell lysates by one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (1D-SDS-PAGE) in combination with LC/MS/MS using 4 min gradients on monolithic columns. Our results indicate higher throughput capabilities of monolithic columns (3-fold gain in time or more) for conventional proteomics applications, such as protein identification and high sequence coverage usually required for detection of post-translational modifications (PTMs). Further optimization of sensitivity and quality of sequence information is discussed, in particular when combined with mass spectrometers that have very fast MS-MS/MS switching and scanning capabilities.     

Analysis of sub-picogram quantities of 238Pu by thermal ionization mass spectrometry

Journal of Radioanalytical and Nuclear Chemistry - A multiple ion-counting total evaporation technique has been developed for precise analysis of sub-picogram (pg) quantities of 238Pu by thermal...     

Applications of type I antifreeze proteins: studies with model membranes & cryoprotectant properties

Antifreeze proteins (AFPs) and antifreeze glycoproteins (AFGPs), found in the body fluids of many species of polar fish allow them to survive in waters colder than the equilibrium freezing point of their blood and other internal fluids. Despite their structural diversity, all AF(G)Ps kinetically depress the temperature at which ice grows in a non-colligative manner and hence exhibit thermal hysteresis. AF(G)Ps also share the ability to interact with and protect mammalian cells and tissues from hypothermic damage (e.g., improved storage of human blood platelets at low temperatures), and are able to stabilize or disrupt membrane composition during low temperature and freezing stress (e.g., cryoprotectant properties in stabilization of sperm and oocytes). This review will summarize studies of AFPs with phospholipids and plant lipids, proposed mechanisms for inhibition of leakage from membranes, and cryoprotectant studies with biological samples. The major focus will be on the alpha-helical type I antifreeze proteins, and synthetic mutants, that have been most widely studied. For completeness, data on glycoproteins will also be presented. While a number of models to explain stabilization and destabilization of different lipid systems have been proposed, it is currently not possible to predict whether a particular AFP will stabilize or destabilize a given lipid system. Furthermore the relationship between the antifreeze property of thermal hysteresis and membrane stabilization is unknown. This lack of detailed knowledge about how AFPs function in the presence of different types of materials has hampered progress toward the development of antifreezes for cold storage of cells, tissues, and organs.     

Ultra Rapid Approaches to Mild Macromolecular Conjugation

In light of the increasing demand for ultra rapid and mild conjugation chemistries for use in macromolecular chemistry, the present Feature Article provides a critical overview of the very latest developments in this field. The principal aim, therefore, is the provision of a quick selection guide to aid in the formulation of a design strategy for novel functional materials and to provide recommendations for future developments in the chemistries discussed.