Mini-gaps and novel giant negative magnetoresistance in InAs/GaSb semimetallic superlattices

We have studied the temperature dependence of the magnetoresistance of semimetallic InAs/GaSb structures with magnetic field applied parallel to the layers. We present the first unambiguous evidence for the presence of a mini-gap at the crossing point between the electron and hole dispersion relations. The resistivity is found to change from semiconductor-like behaviour with a strong temperature dependence at low parallel magnetic fields to that of a semimetal with a weak temperature dependence at high field. Furthermore, the magnetoresistance, for intrinsic samples, is found to decrease with field by as much as 70% at low temperatures. As the parallel magnetic field is increased the centres of the electron and hole dispersions are shifted apart in k-space and at sufficiently high field the mini-gap is destroyed and the bands overlap fully. Finally, a theoretical model allows us to estimate that the mini-gap is of order 7 meV.     

A Stable Carbene Phosphenic Chloride Complex: First Structural Characterization of a PO2Cl Base Adduct [1]

The phosphenic chloride adduct Im—PO₂Cl ( 4 , Im = 2, 3‐dihydro‐1, 3‐diisopropyl‐4, 5‐dimethylimidazol‐2‐ylidene) was prepared by partial hydrolysis of [Im—POCl₂]Cl ( 5 ) and characterized by X‐ray structure analysis.     

Hydrophobic Derivatization of <Emphasis Type="Italic">N</Emphasis>-linked Glycans for Increased Ion Abundance in Electrospray Ionization Mass Spectrometry

A library of neutral, hydrophobic reagents was synthesized for use as derivatizing agents in order to increase the ion abundance of N-linked glycans in electrospray ionization mass spectrometry (ESI MS). The glycans are derivatized via hydrazone formation and are shown to increase the ion abundance of a glycan standard more than 4-fold. Additionally, the data show that the systematic addition of hydrophobic surface area to the reagent increases the glycan ion abundance, a property that can be further exploited in the analysis of glycans. The results of this study will direct the future synthesis of hydrophobic reagents for glycan analysis using the correlation between hydrophobicity and theoretical non-polar surface area calculation to facilitate the development of an optimum tag for glycan derivatization. The compatibility and advantages of this method are demonstrated by cleaving and derivatizing N-linked glycans from human plasma proteins. The ESI-MS signal for the tagged glycans are shown to be significantly more abundant, and the detection of negatively charged sialylated glycans is enhanced.     

Spectral Accuracy and Sulfur Counting Capabilities of the LTQ-FT-ICR and the LTQ-Orbitrap XL for Small Molecule Analysis

Color Index Disperse Yellow 42 (DY42), a high-volume disperse dye for polyester, was used to compare the capabilities of the LTQ-Orbitrap XL and the LTQ-FT-ICR with respect to mass measurement accuracy (MMA), spectral accuracy, and sulfur counting. The results of this research will be used in the construction of a dye database for forensic purposes; the additional spectral information will increase the confidence in the identification of unknown dyes found in fibers at crime scenes. Initial LTQ-Orbitrap XL data showed MMAs greater than 3 ppm and poor spectral accuracy. Modification of several Orbitrap installation parameters (e.g., deflector voltage) resulted in a significant improvement of the data. The LTQ-FT-ICR and LTQ-Orbitrap XL (after installation parameters were modified) exhibited MMA ≤ 3 ppm, good spectral accuracy (χ² values for the isotopic distribution ≤ 2), and were correctly able to ascertain the number of sulfur atoms in the compound at all resolving powers investigated for AGC targets of 5.00 × 10⁵ and 1.00 × 10⁶.     

Thymidine analogues for tracking DNA synthesis

Replicating cells undergo DNA synthesis in the highly regulated, S-phase of the cell cycle. Analogues of the pyrimidine deoxynucleoside thymidine may be inserted into replicating DNA, effectively tagging dividing cells allowing their characterisation. Tritiated thymidine, targeted using autoradiography was technically demanding and superseded by 5-bromo-2-deoxyuridine (BrdU) and related halogenated analogues, detected using antibodies. Their detection required the denaturation of DNA, often constraining the outcome of investigations. Despite these limitations BrdU alone has been used to target newly synthesised DNA in over 20,000 reviewed biomedical studies. A recent breakthrough in "tagging DNA synthesis" is the thymidine analogue 5-ethynyl-2'-deoxyuridine (EdU). The alkyne group in EdU is readily detected using a fluorescent azide probe and copper catalysis using 'Huisgen's reaction' (1,3-dipolar cycloaddition or 'click chemistry'). This rapid, two-step biolabelling approach allows the tagging and imaging of DNA within cells whilst preserving the structural and molecular integrity of the cells. The bio-orthogonal detection of EdU allows its application in more experimental assays than previously possible with other "unnatural bases". These include physiological, anatomical and molecular biological experimentation in multiple fields including, stem cell research, cancer biology, and parasitology. The full potential of EdU and related molecules in biomedical research remains to be explored.     

Primer preactivation of peptidoglycan polymerases

Peptidoglycan glycosyltransferases are highly conserved bacterial enzymes that catalyze glycan strand polymerization to build the cell wall. Because the cell wall is essential for bacterial cell survival, these glycosyltransferases are potential antibiotic targets, but a detailed understanding of their mechanisms is lacking. Here we show that a synthetic peptidoglycan fragment that mimics the elongating polymer chain activates peptidoglycan glycosyltransferases by bypassing the rate-limiting initiation step.     

Methemoglobinemia caused by 8-aminoquinoline drugs: DFT calculations suggest an analogy to H4B's role in nitric oxide synthase

We suggest a possible mechanism of how 8-aminoquinolines (8-AQ's) cause hemotoxicity by oxidizing hemoglobin to methemoglobin. In our DFT calculations, we found that 5-hydroxyprimaquine is able to donate an electron to O(2) to facilitate its conversion to H(2)O(2). Meanwhile, Fe(II) is oxidized to Fe(III) and methemoglobin is formed. In this mechanism, the 8-AQ drug plays a similar role as that of H(4)B in nitric oxide synthase. Furthermore, our study offers an approach to inform the design of less toxic antimalarial drugs.     

The effect of H2 partial pressure on the reaction progression and reversibility of lithium-containing multicomponent destabilized hydrogen storage systems

It is known that the reaction path for the decomposition of LiBH(4):MgH(2) systems is dependent on whether decomposition is performed under vacuum or under a hydrogen pressure (typically 1-5 bar). However, the sensitivity of this multicomponent hydride system to partial pressures of H(2) has not been investigated previously. A combination of in situ powder neutron and X-ray diffraction (deuterides were used for the neutron experiments) have shed light on the effect of low partial pressures of hydrogen on the decomposition of these materials. Different partial pressures have been achieved through the use of different vacuum systems. It was found that all the samples decomposed to form Li-Mg alloys regardless of the vacuum system used or sample stoichiometry of the multicomponent system. However, upon cooling the reaction products, the alloys showed phase instability in all but the highest efficiency pumps (i.e., lowest base pressures), with the alloys reacting to form LiH and Mg. This work has significant impact on the investigation of Li-containing multicomponent systems and the reproducibility of results if different dynamic vacuum conditions are used, as this affects the apparent amount of hydrogen evolved (as determined by ex situ experiments). These results have also helped to explain differences in the reported reversibility of the systems, with Li-rich samples forming a passivating hydride layer, hindering further hydrogenation.