One possible solution of combating issues posed by climate change is the use of the High Temperature (HT) Polymer Electrolyte Membrane (PEM) Fuel Cell (FC) in some applications. The typical HT-PEMFC operating temperatures are in the range of 100e200 o C which allows for co-generation of heat and power, high tolerance to fuel impurities and simpler system design. This paper reviews the current literature concerning the HT-PEMFC, ranging from cell materials to stack and stack testing. Only acid doped PBI membranes meet the US DOE (Department of Energy) targets for high temperature membranes operating under no humidification on both anode and cathode sides (barring the durability). This eliminates the stringent requirement for humidity however, they have many potential drawbacks including increased degradation, leaching of acid and incompatibility with current state-of-the-art fuel cell materials. In this type of fuel cell, the choice of membrane material determines the other fuel cell component material composition, for example when using an acid doped system, the flow field plate material must be carefully selected to take into account the advanced degradation. Novel research is required in all aspects of the fuel cell components in order to ensure that they meet stringent durability requirements for mobile applications.

Circularly polarized luminescence (CPL) is the emission analogue of circular dichroism (CD). While CD spectroscopy has been widely used to investigate the configurational as well as conformational changes in biological systems, CPL also has great, albeit currently under-developed, potential due to the general sensitivity of luminescence measurements combined with the high specificity of the signal for the chiral environment. 1 Lanthanide luminescence (especially Eu(III) and Tb(III)) with its advantageous characteristics (large Stokes shift, long lifetimes, narrow emission bands) is an ideal candidate for the development of chiral CPL probes. 2 We have earlier reported the 2-hydroxyisophthalamide (IAM) motif as a highly efficient sensitizer for the luminescence of four different Ln(III) cations (Sm, Eu, Tb, Dy). 3 In an extension of this work, enantiopure versions were recently successfully developed for use as CPL probes. 4 While these species retain the excellent brightness of their nonchiral analogues, the insolubility in physiologically relevant media remains a limitation for analytical applications. In order to address this problem, enantiopure, octadentate ligands with decreased hydrophobicity have now been developed. As an additional feature of this new approach, the stereogenic centers are introduced in the ligand backbone instead of incorporating them into the sensitizer units, thus separating the chiral information from the chromophore and allowing for a much more generally applicable, modular synthesis of chiral ligands for CPL applications. 1-Hydroxy-2-pyridinone (1,2-HOPO), which has recently proven to be a good sensitizer for Eu(III) luminescence, 5 and IAM (for Tb(III)) were chosen as model chromophores ( Figure 1).The chiral information in H 4 1 (the first chiral ligand with the 1,2-HOPO motif) and H 4 2 is easily accessible from either enantiopure amino acids or by resolution of chiral diamines. In the case of H 4 1, the four stereogenic centers are located in the tetrapodal arms, whereas H 4 2 displays vicinal stereocenters in the central portion of the oligoamine backbone. The synthesis of the ligands is outlined in Scheme 1. 6 The hexamine backbone of H 4 1 was prepared by selective ring opening of enantiopure (R)-2-ethyl-Ntosylaziridine 7 with ethylene diamine, followed by deprotection of the tosyl groups, and ion exchange chromatography in analogy to previous reports. 8 Similarly, the backbone of H 4 2 was prepared from enantiopure (R,R)-1,2-diaminocyclohexane 9 and N-tosylaziridine. 10 The optical purity of both hexamines was confirmed by 1 H NMR spectroscopy after in situ transformation to the corresponding tetrakis(urea) derivatives with commercially available, enantiopure (R)-1-phenylethylisocyanate (Sigma-Aldrich, >98% ee). In each case, only one set of signals was observed with all four arms being equivalent on the NMR time scale, consistent with complete regioand diastereoselectivity of the aziridine ring-opening reaction.Coupling of the two backbones to protected, activated carboxy...

The regio- and chemoselective oxidation of unprotected vicinal polyols with [(neocuproine)Pd(OAc)]2(OTf)2 (1) (neocuproine = 2,9-dimethyl-1,10-phenanthroline) occurs readily under mild reaction conditions to generate α-hydroxy ketones. The oxidation of vicinal diols is both faster and more selective than the oxidation of primary and secondary alcohols; vicinal 1,2-diols are oxidized selectively to hydroxy ketones, whereas primary alcohols are oxidized in preference to secondary alcohols. Oxidative lactonization of 1,5-diols yields cyclic lactones. Catalyst loadings as low as 0.12 mol % in oxidation reactions on a 10 g scale can be used. The exquisite selectivity of this catalyst system is evident in the chemoselective and stereospecific oxidation of the polyol (S,S)-1,2,3,4-tetrahydroxybutane [(S,S)-threitol] to (S)-erythrulose. Mechanistic, kinetic, and theoretical studies revealed that the rate laws for the oxidation of primary and secondary alcohols differ from those of diols. Density functional theory calculations support the conclusion that β-hydride elimination to give hydroxy ketones is product-determining for the oxidation of vicinal diols, whereas for primary and secondary alcohols, pre-equilibria favoring primary alkoxides are product-determining. In situ desorption electrospray ionization mass spectrometry (DESI-MS) revealed several key intermediates in the proposed catalytic cycle.

Recently developed and applied ionization techniques have brought mass spectrometry to bear on previously inaccessible chemistry. We offer our perspective on this field and its application for studying reaction mechanisms.