A "traceless" Staudinger ligation for the chemoselective synthesis of amide bonds

[reaction: see text] Here we report a novel modification of our previously reported "Staudinger ligation" that generates an amide bond from an azide and a specifically functionalized phosphine. This method for the selective formation of an amide bond, which does not require the orthogonal protection of distal functional groups, should find general utility in synthetic and biological chemistry.     

Investigating cellular metabolism of synthetic azidosugars with the Staudinger ligation

The structure of sialic acid on living cells can be modulated by metabolism of unnatural biosynthetic precursors. Here we investigate the conversion of a panel of azide-functionalized mannosamine and glucosamine derivatives into cell-surface sialosides. A key tool in this study is the Staudinger ligation, a highly selective reaction between modified triarylphosphines and azides that produces an amide-linked product. A preliminary study of the mechanism of this reaction, and refined conditions for its in vivo execution, are reported. The reaction provided a means to label the glycoconjugate-bound azidosugars with biochemical probes. Finally, we demonstrate that the cell-surface Staudinger ligation is compatible with hydrazone formation from metabolically introduced ketones. These two strategies provide a means to selectively modify cell-surface glycans with exogenous probes.     

The reaction π−p → K0Σ0 up to 2375 MeV/c

Differential cross-section and polarization measurements for the reaction π^?p → K⁰Σ⁰ are presented from 1395 to 2375 MeV/c incident beam momentum. The polarization data from an earlier experiment, from thershold to 1334 MeV/c, have been re-analysed by an improved method leading to a substantial reduction in the errors.     

Three-space weak barrelledness

Our simple and comprehensive framework consists of the fourteen locally convex space properties that underlie “reinventing weak barrelledness.” Choosing a,b,c from these properties, we determine the truth or falsity of each of the 14³=2744 statements of the form: If the closed subspace F has property a and E/F has property b, then E necessarily has property c. For all 14²=196 choices of a,b a necessary condition on c in order that the statement be true is that ac and bc, and for a majority (100) of these choices the condition is also sufficient. If property a=b=c verifies the statement, it is a three-space property. Exactly seven of the fourteen qualify: the six previously known and Ruess' property (L). Efficiency in solving (the previously unsolved eight of) these fourteen classic three-space problems is the key to finding all 2744 results, an efficiency defined and fostered by the framework.     

Spin-rotation measurements in π−p → K0Λ

The first measurements of spin-rotation in meson-baryon scattering in the resonance region are presented. These measurements, for the reaction π^?p → K⁰Λ, confirm the main predictions of a previous partial-wave analysis. Comments are made on resonant couplings in the reaction π^?p → K⁰Λ.     

Spin-rotation formalism for Meson-Baryon scattering

A spin-rotation formalism is developed for the extraction of physical quantities from the reaction π^- p↑→K°Λ, using the Λ-decay as polarisation analyser. The method described here uses the parameters polarisation,P, and spin-rotation angle, β. Effects due to apparatus acceptance are explicitly included. The method has advantages in minimising the sensitivity to various systematic errors.     

Barrelled Countable Enlargements and the Bounding Cardinal

Replacing c with the bounding cardinal improves two standardBCE results of Robertson, Tweddle and Yeomans, and is optimalfor the BCE codimension/inheritance result of Bonet and PérezCarreras. Indeed, is the smallest infinite-dimensionality formetrizable barrelled spaces, and is the largest cardinal suchthat every subspace of codimension less than in a metrizablebarrelled space is itself barrelled. We thus reconfirm as oneof two ‘optimal cardinals for metrizable barrelled spaces’.Esthetically pleasing, these properties of immediately solvethe normable BCE problem without extra-ZFC axiomatic assumptions,reduce the separable quotient problem to Banach spaces E with density character of E c, and are part of the solution toone version of the metrizable BCE problem found in our sequel,devoted to the other ‘optimal cardinal’.     

Optimal Cardinals for Metrizable Barrelled Spaces

We seek the smallest or largest cardinals for which certainbasic results hold, as did Mazur when he proved that c is thesmallest infinite-dimensionality for a Fréchet space.As with Mazur, we make no axiomatic assumptions outside theusual ZFC model. We discover three instances in which the optimalcardinal is the dominating number and three in which it isthe bounding number b, apparently giving the first locally convexspace characterizations of these venerable and easily describedcardinals. Here are two samples: it is known that for any non-normablemetrizable locally convex space E, the minimal size _b(E) fora fundamental system of bounded sets must satisfy _{1 b}(E) c;we prove that _b(E) = . Again, it is known that if E is a non-normablemetrizable barrelled space of minimal dimension, then ₁ dim(E) c; we prove that dim(E) = b. The most important individualresult is the reconstruction of Tweddle's space without useof the Continuum Hypothesis (₁ = c). The reconstruction is vitalin the characterizations of b and in subsequent papers answeringopen questions about countable enlargements.     

Structure functions at HERA

HERA provides the key facility for the measurement of proton structure functions. Formalism and methods are outlined for the measurement and interpretation of inclusive structure functions, including the use of polarised e ^± beams. The measurement of charm, beauty and photon structure functions is discussed, together with special runs at low proton energy for measurement of the longitudinal structure function. Finally, the functions accessed using polarised beams on polarised targets are indicated.