Synthesis of O-glycolyl-linked neuraminic acids through a spirocyclic intermediate

[reaction: see text] The neuraminic acid derivative 5 is readily converted in several steps to the neuraminic acid dimer 12, linked through the hydroxyl of a 5-N-glycolyl group in an alpha-2,5 glycosidic linkage. The sequence is shown to proceed through a spirocyclic intermediate 9 by in situ NMR experiments. Similar derivatives of N-glycolylneuraminic acid (Neu5Gc), including polymers, have been identified from marine sources, including starfish and sea urchins, often as sulfated derivatives and are thought to mediate sperm-egg recognition.     

Electron-impact promoted fragmentation of some substituted isoxazolidines

A series of substituted isoxazolidinylacetophenones (II to VI) have been shown to fragment subsequent to electron-impact in a generally predictable fashion. One characteristic fragmentation of all the compounds investigated was the loss of H₂O₂ from their respective molecular ions.     

Beyond the T1 limit: singlet nuclear spin states in low magnetic fields

Low-field nuclear spin singlet states may be used to store nuclear spin order in a room temperature liquid for a time much longer than the spin-lattice relaxation time constant T1. The low-field nuclear spin singlets are unaffected by intramolecular dipole-dipole relaxation, which is generally the predominant relaxation mechanism. We demonstrate storage of nuclear spin order for more than 10 times longer than the measured value of T1. This phenomenon may facilitate the development of nuclear spin hyperpolarization methods and may allow the study of motional processes which occur too slowly for existing NMR techniques. This is the first time that the memory of nuclear spins has been extended well beyond the T1 limit in a system lacking intrinsic magnetic equivalence.     

Linking NMR pulse sequences: derivative relation between the responses of two pulse sequences

Examples are shown of how the derivative of the response of an NMR pulse sequence with respect to a variable in that pulse sequence can be obtained by another pulse sequence. This approach holds the potential of being a tool for discovery of new pulse sequences or a means of understanding how some pulse sequences are related to each other.     

IUCLID: an information management tool for existing chemicals and biocides

Because of the large number of chemicals to be risk assessed within the European Union, an electronic data reporting and management tool, IUCLID, was developed supporting all three steps of the risk assessment process, namely data collection, priority-setting, and risk assessment. This paper gives an overview of the IUCLID software, which has been updated and adapted to also be used for the notification phase of the Biocides Program of the European Commission.     

Partial Theta Functions. I. Beyond the Lost Notebook

It is shown how many of the partial theta function identitiesin Ramanujan's lost notebook can be generalized to infinitefamilies of such identities. Key in our construction is theBailey lemma and a new generalization of the Jacobi triple productidentity. By computing residues around the poles of our identitieswe find a surprising connection between partial theta functionidentities and Garrett–Ismail–Stanton-type extensionsof multisum Rogers–Ramanujan identities. 2000 MathematicsSubject Classification 05A30, 33D15, 33D90.     

p-Frames in Separable Banach Spaces

Let X be a separable Banach space with dual X ^*. A countable family of elements {g _i }X ^* is a p-frame (1 p ) if the norm _X is equivalent to the ^p -norm of the sequence {g _i ()}. Without further assumptions, we prove that a p-frame allows every gX ^* to be represented as an unconditionally convergent series g=d _i g _i for coefficients {d _i } ^q , where 1/p+1/q=1. A p-frame {g _i } is not necessarily linear independent, so {g _i } is some kind of overcomplete basis for X ^*. We prove that a q-Riesz basis for X ^* is a p-frame for X and that the associated coefficient functionals {f _i } constitutes a p-Riesz basis allowing us to expand every fX (respectively gX ^*) as f=g _i (f)f _i (respectively g=g(f _i )g _i ). In the general case of a p-frame such expansions are only possible under extra assumptions.     

Quasiparticle lifetimes in the Anderson model

Quasiparticles identified with the maxima in the local density of states for the Anderson model are shown to have a relatively long lifetime. This explains why particular configurations of the impurity orbital can be independently detected in the experiment.