Degree one maps between hyperbolic small 3-manifolds

We construct the first examples of degree one maps between non-homeomorphic closed hyperbolic small 3-manifolds.

     

Gas‐Phase Interactions between Lead(II) Ions and Cytosine: Tandem Mass Spectrometry and Infrared Multiple‐Photon Dissociation Spectroscopy Study

Gas‐phase interactions between Pb²⁺ ions and cytosine (C) were studied by combining tandem mass spectrometry, infrared multiple photon dissociation spectroscopy, and density functional theory (DFT) calculations. Both singly and doubly charged complexes were generated by electrospray. The [Pb(C)?H]⁺ complex was extensively studied, and this study shows that two structures, involving the interaction of the metal with the deprotonated canonical keto‐amino tautomer of cytosine, are generated in the gas phase; the prominent structure is the bidentate form involving both the N1 and O2 electronegative centers. The DFT study also points out a significant charge transfer from the nucleobase to the low‐lying p orbitals of the metal and a strong polarization of the base upon complexation. The various potential energy surfaces explored to account for the fragmentation observed are consistent with the high abundance of the [PbNH₂]⁺ fragment ion.     

Synthesis and anionic ring-opening polymerization of crown-ether-like macrocyclic dilactones: An alternative route to PEG-containing polyesters and related networks

Linear aliphatic polyesters whose structure is made of short polyethylene glycol (PEG) segments connected along the chain by malonate units were synthesized from two PEG-containing macrolactones: 15,15-dimethyl-1,4,7,10,13-pentaoxacyclohexadecane-14,16-dione (1) and 5,8,11,14,17-pentaoxaspiro[2,15]octadecane-4,18-dione (2). Anionic ring-opening polymerization conditions using either thiophenolates or a p-nitrophenolate as initiators yielded poly(ether-ester)s of low to moderate molecular weights, with broad molecular weight distributions. When the monomer also contains an activated cyclopropane unit of the cyclopropane-1,1-dicarboxylate type (such as in 2) and harsher polymerization conditions are used (higher temperatures and bulkier counterions), opening of the cyclopropyl ring can compete with the dilactone polymerization, providing access to crosslinked materials.     

Particle Sizing by Photon Correlation Spectroscopy. Part IV: Resolution of bimodals and comparison with other particle sizing methods

The practical performances of single and multi-angle photon correlation spectroscopy (PCS) for resolving bimodal distributions of industrial poly (methyl methacrylate) samples was investigated in a comparative study by several users affiliated to academic and industrial groups and by two suppliers of commercial equipment. The results for the harmonic intensity averaged diameters obtained by cumulants analysis reported by the different laboratories are in agreement, in addition to the results for the normalized second cumulants. The uncertainty on the latter quantities is large, however. For the bimodal samples with two populations with average diameters in a ratio of about 2.5 : 1, not all users were able to resolve the distribution in its components by single-angle PCS. Some slight improvement was obtained by multi-angle PCS. Other indirect techniques (polarization intensity differential scattering, static light scattering data and disc photosedimentometer) appeared to be superior for resolving the bimodal distributions.     

Conductance of some tetraphenylborides with cryptates as counter-ions in tetrahydrofuran

The conductance behavior of potassium tetraphenylboride and of sodium and potassium tetraphenylborides complexed by macroheterobicycles was studied in tetrahydrofuran over a temperature range of ?70 to +20°C. Stokes' radii of potassium and of alkaline cryptates were compared with ionic radii. The conductance data were analyzed by a more careful method than that usually used for this solvent. This leads to an interpretation of the physical meaning of the distance parameter in agreement with Bjerrum's concept for the distinction between short- and long-range electrostatic interactions.     

Phase transfer catalysis in the chemical modification of polymers. Part II

A soluble partly chloromethylated polystyrene has been successfully modified by compounds containing labile hydrogen and by NaCN or NaSCN, under PTC conditions.     

Assignment strategy for proteins with known structure

In protein NMR the assignment of nuclear spin resonances is a prerequisite for all subsequent applications, such as studies of ligand binding, protein-DNA interactions, and dynamics. Resonance assignment is a time consuming step even when the 3D x-ray structure of the protein is available. A new strategy is presented to solve the "inverse" assignment problem, which is the determination of the NMR resonance assignment from a known 3D protein structure. The protocol employs NMR data in the form of residual dipolar couplings and chemical shifts, while it does not require any sequential NMR connectivity information. The assignment problem is mathematically formulated in terms of a weighted matching problem that can be computationally efficiently solved by a combinatorial optimization algorithm. The protocol is applied to ubiquitin using two or three residual dipolar couplings per amino acid measured in Pfl phage medium together with chemical shift information. The algorithm yields for more than 90% of the protein backbone resonances the correct assignment.     

Synthése totale d'α-disaccharidyles de tridésoxy-2,5,6-streptamine apparentés aux aminosides à partir du maltose et du lactose

Total synthesis of α-disaccharidyl-2,5,6-trideoxy-streptamines related to aminoglycoside antibiotics derived from maltose and lactose The synthesis of the hitherto unknown 4-O-substituted α-linked pseudo-tri-saccharides 1,2 and 3 is described. The key intermediates required in the reaction sequence are the glycals 12, 13 and 14 , prepared from maltose, lactose and the chiral ditosyloxy-cyclohexanol 15 , readily accessible from quinic acid. The pivotal step in the reaction's scheme - a stereospecific α-glycosylution procedure -, is an acid-catalyzed addition of the alcohol 15 to the glycals 12, 13 and 14 leading to the corresponding 2,3-unsaturated trisaccharides. The latter compounds were transformed to the target α-glycosides of 2,5,6-trideoxystreptamine 1, 2 and 3 which were devoid of significant antibacterial activity. These results indicate that the presence of an ether linkage at the position 4′ is probably critical for antibacterial activity.