Oxidation of cellulose fibers mediated by nonpersistent nitroxyl radicals

Three different nonpersistent radicals bearing >NO^? moiety have been used to oxidize the viscose fibers at room temperature and alkaline pH. The generation of the free radical species was achieved in situ, from their corresponding ? OH precursors: 1‐hydroxybenzotriazole, violuric acid, and N‐hydroxy‐3,4,5,6‐tetraphenylphthalimide. Three different routes were used: (i) in the presence of metallic cocatalyst (lead tetraacetate), (ii) under metal‐free conditions (anthraquinone as organic cocatalyst), and (iii) a homolytically scission of ? OH bond through a 365‐nm UV irradiation. The oxidized fibers were subjected to attenuated total reflection FTIR characterization, potentiometric titration, wide angle X‐ray, energy dispersive X‐ray analyses, microscopic investigations, and solid‐state ¹³C‐NMR. The patterns of CP/MAS ¹³C‐NMR spectra revealed that the oxidation occurred at the C6 primary hydroxyl groups of cellulose. Notably, as a result of the introduction of hydrophilic carboxylate groups, the water retention values of the oxidized fibers increased by 35% as compared to the original nonoxidized sample. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Spectral Analysis of Magnetic Laplacians on Conformally Cusp Manifolds

We consider an open manifold which is the interior of a compact manifold with boundary. Assuming gauge invariance, we classify magnetic fields with compact support into being trapping or non-trapping. We study spectral properties of the associated magnetic Laplacian for a class of Riemannian metrics which includes complete hyperbolic metrics of finite volume. When B is non-trapping, the magnetic Laplacian has nonempty essential spectrum. Using Mourre theory, we show the absence of singular continuous spectrum and the local finiteness of the point spectrum. When B is trapping, the spectrum is discrete and obeys the Weyl law. The existence of trapping magnetic fields with compact support depends on cohomological conditions, indicating a new and very strong long-range effect. In the non-gauge invariant case, we exhibit a strong Aharonov–Bohm effect. On hyperbolic surfaces with at least two cusps, we show that the magnetic Laplacian associated to every magnetic field with compact support has purely discrete spectrum for some choices of the vector potential, while other choices lead to a situation of limiting absorption principle. We also study perturbations of the metric. We show that in the Mourre theory it is not necessary to require a decay of the derivatives of the perturbation. This very singular perturbation is then brought closer to the perturbation of a potential. Submitted: February 6, 2007. Accepted: August 20, 2007.     

Regularity of the eta function on manifolds with cusps

On a spin manifold with conformal cusps, we prove under an invertibility condition at infinity that the eta function of the twisted Dirac operator has at most simple poles and is regular at the origin. For hyperbolic manifolds of finite volume, the eta function of the Dirac operator twisted by any homogeneous vector bundle is shown to be entire.     

Modified dispersion relations in Hořava–Lifshitz gravity and Finsler brane models

We study possible links between quantum gravity phenomenology encoding Lorentz violations as nonlinear dispersions, the Einstein–Finsler gravity models, EFG, and nonholonomic (non-integrable) deformations to Hořava–Lifshitz, HL, and/or Einstein’s general relativity, GR, theories. EFG and its scaling anisotropic versions formulated as Hořava–Finsler models, HF, are constructed as covariant metric compatible theories on (co) tangent bundle to Lorentz manifolds and respective anisotropic deformations. Such theories are integrable in general form and can be quantized following standard methods of deformation quantization, A-brane formalism and/or (perturbatively) as a nonholonomic gauge like model with bi-connection structure. There are natural warping/trapping mechanisms, defined by the maximal velocity of light and locally anisotropic gravitational interactions in a (pseudo) Finsler bulk spacetime, to four dimensional (pseudo) Riemannian spacetimes. In this approach, the HL theory and scenarios of recovering GR at large distances are generated by imposing nonholonomic constraints on the dynamics of HF, or EFG, fields.     

Einstein gravity in almost Kähler and Lagrange–Finsler variables and deformation quantization

A geometric procedure is elaborated for transforming (pseudo) Riemannian metrics and connections into canonical geometric objects (metric and nonlinear and linear connections) for effective Lagrange, or Finsler, geometries which, in turn, can be equivalently represented as almost Kähler spaces. This allows us to formulate an approach to quantum gravity following standard methods of deformation quantization. Such constructions are performed not on tangent bundles, as in usual Finsler geometry, but on spacetimes enabled with nonholonomic distributions defining 2+2$2+2$ splitting with associate nonlinear connection structure. We also show how the Einstein equations can be written in terms of Lagrange–Finsler variables and corresponding almost symplectic structures and encoded into the zero-degree cohomology coefficient for a quantum model of Einstein manifolds.     

Cusp geometry and the cobordism invariance of the index

The cobordism invariance of the index on closed manifolds is reproved using the calculus Ψ_c of cusp pseudodifferential operators on a manifold with boundary. More generally, on a compact manifold with corners, the existence of a symmetric cusp differential operator of order 1 and of Dirac type near the boundary implies that the sum of the indices of the induced operators on the hyperfaces is null.     

New conjugates of calix[4]arenes bearing dipyridine and indolizine heterocycles

A simple route to introduce various heterocycles, derivatives of dipyridyls and indolizines on the lower rim of the para-tert-butylcalix[4]arene via ester bond formation to afford 1,3-disubstituted conjugates is described. The conformation of the new compounds and some intermolecular interactions are discussed on the basis of X-ray and NMR analyses. Preliminary complexation properties of some of the new tert-butylcalix[4]arene heterocyclic conjugates with Cu (II), Co (II) and Ni (II) were studied by means of UV–Vis titration.     

Supramolecular synthesis based on piperidone derivatives and pharmaceutically acceptable co‐formers

The target complexes, bis{(E,E)‐3,5‐bis[4‐(diethylamino)benzylidene]‐4‐oxopiperidinium} butanedioate, 2C₂₇H₃₆N₃O⁺·C₄H₄O₄²⁻, (II), and bis{(E,E)‐3,5‐bis[4‐(diethylamino)benzylidene]‐4‐oxopiperidinium} decanedioate, 2C₂₇H₃₆N₃O⁺·C₁₀H₁₆O₄²⁻, (III), were obtained by solvent‐mediated crystallization of the active pharmaceutical ingredient (API) (E,E)‐3,5‐bis[4‐(diethylamino)benzylidene]‐4‐piperidone and pharmaceutically acceptable dicarboxylic (succinic and sebacic) acids from ethanol solution. They have been characterized by melting point, IR spectroscopy and single‐crystal X‐ray diffraction. For the sake of comparison, the structure of the starting API, (E,E)‐3,5‐bis[4‐(diethylamino)benzylidene]‐4‐piperidone methanol monosolvate, C₂₇H₃₅N₃O·CH₄O, (I), has also been studied. Compounds (II) and (III) represent salts containing H‐shaped centrosymmetric hydrogen‐bonded synthons, which are built from two parallel piperidinium cations and a bridging dicarboxylate dianion. In both (II) and (III), the dicarboxylate dianion resides on an inversion centre. The two cations and dianion within the H‐shaped synthon are linked by two strong intermolecular N⁺—H...⁻OOC hydrogen bonds. The crystal structure of (II) includes two crystallographically independent formula units, A and B. The cation geometries of units A and B are different. The main N—C₆H₄—C=C—C(=O)—C=C—C₆H₄—N backbone of cation A has a C‐shaped conformation, while that of cation B adopts an S‐shaped conformation. The same main backbone of the cation in (III) is practically planar. In the crystal structures of both (II) and (III), intermolecular N⁺—H...O=C hydrogen bonds between different H‐shaped synthons further consolidate the crystal packing, forming columns in the [100] and [10] directions, respectively. Salts (II) and (III) possess increased aqueous solubility compared with the original API and thus enhance the bioavailability of the API.