A covalent organic cage compound acting as a supramolecular shadow mask for the regioselective functionalization of C60

A trigonal-bipyramidal covalent organic cage compound serves as an efficient host to form stable 1 : 1-complexes with C₆₀ and C₇₀. Fullerene encapsulation has been comprehensively studied by NMR and UV/Vis spectroscopy, mass spectrometry as well as single-crystal X-ray diffraction. Exohedral functionalization of encapsulated C₆₀via threefold Prato reaction revealed high selectivity for the symmetry-matched all-trans-3 addition pattern.

The taming of the Prato reaction: a covalent organic cage compound serves as a supramolecular template for the regioselective functionalization of C₆₀.     

Converting suffix trees into factor/suffix oracles

Several methods to compress suffix trees were defined, most of them with the aim of obtaining compact (that is, space economical) index structures. Besides this practical aspect, a compression method can reveal structural properties of the resulting data structure, allowing a better understanding of it and a better estimation of its performances.

In this paper, we propose a simple method to compress suffix trees by merging couples of nodes. This idea was already used in the literature in a context different from ours. The originality of our approach is that the nodes we merge are not chosen with respect to their subtrees (which is difficult to test algorithmically), nor with respect to the words spelled along branches (which usually requires testing several branches before finding the good one) but with respect to their position in the tree (which is easy to compute). Another particularity of our method is it needs to read no edge label: it is exclusively based on the topology of the suffix tree. The compact structure resulting after compression is the factor/suffix oracle introduced by Allauzen, Crochemore and Raffinot whose accepted language includes the accepted language of the corresponding suffix tree.

The interest of our paper is therefore threefold:

1. A topology-based compression method is defined for (compact) suffix trees.

2. A new property of a factor/suffix oracle is established, that is, like a DAG, it results from the corresponding suffix tree after a linear number of appropriate node mergings; unlike a DAG, the merged nodes do not necessarily have isomorphical subtrees.

3. A new algorithm to transform a suffix tree into a factor/suffix oracle is given, which has linear running time and thus improves the quadratic complexity previously known for the same task.

High-spin states in the <Superscript>97</Superscript>Tc nucleus

High-spin states in the ⁹⁷Tc nucleus have been studied by in-beam γ-ray spectroscopy with the reaction ⁸²Se(¹⁹F,4nγ) at 68 MeV incident energy. Excited states have been observed up to about 8 MeV excitation and spin 43/2. The observed level scheme is compared with results of shell model calculations. Received: 22 November 2002 / Accepted: 23 December 2002 / Published online: 18 March 2003 RID="a" ID="a"e-mail: bucurescu@tandem.nipne.ro RID="b" ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy. RID="b" ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy. RID="b" ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy. RID="c" ID="c"Present address: Università di Padova, Padova, Italy. Communicated by C. Signorini     

Boundedness of the first eigenvalue of the -Laplacian

We prove that for any 1$">, any compact manifold of three or more dimensions carries Riemannian metrics of volume one with the first eigenvalue of the -Laplacian arbitrarily large.

     

Two‐Step Spin Transition in a 1D FeII 1,2,4‐Triazole Chain Compound

A thermochromic 1D spin crossover coordination (SCO) polymer [Fe(βAlatrz)₃](BF₄)₂ ? 2 H₂O ( 1? 2 H₂O), whose precursor βAlatrz, (1,2,4‐triazol‐4‐yl‐propionate) has been tailored from a β‐amino acid ester is investigated in detail by a set of superconducting quantum interference device (SQUID), ⁵⁷Fe Mössbauer, differential scanning calorimetry, infrared, and Raman measurements. An hysteretic abrupt two‐step spin crossover (T_1/2^↓=230 K and T_1/2^↑=235 K, and T_1/2^↓=172 K and T_1/2^↑=188 K, respectively) is registered for the first time for a 1,2,4‐triazole‐based Fe^II 1D coordination polymer. The two‐step SCO configuration is observed in a 1:2 ratio of low‐spin/high‐spin in the intermediate phase for a 1D chain. The origin of the stepwise transition was attributed to a distribution of chains of different lengths in 1? 2 H₂O after First Order Reversal Curves (FORC) analyses. A detailed DFT analysis allowed us to propose the normal mode assignment of the Raman peaks in the low‐spin and high‐spin states of 1? 2 H₂O. Vibrational spectra of 1? 2 H₂O reveal that the BF₄^? anions and water molecules play no significant role on the vibrational properties of the [Fe(βAlatrz)₃]²⁺ polymeric chains, although non‐coordinated water molecules have a dramatic influence on the emergence of a step in the spin transition curve. The dehydrated material [Fe(βAlatrz)₃](BF₄)₂ ( 1 ) reveals indeed a significantly different magnetic behavior with a one‐step SCO which was also investigated.     

Thermal analysis of new glycopolymers derived from monosaccharides

A novel monomer carrying carbohydrate moiety was prepared by simple reaction of methacrylic acid with 3-O-(2′,3′-epoxy-propyl)-1,2:5,6-di-O-isopropylidene-α-d-glucofuranose. Another d-glucose oligomer was synthesized by the polycondensation of a dicarboxylic acid including the carbohydrate residue into the main polymeric chain, 3-O-benzyl-5,6-(bis-O-(acryloyloxy))-1,2-di-O-isopropylidene-α-d-glucofuranose, with propane-1,3-diol using p-toluenesulfonic acid as catalyst. These products were copolymerized with styrene and 2-hydroxypropyl methacrylate, respectively, at different mass ratios, using benzoyl peroxide as initiator. Differential scanning calorimetry was performed in order to study the copolymerization process of the monomer and oligomer into the chosen co-monomers, respectively, and the activation energy of this process was evaluated using Kissinger–Akahira–Sunose (KAS) method. The storage and loss modulus of the obtained glycopolymers were evaluated using dynamic mechanical analysis. The thermal stability of the obtained products was studied via thermogravimetry.     

Sol-gel based alumina powders with catalytic applications

The sol-gel process provides a new approach to the preparation of oxide materials and offers many advantages for making catalysts. Since homogeneous mixing can be achieved at the molecular scale, the chemical reactivity of the oxide surface can be greatly enhanced; thus powders with high surface area and optimized pore size distribution can be obtained at low temperatures. In the present work NiO/Al₂O₃ sol-gel catalysts were obtained by simultaneous gelation of aluminium isopropoxide and nickel nitrate. A comparative study with pure sol-gel alumina was also realized. By physical-structural studies the changes induced by the introduction of the Ni precursor, before and after aluminium alkoxide hydrolysis were highlighted. The introduction of Ni at the beginning of the reaction favors γ-Al₂O₃ crystallization. When Ni is added at the end of reaction, it delays the alumina crystallization and induces the disorder of the lattice. The obtained Ni doped sol-gel derived alumina has been used as catalyst in the finished form for glycerol reforming to generate H₂ for fuel cell applications. Some evaluation results of Ni-doped alumina combined with TiO₂ in photocatalytic glycerol reforming reaction have been included.     

Capsaicin and Gut Microbiota in Health and Disease

Capsaicin is a widespread spice known for its analgesic qualities. Although a comprehensive body of evidence suggests pleiotropic benefits of capsaicin, including anti-inflammatory, antioxidant, anti-proliferative, metabolic, or cardioprotective effects, it is frequently avoided due to reported digestive side-effects. As the gut bacterial profile is strongly linked to diet and capsaicin displays modulatory effects on gut microbiota, a new hypothesis has recently emerged about its possible applicability against widespread pathologies, such as metabolic and inflammatory diseases. The present review explores the capsaicin–microbiota crosstalk and capsaicin effect on dysbiosis, and illustrates the intimate mechanisms that underlie its action in preventing the onset or development of pathologies like obesity, diabetes, or inflammatory bowel diseases. A possible antimicrobial property of capsaicin, mediated by the beneficial alteration of microbiota, is also discussed. However, as data are coming mostly from experimental models, caution is needed in translating these findings to humans.