Non-covalent interactions in polysaccharide systems

[Chemical structure: see text] This paper describes the behavior of some polysaccharides with well-known chemical structures and in which the influence of cooperative secondary interactions play an important role. The roles played by hydrophobic and ionic interactions (including ionic selectivity) on polysaccharide conformation and gelation are discussed. Electrostatic attractions are also important in the complexes formed between surfactants and polyelectrolytes of opposite charge. Finally, van der Waals dipolar interactions and particularly hydrogen-bond formation are examined. The role of hydrogen bonds in solubility, conformation, and especially the local stiffness of polysaccharides, but also in polymer-polymer complexes frequently obtained with polysaccharides, is developed. Repeat unit for a number polysaccharides.     

Effect of Acute Exposure to Hydrogen Peroxide on the Production of Phytoplankton and Bacterioplankton in a Mesohumic Lake

Abstract— Active oxygen species such as hydrogen peroxide are produced as a result of UV radiation interaction with natural organic matter and can build up to high concentrations in many aquatic environments. Although the resulting oxidizing potential may affect biological materials and processes, the ecological effects have not yet been studied in any detail. We examined the influence of hydrogen peroxide exposure on phytoplankton and bacterioplankton production in Lac Cromwell, a small humic lake in the Laurentian Hills (Quebec, Canada). A range of hydrogen peroxide concentrations were added to natural samples that were incubated in situ; results indicate that even small amounts of added hydrogen peroxide (50 n M inhibited bacterial production in this lake. A 100 n M addition inhibited bacteria by as much as 40%. On the other hand, low concentrations of added hydrogen peroxide usually stimulated photosynthesis. Catalase addition to eliminate hydrogen peroxide from water usually stimulated bacterial production but had no effect on algal carbon fixation. If these results represent true changes in growth rate, they indicate very different sensitivities of phytoplankton and bacteria to oxidative stress.     

Equilibrium Problems and Limit Analysis of Masonry Beams

We consider planar straight and curved masonry beams with the constitutive equation from Orlandi (Ph.D. thesis, 1999) and Zani (Eur. J. Mech. A, Solids 23:467–484, 2004). After stating some results about the solution to the boundary value problem, the limit analysis for this kind of bodies is outlined, based on energetic considerations (Lucchesi et al. in Q. Appl. Math. 68:713–746, 2010). The static and kinematic theorems of limit analysis, which usually are justified in a heuristic way (Heyman in The Masonry Arch, 1982; Kooharian in Proc. - Am. Concr. Inst. 89:317–328, 1953), are examined from this point of view. It is seen that the kinematic theorem does not always hold but can be proved under some hypotheses that are frequently met in applications.     

On the growth kinetics and structure of Pd2Ge and PdGe

The growth of PdGe and Pd₂Ge compounds was investigated by analyzing, after annealing, samples with about 1000–3000 Å thick evaporated Pd, using either bulk (single-crystal) Ge or amorphous (evaporated) Ge as substrate. The growth rate is different in both cases. The grain sizes of each compound, as determined by X-ray diffraction line-broadening, are the same for both Ge substrates. Therefore the hypothesis of formation processes controlled by grain boundary diffusion seems invalid. A different mechanism is suggested.     

Large deviations for statistics of the Jacobi process

This paper aims to derive large deviations for statistics of the Jacobi process already conjectured by M. Zani in her thesis. To proceed, we write in a simpler way the Jacobi semi-group density. Being given by a bilinear sum involving Jacobi polynomials, it differs from Hermite and Laguerre cases by the quadratic form of its eigenvalues. Our attempt relies on subordinating the process using a suitable random time change. This gives a Mehler-type formula whence we recover the desired semi-group density. Once we do, an adaptation of Zani’s result [M. Zani, Large deviations for squared radial Ornstein–Uhlenbeck processes, Stochastic. Process. Appl. 102 (1) (2002) 25–42] to the non-steep case will provide the required large deviations principle.     

Euler equations involving nonlinearities without growth conditions

A functional is considered, whose Euler equation involves a nonlinearity without growth conditions. It is shown that every minimum point of the functional is a solution of the Euler equation in a suitable weak sense.This work was partially supported by a national research grant financed by the Ministero dell'Università e della Ricerca Scientifica e Tecnologica (40%-1992).     

Dimethylzinc-mediated, enantioselective synthesis of propargylic amines

A one-pot, enantioselective synthesis of N-aryl propargylic amines, using alkynylation reagents obtained from dimethylzinc and terminal acetylenes in combination with various aldehydes and o-methoxyaniline as starting materials, has been developed. Enantiopure beta-amino alcohols derived from norephedrine were used as non-covalent chiral auxiliaries, both in stoichiometric or substoichiometric amount. After optimization, propargylic amines were obtained in good to high yields (up to 93%) and with moderate to high enantiomeric excesses (up to 97% ee). The possibility to recover the chiral auxiliary after the reaction was demonstrated.     

Biological activities of ophiobolin K and 6-epi-ophiobolin K produced by the endophytic fungus Aspergillus calidoustus

Endophytic fungi represent ubiquitous microbial organisms able to live in the tissues of different plants around the world and represent a prolific source of bioactive metabolites. In the present study, the endophytic fungus Aspergillus calidoustus was isolated from the medicinal plant Acanthospermum australe (Asteraceae), and identified using molecular, physiological and morphological methods. A methylene chloride crude extract of A. calidoustus has been produced and subjected to antifungal bioassay-directed fractionation which resulted in the isolation of the two bioactive compounds: ophiobolin K and 6-epi-ophiobolin K. These pure compounds displayed antifungal activity against fungal plant pathogens, protozoal activity against Trypanosoma cruzi, and cytotoxic activity against human tumoral cell lines. The results show that A. calidoustus was able to produce the antifungal and cytotoxic metabolites ophiobolin K and 6-epi-ophiobolin K, which may help the fungus to colonise and occupy the substratum as well as survive in natural environments.