Studies of Brønsted acid-base equilibria in water and nonaqueous media

http://www.ester.ee/record=b4328691~S58*es

Basicities of Strong Bases in Water: A Computational Study

Aqueous pKa values of strong organic bases – DBU, TBD, MTBD, different phosphazene bases, etc – were computed with CPCM, SMD and COSMO-RS approaches. Explicit solvent molecules were not used. Direct computations and computations with reference pKa values were used. The latter were of two types: (1) reliable experimental aqueous pKa value of a reference base with structure similar to the investigated base or (2) reliable experimental pKa value in acetonitrile of the investigated base itself. The correlations of experimental and computational values demonstrate that direct computations do not yield pKa predictions with useful accuracy: mean unsigned errors (MUE) of several pKa units were observed. Computations with reference bases lead to MUE below 1 pKa unit and are useful for predictions. Recommended aqueous pKa values are proposed for all investigated bases taking into account all available information: experimental pKa values in acetonitrile and water (if available), computational pKa values, common chemical knowledge

The Role of Salivary Agglutinin and Statherin in the Defence against Micro-organisms

Veerman, E.C.I. [Promotor]Nieuw Amerongen, A. van [Promotor]Ligtenberg, A.J.M. [Copromotor

Desenvolvimento Rural na Sociedade do Conhecimento

Globalization has a concrete territorial expression, with remaining regional asymmetries. Writers in growth and development are far away to achieve consensus about the underpinning reasons of heterogeneity in regional performance. This constitutes an important regional policy issue. This paper is based upon a concrete developing planning experience in a Portuguese rural and peripheral region. The aim of this paper is to build a methodological and procedural setup enabling to mobilize economic agents in order to use the new knowledge-based technologies. In fact, we think that this kind of methodology provides a better decision environment to take advantage and promote new business opportunities, increasing existent firm competitiveness.Strategy, Rural Development, Institucional Networks

A Chiral Sulfoxide-Based C–H Acid

We report the design and synthesis of a strong, chiral, enantiopure sulfoxide-based C–H acid. Single crystal X-ray analysis confirms the proposed structure and its absolute configuration. The new motif shows a high acidity and activity in Brønsted and Lewis acid catalyzed transformations. So far,only little to no enantioselectivities were achieved

No tillage in rainfed Aragon (NE Spain): Effect on organic carbon in the soil surface horizon

25 Pags., 7 Figs. The definitive version is available at: http://www.sciencedirect.com/science/journal/01671987Conservation tillage has been encouraged as a management alternative to preserve soil and water resources in semiarid Aragon (NE Spain). In fact, its adoption by farmers, and especially of no tillage (NT) systems, has increased in recent years. However, little information concerning the soils on which these techniques are applied is available for this region. The objective of this study was to assess the potential of NT to increase organic carbon content at the soil surface (0–20 cm) in rainfed Aragon. To this aim, 22 pairs of adjacent farm fields under NT and conventional tillage (CT) were compared in different cereal production areas. The fields were under continuous NT between 5 and 19 years but half were over 10 years. Soil organic carbon (SOC) in NT ranged from 7.06 to 18.53 g kg−1 (0–20 cm depth) and was higher than 12 g kg−1 in nearly 30% of the fields. These contents represented between 8% less (only one case) and 55% more SOC under NT than under CT with an average gain of 20% in favour of NT. The highest SOC contents were found in the NT fields of longer duration (>10 years) and/or managed with practices that enhance the return of more crop biomass to the soil (complete residue return, cropping intensification and manure application). The identification of the current management practices used by farmers has allowed us to know the diversity of the NT-based cropping systems and the reality of the conservation agriculture in our region. Overall, results from this on-farm study indicate that NT can be recommended as a viable alternative to CT to increase organic carbon at the soil surface in cereal production areas of Aragon.This research was supported by the Comisión Interministerial de Ciencia y Tecnología of Spain (Grants AGL2010-22050-CO3-02/AGR and AGL2007-66320-C02-02/AGR) and the European Union (FEDER Funds). N. Blanco-Moure was awarded with a PhD fellowship (FPI Program) by the Spanish Ministry of Science and Innovation.Peer reviewe

Inducing a pH-dependent conformational response by competitive binding to Zn2+ of a series of chiral ligands of disparate basicity

Molecules that change shape in response to environmental conditions are central to biological molecular communication devices and their synthetic chemical analogues. Here we report a molecular system in which a series of chiral anionic ligands of differing basicity are selectively protonated according to the pH of the medium. A cationic circular dichroism (CD) reporter complex responds to anion binding by selecting one of two alternative enantiomeric conformations. Exploiting the principle that less basic anions have, in general, weaker electrostatic interactions than more basic anions, a set of three chiral acids with large (>5 unit) pK(a) differences and differing configurations were sequentially deprotonated in acetonitrile by addition of base, allowing the most basic anion in the mixture at any time to bind to the reporter complex. A characteristic CD output resulted, which changed in sign as the next-most basic anion was revealed by the next deprotonation in the series. Four cycles of switching between three ligand-bound states were achieved with minimal changes in signal magnitude, by alternating addition of base and acid. The pH-dependent conformational response was used to transduce a signal by appending to the binding site a 2-aminoisobutyric acid (Aib) oligomer, whose M or P helical conformation depended on the chirality of the bound ligand, and was reported by a remote (13)C-labelled NMR reporter group. The multicomponent system thus converts a pH signal into a programmable conformational response which induces a remote spectroscopic effect