Quantum SUSY signatures in low and high energy processes

In the search for phenomenological evidence of supersymmetry through the indirect method of quantum signatures, it is useful to seek correlations of the non-standard quantum effects in low and high energy proceses, such as those involving on one hand the properties of theB-mesons and on the other hand the physics of the top quark and of the Higgs bosons. There are regions of the MSSM parameter space where the potential quantum SUSY signatures in the two energy regimes are strongly interwoven and therefore the eventual detection of these correlated quantum effects would strongly point towards the existence of underlying supersymmetric dynamics.     

Electron-pairing analysis from localization and delocalization indices in the framework of the atoms-in-molecules theory

This article presents an overview of recent advances in the study of electron pairing through the use of localization and delocalization indices obtained from double integration over atomic basins of the exchange–correlation density in the framework of the atoms-in-molecules theory. These localization and delocalization indices describe the intra- and interatomic distribution of the electron pairs in a molecule. The main results of the application of these second-order indices to the analysis of molecular structure and chemical reactivity are briefly reviewed. It is shown that localization and delocalization indices represent a powerful tool to describe the electron-pair structure of molecules, which, in turn, provides deeper insight into relevant chemical phenomena such as electron correlation effects and the formation of localized α, β electron pairs. Received: 8 April 2002 / Accepted: 26 June 2002 / Published online: 6 September 2002 Acknowledgements. Financial help was furnished by the Spanish DGES projects no. PB98-0457-C02-01 and BQU2002-04112-C02-02. J.P. thanks the Departament d'Universitats, Recerca i Societat de la Informació de la Generalitat de Catalunya for benefiting from a doctoral fellowship, no. 2000FI-00582. M.S. is indebted to the Departament d'Universitats, Recerca i Societat de la Informació of the Generalitat de Catalunya for financial support through the Distinguished University Research Promotion, 2001. We also thank the Centre de Supercomputació de Catalunya for providing us with computing facilities. Correspondence to: M. Solà e-mail: miquel.sola@udg.es     

Isotactic rac‐Lactide Polymerization with Copper Complexes: The Influence of Complex Nuclearity

Diiminopyrrolide copper alkoxide complexes, LCuOR (OR¹=N,N‐dimethylamino ethoxide, OR²=2‐pyridyl methoxide), are active for the polymerization of rac‐lactide at ambient temperature in benzene to yield polymers with M_w/M_n=1.0–1.2. X‐ray diffraction studies showed bridged dinuclear complexes in the solid state for both complexes. While LCuOR¹ provided only atactic polylactide, LCuOR² produced partially isotactic polylactide (P_m=0.7). The difference in stereocontrol is attributed to a dinuclear active species for LCuOR² in contrast to a mononuclear species for LCuOR¹.     

Biomimetic versus enzymatic high-potential electrocatalytic reduction of hydrogen peroxide on a functionalized carbon nanotube electrode

We report the non-covalent functionalization of a multi-walled carbon nanotube (MWCNT) electrode with a biomimetic model of the horseradish peroxidase (HRP) active site. By modifying the MWCNT electrode surface with imidazole-modified polypyrrole, a new biomimetic complex of HRP was synthesized on the MWCNT sidewalls via the coordination of imidazole (Im) to the metal centre of iron protoporphyrin IX, affording (Im)(PP)Fe^III. Compared to the pi-stacking of non-coordinated (PP)Fe^III on a MWCNT electrode, the (Im)(PP)Fe^III-modified MWCNT electrode exhibits higher electrocatalytic activity with an I _max = 0.52 mA cm^–2 for the reduction of H₂O₂, accompanied by a high onset potential of 0.43 V vs. Ag/AgCl. The performances of these novel surface-confined HRP mimics were compared to those of a MWCNT electrode modified by HRP. Although the enzyme electrode displays a higher electrocatalytic activity towards H₂O₂ reduction, the (Im)(PP)Fe^III-modified MWCNT electrode exhibits a markedly higher operational stability, retaining 63% of its initial activity after one month.     

Interactions of histatin-3 and histatin-5 with actin

Background

Histatins are histidine rich polypeptides produced in the parotid and submandibular gland and secreted into the saliva. Histatin-3 and ?5 are the most important polycationic histatins. They possess antimicrobial activity against fungi such as Candida albicans. Histatin-5 has a higher antifungal activity than histatin-3 while histatin-3 is mostly involved in wound healing in the oral cavity. We found that these histatins, like other polycationic peptides and proteins, such as LL-37, lysozyme and histones, interact with extracellular actin.

Results

Histatin-3 and ?5 polymerize globular actin (G-actin) to filamentous actin (F-actin) and bundle F-actin filaments. Both actin polymerization and bundling by histatins is pH sensitive due to the high histidine content of histatins. In spite of the equal number of net positive charges and histidine residues in histatin-3 and ?5, less histatin-3 is needed than histatin-5 for polymerization and bundling of actin. The efficiency of actin polymerization and bundling by histatins greatly increases with decreasing pH. Histatin-3 and ?5 induced actin bundles are dissociated by 100 and 50 mM NaCl, respectively. The relatively low NaCl concentration required to dissociate histatin-induced bundles implies that the actin-histatin filaments bind to each other mainly by electrostatic forces. The binding of histatin-3 to F-actin is stronger than that of histatin-5 showing that hydrophobic forces have also some role in histatin-3- actin interaction. Histatins affect the fluorescence of probes attached to the D-loop of G-actin indicating histatin induced changes in actin structure. Transglutaminase cross-links histatins to actin. Competition and limited proteolysis experiments indicate that the main histatin cross-linking site on actin is glutamine-49 on the D-loop of actin.

Conclusions

Both histatin-3 and ?5 interacts with actin, however, histatin 3 binds stronger to actin and affects actin structure at lower concentration than histatin-5 due to the extra 8 amino acid sequence at the C-terminus of histatin-3. Extracellular actin might regulate histatin activity in the oral cavity, which should be the subject of further investigation.

     

Performance evaluation of CAESAR–QSAR output using PAHs as a case study

The set of 16 polycyclic aromatic hydrocarbon compounds was examined with the Internet available quantitative structure–activity relationship (QSAR) CAESAR models. For mutagenicity, carcinogenicity, developmental toxicity, and skin sensitization, the report includes the predicted classifications, the analysis of applicability domains, and the similarity sets, which consist of the similar compounds from the training sets. These results were further analyzed with chemometrical methods, that is, hierarchical clustering, principal component analysis, and self‐organizing maps, which were used for clustering and to define the cluster indicators. Such analysis assists the users in planning the application of QSAR models for hazard communication in regulatory compliance and in research of new active compounds. Copyright © 2013 John Wiley & Sons, Ltd.     

Catalytic 1,3-difunctionalisation of organic backbones through a highly stereoselective, one-pot, boron conjugate-addition/reduction/oxidation process

A simple one-pot, three-step synthetic route to chiral 1,3-amino alcohols and 1,3-diols has been established. Considering the overall stereocontrol of the synthetic protocol, the first and key step is an enantioselective β-boration of α,β-unsaturated imines and ketones, respectively. The enantioselectivity provided by the Cu(I) catalyst modified with Josiphos- and Mandyphos-type ligands has been examined. The oxidative substitution of the boryl unit with a hydroxyl group proceeds with complete retention of configuration at the C(β)-atom. In parallel, the stoichiometric reduction of the imino or carbonyl group provides a second stereogenic centre. Depending on the nature of the reducing reagent, exceptionally high diastereoselectivity is achieved, especially for syn-1,3-amino alcohols and 1,3-diols.     

Intramolecular [2+2+2] cycloaddition reactions of yne-ene-yne and yne-yne-ene enediynes catalysed by Rh(I): experimental and theoretical mechanistic studies

N-tosyl-linked open-chain yne-ene-yne enediynes 1 and 2 and yne-yne-ene enediynes 3 and 4 have been satisfactorily synthesised. The [2+2+2] cycloaddition process catalysed by the Wilkinson catalyst [RhCl(PPh(3))(3)] was tested with the above-mentioned substrates resulting in the production of high yields of the cycloadducts. Enediynes 1 and 2 gave standard [2+2+2] cycloaddition reactions whereas enediynes 3 and 4 suffered β-hydride elimination followed by reductive elimination of the Wilkinson catalyst to give cycloadducts, which are isomers of those that would be obtained by standard [2+2+2] cycloaddition reactions. The different reactivities of these two types of enediyne have been rationalised by density functional theory calculations.     

Highly aminated mesoporous silica nanoparticles with cubic pore structure

Mesoporous silica with cubic symmetry has attracted interest from researchers for some time. Here, we present the room temperature synthesis of mesoporous silica nanoparticles possessing cubic Pm3?n symmetry with very high molar ratios (>50%) of 3-aminopropyl triethoxysilane. The synthesis is robust allowing, for example, co-condensation of organic dyes without loss of structure. By means of pore expander molecules, the pore size can be enlarged from 2.7 to 5 nm, while particle size decreases. Adding pore expander and co-condensing fluorescent dyes in the same synthesis reduces average particle size further down to 100 nm. After PEGylation, such fluorescent aminated mesoporous silica nanoparticles are spontaneously taken up by cells as demonstrated by fluorescence microscopy.