Biogenetic hypothesis and first steps towards a biomimetic synthesis of haouamines

A detailed hypothesis for the biogenesis of haouamines is reported herein, supported by experiments headed towards biomimetic synthesis of these compounds.     

Reactivity of substituted 3‐(diethylphosphonyl)‐1‐(trialkylsilyl)alka‐1,3‐dienes: Regioselective epoxidation and cyclopropanation reactions

When treated with electrophilic m‐CPBA reagent, dienes 1 were efficiently epoxidized at the silylated 1,2‐double bond exclusively. Otherwise, regioselective cyclopropanation of the phosphonylated 3,4‐double bond was achieved by using the nucleophilic Corey's reagent. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10:231–236, 1999     

Magnetic structure of the ferromagnetic new ternary silicide Nd5CoSi2

Nd(5)CoSi(2) was obtained from the elements by arc-melting followed by annealing at 883 K. Its investigation by single-crystal x-ray and neutron powder diffraction shows that this ternary silicide crystallizes as Nd(5)Si(3) in a tetragonal structure deriving from the Cr(5)B(3)-type (I4/mcm space group; a = 7.7472(2) and c = 13.5981(5) ? as unit cell parameters). The structural refinements confirm the mixed occupancy on the 8h site between Si and Co atoms, as already observed for Gd(5)CoSi(2). Magnetization and specific heat measurements reveal a ferromagnetic behavior below T(C) = 55 K for Nd(5)CoSi(2). This magnetic ordering is further evidenced by neutron powder diffraction investigation revealing between 1.8 K and T(C) a canted ferromagnetic structure in the direction of the c-axis described by a propagation vector k = (0 0 0). At 1.8 K, the two Nd(3+) ions carry ordered magnetic moments equal respectively to 1.67(7) and 2.37(7) μ(B) for Nd1 and Nd2; these two moments exhibit a canting angle of θ = 4.3(6)°. This magnetic structure presents some similarities with that reported for Nd(5)Si(3).     

DSC and TSDC Study of Unsaturated Polyester Resin. Influence of the promoter content

This work reports on the curing kinetics of unsaturated polymer resins (UPRs) cured with styrene, studied by differential scanning calorimetry and Fourier transform infrared spectroscopy. The data lead to determination of the experimental conditions with which to obtain a fully cured material and open the way for study of the relaxation phenomena by means of thermally stimulated depolarization current analysis (TSDC). In relaxation studies on fully cured resins, the TSDC spectra revealed important overlapping of the main relaxation peak with an extra upper peak. The importance of this extra peak a priori prevents further analysis of the main relaxation. To identify the origins of this peak (space charge or other), the purity of the resin was checked by X-ray fluorescence spectroscopy. The use of UPR specimens with different compositions (in terms of the resin/activator/initiator ratio) demonstrated that the bulk of the impurities Cl, K, Ca, Sr, Zr and Ba are due to the promoter. Decoupling of the mixed peaks (α-relaxation and extra) revealed that the a peak is independent of the proportion of the promoter in the resin and that the extra peak is principally due to the presence of these impurities. This revised version was published online in July 2006 with corrections to the Cover Date.     

High Pressure Calorimetry. Comparison of two systems (differential vs. single cell). Application to the phase change of water under pressure

In high pressure calorimetry the pressure change is used to obtain the desired phenomenon (i.e. phase change) at constant temperature. Two high pressure calorimeters have been developed to measure the latent heat of fusion of pure water (hexagonal ice-type I) at subzero temperature. Both calorimeters used a constant pressurisation rate produced with a high pressure pump driven by a step motor. The first calorimeter was a single cell calorimeter where mercury acted as the pressurisation fluid, while the second one was differential (two cells) and was pressurised with pentane. Both calorimeters gave high accuracy data of latent heat of fusion of pure water, which were determined taking into account that either the fluid used to pressurise or the pressurisation rate affected the calorimetric signal. This revised version was published online in July 2006 with corrections to the Cover Date.     

Orthosymmetric ortholattices and Rickart*-rings

Orthosymmetric ortholattices (OSOLs) have been introduced in order to approximate ortholattices of closed subspaces of a Hilbert space. In this paper, some new properties of OSOLs are proved and the main result states that lattices of projections of Rickart^*-rings, satisfying 2x=0 impliesx=0, carry a natural structure of OSOL.     

Orthosymmetries and Jordan Triples

Orthosymmetric ortholattices (OSOLs) have beenintroduced in order to approximate Hilbertian lattices(ortholattices of closed subspaces of a Hilbert space).Axioms of OSOLs are selected properties of usual orthogonal symmetries on a Hilbertian latticeand many posets defined by means of associative orJordan algebras possess a set of automorphismssatisfying these axioms. In this paper, we describe andillustrate a method using Jordan triples and whichprovides a common setting for the study oforthosymmetries in associative algebras and Jordanalgebras.     

Studies on Highly Porous Hybrids Prepared by a Novel Fast Gellation Process Under Ambient Pressure

Supercritical drying of hydrolyzed alkoxysilanes is a typical method for making aerogels that exhibit over 75% porosity. Recent works demonstrated the possibility to prepare, under ambient pressure, aerogel-type of highly porous materials. However, multiple step process is being required for surface modification of pore walls to avoid collapsing effect caused by drying shrinkage. We wish to describe in here a novel fast, single step sol-gel route for the preparation of ultra high porous materials. Commercially available hydrogensilsesquioxane was used as precursor in this approach, leading through a simple, single step process to gels within minutes and thus without any further surface modification needed. Systematic studies of this novel fast gellation process were carried out through careful variation of experimental conditions to gain porosity control and enable improved design of this class of ultra high porous monolithic materials.     

Late‐Stage Isotopic Carbon Labeling of Pharmaceutically Relevant Cyclic Ureas Directly from CO2

A robust, click‐chemistry‐inspired procedure for radiolabeling of cyclic ureas was developed. This protocol, suitable for all carbon isotopes (¹¹C, ¹³C, ¹⁴C), is based on the direct functionalization of carbon dioxide: the universal building block for carbon radiolabeling. The strategy is operationally simple and reproducible in different radiochemistry centers, exhibits remarkably wide substrate scope with short reaction times, and demonstrates superior reactivity as compared to previously reported systems. With this procedure, a variety of pharmaceuticals and an unprotected peptide were labeled with high radiochemical efficiency.