Surface plasmons reveal spin crossover in nanometric layers

Nano-objects and thin films displaying molecular spin-crossover phenomena have recently attracted much attention. However, the investigation of spin crossover at reduced sizes is still a big challenge. Here we demonstrate that surface plasmon polariton waves propagating along the interface between a metal and a dielectric layer can be used to detect the spin-state changes in the latter with high sensitivity, even at the nanometer scale.     

Use of high-performance liquid chromatography-thermospray mass spectrometry and gas chromatography-electron-impact mass spectrometry in the identification of the metabolites of alpha-methylacetohydroxamic acids, potential anti-asthmatic agents

Two potential anti-asthmatic alpha-methylacetohydroxamic acids, compound 1 and compound II were metabolised to two major products (metabolite 1 and metabolite 2) after oral dosing to rabbits. Metabolite 1, extracted under acid conditions from the plasma and urine of dosed animals, was identified as a glucuronide by incubation with beta-glucuronidase and subsequent high-performance liquid chromatographic-mass spectrometric (HPLC-MS) analysis of the aglycone. HPLC-MS analysis of metabolite 2 suggested that it was the acetamide, however, unequivocal identification was obtained by further analysis using gas chromatography-mass spectrometry (GC-MS) of its trimethylsilyl derivative and by comparison with the mass spectra of the authentic acetamides. This study shows the advantages of combining HPLC-MS with other techniques such as GC-MS for the identification of metabolites.     

Discrete harmonics for stream function-vorticity Stokes problem

Summary. We consider the bidimensional Stokes problem for incompressible fluids in stream function-vorticity. For this problem, the classical finite element method of degree one converges only in for the norm of the vorticity. We propose to use harmonic functions to approach the vorticity along the boundary. Discrete harmonics are functions that are used in practice to derive a new numerical method. We prove that we obtain with this numerical scheme an error of order for the norm of the vorticity. Received January, 2000 / Revised version received May 15, 2001 / Published online December 18, 2001     

16-fold degeneracy of peptide plane orientations from residual dipolar couplings: analytical treatment and implications for protein structure determination

Residual dipolar couplings (RDCs) measured for internally rigid molecular fragments provide important information about the relative orientations of these fragments. Dependent on the symmetry of the alignment tensor and the symmetry of the molecular fragment, however, there generally exist more than one solution for the fragment orientation consistent with the measured RDCs. Analytical solutions are presented that describe the complete set of orientations of internally rigid fragments that are consistent with multiple dipolar couplings measured in a single alignment medium that is rhombic. For the first time, it is shown that, for a planar fragment such as the peptide plane, there generally exist 16 different solutions with their analytical expressions presented explicitly. The presence of these solutions is shown to be highly relevant for standard structure determination protocols using RDCs to refine molecular structures. In particular, when using standard protein structure refinement with RDCs that were measured in a single alignment medium as constraints, it is found that often more than one of the peptide plane solutions is physically viable; i.e., despite being consistent with measured RDCs, the local backbone structure can be incorrect. On the basis of experimental and simulated examples, it is rationalized why protein structures that are refined against RDCs measured in a single medium can have lower resolution (precision) than one would expect on the basis of the experimental accuracy of the RDCs. Conditions are discussed under which the correct solution can be identified.     

Investigation of the two-step spin crossover complex Fe[5-NO2-sal-(1,4,7,10)] using density functional theory

A quantum chemical study of the Fe[5-NO2-sal-(1,4,7,10)] ((1,10-bis(5-nitrosalicylaldehyde)-1,4,7,10-tetra-ezdecane-O,O',N,N',N' ',N' ')iron(II)) molecule was performed using density functional theory (DFT). Starting from the different X-ray crystallographic structures, geometry optimizations have been performed. These calculations confirmed the conformational isomerism of this complex in each spin states of the molecule ((1)A(1g) and (5)T(2g)). Each employed DFT method (B3LYP, B3LYP*, BP86, HCTH407) reproduced correctly the structural differences between the two calculated conformers when compared to the experimental structures. Furthermore, electronic polarizabilities have been calculated in each spin state and for each conformer. These calculations revealed a higher polarizability in the singlet state in agreement with the measured higher dielectric constant in this state.     

Molecular spin crossover phenomenon: recent achievements and prospects

Recently we assisted a strong renewed interest in the fascinating field of molecular spin crossover complexes by (1) the emergence of nanosized spin crossover materials through direct synthesis of coordination nanoparticles and nanopatterned thin films as well as by (2) the use of novel sophisticated high spatial and temporal resolution experimental techniques and theoretical approaches for the study of spatiotemporal phenomena in cooperative spin crossover systems. Besides generating new fundamental knowledge on size-reduction effects and the dynamics of the spin crossover phenomenon, this research aims also at the development of practical applications such as sensor, display, information storage and nanophotonic devices. In this critical review, we discuss recent work in the field of molecule-based spin crossover materials with a special focus on these emerging issues, including chemical synthesis, physical properties and theoretical aspects as well (223 references).     

Protein crystal structures with ferrocene and ruthenocene-based enzyme inhibitors

We have determined the protein X-ray crystal structures of four organometallic inhibitors in complex with their target enzyme carbonic anhydrase II. The barrel-shaped hydrophobic ferrocene and ruthenocene moieties have provided a structure-based avenue to better occupy the hydrophobic binding patch within the enzyme active site.     

Biocompatibility of some materials used in dental implantology: histological study

This study deals with bioreactive materials for potential applications as endosseus dental implants. Currently used dental implants are made of dental alloys but due to cytotoxic problems, high strength ceramic materials appear as an interesting alternative to these alloys. In order to combine good mechanical properties and promotion of the osteointegration process, a ceramic composite material composed of 10 wt.% tricalcium phosphate (TCP) mixed with partially stabilized zirconia has been elaborated. Such a ceramic has been implanted into albino rats, the sites of implantation being the adrenal gland for the toxicity evaluation and the sphenoid bone to estimate the osteogenesis potential. These results have been compared to those obtained with implants made of alumina (Al₂O₃), zirconia (ZrO₂) or poly(ethylene terephthalate) (Dacron®). In all cases no rejection effect was observed. The histological study indicated that ZrO₂-TCP ceramics induced a marginal and subjacent cell disorganization. However, the existence of an irregular cellular band indicated a cellular colonization process on the TCP particles. The microscopy study of the implants after removal confirmed the bioresorption of TCP.