Substituent effects on the thermochemistry of thiophenes. a theoretical (G3(MP2)//B3LYP and G3) study

Very good linear correlations between experimental and calculated enthalpies of formation in the gas phase (G3(MP2)//B3LYP and G3) for 48 thiophene derivatives have been obtained. These correlations permit a correction of the calculated enthalpies of formation in order to estimate more reliable "experimental" values for the enthalpies of formation of substituted thiophenes, check the reliability of experimental measurements, and also predict the enthalpies of formation of new thiophenes that are not available in the literature. Moreover, the difference between the enthalpies of formation of isomeric thiophenes with the same substituent in positions 2 and 3 of the ring has been analyzed. Likewise, a comparison of the substituent effect in the thiophene and benzene rings has been established.     

Supramolecular assembly of strongly chemisorbed size- and shape-defined chiral clusters: S- and R-alanine on Cu(110)

The bonding and self-assembly of a chirally organized monolayer of alanine on the Cu(110) surface has been investigated using reflection-absorption infrared spectroscopy, low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). This multitechnique approach has enabled an in-depth understanding of the hierarchy of chirality transfer: from a single adsorbed molecule, to size-defined chiral clusters, and then to an overall chiral assembly. The data have indicated that the alanine is in its anionic form, bound to the copper surface through the oxygens of the ionized carboxylate group and the nitrogen of the neutral amino group. Importantly, the methyl group is held away from the surface, resulting in direct chirality transfer into the footprint of the adsorbed alanine molecules, with the local adsorption motif for S-alanine being the mirror image of that created for R-alanine. STM has shown that S-alanine molecules self-organize to form size-defined chiral clusters of six or eight molecules at the surface, interspersed with chiral channels of bare metal. Together, these clusters and channels further self-assemble into a chiral array with one unique chiral domain sustained across the entire surface. A similar chiral assembly, but with the mirror organization, has been observed for R-alanine. Structural models for the individual clusters are proposed, and in conjunction with LEED data, overall models for these chiral phases of both S- and R-alanine have been constructed. Overall, this adsorption system has been found to be both strongly chemisorbed and capable of extensive intermolecular H-bonding, causing stresses that lead not only to the chiral self-organization of molecules but also to a specific self-organization of the empty chiral channels and spaces that intersperse the structure which, in turn, chirally assemble across macroscopic length scales to give a surface with global organizational chirality.     

Bacteria encapsulation in colloidal inorganic matrices: Is it a general method?

Zirconium oxyhydroxide nanoparticles prepared by an aqueous route were evaluated for Escherichia coli bacteria encapsulation. A low viability rate was measured 24 hours after immobilization that could be attributed to nanoparticle cytotoxicity. Moreover, the presence of glycerol, a long-term cell-preserving molecule, hindered gel formation, probably due to its adsorption on the nanoparticle surface. A comparison with boehmite and ferrihydrite gels previously synthesized following a similar aqueous colloidal route suggests that the generalization of this method will rely on a careful control of the nanoparticle surface reactivity and may require surface chemical modification.     

A theoretical study of aqueous solvation of K comparing ab initio, polarizable, and fixed-charge models

The hydration of K(+) is studied using a hierarchy of theoretical approaches, including ab initio Born-Oppenheimer molecular dynamics and Car-Parrinello molecular dynamics, a polarizable force field model based on classical Drude oscillators, and a nonpolarizable fixed-charge potential based on the TIP3P water model. While models based more directly on quantum mechanics offer the possibility to account for complex electronic effects, polarizable and fixed-charges force fields allow for simulations of large systems and the calculation of thermodynamic observables with relatively modest computational costs. A particular emphasis is placed on investigating the sensitivity of the polarizable model to reproduce key aspects of aqueous K(+), such as the coordination structure, the bulk hydration free energy, and the self diffusion of K(+). It is generally found that, while the simple functional form of the polarizable Drude model imposes some restrictions on the range of properties that can simultaneously be fitted, the resulting hydration structure for aqueous K(+) agrees well with experiment and with more sophisticated computational models. A counterintuitive result, seen in Car-Parrinello molecular dynamics and in simulations with the Drude polarizable force field, is that the average induced molecular dipole of the water molecules within the first hydration shell around K(+) is slightly smaller than the corresponding value in the bulk. In final analysis, the perspective of K(+) hydration emerging from the various computational models is broadly consistent with experimental data, though at a finer level there remain a number of issues that should be resolved to further our ability in modeling ion hydration accurately.     

Stereochemistry and dynamic behavior of some synthetic “angular” profisetinidin tetraflavanoid derivatives

The structure and stereochemistry of four synthetic “angular” tetraflavanoid-condensed tannin derivatives are examined by high-resolution variable temperature ¹H NMR. spectroscopy, and hence correlated with their dynamic behavior. Three “angular” oligomers exist as stable rotational isomers at ambient temperatures, thus contrasting with the mobility about their interflavanoid bonds of most natural profisetinidin “trimeric” and “tetrameric” homologs. A “linear” tetraflavanoid analog results from one of these regioselectively controlled condensations.     

Liquid chromatographic analysis of propranolol enantiomers in human blood using precolumn derivatization with (+)-1-(9-fluorenyl)ethyl chloroformate.

A method for the determination of the R-(+) and S-(-) enantiomers of propranolol in blood was developed. After extraction with heptane-isopentanol and derivatization with (+)-1-(9-fluorenyl)ethyl chloroformate, excess reagent was removed using solid-phase extraction. The enantiomers were separated on an achiral, reversed-phase, radially compressed column, and detected by fluorescence with excitation and emission wavelengths of 260 and 340 nm, respectively. The limit of quantification was 0.5 ng/ml. This method was used for pharmacokinetic analysis of propranolol enantiomers after administration of immediate-release (80 mg) or sustained-release (160 mg) racemic propranolol.     

CALCIUM-REGULATED NUCLEAR ENZYMES: POTENTIAL MEDIATORS OF PHYTOCHROME-INDUCED CHANGES IN NUCLEAR METABOLISM?

Calcium ions have been proposed to serve as important regulatory elements in stimulus-response coupling for phytochrome responses. An important test of this hypothesis will be to identify specific targets of calcium action that are required for some growth or development process induced by the photoactivated form of phytochrome (Pfr). Initial studies have revealed that there are at least two enzymes in pea nuclei that are stimulated by Pfr in a Ca(2+)-dependent fashion, a calmodulin-regulated nucleoside triphosphatase and a calmodulin-independent but Ca(2+)-dependent protein kinase. The nucleoside triphosphatase appears to be associated with the nuclear envelope, while the protein kinase co-purifies with a nuclear fraction highly enriched for chromatin. This short review summarizes the latest findings on these enzymes and relates them to what is known about Pfr-regulated nuclear metabolism.     

Lamellar-to-nematic phase transition in a lipid-surfactant mixture

A lyotropic system, consisting of a lecithin (DMPC) and a non-ionic surfactant (C₁₂E₅) in water was studied. The system exhibits a lamellar-to-nematic phase transition. The nematic phase appears as the temperature is decreased and only exists in a very limited temperature and concentration range, for specific lipid-to-surfactant ratios. While a lamellar phase is found at higher temperatures in both mixed and pure C₁₂E₅ systems, the transition to the nematic phase at lower temperatures coincides with a micellar phase in the pure C₁₂E₅ system. The transition appears to be driven by the strong temperature dependence of the surfactant film spontaneous curvature. The structural properties of the lamellar phase close to the lamellar-to-nematic boundary have been studied by polarised light microscopy and small-angle neutron and X-ray scattering experiments. The signature of a helical defect with Burgers vector of magnitude 2 is apparent in our data, close to the lamellar-to-nematic phase transition. The proliferation of screw dislocations in the lamellar phase might be a plausible mechanism for driving this transition. Received 6 July 1999 and Received in final form 17 April 2000     

Exploring time series retrieved from cardiac implantable devices for optimizing patient follow-up

Current cardiac implantable devices (IDs) are equipped with a set of sensors that can provide useful information to improve patient follow-up and prevent health deterioration in the postoperative period. In this paper, data obtained from an ID with two such sensors (a transthoracic impedance sensor and an accelerometer) are analyzed in order to evaluate their potential application for the follow-up of patients treated with a cardiac resynchronization therapy (CRT). A methodology combining spatiotemporal fuzzy coding and multiple correspondence analysis (MCA) is applied in order to: 1) reduce the dimensionality of the data and provide new synthetic indexes based on the "factorial axes" obtained from MCA; 2) interpret these factorial axes in physiological terms; and 3) analyze the evolution of the patient's status by projecting the acquired data into the plane formed by the first two factorial axes named "factorial plane." In order to classify the different evolution patterns, a new similarity measure is proposed and validated on the simulated datasets, and then, used to cluster observed data from 41 CRT patients. The obtained clusters are compared with the annotations on each patient's medical record. Two areas on the factorial plane are identified, one being correlated with a health degradation of patients and the other with a stable clinical state.