HF/6‐31G* energy surfaces for disaccharide analogs

The HF/6‐31G* level of theory was used to calculate relaxed potential energy surfaces for 12 analogs of disaccharides. The analogs were made by replacing glucose with tetrahydropyran and fructose with 2‐methyltetrahydrofuran. Molecules had zero, one or two anomeric carbon atoms, and di‐axial, axial‐equatorial, and di‐equatorial linkages. Despite the absence of hydroxyl groups, the surfaces account well for conformations that are observed in crystals of the parent disaccharides. Thus, torsional energy and the simple bulk of ring structures are major factors in determining disaccharide conformation. The contour shapes around the global minima depend on the number of anomeric carbons involved in the linkage, while the presence of alternative minima that have relative energies less than 4 kcal/mol mostly requires equatorial bonds. However, molecules with two adjacent anomeric centers gave exceptions to these rules. Flexibility values related to a partition function show that the di‐axial trehalose analog is the most rigid. The di‐equatorial pseudodisaccharide analog with no anomeric centers is most flexible. Reproduction of these surfaces is proposed as a simple test of force fields for modeling carbohydrates. Also, these surfaces can be used in a simple hybrid method for calculating disaccharide energy surfaces. © 2000 John Wiley & Sons, Inc. * J Comput Chem 22: 65–78, 2001     

Pressure crystallized and solid-state extruded poly - ethylene. Precision determination of lattice parameters

Precision determination of high density polyethylene unit-cell dimensions are reported. The crystallographic analysis was carried out on pressure crystallized and subsequently solid-state extruded samples respectively, by means of x-ray photographic and diffractometric procedures. In all cases the crystal data was derived from a large number of independent reflections. It was shown that the unit-cell dimensions and the corresponding crystallographic densities of all the specimens are invariant with respect to either crystallization pressure or nominal draw ratio. The effects of deformation on macroscopic density are attributed, therefore, to changes of the degree of crystallinity and to an increase of the density of the amorphous phase. This interpretation is consistent with the experimental data in the framework of the two-phase model of polymer morphology.     

Luminescent bacteria-based sensing method for methylmercury specific determination

A bacterial biosensor method for the selective determination of a bioavailable organomercurial compound, methylmercury, is presented. A recombinant luminescent whole-cell bacterial strain responding to total mercury content in samples was used. The bacterial cells were freeze-dried and used as robust, reagent-like compounds, without batch-to-batch variations. In this bacteria-based sensing method, luciferase is used as a reporter, which requires no substrate additions, therefore allowing homogenous, real-time monitoring of the reporter gene expression. A noninducible, constitutively light-producing control bacterial strain was included in parallel for determining the overall cytotoxicity of the samples. The specificity of the total mercury sensor Escherichia coli MC1061 (pmerRBlux) bacterial resistance system toward methylmercury is due to a coexpressed specific enzyme, organomercurial lyase. This enzyme mediates the cleavage of the carbon–mercury bond of methylmercury to yield mercury ions, which induce the reporter genes and produce a self-luminescent cell. The selective analysis of methylmercury with the total mercury strain is achieved by specifically chelating the inorganic mercury species from the sample using an optimized concentration of EDTA as a chelating agent. After the treatment with the chelating agent, a cross-reactivity of 0.2% with ionic mercury was observed at nonphysiological ionic mercury concentrations (100 nM). The assay was optimized to be performed in 3 h but results can already be read after 1 h incubation. Total mercury strain E. coli MC1061 (pmerRBlux) has been shown to be highly sensitive and capable of determining methylmercury at a subnanomolar level in optimized assay conditions with a very high dynamic range of two decades. The limit of detection of 75 ng/l (300 pM) allows measurement of methylmercury even from natural samples.     

A Tunable Er3+-Doped Fiber Laser by Use of an Integrated Optics Mach-Zehnder Interferometer

Wavelength tunability of an Er³⁺-doped fiber laser is reported by the use of an integrated optics Mach-Zehnder interferometer driven electro-optically. A pump laser threshold of 5 mW and a continuous tunable band from 1530 nm to 1554 nm are achieved with a drive voltage varying between 0 to +7 volts. An evaluation of the design and improvements are given based on the experimental and theoretical analysis.     

Synthesis and self‐assembly in water of coil‐rod‐coil amphiphilic block copolymers with central π‐conjugated sequence

The purpose of this study is to correlate the nano‐organization in water of coil‐rod‐coil amphiphilic block copolymers constituted of a conjugated segment to their optoelectronic properties. The ABA block copolymer structures, easily achieved via coupling reactions, are based on conjugated rod of dihexylfluorene and 3,4‐ethylenedioxythiophene units linked to two flexible poly(ethylene oxide) or poly[(ethylene oxide)‐ran‐(propylene oxide)] chains. These well‐defined copolymers exhibited a range of specific morphologies in water, a good solvent of coil blocks and a bad solvent of the conjugated rod. Particularly, vesicles and micelles with spherical, cylindrical, or elongated shape were noticed. Correlations were attempted to be established between the weight percent of the conjugated sequence contained in the copolymers, the morphology of the nanostructures obtained by self‐assembly in solution and the resulting optical properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4602–4616, 2008     

N-Pyridinium imidates as new sources of 2-aminoimidazole and imidazoline derivatives

New 2-aminoimidazole (2-AI) and imidazoline derivatives were obtained in three steps through the reduction of N-pyridinium imidates into 1,2-dihydropyridine imidates and oxidative addition of guanidine derivatives. Among the possible transformations, imidate substitution allows selectivity in the last deprotection step, leading to an original 2-aminoimidazolo-imidazoline skeleton.