Equilibrium vs ground-state planarity of the CONH linkage

Planarity of the XC(=)NHY linkage has been investigated in unprecedented detail in a number of relatively simple compounds, including formamide (X = Y = H), acetamide (X = CH3, Y = H), urea (X = NH2, Y = H), carbamic acid (X = OH, Y = H), and methyl carbamate (X = OCH3, Y = H). Reliable estimates of the equilibrium structures of formamide, cyanamide, acetamide, urea, carbamic acid, methylamine, dimethyl ether, and methyl carbamate are derived, mostly for the first time. It is shown that formamide, considered prototypical for the amide linkage, is not typical as it has a planar equilibrium amide linkage corresponding to a single-minimum inversion potential around N. In contrast, several molecules containing the CONH linkage seem to have a pyramidalized nitrogen at equilibrium and a double-minimum inversion potential with a very small inversion barrier allowing for an effectively planar ground-state structure. Observables of rotational spectroscopy, including ground-state inertial defects, quadrupole coupling and centrifugal distortion constants, and dipole moment components, as well as equilibrium C=O and C-N bond lengths are reviewed in their ability to indicate the planarity of the effective and possibly the equilibrium structures.     

Peptide shifter: Enhancing separation reproducibility using correlated expression profiles

Chromatographic protein and peptide separation technologies enable comprehensive proteomic analysis of plasma and other complex biological samples by mass spectrometry. However, as the number of separations and/or fractions increases, so does the number of peptides split across fraction boundaries. Irreproducibility of peptide chromatographic separation results in peptides on or near the boundary moving partially or entirely into adjacent fractions. Peptide shifting across fraction boundaries increases the variability of measured peptide abundance, and so there is a trade-off between proteomic comprehensiveness using separation technologies and accurate quantitative proteomic measurements. In this paper, a method for detecting and correcting split peptides, called Peptide Shifter, is introduced and evaluated. An essential component of Peptide Shifter is a global peptide expression profile analysis that allows the inference of the underlying peptide shift pattern without the use of peptide labeling or internal standards. A controlled proteomic analysis of plasma samples demonstrates a 34% decrease in peptide intensity variability after the application of Peptide Shifter.     

Shot-noise-limited operation of a monomode high-cavity-finesse semiconductor laser for microwave photonics applications

Shot-noise-limited laser operation over a wide spectral bandwidth is demonstrated by using a semiconductor active medium inserted into a high-Q external cavity. This approach ensures, with a compact design, a sufficiently long photon lifetime to reach the oscillation-relaxation-free class A regime. The laser relative intensity noise is limited to the shot-noise relative floor, -156 dB/Hz for a 1 mA detected photocurrent, over the 100 MHz to 18 GHz bandwidth. The optimization of the laser cavity is discussed, and convenient shot-noise-limited operation is shown to be a trade-off between the cavity length and laser mode filtering.     

Influence of core materials on thermal properties of melamine-formaldehyde microcapsules

A series of melamine-formaldehyde microcapsules as an intrinsic intumescent system was prepared by an in situ polymerization. The structural and thermal properties of the resultant microcapsules were studied. The surface morphology and chemical structure of microcapsules were investigated using scanning electron microscope (SEM), and Fourier-transform infrared spectroscope (FT-IR), respectively. The thermal properties of samples were investigated by thermogravimetric analysis (TGA) and by differential scanning calorimetry (DSC). The results showed that the thermo-physical properties are strongly dependant on the nature core content and the synthesis conditions. From the thermal analysis, it was concluded that microcapsules containing di-ammonium hydrogen phosphate exhibits characteristics of an intumescent system during their thermal degradation and could be interpreted due to the interaction between phosphate and melamine.     

Small-angle neutron scattering study of microemulsion-polymer mixtures in the protein limit

Contrast variation small-angle neutron scattering (SANS) has been employed to study complex fluids comprising model microemulsions and polymers. The systems are water-in-oil microemulsions with added non-adsorbing polymer, under good polymer solvency conditions and semidilute polymer concentrations. The polymer/colloid size ratio was q approximately 11, which is well within the "protein limit". Four scattering contrasts were produced by selective deuteration of the dispersed and continuous phases and also the surfactant. In this way, the separate partial structure factors (PSF) for colloid-colloid (c-c), polymer-polymer (p-p), and colloid-polymer (c-p) have been obtained. The c-c PSF has been compared with theoretical predictions, allowing determination of a polymer correlation length. This is compared with a similar correlation length obtained from the p-p PSF, which is shown to increase with colloid concentration. In this sense, adding microemulsion has a similar effect on the dissolved polymer as reducing the solvent quality, and an effective Flory-Huggins chi parameter has been calculated. The cross-term PSF shows a distinct anti-correlation. This is the first time such structure factors have been determined experimentally for colloid-polymer systems in the protein limit and these allow a more detailed understanding of the structural interactions in these systems.     

Effect of solvent quality on aggregate structures of common surfactants

Aggregate structures of two model surfactants, AOT and C12E5 are studied in pure solvents D2O, dioxane-d8 (d-diox) and cyclohexane-d12 (C6D12) as well as in formulated D2O/d-diox and d-diox/C6D12 mixtures. As such these solvents and mixtures span a wide and continuous range of polarities. Small-angle neutron scattering (SANS) has been employed to follow an evolution of the preferred aggregate curvature, from normal micelles in high polarity solvents, through to reversed micelles in low polarity media. SANS has also been used to elucidate the micellar size, shape as well as to highlight intermicellar interactions. The results shed new light on the nature of aggregation structures in intermediate polarity solvents, and point to a region of solvent quality (as characterized by Hildebrand Solubility Parameter, Snyder polarity parameter or dielectric constant) in which aggregation is not favored. Finally these observed trends in aggregation as a function of solvent quality are successfully used to predict the self-assembly behavior of C12E5 in a different solvent, hexane-d14 (C6D14).     

Formation of surfactant-stabilized silica organosols

Organosols comprising silica nanoparticles, stabilized by adsorbed surfactant layers in low dielectric organic solvents were formulated, and their properties studied. A range of different methods for organosol formation starting from aqueous sols were evaluated and compared, in order to determine the most reliable and reproducible approach. To understand the influence of surfactant type and solvent on stability, samples were prepared with a range of surfactants and in different solvents and solvent blends. Structural properties and interparticle interactions were probed using dynamic light scattering (DLS), zeta potentials were determined, and the surfactant layers were investigated with contrast-variation SANS. SANS data suggest that for systems stabilized by ionic surfactants, the nanoparticles are in equilibrium with a population of reverse micelles, but this is apparently not the case for those stabilized by nonionic surfactants. Low zeta potentials show evidence of a small amount of surface charging in these nonaqueous systems, although it is unlikely to have any significant effect on their overall stability.     

FTIR of touch imprint cytology: a novel tissue diagnostic technique

Fourier transform infrared spectroscopic (FTIR) interrogation of biological tissues in real time has largely been a challenging proposition because of the strong absorption of mid-infrared light in water filled tissues. To enable sampling of tissues they must be sectioned and dried, which has time and resource implications. FTIR of touch imprint cytology (TIC) has been proposed to circumvent this problem. TIC is a well known histopathological method of rapidly analysing biological tissues. In this article we demonstrate the ability of FTIR of TIC to provide detailed spectra which can be used to differentiate various tissue pathologies. FTIR spectral profiles of TIC of lymph node and thyroid tissues differ visually when compared with TIC spectra of parathyroid tissue. The lymph node showed strong lipid spectral peaks at 1166cm(-1) and 1380cm(-1) including a very strong carbonyl-ester band at 1748cm(-1), and a strong methylene bending band (scissoring, at 1464cm(-1)). Smaller intensity protein peaks at 1547cm(-1) and 1659cm(-1) were also seen. The thyroid spectra, in addition to evident strong protein peaks at 1547cm(-1) and 1659cm(-1), also demonstrated possible nucleic acid signals at 1079cm(-1) and 1244cm(-1). The C-OH peak at 1037cm(-1) was attributed to carbohydrate signals. Parathyroid adenoma showed a marginal shift to lower wavenumbers with decreased amide I and II peak intensities when compared to hyperplasia. Nucleic acid peak positions at 1079cm(-1) and 1244cm(-1) were of higher intensity in adenomas compared to hyperplastic glands possibly demonstrating an increase in cell proliferation and growth. This study demonstrates the feasibility of cytoimprint FTIR for the intraoperative diagnosis of tissue during surgical neck exploration for the management of hyperparathyroidism. There is potential for the application of the technique in sentinel lymph node biopsy diagnosis and tumour margin evaluation.     

Validation of gravimetry for high-accuracy analysis of uranium

Journal of Radioanalytical and Nuclear Chemistry - Gravimetry after calcination is an assay method for determining the quantity of a given element from the mass measurement. This method, adapted...     

Quantifying the Interactions in the Aggregation of Thermoresponsive Polymers: The Effect of Cononsolvency

The aggregation kinetics of thermoresponsive core–shell micelles with a poly(N‐isopropyl acrylamide) shell in pure water or in mixtures of water with the cosolvents methanol or ethanol at mole fractions of 5% is investigated during a temperature jump across the respective cloud point. Characteristically, these mixtures give rise to cononsolvency behavior. At the cloud point, aggregates are formed, and their growth is followed with time‐resolved small‐angle neutron scattering. Using the reversible association model, the interaction potential between the aggregates is determined from their growth rate in dependence on the cosolvents. The effect of the cosolvent is attributed to the interaction potential on the structured layer of hydration water around the aggregates. It is surmised that the latter is perturbed by the cosolvent and thus the residual repulsive hydration force between the aggregates is reduced. The larger the molar volume of the cosolvent, the more pronounced is the effect. This framework provides a molecular‐level understanding of solvent‐mediated effective interactions in polymer solutions and new opportunities for the rational control of self‐assembly in complex soft matter systems.