Structure of human transthyretin complexed with bromophenols: a new mode of binding

The binding of two organohalogen substances, pentabromophenol (PBP) and 2,4,6-tribromophenol (TBP), to human transthyretin (TTR), a thyroid hormone transport protein, has been studied by in vitro competitive binding assays and by X-ray crystallography. Both compounds bind to TTR with high affinity, in competition with the natural ligand thyroxine (

Effelsberg Observations of Excited-State (6.0 GHz) OH in Supernova Remnants and W3(OH)

While masers in the 1720 MHz transition of OH are detected toward many supernova remnants (SNRs), no other OH transition is seen as a maser in SNRs. We present a search for masers at 6049 MHz, which has recently been predicted to produce masers by pure collisional excitation at conditions similar to that required for 1720 MHz masing. The Effelsberg 100 m telescope was used to observe the excited-state 6016, 6030, 6035, and 6049 MHz lines of OH toward selected SNRs, most of which have previously-detected bright 1720 MHz masers. No excited-state masers are found toward SNRs, consistent with previous observations of the 6049 MHz and other excited-state transitions. We do not see clear evidence of absorption toward SNR target positions, although we do see evidence of absorption in the molecular cloud at +50 km/s near Sgr A East. Weak absorption is detected at 6016 MHz toward W3(OH), while stronger, narrower emission is seen at 6049 MHz, suggesting that the 6049 MHz emission is a low-gain maser. We conclude that conditions in SNRs are not conducive to excited-state maser emission, especially in excited-state satellite lines.Comment: 4 pages using emulateapj.cls including 2 tables and 1 figure, accepted to ApJ

Doppler-Free Spectroscopy of Weak Transitions: An Analytical Model Applied to Formaldehyde

Experimental observation of Doppler-free signals for weak transitions can be greatly facilitated by an estimate for their expected amplitudes. We derive an analytical model which allows the Doppler-free amplitude to be estimated for small Doppler-free signals. Application of this model to formaldehyde allows the amplitude of experimentally observed Doppler-free signals to be reproduced to within the experimental error.Comment: 7 pages, 7 figures, 1 table, v2: many small improvements + corrected line assignmen

Rotational Cooling of Polar Molecules by Stark-tuned Cavity Resonance

A general scheme for rotational cooling of diatomic heteronuclear molecules is proposed. It uses a superconducting microwave cavity to enhance the spontaneous decay via Purcell effect. Rotational cooling can be induced by sequentially tuning each rotational transition to cavity resonance, starting from the highest transition level to the lowest using an electric field. Electrostatic multipoles can be used to provide large confinement volume with essentially homogeneous background electric field.Comment: 10 pages, 6 figure

The influence of swelling on elastic properties of polyacrylamide hydrogels

Polyacrylamide (PAM) hydrogels are commonly used as substrates for cell mechanical and mechanobiological studies because of their tunable stiffness and ease of handling. The dependence of bulk rheological and local elastic properties (assessed by Atomic Force Microscopy, or AFM) of PAM hydrogels on its composition and polymerization temperature has been extensively studied. PAM hydrogels swell when immersed in media, but the influence of swelling on local elastic properties is poorly characterized. Direct measurements of the effect of swelling on PAM elastic properties are scarce. We report here, for the first time, the direct measurements of volumetric swelling and local elastic properties of PAM gels throughout the post-polymerization swelling process until equilibrium. First, local and global elastic properties (measured by rheology), were obtained during polymerization in the absence of swelling, and showed good agreement with each other. Four PAM hydrogel compositions were characterized thus, with corresponding storage shear moduli (as measured immediately after polymerization) of 4,530 Pa (termed stiffest), 2,900 Pa (stiff), 538 Pa (soft), and 260 Pa (softest). Next, all compositions were subjected to swelling in phosphate buffered saline. Swelling ratios and local elastic moduli were measured at 0, 3, 6, 9, 12, and 24 h post-polymerization for the soft and softest compositions, and once daily till 6 days post-polymerization for all four compositions. For the stiffest and stiff gels, swelling ratio, and local elastic modulus changed negligibly with time, while for the soft and softest gels, substantial changes between Day 0 and Day 1 were found for both swelling ratio (increased by 21.6 and 133%, respectively), and local elastic modulus decreased (by 33.7 and 33.3%, respectively), substantially. Experimental data were analyzed by a model that combined ideal elastomer mechanics and poroelastic swelling kinetics model. Model predictions confirmed the validity of present measurements with respect to past studies where swelling and elastic properties were not measured simultaneously. The present study underlines the important effect swelling can have on PAM elastic properties and provides detailed quantitative data to guide the duration taken to reach equilibrium—a useful information for cell mechanics experiments. In addition, the simultaneous measurements of swelling and local elastic moduli provide novel data for the validation of theoretical models

Enhancing the rheological performance of wheat flour dough with glucose oxidase, transglutaminase or supplementary gluten

The enzymes glucose oxidase and transglutaminase are frequently used to improve the breadmaking performance of wheat flours, as they have the ability to considerably alter the viscoelastic nature of the gluten network. To evaluate a flour’s breadmaking performance, rheological tests offer an attractive framework. In this study, the rheological impact of adding glucose oxidase or transglutaminase to wheat flour dough is investigated by means of linear oscillatory shear tests, creep-recovery shear tests and startup extensional tests. The former tests reveal that the enzymes render the dough stiffer and enhance its elastic character, until saturation is reached. In the breadmaking process, the use of excessive amounts of enzyme is known to be counterproductive. The strain-hardening index clearly reveals this overcross-linking effect. Besides enzymes, the gluten network can also be reinforced by adding supplementary gluten, which was indeed found to enhance the extent of strain-hardening.</p

High resolution lifetime measurements of the perturbed J’=0 levels of the 1B3u state of pyrazine

The lowest excited singlet 1B3u state of pyrazine is known to be coupled to a number of triplet 3B3u states. Using a strongly collimated molecular beam and a single frequency laser it is shown that the J’=0 of the 000 transition contains at least 36 states. We have individually excited eight of these states and studied its decay. The lifetimes found (typically 450 ns) do not scale with the intensities of the excitation spectrum. This deviation is caused by a nonradiative decay of the zero order 3B3u states. With a simple model it was possible to reconstruct the absorption spectrum, the energies of the zero order states and its coupling strengths. The zero order decay rates of the singlet and triplet states have been determined. The value obtained for the zero order singlet state is 5 MHz; the values for the triplet states range from 0.6 to about 5 MHz

Discovery of interstellar mercapto radicals (SH) with the GREAT instrument on SOFIA

We report the first detection of interstellar mercapto radicals, obtained along the sight-line to the submillimeter continuum source W49N. We have used the GREAT instrument on SOFIA to observe the 1383 GHz Doublet Pi 3/2 J = 5/2 - 3/2 lambda doublet in the upper sideband of the L1 receiver. The resultant spectrum reveals SH absorption in material local to W49N, as well as in foreground gas, unassociated with W49N, that is located along the sight-line. For the foreground material at velocities in the range 37 - 44 km/s with respect to the local standard of rest, we infer a total SH column density ~ 2.6 E+12 cm-2, corresponding to an abundance of ~ 7 E-9 relative to H2, and yielding an SH/H2S abundance ratio ~ 0.13. The observed SH/H2S abundance ratio is much smaller than that predicted by standard models for the production of SH and H2S in turbulent dissipation regions and shocks, and suggests that the endothermic neutral-neutral reaction SH + H2 -> H2S + H must be enhanced along with the ion-neutral reactions believed to produce CH+ and SH+ in diffuse molecular clouds.Comment: Accepted for publication in Astronomy and Astrophysics (SOFIA/GREAT special issue

Implications des relations sol-plante en ingénierie écologique des habitats et sols métallifères dégradés: le cas des habitats riches en cuivre du Katanga (République Démocratique du Congo)

International audienceLa restauration écologique des habitats dégradés et des sols nus riches en métaux lourds créés par l'activité minière est devenue aujourd'hui un enjeu environnemental majeur pour réduire l'érosion de la biodiversité et la dégradation des paysages, des sols et de l'eau. Les études de restauration écologique basées sur l'identification des espèces sans faire référence aux traits fonctionnels des plantes sont limitées au réservoir régional des espèces et rendent difficile les interprétations et les applications dans des contextes écologiques variés. En comparant les traits fonctionnels des plantes entre l'habitat métallifère non dégradé et un gradient de succession d'habitats secondaires, il est possible de définir des traits liés à la capacité de colonisation des sols nus riches en métaux lourds. Cette première tentative d'analyse des traits sur les habitats riches en métaux lourds permet ainsi d'identifier les traits candidats pour la phytoremediation. Un des futurs challenges est de créer de nouveaux écosystèmes fonctionnels sur les sols nus contaminés par les métaux lourds e

The importance of non-LTE models for the interpretation of observations of interstellar NO

Context. The ALMA and Herschel missions promise to deliver data of high spatial and spectral resolution at far-infrared and submillimeter wavelengths. Modeling these data will require the knowledge of accurate radiative and collisional rates for species of astrophysical interest. Aims. We calculate the rotational excitation rate coefficients of NO in collisions with He and check the validity of the LTE approach in interpreting observations of rotational lines of NO. Methods. State-to-state rate coefficients between the 360 lowest hyperfine levels of NO were calculated using the M(J) randomizing limit method for temperatures from 10 K to 350 K. We performed calculations of the excitation of NO using the new rate coefficients using a large velocity gradient (LVG) radiative transfer code. Results. The critical densities of the lines are found to be at greater than or similar to 10(15) cm(-3). The low dipole moment of NO ensures that the line emission is optically thin up to column densities of similar to 10(15) cm(-2). Lines in the ground (Omega = 1/2) state are readily detectable in typical conditions (N(NO) = 10(13) cm(-2); T = 10-30 K), whereas lines in the excited Omega = 3/2 state are observed only in warm (T > 50 K) regions with higher column densities (N(NO) = 10(14) cm(-2)). Line ratios of NO may well be used to constrain the ambient temperature and/or density. Conclusions. The new rate coefficients will help significantly in interpreting NO emission lines observed with current and future telescopes, and enable this molecule to become a powerful astrophysical tool