Characterizations of Thermoplastic Block Elastomers Based on Polybutadiene and ε -Caprolactone

A broad series of tri- and multiblock copolymers based on linear and branched oligomers of polybutadiene as central blocks and polycaprolactone (PCL) as block extremities are characterized by SEC, DSC, DMA, Dynamical Rheology and DRX. DSC analyses reveal phase separation between the two amorphous PB and PCL phases. By thermal analysis, the glass transition temperature of PCL is only detected for materials containing at least 80% w/w of PCL. This is attributed to the small length of the polyester blocks for copolymers containing less than 80% w/w of PCL. The increase of fusion heat with increasing PCL content in the copolymers is correlated to the greater ability of PCL chains to rearrange as HTPB amount decrease in the material. Regarding the evolution of the melting temperature of the various copolymers, the characterization by DMA and dynamical rheology confirms the behaviour observed by DSC. Mechanical and rheological properties (i.e., storage modulus and complex viscosities) were studied and reveal that the behavior of the copolymers depends on both the rate of PCL chains and on the nature of the elastomeric block.     

Study of the droplet size effect coupled with the laser light scattering in sprays for two-color LIF thermometry measurements

The present paper deals with a new optical diagnostic that aims to perform droplet temperature measurements based on the two-color laser-induced fluorescence (2cLIF). The 2cLIF requires a single tracer, and the fluorescence intensity is collected on two spectral bands. The ratio of both intensities measured in the case of single monodisperse droplets depends in principle only on the temperature. However, the application in the case of polydispere sprays failed. Indeed, a dependence of the droplet size correlated to the depth of field of the optics, used for fluorescence collection, induces a bias in the ratio value. This work analyses these coupled effects by using combined LIF and Phase Doppler Analyser measurements. This device allows achieving fluorescence ratio measurements per droplet size class. The study is conducted with two different sprays in terms of particles size and density. The use of a third spectral band of detection (3cLIF) and a long distance microscope leads to correct the size effect and reduce the depth of field effect, respectively. These investigations are then demonstrated by measuring temperatures in an overheated water spray.     

FT-Raman spectroscopy: A positive means of evaluating the impact of whale bone preservation treatment

The degreasing methods currently used for osteological collections are not always completely satisfactory. Numerous natural history museums encounter the problem of grease seeping to the surface of bones. FT-Raman spectroscopy was used to characterise cetacean bones, before and after degreasing treatment, in order to evaluate the efficacy of treatment and the impact thereof on bone constituents. The Raman spectra made it possible to monitor the changes in the main bone constituents: the mineral component with the apatite band at 960 cm⁻¹, the organic component with the collagen amide III band at 1270 cm⁻¹ and fat with the lipid CH₂ band at 2850 cm⁻¹. The band associated with lipids decreased and even disappeared with degreasing treatment containing chlorinated solvents. This type of treatment enables fat to be extracted both from the surface and from the bone core; however, it debases the organic component of bone by denaturing collagen. Alternative types of treatment (acetone or enzyme baths) were tested over a limited period, which did not enable their true efficacy to be demonstrated. During the alternative treatments, no bone degradation was observed. Only the acetone solution was able to extract fat, though only from the surface.     

New insight into two-color LIF thermometry applied to temperature measurements of droplets

When laser-induced fluorescence of droplets is used for measurements such as droplet temperature, a new dependence of the droplet size on the spectral distribution of fluorescence has been highlighted. The two-color laser-induced fluorescence technique applied to droplet temperature measurement requires a single fluorescent tracer and two spectral bands of detection for which the temperature sensitivity is different. Generally, the ratio of the intensities measured on each of the spectral bands of detection is assumed to be only temperature dependent. However, droplet dependence on diameter is also likely to influence the intensities ratio. This study provides some illustrations of the phenomenon, first on sprays with different mean statistical diameters and secondly on single droplets, for two temperature-sensitive fluorescent tracers in their solvents: sulforhodamine B dissolved in water and pyrromethene 597-8C9 dissolved in n-decane.     

Wavelength-tunable ultraviolet photodissociation (UVPD) of heparin-derived disaccharides in a linear ion trap

A set of three heparin-derived disaccharide deprotonated ions was isolated in a linear ion trap and subjected to UV laser irradiation in the 220–290 nm wavelength range. The dissociation yields of the deprotonated molecular ions were recorded as a function of laser wavelength. They revealed maximum absorption at 220 nm for the nonsulfated disaccharide, but centered at 240 nm for the sulfated species. The comparison of the fragmentation patterns between ultraviolet photodissociation (UVPD) at 240 nm and CID modes showed roughly the same distribution of fragment ions resulting from glycosidic bond cleavages. Interestingly, UVPD favored additional cross ring cleavages of A and X type ion series enabling easier sulfate group location. It also reduced small neutral losses (H₂O).     

Rh(II) carbene-promoted activation of the anomeric C-H bond of carbohydrates: a stereospecific entry toward α- and β-ketopyranosides

In this communication we report a new strategy toward ketopyranosides based on a carbene-mediated activation of the anomeric C-H bond of carbohydrates. By forming a new carbon-carbon bond after a glycosylation step, this approach enables the preparation of both α- and β-ketopyranosides from advanced precursors.     

Statistical Analysis of Ion Mobility Spectrometry. I. Unbiased and Guided Replica-Exchange Molecular Dynamics

Achieving (bio)macromolecular structural assignment from the interpretation of ion mobility spectrometry (IMS) experiments requires successful comparison with computer modeling. Replica-exchange molecular dynamics simulations with suitable force fields not only offer a convenient framework to locate relevant conformations, especially in the case of multiple-funnel energy landscapes, but they are also well suited to statistical analyses. In the present paper, we discuss two extensions of the method used to improve its efficiency in the context of IMS. Two doubly-protonated polyalanines [RA₄XA₄K + 2H]²⁺ with X = V and D appear as favorable cases for which the calculated collision cross-section distributions naturally agree with the measurements, providing reliable candidate structures. For these compounds, a careful consideration of other order parameters based on the weighted histogram method resolves several otherwise hidden underlying conformational families. In the case of a much larger peptide exhibiting bistability, assignment is more difficult but could be achieved by guiding the sampling with an umbrella potential using the square gyration radius as the biasing coordinate. Applied to triply protonated bradykinine, the two presented methods indicate that different conformations compatible with the measurements are very close in energy.     

Efficient Structural Characterization of Poly(Methacrylic Acid) by Activated-Electron Photodetachment Dissociation

Characterization of end-groups in poly(methacrylic acid) (PMAA) was achieved using tandem mass spectrometry after activated-electron photodetachment dissociation (activated-EPD). In this technique, multiply deprotonated PMAA oligomers produced in the negative-ion mode of electrospray ionization were oxidized into radical anions upon electron photodetachment using a 220 nm laser wavelength, and further activated by collision. In contrast to conventional collision induced dissociation of negatively charged PMAA, which mainly consists of multiple dehydration steps, fragmentation of odd-electron species is shown to proceed via a radical-induced decarboxylation, followed by reactions involving backbone bond cleavages, giving rise to product ions containing one or the other oligomer termination. A single radical-induced mechanism accounts for the four main fragment series observed in MS/MS. The relative position of the radical and of the anionic center in distonic precursor ions determines the nature of the reaction products. Experiments performed using PMAA sodium salts allowed us to account for relative abundances of product ions in series obtained from PMAA, revealing that ion stability is ensured by hydrogen bonds within pairs of MAA units.     

Formation and Characterisation of the Silver Hydride Nanocluster Cation [Ag3H2((Ph2P)2CH2)]+ and Its Release of Hydrogen

Multistage mass spectrometry and density functional theory (DFT) were used to characterise the small silver hydride nanocluster, [Ag₃H₂L]⁺ (where L=(Ph₂P)₂CH₂) and its gas‐phase unimolecular chemistry. Collision‐induced dissociation (CID) yields [Ag₂HL]⁺ as the major product while laser‐induced dissociation (LID) proceeds via H₂ formation and subsequent release from [Ag₃H₂L]⁺, giving rise to [Ag₃L]⁺ as the major product. Deuterium labelling studies on [Ag₃D₂L]⁺ prove that the source of H₂ is from the hydrides and not from the ligand. Comparison of TD‐DFT absorption patterns obtained for the optimised structures with action spectroscopy results, allows assignment of the measured features to structures of precursors and products. Molecular dynamics “on the fly” reveal that AgH loss is favoured in the ground state, but H₂ formation and loss is preferred in the first excited state S₁, in agreement with CID and LID experimental findings. This indicates favourable photo‐induced formation of H₂ and subsequent release from [Ag₃H₂L]⁺, an important finding in context of metal hydrides as a hydrogen storage medium, which can subsequently be released by heating or irradiation with light.