Multipoint laser Doppler vibrometry using holographic optical elements and a CMOS digital camera

A laser Doppler vibrometer (LDV) is described in which holographic optical elements are used to provide the interferometer reference and object illumination beams. A complementary metal-oxide semiconductor camera, incorporating a digital signal processor, is used to carry out real-time signal processing of the interferometer output to allow multipoint LDV to be implemented.     

Direct access to new β-d-galactofuranoconjugates: application to the synthesis of galactofuranosyl-l-cysteine and l-serine

Galactofuranose post-translational modifications, although quite rare, were detected in some biomolecules produced by parasites. While hexopyranosides were already linked to various peptides and proteins, few hexofuranosides have been artificially conjugated to amino acids. We thus report herein a robust glycosylation methodology to obtain S-alkyl, O-serine and S-cysteine-β-d-galactofuranosides starting from readily available galactofuranose donors. O-Acetyl, thioimidoyl and acetimidoyl donors were compared in terms of yields and selectivity when reacted with mercaptans, l-cysteine and l-serine. Acetimidates turned out to be the best notably for amino acids glycosylation.     

Solid-state (55)Mn NMR spectroscopy of bis(μ-oxo)dimanganese(IV) [Mn(2)O(2)(salpn)(2)], a model for the oxygen evolving complex in photosystem II

We have examined the antiferromagneticly coupled bis(μ-oxo)dimanganese(IV) complex [Mn(2)O(2)(salpn)(2)] (1) with (55)Mn solid-state NMR at cryogenic temperatures and first-principle theory. The extracted values of the (55)Mn quadrupole coupling constant, C(Q), and its asymmetry parameter, η(Q), for 1 are 24.7 MHz and 0.43, respectively. Further, there was a large anisotropic contribution to the shielding of each Mn(4+), i.e. a Δσ of 3375 ppm. Utilizing broken symmetry density functional theory, the predicted values of the electric field gradient (EFG) or equivalently the C(Q) and η(Q) at ZORA, PBE QZ4P all electron level of theory are 23.4 MHz and 0.68, respectively, in good agreement with experimental observations.     

Facile syntheses of quater-, penta-, and sexipyrroles

alpha,alpha-Linked oligopyrroles are attractive precursors for both expanded porphyrin and conducting polymer chemistry. We demonstrate facile methods for synthesizing quater-, penta-, and sexipyrroles from more readily available bi- and terpyrrole intermediates. These products demonstrate stability in their brightly colored oxidized forms, while reduction using borohydride reagents gives the corresponding all-pyrrole oligomers, which oxidize readily in air. The oxidized quater- and sexipyrroles were characterized by single-crystal X-ray diffraction analysis.     

Surface stress, kinetics, and structure of alkanethiol self-assembled monolayers

The surface stress induced during the formation of alkanethiol self-assembled monolayers (SAMs) on gold from the vapor phase was measured using a micromechanical cantilever-based chemical sensor. Simultaneous in situ thickness measurements were carried out using ellipsometry. Ex situ scanning tunneling microscopy was performed in air to ascertain the final monolayer structure. The evolution of the surface stress induced during coverage-dependent structural phase transitions reveals features not apparent in average ellipsometric thickness measurements. These results show that both the kinetics of SAM formation and the resulting SAM structure are strongly influenced both by the surface structure of the underlying gold substrate and by the impingement rate of the alkanethiol onto the gold surface. In particular, the adsorption onto gold surfaces having large, flat grains produces high-quality self-assembled monolayers. An induced compressive surface stress of 15.9 +/- 0.6 N/m results when a c(4x2) dodecanethiol SAM forms on gold. However, the SAMs formed on small-grained gold are incomplete and an induced surface stress of only 0.51 +/- 0.02 N/m results. The progression to a fully formed SAM whose alkyl chains adopt a vertical (standing-up) orientation is clearly inhibited in the case of a small-grained gold substrate and is promoted in the case of a large-grained gold substrate.     

Synthesis and reactivity of pyrrolo[3,2-d][1,3]oxazine-2,4-dione. Access to new pyrrolo[3,2-e][1,4]diazepine-2,5-diones

A convenient synthesis of pyrrolo[3,2-d][1,3]oxazine-2,4-dione 4 is described and its reactivity towards various nucleophiles studied. The regioselective ring opening of anhydride 4 or its N-alkylated analog 25 in the presence of alanine or proline afforded, respectively, imidazolidinedione 22 and N-protected pyrrolo[3,2-e][1,4]diazepines 30 and 31 in a one-pot process. In a last part of this study, an alternative route to produce a library of eight non protected pyrrolo[3,2-e][1,4]diazepine-2,5-diones 35a–h is described to overcome the limited reactivity of anhydride 4.     

A stable anionic N-heterocyclic carbene and its zwitterionic complexes

Pyrimidinium beta?nes (1), readily accessible via a straightforward modular synthesis from a formamidine and a monosubstituted malonic acid, are readily deprotonated by nBuLi (or KHMDS) to give the stable carbene species [2]Li+ (abbreviated as maloNHC). The latter represents the archetype of a subgroup of N-heterocyclic carbenes incorporating a malonate as remote anionic functional group within their heterocyclic backbone. While playing the dual role of monodentate 2 e- L type donor and noncoordinating charge carrier X, such ligands are seen to provide a rational route to zwitterionic complexes, as illustrated here by three examples (Rh, Fe, Ag). In particular, the reaction of [2]Li+ with [RhCl(1,5-COD)]2 produces the neutral 14 e- complex Rh(maloNHC)(COD) (3) in which coordinative unsaturation at the metal is relieved in the solid state by an uncommon labile bonding interaction between the Cipso of one of the mesityl arms and the Rh center.     

Adhesive properties of Staphylococcus epidermidis probed by atomic force microscopy

Mapping of the surface properties of Staphylococcus epidermidis and of biofilm forming bacteria in general is a key to understand their functions, particularly their adhesive properties. To gain a comprehensive view of the structural and chemical properties of S. epidermidis, four different strains (biofilm positive and biofilm negative strains) were analyzed using in situ atomic force microscopy (AFM). Force measurements performed using bare hydrophilic silicon nitride tips disclosed similar adhesive properties for each strain. However, use of hydrophobic tips showed that hydrophobic forces are not the driving forces for adhesion of the four strains. Rather, the observation of sawtooth force-distance patterns on the surface of biofilm positive strains documents the presence of modular proteins such as Aap that may mediate cell adhesion. Treatment of two biofilm positive strains with two chemical inhibitor compounds leads to a loss of adhesion, suggesting that AFM could be a valuable tool to screen for anti-adhesion molecules.     

Epoxy composites with ceramic core–shell fillers for thermal management in electrical devices

In this work, a novel core–shell material has been manufactured in order to enhance the thermal conductivity of epoxy‐based composites. The polymer derived ceramics technique has been used to produce fillers whose core is composed of a standard material – silica, and whose outer layer consists of a boron nitride or silicon nitride shell. The synthesized filler was characterized by infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy coupled with an energy dispersive spectroscopy analysis. The successful formation of core–shell structure was proven. Composite samples based on an epoxy resin filled with 31 vol% of synthetized core–shell filler have been investigated in order to determine the effective thermal conductivity of the modified system. The resulting core–shell composite samples exhibited improvements in thermal conductivity of almost 30% in relation to standard systems, making them a promising material for heat management applications. Additionally, the temperature dependence of the thermal conductivity was investigated over a broad temperature range indicating that the thermal behavior of the composite with incorporated core–shell filler is stable. This stability is a crucial factor when considering the potential of using this technology in applications such as electronics and power systems. Copyright © 2017 John Wiley & Sons, Ltd.