Imaging the Gouy phase shift in photonic jets with a wavefront sensor

A wavefront sensor is used as a direct observation tool to image the Gouy phase shift in photonic nanojets created by micrometer-sized dielectric spheres. The amplitude and phase distributions of light are found in good agreement with a rigorous electromagnetic computation. Interestingly the observed phase shift when travelling through the photonic jet is a combination of the awaited π Gouy shift and a phase shift induced by the bead refraction. Such direct spatial phase shift observation using wavefront sensors would find applications in microscopy, diffractive optics, optical trapping, and point spread function engineering.     

Use of the HS-PTR-MS for online measurements of pyrethroids during indoor insecticide treatments

A high-sensitivity proton transfer reaction mass spectrometer (HS-PTR-MS) has been used to study the temporal evolution of pesticide concentrations in indoor environments. Because of the high time variability of the indoor air concentrations during household pesticide applications, the use of this online high time resolution instrument is found relevant. Four pyrethroid pesticides of the latest generation that are commonly found in electric vaporizer refills, namely, transfluthrin, empenthrin, tetramethrin, and prallethrin, were considered. A controlled pesticide generation system was settled and coupled to a HS-PTR-MS analyzer, and a calibration procedure based on the fragmentation patterns of the protonated molecules was performed. To illustrate the functionality of the method, measurements of the concentration-time profiles of transfluthrin contained in an electric vaporizer were carried out in a full-scale environmental room under air exchange rate-controlled conditions. This study demonstrates that the HS-PTR-MS technique can provide online and high time-resolved measurements of semi-volatile organic compounds such as pyrethroid insecticides.     

Synthesis,Crystal Structure and Hydrogen-Bonding Patterns in (RS)-1-Carbamoyl Pyrrolidine-2-Carboxylic Acid

Abstract  

The title compound, N-carbamoyl-dl-proline, C₆H₁₀N₂O₃, crystallizes in the triclinic P-1 space group with unit cell parameters a = 7.610 (4) Å, b = 9.259 (5) Å, c = 11.749 (7) Å, α = 110.294 (11)°, β = 101.304 (13)°, γ = 91.391 (16)°, with two crystallographically independent molecules in the asymmetric unit. The ureido and carboxyl groups are equatorial and axial to the pyrrolidine rings, respectively. The pyrrolidine rings adopt envelope and twisted conformations in the residue A and B, respectively. The molecules are joined by N–H···O and O–H···O hydrogen bonds into cyclic structures with graph set R ₂²(8), forming infinite chains parallel to the cb plane with graph set C ₂²(14), that are further connected via N–H···O hydrogen bonds into a three-dimensional network.     

Charge collection in amorphous silicon solar cells: Cell analysis and simulation of high-efficiency pin devices

The drift length L_drift = μτE within the i layer of a-Si:H solar cells is a crucial parameter for charge collection and efficiency. It is strongly reduced not only by light-induced reduction of μτ, but also by electric field deformation ΔE by charges near the p–i and i–n interfaces. Here, a simple model is presented to estimate contributions of free carriers, charges trapped in band tails and charged dangling bonds to ΔE. It is shown that the model reproduces correctly trends observed experimentally and by ASA simulations: charged dangling bonds contribute most to ΔE of meta-stable cells. Electrons trapped in the conduction band tail near the i–n interface lead to the strongest field deformation in the initial state, while positively charged dangling bonds near the p–i interface get more important with degradation under AM1.5g spectrum. The measurable parameter V_coll is proposed as an indirect parameter to estimate the electric field, and an experimental technique is presented that could enable the distinction of defects near the p–i and the i–n interfaces.     

Vinyl MIDA boronate: a readily accessible and highly versatile building block for small molecule synthesis

Iterative cross-coupling represents a potentially general approach for the simple, efficient, and flexible construction of natural products, pharmaceuticals, and materials. N-Methyliminodiacetic acid (MIDA) boronates represent a promising platform for the development of this type of synthesis strategy. This report describes the discovery that vinyl MIDA boronate (1) is an air- and chromatographically stable compound that can be conveniently prepared on a multigram scale and serve as a versatile starting material for the preparation of a range of new MIDA boronate building blocks. Analogous to tert-butylethylene, 1 is also an excellent substrate for olefin cross-metathesis, providing access to a range of trans-alkenyl MIDA boronates as single stereoisomers. An improved synthesis of the very versatile bifunctional building block trans-(2-bromovinyl) MIDA boronate (2) is also described. Collectively, these results contribute to the expanding generality of the iterative cross-coupling approach.     

New trans–β–bergamotene derivatives in the root and the flower essential oils of Cyanthillium cinereum (L.) H. Rob. from Côte d’Ivoire

Root and flower essential oils of Cyanthillium cinereum (L.) H. Rob. (Synonym Vernonia cinerea (L.) Less.) (Asteraceae) collected in Southern Côte d’Ivoire was investigated using a combination of chromatographic and spectroscopic techniques. The root oil composition was dominated by trans–β–bergamotene (20.7%), β–elemene (19.0%), cyperene (10.6%), germacrene A (7.1%) and β–pinene (3.8%), whereas γ–humulene (31.0%), (E)–β–caryophyllene (17.0%), trans–β–bergamotene (7.7%), β–pinene (7.5%) and (E)–β–farnesene (6.0%) were the major components of flower oil. Two new compounds bearing the trans–β–bergamotene framework were identified: trans–β–bergamotenone and (E)–trans–β–bergamotenol.     

Characterization of a new epoxy-hydroxycarvotanacetone derivative from the leaf essential oil of Laggera pterodonta from Côte d’Ivoire

The leaf essential oil of Laggera pterodonta (DC.) Sch. Bip. ex Oliv. (Asteraceae) collected in the Eastern Côte d’Ivoire was investigated using a combination of chromatographic (GC-RI, CC, pc-GC) and spectroscopic (GC-MS, ¹³C NMR) techniques. Eighty-three components accounting for 98.0% of the whole composition were identified with 2,5-dimethoxy-p-cymene (43.3%), sabinene (14.1%), α-humulene (9.8%), (E)-β-caryophyllene (7.2%) and germacrene D (5.2%) as major compounds. This study led to the structural elucidation of a new natural compound, (3αH,4βH,6αH,1αMe)-1,6-epoxy-3-hydroxycarvotanacetone, angelic acid ester from the leaf oil by 1D and 2D NMR spectroscopy.     

Stress-induced crystal preferred orientation in the poromechanics of in-pore crystallization

A non-hydrostatic stress field affects the orientation of crystals growing in the pore network of an elastic porous medium. The hypothesis of a hydrostatic state of stress within the crystal has been implicitly made in the recent extension of poromechanics to in-pore crystalization (Coussy, 2006). This underlying hypothesis is revisited on a small-scale conceptual model based on Eshelby's problem and shows that chemo-mechanical equilibrium requires that the crystal adapts its shape and orientation to the far-field stress, therefore resulting at equilibrium in a hydrostatic state of stress within the crystal. The optimum crystal shape as a function of the far-field stress is consistently investigated, highlighting limiting cases. The small scale model allows to understand the macroscopic effects associated with deviatoric stresses in the poromechanics of in-pore crystallization. Moreover, it provides the building block for an up-scaling of the macroscopic tangent poroelastic properties, which depend on both the current crystal saturation and the state of stress. A dilute micromechanical scheme illustrates the variation of the macroscopic Biot's coefficient tensor as a function of deviatoric stresses. A simple configuration akin to a potential laboratory experiment finally illustrates the strong induced anisotropy of the crystallization induced macroscopic strain when deviatoric stresses are applied to the material prior to crystallization.     

Chemical Variability and In Vitro Anti-Inflammatory Activity of Leaf Essential Oil from Ivorian Isolona dewevrei (De Wild. & T. Durand) Engl. & Diels

The chemical variability and the in vitro anti-inflammatory activity of the leaf essential oil from Ivorian Isolona dewevrei were investigated for the first time. Forty-seven oil samples were analyzed using a combination of CC, GC(RI), GC-MS and ¹³C-NMR, thus leading to the identification of 113 constituents (90.8–98.9%). As the main components varied drastically from sample to sample, the 47 oil compositions were submitted to hierarchical cluster and principal components analyses. Three distinct groups, each divided into two subgroups, were evidenced. Subgroup I−A was dominated by (Z)-β-ocimene, β-eudesmol, germacrene D and (E)-β-ocimene, while (10βH)-1β,8β-oxido-cadina-4-ene, santalenone, trans-α-bergamotene and trans-β-bergamotene were the main compounds of Subgroup I−B. The prevalent constituents of Subgroup II−A were germacrene B, (E)-β-caryophyllene, (5αH,10βMe)-6,12-oxido-elema-1,3,6,11(12)-tetraene and γ-elemene. Subgroup II−B displayed germacrene B, germacrene D and (Z)-β-ocimene as the majority compounds. Germacrene D was the most abundant constituent of Group III, followed in Subgroup III−A by (E)-β-caryophyllene, (10βH)-1β,8β-oxido-cadina-4-ene, germacrene D-8-one, and then in Subgroup III−B by (Z)-β-ocimene and (E)-β-ocimene. The observed qualitative and quantitative chemical variability was probably due to combined factors, mostly phenology and season, then harvest site to a lesser extent. The lipoxygenase inhibition by a leaf oil sample was also evaluated. The oil IC₅₀ (0.020 ± 0.005 mg/mL) was slightly higher than the non-competitive lipoxygenase inhibitor NDGA IC₅₀ (0.013 ± 0.003 mg/mL), suggesting a significant in vitro anti-inflammatory potential.