Electro‐Optic (E‐O) Molecular Glasses

This Focus Review describes molecular glasses as a new class of materials for nonlinear optical (NLO) applications, especially for electro‐optic (E‐O) devices. Examples of E‐O molecular glasses are reviewed with a focus on the molecular design of NLO chromophores and solid‐state engineering of molecular glasses. Molecular glasses based on dendrimers of multiple chromophores, molecular glass blends of chromophores, and molecular glasses based on reversible self‐assembly of chromophores are introduced as promising architectures to prepare morphologically stable molecular glasses with large E‐O activities and improved material properties for device applications. Future directions to fully exploit the potential of molecular glasses for NLO materials are presented.     

Potent E‐Selectin Antagonists

In the search for drugs that could control excessive leukocyte extravasation, we now report on modifications of the already known potent E‐selectin antagonist 3 containing a cyclohexyllactic acid residue and a glucal‐derived building block. Thus, we describe the synthesis and biological evaluation of a series of derivatives 6 with modified glucal‐derived moieties (CH₂NR¹R² instead of CH₂OH in 3 ) to explore a hypothetical potential complementary interaction with E‐selectin. However, similar activity profiles of most derivatives 6 and compound 3 do not support such an interaction, but rather indicate topological‐structure changes of 6 (and 3 ) in the orientation of the neighboring fucose and galactose due to intramolecular steric interactions. The most potent E‐selectin antagonist 6v showed >50‐fold improved E‐selectin inhibition compared to the weak selectin ligand sialyl Lewis^x (sLe^x, 1 ; IC₅₀=1000 – 1500 μM ), but only a 2‐fold improvement compared to 3 . Compound 6x was tested in vivo in a murine model of acute inflammation and found to be as potent as 3 (ED₅₀=15 mg/kg).     

An Alkene‐Promoted Borane‐Catalyzed Highly Stereoselective Hydrogenation of Alkynes to Give Z‐ and E‐Alkenes

The stereoselective hydrogenation of alkynes to alkenes is an extremely useful transformation in synthetic chemistry. Despite numerous reports for the synthesis of Z‐alkenes, the hydrogenation of alkynes to give E‐alkenes is still not well resolved. In particular, selective preparation of both Z‐ and E‐alkenes by the same catalytic hydrogenation system using molecular H₂ has rarely been reported. In this paper, a novel strategy of using simple alkenes as promoters for the HB(C₆F₅)₂‐catalyzed metal‐free hydrogenation of alkynes was adopted. Significantly, both Z‐ and E‐alkenes can be furnished by hydrogenation with molecular H₂ in high yields with excellent stereoselectivities. Further experimental and theoretical mechanistic studies suggest that interactions between H and F atoms of the alkene promoter, borane intermediate, and H₂ play an essential role in promoting the hydrogenolysis reaction.     

Dimedone‐catalyzed Addition of Amines into Cyano Group: Facile Synthesis of Thiazol‐2‐yl Substituted E‐Acrylonitriles

An efficient dimedone‐catalyzed synthesis of highly functionalized thiazol‐2‐yl substituted E‐acrylonitrile derivatives has been established through two‐step reaction of α‐thiocyanate ketones with malononitrile and amines. The α‐thiocyanate ketones were subjected with malononitrile to provide thiazol‐2‐ylidenemalononitrile derivatives, followed with various amines in the present of dimedone to yield the final thiazol‐2‐yl substituted acrylonitrile derivatives.     

Investigation of a waterborne epoxy for E‐glass composites

We present a continuing investigation of epoxies based on diglycidyl ether of bisphenol A cured with 2‐ethyl‐4‐methylimidazole in the presence of the nonionic surfactant Triton X‐100. Interest in this epoxy system is due partially to its potential application as a waterborne replacement for solvent‐cast epoxies in E‐glass‐laminated printed circuit boards. The surfactant additive could potentially alter the interfacial properties and durability of composite materials. Previous studies revealed that the viscoelastic behavior of the cured epoxy is altered when it serves as the matrix in a glass‐fiber‐reinforced composite. The additional constraining and coupling of the E‐glass fibers to the segmental motion of the epoxy matrix results in an apparent increased level of viscoelastic cooperativity. Current research has determined that the cooperativity of an epoxy/E‐glass composite is also sensitive to the surface chemistry of the glass fibers. Model epoxy/E‐glass composites were constructed in which the glass was pretreated with either 3‐aminopropyltriethoxysilane or 3‐glycidoxypropyltrimethoxysilane coupling agents. Dynamic mechanical analysis was then used to create master curves of the storage modulus in the frequency domain. The frequency response of the master curves and resulting cooperativity plots clearly varied with the surface pretreatment of the glass fibers. The surfactant had surprisingly little effect in the observed trends in the cooperativity of the composites. However, the changes in cooperativity due to the surface pretreatment of the glass were lessened when the samples were prepared from waterborne emulsions. Moisture‐uptake experiments were also performed on epoxy samples that were filled with spherical glass beads as well as multi‐ply laminated composites. No increases in the diffusion constant could be attributed to the surfactant. However, the surfactant did enhance the final equilibrium moisture‐uptake levels. These equilibrium moisture‐uptake levels were also sensitive to the surface pretreatment of the E‐glass. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2351–2365, 2000     

Density functional theory and RRKM calculations of decompositions of the metastable E‐2,4‐pentadienal molecular ions

The potential energy profiles for the fragmentations that lead to [C₅H₅O]⁺ and [C₄H₆]^+? ions from the molecular ions [C₅H₆O]^+? of E‐2,4‐pentadienal were obtained from calculations at the UB3LYP/6‐311G + + (3df,3pd)//UB3LYP/6‐31G(d,p) level of theory. Kinetic barriers and harmonic frequencies obtained by the density functional method were then employed in Rice–Ramsperger–Kassel–Marcus calculations of individual rate coefficients for a large number of reaction steps. The pre‐equilibrium and rate‐controlling step approximations were applied to different regions of the complex potential energy surface, allowing the overall rate of decomposition to be calculated and discriminated between three rival pathways: C? H bond cleavage, decarbonylation and cyclization. These processes should have to compete for an equilibrated mixture of four conformers of the E‐2,4‐pentadienal ions. The direct dissociation, however, can only become important in the high‐energy regime. In contrast, loss of CO and cyclization are observable processes in the metastable kinetic window. The former involves a slow 1,2‐hydrogen shift from the carbonyl group that is immediately followed by the formation of an ion‐neutral complex which, in turn, decomposes rapidly to the s‐trans‐1,3‐butadiene ion [C₄H₆]^+?. The predominating metastable channel is the second one, that is, a multi‐step ring closure which starts with a rate‐limiting cis—trans isomerization. This process yields a mixture of interconverting pyran ions that dissociates to the pyrylium ions [C₅H₅O]⁺. These results can be used to rationalize the CID mass spectrum of E‐2,4‐pentadienal in a low‐energy regime. Copyright © 2010 John Wiley & Sons, Ltd.     

E‐MALDI: optimized conditions during electrowetting‐enhanced drop drying for MALDI‐MS

We recently showed that electrowetting‐enhanced sample preparation for MALDI‐MS (eMALDI) can increase the intensity of the MALDI signal by 2–25 times compared with conventional drop drying by concentrating all the dried sample in a single spot rather than leaving behind a heterogeneous coffee‐stain pattern. Here, we demonstrate that the eMALDI signal enhancement can be further increased to more than 100 times by systematically optimizing the electrowetting actuation frequency and amplitude. This enables 30 times signal increase for a peptide standard. Simultaneously, drop drying times can be reduced approximately five times by increasing the actuation voltage and/or decreasing the initial drop volume. Copyright © 2017 John Wiley & Sons, Ltd.     

Crystallographic report: 2,4‐Diphenyl‐1,3‐bis(4,4,5,5‐tetramethyl[1,3,2] dioxaborolan‐2‐yl)‐buta‐1Z,3E‐diene

The compound comprises a 1Z,3E‐butadiene moiety substituted by two pinacol boronate functional groups. Copyright © 2005 John Wiley & Sons, Ltd.     

1H‐HRMAS NMR study of cold smoked Atlantic salmon (Salmo salar) treated with E‐beam

¹H High resolution magic angle spinning (HRMAS) NMR spectroscopic data in combination with principal components analysis and analysis of variance were used to differentiate between irradiated and non‐irradiated cold‐smoked Atlantic salmon (Salmo salar). NMR profiling was obtained, with a spectral acquisition time of less than 8 min, from a small sample size of intact white salmon muscle, by non‐destructive analysis that includes a very simple and rapid sample preparation step. Results obtained enable the use of creatine, trimethylamine oxide and the sum of phosphorylcholine and glycerophosphorylcholine as diagnostic compounds to detect irradiation treatment. This study shows the potential of ¹H‐HRMAS to be a rapid method for investigating compositional changes due to food processing as well as to confirm the presence or absence of some bioactive compounds in irradiated samples. Copyright © 2013 John Wiley & Sons, Ltd.