Prompt and Slow Electron‐Detachment‐Dissociation/Electron‐Photodetachment‐Dissociation of a 21‐Mer Peptide

Electron detachment dissociation (EDD) and electron photodetachment dissociation (EPD) are relatively new dissociation methods that involve electron detachment followed by radical‐driven dissociation from multiply deprotonated species. EDD yields prompt dissociation whereas only electron detachment is obtained by EPD; subsequent vibrational activation of the charge‐reduced radical anion is required to obtain the product ions. Herein, the fragmentation patterns that were obtained by EDD and by vibrational activation of the charge‐reduced radical anions that were produced through EDD or EPD (activated‐EDD and activated‐EPD) were compared. The observed differences were related to the dissociation kinetics and/or the contribution of electron‐induced dissociation (EID). Time‐resolved double‐resonance experiments were performed to measure the dissociation rate constants of the EDD product ions. Differences in the formation kinetics were revealed between the classical EDD/EPD ′a^._i/′′x_j complementary ions and some ′a^._i/c_i/′′′z^._j product ions, which were produced with slower dissociation rate constants, owing to the presence of specific neighbouring side chains. A new fragmentation pathway is proposed for the formation of the slow‐kinetics ′a^._i ions.     

Modulating the Ground‐ and Excited‐State Oxidation Potentials of Diaminonaphthalene by Sequential N‐Methylation

A series of 1,5‐diaminonaphthalene derivatives were synthesized and characterized to provide ground‐ and excited‐state electron donors of similar structure but varying potential. Electrochemical and spectroscopic properties of the series are reported and together illustrate two opposing consequences of alkyl substitution on the aryl amines. Inductive effects of methylation are evident from the decrease in ground‐state oxidation potential for derivatives containing monomethylamino substituents. In contrast, steric effects seem to dominate the increase in the ground‐state oxidation potential of derivatives containing dimethylamino substituents since the conformational constraints created by dimethylation suppress delocalization of the nonbonding electrons. Absorption and emission properties also respond to increasing levels of N‐methylation, and the excited‐state oxidation potentials of the parent 1,5‐diaminonaphthalene and its monomethylamine derivatives (ca. ?3.2 V) are approximately 200 mV lower than the corresponding dimethylamino derivatives (?3.0 V).     

Structural polymorphism in poly(dodecamethylen‐di‐O‐methyl‐L‐tartaramide)

Structural characterization of poly(dodecamethylen‐di‐O‐methyl‐L‐tartaramide) was carried out with optical microscopy, thermal analysis, X‐ray diffraction, and electron microscopy. Two different crystalline forms were found in accordance with the thermograms, powder and fiber X‐ray diffraction diagrams. The electron microscopy allows corroboration of the morphological and crystallographic differences. Molecular modeling was used to conclude the structural analogies and differences between the two crystalline forms that were related to the chain packing and orientation in the crystal cell, respectively. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2523–2530, 2002     

Monte‐Carlo simulation of secondary electron emission by x‐ray irradiation—an application of x‐ray absorption near‐edge structure (XANES)

A Monte‐Carlo simulation program has been developed for describing x‐ray absorption near‐edge structure (XANES) observed by synchrotron radiation. The Monte‐Carlo simulation was applied for interpreting XANES spectroscopy on a polycrystalline Ag specimen under synchrotron irradiation with photon energy 3340–3390 eV around the absorption edge of the Ag L_α line at 3352 eV. The results clearly indicate that Monte‐Carlo simulation describes the experimental results with considerable success. Dependence of secondary electron yield on the incident angle of synchrotron radiation was also studied. Copyright © 2004 John Wiley & Sons, Ltd.     

Intrachain versus Interchain Electron Transport in Poly(fluorene‐alt‐benzothiadiazole): A Quantum‐Chemical Insight

Poly(9,9‐di‐n‐octylfluorene‐alt‐benzothiadiazole) [F8BT], displays very different charge‐transport properties for holes versus electrons when comparing annealed and pristine thin films and transport parallel (intrachain) and perpendicular (interchain) to the polymer axes. The present theoretical contribution focuses on the electron‐transport properties of F8BT chains and compares the efficiency of intrachain versus interchain transport in the hopping regime. The theoretical results rationalize significantly lowered electron mobility in annealed F8BT thin films and the smaller mobility anisotropy (μ_∥/μ_⊥) measured for electrons in aligned films (i.e. 5–7 compared to 10–15 for holes).     

Electron‐Beam Irradiation in TEM of Hard‐Segment Homopolymers and Polyurethanes with Different Hard‐Segment Content

Summary: A hard‐segment homopolymer (HSH) and segmented poly(ester urethanes) (PESU) were studied by TEM to estimate their stability against electron‐beam irradiation. The bright‐field image and electron‐diffraction modes in TEM and optical polarised microscopy were used. It is shown that both soft and hard segments are sensitive to the electron beam. None of the films was stable enough to register an electron‐diffraction pattern without damage.

Electron‐diffraction pattern taken from the film of hard‐segment homopolymer crystallised at 100 °C from DMF: (a) the pattern registered immediately; (b) the pattern registered after 5 s of exposure in the TEM at the same place.     

2-萘-(OCH2CH2)n-金刚胺与6-单取代环糊精衍生物的光诱导电子转移反应

A number of naphthalene donor compounds that possess an adamantanamine binding moiety and an (OCH2CH2)n (nn1, 2, 3, 4, 6, 8) spacer were synthesized. The fluorescence quenching between these donor substrates and mono-6-O-p-nitrobenzoyl-β-cyclodextrin (pNBCD) and mono-6-O-m-nitrobenzoyl-β-cyclodextrin(mNBCD) was studied in detail. It was found that very efficient fluorescence quenching could occur in these supramolecular systems. This quenching was attributed to the photoinduced electron transfer inside the supramolecular assembly between the naphthalene donors and cyclodextrin acceptors. Detailed Stern-Volmer constants were measured and they were partitioned into dynamic Stern-Volmer quenching constants and static binding constants. It was demonstrated that the binding constants between all the naphthalene compounds and cyclodextrins are the same as they possess the same binding site, i.e., adamantanamine.     

Base‐Free Generation of Organic Electron Donors from Air‐Stable Precursors

Organic electron donors (OEDs) are powerful reducing agents recognized for their potential in the reduction of challenging substrates and in original applications. Nonetheless, their low stability in atmospheric oxygen or over time complicates their manipulation and storage. To overcome these constraints and enhance OED practicality, new air‐ and moisture‐stable aminopyridinium carboxylate and carbonate precursors were synthesized and thermally activated to generate the potent electron donor in situ. Carboxylate adducts proved to be excellent latent OED systems, enabling the facile and efficient reduction of challenging substrates. Their reduction properties were correlated to their structural characteristics by thermogravimetric and spectroscopic analysis.     

Solvent‐Free Photooxidation of Alkanes by Dioxygen with 2,3‐Dichloro‐5,6‐dicyano‐p‐benzoquinone via Photoinduced Electron Transfer

Photooxidation of alkanes by dioxygen occurred under visible light irradiation of 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ) which acts as a super photooxidant. Solvent‐free hydroxylation of cyclohexane and alkanes is initiated by electron transfer from alkanes to the singlet and triplet excited states of DDQ to afford the corresponding radical cations and DDQ^??, as revealed by femtosecond laser‐induced transient absorption measurements. Alkane radical cations readily deprotonate to produce alkyl radicals, which react with dioxygen to afford alkylperoxyl radicals. Alkylperoxyl radicals abstract hydrogen atoms from alkanes to yield alkyl hydroperoxides, accompanied by regeneration of alkyl radicals to constitute the radical chain reactions, so called autoxidation. The radical chain is terminated in the bimolecular reactions of alkylperoxyl radicals to yield the corresponding alcohols and ketones. DDQ^??, produced by the photoinduced electron transfer from alkanes to the excited state of DDQ, disproportionates with protons to yield DDQH₂.     

Activation of Electron‐Deficient Quinones through Hydrogen‐Bond‐Donor‐Coupled Electron Transfer

Quinones are important organic oxidants in a variety of synthetic and biological contexts, and they are susceptible to activation towards electron transfer through hydrogen bonding. Whereas this effect of hydrogen bond donors (HBDs) has been observed for Lewis basic, weakly oxidizing quinones, comparable activation is not readily achieved when more reactive and synthetically useful electron‐deficient quinones are used. We have successfully employed HBD‐coupled electron transfer as a strategy to activate electron‐deficient quinones. A systematic investigation of HBDs has led to the discovery that certain dicationic HBDs have an exceptionally large effect on the rate and thermodynamics of electron transfer. We further demonstrate that these HBDs can be used as catalysts in a quinone‐mediated model synthetic transformation.     

Surface‐Modifiable Free‐Floating Films Formed by Multiway Connection of Collagen‐Like Triple‐Helical Peptides

Square‐millimeter‐sized free‐floating translucent films are formed in physiological buffer by multiway connections between biotinylated collagen‐like triple‐helical peptides and avidin. Although the compositions of the films are almost constant, regardless of the ratios of the components loaded, their thicknesses can be controlled by the concentrations of the components. The film surfaces can be further modified by taking advantage of exposed biotin (or avidin) functionalities. The self‐assembled films could serve as novel materials in biomedical and biosensing applications.     

Asymmetric Radical–Radical Cross‐Coupling through Visible‐Light‐Activated Iridium Catalysis

Combining single electron transfer between a donor substrate and a catalyst‐activated acceptor substrate with a stereocontrolled radical–radical recombination enables the visible‐light‐driven catalytic enantio‐ and diastereoselective synthesis of 1,2‐amino alcohols from trifluoromethyl ketones and tertiary amines. With a chiral iridium complex acting as both a Lewis acid and a photoredox catalyst, enantioselectivities of up to 99 % ee were achieved. A quantum yield of <1 supports the proposed catalytic cycle in which at least one photon is needed for each asymmetric C? C bond formation mediated by single electron transfer.     

High‐Silica Zeolite SSZ‐61 with Dumbbell‐Shaped Extra‐Large‐Pore Channels

The synthesis of the high‐silica zeolite SSZ‐61 using a particularly bulky polycyclic structure‐directing agent and the subsequent elucidation of its unusual framework structure with extra‐large dumbbell‐shaped pore openings are described. By using information derived from a variety of X‐ray powder diffraction and electron microscopy techniques, the complex framework structure, with 20 Si atoms in the asymmetric unit, could be determined and the full structure refined. The Si atoms at the waist of the dumbbell are only three‐connected and are bonded to terminal O atoms pointing into the channel. Unlike the six previously reported extra‐large‐pore zeolites, SSZ‐61 contains no heteroatoms in the framework and can be calcined easily. This, coupled with the possibility of inserting a catalytically active center in the channel between the terminal O atoms in place of H⁺, afford SSZ‐61 intriguing potential for catalytic applications.     

Three‐Dimensional Characterization of Noble‐Metal Nanoparticles and their Assemblies by Electron Tomography

New developments in the field of nanomaterials drive the need for quantitative characterization techniques that yield information down to the atomic scale. In this Review, we focus on the three‐dimensional investigations of metal nanoparticles and their assemblies by electron tomography. This technique has become a versatile tool to understand the connection between the properties and structure or composition of nanomaterials. The different steps of an electron tomography experiment are discussed and we show how quantitative three‐dimensional information can be obtained even at the atomic scale.     

Ultrahigh‐molecular‐weight‐polyethylene‐fiber surface treatment by electron‐beam‐irradiation‐induced graft polymerization and its effect on adhesion in a styrene–butadiene rubber matrix

Aiming to develop a high‐performance fiber‐reinforced rubber from styrene–butadiene rubber (SBR), we applied a special technique using electron‐beam (EB)‐irradiation‐induced graft polymerization to ultrahigh‐molecular‐weight‐polyethylene (UHMWPE) fibers. The molecular interaction between the grafted UHMWPE fibers and an SBR matrix was studied through the evaluation of the adhesive behavior of the fibers in the SBR matrix. Although UHMWPE was chemically inert, two monomers, styrene and N‐vinyl formamide (NVF), were examined for graft polymerization onto the UHMWPE fiber surface. Styrene was not effective, but NVF was graft‐polymerized onto the UHMWPE fibers with this special method. A methanol/water mixture and dioxane were used as solvents for NVF, and the effects of the solvents on the grafting percentage of NVF were also examined. The methanol/water mixture was more effective. A grafting percentage of 16.4% was the highest obtained. This improved the adhesive force threefold with respect to that of untreated UHMWPE fibers. These results demonstrated that EB irradiation enabled graft polymerization to occur even on the inert surface of UHMWPE fibers. However, the mechanical properties of the fibers could be compromised according to the dose of EB irradiation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2595–2603, 2004     

Interlaboratory study comparing analyses of simulated angle‐resolved X‐ray photoelectron spectroscopy data

An interlaboratory study has been conducted to determine the following: (i) the similarities and differences of film thicknesses and composition profiles obtained from analyses of simulated angle‐resolved X‐ray photoelectron spectroscopy (ARXPS) data by different analysts using different algorithms for data analysis, and (ii) the effects of two assumptions commonly made in data‐analysis algorithms for ARXPS on derived film thicknesses and composition profiles. The analyzed data were generated by the National Institute of Standards and Technology Database for the Simulation of Electron Spectra for Surface Analysis, (SESSA) which provides a simple way to study the influence of the aforementioned effects on compositional depth profile reconstruction. Sets of simulated ARXPS data were produced for thin films of SiO₂, SiON, HfO₂, and HfON of varying thicknesses on a Si substrate. For some HfON films, the N concentration varied with depth. Eleven groups participated in the round robin study. The majority (eight) employed a commercial ARXPS instrument in which the angular distribution is measured for a fixed sample geometry, in contrast to conventional ARXPS in which the sample is tilted for angular variation. The average deviations between the reported average depth, film thickness, and amount of material typically varied between 20% and 30% but were considerably larger, between 30% and 80%, for some cases. The average errors were generally larger for simulations that included elastic scattering and the finite analyzer‐acceptance angle (realistic conditions) than those for simulations that neglected elastic scattering and the finite analyzer‐acceptance angle (simplified conditions). The retrieved N depth profiles were quantitatively different from the true depth profiles and showed substantial variability among the group of members who used the same instrument and analysis software. Copyright © 2014 John Wiley & Sons, Ltd.     

Highly Air‐Stable Electron‐Transport Material for Ink‐Jet‐Printed OLEDs

A novel cross‐linkable electron‐transport material has been designed and synthesized for use in the fabrication of solution‐processed OLEDs. The material exhibits a low LUMO level of ?3.51 eV, a high electron mobility of 1.5×10^?5 cm² V^?1 s^?1, and excellent stability. An average 9.3 % shrinkage in film thickness was observed for the film after thermal curing. A maximum external quantum efficiency (EQE) of 15.6 % (35.0 cd A^?1) was achieved for blue‐phosphorescent OLEDs by spin‐coating and 13.8 % (31.0 cd A^?1) for an ink‐jet‐printed device, both of which are better than the EQE of a control device prepared by vacuum‐deposition (see figure).     

Layered Thiadiazoloquinoxaline‐Containing Long Pyrene‐Fused N‐Heteroacenes

Three thiadiazoloquinoxaline‐containing long pyrene‐fused N‐heteroacenes with 8, 13, and 18 rings were designed and synthesized. They show high electron affinities (EAs) of approximately 4.1 eV, which were derived from the onset of the reduction peaks in cyclic voltammetry. Crystal structure analysis revealed in‐plane extension through close contacts between thiadiazole units as well as layered packing, enabling in‐plane and interlayer electron transport. Organic field‐effect transistor devices provided electron mobilities, which suggest a potential way to enhance the charge transport in long N‐heteroacenes.     

On the Role of Pre‐ and Post‐Electron‐Transfer Steps in the SmI2/Amine/H2O‐Mediated Reduction of Esters: New Mechanistic Insights and Kinetic Studies

The mechanism of the SmI₂‐mediated reduction of unactivated esters has been studied using a combination of kinetic, radical clocks and reactivity experiments. The kinetic data indicate that all reaction components (SmI₂, amine, H₂O) are involved in the rate equation and that electron transfer is facilitated by Brønsted base assisted deprotonation of water in the transition state. The use of validated cyclopropyl‐containing radical clocks demonstrates that the reaction occurs via fast, reversible first electron transfer, and that the electron transfer from simple Sm(II) complexes to aliphatic esters is rapid. Notably, the mechanistic details presented herein indicate that complexation between SmI₂, H₂O and amines affords a new class of structurally diverse, thermodynamically powerful reductants for efficient electron transfer to carboxylic acid derivatives as an attractive alternative to the classical hydride‐mediated reductions and as a source of acyl‐radical equivalents for C?C bond forming processes.