Influence of Intermolecular Vibrations on the Electronic Coupling in Organic Semiconductors: The Case of Anthracene and Perfluoropentacene

We have performed classical molecular dynamics simulations and quantum‐chemical calculations on molecular crystals of anthracene and perfluoropentacene. Our goal is to characterize the amplitudes of the room‐temperature molecular displacements and the corresponding thermal fluctuations in electronic transfer integrals, which constitute a key parameter for charge transport in organic semiconductors. Our calculations show that the thermal fluctuations lead to Gaussian‐like distributions of the transfer integrals centered around the values obtained for the equilibrium crystal geometry. The calculated distributions have been plugged into Monte‐Carlo simulations of hopping transport, which show that lattice vibrations impact charge transport properties to various degrees depending on the actual crystal structure.     

Synthesis of linear block copolymers from methacrylic monomers using 4,6-di-tert-butyl-N-2,6-diisopropylphenyl)-o-iminobenzoquinone

Polymers based on methacrylic monomers were synthesized using 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-iminobenzoquinone. They can be used for the directed synthesis of linear block copolymers with various compositions in the wide range of molecular weights under conditions of the polymerization according to the mechanism of reversible inhibition. It has been demonstrated that a structure of monomer plays the key role in the synthesis of block copolymers with relatively low values of the polydispersity coefficient. The optimal conditions for the synthesis of linear block copolymers based on methacrylic structures monomers have been revealed.

     

Is the brittle–ductile transition preceding melting related to 5- and 7-membered ring defects in graphite?

The brittle–ductile transition (BDT) is a very general phenomenon in materials science. The temperature T _BDT in numerous materials correlates somewhat with the higher melting temperature T _m. We have earlier proposed the disclination (or rotation-dislocation) as a universal ingredient in the BDT. The present study is exclusively concerned with graphite, where T _m?≈?4000?K. Our conclusion is that the energetics of 5- and 7-membered rings play a crucial role in determining these temperatures. However, experiment is to be invoked, should T _BDT eventually be measured for graphite, so as to decide between various mechanisms, all of which here depend on 5- and 7-membered rings. One mechanism involves interlayer van der Waals coupling, whence a pressure experiment may hold the key.     

Strategies for the Total Synthesis of Clavicipitic Acid

Clavicipitic acid is an ergot alkaloid, which was isolated from Claviceps strain and Claviceps fusiformis. Its unique tricyclic azepinoindole skeleton has attracted synthetic chemists, and various strategies have been developed for its total synthesis. These strategies can be generally categorized into two types based on the synthetic intermediates, namely, 4‐substituted gramine derivatives and 4‐substituted tryptophan derivatives. This Minireview summarizes the reported total syntheses from the point of these two key intermediates     

A Convenient and efficient method for the preparation of 6-Acyl-2(3H)-benzoxazolones

Benzoxazolinone derivatives have been found to exhibit various pharmacological properties and 6-acyl-2(3H)-benzoxazolones are considered as key starting materials for the preparation of these compounds. Reported here are the optimal conditions for a regioselective acylation at the 6-position of the benzoxazolinone ring. A general method leading to the expected products in excellent yields consists in using a mixture of aluminum chloride-dimethylformamide as catalyst and acid anhydrides or chlorides as acylating agents.     

Synthesis of 1,3-cis-Fused Tricyclic System through Regio- and Stereoselective Epoxidation and Ring-Rearrangement Metathesis: Access To Basic Core of Presilphiperfolanols

Here, we report a new synthetic approach to a highly strained 1,3-fused cis-cis-cis-5/5/6 tricyclic system that appeared among the presilphiperfolanol analogues. The cis-fusion of six-membered ring to a diquinane moiety is accomplished by substrate-controlled regio- and stereoselective epoxidation, and ring-rearrangement metathesis (RRM) sequence. In this regard, both early-, and late-stage epoxidation and RRM reactions were studied. The target compound, cis-cis-cis-5/5/6 tricyclic ketone with an α,β-oxirane ring can serve as a key building block to produce various presilphiperfolanol analogues. The cis-cis-cis-5/5/6-tricyclic-α,β-epoxyketone can also act as masked enone and therefore useful for various chemical transformations in organic synthesis. The short synthetic sequence disclosed here may be useful to design various biologically important molecules. The newly reported molecules are well-characterized by NMR, HRMS, and IR spectral data.     

Secretion-Catalyzed Assembly of Protein Biomaterials on a Bacterial Membrane Surface

Protein-based biomaterials have played a key role in tissue engineering, and additional exciting applications as self-healing materials and sustainable polymers are emerging. Over the past few decades, recombinant expression and production of various fibrous proteins from microbes have been demonstrated; however, the resulting proteins typically must then be purified and processed by humans to form usable fibers and materials. Here, we show that the Gram-positive bacterium Bacillus subtilis can be programmed to secrete silk through its translocon via an orthogonal signal peptide/peptidase pair. Surprisingly, we discover that this translocation mechanism drives the silk proteins to assemble into fibers spontaneously on the cell surface, in a process we call secretion-catalyzed assembly (SCA). Secreted silk fibers form self-healing hydrogels with minimal processing. Alternatively, the fibers retained on the membrane provide a facile route to create engineered living materials from Bacillus cells. This work provides a blueprint to achieve autonomous assembly of protein biomaterials in useful morphologies directly from microbial factories.     

Coarse‐grained molecular dynamics simulation study on spherical and tube‐like vesicles formed by amphiphilic copolymers

Molecular‐level understanding of the vesicular structure and formation process is beneficial for potential vesicle applications, especially in drug delivery. In this article, coarse‐grained molecular dynamics simulation was used to study the self‐assembly behavior of amphiphilic poly(acrylic acid)‐b‐polystyrene copolymers in water at different concentrations and PS/PAA block ratios. It was found that various spherical and tube‐like vesicles formed at PS/PAA 3:3 and 4:2. For spherical vesicles, analysis of vesicular structure indicated that the cavity size was influenced by copolymer concentration and wall thickness by the block ratio. Tube‐like vesicle was formed via the fusion of two spherical vesicles, and a key factor for this morphology is polymer movements between inner and outer layer. This simulation study identifies the key factors governing vesicle formation and structure, and provides a guidance to design and prepare various vesicles for wide applications in drug delivery. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1220–1226     

Expedient and Diastereodivergent Assembly of Terpenoid Decalin Subunits having Quaternary Stereocenters through Organocatalytic Robinson Annulation of Nazarov Reagent

We report an expedient approach to highly functionalized cis‐ and trans‐decalines that could function as key structural subunits toward the synthesis of various classes of terpenoids. Key to the strategy is an organocatalyzed Robinson annulation reaction of the Nazarov reagent that affords chiral enone building blocks with high enantioselectivities. The quaternary carbon stereogenic center can direct the subsequent reactions and allow the rapid and diastereoconvergent assembly of complex decalines with contiguous stereocenters.     

Investigation of Masked N-Acyl-N-isocyanates: Support for Oxadiazolones as Blocked N-Isocyanate Precursors

In contrast to carbon-substituted isocyanates that are common building blocks, N-substituted isocyanates remain underdeveloped and reports on their N-acyl derivatives (i. e. amido-isocyanates) are exceedingly rare. Herein, amido-isocyanates were investigated in the context of syntheses of aza-tripeptide and hydantoins subunits starting from simple bench-stable precursors. A key finding is that the amido-isocyanate formed in situ cyclized to yield an oxadiazolone, and that under suitable reaction conditions this heterocycle is a traceless blocked (masked) N-isocyanate. Using organic bases as catalysts and upon heating, oxadiazolone formation is observed, and various nucleophiles to provide the desired aza-dipeptides or hydantoins in moderate to high yields. Further support for an amido-isocyanate intermediate was obtained using carboxylic acids as nucleophiles, affording N-acylhydrazide products.     

A combined mass spectrometry strategy for complete posttranslational modification mapping of Neisseria meningitidis major pilin

Herein, we report a new approach, based on the combination of mass profiling and tandem mass spectrometry, to address the issue of localising all post‐translational modifications (PTMs) on the major pilin protein PiIE expressed by the pathogenic Neisseria species. PilE is the main component of type IV pili; filamentous organelles expressed at the surface of many bacterial pathogens and important virulence factors. Previous reports have shown that PilE can harbour various combinations of PTMs and have established strong links between PTM and pathogenesis. Complete PTM mapping of proteins involved in bacterial infection is therefore highly desirable. The methodology we propose here allowed us to fully characterise the PilE proteoforms of Neisseria meningitidis strain 8013, definitively identifying all PTMs present on all proteoforms and localising their position on the protein backbone. These modifications include a processed and methylated N‐terminus, disulfide bridge, glycosylation and glycerophosphorylation at two different sites. A key element of our approach is high resolution, intact mass measurement of the proteoforms, a piece of information completely lacking in all classical bottom–up proteomics strategies used for PTM analysis and without which it is difficult to ensure complete PTM mapping. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of 3,4-Dihydro-2H-Pyrroles from Ketones,Aldehydes, and Nitro Alkanes via Hydrogenative Cyclization

Syntheses of N-heterocyclic compounds that permit a flexible introduction of various substitution patterns by using inexpensive and diversely available starting materials are highly desirable. Easy to handle and reusable catalysts based on earth-abundant metals are especially attractive for these syntheses. We report here on the synthesis of 3,4-dihydro-2H-pyrroles via the hydrogenation and cyclization of nitro ketones. The latter are easily accessible from three components: a ketone, an aldehyde and a nitroalkane. Our reaction has a broad scope and 23 of the 33 products synthesized are compounds which have not yet been reported. The key to the general hydrogenation/cyclization reaction is a highly active, selective and reusable nickel catalyst, which was identified from a library of 24 earth-abundant metal catalysts.     

Evaluation of heat capacity measurements by temperature-modulated differential scanning calorimetry

Temperature-modulated differential scanning calorimetry (TMDSC) is known to have the ability to measure heat capacity of materials more accurately than the conventional differential scanning calorimeter. However, the accuracy of the measured heat capacity displays significant dependence on various experimental parameters such as period of modulation (p), amplitude of modulation (a), geometry of sample (g), heating rate (r), etc. One of the key features of this system is the ability to measure heat capacity under quasi-isothermal conditions. In the present investigation, heat capacity of a well-established system namely sapphire and thoria was measured by TMDSC under dynamic mode and also under quasi-isothermal mode. The experimental parameters, mentioned above p, a, g, and r are varied to establish the conditions for measuring heat capacity accurately.     

Thermodynamics of the Complexation of the p-Sulfonatocalix[4]arene with Simple Model Guests in Water: a Microcalorimetric Study

The formation of supramolecular complexes in water involves interactions of various types which are not always easy to identify, especially when complicated species are involved. A complete thermodynamic characterization of the binding process, which includes the enthalpies and entropies of complexation, is obviously one of the key elements in identifying the stabilizing factors and in understanding how the host and guest assemble. In order to thermodynamically characterize typical interactions of various types, we have thus undertaken a microcalorimetric study of the complexation of p-sulfonatocalixarenes with simple guests bearing different functional groups. Association constants, free energies, enthalpies and entropies for the complexation of the p-sulfonatocalix[4]arene with normal alcohols, alkylammonium, carboxylate and guanidinium ions in water, at pH 7.5 and 298.15?K, are reported. The properties for the binding of lysine and arginine, which bear similar functional groups, are also given. The comparison of the thermodynamic behaviour of these different guests allows the driving factors to be identified. This may constitute a starting point for the understanding of the recognition of more complicated guests.     

Asymmetric reduction of 7,8-difluoro-3-methyl-2H-1,4-benzoxazine. Synthesis of a key intermediate of (S)-(-)-ofloxacin (DR-3355)

An efficient, highly enantioselective synthesis of (S)-(-)-7,8-difluoro-2,3-dihydro-3-methyl-4H-1,4-benzoxazine, a key intermediate of (S)-(-)-ofloxacin, using various chiral sodium triacyloxyborohydrides as reducing agents is reported.     

Applications of Pillar[n]arene‐Based Supramolecular Assemblies

Macrocycles are an important player in supramolecular chemistry. In 2008, a new class of macrocycles, “pillar[n]arenes”, were first discovered. Research efforts in the area of pillar[n]arenes have elucidated key properties, such as their shape, reaction mechanism, host–guest properties, and their versatile functionality, which has contributed to the development of pillar[n]arene chemistry and their applications to various fields. This Minireview describes how pillar[n]arene‐based supramolecular assemblies can be applied to supramolecular gel formation, reactions, light‐harvesting systems, drug‐delivery systems, biochemical applications, separation and storage materials, and surface chemistry.     

Synthesis and Reaction of Some Indenopyridine and Thieno[2,3-b]Indeno[2,1-e]Pyridine Derivatives

Synthesis of indenopyridine-2-thione derivatives 6a-e via reaction of compound 1 with thioamides 2a-e in good yields. Several thieno[2,3-b]indeno[2,1-e]pyridine 9a-e have been synthesized. Some of them was used as a key intermediate in synthesis of 10-12. On the other hand, compound 1 reacted with various reagents to yield 16, 19, 21-24.     

A Facile Cell Free Synthesis of Isotopically Labeled (E)‐4‐Hydroxy‐3‐methylbut‐2‐enyl Diphosphate,a Precursor of the Plant Hormone Zeatin

(E)‐4‐Hydroxy‐3‐methylbut‐2‐enyl diphosphate ( 1 ) is a key intermediate of the deoxyxylulose phosphate pathway of isoprenoid biosynthesis and a precursor of the plant hormone zeatin. The availability of this intermediate with various labeling patterns is pivotal for its use in biosynthetic studies. The number of positions, however, that can be easily labeled by chemical synthesis is limited, and the synthesis by means of recombinant enzymes is laborious and time consuming. We demonstrated that chromoplasts from Capsicum annuum, whose enzyme activity was impaired by freeze‐thawing, accumulate 1 . This observation built the basis for the development of a cell‐free system allowing the synthesis of this intermediate with labels in various positions. With 2C‐methyl‐D ‐erythritol 2,4‐cyclodiphosphate ( 5 ) as substrate, yields were in the range of 50%.     

Laboratory effects models for interlaboratory comparisons

The statistical analysis of results from inter-laboratory comparisons (for example Key Comparisons, or Supplemental Comparisons) produces an estimate of the measurand (reference value) and statements of equivalence of the results from the participating laboratories. Methods to estimate the reference value have been proposed that rest on the idea of finding a so-called consistent subset of laboratories, that is, eliminating allegedly outlying participants. We propose an alternative statistical model that accommodates all participant data and incorporates the dispersion of the measurement values obtained by different laboratories into the total uncertainty of the various estimates. This model recognizes the fact that the dispersion of values between laboratories often is substantially larger than the measurement uncertainties provided by the participating laboratories. We illustrate the methods on data from key comparison CCQM–K25.