Synthesis of Heptagon-Containing Polyarenes by Catalytic C−H Activation

Nanocarbons incorporating non-hexagonal aromatic rings - such as five-, seven-, and eight-membered rings - have various intriguing physical properties such as curved structures, unique one-dimensional packing, and promising magnetic, optical, and conductivity properties. Herein, we report an efficient synthetic approach to polycyclic aromatics containing seven-membered rings via a palladium-catalyzed intramolecular Ar−H/Ar−Br coupling. In addition to all-hydrocarbon scaffolds, heteroatom-embedded heptagon-containing polyarenes can be efficiently constructed with this method. Rhodium- and palladium-catalyzed sequential six- and seven-membered ring formations also afford complex heptagon-containing molecular nanocarbons from readily available arylacetylenes and biphenyl boronic acids. Detailed mechanistic analysis by DFT calculations showed the feasibility of seven-membered ring formation by a concerted metalation-deprotonation mechanism. This reaction can serve as a template for the synthesis of a wide range of seven-membered ring-containing molecular nanocarbons.     

First total synthesis of cyclic pentadepsipeptides Hikiamides A–C

The first total syntheses of naturally occurring cyclodepsipeptides Hikiamides A–C are described. The key linear pentapeptide precursors, prepared efficiently via Fmoc-solid-phase synthesis, were cyclized in dilute solution to provide the target Hikiamides A–C. The structures of the synthetic Hikiamides A–C were characterized by NMR and HRMS spectroscopy which were in agreement with those of natural products.     

A Quintuple [6]Helicene with a Corannulene Core as a C5‐Symmetric Propeller‐Shaped π‐System

The synthesis and structural analysis of a quintuple [6]helicene with a corannulene core is reported. The compound was synthesized from corannulene in three steps including a five‐fold intramolecular direct arylation. X‐ray crystallographic analysis revealed a C₅‐symmetric propeller‐shaped structure and one‐dimensional alignment in the solid state. The enantiomers of the quintuple [6]helicene were successfully separated by HPLC, and the chirality of the two fractions was identified by CD spectroscopy. A kinetic study yielded a racemization barrier of 34.2 kcal mol^?1, which is slightly lower than that of pristine [6]helicene. DFT calculations indicate a rapid bowl‐to‐bowl inversion of the corannulene moiety and a step‐by‐step chiral inversion pathway for the five [6]helicene moieties.     

Directing Aluminum Atoms into Energetically Favorable Tetrahedral Sites in a Zeolite Framework by Using Organic Structure‐Directing Agents

The Al location in zeolites can have massive influences on the zeolite properties because it directly correlates with the cationic active sites. Herein, the synthesis of IFR zeolites with controlled Al distribution at different tetrahedral sites (T sites) is reported. The computational calculations suggest that organic structure‐directing agents (OSDAs) used for zeolite synthesis can alter the energetically favorable T sites for Al. Zeolite products synthesized under identical conditions but with different OSDAs are found to have altered fractions of Al at different T sites in accordance with the energies derived from the zeolite–OSDA complexes. Our finding thus provides evidence for the ability of OSDAs to direct Al into more energetically favorable T sites, thereby offering rational synthetic guidelines for the selective placement of Al into specific crystallographic sites.     

Gas permeability and permselectivity of fluorinated polybenzoxazoles

Gas permeability and permselectivity are investigated for polybenzoxazoles from bis(3-amino-4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropane (BAHHP) and aromatic diacid chlorides. Effects of thermal cyclization on the permeation properties are also investigated. The polybenzoxazole from BAHHP and 4,4′-(1,1,1,3,3,3-hexafluoroisopropylidene)dibenzoyl chloride (HFDB) displays high performance for CO₂/CH₄ separation ( $ {\rm P}_{{\rm CO}_2 } $ = 6.1 × 10^?9 cm³ (STP) cm^?1 s^?1 cm-Hg^?1, and $ {{{\rm P}_{{\rm CO}_2 } } \mathord{\left/ {\vphantom {{{\rm P}_{{\rm CO}_2 } } {{\rm P}_{{\rm CH}_4 } }}} \right. \kern-\nulldelimiterspace} {{\rm P}_{{\rm CH}_4 } }} $ = 38 at 35°C). The polybenzoxazole from BAHHP and 2,6-naphthalene dicarbonyl chloride displays high performance for H₂/CO or H₂/CH₄ separation ( $ {\rm P}_{{\rm H}_2 } $ = 2.4 × 10^?9 cm³ (STP) cm^?1 s^?1 cm-Hg^?1, $ {{{\rm P}_{{\rm H}_2 } } \mathord{\left/ {\vphantom {{{\rm P}_{{\rm H}_2 } } {{\rm P}_{{\rm CO}} }}} \right. \kern-\nulldelimiterspace} {{\rm P}_{{\rm CO}} }} $ = 71, and $ {{{\rm P}_{{\rm H}_2 } } \mathord{\left/ {\vphantom {{{\rm P}_{{\rm H}_2 } } {{\rm P}_{{\rm CH}_{\rm 4} } }}} \right. \kern-\nulldelimiterspace} {{\rm P}_{{\rm CH}_{\rm 4} } }} $ = 250). Permeation properties for the polybenzoxazole from BAHHP and HFDB are close to those for a polyimide of similar chemical structure. The permeation properties are discussed in connection with packing density and local segmental mobility. © 1992 John Wiley & Sons, Inc.     

Bifurcation approach to a logistic elliptic equation with a homogeneous incoming flux boundary condition

In this paper, we consider a semilinear elliptic boundary value problem in a smooth bounded domain, having the so-called logistic nonlinearity that originates from population dynamics, with a nonlinear boundary condition. Although the logistic nonlinearity has an absorption effect in the problem, the nonlinear boundary condition is induced by the homogeneous incoming flux on the boundary. The objective of our study is to analyze the existence of a bifurcation component of positive solutions from trivial solutions and its asymptotic behavior and stability. We perform this analysis using the method developed by Lyapunov and Schmidt, based on a scaling argument.     

DNA PHOTOREACTIVATING ENZYME FROM SILKWORM

An ammonium-sulfate-precipitable (33–70%) fraction in extracts from eggs of silkworm Bombyx mori contains photoreactivating enzyme that reactivates the transforming activity of UV inactivated Hemophilus influenzae DNA. The action spectrum for in vitro photoreactivation with the enzyme has a broad peak around 365–385 nm, with a shoulder extending to 460 nm. This relatively higher photoreactivation efficiency at wavelengths longer than 450 nm seems to be a unique feature of DNA photoreactivating enzyme of silkworm. Using gel filtration, a mol wt of 42,000 was estimated for the enzyme. Optimum and isoionic pH of the enzyme were 7.2 and 5.4, respectively. These properties of silkworm enzyme are within the range of variations in reported biochemical characteristics of photoreactivating enzymes from different species.     

An indefinite concave-convex equation under a Neumann boundary condition I

We investigate the problem (P _λ) ?Δu = λb(x)|u| ^q?2 u + a(x)|u| ^p?2 u in Ω, ?u/?n = 0 on ?Ω, where Ω is a bounded smooth domain in R ^N (N ≥ 2), 1 < q < 2 < p, λ ∈ R, and a, b ∈ \({C^\alpha }\left( {\overline \Omega } \right)\) with 0 < α < 1. Under certain indefinite type conditions on a and b, we prove the existence of two nontrivial nonnegative solutions for small |λ|. We then characterize the asymptotic profiles of these solutions as λ → 0, which in some cases implies the positivity and ordering of these solutions. In addition, this asymptotic analysis suggests the existence of a loop type component in the non-negative solutions set. We prove the existence of such a component in certain cases, via a bifurcation and a topological analysis of a regularized version of (P _λ).     

On eigenvalue problems with Robin type boundary conditions having indefinite coefficients

A Robin type boundary condition with a sign-changing coefficient is treated. First, the associated linear elliptic eigenvalue problem is studied, where the existence of a principal eigenvalue is discussed by the use of a variational approach. Second, the associated semilinear elliptic boundary value problem of logistic type is studied and the one parameter-dependent structure of positive solutions is investigated, where results obtained are due to the construction of suitable super- and subsolutions by using the principal positive eigenfunctions of the linear eigenvalue problem.