A Unified Strategy to 6–5–6–5–6‐Membered Epipolythiodiketopiperazines: Studies towards the Total Synthesis of Scabrosin Diacetate and Haematocin

The family of epipolythiodiketopiperazine (ETP) natural products consists of over 200 members possessing a wide diversity of structures and biological activity. Recently, the subgroup of 6–5–6–5–6‐membered ETPs has gained substantial attention, which has resulted in several total syntheses. Despite all the efforts that have been invested into accessing these complex structures, no synthesis of scabrosin diacetate ( 1 a ) and its related esters has been reported. Herein, our attempts towards scabrosin diacetate ( 1 a ) and haematocin ( 3 ) starting from diketopiperazine 12 a as a late‐stage intermediate are presented. Diketopiperazine 12 a can be conveniently accessed in multigram quantities from aldehyde 18 and diketopiperazine 21 and was envisioned to serve as a general platform for the synthesis of 6–5–6–5–6‐membered ETPs.     

Improving the mechanical properties of CNF films by NMMO partial dissolution with hot calender activation

Reinforcing of cellulose nanofibril (CNF) films by partial dissolution with N-methylmorpholine-N-oxide (NMMO) was investigated. The method investigated is composed of impregnation of CNF film with liquid solution of NMMO followed by dry heat activation. The heat activation of the impregnated film was carried out using a heated calendering nip, which enabled simultaneous heating and compression. The partial dissolution of cellulose by NMMO caused a significant increase in the transparency of CNF film due to the decrease of film porosity and increased surface smoothness. The dry strength of the reinforced film was increased from 122 up to 195 MPa. Furthermore, the wet strength of the reinforced film was up to 70% greater than the dry strength of pure CNF film. The changes in the fibrillar structure were investigated with topographical imaging (SEM and AFM) and spectroscopically using NMR and FTIR. No significant changes in the fibril structure or cellulose morphology were observed. Moreover, the treated film resisted significant water pressure, highlighting CNF film’s permanent water resistance. The partial dissolution process with NMMO was also capable of reinforcing a CNF composite film with macro scale structural elements (lyocell short-cut fibres). The strategy investigated is a robust and fast method to improve the mechanical properties of fibrillary cellulose films, allowing them utilization in applications where improved water resistance and fully cellulosic character are required properties.     

Large Strain Gradient Plasticity Theory with a Discontinuous Grain Boundary Yield Condition

An equivalent plastic strain gradient theory [1] is extended to account for finite strains. The presented model considers discontinuities of the equivalent plastic strain at grain boundaries by using enriched trial functions in the Finite-Element discretization. As a consequence, a grain boundary flow rule is introduced, depending on both the mean value and the jump of the equivalent plastic strain. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Gradient based enhanced finite element formulation for diffuse phase interfaces

Interfaces between adjacent phases, so-called domain walls, appear as non-linear gradients of order parameters in diffuse phase field models. Usually, the interface width is much smaller than the dimension of the simulated region. Since the position of domain walls is not known a priori the maximum size of finite elements needs to be adapted to the length scale of interfaces within the entire region. We suggested a selective finite element method to improve the numerical solution of diffuse phase field models [1, 2]. It enhances the finite element interpolation space using supplementary local degrees of freedom. However, corresponding additional nodes are strictly located in the interior of elements, thus, C⁰-continuity at element border is guaranteed. Since C⁰-continuity limits the performance of this method we propose in this paper a relaxation of C⁰-requirements perpendicular to the gradient of the order parameter. Therefore, the direction of interfaces is analyzed as additional information for further adaptive improvement of the interpolation space. A dual phase field model is used to validate the proposed method. The analytical solution of a stationary domain wall allows error analysis of regular and distorted finite element meshes. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Parallel implementation of γ‐point pseudopotential plane‐wave DFT with exact exchange

Semi‐local functionals commonly used in density functional theory (DFT) studies of solids usually fail to reproduce localized states such as trapped holes, polarons, excitons, and solitons. This failure is ascribed to self‐interaction which creates a Coulomb barrier to localization. Pragmatic approaches in which the exchange correlation functionals are augmented with small amount of exact exchange (hybrid‐DFT, e.g., B3LYP and PBE0) have shown to promise in rectifying this type of failure, as well as producing more accurate band gaps and reaction barriers. The evaluation of exact exchange is challenging for large, solid state systems with periodic boundary conditions, especially when plane‐wave basis sets are used. We have developed parallel algorithms for implementing exact exchange into pseudopotential plane‐wave DFT program and we have implemented them in the NWChem program package. The technique developed can readily be employed in Γ‐point plane‐wave DFT programs. Furthermore, atomic forces and stresses are straightforward to implement, making it applicable to both confined and extended systems, as well as to Car‐Parrinello ab initio molecular dynamic simulations. This method has been applied to several systems for which conventional DFT methods do not work well, including calculations for band gaps in oxides and the electronic structure of a charge trapped state in the Fe(II) containing mica, annite. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Observation of bi-polarons in blends of conjugated copolymers and fullerene derivatives

From a fundamental and application point of view it is of importance to understand how charge carrier generation and transport in a conjugated polymer (CP):fullerene blend are affected by the blend morphology. In this work light-induced electron spin resonance (LESR) spectra and transient ESR response signals are recorded on non-annealed and annealed blend layers consisting of alkyl substituted thieno[3,2-b]thiophene copolymers (pATBT) and the soluble fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) at temperatures ranging from 10 to 180 K. Annealing of the blend sample leads to a reduction of the steady state concentration of light-induced PCBM anions within the blend at low temperatures (T = 10 K) and continuous illumination. This is explained on the basis of the reducing interfacial area of the blend composite on annealing, and the high activation energy for electron diffusion in PCBM blends leading to trapped electrons near the interface with the CP. As a consequence, these trapped electrons block consecutive electron transfer from an exciton on a CP to the PCBM domain, resulting in a relatively low concentration charge carriers in the annealed blend. Analysis of the transient ESR data allows us to conclude that in annealed samples diamagnetic bi-polaronic states on the CPs are generated at low temperature. The formation of these states is related to the generation and interaction of multiple positive polarons in the large crystalline polymer domains present in the annealed sample.     

Photodissociation mass spectra and mass-selected resonant (1+1)-photodissociation spectroscopy of some alkyl iodide radical cations

Photodissociation (PD) mass spectra and mass selected (1+1)-photodissociation spectra of C(2)H(5)I(+?), C(2)D(5)I(+?),1- C(3)H(7)I(+?), 2-C(3)H(7)I(+?), 1-C(4)H(9)I(+?) and 2- C(4)H(9)I(+?) radical cations were studied within the ? ← X~ absorption band. The photodissociation mass spectra within the range 13,600-15,900 cm(-1) (1.68-1.97 eV) evidence only a simple cleavage of the C-I bond and formation of the corresponding alkyl ions. The resonant (1+1)-photodissociation spectra of C(2)H(5)I(+?) and C(2)D(5)I(+?) show intense vibrational structure in the excited ? state. The thresholds for formation of the states of C(2)H(5)I(+?) and C(2)D(5)I(+?) were estimated to be (13,278 ± 12) cm(-1) (1.6462 ± 0.0014 eV)and (13,363 ± 12) cm(-1) (1.6586 ± 0.0014 eV), respectively. Whereas a few resonant vibronic excitations could be identified with 1-C(3)H(7)I(+?) and 1- C(4)H(7)I(+), no vibrational features were observable with 2- C(3)H(7)I(+?) and 2-C(4)H(9)I(+?). It is concluded that 1- and 2-iodoalkane radical cations do not rearrange, even under the conditions of electron ionisation used to generate the molecular ions.     

Über Reaktionen von Antimonhalogeniden. II. Die Reaktion von SbCl5 mit Oxalsäure-bis-(methylamid)

Reactions of Antimony Halides. II. The Reaction of SbCl₅ with Oxalic Acid Bis(methylamide) The reaction of antimony pentachloride with the dimethylamide of oxalic acid results in the formation of a five-ring heterocyclic compound C₄H₇Cl₄N₂O₂Sb(I), in which the ring components are Sb, N, C and O. It's synthesis and properties are discussed. Results of the mass spectrum see Table 1, a fraction scheme is given.