Photosynthetic Antenna‐Reaction Center Mimicry with a Covalently Linked Monostyryl Boron‐Dipyrromethene–Aza‐Boron‐Dipyrromethene–C60 Triad

An efficient functional mimic of the photosynthetic antenna‐reaction center has been designed and synthesized. The model contains a near‐infrared‐absorbing aza‐boron‐dipyrromethene (ADP) that is connected to a monostyryl boron‐dipyrromethene (BDP) by a click reaction and to a fullerene (C₆₀) using the Prato reaction. The intramolecular photoinduced energy and electron‐transfer processes of this triad as well as the corresponding dyads BDP‐ADP and ADP‐C₆₀ have been studied with steady‐state and time‐resolved absorption and fluorescence spectroscopic methods in benzonitrile. Upon excitation, the BDP moiety of the triad is significantly quenched due to energy transfer to the ADP core, which subsequently transfers an electron to the fullerene unit. Cyclic and differential pulse voltammetric studies have revealed the redox states of the components, which allow estimation of the energies of the charge‐separated states. Such calculations show that electron transfer from the singlet excited ADP (¹ADP*) to C₆₀ yielding ADP^.+‐C₆₀^.? is energetically favorable. By using femtosecond laser flash photolysis, concrete evidence has been obtained for the occurrence of energy transfer from ¹BDP* to ADP in the dyad BDP‐ADP and electron transfer from ¹ADP* to C₆₀ in the dyad ADP‐C₆₀. Sequential energy and electron transfer have also been clearly observed in the triad BDP‐ADP‐C₆₀. By monitoring the rise of ADP emission, it has been found that the rate of energy transfer is fast (≈10¹¹ s^?1). The dynamics of electron transfer through ¹ADP* has also been studied by monitoring the formation of C₆₀ radical anion at 1000 nm. A fast charge‐separation process from ¹ADP* to C₆₀ has been detected, which gives the relatively long‐lived BDP‐ADP^.+C₆₀^.? with a lifetime of 1.47 ns. As shown by nanosecond transient absorption measurements, the charge‐separated state decays slowly to populate mainly the triplet state of ADP before returning to the ground state. These findings show that the dyads BDP‐ADP and ADP‐C₆₀, and the triad BDP‐ADP‐C₆₀ are interesting artificial analogues that can mimic the antenna and reaction center of the natural photosynthetic systems.     

Three‐Dimensional Architectures Incorporating Stereoregular Donor–Acceptor Stacks

We report the synthesis of two [2]catenane‐containing struts that are composed of a tetracationic cyclophane (TC⁴⁺) encircling a 1,5‐dioxynaphthalene (DNP)‐based crown ether, which bears two terphenylene arms. The TC⁴⁺ rings comprise either 1) two bipyridinium (BIPY²⁺) units or 2) a BIPY²⁺ and a diazapyrenium (DAP²⁺) unit. These degenerate and nondegenerate catenanes were reacted in the presence of Cu(NO₃)₂?2.5 H₂O to yield Cu‐paddlewheel‐based MOF‐1050 and MOF‐1051. The solid‐state structures of these MOFs reveal that the metal clusters serve to join the heptaphenylene struts into grid‐like 2D networks. These 2D sheets are then held together by infinite donor–acceptor stacks involving the [2]catenanes to produce interpenetrated 3D architectures. As a consequence of the planar chirality associated with both the DNP and hydroquinone (HQ) units present in the crown ether, each catenane can exist as four stereoisomers. In the case of the nondegenerate (bistable) catenane, the situation is further complicated by the presence of translational isomers. Upon crystallization, however, only two of the four possible stereoisomers—namely, the enantiomeric RR and SS forms—are observed in the crystals. An additional element of co‐conformational selectivity is present in MOF‐1051 as a consequence of the substitution of one of the BIPY²⁺ units by a DAP²⁺ unit: only the translational isomer in which the DAP²⁺ unit is encircled by the crown ether is observed. The overall topologies of MOF‐1050 and MOF‐1051, and the selective formation of stereoisomers and translational isomers during the kinetically driven crystallization, provide evidence that weak noncovalent bonding interactions play a significant role in the assembly of these extended (super)structures.     

Bootstrapping and Askey–Wilson polynomials

The mixed moments for the Askey–Wilson polynomials are found using a bootstrapping method and connection coefficients. A similar bootstrapping idea on generating functions gives a new Askey–Wilson generating function. Modified generating functions of orthogonal polynomials are shown to generate polynomials satisfying recurrences of known degree greater than three. An important special case of this hierarchy is a polynomial which satisfies a four term recurrence, and its combinatorics is studied.     

Magnetic Resonance Access to Transiently Formed Protein Complexes

Protein–protein interactions are of utmost importance to an understanding of biological phenomena since non-covalent and therefore reversible couplings between basic proteins leads to the formation of complex regulatory and adaptive molecular systems. Such systems are capable of maintaining their integrity and respond to external stimuli, processes intimately related to living organisms. These interactions, however, span a wide range of dissociation constants, from sub-nanomolar affinities in tight complexes to high-micromolar or even millimolar affinities in weak, transiently formed protein complexes. Herein, we demonstrate how novel NMR and EPR techniques can be used for the characterization of weak protein–protein (ligand) complexes. Applications to intrinsically disordered proteins and transiently formed protein complexes illustrate the potential of these novel techniques to study hitherto unobserved (and unobservable) higher-order structures of proteins.     

Towards a finite element simulation of coating by means of thermal spraying

Metal sheet forming processes like deep drawing are applied in order to produce carriage parts in mass production. Therefore, forming tools are required that are well protected against wear. For such forming tools, wear resistant surfaces are, e.g., produced by thermal spraying of hard material coatings. The thermal spraying process itself is a highly transient thermo-mechanical process. In order to gain a better understanding of the heat input and transfer during thermal spraying, a simulation framework for thermal spraying processes is presented. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Actuating Shape Memory Polymer for Thermoresponsive Soft Robotic Gripper and Programmable Materials

For soft robotics and programmable metamaterials, novel approaches are required enabling the design of highly integrated thermoresponsive actuating systems. In the concept presented here, the necessary functional component was obtained by polymer syntheses. First, poly(1,10-decylene adipate) diol (PDA) with a number average molecular weight M_n of 3290 g·mol⁻¹ was synthesized from 1,10-decanediol and adipic acid. Afterward, the PDA was brought to reaction with 4,4′-diphenylmethane diisocyanate and 1,4-butanediol. The resulting polyester urethane (PEU) was processed to the filament, and samples were additively manufactured by fused-filament fabrication. After thermomechanical treatment, the PEU reliably actuated under stress-free conditions by expanding on cooling and shrinking on heating with a maximum thermoreversible strain of 16.1%. Actuation stabilized at 12.2%, as verified in a measurement comprising 100 heating-cooling cycles. By adding an actuator element to a gripper system, a hen’s egg could be picked up, safely transported and deposited. Finally, one actuator element each was built into two types of unit cells for programmable materials, thus enabling the design of temperature-dependent behavior. The approaches are expected to open up new opportunities, e.g., in the fields of soft robotics and shape morphing.     

Mediated Generation of Conjugate Acid by UV and Blue Sensitizers with Upconversion Nanoparticles at 980 nm

NIR and UV exposure of systems comprising upconversion nanoparticles ( UCNP ) based on NaYF₄:Tm/Yb@NaYF₄, a sensitizer absorbing either in the blue or UV region, and an onium salt with weak coordinating anion resulted in formation of conjugate acid (con-H⁺). That was namely Ivocerin (di(4-methoxybenzoyl)diethylgermane), ITX (2-iso-propyl thioxanthone), anthracene, pyrene, rubrene, camphore quinone, and a strong fluorescent coumarin (1,1,6,6,8-pentamethyl-2,3,5,6-tetrahyhdro-1H,4H-11-oxa-3a-aza-benzo[de]anthracene-10-one). Quantification occurred by treatment with Rhodamine B lactone whose color switched to intensive red after photolytic formation of con-H⁺. Exposure with a NIR laser at 980 nm resulted in less con-H⁺ compared to 395 nm where all sensitizers absorb radiation. UCNP did not mainly interfered formation of con-H⁺. The different rates obtained in both experiments responsibly explain the failure and success to initiate polymerization of epoxides applying ether 980 nm or 395 nm excitation, respectively.     

Isolation of a 16π-Electrons 1,4-Diphosphinine-1,4-diide with a Planar C4P2 Ring

Herein, we report the first 1,4-diphosphinine-1,4-diide compound [(ADC^Ph)P]₂ ( 5-Ph ) (ADC^Ph=PhC{(NDipp)C}₂; Dipp=2,6-iPr₂C₆H₃) derived from an anionic dicarbene (ADC^Ph) as a red crystalline solid. Compound 5-Ph containing a 16π-electron planar fused-tricyclic ring system was obtained by the 4e reduction of [(ADC^Ph)PCl₂]₂ ( 4-Ph ) with Mg (or KC₈) in a quantitative yield. Experimental and computational results imply that the central 8π-electrons C₄P₂ ring of 5-Ph , which is fused between two 6π-electrons C₃N₂ aromatic rings, is antiaromatic. Thus, each of the phosphorus atoms of 5-Ph has two electron-lone-pairs, one in a p-type orbital is in conjugation with the C=C bonds of the C₄P₂ ring, while the second resides in a σ-symmetric orbital. This can be shown with the gold complex [(ADC^Ph)P(AuCl)₂]₂ ( 6-Ph ) obtained by reacting 5-Ph with (Me₂S)AuCl. A mixture of 5-Ph and 4-Ph undergoes comproportionation in the presence of MgCl₂ to form the intermediate oxidation state compound [(ADC^Ar)P]₂(MgCl₄) ( 7-Ph ), which is an aromatic species.