Octamethyl‐1, 1′‐di(2‐pyridyl)ferrocene: A Redox‐Active Ligand with a Pronounced Selectivity for Divalent Metal Ions

Octamethyl‐1, 1′‐di(2‐pyridyl)ferrocene ( 1 ) acts as molecular electrochemical sensor for magnesium, calcium, zinc, and cadmium ions in acetonitrile solution. The new redox peak, anodically shifted by ca. 0.40 V, which appears in the cyclic voltammogram of 1 in the presence of even small amounts (10 mol %) of these ions, is unaffected by an excess of alkali metal ions. Metal complexation is accompanied by a batho‐ and hyper‐chromic shift of the band in the visible region of the UV‐Vis spectrum of 1 . A detailed study of the behaviour of 1 towards zinc chloride in acetonitrile solution has revealed that 1 is able to accommodate a maximum of two zinc ions. Oxidation of zinc‐coordinated 1 leads to partial decomplexation. The N‐methyl and N‐benzyl species 1 Me⁺, 1 Me₂²⁺, 1 Bzl⁺ and 1 Bzl₂²⁺ have been synthesized and the former two structurally investigated by X‐ray diffraction. Alkylation causes an anodic shift of the redox potential of the ferrocene nucleus, which is linearly dependent on the number of alkyl groups introduced. Octamethyl‐1, 1′‐di(2‐thiophenyl)ferrocene ( 2 ) has also been synthesized and structurally characterized by X‐ray diffraction. Cyclic voltammetry has revealed that, in contrast to 1 , 2 does not respond to the divalent metal ions studied.     

A Rational Approach to Tetra-Functional Photo-Switches

α,ω-Bis(1,8-dichloroanthracen-10-yl)alkanes with (CH₂)_n-linker units (n=1–4) were synthesized starting from 1,8-dichloroanthracen-10(9H)-one. This was transformed into anthracenes with allyl, bromomethyl and propargyl substituents in position 10; these were converted in various C−C-bond formation reactions (plus hydrogenation), leading to two anthracene units flexibly linked by α,ω-alkandiyl groups. 1,2-Ethandiyl- and 1,3-propandiyl-linked derivatives were functionalized with ethynyl groups in positions 1, 8, 1’ and 8’, and these terminally functionalized by Me₃Sn groups using Me₂NSnMe₃. All linked bisanthracenes were subjected to UV light induced cyclomerization and a series of 9,10 : 9’,10’-photo-cyclomers were obtained. Their thermal cycloreversion and (repeated) switchability was demonstrated. 1,3-Bis{1,8-bis[(trimethylstannyl)ethynyl]anthracen-10-yl}propane served as model compound for photo-switchable acceptor molecules and its open and closed forms were characterized by NMR and DOSY experiments.     

Electron correlation contribution to the /ceria(1 1 1) interaction

We have investigated the electron correlation contribution to the interaction energy of the N₂O/ceria(1 1 1) system at the CCSD(T) level. N₂O binds either with the N-end towards the surface with an interaction energy or with the O-end with . In the former case almost the entire binding energy is due to electron correlation effects, in the latter these effects contribute with about 60%. Analyses of the interaction energy contributions show that most of the electron correlation part originates from the interaction of N₂O with the O ions in the topmost surface layer.     

[2,6‐(Trip)2H3C6 ](Cp*)Si: A Stable Monomeric Arylsilicon(II) Compound

Si takes a rest : A bulky σ‐bound terphenyl substituent and a π‐bound Cp* ligand enable the isolation and full characterization of the first aryl‐substituted, monomeric silicon(II) compound 1 , which can be regarded as the “resting state” of a true silylene containing a σ‐bound Cp* group. The conformation of the aryl group prevents aryl–Si π back‐bonding.

     

(Sub)-picosecond spectral evolution of fluorescence in photoactive proteins studied with a synchroscan streak camera system

The spectral evolution of three photoactive proteins has been investigated by measuring the fluorescence with good temporal and wavelength resolution and a high signal-to-noise ratio. Upon excitation at 400 nm wild-type (wt) PYP both at neutral pH and in the low-pH blueshifted pBdark state exhibited a strong quenching of the fluorescence, the major part of which could be described by lifetimes of about 1.7 and 7.7 ps. The remaining fluorescence decay occurred multiexponentially with lifetimes between 30 and 125 ps. Additionally, in wtPYP at neutral pH, a dynamic Stokes shift was found to occur with a time constant of about 0.25 ps. In a PYP preparation that was reconstituted with the chromophore 7-hydroxy-coumarin-3- carboxylic acid rather than the native coumaric acid, and which is therefore not capable of performing the cis-trans-isomerization that initiates the photocycle in wtPYP, the fluorescence was found to decay multiexponentially with lifetimes of 51 ps, 0.33 and 3.77 ns. Additionally, dynamic Stokes shifts were observed with time constants of about 0.1 and 3.5 ps. Upon comparison of the dynamics of this preparation with that of wtPYP the multiexponential decay with lifetimes of 1.7 and 7.7 ps found in wtPYP was attributed to photochemistry of the p-coumaric-acid chromophore. The emission from bacteriorhodopsin mutant D85S upon excitation at 635 nm decays biexponentially with estimated lifetimes of 5.2 and 19.1 ps. No dynamic Stokes shift was observed here. Four lifetimes were needed to describe the decay of the emission from the A* state in the green fluorescent protein. From a target analysis it was concluded that the longer lifetimes are accompanied by a decreasing probability of forming I*, which approaches zero with the longest A* lifetime of 1.5 ns. These observations may be explained by heterogeneity of A and by relaxation of A*. In all three systems studied, multiexponential decay of emission was present, suggesting that heterogeneity is a common feature of these chromophore protein complexes.     

Palladium mediated activation of C-F bonds in 2,4,6-trifluoropyrimidine: Synthesis and structure of palladium pyrimidyloxy and pyrimidinone derivatives

[PdMe₂(dcpm)] (1) reacts with 2,4,6-trifluoropyrimidine in the presence of water to give the palladium derivative [PdMe{4-C₄N₂F₂H(O)}(dcpm)] (2). When additional triethylamine is present complex [PdMe(2-OC₄N₂F₂H)(dcpm)] (4) in addition to 2 is formed. Compound 2 converts slowly into the binuclear complex [Pd{4-C₄N₂F₂H(O)}(μ-dcpm)]₂ (5). The molecular structure of 5 was determined by X-ray crystallography. The palladium-palladium distance is 2.5898(3) Å.     

On‐chip THz spectrometer for bunch compression fingerprinting at fourth‐generation light sources

The layout of an integrated millimetre‐scale on‐chip THz spectrometer is presented and its peformance demonstrated. The device is based on eight Schottky‐diode detectors which are combined with narrowband THz antennas, thereby enabling the simultaneous detection of eight frequencies in the THz range on one chip. The size of the active detector area matches the focal spot size of superradiant THz radiation utilized in bunch compression monitors of modern linear electron accelerators. The 3 dB bandwidth of the on‐chip Schottky‐diode detectors is less than 10% of the center frequency and allows pulse‐resolved detection at up to 5 GHz repetition rates. The performance of a first prototype device is demonstrated at a repetition rate of 100 kHz at the quasi‐cw SRF linear accelerator ELBE operated with electron bunch charges between a few pC and 100 pC.     

Nuclear inelastic scattering and Mössbauer spectroscopy as local probes for ligand binding modes and electronic properties in proteins: vibrational behavior of a ferriheme center inside a β-barrel protein

In this work, we present a study of the influence of the protein matrix on its ability to tune the binding of small ligands such as NO, cyanide (CN(-)), and histamine to the ferric heme iron center in the NO-storage and -transport protein Nitrophorin 2 (NP2) from the salivary glands of the blood-sucking insect Rhodnius prolixus. Conventional M?ssbauer spectroscopy shows a diamagnetic ground state of the NP2-NO complex and Type I and II electronic ground states of the NP2-CN(-) and NP2-histamine complex, respectively. The change in the vibrational signature of the protein upon ligand binding has been monitored by Nuclear Inelastic Scattering (NIS), also called Nuclear Resonant Vibrational Spectroscopy (NRVS). The NIS data thus obtained have also been calculated by quantum mechanical (QM) density functional theory (DFT) coupled with molecular mechanics (MM) methods. The calculations presented here show that the heme ruffling in NP2 is a consequence of the interaction with the protein matrix. Structure optimizations of the heme and its ligands with DFT retain the characteristic saddling and ruffling only if the protein matrix is taken into account. Furthermore, simulations of the NIS data by QM/MM calculations suggest that the pH dependence of the binding of NO, but not of CN(-) and histamine, might be a consequence of the protonation state of the heme carboxyls.