Measurement of cation exchange capacity (CEC) of plant cell walls by X-ray microanalysis (EDX) in the transmission electron microscope.

Cation exchange capacity (CEC) characterizes the number of fixed negative charges of plant cell walls and is an important parameter in studies dealing with the uptake of ions into plant tissues, especially in roots. Conventional methods of CEC determination use bulk tissue, the results are the mean of many cells, and differences in the CEC of different tissue types are masked. Energy-dispersive microanalysis (EDX) in the transmission electron microscope allows CEC determinations on much finer scales. Shoot and fine root tissue of Picea abies was acid washed to remove exchangeable cations. Tissue blocks or semithin tissue sections were loaded with 0.2 mM CaCl2, AlCl3, or Pb(NO3)2 at pH 4.0. The amount of Ca, Al, or Pb adsorbed to the exchange sites of cell walls was determined by EDX. The CEC of cell walls of different tissue types was highly different, ranging in shoot tissues from 0 to 856 mM Ca and 5.8 to 1463 mM Al (block loading) or 4.3 to 1116 mM Ca and 0 to 2830 mM Al (section loading). In root tissue, Pb adsorption to semithin sections yielded CEC values between 29.1 and 954 mM Pb. In most P. abies shoot tissues, the binding capacity was clearly higher for Al than for Ca.     

On the characterization of p ‐adic Colombeau–Egorov generalized functions by their point values

We show that contrary to recent papers by S. Albeverio, A. Yu. Khrennikov and V. Shelkovich, point values do not determine elements of the so‐called p ‐adic Colombeau–Egorov algebra ??(?ⁿ _p ) uniquely. We further show in a more general way that for an Egorov algebra ??(M, R) of generalized functions on a locally compact ultrametric space (M, d) taking values in a nontrivial ring, a point value characterization holds if and only if (M, d) is discrete. Finally, following an idea due to M. Kunzinger and M. Oberguggenberger, a generalized point value characterization of ??(M, R) is given. Elements of ??(?ⁿ _p ) are constructed which differ from the p ‐adic δ ‐distribution considered as an element of ??(?ⁿ _p ), yet coincide on point values with the latter. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A Fast and Efficient Track to Allosteric Modulators of Muscarinic Receptors: Microwave-Assisted Syntheses

Summary. By using microwave irradiation bisammonium-and bispyridinium-type allosteric modulators of muscarinic receptors can be obtained fast and efficiently.     

The interplay of skeletal deformations and ultrafast excited-state intramolecular proton transfer: Experimental and theoretical investigation of 10-hydroxybenzo[h]quinoline

The excited-state intramolecular proton transfer in the aromatic polycycle 10-hydroxybenzo[h]quinoline is investigated by means of transient absorption experiments with 30 fs time resolution, classical dynamics and wavepacket dynamics. The experiments establish the ultrafast transfer after UV excitation and show signatures of coherent vibrational motion in the keto product. To elucidate details of the proton transfer mechanism, the classical dynamics is also performed for 2-(2′-hydroxyphenyl)benzothiazole and the results are compared. For both systems the proton transfer takes place on the ultrafast scale of 30–40 fs, with good agreement between the theoretical investigations and the measurements. The dynamics simulations show that for both molecules the proton is handed over by means of skeletal deformation of the molecule. Due to the more rigid structure of 10-hydroxybenzo[h]quinoline the hydrogen migration mode participates more actively than in 2-(2′-hydroxyphenyl)benzothiazole.     

Electronic structures of organometallic complexes of f elements LXXIII: Parametric analysis of the crystal field splitting pattern of tris(η-pentamethylcyclopentadienyl)cerium(III)

By comparing the far infrared (polyethylene pellets, room temperature) and mid-infrared spectra (KBr pellets, room temperature and ca. 90 K) of pseudo trigonal planar Ce(η⁵-C₅Me₅)₃ (1) with the corresponding ones of La(η⁵-C₅Me₅)₃ (2) and considering the low temperature paramagnetic susceptibility data of 1 the crystal field (CF) splitting pattern of 1 could be derived. The free parameters of a phenomenological Hamiltonian were fitted to this pattern achieving an r.m.s. deviation of 8.9 cm⁻¹ for seven assignments. The fact that the difference of the experimental energies of the barycenters of CF levels of the multiplets ²F_7/2 and ²F_5/2 is larger than in the gaseous free Ce³⁺ ion (experimental “anti”-relativistic nephelauxetic effect) could be explained by coupling effects of these multiplets via the CF, resulting in a lower spin-orbit coupling parameter than in the case of the free gaseous Ce³⁺ ion. The experimental CF splitting pattern of 1 is compared to the results of a relativistic DV-Xα calculation on the pseudo trigonal planar model compound Ce(η⁵-C₅H₅)₃. In addition, the prediction of the energies of f → d and charge transfer transitions of Ce(η⁵-C₅H₅)₃ are compared to the absorption and luminescence spectra of complex 1.     

The synthesis, crystal structures and NMR spectroscopic investigation of 3,7,10-trimethylsilatranes and carbasilatranes

The first representatives of aryloxy-trimethylsilatranes, C₆H₅OSi[OCH(CH₃)CH₂]₃N, of aryloxy-carbasilatranes, C₆H₅OSi(CH₂CH₂CH₂)(OCH₂CH₂)₂N, and a number of novel 3,7,10-trimethylsilatranes (RSi[OCH(CH₃)CH₂]₃N) and carbasilatranes (RSi(CH₂CH₂CH₂)(OCH₂CH₂)₂N) have been prepared and characterised, both structurally and by NMR spectroscopy. The influence of various Si substituents (R = alkyl, aryl, alkoxy and aryloxy) as well as the influence of the substitution in the skeleton of the trimethylsilatranes and carbasilatranes on the chemical shift in the ²⁹Si, ¹H and ¹³C NMR spectra has been investigated. The crystal structures of both diastereomers of phenyl-3,7,10-trimethylsilatrane and of the symmetrical isomer of p-tolyl-3,7,10-trimethylsilatrane were determined by X-ray diffraction after separation of the diastereomers by means of HPLC. All three crystal structures are centrosymmetric.     

Real time observation of microwave-enhanced reactions via fast FTIR spectroscopy

Microwave-enhanced reactions are very fast in comparison to thermal reactions. The determination of optimal end point often fails because conventional analytical methods are too slow. Therefore, we established a fast method using FTIR spectroscopy. The result of the reaction control analysis is obtained within less than 1 min.     

Synthesis and Crystal Structure of a Bixbyite‐Type Solid Solution Zr0.43Er0.57O1.07N0.43

A powder of the composition 40 mol‐% Er₂O₃ and 60 mol‐% ZrO₂ has been prepared. The anion deficient fluorite related compound Zr₃Er₄O₁₂ [R\bar{3} : a = 971.79(7) pm and c = 907.976(0) pm] was produced. This precursor was treated with gaseous ammonia at temperatures between 25 and 1200 °C. The reaction was followed in situ by X‐ray diffraction in a high temperature reaction chamber under a constant flow of ammonia. The nitridation of Zr₃Er₄O₁₂ led to a nitride oxide of the solid‐solution‐type with an apparent composition Zr_0.43Er_0.57O_1.07N_0.43 The compound crystallizes isostructural to bixbyite due to vacancy ordering [Ia\bar{3} : a = 1036.37(4) pm]. The reoxidation of the nitride oxide was monitored in DTA/TG experiments exhibiting an almost complete reoxidation to the starting composition except for some inclusions of dinitrogen.     

Role of structural order and excess energy on ultrafast free charge generation in hybrid polythiophene/Si photovoltaics probed in real time by near-infrared broadband transient absorption

Despite the central role of light absorption and the subsequent generation of free charge carriers in organic and hybrid organic-inorganic photovoltaics, the precise process of this initial photoconversion is still debated. We employ a novel broadband (UV-Vis-NIR) transient absorption spectroscopy setup to probe charge generation and recombination in the thin films of the recently suggested hybrid material combination poly(3-hexylthiophene)/silicon (P3HT/Si) with 40 fs time resolution. Our approach allows for monitoring the time evolution of the relevant transient species under various excitation intensities and excitation wavelengths. Both in regioregular (RR) and regiorandom (RRa) P3HT, we observe an instant (<40 fs) creation of singlet excitons, which subsequently dissociate to form polarons in 140 fs. The quantum yield of polaron formation through dissociation of delocalized excitons is significantly enhanced by adding Si as an electron acceptor, revealing ultrafast electron transfer from P3HT to Si. P3HT/Si films with aggregated RR-P3HT are found to provide free charge carriers in planar as well as in bulk heterojunctions, and losses are due to nongeminate recombination. In contrast for RRa-P3HT/Si, geminate recombination of bound carriers is observed as the dominant loss mechanism. Site-selective excitation by variation of pump wavelength uncovers an energy transfer from P3HT coils to aggregates with a 1/e transfer time of 3 ps and reveals a factor of 2 more efficient polaron formation using aggregated RR-P3HT compared to disordered RRa-P3HT. Therefore, we find that polymer structural order rather than excess energy is the key criterion for free charge generation in hybrid P3HT/Si solar cells.