Bromo­di­methyl(N‐methyl­pyrrolidin‐2‐one‐O)­tin(IV)‐di‐μ‐bromo‐bromo­di­methyl­tin(IV)

The preparation and X‐ray analysis of the title compound, [Sn₂Br₄(CH₃)₄(C₅H₉NO)], are described. The compound contains two Sn atoms in the asymmetric unit, that complexed by N‐methyl­pyrrolidin‐2‐one being hexacoordinated (a), the other exhibiting pentacoordination (b). The most important features are three different Sn—Br bond lengths at both Sn atoms with the following values: (a) 2.5060 (9), 2.7152 (10) and 3.7118 (10) Å; (b) 2.5084 (10), 2.5279 (9) and 3.5841 (10) Å.     

New open-chain tetrapyrroles as chromophores in the plant photoreceptor phytochrome

A series of six open-chain tetrapyrroles has been synthesized and used as chromophores for the plant photoreceptor protein phytochrome. The novel chromophores vary in the size of substituents 17 and 18 at ring D. This ring undergoes maximal conformational change upon light excitation ( Z --> E photoisomerization of the 15,16-double bond). Instead of methyl and vinyl substituents (positions 17, 18) as present in the native chromophore phytochromobilin, dimethyl, methyl and isopropyl, methyl and tert-butyl, ethyl and methyl, vinyl and methyl, and isopropyl and methyl substituents have been generated. All novel chromophores assemble with the apoprotein. The obtained chromoproteins show hypsochromic shifts of the absorbance maxima by 10 nm maximally, compared to the native pigment, except for the 17-isopropyl-18-methyl-substituted compound which showed a 100 nm hypsochromic shift of selectively the P r form. The assembly kinetics were slowed down in correlation to the increasing size of the substituents, with stronger effects for modified substituents at position 17. The thermal stability of the photoinduced P fr form for the 18-isopropyl and the 18- tert butyl substituents was even greater than that of the native pigments. Those chromophores carrying substituents at position 17 larger than the methyl group (ethyl and isopropyl) showed a very low stability of the respective P fr forms. Time-resolved detection of the P r to P fr conversion (laser-induced flash photolysis) revealed a slower formation of the P fr form for those chromophores carrying larger substituents at position 18, whereas the rise and decay kinetics of the early intermediates are only moderately changed. Introduction of larger substituents at position 17 (ethyl, vinyl, and isopropyl) causes drastic changes in the kinetics; in particular the formation of the first thermally stable intermediate, I 700, is significantly slowed, making a detection of its rise possible.     

Influence of Process Parameters on the Reaction Kinetics of the Chromium‐Catalyzed Trimerization of Ethylene

In this paper we report the results of an extensive experimental kinetic study carried out on the novel ethylene trimerization catalyst system, comprising the chromium source [CrCl₃(thf)₃] (thf=tetrahydrofuran), a Ph₂P‐N(iPr)‐P(Ph)‐N(iPr)H (PNPNH) ligand (Ph=phenyl, iPr=isopropyl), and triethylaluminum (AlEt₃) as activator. It could be shown that the initial activity shows a first‐order dependency on the ethylene concentration. Also, a first‐order dependency was found for the catalyst concentration. The initial activity follows a typical Arrhenius behavior with an experimentally determined activation energy of 52.6 kJ mol^?1. At elevated temperatures (ca. 80 °C), a significant deactivation was observed, which can be tentatively traced back to a ligand rearrangement in the presence of AlEt₃. After a fast initial phase, a pronounced ‘kink’ in the ethylene‐uptake curve is observed, followed by a slow, almost linear, further increase of the total ethylene consumption. The catalyst composition, in particular the ligand/chromium and the cocatalyst/chromium molar ratio, has a strong impact on the catalytic performance of the trimerization of ethylene.     

Method for Simultaneously Improving the Thermal Stability and Mechanical Properties of Poly(lactic acid): Effect of High-Energy Electrons on the Morphological, Mechanical, and Thermal Properties of PLA/MMT Nanocomposites

Nanocomposites derived from poly(lactic acid) (PLA) and organically modified montmorillonite (oMMT) have been cross-linked by high-energy electrons in the presence of triallyl cyanurate (TAC). The morphology of untreated and cross-linked PLA/MMT nanocomposites was characterized by wide-angle X-ray scattering (WAXS) and transmission electron microscopy (TEM). This treatment can improve both the thermal stability and the glass-transition temperatures of the PLA nanocomposites (e.g., PLA-MMT-TAC 30kGy, 50kGy, and 70kGy) because of the formation of cross-linking structures in the nanocomposites that will considerably reduce the mobility of polymers. Interestingly, at relatively low irradiation doses (e.g., 30 and 50 kGy) a good balance between tensile strength and elongation at break for the PLA nanocomposites could be achieved. These mechanical properties are superior to those of pure PLA. Therefore, combining nanotechnology and electron beam cross-linking is a promising new method of simultaneously improving the mechanical properties (toughness and tensile strength) and thermal stability of PLA.     

Nonlinear current-voltage relationship of the plasma membrane of single CHO cells

The application of electric field pulses to Chinese Hamster Ovary (CHO) cells causes membrane electroporation (MEP). If a voltage or current ramp is applied to the cellular membrane of a single CHO cell, the membrane conductance increases nonlinearly with field strength reaching saturation. In particular, the kinetics of the induced conductance changes represents the data basis for the interpretation in terms of underlying structural changes. The current/voltage characteristic is found to be continuous, but displays occasionally a sharp increase in the conductance. The step-like increases are interpreted to reflect the formation of one (or more) larger pore(s). The analysis of current clamp data yields pores of radius (r(p)) in the range of 2.5< or =r(p)/nm< or =20; the pores of the voltage clamp data are in the range of 2.5< or =r(p)/nm< or =55. The larger pores occur predominantly during hyperpolarising and less frequently during depolarising conditions, respectively. The different kinetics of pore formation in the hyperpolarising condition, where the inward field increases, and the depolarising condition, where the inward field first decreases and then increases in the opposite direction, suggests structural asymmetry with respect to the direction of the electric membrane field. At the required higher voltage, the effect of the resting potential is negligibly small.     

On the Track of Novel Triel‐Stabilised Silylaminoiminoborenes

Borenes and boranes : Silylaminoiminoborenes, such as depicted, were isolated after treatment of halogen triels with silylaminofluoroboranes. In addition, novel aryl‐ and silyl‐substituted diaminofluoroboranes were also prepared in order to substantiate this reaction route.

     

Aldehyde cruciforms: dosimeters for primary and secondary amines

We demonstrate that aldehyde-substituted donor-acceptor cruciforms [1,4-bis(arylethynyl)-2,5-distyrylbenzenes] are useful dosimeters for primary amines, primary diamines, and secondary amines. The 1,n-diamines are particularly reactive towards this dosimeter and can be detected in less than 100 ppm concentration. Using a single aldehyde-functionalized cruciform in seven different solvents allowed us to discern fourteen different amines by digital photography and statistical evaluation of the response patterns extracted as red, green, blue (RGB) values.