Stahl

Ohne Zusammenfassung     

Splitting of the Cr 2p ions states in some ternary sulphides and selenides

X-ray photoelectron spectroscopy was used to investigate ACr₂S₄ (, Zn, Mn, Fe, Fe:Cu) and BCr₂Se₄ (, Cu, Hg, Hg:Cu) single crystals. Well defined splitting of the Cr 2p core level has been found. The local magnetic moments of the Cr ions are responsible for the observed effect. Received 2 November 1999     

Encapsulated clay particles in polystyrene by RAFT mediated miniemulsion polymerization

RAFT grafted montmorillonite (MMT) clays [i.e., N,N‐dimethyl‐N‐(4‐(((phenylcarbonothioyl)thio)methyl)benzyl)ethanammonium‐MMT (PCDBAB‐MMT) and N‐(4‐((((dodecylthio)carbonothioyl)thio)methyl)benzyl)‐N,N‐dimethylethanammo‐nium‐MMT (DCTBAB‐MMT)] of various loadings were dispersed in styrene (S) monomer and the resultant mixtures emulsified and sonicated in the presence of a hydrophobe (hexadecane) into miniemulsions. The stable miniemulsions thus obtained were polymerized to yield encapsulated polystyrene‐clay nanocomposites (PS‐CNs). The molar mass and polydispersity index (PDI) of the PS‐CNs depended on the amount of RAFT agent in the system, in accordance with the features of the RAFT process. The morphology of the PS‐CNs ranged from partially exfoliated to an intercalated morphology, depending on the percentage clay loading. The thermomechanical properties of the PS‐CNs were better than those of the neat PS polymer, and were dependent on the molar mass, PS‐CN morphology and clay loading. The similarities and differences of the PS‐CNs prepared here by miniemulsion polymerization were compared to those prepared using the same RAFT agents and polymer system by bulk polymerization (as reported by us in a previous article). © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7114–7126, 2008     

PHOTOCHROMIC SYNERGISM OF BACTERIORHODOPSIN- and HALORHODOPSIN-MEDIATED PHOTOPHOSPHORYLATION IN Halobacterium halobium*

Quantitative action spectroscopy was performed in Halobacterium halobium. using four suited pigment mutants, namely the bacteriorhodopsin and halorhodopsin positive mutant strain M-l (BR⁺, HR⁺), the bacteriorhodopsin positive but halorhodopsin negative strain M-18 (BR⁺, HR^-), the bacteriorhodopsin negative but halorhodopsin positive strain L-33 (BR^-, HR⁺), and the bacteriorhodopsin and halorhodopsin negative strain L-07 (BR^-, HR⁺). The approached questions were: First, photoenergetic synergism of halorhodopsin and bacteriorhodopsin in intact cells; second, photochromism and cellular function of the blue light-absorbing intermediates, i.e. M-412 and HR-410 in bacteriorhodopsin and in halorhodopsin, respectively. Dark-adapted cells of mutant strain M-l show wavelength-dependency of quantum yield of photo-phosphorylation, φ_ATP. An 1.4-fold enhancement was found at 575 nm wavelength where the long wavelength absorbance bands of bacteriorhodopsin and halorhodopsin intersect. The enhancement vanished after a 30 min pulse of orange light (600 Wm^-2 bandpass from 495 to 750 nm), but was restored after a 30 min pulse of blue light (100 Wm^-2 bandpass from 325 to 480 nm). Photoreversibility of this enhancement probably reflects phototransformation of halorhodopsin from its ground state into its inactive intermediate, HR-410, and vice versa. The halorhodopsin-mediated enhancement with maximum quantum yield of photophosphorylation, φ_ATP= 0.06, i.e. a quantum requirement of = 17 photons/ATP, is partly substituted by a rise in phosphate potential and explained in terms of a voltage-regulated gating effect on the H⁺-driven ATP-synthase, superimposed on the chemiosmotic mechanism of energy coupling. The blue-absorbing photochromic intermediate, M-412 of bacteriorhodopsin, dissipates light energy upon photoexcitation that is reflected by a spectral decline in quantum yield of photophosphorylation to a minimum value of = 0.01 at 415 nm, i.e. a quantum requirement of = 100 photons/ATP.