Synthesis of fluorescently labeled mono- and diprenylated Rab7 GTPase

Modification of proteins with isoprenoid lipids is a widespread phenomenon in eukaryotic organisms that has received much attention due to its involvement in the progression of several diseases including cancer. Progress in studies of prenylated proteins has been hampered by difficulties associated with isolation of these proteins from native or recombinant sources. Small GTPases of the Rab family represent a particularly difficult example since they are doubly C-terminally geranylgeranylated and in some cases methylated. Here, we report an efficient and versatile strategy for the synthesis of mono- and digeranylgeranylated fluorescent RabGTPases using a combination of chemical synthesis and expressed protein ligation. Using this approach we generated fluorescent mono- and diprenylated Rab7 proteins that display near-native properties and form stoichiometric complexes with their natural chaperone REP-1. We demonstrate that the complex formed from semisynthetic monoprenylated Rab7 and REP-1 represents a genuine intermediate of the Rab prenylation reaction and thus provides a unique tool for studies of the Rab prenylation mechanism. Semisynthetic Rab7 proteins were used to develop a novel fluorescence-based in vitro prenylation assay. Using this assay we dissected the mechanism of the Rab7 double-geranylgeranylation reaction mediated by Rab geranylgeranyl transferase. We conclude that the reaction follows a random sequential mechanism. These results highlight the usefulness of the semisynthetic reaction intermediates in the study of protein posttranslational modification.     

Nucleophilic beta-oniovinylation: concept, mechanism, scope, and applications

Insertion of an electron-deficient alkyne A-C[triple bond]C-A (A = CO2Me) into the C-L+ bond of an acyl-onio salt R-C(O)-L+ (R = Ar, OAlk; L = 4-dimethylaminopyridine, PPh3) has for the first time been achieved in the presence of catalytic amounts of the nucleophile L. For R = OMe, a second insertion of the alkyne was observed. X-ray structures were obtained for a number of such beta-oniovinylation products. Depending on reaction conditions, preferentially E- or Z-stereochemistry was observed, the Z-isomer being the thermodynamically more stable. A mechanism for this novel insertion reaction is presented which accounts for the topology of the products and rationalizes the observed stereochemistry. The beta-onio-activated Michael systems thus generated represent a virtually unexplored class of compounds. The onio substituent in such compounds can be selectively replaced by a number of nucleophiles. Thus a series of Michael systems with donor functions in the beta-position is easily synthesized. These compounds represent a source for useful further transformations, for example, cyclizations to quinolones, thiochromones, and pyrazoles.     

Gas-phase C-H and N-H bond activation by a high valent nitrido-iron dication and NH-transfer to activated olefins

A tetrapodal pentadentate nitrogen ligand (2,6-bis(1,1-di(aminomethyl)ethyl)pyridine, 1) is used for the synthesis of the azido-iron(III) complex [(1)Fe(N3)]X2 where X is either Br or PF6. By means of electrospray ionization mass spectrometry, the dication [(1)Fe(N3)]2+ can be transferred into the gas phase as an intact entity. Upon collisional activation, [(1)Fe(N3)]2+ undergoes an expulsion of molecular nitrogen to afford the dicationic nitrido-iron species [(1)FeN]2+ as an intermediate, which upon further activation can intramolecularly activate C-H- and N-H bonds of the chelating ligand 1 or can transfer an NH unit in bimolecular reactions with activated olefins. The precursor dication [(1)Fe(N3)]2+, the resulting nitrido species [(1)FeN]2+, and its possible isomers are investigated by mass spectrometric experiments, isotopic labeling, and complementary computational studies using density functional theory.     

On finite intersections of “henselian valued” fields

In this note we study finite intersections of henselian valued fields, i.e. fields carrying either a henselian valuation ring or a henselian absolute value which is (real-) archimedean. To be more precise, we intersect a finite number of henselian valued respectively real closed fields such that the induced valuation rings respectively orderings generate different V-topologies on the intersection, and investigate its algebraic and valuation-theoretic properties.     

Ermittlung optimaler Meßbedingungen für die atomabsorptions-spektroskopische Bestimmung von Edelmetallen

The parameters for the determination of noble metals by atomic absorption technique are optimized by minimizing of the coeffizients of variation. The optimal conditions for the determination of the elements Ag, Au, Ir, Pd, Pt, Rh and Ru are given.     

Untersuchungen zum elektronischen Einfluß von Organoliganden. XIII. Synthese und Charakterisierung von 2-funktionalisierten Vinylrhodoximen

Studies on the Electronic Influence of Organoligands. XIII. Synthesis and Characterization of 2-Functionalized Vinyl Rhodoximes 2-Functionalized vinyl rhodoximes [Rh(dmgH)₂ (PPh₃)cis/trans-CH = CHZ] ([Rh]? CH = CHZ) ) ( 1 ) can be prepared with a wide variation of the substituent Z (cis: OEt ( 1 a ), OPh ( 1 b ), Cl ( 1 c ), Me ( 1 j ), Ph ( 1 k ), SMe ( 1 l ), SPh ( 1 m ); trans: SPh ( 1 d ), Me ( 1 e ), Ph ( 1 f ), CMe₃ ( 1 g ), SiMe₃ ( 1 h )) by oxidative addition of XCH = CHZ and/or by nucleophilic addition of HC?CZ and Me₃SiC?CZ, respectively, to [Rh]^?. 1 a is converted to [Rh]? CH₂CHO ( 2 ) already in a weakly acid medium. 1 l is isomerized to trans-[Rh]? CH = CHSMe ( 1 n ) in the presence of acids. The complexes 1 are characterized by microanalysis and by ¹H, ¹³C and ³¹P NMR spectroscopy. The magnitude of the coupling constants ¹J(¹⁰³Rh, ³¹P) reveals only a small effect of Z on the (NMR) trans influence of the vinyl ligands CH = CHZ. The molecular structures of cis-[Rh]? CH = CHSPh ( 1 m ) and trans-[Rh]? CH = CHSPh ( 1 d ) show a distorted octahedral coordination of Rh with a mutual trans position of triphenyl-phosphine and the 2-phenylmercaptovinyl ligands. Van der Waals interactions exist between the sulfur and the equatorial dimethylglyoximato ligands in the cis complex 1 m .     

Activation of SO2 and CO2 by Trivalent Uranium Leading to Sulfite/Dithionite and Carbonate/Oxalate Complexes

The first sulfite [{((^nP,MeArO)₃tacn)U^IV}₂(μ‐κ¹:κ²‐SO₃)] (tacn=triazacyclononane) and dithionite [{((^nP,MeArO)₃tacn)U^IV}₂(μ‐κ²:κ²‐S₂O₄)] complexes of uranium from reaction with gaseous SO₂ have been prepared. Additionally, the reductive activation of CO₂ was investigated with respect to the rare oxalate [{((^nP,MeArO)₃tacn)U^IV}₂(μ‐κ²:κ²‐C₂O₄)] formation. This ultimately provides the unique S₂O₄^2?/C₂O₄^2? and SO₃^2?/CO₃^2? complex pairs. All new complexes were characterized by a combination of single‐crystal X‐ray diffraction, elemental analysis, UV/Vis/NIR electronic absorption, IR vibrational, and ¹H NMR spectroscopy, as well as magnetization (VT SQUID) studies. Moreover, density functional theory (DFT) calculations were carried out to gain further insight into the reaction mechanisms. All observations, together with DFT, support the assumption that SO₂ and CO₂ show similar (dithionite/oxalate) to analogous (sulfite/carbonate) activation behavior with uranium complexes.     

Damage processes coupled with phase separation in elastically stressed alloys

In micro-electronic materials such as solder alloys, phase-separation and coarsening as well as damage phenomena occur at the same time and influences each other. In this note, a unifying model which couples multi-component Cahn-Hilliard systems with elasticity and uni-directional damage processes is presented. We outline the equations and their initial-boundary conditions in a classical setting and cite some existence results for weak solutions recently proved in [8, 9]. The damage is assumed to be incomplete, i.e. the maximal damaged material parts still feature elastic properties. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)