Anisotropic Microgels by Supramolecular Assembly and Precipitation Polymerization of Pyrazole-Modified Monomers.

Soft colloidal macromolecular structures with programmable chemical functionalities, size, and shape are important building blocks for the fabrication of catalyst systems and adaptive biomaterials for tissue engineering. However, the development of the easy upscalable and template-free synthesis methods to obtain such colloids lack in understanding of molecular interactions that occur in the formation mechanisms of polymer colloids. Herein, a computer simulation-driven experimental synthesis approach based on the supramolecular self-assembly followed by polymerization of tailored pyrazole-modified monomers is developed. Simulations for a series of pyrazole-modified monomers with different numbers of pyrazole groups, different length and polarity of spacers between pyrazole groups and the polymerizable group are first performed. Based on simulations, monomers able to undergo π-π stacking and guide the formation of supramolecular bonds between polymer segments are synthesized and these are used in precipitation polymerization to synthesize anisotropic microgels. This study demonstrates that microgel morphologies can be tuned from spherical, raspberry-like to dumbbell-like by the increase of the pyrazole-modified monomer loading, which is concentrated at periphery of growing microgels. Combining experimental and simulation results, this work provides a quantitative and predictive approach for guiding microgel design that can be further extended to a diversity of colloidal systems and soft materials with superior properties.

Formate complexes of tri- and tetravalent titanium supported by a tris(phenolato)amine ligand.

Titanium(III) and titanium(IV) formate complexes supported by the sterically encumbering tris(phenolato)amine ligand (H3(O3N) = tris(4,6-di-tert-butyl-2-hydroxybenzyl)amine) are described. Salt metathesis of the chlorido precursor [(O3N)TiCl] (1-Cl) with sodium formate in a 2 : 1 ratio in THF gave a dimer of sodium dititanium triformate units with 12-membered ring [Na{(O3N)Ti}2(µ-OCHO-ηO:ηO')3]2 (3-Na) when crystallized from acetonitrile. Complex 3-Na was also prepared by reacting the previously reported terminal formate complex [(O3N)Ti(OCHO)] (2) with excess sodium formate. Salt metathesis of 1-Cl with potassium formate gave a tetratitanium cluster of the composition [K3{(O3N)Ti}4(OCHO)7] (3-K) which can be also obtained by treating 2 with potassium formate. In 3-K both Ti and K centers are six-coordinate. The titanium(III) complexes [(O3N)Ti(L)] (4-L, L = THF, THP, Et2O) and solvent free dimeric [(O3N)Ti]2 (5) were synthesized by reduction of 1-Cl with sodium sand or magnesium in THF, THP, Et2O, and n-pentane, respectively. The tert-butyl formate adduct of titanium(III)-[(O3N)Ti(tBuOCHO)] (6) was isolated by reacting 4-L or 5 with tert-butyl formate. Complex 6 is thermolabile and slowly decomposed in solution to produce a formate-bridged mixed-valence titanium(III)/titanium(IV) complex [{(O3N)Ti}2(µ-OCHO-ηO:ηO')] (7) which further decomposed to a mixture containing 2, [(O3N)Ti(OH)] and [(O3N)Ti-O-Ti(O3N)]. All new complexes were isolated in moderate to good yields and fully characterized by elemental analysis, 1H and 13C NMR spectroscopy, and single crystal X-ray diffraction analysis. For the titanium(III) complexes solution magnetic moments were measured by the Evans method and EPR spectra recorded as toluene glass at 77 K.

Enhanced catalytic activity of copper complexes in microgels for aerobic oxidation of benzyl alcohols.

Catalytically active copper bis(pyrazolyl)methane complexes have been anchored into pVCL-GMA microgels on specified positions within the microgel network. Functionalized microgels act as nanoreactors providing a tailored environment and stabilization for the copper complexes thus increasing the product yield. The oxidation of benzyl alcohols to their respective aldehydes was chosen as a test reaction to show the enhancement of catalytic activity due to the immobilization of the copper complex compared to the copper salt and the molecular copper complex.

Pyrophosphate modulates plant stress responses via SUMOylation.

Pyrophosphate (PPi), a byproduct of macromolecule biosynthesis is maintained at low levels by soluble inorganic pyrophosphatases (sPPase) found in all eukaryotes. In plants, H+-pumping pyrophosphatases (H+-PPase) convert the substantial energy present in PPi into an electrochemical gradient. We show here, that both cold- and heat stress sensitivity of fugu5 mutants lacking the major H+-PPase isoform AVP1 is correlated with reduced SUMOylation. In addition, we show that increased PPi concentrations interfere with SUMOylation in yeast and we provide evidence that SUMO activating E1-enzymes are inhibited by micromolar concentrations of PPi in a non-competitive manner. Taken together, our results do not only provide a mechanistic explanation for the beneficial effects of AVP1 overexpression in plants but they also highlight PPi as an important integrator of metabolism and stress tolerance.

Copper Guanidinoquinoline Complexes as Entatic State Models of Electron-Transfer Proteins.

The electron-transfer abilities of the copper guanidinoquinoline (GUAqu) complexes [Cu(TMGqu)2 ]+/2+ and [Cu(DMEGqu)2 ]+/2+ (TMGqu=tetramethylguanidinoquinoline, DMEGqu=dimethylethylguanidinoquinoline) were examined in different solvents. The determination of the electron self-exchange rate based on the Marcus theory reveals the highest electron-transfer rate of copper complexes with pure N-donor ligands (k11 =1.2×104  s-1 m-1 in propionitrile). This is supported by an examination of the reorganisation energy of the complexes by using Eyring theory and DFT calculations. The low reorganisation energies in nitrile solvents correspond with the high electron-transfer rates of the complexes. Therefore, the [Cu(GUAqu)2 ]+/2+ complexes act as good entatic states model of copper enzymes. The structural influence of the complexes on the kinetic parameters shows that the TMGqu system possesses a higher electron-transfer rate than DMEGqu. Supporting DFT calculations give a closer insight into the kinetics and thermodynamics (Nelsen's four-point method and isodesmic reactions) of the electron transfer.

The endoplasmic reticulum is the main membrane source for biogenesis of the lytic vacuole in Arabidopsis.

Vacuoles are multifunctional organelles essential for the sessile lifestyle of plants. Despite their central functions in cell growth, storage, and detoxification, knowledge about mechanisms underlying their biogenesis and associated protein trafficking pathways remains limited. Here, we show that in meristematic cells of the Arabidopsis thaliana root, biogenesis of vacuoles as well as the trafficking of sterols and of two major tonoplast proteins, the vacuolar H(+)-pyrophosphatase and the vacuolar H(+)-adenosinetriphosphatase, occurs independently of endoplasmic reticulum (ER)-Golgi and post-Golgi trafficking. Instead, both pumps are found in provacuoles that structurally resemble autophagosomes but are not formed by the core autophagy machinery. Taken together, our results suggest that vacuole biogenesis and trafficking of tonoplast proteins and lipids can occur directly from the ER independent of Golgi function.