New catalytic systems based on fluorine-containing titanium(iv) alkoxides for the synthesis of ultrahigh-molecular-weight polyethylene and olefin elastomers

The catalytic activity of the systems based on titanium(iv) alkoxides (Ti(OPrⁱ)₄, Ti(OPrⁱ)₂(OCH(CF₃)₂)₂, and Ti(OCH(CF₃)₂)₄) and mixtures of alkylaluminum chlorides (Et₂AlCl or Et₃Al₂Cl₃) with dibutylmagnesium in ethylene polymerization and ethylene copolymerization with propylene and 5-ethylidene-2-norbornene was studied. Ultrahigh-molecular-weight polyethylene with the molecular weight reaching 4.9 · 10⁶ Da was found to be formed in the homopolymerization reaction, whereas copolymerization gives ter-copolymers containing propylene (up to 35 mol.%) and 5-ethylidene-2-norbornene (4.3 mol.%) units.

     

PASE synthesis of 1-azolyl-1H-1,2,4-triazoles by the reaction of diazoazoles with ethyl isocyanoacetate

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Modeling of the glycine tripeptide cyclization in the Ser65Gly/Tyr66Gly mutant of green fluorescent protein

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Binuclear copper(II) complex with 2-imidazolylbenzothiazole and bridged chloride ligands

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Observation of field induced anomalous quantum criticality in Ce0.6Y0.4NiGe2 compound

We report the results of our investigation of magnetization and heat capacity on a series of compounds Ce${}_{1?x}$Y_xNiGe₂ ($x=0.1,0.2\text{ and }0.4$) under the influence of external magnetic field. Our studies of the thermodynamic quantity $?\mathrm{d}M/\mathrm{d}T$ on these compounds indicate that magnetic frustration persists in Ce_0.9Y_0.1NiGe₂, as also reported for the parent compound CeNiGe₂. The weak signature of this frustration is also noted in Ce_0.8Y_0.2NiGe₂, whereas, it is suppressed in Ce_0.6Y_0.4NiGe₂. Heat capacity studies on Ce_0.9Y_0.1NiGe₂ and Ce_0.8Y_0.2NiGe₂ indicate the presence of a new magnetic anomaly at high field which indicates that quantum criticality is absent in these compounds. However, for Ce_0.6Y_0.4NiGe₂ such an anomaly is not noted. For this later compound, the magnetic field (H) and temperature (T) dependence of heat capacity and magnetization obey $H/T$ scaling above critical fields. However, the obtained scaling critical parameter (δ) is 1.6, which is away from mean field value of 3. This deviation suggests the presence of unusual fluctuations and anomalous quantum criticality in these compounds. This unusual fluctuation may arise from disorderness induced by Y-substitution.     

Separation technique based on electrophoresis,chromatography and magnetism phenomena: the migration time and peak broadening

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Pericyclic reactions in the synthesis of new 5-aryl-5,6-dihydroquinolino[2,1-b]quinazolin-12-ones

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Structural impact of GTP binding on downstream KRAS signaling

Oncogenic RAS proteins, involved in ∼30% of human tumors, are molecular switches of various signal transduction pathways. Here we apply a new protocol for the NMR study of KRAS in its (inactive) GDP- and (activated) GTP-bound form, allowing a comprehensive analysis of the backbone dynamics of its WT-, G12C- and G12D variants. We found that Tyr32 shows opposite mobility with respect to the backbone of its surroundings: it is more flexible in the GDP-bound form while more rigid in GTP-complexes (especially in WT- and G12D-GTP). Using the G12C/Y32F double mutant, we showed that the presence of the hydroxyl group of Tyr32 has a marked effect on the G12C-KRAS-GTP system as well. Molecular dynamics simulations indicate that Tyr32 is linked to the γ-phosphate of GTP in the activated states – an arrangement shown, using QM/MM calculations, to support catalysis. Anchoring Tyr32 to the γ-phosphate contributes to the capture of the catalytic waters participating in the intrinsic hydrolysis of GTP and supports a simultaneous triple proton transfer step (catalytic water → assisting water → Tyr32 → O1G of the γ-phosphate) leading to straightforward product formation. The coupled flip of negatively charged residues of switch I toward the inside of the effector binding pocket potentiates ligand recognition, while positioning of Thr35 to enter the coordination sphere of the Mg²⁺ widens the pocket. Position 12 mutations do not disturb the capture of Tyr32 by the γ-phosphate, but (partially) displace Gln61, which opens up the catalytic pocket and destabilizes catalytic water molecules thus impairing intrinsic hydrolysis.

Nucleotide exchange to the physiological, activated, GTP-bound form of KRAS results in the anchoring of Tyr32 within the active site.