Cationic olefin Pd(II) complexes bearing α-iminoketone N,O-ligands: unprecedented isomerisation of the methoxycyclooctenyl ligand

The reaction of [Pd(η¹,η²-C₈H₁₂OMe)Cl]₂ with α-iminoketone ligands affords cationic η¹,η²-5-methoxycyclooctenyl Pd(II) complexes, the intramolecular and interionic structures of which were investigated in both solution and solid state; such complexes undergo unprecedented isomerisation to η¹,η²-1-methoxycyclooctenyl complexes assisted by weak nucleophiles such as olefins or alkynes.     

Adsorbed states of K on the diamond (100)(2×1) surface

The adsorbed states of K on the C(100)(2×1) surface have been studied by electron energy loss spectroscopy (EELS), work function change (Δφ) measurement and thermal desorption spectroscopy (TDS). In the region where the K coverage is less than one-half of a monolayer (θ_K≤0.5), a loss is observed from ∼1.2 eV (θ_K=0.2) to 1.0 eV (θ_K=0.5); the work function decreases upon K adsorption until reaching a shallow minimum of Δφ=−3.35 eV at θ_K=∼0.5; and a desorption peak (β) is observed from ∼825 K (θ_K=0.05) to 525 K (θ_K=0.5). These results indicate that the K–substrate bond is highly polarized; the 1.2 eV loss is attributed to the electronic transition from the bonding to antibonding states formed at the K–substrate interface. In the region between θ_K=0.5 and 1, two losses are observed at 0.7 and 1.4 eV (θ_K=0.6); there is only a small increase of the work function; and a desorption peak (α) is observed in addition to the β peak. These results indicate that the K regains its electron and becomes, essentially, neutral. The 1.4-eV loss is ascribed to the transition from the 4s to 4p states of K. The origin of the 0.7-eV loss is discussed. The Δφ and TDS results are analyzed by the depolarization model.     

Insertion of heme b into the structure of the Cys34-carbamidomethylated human lipocalin α(1)-microglobulin: formation of a [(heme)(2) (α(1)-Microglobulin)](3) complex

α(1)-Microglobulin (α(1)m) is a 26 kDa plasma and tissue protein belonging to the lipocalin protein family. Previous investigations indicate that the protein interacts with heme and suggest that it has a function in heme metabolism. However, detailed characterizations of the α(1)m-heme interactions are lacking. Here, we report for the first time the preparation and analysis of a stable α(1)m-heme complex upon carbamidomethylation of the reactive Cys34 by using recombinantly expressed human α(1)m. Analytical size-exclusion chromatography coupled with a diode-array absorbance spectrophotometry demonstrates that at first an α(1)m-heme monomer is formed. Subsequently, a second heme triggers oligomerization that leads to trimerization. The resulting (α(1)m[heme](2))(3) complex was characterized by resonance Raman and EPR spectroscopy, which support the presence of two ferrihemes, thus indicating an unusual spin-state admixed ground state with S=(3)/(2), (5)/(2).     

Unusual thermal stabilities of some proteins and enzymes bound in the galleries of layered α-Zr(IV)phosphate/phosphonates

Significant improvements in the thermal stabilities of proteins and enzymes (increase in denaturation temperatures as large as 33 °C) bound in the galleries of crystalline α-Zr(IV) phosphate (α-Zr(PO₄)₂·H₂O, abbreviated as α-ZrP) and α-Zr(IV) phosphonates (α-Zr(RPO₃)₂·H₂O, RCH₂COOH, CH₂CH₂COOH, abbreviated as ZrCMP, and ZrCEP, respectively) are demonstrated, in specific cases. The thermal stabilities are monitored using attenuated total reflection Fourier transform infrared spectroscopy (ATR FTIR), powder X-ray diffraction, absorption, and fluorescence methods. The amide I and amide II vibrational bands of the protein/inorganic materials are monitored in ATR FTIR studies, as a function of temperature, and these indicated sharp shifts in the band positions at specific temperatures. These shifts served as markers for protein denaturation. The denaturation temperatures of met hemoglobin/α-ZrP, glucose oxidase/α-ZrRP (ROH, CH₂CH₂COOH), and Cytochrome c/α-ZrRP (ROH, CH₂CH₂COOH), for example, are >95, 55, 65, 100, and 75 °C, respectively. These values are greater than the denaturation temperatures of the corresponding free proteins in the solid state (70, 50, and 67 °C, respectively). Proteins bound to α-ZrP, and α-ZrCEP, in general, indicated stabilities that are greater than or comparable to those of the free proteins, while binding to α-ZrCMP resulted in diminished stabilities except in case of Hb. The interactions of the surface functions of the solid matrix with the bound protein, therefore, are crucial in determining the bound protein stability. The improved stabilities observed in specific cases are welcome changes for applications of these materials in biocatalysis, biosensors, and biomedical devices.     

Effect of pressure and treatment temperature on the structural evolution of mechanically alloyed Ti(W)(C,N)–Al admixes in boron nitride

The effect of pressure and temperature on the structural changes of admixtures of cBN, Al and Ti(C_0.5N_0.05) or Ti(C_0.5N_0.5)_0.6 mechanically alloyed powders with 40 mass% W were investigated by means of the X-ray diffraction technique. It emerged that pressure and temperature affected the crystal structures and compositions of the binder phases as well as the behaviour of the contaminating Fe. High pressure–high temperature (HPHT) sintering favoured the formation of Ti(W,Al)(C,N) solid-solutions, whereas vacuum annealing favoured the formation of W(Ti,Al) solid-solutions. Products of Ti(C,N)-based crystal lattices remained stable under high pressure (5 GPa), whereas W based crystal lattices were more stable under vacuum (0.001 Pa). Inert single phase binders were formed in HPHT sintered PcBN compacts. Formation of Ti(W,Al)(C,N) by reactions between mechanical alloyed Ti(W)(C,N) powder particles and liquid Al prevented the formation of AlN, AlB₂, α-AlB₁₂, TiN and TiB₂ particles in PcBN compacts. Sintering of PcBN occurred by dissolution of B and N atoms in Ti(W,Al)(C,N) and re-precipitation on cBN particles.     

Supported Ziegler type catalysts for production of polyethylene (PE): Effect of the composition of the active component,the methods of its formation,and the use of modifying agents on catalytic activity and molecular structure of PE and copolymers of ethylene with α-olefins

Summarized results are presented from studying the formation of the active component of supported Ziegler type catalysts, investigating the effect of the composition of these catalysts on the molecular mass characteristics of PE, and seeking new methods for producing catalysts with optimum morphology.     

Hydrothermal synthesis of α-MnO2/MIL-101(Cr) composite and its bifunctional electrocatalytic activity for oxygen reduction/evolution reactions

An α-MnO₂/MIL-101(Cr) composite catalyst was synthesised using a hydrothermal process. In this composite, α-MnO₂ nanoparticles are embedded in an MIL-101(Cr) matrix with abundant micropores and a high specific surface area, which improves the reactant's accessibility to catalytically active sites, resulting in a significant improvement in oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in an alkaline electrolyte. The strong interactions between α-MnO₂ nanoparticles and MIL-101(Cr) matrix result in a high structural stability and therefore excellent activity stability.     

Kinetics studies on the inhibition mechanism of pancreatic α-amylase by glycoconjugated 1H-1,2,3-triazoles: a new class of inhibitors with hypoglycemiant activity

Glycoconjugated 1H-1,2,3-triazoles (GCTs) comprise a new class of glycosidase inhibitors that are under investigation as promising therapeutic agents for a variety of diseases, including type 2 diabetes mellitus. However, few kinetics studies have been performed to clarify the mode of inhibition of GCTs with their target glycosidases. Our group has previously shown that some methyl-β-D-ribofuranosyl-1H-1,2,3-triazoles that inhibit baker's yeast maltase were also able to reduce post-prandial glucose levels in normal rats. We hypothesized that this hypoglycemiant activity was attributable to inhibition of mammalian α-glucosidases involved in sugar metabolism, such as pancreatic α-amylase. Hence, the aim of this work was to test a series of 26 GCTs on porcine pancreatic α-amylase (PPA) and to characterize their inhibition mechanisms. Six GCTs, all ribofuranosyl-derived GCTs, significantly inhibited PPA, with IC(50) values in the middle to high micromolar range. Our results also demonstrated that ribofuranosyl-derived GCTs are reversible, noncompetitive inhibitors when using 2-chloro-4-nitrophenyl-α-D-maltotrioside as a substrate. E/ES affinity ratios (α) ranged from 0.3 to 1.1, with the majority of ribofuranosyl-derived GCTs preferentially forming stable ternary ESI complexes. Competition assays with acarbose showed that ribofuranosyl-derived GCTs bind to PPA in a mutually exclusive fashion. The data presented here show that pancreatic α-amylase is one of the possible molecular targets in the pharmacological activity of ribofuranosyl-derived GCTs. Our results also provide important mechanistic insight that can be of major help to develop this new class of synthetic small molecules into more potent compounds with anti-diabetic activity through rational drug design.     

The effect of annealing at 1400 °C on the structural evolution of porous C-rich silicon (boron)oxycarbide glass

A precursor SiBOC glass was annealed at 1400 °C for 1, 3, 5 and 10 h and then it was HF etched in order to dissolve the SiO₂/B₂O₃ phase and to obtain a porous C-rich oxycarbide glass. The porous material was studied by N₂ absorption. The pore diameter of the porous C-rich SiBOC glass ranges between 2 and 5 nm and continuously increases with increasing annealing time. The pore volume also increases with the annealing time up to ≈1.0 cm³/g which is close to the pore volume estimated from the chemical composition (1.04 cm³/g) assuming complete dissolution of the silica-based phase.     

Quantum chemical study of the addition effect on the geometry of the [Mo6S8(CN)6]6− cluster

The geometrical structure and bonding in adducts [Mo₆S₈(CN)₁₂ · Cr(CO)₄L]⁶⁻ (L = CO, PH₃, PF₃, P(OCH₃)₃) were studied on the base of quantum chemical calculations. The main attention was paid to the study of the changes in the cluster geometry under the influence of the attached Cr(CO)₄L group. The large deformations in the Mo₆ core were found and explained by the electrostatic interaction and the pseudo-Jhan–Teller effect. The high values of the calculated polarizabilities of the compounds under consideration are in accord with the obtained results.     

Antioxidant activity of burdock (Arctium lappa Linné): Its scavenging effect on free-radical and active oxygen

The antioxidant activity and free-radical and active oxygen-scavenging activity of burdock extracts were investigated. Of the solvents used for extraction, water yielded the greatest amount of extract that exhibited the strongest antioxidant activity. Water extracts of burdock (WEB) and hot water extracts of burdock (HWEB) exhibited comparable and marked activity on inhibition of linoleic acid peroxidation, indicating that heat treatment did not alter the antioxidant activity of WEB. WEB and HWEB produced significantly lower (P<0.05) malondialdehyde (MDA) in both linoleic acid and liposome model systems than did the control. Moreover, mixtures of tocopherol (Toc), WEB, and HWEB exhibited a remarkable synergistic antioxidant effect in a liposome system; WEB and HWEB thus potentiated the action of Toc. Furthermore, WEB and HWEB displayed a marked inhibitory effect on lipid peroxidation of rat liver homogenate in vitro. WEB and HWEB exhibited an 80% scavenging effect on α,α-diphenyl-β-picrylhydrazyl radical and marked reducing power, indicating that WEB and HWEB act as primary antioxidants. Both extracts at a dose of 1.0 mg exhibited a 60.4–65.0% scavenging effect on superoxide and an 80.5% scavenging effect on hydrogen peroxide. They also showed a marked scavenging effect on the hydroxyl radical. These results revealed that WEB and HWEB are also active as oxygen scavengers and as secondary antioxidants. Based on these results, termination of free-radical reactions and quenching of reactive oxygen species in burdock extracts are suggested to be, in part, responsible for the antioxidant activity of burdock extracts.     

Effects of sublethal deltamethrin on the chemical communication system and PBAN activity of Asian corn borer,Ostrinia furnacalis (Güenee)

Topically applied sublethal doses of deltamethrin may interrupt chemical communication between the two sexes of the Asian corn borer, Ostrinia furnacalis (Güenee), by affecting the probability of calling behavior, sex pheromone titer and PBAN-like activity. At the 1st, 2nd, and 4th day of posttreatment with deltamethrin (1 ng/moth), female O. furnacalis showed 32, 36, and 46% calling probabilities of control female moths, while the sex pheromone titer of females was only 15, 20, and 25% the amount of control females, respectively. The chemical communication system was significantly affected even at the 4th day post-treatment. By injections of 1, 1/2, 1/4, and 1/8 female equivalent of brain and subesophageol ganglion homogenate of 1 ng deltamethrin-treated females into decapitated females, female pheromone production was reduced to 64, 31, 30.7, and 8.1% of that of control female moths, respectively. This result appears to indicate that sublethal deltamethrin affected the activity of the PBAN-like factor of O. furnacalis.     

Preferred partitioning: the influence of coalescents on the build-up of mechanical properties in acrylic core–shell particles (I)

The partitioning of three coalescents of different polarity in different phases of multiphase acrylic particles was studied to provide a rationale for obtaining the desired performance of binders for wood coatings in terms of the ideal balance between hardness development, blocking resistance, and blushing resistance. Minimum film formation temperature- and aqueous differential scanning calorimetry-measurements on the hard phase polymer by itself showed the different extents to which both hydroplasticization and plasticization by the coalescent occur. Dynamic mechanical thermal analysis was subsequently used to visualize wet-T _g effects of three different coalescents in the hard and soft polymer phase of these multiphase acrylic particles. The results have important consequences for the formulation of such binders in applications for exterior wood coatings and coatings in general.     

Unexpected fragmentation of the Fe3(CO)9(μ3-Se)(μ3-AsCH3) cluster core in the reaction with CpCo(CO)2: synthesis and structure of Fe3(CO)6(μ3-Se)(μ-AsCH3{CpFe(CO)2})2(μ-CO)

The [Fe₃(CO)₆(μ₃-Se)(μ-AsCH₃{CpFe(CO)₂})₂(μ-CO)] (Cp=η⁵-C₅H₅) cluster has been obtained by the reaction of [Fe₃(CO)₉(μ₃-Se)(μ₃-AsCH₃)] with [CpCo(CO)₂]. Its crystal and molecular structures have been determined by X-ray analysis.     

Comparative Studies on the Induction of Trichoderma harzianum Mutanase by α-(1→3)-Glucan-Rich Fruiting Bodies and Mycelia of Laetiporus sulphureus

Mutanase (α-(1→3)-glucanase) is a little-known inductive enzyme that is potentially useful in dentistry. Here, it was shown that the cell wall preparation (CWP) obtained from the fruiting body or vegetative mycelium of polypore fungus Laetiporus sulphureus is rich in α-(1→3)-glucan and can be successfully used for mutanase induction in Trichoderma harzianum. The content of this biopolymer in the CWP depended on the age of fruiting bodies and increased along with their maturation. In the case of CWP prepared from vegetative mycelia, the amount of α-(1→3)-glucan depended on the mycelium age and also on the kind of medium used for its cultivation. All CWPs prepared from the individually harvested fruiting body specimens induced high mutanase activity (0.53-0.82 U/mL) in T. harzianum after 3 days of cultivation. As for the CWPs obtained from the hyphal mycelia of L. sulpureus, the maximal enzyme productivity (0.34 U/mL after 3 days of incubation) was recorded for CWP prepared from the 3 week-old mycelium cultivated in Sabouraud medium. Statistically, a high positive correlation was found between the total percentage content of α-(1→3)-glucan in the CWP and the mutanase activity.     

Polypropylene (PP)–Acacia mangiumcomposites: the effect of acetylation on mechanical and water absorption properties

Acacia mangiumwood flour (AMWF)–polypropylene (PP) composites were produced at different filler loading (20, 30, 40, and 50 w/w) and mesh no. (35, 60, 80, and 100 mesh). The AMWF–PP composites (using unmodified or modified wood flour) were compounded using a Haake Rheodrive 500 twin screw compounder. The mechanical and water absorption (WA) properties of modified (only at mesh no. 100) and unmodified AMWF–PP composites were investigated. Increase in the mesh number (35–100) of the unmodified AMWF showed increased flexural and impact properties. Flexural modulus exhibited higher properties as the filler loading increased (20–50). However, flexural and impact strength showed the opposite phenomenon. Water absorption and thickness swelling increased as the mesh number and filler loading increased. This has been attributed to the presence of hydrophilic hydroxyl groups of the filler. Modified AMWF–PP composites exhibited higher mechanical properties and good water resistance when compared to unmodified AMWF–PP composites at all values of filler loading. The evidence of the failure mechanism (from impact strength) of the filler–matrix interface was analyzed using scanning electron microscope.     

Oxidation of cobalt(II) to cobalt(III) in the presence of phosphorus and sulphur donors via –O–C bond cleavage: synthesis and structure of [CoIII(dppe)(EtOCS2)(COS2)] (dppe=1,2-bis(diphenyl phosphino)ethane)

An ethanolic solution of cobalt(II) reacts with dppe (1,2-bis(diphenyl phosphino)ethane) and etxant (ethyl xanthate) affording an intensely coloured Co^III complex, [Co^III(dppe)(etxant)(COS₂)], by eliminating [EtOC(S)(SEt)] via –O–C bond rupture. The structure of the cobalt(III) complex has been confirmed by X-ray crystallography, NMR and mass spectrometry.