Presence Of Hexane Research Articles

A Continuous-Wave EPR Investigation into the Photochemical Transformations of the Chromium(I) Carbonyl Complex [Cr(CO)4bis(diphenylphosphino)]+ and Reactivity with 1-hexene.

Chromium complexes containing a bis(diphenylphosphino) ligand have attracted significant interest over many years due to their potential as active catalysts for ethylene oligomerisation when combined with suitable co-catalysts such as triethylaluminium (TEA) or methylaluminoxane (MAO). While there has been considerable attention devoted to the possible reaction intermediates and the nature of the Cr oxidation states involved, the potential UV photoactivity of the Cr(I) complexes has so far been overlooked. Therefore, to explore the photoinduced transformations of bis(diphenylphosphino) stabilized Cr(I) complexes, we used continuous-wave (CW) EPR to study the effects of UV radiation on a cationic [Cr(CO)4(dppp)]+[Al(OC(CF3)3)4]- complex (1), where dppp represents the 1,3 bis-(diphenylphosphino)propane ligand, Ph2P(C3H6)PPh2. Our preliminary investigations into the photochemistry of this complex revealed that [Cr(CO)4(dppp)]+ (1) can be readily photo-converted into an intermediate mer-[Cr(CO)3(κ1-dppp)(κ2-dppp)]+ complex (2) and eventually into a trans-[Cr(CO)2(dppp)2]+ complex (3) in solution at room temperature under UV-A light. Here, we show that the intermediate species (2) involved in this transformation can be identified by EPR at much lower temperature (140 K) and at a specific wavelength (highlighting the wavelength dependency of the reaction). In addition, small amounts of a 'piano-stool'-type complex, namely [Cr(CO)2(dppp-η6-arene)]+ (4), can also be formed during the photoconversion of [Cr(CO)4(dppp)]+ using UV-A light. There was no evidence for the formation of the [Cr(L-bis-η6-arene)]+ complex (5) in these UV irradiation experiments. For the first time, we also evidence the formation of a 1-hexene coordinated [Cr(CO)3(dppp)(1-hexene)]+ complex (6) following UV irradiation of [Cr(CO)4(dppp)]+ in the presence of 1-hexene; this result demonstrates the unprecedented opportunity for exploiting light activation during Cr-driven olefin oligomerisation catalysis, instead of expensive, difficult-to-handle, and hazardous chemical activators.

Molecular cloning, overexpression, characterization, and In silico modelling analysis of a novel GDSL autotransporter-dependent outer membrane lipase (OML) of Pseudomonas guariconensis

The outer membrane lipase (oml) gene, encoding a novel autotransporter-dependent lipase from Pseudomonas guariconensis, was cloned and sequenced. The oml gene has an open reading frame of 1866 bp. It encodes the 621 amino acid autotransporter-dependent GDSL lipase (OML), which has the highest sequence similarity (64.08 %) with the EstA of Pseudomonas aeruginosa (PDB:3kvn.1. A). OML was expressed and purified, which showed a purified band of approximately 70 kDa. The purified enzyme showed maximum activity at pH 9 and 40 °C. Substrate specificity studies and kinetic study by Lineweaver-Burk plot of purified OML showed Km of 1.27 mM and Vmax of 333.33 U/mL with p-nitrophenyl palmitate. The purified enzyme showed good stability in the presence of hexane, methanol, and ethanol, while the presence of the metal ion Mg2+ showed maximum lipase activity. Bioinformatics analysis supported the in vitro findings by predicting enzyme substrate specificity towards long-chain fatty acids and fatty acids with shorter chain lengths. The stability of the interaction of the protein-ligand complex (OML-ricinoleic acid) was confirmed using MDS and castor oil bioconversion using purified OML was confirmed using High-Performance Liquid Chromatography (HPLC).

Morphofunctional vascular changes in employees of a potash fertilizer plant

The relevance of the work is due to the high risk of the development of production-related pathology in employees of the enterprise for the production of potash fertilizers. The study aims to assess the morphofunctional state of the arteries as an early marker of production-related pathology in employees of a potash fertilizer plant. The authors examined 160 workers engaged in the production of potash fertilizers and engaged in work with harmful working conditions (observation group). The comparison group included 82 people who were not exposed to harmful production factors in the course of their work. We conducted an analysis of working conditions, an assessment of the air quality in the work area for the content of hexane, heptane and formaldehyde. To determine the studied chemical compounds in biological media (blood, urine), the researchers used chemical-analytical methods. The scientists used ultrasound diagnostics to assess endothelium-dependent vasodilation of the brachial artery, and also used sphygmomanometry to study the stiffness of the arterial wall. There is a presence of hexane, heptane and formaldehyde in the air of the working area of the observation group. In those working in harmful working conditions, the content of formaldehyde in the blood, heptane and hexane in the urine exceeded the indicators of the comparison group by 1.2-1.5 times. 65.3% of the employees of the observation group showed a decrease in the extensibility of the vascular wall, while the risk of developing these changes in them is 1.5 times higher than the comparison group. In 29.8% of cases in the observation group, we diagnosed signs of endothelial dysfunction, mainly of moderate severity, due to increased levels of formaldehyde in the blood and heptane in the urine. The risk of developing endothelial dysfunction in workers in harmful working conditions was 2.3 times higher. The revealed violations in workers engaged in the production of potash fertilizers in the form of a decrease in the extensibility of the vascular wall and signs of endothelial dysfunction indicate the presence of additional risk factors for cardiovascular diseases.

Development of the production process of biodiesel from soy seed with cosolvent

Due to the expected depletion of the energy generated by non-renewable fuel sources, the development of biofuels is needed. This investigation proposed developing a process for biodiesel with two-phase solvent extraction technology. The seed fed in the process was extracted with Hexane, methanol, and water solution with a mass proportion of 3:5.4:1 (Hexane: methanol: oil) to separate the free fatty acids from the crude oil. The reaction happened with homogeneous alkali catalysis in the presence of Hexane (cosolvent). It used a molar ratio of methanol: oil of 6:1 and a mass ratio of 0.75% NaOH and 1.49 Hexane. After the purification, 0.941 kg of biodiesel per kg of oil fed to the process was obtained, and it meets the ANP regulations in some of the physicochemical proprieties. It also obtained 0.0985 kg of glycerine per kg of oil fed to the process with 99% purity.

Preparation and mechanical characterization of (rubber blend - micro lead) rubbery composites for shielding application

This present work, includes the preparation of rubber batches containing silicone rubber (SIR) (80pphr) and polyurethane (PU) (20pphr) with micro-lead powder in different loading, respectively (0,20.40,60,80,100,150,200,250,300pphr). The mechanical properties measured the device universal tensometer, such as tensile strength, elongation and modulus of elasticity, according standard specified of (ASTM D-412) were followed and the hardness property measured by (Hardness Shore A) was put through its steps according to the standard specification (ASTMD-1415). The results were selected, and the sample (10) consisting of (SIR 80/PU20 and micro-lead 300pphr) was chosen because it is more suitable for the required mechanical properties. The results observed that the ratios of micro-lead loading increased, the tensile and elongation decreased, and the hardness and elastic modulus increased. Rubber batches reinforced with micro-lead were exposed to an infrared (FTIR) test device with the addition of hexane, where there were no changes in the infrared spectrum of the rubber composites (SIR80/PU20/Micro-Pb). Sample No. (10) was shown that the scanning electron microscope (SEM) before and after adding hexane, where it was noted that the image (A) without hexane, the absence of homogeneity of lead. As for image (B) in the presence of hexane, we note the homogeneity of lead and the distribution of lead equally, so that radiation examination were measured the Geiger counter of two sources of radioactive elements were used, the caesium source Cs137 and the cobalt source Co60. The radiation is attenuated through the material, while the thickness of the half (X1/2) gradually contrasts according to the attenuation of the radiation. This work is applied in the applications of shields as a protective suit against harmful radiation.

Enhanced Laplace Pressures for Functional Surfaces: Wicking, Switchability, and Selectivity

AbstractWetting functionalities of rough surfaces are largely determined by the Laplace pressure generated across liquid–gas interfaces formed within surface structures. Typically, rough wetting surfaces create negative Laplace pressures, enabling capillary wicking, while rough non‐wetting surfaces create positive Laplace pressures, exhibiting fluid repellency. Here, with microfabricated reentrant structures, it is shown that the same surface can exhibit either a negative or positive Laplace pressure, regardless of its intrinsic wettability. This material‐independent Laplace pressure duality enables or enhances a range of wetting functionalities including wicking, switchability, and selectivity. On the same surface, capillary rise, capillary dip, and the combination of the two which leads to further enhancement of the total sustainable capillary height and Laplace pressure, the driving force for wicking is demonstrated. Further, active switching of wetting states between the hemiwicking and the repellent Cassie state on reentrant structures is shown. Moreover, with a water‐hexane mixture system, selective wetting of reentrant structures are demonstrated, that is, water can be selectively wicked or repelled in the presence of hexane, and vice versa. These functionalities are achieved, which would typically require complex chemical coatings, solely using surface structures, thus largely expanding the design space for a wide range of thermofluidic applications.

Textural, rheological and sensorial properties of mayonnaise fortified with Asian sea bass bio‐calcium

AbstractAsian sea bass bio‐calcium (ASBC) can be fortified in low calcium food product such as mayonnaise. To ensure the smoothness of fortified products, the particle size and fishy compounds of ASBC must be reduced. Ultrasonicated ASBC (U‐ASBC) was applied for different times (5–15 min) in the presence of hexane. ASBC and U‐ASBC had mean particle size (D43) of 21.87 ± 19.54 and 7.83 ± 7.10 μm, respectively. U‐ASBC had lowered volatile compounds. Mayonnaise fortified with ASBC had the augmented firmness, consistency and cohesiveness with increasing ASBC levels (0%–10%) (p < 0.05). ASBC raised lightness (L*) and total color difference (ΔE*), but decreased a* and b*‐values of mayonnaise in a dose dependent manner (p < 0.05). Higher G′, G″, viscosity and shear stress value were observed in mayonnaise sample added with ASBC. However, lower acceptability was attained when mayonnaise was added with ASBC at level higher than 2.5% due to fishy odor and grittiness perceived by panelists. The lower droplet size with higher zeta potential of mayonnaise added with ASBC or U‐ASBC was related with the lower creaming index. Mayonnaise added with 7.5% U‐ASBC (M‐UBC‐7.5) had higher viscosity with lower creaming and thermal creaming index (p < 0.05) than control and that containing 2.5% ASBC (M‐BC‐2.5). Denser and smaller droplet sizes were observed for M‐BC‐2.5 and M‐UBC‐7.5 than control. Lowest moisture, fat and carbohydrate contents were attained for M‐UBC‐7.5 with the higher protein, ash and calcium content (p < 0.05). Fortification of mayonnaise with ASBC at 2.5% or U‐ASBC at 7.5% increased calcium content by 54 or 174 times, respectively, without sensorial changes.

Influence of unsaturated aliphatic and aromatic volatile organic compounds on the oxidation of aqueous sulfur dioxide by oxygen in aqueous medium

The trace atmospheric volatile organic compounds(VOCs) are reported to influence the oxidation of dissolved sulfur dioxide, S(IV), by oxygen, which is an important reaction in atmospheric acid formation. In this work, the influence of 15 VOCs on uncatalyzed oxidation of S(IV) by oxygen has been investigated by following the disappearance of [O2]. The inhibition of oxidation reaction by toluene, aniline, benzene, cinnamic acid, hydroquinone, acrylamide, acrylonitrile and allyl alcohol was defined by the rate law(A):kVOC = k0/(1+B [Inh]) (A)where, kVOC, and k0 are the first order rate constants in the presence and the absence of VOCs respectively. B is the inhibition parameter and [Inh] is the concentration of inhibitor.On the other hand, fumaric, maleic and crotonic acids, which have conjugated CC bonds, catalyze the reaction defined by the rate law(B):kVOC = k0 + kcat [VOC] (B)where kcat is catalytic constant and [VOC] is the concentration of catalytic VOC.Interestingly, presence of 1-hexene, cyclohexene, methacrylic acid, methyl acrylate was without any significant effect on the rate of reaction.

Comparative analysis of the catalysis and stability of the native, recombinant and metagenomic alkaline proteases in organic solvents.

The effect of organic solvents on alkaline proteases was assessed for native, recombinant, and metagenomically derived alkaline proteases. Their stability and the effects of physicochemical parameters were studied in the presence of hexane. The native enzyme was comparatively more resistant against the organic solvents than the recombinant counterparts. On the other hand, the metagenomically derived alkaline protease was minimally resistant against solvents. A similar trend was apparent for the stability of enzyme in organic solvents. The novelty of this study lies in the fact that the majority of the studies on the solvent tolerance have focused on the mesophilic enzymes, while those from the haloalkaliphilic bacteria have received little attention. The comparative tolerance of the native, recombinant, and metagenomic alkaline proteases against the organic solvent has practical importance. The phylogenetic relatedness among the various protease sequences will be described.

Novel Cold-Adapted Recombinant Laccase KbLcc1 from Kabatiella bupleuri G3 IBMiP as a Green Catalyst in Biotransformation.

Cold-adapted enzymes are useful tools in the organic syntheses conducted in mixed aqueous-organic or non-aqueous solvents due to their molecular flexibility that stabilizes the proteins in low water activity environments. A novel psychrophilic laccase gene from Kabatiella bupleuri, G3 IBMiP, was spliced by Overlap-Extension PCR (OE-PCR) and expressed in Pichia pastoris. Purified recombinant KbLcc1 laccase has an optimal temperature of 30 °C and pH of 3.5, 5.5, 6.0, and 7.0 in the reaction with 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), guaiacol, sinapic acid, and syringaldazine, respectively. Moreover, laccase KbLcc1 is highly thermolabile, as it loses 40% of activity after 30 min at 40 °C and is inactivated at 50 °C after the same period of incubation. The new enzyme remained active with 1 mM of Ni2+, Cu2+, Mn2+, and Zn2+ and with 2 mM of Co2+, Ca2+, and Mg2+, but Fe2+ greatly inhibited the laccase activity. Moreover, 1% ethanol had no impact on KbLcc1, although acetone and ethyl acetate decreased the laccase activity. The presence of hexane (40%, v/v) caused a 58% increase in activity. Laccase KbLcc1 could be applied in the decolorization of synthetic dyes and in the biotransformation of ferulic acid to vanillin. After 5 days of reaction at 20 °C, pH 3.5, with 1 mM ABTS as a mediator, the vanillin concentration was 21.9 mg/L and the molar yield of transformation reached 14.39%.

Smartphone-based detection of lung cancer-related volatile organic compounds (VOCs) using rapid synthesized ZnO nanosheet

Point of care (POC) determination of volatile organic compounds (VOCs) in the ppb level is essential for non-invasive diagnosis applications. Chemical sensors are promising options to monitor VOCs in exhaled breath as disease biomarkers. Gas sensors based on nanostructured ZnO have received significant attention because of their advantages in enhancing gas sensing performance. In this study, a simple direct method is introduced for the rapid synthesis of zinc oxide nanosheet, and its application to fabricate a susceptible sensitive, smartphone-based resistive gas sensor for measurement of VOCs, that, are considered as lung cancer biomarkers. Zinc foil was anodized in KNO3 aqueous electrolyte at room temperature to synthesize nanosheets with approximate widths of 24 nm. The fabricated chemiresistive gas sensor using the synthesized ZnO nanosheet structure showed high sensitivity to measure VOCs such as diethyl ketone, acetone, and Isopropanol. An Arduino Uno with a Bluetooth module was used to read the fabricated ZnO-based sensor and send data to a smartphone. The smartphone-based chemiresistor device exhibited a high response to a low concentration of lung cancer-related volatile organic compounds. High humidity and the presence of hexane, ammonia, and carbon dioxide in the sensor environment didn’t affect the sensor response. The fabricated devices have the potential for non-invasive diagnosis of lung cancer in the early stage by analyzing relative biomarkers in exhaled breath.

Biodiesel production from milk thistle seed oil as nonedible oil by cosolvent esterification–transesterification process

AbstractThe crude oil extracted from milk thistle seeds was employed as a precursor for creating biodiesel (BD) via the cosolvent esterification–transesterification process. The high acid value of the extracted oil (11.90 mg KOH/g) encouraged its pre‐esterification in the occurrence of hexane as a cosolvent. The cosolvent esterification of oil diminished its acidity index to below 2.0 mg KOH/g using 1.5:1 hexane:methanol volume ratio, 50°C, 60‐min reaction time, 6:1 methanol:oil molar ratio, and 0.75 wt.% HCl. Alcoholysis reaction of the esterified oil with methanol and a blend of methanol:ethanol to synthesize, respectively, methylic BD and methylic/ethylic BD was accomplished in the presence of hexane as a cosolvent as well. Under the ideal reaction conditions, methylic BD yield and methylic/ethylic BD yield were 96.23% and 95.63%, respectively. The Fourier‐transform infrared (FTIR) and 1H nuclear magnetic resonance (NMR) spectra affirmed the lipid transformation from milk thistle seeds into BD. The attained samples of BD exhibited properties conforming to those specified by ASTM D6751. Also, the cosolvent methanolysis kinetic obeyed the pseudo‐first‐order with 35.94 KJ/mol activation energy and 6.32‐s frequency factor.

Aliphatic and aromatic hydrocarbons in comet 67P/Churyumov-Gerasimenko seen by ROSINA

Context.Unlike all previous cometary space missions, the Rosetta spacecraft accompanied its target, comet 67P/Churyumov-Gerasimenko, for more than two years on its way around the Sun. Thereby, an unexpected diversity and complexity of the chemical composition was revealed.Aims.Our first step of decrypting the exact chemical composition of the gaseous phase is the identifying and quantifying the bulk composition of the pure aromatic and aliphatic hydrocarbons.Methods.For this study, data from ROSINA–Double Focusing Mass Spectrometer (DFMS) onboard the Rosetta spacecraft and the laboratory twin model were used. A joint campaign of laboratory calibration measurements and space data analysis was performed to derive the hydrocarbon bulk composition for the post-inbound equinox period at 1.52 AU in May 2015. Furthermore, several other mission phases were investigated to determine the dependencies of season, location, and heliocentric distance on the relative abundances of hydrocarbons.Results.It is shown that the bulk composition of the gaseous phase includes a high number of aliphatic compounds such as methane, ethane, and propane, as well as the aromatic compounds benzene and toluene. Butane and pentane were successfully identified in measurements at closer distance to the comet in May 2016. Furthermore, the presence of hexane and heptane in the coma is confirmed on rare occasions during the mission. Their presence in DFMS space data appears to be linked to days or periods of high dust activity. In addition to the saturated aliphatic and aromatic compounds, a high number of remaining unsaturated species is present, which cannot be explained by fragmentation of saturated species or contribution from other organic molecules in addition to pure hydrocarbons. This indicates the existence of unsaturated aliphatic and aromatic hydrocarbon molecules in the coma of comet 67P.

Effect of 1-Propanol and TBAB on Gas Hydrates Dissociation Conditions for CO2 + Hexane + Water Systems

Hydrate equilibrium conditions of carbon dioxide in the presence of hexane in aqueous solutions of 1-propanol/tetra-n-butyl ammonium bromide (TBAB) have been studied in this Article. The hydrate di...

Studies on sorption of bifenthrin and diazinon insecticides on molecularly imprinted polymers

Synthesis and characterization of polymeric matrices for molecular recognition of pesticides are presented. For their preparation, methacrylic acid as a functional monomer and ethylene glycol dimethacrylate as a cross‐linking agent were used. As template molecules, diazinon and bifenthrin were applied. Syntheses were carried out in the presence of different porogens. Chemical structures were studied using FTIR‐ATR, elemental analysis, and alkacymetric titration, morphology by laser diffraction particle size analyzer and by particle size, and shape analyzer based on image analysis, whereas porous structure by nitrogen adsorption/desorption method. To study selectivity of the sorbent toward template molecule, breakthrough volumes and sorption kinetics for molecularly imprinted polymers and nonimprinted analogues were determined. Particle sizes of the studied sorbents (expressed as CE diameter) were in the range 40 to 44 μm (except sorbent obtained in the presence of hexane). The chemical composition of all obtained sorbents was close to theoretical one (60.13% C, 7.11% H, 32.77% O). The values of specific surface area of the sorbents were in the range 2 to 338 m2/g.

A novel beta-1,4 glucanase produced by symbiotic Bacillus sp. CF96 isolated from termite (Anacanthotermes)

A novel beta-1,4-glucanase was purified and characterized from symbiotic Bacillus sp. CF96 of termite. The SDS-PAGE and zymogram analyses revealed a molecular mass of 35.6 kDa. Optimal activity was at 50 °C and pH 5.5, while the enzyme was active over a wide range of temperature 20-80 °C and pH 4-10 and interestingly more than 60% of the maximum activity remained up to pH 9. The enzyme activity increased in the presence of hexane, chloroform and methanol (20% v/v). while, the enzyme activity was inhibited by metal ions such as Mn2+, Hg2+, Cu2+, Zn2+, Mg2+, Fe2+. The isolated enzyme was able to degrade carboxymethyl cellulose (CMC), avicel and cellulose. Cellobiose was the hydrolytic product of enzymatic reaction based on thin layer chromatography (TLC) analysis. Regarding beta-1,4 endo/exoglucanase activity and high temperature, pH and solvent stability, the enzyme has potential for various industrial applications especially in designing pesticide for termite.

Composition and Property Changes in Oil Dispersions After Hydrothermal Treatment of Rock-Forming Minerals with Hydrocarbon Solvents

Group and elemental compositions and structures of hydrocarbon dispersions in super-viscous oil resulting from steam and heat exposure at 140-190°C and 3-6 atm in the presence of hexane and benzene are established using simplified models of terrigenous and carbonate reservoirs. A relationship between the composition and structure of the oil dispersions after steam-heat action and a temperature dependence of viscosity are established. Solvate shells of increased thickness around complex structural unit nuclei and a greater proportion of dispersion medium are distinctive features of the low-viscosity displaced oil. Studies show that the dispersion medium impacts greatly the formation and properties of the oil dispersion. Benzene in the displacing agent decreases the degree of dispersion of the system and the viscosity of the displaced oil.

Molecular mechanism of enzyme tolerance against organic solvents: Insights from molecular dynamics simulation

Biocatalysis in presence of organic solvents has numerous industrially attractive advantages in comparison to traditional aqueous solvents. In some cases, the presence of organic molecules such as methanol in the processes such as enzymatic production of biodiesel is inevitable. However, enzyme inactivation and/or instability in organic solvents limits such biotechnological processes. Although it was found that some enzymes are more and others are less tolerant against organic solvents, the structural basis of such differences is relatively unknown. In this work, using molecular dynamics simulations, we have investigated the structural behavior of enzymes with completely different structural architecture including lipase, laccase and lysozyme in the presence of methanol as polar and hexane as non-polar organic solvents. In agreement with the previous experimental observations, simulations showed that lipase is more tolerant against both polar and non-polar organic solvents. It is found that lipase has high stability in pure hexane even higher than that obtained in the aqueous solvent. In contrast, laccase shows better stability in the aqueous conditions. To obtain general mechanism of enzyme inactivation in the presence of methanol and hexane, we have treated lysozyme as model enzyme in the different percentages of these solvents in long MD simulations. It is found that lysozyme is completely denatured at high concentration- of methanol, but it remains native at low concentration of this solvent. Interestingly, the concentration-dependence structural behavior of enzyme was completely different in the presence of hexane. It was obtained that low concentrations of hexane may impose more instability on the enzyme conformation than higher percentages. Results also showed that presence of water is determining factor in the enzyme stability at high concentrations of hexane. Pure hexane may also lead to the surface denaturation of the enzymes. Both methanol and hexane denaturation mechanisms were initiated by diffusion of organic solvent in hydrophobic core. However, enzyme denaturation in hexane was continued by a collapse of hydrophobic core and entering hexane molecules to the core, but in methanol it was completed by decomposition of the secondary structures. In both cases it was found that beta structures are more prone to destabilize than helix structures. This may be a reason for obtained results about lower stability of laccase with β-barrel architecture than lipase with multiple helixes at it surface. In total, by our extensive structural data, it was found that the forces which stabilize tertiary structure have pivotal role in enzyme tolerance against both polar and non-polar organic solvents.

How Close Is Too Close? Polymerization Behavior and Monomer-Dependent Reorganization of a Bimetallic Salphen Organotitanium Catalyst

The binuclear salphen Ti polymerization catalyst N,N′-1,2-phenylene[(salicylideneaminato)Ti(Cp*)Me2)]2 (2) is synthesized by reaction of salphen-H2 with Cp*TiMe3. Mononuclear [N-(2,6-diisopropyl)phenyl(salicylideneaminato)]Ti(Cp*)Me2 (1) serves as a control. Activation studies of 2 with cocatalyst Ph3C+B(C6F5)4– yield the cationic polymerization-inactive complex [N,N′-1,2-phenylene(salicylideneaminato)Ti(Cp*)]+B(C6F5)4– (4) and polymerization-active Cp*TiMe2+B(C6F5)4–. Polymerization studies comparing 2 with Cp*TiMe3 suggest that, within the catalytic time frame, while 2 retains bimetallic character under an ethylene atmosphere, it rapidly decomposes to 4 and Cp*TiMe2+ in the presence of 1-hexene. These monomer-dependent reorganization results highlight the importance of olefin polymerization activation mechanistic studies while providing insight for improved bimetallic catalyst design.

Nanoscale liquid crystal lubrication controlled by surface structure and film composition.

Liquid crystals have emerged as potential candidates for next-generation lubricants due to their tendency to exhibit long-range ordering. Here, we construct a full atomistic model of 4-cyano-4-hexylbiphenyl (6CB) nematic liquid crystal lubricants mixed with hexane and confined by mica surfaces. We explore the effect of the surface structure of mica, as well as lubricant composition and thickness, on the nanoscale friction in the system. Our results demonstrate the key role of the structure of the mica surfaces, specifically the positions of potassium (K+) ions, in determining the nature of sliding friction with monolayer lubricants, including the presence or absence of stick-slip dynamics. With the commensurate setup of confining surfaces, when the grooves created between the periodic K+ ions are parallel to the sliding direction we observe a lower friction force as compared to the perpendicular situation. Random positions of ions exhibit even smaller friction forces with respect to the previous two cases. For thicker lubrication layers the surface structure becomes less important and we observe a good agreement with the experimental data on bulk viscosity of 6CB and the additive hexane. In case of thicker lubrication layers, friction may still be controlled by tuning the relative concentrations of 6CB and hexane in the mixture.