SciCombinator

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Concept: Hydroxide

28

The present paper investigates the various features of NaOH aqueous solution when applied as an absorbent to capture carbon dioxide (CO(2)) emitted with relatively high concentration in the flue gas. The overall CO(2) absorption reaction was carried out according to consecutive reaction steps that are generated in the order of Na(2)CO(3) and NaHCO(3). The reaction rate and capture efficiency were strongly dependent on the NaOH concentration in the Na(2)CO(3) production range, but were constant in the NaHCO(3) production step, irrespective of the NaOH concentration. The amount of CO(2) absorbed in the solution was slightly less than the theoretical value, which was ascribed to the low trona production during the reaction and the consequent decrease in CO(2) absorption in the NaOH solution. The mass ratio of absorbed CO(2) that participated in the Na(2)CO(3), NaHCO(3), and trona production reactions was calculated to be 20:17:1, respectively.

Concepts: Carbon dioxide, Chemical reaction, Concentration, Chemistry, Sodium hydroxide, Chlorine, Cellulose, Hydroxide

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To compare the treatment outcomes when calcium hydroxide and mineral trioxide aggregate are used for partial pulpotomy in cariously-exposed young permanent molars in a randomized control trial.

Concepts: Randomized controlled trial, Magnesium, Calcium, Oxide, Calcium carbonate, Hydroxide, Calcium oxide, Calcium hydroxide

27

The reaction of OH with dimethyl ether (CH3OCH3) has been studied from 195 - 850 K using laser flash photolysis coupled to laser induced fluorescence detection of OH radicals. The rate coefficient from this work can be parameterised by the modified Arrhenius expression k = (1.23 ± 0.46) × 10-12 (T/298)2.05±0.23 exp((257 ± 107)/T) cm3 molecule-1 s-1. Including other recent literature data (923 - 1423 K) gives a modified Arrhenius expression of k1 = (1.54 ± 0.48) × 10-12 (T/298K)1.89±0.16 exp((184 ± 112)/T) cm3 molecule-1 s-1 over the range 195 - 1423 K. Various isotopomeric combinations of the reaction have also been investigated with deuteration of dimethyl ether leading to a normal isotope effect. Deuteration of the hydroxyl group leads to a small inverse isotope effect. To gain an insight into the reaction mechanisms and to support the experimental work, theoretical studies have also been undertaken calculating the energies and structures of the transition states and complexes using high level ab initio methods. The calculations also identify pre and post-reaction complexes. The pre reaction complex (binding energy of ~22 kJ mol-1) may contribute to the kinetics of the reaction, especially at low temperatures, but there is no direct evidence of this occurring under our experimental conditions, although the Arrhenius plot for the rate coefficient shows considerable curvature. The experimental data have been modelled using the recently developed MESMER (Master Equation Solver for Multi Energy Well Reactions) code giving good agreement. The calculations qualitatively reproduce the observed isotope effects closely above ~600 K but overestimate them at low temperatures, which may derive from an inadequate treatment of tunnelling and of an enhanced role of an outer transition state leading to the pre-reaction complex.

Concepts: Fluorescence, Mathematics, Transition state, Ab initio, Chemical kinetics, Hydroxide, Reaction rate, Dimethyl ether

27

In Suzuki-Miyaura reactions, anionic bases F(-) and OH(-) (used as is or generated from CO3 (2-) in water) play multiple antagonistic roles. Two are positive: 1) formation of trans-[Pd(Ar)F(L)2 ] or trans-[Pd(Ar)- (L)2 (OH)] (L=PPh3 ) that react with Ar'B(OH)2 in the rate-determining step (rds) transmetallation and 2) catalysis of the reductive elimination from intermediate trans-[Pd(Ar)(Ar')(L)2 ]. Two roles are negative: 1) formation of unreactive arylborates (or fluoroborates) and 2) complexation of the OH group of [Pd(Ar)(L)2 (OH)] by the countercation of the base (Na(+) , Cs(+) , K(+) ).

Concepts: Chemical reaction, SN1 reaction, Hydroxide, Elimination reaction, Organometallic chemistry, Reaction mechanisms

27

A highly stable high-temperature CO2 sorbent consisting of scaffold-like Ca-rich oxides (CaAlO) with rapid absorption kinetics and a high capacity is described. The Ca-rich oxides were prepared by annealing CaAlNO3 layered double hydroxide (LDH) precursors through a sol-gel process with Al(O(i) P)3 and Ca(NO3 )2 with Ca(2+) /Al(3+) ratios of 1:1, 2:1, 4:1, and 7:1. XRD indicated that only LDH powders were formed for Ca(2+) /Al(3+) ratios of 2:1. However, both LDH and Ca(OH)2 phases were produced at higher ratios. Both TEM and SEM observations indicated that the CaAlNO3 LDHs displayed a scaffold-like porous structure morphology rather than platelet-like particles. Upon annealing at 600 °C, a highly stable porous network structure of the CaO-based CaAlO mixed oxide (CAMO), composed of CaO and Ca12 Al14 O33 , was still present. The CAMO exhibited high specific surface areas (up to 191 m(2)  g(-1) ) and a pore size distribution of 3-6 nm, which allowed rapid diffusion of CO2 into the interior of the material, inducing fast carbonation/calcination and enhancing the sintering-resistant nature over multiple carbonation/calcination cycles for CO2 absorption at 700 °C. Thermogravimetric analysis results indicated that a CO2 capture capacity of approximately 49 wt % could be obtained with rapid absorption from the porous 7:1 CAMO sorbents by carbonation at 700 °C for 5 min. Also, 94-98 % of the initial CO2 capture capability was retained after 50 cycles of multiple carbonation/calcination tests. Therefore, the CAMO framework is a good isolator for preventing the aggregation of CaO particles, and it is suitable for long-term cyclic operation in high-temperature environments.

Concepts: Oxygen, Carbon dioxide, Oxide, Oxides, Hydroxide, Specific surface area, Hydroxides, Layered double hydroxides

27

A MOF bearing the aqua-hydroxo species (O2H3)-in the framework, as well as the processes that govern the equilibrium aqua-hydroxo (O2H3)-↔hydroxyl (OH) in Sc-MOFs are experimentally and theoretically studied. Computational studies were employed to determine the relative energies for the two compounds that coexist under certain hydrothermal conditions at pH lower than 2.8. The thermodynamically more stable[Sc3(3,5-DSB)2(μ-O2H3)(μ-OH)2(H2O)2] ((O2H3)Sc-MOF from now on) has been ob-tained as a pure and stable phase. The[Sc3(3,5-DSB)2(μ-OH)3(H2O)4] ((OH)3Sc-MOF (from now on) was impossible to isolate as pure phase, as it resulted to be the precursor of (O2H3)Sc-MOF. Additionally, a third compound that appears at pH between 3.5 and 4 [Sc3(3,5-DSB)(μ-OH)6(H2O)]((μ-OH)6Sc-MOF from now on), and a fourth [Sc(3,5-DSB) (Phen) (H2O)] H2O ((Phen)Sc-MOF from now on) in whose formula neither OH-group nor H3O2- anion appear, are also reported for comparative purpose. A study of the (O2H3)Sc-MOF electronic structure, and some heterogeneous catalytic tests in cyanosilylation of aldehydes reactions are also reported.

Concepts: Chemical reaction, Hydrogen, Chemistry, Science, Ligand, Chemical compound, Cultural studies, Hydroxide

27

This paper describes the effects of hydroxylated biodiesel (castor oil methyl ester - COME) on the properties, combustion and emissions of butanol-diesel blends used within compression ignition engines. The study was conducted to investigate the influence of COME as a means of increasing the butanol concentration in a stable butanol-diesel blend. Tests were compared with baseline experiments using rape methyl esters (RME). A clear benefit in terms of the trade-off between NOX and soot emissions with respect to ULSD and biodiesel-diesel blends with the same oxygen content was obtained from the combination of biodiesel and butanol, while there was no penalty in regulated gaseous carbonaceous emissions. From the comparison between the biodiesel fuels used in this work, COME improved some of the properties (for example lubricity, density and viscosity) of butanol-diesel blends with respect to RME. The existence of hydroxyl group in COME also reduced further soot emissions and decreased soot activation energy.

Concepts: Alcohol, Functional groups, Liquid, Ester, Hydroxide, Internal combustion engine, Diesel engine, Biodiesel

27

Microporous anodic aluminum oxide (AAO) membranes were modified by 3-glycidoxypropyltrimethoxysilane to produce terminal epoxy groups. These were used to covalently link hydroxyethyl celluloses (HEC) to amplify reactive groups of AAO membrane. The hydroxyl groups of HEC-AAO composite membrane were further modified with 1,4-butanediol diglycidyl ether to link arginine as an affinity ligand. The contents of HEC and arginine of arginine-immobilized HEC-AAO membrane were 52.1 and 19.7mg/g membrane, respectively. As biomedical adsorbents, the arginine-immobilized HEC-AAO membranes were tested for bilirubin removal. The non-specific bilirubin adsorption on the unmodified HEC-AAO composite membranes was 0.8mg/g membrane. Higher bilirubin adsorption values, up to 52.6mg/g membrane, were obtained with the arginine-immobilized HEC-AAO membranes. Elution of bilirubin showed desorption ratio was up to 85% using 0.3M NaSCN solution as the desorption agent. Comparisons equilibrium and dynamic capacities showed that dynamic capacities were lower than the equilibrium capacities. In addition, the adsorption mechanism of bilirubin and the effects of temperature, initial concentration of bilirubin, albumin concentration and ionic strength on adsorption were also investigated.

Concepts: Oxygen, Alcohol, Functional group, Electrochemistry, Aluminium, Adsorption, Analytical chemistry, Hydroxide

27

Correlations between hydrogen bonds and solvent effects on phenol -OH proton shieldings, temperature coefficients (Δδ/ΔT) and effects on OH diffusion coefficients for numerous phenolic acids, flavonols, flavones, and oleuropein derivatives of biological interest were investigated in several organic solvents and were shown to serve as reliable indicators of hydrogen bonding and solvation state of -OH groups. The temperature coefficients span a range of -0.5 to -12.3 ppb K(-1). Shielding differences of 2.0 to 2.9 ppm at 298 K were observed for solvent exposed OH groups between DMSO-d(6) and CD(3)CN which should be compared with a shielding range of ∼7 ppm. This demonstrates that the solvation state of hydroxyl protons is a key factor in determining the value of the chemical shift. For -OH protons showing temperature gradients more positive than -2.5 ppb K(-1), shielding changes between DMSO-d(6) and CD(3)CN below 0.6 ppm, and diffusion coefficients significantly different from those of traces of H(2)O, there is an intramolecular hydrogen bond predictivity value of 100%. The C-3 OH protons of flavonols show very significant negative temperature coefficients and shielding changes between DMSO-d(6) and CD(3)CN of ∼2.3 ppm, which indicate the absence of persistent intramolecular hydrogen bonds, contrary to numerous X-ray structures.

Concepts: Oxygen, Hydrogen, Hydrogen bond, Solvent, Covalent bond, Hydronium, Hydroxide, Formic acid

24

We propose a novel route for the stabilization of oil-in-water Pickering emulsions using inherently hydrophilic nanoparticles. In the case of dialkyl adipate oils, in situ hydrophobisation of the particles by dissolved oil molecules in the aqueous phase enables stable emulsions to be formed. Emulsion stability is enhanced upon decreasing the chain length of the oil due to its increased solubility in the precursor aqueous phase. The oil thus acts like a surfactant in this respect in which hydrogen bonds form between the carbonyl group of the ester oil and the hydroxyl group on particle surfaces. The particles chosen include both fumed and precipitated anionic silica and cationic zirconia. Complementary experiments including relevant oil-water-solid contact angles and infra-red analysis of dried particles after contact with oil support the proposed mechanism.

Concepts: Oxygen, Functional group, Water, Solubility, Liquid, Emulsion, Surfactant, Hydroxide