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Endothermic reactions

JungSoo Kim, Richard M Cox, P B Armentrout
The kinetic-energy dependences of the reactions M(+) + CO where M(+) = Re(+), Os(+), and Ir(+) are studied using guided ion-beam tandem mass spectrometry. Formation of both MO(+) and MC(+) was observed in endothermic processes for all three metals. Modeling of the data provides thresholds that yield 0 K bond dissociation energies (BDEs, in eV) of 4.67 ± 0.09 (Re(+)-O), 4.82 ± 0.14 (Os(+)-O), 4.25 ± 0.11 (Ir(+)-O), 5.13 ± 0.12 (Re(+)-C), 6.14 ± 0.14 (Os(+)-C), and 6.58 ± 0.12 (Ir(+)-C). These BDEs agree well with literature values within experimental uncertainties demonstrating that ground state products are formed for all cases even though some of the reactions are formally spin forbidden...
November 21, 2016: Journal of Chemical Physics
Hao Zhang, Xing Zhou, Jian He, Tao Wang, Xiaohu Luo, Li Wang, Ren Wang, Zhengxing Chen
Recombinant amylosucrase from Neisseria polysaccharea was utilized to modify native and acid-thinned starches. The molecular structures and physicochemical properties of modified starches were investigated. Acid-thinned starch displayed much lower viscosity after gelatinization than did the native starch. However, the enzyme exhibited similar catalytic efficiency for both forms of starch. The modified starches had higher proportions of long (DP>33) and intermediate chains (DP 13-33), and X-ray diffraction showed a B-type crystalline structure for all modified starches...
April 1, 2017: Food Chemistry
Chao Liu, Huiyan Zhang, Rui Xiao, Shubin Wu
Thermogravimetric characteristics of chitin and chitosan and their potentials to produce value-added organonitrogen chemicals were separately evaluated via TG/DSC-FTIR and Py-GC/MS. Results shown that chitin had the better thermal stability and higher activation energy than chitosan because of the abundant acetamido group. Furthermore, the dominated volatilization in active pyrolysis of chitin contributed to its endothermic property, whereas the charring in chitosan led to the exothermal. During fast pyrolysis, the acetamido group in chitin and chitosan was converted into acetic acid or acetamide...
January 20, 2017: Carbohydrate Polymers
B B Xiao, X B Jiang, X L Yang, Q Jiang, F Zheng
Pt1ML/Pd3Al, which comprises a Pd3Al core protected by a Pt monolayer, may experience Al dealloying because of the strong affinity of Al toward O. To circumvent this issue, the Pt2ML/Os/Pd3Al catalyst has been designed to suppress the migration of Al by inserting an Os monolayer at the interface between the Pd3Al core and two Pt monolayers. On the basis of segregation energies, Al leaching from the core to the 1st layer is determined to be endothermic even under O coverage, indicating an energetic preference for Al to reside in the core structure...
October 25, 2016: Physical Chemistry Chemical Physics: PCCP
Maria Demireva, JungSoo Kim, P B Armentrout
Guided ion beam mass spectrometry (GIBMS) is used to measure the kinetic energy dependent product ion cross sections for reactions of the lanthanide metal gadolinium cation (Gd(+)) with O2, CO2, and CO and for reactions of GdO(+) with CO, O2, and Xe. GdO(+) is formed through barrierless and exothermic processes in the reactions of Gd(+) with O2 and CO2. All other reactions observed are endothermic, and analyses of their kinetic energy dependent cross sections yield 0 K bond dissociation energies (BDEs) for GdO(+), GdC(+), and GdCO(+)...
October 21, 2016: Journal of Physical Chemistry. A
Xu Jiao, Yuvaraja Gutha, Weijiang Zhang
The utilization of CS/PVA/CuO as a novel adsorbent for the removal of Pb(II) from aqueous solution has been examined in a batch adsorption process with several experimental conditions including initial solution pH, dose, contact time, initial metal ion concentration, and temperature. The new and novel material was characterized by structural (XRD), spectral (FTIR), morphological with elemental (SEM with EDS), and size of the nanoparticles (TEM) analyses. The pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetics equations were used to analyze the kinetic data of the adsorption process and the data was fitted well with the pseudo-second-order kinetic model with R(2) values (close to the unity)...
October 13, 2016: Colloids and Surfaces. B, Biointerfaces
Peter Portius, Martin Davis
A convenient synthetic route to poly(tetrazolato) silicon complexes is described based on the four reactive centres of the N-rich, highly endothermic tetraazides of the type Si(N3)4(L2). Hypercoordinate azido(tetrazolato) silicon complexes Si(N3)2(N4C-R)2(L2), R = CH3, C6H5, 4-C6H4CH3 (4a, 5, 6, 7) and Si(N3)2(N4C-L)2 (9, L = 2-C5H4N), L2 = 2,2'-bipyridine, 1,10-phenanthroline, with SiN6 skeletons were synthesised via multiple [3 + 2] dipolar cycloaddition reactions starting from Si(N3)4(L2) and a nitrile. The isolated new complexes were characterised by standard analytical methods, single crystal X-ray diffraction and differential scanning calorimetry (4a,b)...
October 13, 2016: Dalton Transactions: An International Journal of Inorganic Chemistry
Frank Tambornino, Jonathan Sappl, Felix Pultar, Trung Minh Cong, Sabine Hübner, Tobias Giftthaler, Constantin Hoch
Isothermal electrolysis is a convenient preparation technique for a large number of intermetallic phases. A solution of the salt of a less-noble metal is electrolyzed on a cathode consisting of a liquid metal or intermetallic system. This yields crystalline products at mild reaction conditions in a few hours. We show the aptness and the limitations of this approach. First, we give an introduction into the relevance of electrolytic synthesis for chemistry. Then we present materials and techniques our group has developed for electrocrystallization that are useful for electrochemical syntheses in general...
October 10, 2016: Inorganic Chemistry
Manisha Ray, Arjun Saha, Krishnan Raghavachari
Density functional theory (DFT) calculations using a small metal cluster couple, Mo2O4(-)/Mo2O5(-), are used to model a complete catalytic cycle for H2 production from water. While Mo2O4(-) is known to readily react with water to form Mo2O5(-) and release H2, the principal challenge is in reducing Mo2O5(-) to Mo2O4(-) to complete the cycle. We investigate the role of several potential sacrificial reagents (ethylene, propylene, CO and acetylene) that can reduce Mo2O5(-) after the initial oxidation. DFT calculations of the free energy reaction pathways demonstrate the presence of overall kinetically accessible barriers that are below the entrance channel (separated reactants) in the Mo2O4(-) + H2O reaction (step I) followed by the Mo2O5(-) + sacrificial reagent reactions (step II)...
September 14, 2016: Physical Chemistry Chemical Physics: PCCP
Yanchen Wu, Houjuan Qi, Beizhan Li, Huang Zhanhua, Wei Li, Shouxin Liu
In order to improve the superhydrophobic and oil-wet properties of raw cotton fibers come from Jiangsu province, China. A novel adsorbent, hydrophobic cotton fibers (HCF) with an excellent superhydrophobic and larger length was synthesized via modified sol-gel method and examined for the removal of nitrobenzene in aqueous solution. Results show that the treated raw cotton fibers exhibited outstanding non-wettability with the WCA of 152° and the larger length of 0.2-0.4cm, which offers an opportunity to separation in for the removal of nitrobenzene...
January 2, 2017: Carbohydrate Polymers
Mei-Fang Li, Yun-Guo Liu, Guang-Ming Zeng, Shao-Bo Liu, Xin-Jiang Hu, Ding Shu, Lu-Hua Jiang, Xiao-Fei Tan, Xiao-Xi Cai, Zhi-Li Yan
A novel magnetic nanomaterial was synthesized by grafting nitrilotriacetic acid to magnetic graphene oxide (NDMGO), which was applied as an adsorbent for removing tetracycline (TC) from aqueous solutions. The nanomaterial was characterized using TG-DTA, SEM, TEM, XRD, VSM, XPS, Raman, BET surface area and zeta potential measurements. Several experimental conditions (solution pH, adsorption time, temperature, ionic strength and foreign ions) affecting the adsorption process were investigated. The results showed that the TC adsorption capacity could be affected by solution pH...
January 1, 2017: Journal of Colloid and Interface Science
Sanliang Ling, Maciej Gutowski
Computational results have been reported for 2'-deoxycytidine (dC), its gas phase isomers, tautomers, and their conformers, as well as for the crystalline phase. In addition to the neutral gas phase molecules, we have also considered associated radical anions and cations. The structural calculations were performed at the density functional and MP2 levels of theory. Vertical electron ionization energies and excess electron binding energies were determined using electron propagator theory. The α-anomer proved to be more stable by a fraction of kcal/mol than the biologically relevant canonical β-anomer...
October 6, 2016: Journal of Physical Chemistry. A
Changsong Zhao, Jun Liu, Hong Tu, Feize Li, Xiyang Li, Jijun Yang, Jiali Liao, Yuanyou Yang, Ning Liu, Qun Sun
Uranium(VI) biosorption from aqueous solutions was investigated in batch studies by using fungus Pleurotus ostreatus biomass. The optimal biosorption conditions were examined by investigating the reaction time, biomass dosage, pH, temperature, and uranium initial concentration. The interaction between fungus biomass and uranium was confirmed using Fourier transformed infrared (FT-IR), scanning electronic microscopy energy dispersive X-ray (SEM-EDX), and X-ray photoelectron spectroscopy (XPS) analysis. Results exhibited that the maximum biosorption capacity of uranium on P...
September 23, 2016: Environmental Science and Pollution Research International
Phuong D Dau, Rémi Maurice, Eric Renault, John K Gibson
A central goal of chemistry is to achieve ultimate oxidation states, including in gas-phase complexes with no condensed phase perturbations. In the case of the actinide elements, the highest established oxidation states are labile Pu(VII) and somewhat more stable Np(VII). We have synthesized and characterized gas-phase AnO3(NO3)2(-) complexes for An = U, Np, and Pu by endothermic NO2 elimination from AnO2(NO3)3(-). It was previously demonstrated that the PuO3(+) core of PuO3(NO3)2(-) has a Pu-O(•) radical bond such that the oxidation state is Pu(VI); it follows that in UO3(NO3)2(-) it is the stable U(VI) oxidation state...
October 3, 2016: Inorganic Chemistry
Yan Xu, Yunguo Liu, Shaobo Liu, Xiaofei Tan, Guangming Zeng, Wei Zeng, Yang Ding, Weicheng Cao, Bohong Zheng
In this work, a novel potential adsorbent, citric acid (CA)-modified biochar, named as CAWB, was obtained from water hyacinth biomass by slow pyrolysis in a N2 environment at 300 °C. The CA modification focused on enhancing the contaminants adsorption capacity of biochar pyrolyzed at relatively low temperature. Over 90 % of the total methylene blue (MB) could be removed at the first 60 min by CAWB, and the maximum MB adsorption capacity could reach to 395 mg g(-1). The physicochemical properties of CAWB was examined by FTIR, XPS, SEM, and BET analysis...
December 2016: Environmental Science and Pollution Research International
M Arshadi, F Mousavinia, M J Amiri, A R Faraji
In this work synthesis of Mn-nanoparticles (MnNPs) supported on the Schiff base modified nano-sized SiO2Al2O3 mixed-oxides (Si/Al) and its implementation as an adsorbent for the removal of organic pollutions such as methyl orange (MO) and salicylic acid (SA) was investigated. Si/Al were functionalized by grafting Schiff base ligand and in the next step, MnNPs were prepared over the modified nano sol-gel Si/Al. Structures and adsorption characteristics of the obtained organometallic-modified SiO2/Al2O3 mixed oxide were studied by several methods such as elemental analysis, diffuse reflectance UV-vis spectroscopy, FT-IR spectroscopy, nitrogen adsorption/desorption, scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive X-ray (EDX), inductively coupled plasma (ICP-AES), Electron Paramagnetic Resonance (EPR), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV)...
December 1, 2016: Journal of Colloid and Interface Science
Yiwei Hu, Guangxian Zhang, Fengxiu Zhang
In this article, the conformation and thermodynamics of α-amylase interaction with ethylene in vitro were investigated. The ultraviolet (UV) absorption showed a strong peak of α-amylase treated with 6.04, 29.32 and 262.11μmolL(-1) ethylene appears at ~222nm and a weak peak at 278nm blue-shifted 1nm. Circular dichroism (CD) spectra indicated that the conformations of α-amylase treated with 29.32 and 262.11μmolL(-1) ethylene were obviously changed in which α-helix content were decreased by 20 and 31% respectively, and β-sheet, β-turn and random coil contents were increased by contrast...
October 2016: Journal of Photochemistry and Photobiology. B, Biology
Toshimori Sekine, Norimasa Ozaki, Kohei Miyanishi, Yuto Asaumi, Tomoaki Kimura, Bruno Albertazzi, Yuya Sato, Youichi Sakawa, Takayoshi Sano, Seiji Sugita, Takafumi Matsui, Ryosuke Kodama
Forsterite (Mg2SiO4) is one of the major planetary materials, and its behavior under extreme conditions is important to understand the interior structure of large planets, such as super-Earths, and large-scale planetary impact events. Previous shock compression measurements of forsterite indicate that it may melt below 200 GPa, but these measurements did not go beyond 200 GPa. We report the shock response of forsterite above ~250 GPa, obtained using the laser shock wave technique. We simultaneously measured the Hugoniot and temperature of shocked forsterite and interpreted the results to suggest the following: (i) incongruent crystallization of MgO at 271 to 285 GPa, (ii) phase transition of MgO at 285 to 344 GPa, and (iii) remelting above ~470 to 500 GPa...
August 2016: Science Advances
Mudasir Ahmad, Kaiser Manzoor, Perumal Venkatachalam, Saiqa Ikram
A modified biomacromolecule, chitosan-thiosemicarbazide framework (TSCS) as an adsorbent for Cu(II) was prepared from dialdehyde chitosan through condensation reaction with thiosemicarbazide, stabilized by the reduction reaction with sodium borohydride. TSCS was characterized by means of FT-IR and XPS. Surface morphologies were studied by FESEM and BET, which revealed the highly macro porous structure. The thermal analyses was done through TGA showing much stable chemical configuration at about ≥400°C. The experimental equilibrium data was evaluated by Langmuir, Freundlich and Dubinin-Radushkevich isotherm models...
November 2016: International Journal of Biological Macromolecules
P L Zanonato, P Di Bernardo, Z Zhang, Y Gong, G Tian, J K Gibson, L Rao
Hydrolysis of Th(iv) was studied in tetraethylammonium perchlorate (0.10 mol kg(-1)) at variable temperatures (283-358 K) by potentiometry and microcalorimetry. Three hydrolysis reactions, mTh(4+) + nH2O = Thm(OH)n((4m-n)+) + nH(+), in which (n,m) = (2,2), (8,4), and (15,6), were invoked to describe the potentiometric and calorimetric data for solutions with the [hydroxide]/[Th(iv)] ratio ≤ 2. At higher ratios, the formation of (16,5) cannot be excluded. The hydrolysis constants, *β2,2, *β8,4, and *β15,6, increased by 3, 7, and 11 orders of magnitude, respectively, as the temperature was increased from 283 to 358 K...
August 9, 2016: Dalton Transactions: An International Journal of Inorganic Chemistry
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