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101.
Cavalleri M Näslund LA Edwards DC Wernet P Ogasawara H Myneni S Ojamäe L Odelius M Nilsson A Pettersson LG 《The Journal of chemical physics》2006,124(19):194508
We present a combined x-ray absorption spectroscopy/computational study of water in hydrochloric acid (HCl) solutions of varying concentration to address the structure and bonding of excess protons and their effect on the hydrogen bonding network in liquid water. Intensity variations and energy shifts indicate changes in the hydrogen bonding structure in water as well as the local structure of the protonated complex as a function of the concentration of protons. In particular, in highly acidic solutions we find a dominance of the Eigen form, H(3)O(+), while the proton is less localized to a specific water under less acidic conditions. 相似文献
102.
Oström H Ogasawara H Näslund LA Andersson K Pettersson LG Nilsson A 《The Journal of chemical physics》2007,127(14):144702
The electronic structure of methane adsorbed on Pt(977) is investigated using angle-resolved x-ray absorption spectroscopy (XAS) in combination with density functional theory spectrum calculations. XAS, which probes the unoccupied states atom specifically, shows the appearance of the symmetry-forbidden gas-phase lowest unoccupied molecular orbital due to s-p rehybridization. In addition new adsorption-induced states appear just above the Fermi level. A systematic investigation, where computed XA spectra are compared with the experiment, indicates elongation of the C-H bond pointing toward the surface to 1.18+/-0.05 A. The bond elongation arises due to mixing between bonding and antibonding C-H orbitals. Computed charge density difference plots show that no covalent chemical bond is formed between the adsorbate and substrate upon adsorption. The changes in electronic structure arise in order to minimize the Pauli repulsion by polarizing charge away from the surface toward the carbon atom of the methane molecule. 相似文献
103.
104.
Relative populations of S-form (D-E rings: boat-boat form) and F-form (D-E rings: chair-chair form) conformers, in equilibrium in CDCl3 solutions, of 20 derivatives (2-21) of bryonolic acid (D:C-friedoolean-8-en-3beta-ol-29-oic acid) (1) were calculated from NMR spectral data (J-values and chemical shifts), with the aid of molecular mechanic calculation using a MM2/CONFLEX program system. The principal deciding factor of the population ratio was found to be whether the functionality at C-29 is trigonal or tetrahedral; the S-form: F-form was 0:100-32:68 for the "trigonal" type and 48:52-100:0 for the "tetrahedral." The reliability of the results is discussed. 相似文献
105.
Microfluidics can be used to handle relatively small volumes of samples and to conduct reactions in microliter‐sized volumes. Electrospray ionization can couple microfluidics with mass spectrometry (MS) to monitor chemical reactions online. However, fabricating microfluidic chips is time‐consuming. We herein propose the use of a micro‐reactor that is sustained by two capillaries and an ultrasonicator. The inlets of the capillaries were individually immersed to two different sample vials that were subjected to the ultrasonicator. The tapered outlets of the two capillaries were placed cross with an angle of ~60° close to the inlet of the mass spectrometer to fuse the eluents. On the basis of capillary action and ultrasonication, the samples from the two capillaries can be continuously directed to the capillary outlets and fuse simultaneously to generate gas phase ions for MS analysis through ultrasonication‐assisted spray ionization (UASI). Any electric contact applied on the capillaries is not required. Nevertheless, UASI spray derived from the eluents can readily occur in front of the mass spectrometer. That is, a micro‐reactor was created from the fusing of the eluent containing different reactants from these two UASI capillaries, allowing reactions to be conducted in situ. The solvent in the fused droplets was evaporated quickly, and the product ions could be immediately observed by MS because of the extreme rise in the concentration of the reactants. For proof of concept, pyrazole synthesis reaction and cortisone derivatization by Girard T reagent were selected as the model reactions. The results demonstrated the feasibility of using UASI‐based micro‐reactor for online MS analysis to detect reaction intermediates and products. 相似文献
106.
Shohei Hayashi Yasuharu Satoh Yasushi Ogasawara Chitose Maruyama Yoshimitsu Hamano Tetsuro Ujihara Tohru Dairi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(8):2348-2352
Polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (ARA) are essential fatty acids for humans. Some microorganisms biosynthesize these PUFAs through PUFA synthases composed of four subunits with multiple catalytic domains. These PUFA synthases each create a specific PUFA without undesirable byproducts, even though the multiple catalytic domains in each large subunit are very similar. However, the detailed biosynthetic pathways and mechanisms for controlling final‐product profiles are still obscure. In this study, the FabA‐type dehydratase domain (DHFabA) in the C‐subunit and the polyketide synthase‐type dehydratase domain (DHPKS) in the B‐subunit of ARA synthase were revealed to be essential for ARA biosynthesis by in vivo gene exchange assays. Furthermore, in vitro analysis with truncated recombinant enzymes and C4‐ to C8‐acyl ACP substrates showed that ARA and EPA synthases utilized two types of DH domains, DHPKS and DHFabA, depending on the carbon‐chain length, to introduce either saturation or cis double bonds to growing acyl chains. 相似文献
107.
Chie Tsukada Hikaru Yoshida Satoshi Ogawa Akitaka Yoshigoe Shinya Yagi Tsuyoshi Yaita 《Surface and interface analysis : SIA》2019,51(1):85-88
In this study, gold nanoparticles (AuNPs) prepared in a 5 mM CsCl aqueous solution using the solution-plasma method are characterized via transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy with synchrotron radiation (SR-XPS). The particle diameter is measured over the process time via TEM. During the solution-plasma process, small particles of 2.1 to 2.2-nm diameter are generated in the CsCl aqueous solution; these particles then enlarge via Ostwald ripening over time until they reach an equilibrium size of ~13 nm after 36 days. In addition, the surface chemical states of the AuNPs are characterized at different depths via SR-XPS. The SR-XPS measurements obtained using incident X-ray energy (hν) of 945.0 eV revealed that Cs─Au, Cl─Au, and Cs─Cl─Au bonds are present 1.2 nm below the surface. The measurements obtained at an incident X-ray energy of 2515.0 eV showed that Cs─Cl─Au bonding is also present 2.5 nm below the surface, indicating that Cs and Cl strongly interact with Au. The TEM and SR-XPS measurements revealed that 2 processes occur cyclically during the growth process via Ostwald ripening: (i) the Cs and Cl in the aqueous solution adsorb on the AuNP surface and (ii) Au atoms subsequently bond to the AuNPs surface. 相似文献
108.
Real time monitoring of accelerated chemical reactions by ultrasonication‐assisted spray ionization mass spectrometry 下载免费PDF全文
Shu‐Hsuan Lin Ta‐Ju Lo Fang‐Yin Kuo Yu‐Chie Chen 《Journal of mass spectrometry : JMS》2014,49(1):50-56
Ultrasonication has been used to accelerate chemical reactions. It would be ideal if ultrasonication‐assisted chemical reactions could be monitored by suitable detection tools such as mass spectrometry in real time. It would be helpful to clarify reaction intermediates/products and to have a better understanding of reaction mechanism. In this work, we developed a system for ultrasonication‐assisted spray ionization mass spectrometry (UASI–MS) with an ~1.7 MHz ultrasonic transducer to monitor chemical reactions in real time. We demonstrated that simply depositing a sample solution on the MHz‐based ultrasonic transducer, which was placed in front of the orifice of a mass spectrometer, the analyte signals can be readily detected by the mass spectrometer. Singly and multiply charged ions from small and large molecules, respectively, can be observed in the UASI mass spectra. Furthermore, the ultrasonic transducer used in the UASI setup accelerates the chemical reactions while being monitored via UASI–MS. The feasibility of using this approach for real‐time acceleration/monitoring of chemical reactions was demonstrated. The reactions of Girard T reagent and hydroxylamine with steroids were used as the model reactions. Upon the deposition of reactant solutions on the ultrasonic transducer, the intermediate/product ions are readily generated and instantaneously monitored using MS within 1 s. Additionally, we also showed the possibility of using this reactive UASI–MS approach to assist the confirmation of trace steroids from complex urine samples by monitoring the generation of the product ions. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
109.
Kosuke Makiguchi Seiya Kikuchi Kazuma Yanai Yoshitaka Ogasawara Shin‐ichiro Sato Toshifumi Satoh Toyoji Kakuchi 《Journal of polymer science. Part A, Polymer chemistry》2014,52(7):1047-1054
The ring‐opening polymerizations (ROPs) of ε‐caprolactone (ε‐CL) and L ‐lactide (LLA) have been studied using the organocatalysts of diphenyl phosphate (DPP) and 4‐dimethylaminopyridine (DMAP). The “dual activation” property of DPP and the “bifunctional activation” property of DPP/DMAP were confirmed by the NMR measurement for ε‐CL and its chain‐end model of poly(ε‐caprolactone) and for LLA and its chain‐end model of poly(L ‐lactide) (PLLA), respectively. The molar ratio of DPP/DMAP was optimized as 1/2 for the ROP of LLA leading to the well‐defined PLLA, such as the molecular weight determined from 1H NMR measurement of 19,200 g mol?1 and the narrow polydispersity of 1.10. Additionally, functional initiators were utilized for producing the end‐functionalized PLLAs. The DPP‐catalyzed ROPs of ε‐CL and its analogue cyclic monomers and then the DPP/DMAP‐catalyzed ROP of LLA produced block copolymers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1047–1054 相似文献
110.
Baba K Okamura TA Suzuki C Yamamoto H Yamamoto T Ohama M Ueyama N 《Inorganic chemistry》2006,45(2):894-901
Novel molybdenum dithiolene compounds having neighboring amide groups as models for molybdoenzymes, (NEt(4))(2)[Mo(IV)O{1,2-S(2)-3,6-(RCONH)(2)C(6)H(2)}(2)] (R = CH(3), CF(3), t-Bu, Ph(3)C), were designed and synthesized. The contributions of the NH...S hydrogen bond to the electrochemical properties of the metal ion and the reactivity of the O-atom-transfer reaction were investigated by a comparison with [Mo(IV)O(1,2-S(2)C(6)H(4))(2)](2)(-). The MoOS(4) core of [Mo(IV)O{1,2-S(2)-3,6-(CH(3)CONH)(2)C(6)H(2)}(2)](2)(-) shows no significant geometrical difference from that of [Mo(IV)O(1,2-S(2)C(6)H(4))(2)](2)(-) in the crystal. The hydrogen bonds positively shifted the Mo(IV/V) redox potential and accelerated the reduction of Me(3)NO. 相似文献