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51.
Pornpun Rattananakin Charles U. PittmanJr. Willard E. Collier Svein Saebø 《Structural chemistry》2007,18(3):399-407
Twelve push–pull ethylene derivatives, NH2CH=CHX, NH2C≡CCH=CHX, and −OCHX=CHX (with X=BH2, C≡N, NO2, and CH2
+) have been studied by ab initio calculations. The rotational barrier around the central double bond was chosen as a probe
for push–pull effects, as push–pull effects would remove electron density from the central double bond. The amount of reduction
of double bond character will increase with the contribution of the zwitterionic resonance hybrid structure. Complete geometry
optimizations and calculations of vibrational frequencies were performed for all minima and transition state structures of
these 12 systems. The calculations were carried out with the B3LYP and MP2 methods using the 6-311+G(d,p) and the 6-311++G(d,p)
basis sets. All the systems investigated exhibited properties consistent with push–pull effects such as elongated C=C double
bonds, dipolar electronic structures, and reduced barriers to internal rotation. 相似文献
52.
Ortho‐Stabilized 18F‐Azido Click Agents and their Application in PET Imaging with Single‐Stranded DNA Aptamers 下载免费PDF全文
Lu Wang Dr. Orit Jacobson Din Avdic Dr. Benjamin H. Rotstein Dr. Ido D. Weiss Dr. Lee Collier Prof. Dr. Xiaoyuan Chen Prof. Dr. Neil Vasdev Prof. Dr. Steven H. Liang 《Angewandte Chemie (International ed. in English)》2015,54(43):12777-12781
Azido 18F‐arenes are important and versatile building blocks for the radiolabeling of biomolecules via Huisgen cycloaddition (“click chemistry”) for positron emission tomography (PET). However, routine access to such clickable agents is challenged by inefficient and/or poorly defined multistep radiochemical approaches. A high‐yielding direct radiofluorination for azido 18F‐arenes was achieved through the development of an ortho‐oxygen‐stabilized iodonium derivative (OID). This OID strategy addresses an unmet need for a reliable azido 18F‐arene clickable agent for bioconjugation reactions. A ssDNA aptamer was radiolabeled with this agent and visualized in a xenograft mouse model of human colon cancer by PET, which demonstrates that this OID approach is a convenient and highly efficient way of labeling and tracking biomolecules. 相似文献
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The static structure factor S(k) of liquid indium has been measured accurately down to using CuKα radiation with reflection geometry. The direct pair correlation function in k space is analyzed to demonstrate the utility of this technique in reducing errors in the resulting direct pair correlation function in configuration space. 相似文献
55.
F. J. Liu J. S. Kokorudz H. L. Collier 《Journal of polymer science. Part A, Polymer chemistry》1988,26(11):3015-3029
A heterocyclic nitrogen-containing system having substituent primary diol function, i.e., 1,1′-dihydroxethyl-2,2′-biimidazole ( I ), has been prepared and used to synthesize a series of new polyurethanes based on aromatic diisocyanates (TDI, MDI). Variation of solution polymerization parameters permitted the isolation and infrared, NMR, molecular weight, and thermal characterization of polymeric materials. Isolated polymers exhibit a linear structure and have Tg (150–170°C) and thermal stability (205–250°C for 20% weight loss) properties comparable to other typical urethane polymers. Zn2+ complexation was indicated by shifts in the imidazole ringmode infrared vibrational bands at 917 and 1133 cm?1 to higher frequencies. 相似文献
56.
57.
The cavity ringdown technique (CRLAS) has been employed to measure the gas phase absorption spectrum of the platinum silicide molecule in the 350 nm region. All nine of the measured rovibronic bands are assigned to a single 1 sigma-1 sigma electronic transition, with a ground state vibrational frequency of omega "e = 549.0(3) cm-1, and a bond length of r"0 = 2.069(1) angstroms. The results of this study are compared with experimental data for the coinage metal silicides. Additionally, time-of-flight mass spectrometric results indicate that a variety of polyatomic metal silicides are formed in our molecular jet expansion. 相似文献
58.
Characterization of copolymer hydroxybutyrate/hydroxyvalerate from saponified vernonia,soybean, and "spent" frying oils 总被引:1,自引:0,他引:1
Poly(beta-hydroxyalkanoate)s (PHAs) were biosynthesized by Ralstonia eutropha (formerly known as Alcaligenes eutrophus) by using saponified soybean, vernonia, and "spent" frying oils. These PHAs were isolated and characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS), gas chromatography/mass spectrometry (GC/MS), proton nuclear magnetic resonance spectrometry (1H NMR), and 2-dimensional homonuclear (1H-1H) correlation spectroscopy (COSY). The analytical results revealed that the PHAs produced from saponified vernonia and soybean oils were copolymers of hydroxybutyrate (HB) and hydroxyvalerate (HV), that is, P(HB/HV)s, whereas the saponified "spent" frying oil produced only poly(beta- hydroxybutyrate) (PHB) homopolymer. MALDI-MS, GC/MS, and NMR independently confirmed the composition of the PHAs. Saponified soybean oil and vernonia oil PHAs contained approximately 4 and 1% HV units, respectively. For comparison, commercial PHB and P(HB/HV), produced by R. eutropha by using glucose and a cosubstrate of glucose and propionic acid, respectively, as carbon sources, were similarly characterized. 相似文献
59.
Fast mixing and reaction initiation control of single-enzyme kinetics in confined volumes 总被引:1,自引:0,他引:1
A device with femtoliter-scale chambers and controlled reaction initiation was developed for single-molecule enzymology. Initially separated substrate and enzyme streams were rapidly mixed in a microfluidic device and encapsulated in an array of individual microreactors, allowing for enzyme kinetics to be monitored with millisecond dead times and single-molecule sensitivity. Because the arrays of chambers were fabricated by micromolding in PDMS, the chambers were monodisperse in size, and the chamber volume could be systematically controlled. Microreactors could be purged and replenished with fresh reactants for consecutive rounds of observation. Repeated experiments with statistically identical initial conditions could be performed rapidly, with zero cross-talk between chambers in the array. 相似文献
60.
Acerbi N Tsang SC Golunski S Collier P 《Chemical communications (Cambridge, England)》2008,(13):1578-1580
When ceria is deposited over supported PGM catalysts its reducibility is dependent on the work function of the underlying metal. 相似文献