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151.
X-ray analysis of tetraisopropylethylene has revealed that the structure is disordered since there are two molecules (population factors 0.85 and 0.15 respectively) rotated by 90° with respect to each other around the normal to the ethylenic plane through the origin, which is the midpoint of the CC double bond. The ethylenic skeleton is planar and bond angles and distances are in the normal range. 相似文献
152.
Laura Mgrdichian Arhonda Gogos Peter W. Stephens Lawrence Shapiro D. Peter Siddons Gianluigi De Geronimo 《Synchrotron Radiation News》2013,26(5):13-18
The advantages of synchrotron infrared radiation for micro-spectroscopy have already been demonstrated and exploited in most of the synchrotron facilities. The development of a similar instrument at the ESRF was driven by a twofold motivation. 相似文献
153.
In this Communication, we report evidence for the dealkylation of trialkyltin compounds by a short linear peptide extracted from a small membrane protein (stannin) involved in cellular apoptosis and containing a CXC motif. We show that (a) organotin binding induces the formation of a beta-turn in the linear peptide, (b) both cysteines are necessary for the dealkylation reaction, and (c) stable 1:1 complexes are formed between the peptide and diorganotins that can be observed by ESI-MS. Organotin degradation by biological dithiols may be responsible for both the delayed activity of these toxins in humans and the organotin resistance mechanisms in bacteria. 相似文献
154.
Yao Z Braidy N Botton GA Adronov A 《Journal of the American Chemical Society》2003,125(51):16015-16024
Single-walled carbon nanotubes were functionalized along their sidewalls with phenol groups using the 1,3-dipolar cycloaddition reaction. These phenols could be further derivatized with 2-bromoisobutyryl bromide, resulting in the attachment of atom transfer radical polymerization initiators to the sidewalls of the nanotubes. These initiators were found to be active in the polymerization of methyl methacrylate and tert-butyl acrylate from the surface of the nanotubes. However, the polymerizations were not controlled, leading to the production of high molecular weight polymers with relatively large polydispersities. The resulting polymerized nanotubes were analyzed by IR, Raman spectroscopy, DSC, TEM, and AFM. The nanotubes functionalized with poly(methyl methacrylate) were found to be insoluble, while those functionalized with poly(tert-butyl acrylate) were soluble in a variety of organic solvents. The tert-butyl groups of these appended polymers could also be removed to produce nanotubes functionalized with poly(acrylic acid), resulting in structures that are soluble in aqueous solutions. 相似文献
155.
An effective approach to the new isoxazolo[3,4-d]thieno[2,3-b]pyridine system was provided by way of an intramolecular nitrone cycloaddition. The required nitrones were built in good yields starting from thiophene-2-carboxylic acids. The same skeleton was achieved in optically active form employing chiral nitrones derived from N-α-methylbenzyl- and the N-α-hydroxymethylbenzyl-hydroxylamines. The absolute configuration of the products was assigned by X-ray analysis. 相似文献
156.
Pozzoli L Gilardoni S Perrone MG De Gennaro G De Rienzo M Vione D 《Annali di chimica》2004,94(1-2):17-32
This is the first of a series of two papers intended to review the state-of-the-art knowledge on atmospheric PAHs, concerning their monitoring, sources and transformation processes in the atmosphere. The monitoring section briefly introduces this class of compounds, mainly focusing on the 16 PAHs indicated by the US-EPA as priority pollutants. These compounds undergo partitioning between the gas phase and particulate, which has to be considered in the choice of the sampling methodology. Furthermore, sampling artifacts may arise from further phase transfers inside the sampling device. After sampling, extraction, clean up and detection/quantification procedures will follow. They are closely related since the choice of the extraction technique will heavily condition the clean-up step, and both procedures will place demands on the performance of the detection technique (usually GC-MS or HPLC). This is particularly true in the case of complex samples such as those arising from atmospheric sampling. The sources of atmospheric PAHs are then discussed with a particular focus on receptor models, which can allow the apportionment of PAH sources based on concentration data that can be routinely obtained by pollution control networks. 相似文献
157.
Gabriele Albertin Stefano Antoniutti Marco Bortoluzzi Gianluigi Zanardo 《Journal of organometallic chemistry》2005,690(7):1726-1738
Chloro phosphite complexes RuClTpL(PPh3) (1a, 1b) [L = P(OEt)3, PPh(OEt)2] and RuClTp[P(OEt)3]2 (1c) [Tp = hydridotris(pyrazolyl)borate] were prepared by allowing RuClTp(PPh3)2 to react with an excess of phosphite. Treatment of the chloro complexes 1 with NaBH4 in ethanol yielded the hydride RuHTpL(PPh3) (2a, 2b) and RuHTp[P(OEt)3]2 (2c) derivatives. Protonation reaction of 2 with Brønsted acids was studied and led to thermally unstable (above 10 °C) dihydrogen [Ru(η2- H2)TpL(PPh3)]+ (3a, 3b) and [Ru(η2-H2)Tp{P(OEt)3}2]+ (3c) complexes. The presence of the η2-H2 ligand is indicated by short T1 min values and JHD measurements of the partially deuterated derivatives. Aquo [RuTp(H2O)L(PPh3)]BPh4 (4), carbonyl [RuTp(CO)L(PPh3)]BPh4 (5), and nitrile [RuTp(CH3CN)L(PPh3)]BPh4 (6) derivatives [L = P(OEt)3] were prepared by substituting H2 in the η2-H2 derivatives 3. Vinylidene [RuTp{CC(H)R}L(PPh3)]BPh4 (7, 8) (R = Ph, tBu) and allenylidene [RuTp(CCCR1R2)L(PPh3)]BPh4 (9-11) complexes (R1 = R2 = Ph, R1 = Ph R2 = Me) were also prepared by allowing dihydrogen complexes 3 to react with the appropriate HCCR and HCCC(OH)R1R2 alkynes. Deprotonation of vinylidene complexes 7, 8 with NEt3 was studied and led to acetylide Ru(CCR)TpL(PPh3) (12, 13) derivatives. The trichlorostannyl Ru(SnCl3)TpL(PPh3) (14) compound was also prepared by allowing the chloro complex RuClTpL(PPh3) to react with SnCl2 · 2H2O in CH2Cl2. 相似文献
158.
Three sets of oligomers containing the 4-carboxy-5-methyloxazolidin-2-one (Oxd) moiety have been synthesized with the aim of checking whether these molecules are able to fold in ordered structures: A set [Boc-(L-Ala-L-Oxd)(n)-OR], B set [Boc-(L-Ala-D-Oxd)(n)-OR], and C set [Boc-(Aib-L-Oxd)(n)-OR] preferential conformations have been analyzed with IR absorption, NMR, and CD. We have noticed that in these oligomers three stabilizing effects are active: (i) the rigid Oxd -CO-N(CH<)-CO- moiety, which always tend to assume a trans conformation; (ii) the formation of Oxd C=O...H-(alpha)C intramolecolar H-bonds; (iii) the alternate formation of 1 <-- 4 intramolecular C=O...H-N H-bonds. Through the analysis of the experimental data, we could demonstrate that only the oligomers of the B set are able to meet all three requirements listed above. By a deeper insight into the CD spectra, we gathered that the secondary structure adopted by the B set oligomers is a beta-bend ribbon spiral, which is a subtype of the 3(10)-helix. 相似文献
159.
The 3D Nanoscale Evolution of Platinum–Niobium Oxide Fuel Cell Catalysts via Identical Location Electron Tomography
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David Rossouw Lidia Chinchilla Natalia Kremliakova Gianluigi A. Botton 《Particle & Particle Systems Characterization》2017,34(7)
Current state‐of‐the‐art catalysts for polymer electrolyte membrane fuel cells, comprised of platinum nanoparticles on a high surface area carbon support, are susceptible to platinum dissolution and carbon support corrosion during operation. The use of transition metal oxides in the support material is proposed to stabilize the catalyst material by minimizing platinum dissolution and carbon corrosion. Here, the 3D structural changes are tracked for a hybrid Pt–Nb oxide on carbon catalyst before and after potential cycling utilizing identical location electron tomography. Pt dissolution is observed to varying degrees in both high and low Nb oxide content structures and appreciable carbon support corrosion in the high Nb oxide content structure but not in the low Nb oxide structure. 相似文献
160.
Luppi G Garelli A Prodi L Broxterman QB Kaptein B Tomasini C 《Organic & biomolecular chemistry》2005,3(8):1520-1524
With the aim of designing a new calcium receptor, the synthesis and the conformational analysis of a small library of dipeptides having the general formula Ac-Oxx-L-Xaa-OBn [Oxx = L-Oxd, (4S,5R)-4-methyl-5-carboxyoxazolidin-2-one; D-Oxd, (4R,5S)-4-methyl-5-carboxyoxazolidin-2-one; or D-Oxac (4R)-(2-oxo-1,3-oxazolidin-4-yl)-acetic acid] is reported. Ac-L-Oxd-L-Ala-OBn was identified as the most promising compound by MS-ESI analysis and this outcome was confirmed by photoluminescence spectroscopy. 相似文献