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71.
Börner J Vieira Idos S Pawlis A Döring A Kuckling D Herres-Pawlis S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(16):4507-4512
Zinc bis(chelate) guanidine complexes promote living lactide polymerization at elevated temperatures. By means of kinetic and spectroscopic analyses the mechanism has been elucidated for these special initiators that make use of neutral N-donor ligands. The neutral guanidine function initiates the polymerization by a nucleophilic ring-opening attack on the lactide molecule. DFT calculations on the first ring-opening step show that the guanidine is able to act as a nucleophile. Three transition states were located for ligand rearrangement, nucleophilic attack, and ring-opening. The second ring-opening step was modeled as a representation for the chain growth because here, the lactate alcoholate opens the second lactide molecule via two transition states (nucleophilic attack and ring-opening). Additionally, the resulting reaction profile proceeds overall exothermically, which is the driving force for the reaction. The experimental and calculated data are in good agreement and the presented mechanism explains why the polymerization proceeds without co-initiators. 相似文献
72.
73.
Alessandro D'Aprano Ines Dorina Donato Vincenzo Turco Liveri 《Journal of solution chemistry》1989,18(8):785-793
Static dielectric constants, refractive indices and viscosities of 1-pentanol +2-methyl-2-butanol mixtures were measured at 5, 25 and 45°C. The results show that the mixing of the two isomers modifies the polarizability and the resistence of viscous flow of the system depending on the composition and temperature. Short range intermolecular interactions producing hetero-alcohol open dimers are considered. 相似文献
74.
It is shown that an unidentified marine demosponge of Brittany contains two unique lipids consisting of glycerol etherified by a C12 trienic linear alcohol and esterified by 4-hydroxybenzoic acid. The latter is attached to the secondary position of glycerol in bretonin A (= 3-[((4E, 6E, 8E)-dodeca-4,6,8-trienyl)oxy]-2-(4-hydroxy-benzoyl)propan-1-ol; 1a ), and to the other primary position of glycerol in isobretonin A ( = (+)-3-[((4E, 6E, 8E)-dodeca-4,6,8-trienyl)oxy]-1-(4-hydroxybenzoyl)propan-2-ol; (+) -2 ). The structures are based on NMR and MS data, including the ones of the acetylation product (?)- 1b of 1a . 相似文献
75.
Niko Kivel Dorothea Schumann Ines Günther-Leopold 《Analytical and bioanalytical chemistry》2013,405(9):2965-2972
In many scientific fields, the half-life of radionuclides plays an important role. The accurate knowledge of this parameter has direct impact on, e.g., age determination of archeological artifacts and of the elemental synthesis in the universe. In order to derive the half-life of a long-lived radionuclide, the activity and the absolute number of atoms have to be analyzed. Whereas conventional radiation measurement methods are typically applied for activity determinations, the latter can be determined with high accuracy by mass spectrometric techniques. Over the past years, the half-lives of several radionuclides have been specified by means of multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) complementary to the earlier reported values mainly derived by accelerator mass spectrometry. The present paper discusses all critical aspects (amount of material, radiochemical sample preparation, interference correction, isotope dilution mass spectrometry, calculation of measurement uncertainty) for a precise analysis of the number of atoms by MC-ICP-MS exemplified for the recently published half-life determination of $^{60}$ Fe (Rugel et al, Phys Rev Lett 103:072502, 2009). 相似文献
76.
Niko Kivel Natalia Shcherbina Ines Günther-Leopold 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(1):557-561
Novel reprocessing schemes and techniques are the focus of the Euratom FP7 project “Actinide Recycling for Separation and Transmutation” (ACSEPT), where the Paul Scherrer Institute (PSI) is represented in the pyrochemical domain. The subject of investigation is the selective separation of fission products (FPs) from spent nuclear fuel as a head-end step to either classical hydro based or pyro processes which are not yet applied on a large scale. The selective removal of FPs that are major contributors to the overall radiation dose or bear great potentials in terms of radiotoxicity (i.e. cesium or iodine), is advantageous for further processes. At PSI a device was developed to release volatile FPs by means of inductive heating. The heating up to 2,300 °C promotes the release of material that is further transported by a carrier gas stream into an inductively coupled plasma mass spectrometer for online detection. The carrier gas can be either inert (Ar) or can contain reducing or oxidizing components like hydrogen or oxygen, respectively. The development of the device by computer aided engineering approaches, the commissioning and evaluation of the device and data from first release experiments on a simulated fuel matrix are discussed. 相似文献
77.
Uwe Bhme Ines C. Foehn 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(11):o613-o616
TBPY‐5‐34‐(Butane‐1,4‐diyl)(2‐{[1‐(2‐oxidophenyl)ethylidene‐κO]amino‐κN}ethanolato‐κO)silicon, C14H19NO2Si, crystallizes in two modifications. The monoclinic form, (IIm), was obtained by crystallization over a period of 2 d at room temperature; the orthorhombic form, (IIo), crystallized overnight at 248 K. The main difference between the two molecular structures involves the angles in the equatorial plane of the trigonal bipyramid around silicon. Form (IIm) has an O—Si—O angle of ca 121° and O—Si—C angles of ca 121 and 116°. In form (IIo), the corresponding angles are ∼123, 124 and 111°. There are also significant differences in the packing: (IIm) shows π stacking, whereas (IIo) does not. 相似文献
78.
Dr. Ines E. Collings Dr. Elena Bykova Dr. Maxim Bykov Dr. Sylvain Petitgirard Dr. Michael Hanfland Dr. Damian Paliwoda Prof. Leonid Dubrovinsky Prof. Natalia Dubrovinskaia 《Chemphyschem》2016,17(21):3369-3372
The incorporation of noble gas atoms, in particular neon, into the pores of network structures is very challenging due to the weak interactions they experience with the network solid. Using high‐pressure single‐crystal X‐ray diffraction, we demonstrate that neon atoms enter into the extended network of ammonium metal formates, thus forming compounds Nex[NH4][M(HCOO)3]. This phenomenon modifies the compressional and structural behaviours of the ammonium metal formates under pressure. The neon atoms can be clearly localised within the centre of [M(HCOO)3]5 cages and the total saturation of this site is achieved after ~1.5 GPa. We find that by using argon as the pressure‐transmitting medium, the inclusion inside [NH4][M(HCOO)3] is inhibited due to the larger size of the argon. This study illustrates the size selectivity of [NH4][M(HCOO)3] compounds between neon and argon insertion under pressure, and the effect of inclusion on the high‐pressure behaviour of neon‐bearing ammonium metal formates. 相似文献
79.
Ammar S Mahjoub MA Charfi N Skandarani I Chekir-Ghedira L Mighri Z 《Chemical & pharmaceutical bulletin》2007,55(3):385-388
A new skeleton of an O-heteroside natural substance named zinolol, the first representative of a new class of aminated hydroxyhydroquinone, has been isolated from the whole plant Anagallis monelli. Its structure has been established by one and two dimensional NMR spectroscopic procedures. Antioxidant, mutagenic, antimutagenic activities were realised and positive results were recorded. 相似文献
80.
Raabe I Antonijevic S Krossing I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(26):7510-7522
In an earlier publication (J. Am. Chem. Soc. 2002 , 124, 7111) we showed that polymeric cationic [Ag(P4S3)n]+ complexes (n=1, 2) are accessible if partnered with a suitable weakly coordinating counterion of the type [Al(ORF)4]? (ORF: poly‐ or perfluorinated alkoxide). The present work addresses the following questions that could not be answered in the initial report: How many P4S3 cages can be bound to a Ag+ ion? Why are these complexes completely dynamic in solution in the 31P NMR experiments? Can these dynamics be frozen out in a low‐temperature 31P MAS NMR experiment? What are the principal binding sites of the P4S3 cage towards the Ag+ ion? What are likely other isomers on the [Ag(P4S3)n]+ potential energy surface? Counterion influence: Reactions of P4S3 with Ag[Al{OC(CH3)(CF3)2}4] (Ag[hftb]) and Ag[{(CF3)3CO}3Al‐F‐Al{OC(CF3)3)}3] (Ag[al‐f‐al]) gave [(P4S3)Ag[hftb]]∞ ( 7 ) as a molecular species, whereas [Ag2(P4S3)6]2+[al‐f‐al]?2 ( 8 ) is an isolated 2:1 salt. We suggest that a maximum of three P4S3 cages may be bound on average to an Ag+ ion. Only isolated dimeric dications are formed with the largest cation, but polymeric species are obtained with all other smaller aluminates. Thermodynamic Born–Haber cycles, DFT calculations, as well as solution NMR and ESI mass spectrometry indicate that 8 exhibits an equilibrium between the dication [Ag2(P4S3)6]2+ (in the solid state) and two [Ag(P4S3)3]+ monocations (in the gas phase and in solution). Dynamics: 31P MAS NMR spectroscopy showed these solid adducts to be highly dynamic, to an extent that the 2JP,P coupling within the cages could be resolved (J‐res experiment). This is supported by DFT calculations, which show that the extended PES of [Ag(P4S3)n]+ (n=1–3) and [Ag2(P4S3)2]+ is very flat. The structures of α‐ and γ‐P4S3 were redetermined. Their variable‐temperature 31P MAS NMR spectra are discussed jointly with those of all four currently known [Ag(P4S3)n]+ adducts with n=1, 2, and 3. 相似文献