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141.
Milios CJ Prescimone A Mishra A Parsons S Wernsdorfer W Christou G Perlepes SP Brechin EK 《Chemical communications (Cambridge, England)》2007,(2):153-155
A {Mn(III)4} distorted cube has been synthesized that possesses an S = 8 ground state and single-molecule magnetism behaviour. 相似文献
142.
This review is a brief account on the application of a novel methodology to the quality control and authentication of extra-virgin olive oil. This methodology is based on the derivatization of the labile hydrogens of functional groups, such as hydroxyl and carboxyl groups, of olive oil constituents with the phosphorus reagent 2-chloro-4,4,5,5-tetramethyldioxaphospholane, and the use of the (31)P chemical shifts to identify the phosphitylated compounds. Various experimental aspects such as pertinent instrumentation, sample preparation, acquisition parameters and properties of the phosphorus reagent are reviewed. The strategy to assign the (31)P signals of the phosphitylated model compounds and olive oil constituents by employing 1D and 2D NMR experiments is presented. Finally, the capability of this technique to assess the quality and the genuineness of extra-virgin olive oil and to detect fraud is discussed. 相似文献
143.
144.
We construct several new large sets of t-designs that are invariant under Frobenius groups, and discuss their consequences. These large sets give rise to further new large sets by means of known recursive constructions including an infinite family of large sets of 3 − (v, 4, λ) designs. © 1998 John Wiley & Sons, Inc. J Combin Designs 6: 293–308, 1998 相似文献
145.
The high-resolution 13C and 1H nuclear magnetic resonance (NMR) linewidths of semi-crystalline poly(4-hydroxybutyrate), P4HB, and poly(3-hydroxybutyrate-co-4-hydroxybutyrate), (P3/4HB-18, 18% 4HB units) in the amorphous phase and in the melt are studied as a function of temperature and magnetic field strength. Measurements of the 13C spin-spin relaxation times under the same experimental conditions show that the natural line-width is a minor contributor to the line-broadening observed in the 13C spectra of the solid polymers. A variety of coherent averaging solid-state NMR methods are used to examine possible contributions from various line-broadening mechanisms. It is shown that magnetic susceptibility and chemical shift dispersion are the major factors for the broadening of the proton and carbon resonances of P4HB in the amorphous phase and the melt, respectively. Incomplete motional narrowing due to a slow motional mode restricted in amplitude by the presence of crystallites and/or chain constraints was found to be the major line-broadening factor for P3/4HB-18 in the amorphous phase. Correlations between crystalline morphology, physical and mechanical properties, and polymer chain dynamics are discussed, along with the way these factors affect the NMR linewidth data presented. © 1996 John Wiley & Sons, Inc. 相似文献
146.
Stamatakis G Knuutinen U Laitinen K Spyros A 《Analytical and bioanalytical chemistry》2010,398(7-8):3203-3214
Two original art installations constructed from unsaturated polyester resins (UPR) and four different reference UPR products (before and after UVB aging) were analyzed by high-resolution 1D and 2D nuclear magnetic resonance (NMR) spectroscopy. Breaking strain studies were also conducted for the four UPR model products before and after different aging procedures (moisture, UVB exposure, melt/freeze). NMR analysis of the chemical composition of the UPR resin extracts showed they contain several low MW organic compounds and oligomers rich in polar -OH groups that play a significant role in the degradation behavior of the composite UPR materials. Statistical analysis of the NMR compositional data showed that styrene and benzaldehyde contents can be used to differentiate between fresh and aged UPR samples. The phthalate and propylene glycol unit speciation (esterified, primary or secondary -OH) of the extracts provided evidence that UPR resin C was used in the construction of the two art installations, and direct comparison of (1)H and (13)C NMR spectra verified this compositional similarity. UPR resin C was shown by both NMR and breaking strain studies to be the reference UPR most susceptible to degradation by different aging procedures, a characteristic attributed to the lower styrene content of resin C. 相似文献
147.
Efthimios Bakarezos Vasilios Vathis Spyros Brezas Yannis Orphanos Nektarios A. Papadogiannis 《Applied Acoustics》2012,73(5):478-483
The acoustics of an authentically reconstructed ancient Greek tortoise-shell lyre, known as Chelys, is investigated for the first time. Modern experimental methods are employed, such as electronic speckle pattern laser interferometry and impulse response, to extract the vibrational behavior of the instrument and its main parts. Additionally, the emitted sound from the instrument was recorded, under controlled conditions, and spectrally analyzed. Major findings include the concentration of the emitted sound between 400 Hz and 800 Hz, with an amplitude modified in a manner consistent with the experimentally measured vibrational characteristics of the instrument’s sound box and bridge. The experimental results validate the historical evidence that Chelys was used in Greek antiquity as an accompaniment instrument to the human voice. 相似文献
148.
A DFT study on the intramolecular thermal phenyl migration in iodonium ylides supports a concerted mechanism. In contrast to the two, different than each other, suggested mechanisms, involving only intermediates, this study indicates a single-step, transition-state one--involving a five-membered cyclic ring--with no intermediates. The frontier-orbital-controlled migration also confirms the different thermal behavior of two different ylides. 相似文献
149.
Constantinos G. Efthymiou Catherine P. Raptopoulou Aris Terzis Spyros P. Perlepes Albert Escuer Constantina Papatriantafyllopoulou 《Polyhedron》2010
The reactions of representative 2-pyridyl oximes with NiII salts in the presence of a base have been investigated. The synthetic study has led to the new triangular complexes [Νi3(ppko)6]·2H2O·0.5EtOH·MeOH (1·2H2O·0.5EtOH·MeOH), [Νi3(mpko)3(HCO2)2(mpkoH)2](ClO4) (2) and [Νi3(ppko)3(HCO2)2(ppkoH)2](ClO4) (3), where ppko− is the anion of phenyl(2-pyridyl)ketone oxime and mpko− is the anion of methyl(2-pyridyl)ketone oxime. The structures of compounds 1 and 2 have been determined by single crystal X-ray diffraction. The ppko− ligand in 1 adopts four different coordination modes including the unique NpyridylOoximate chelating one which gives rise to a 6-membered chelating ring, while the neutral and the deprotonated oxime ligands in 2 adopt three different coordination modes. The magnetic properties of 1 and 2 have been studied by variable-temperature dc magnetic susceptibility techniques which indicate antiferromagnetic interactions. 相似文献