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961.
Kirsten H. Chalmers Elena De Luca Naomi H. M. Hogg Alan M. Kenwright Dr. Ilya Kuprov Dr. David Parker Prof. Mauro Botta Prof. J. Ian Wilson Dr. Andrew M. Blamire Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(1):134-148
The synthesis and spectroscopic properties of a series of CF3‐labelled lanthanide(III) complexes (Ln=Gd, Tb, Dy, Ho, Er, Tm) with amide‐substituted ligands based on 1,4,7,10‐tetraazacyclododecane are described. The theoretical contributions of the 19F magnetic relaxation processes in these systems are critically assessed and selected volumetric plots are presented. These plots allow an accurate estimation of the increase in the rates of longitudinal and transverse relaxation as a function of the distance between the LnIII ion and the fluorine nucleus, the applied magnetic field, and the re‐rotational correlation time of the complex, for a given LnIII ion. Selected complexes exhibit pH‐dependent chemical shift behaviour, and a pKa of 7.0 was determined in one example based on the holmium complex of an ortho‐cyano DO3A‐monoamide ligand, which allowed the pH to be assessed by measuring the difference in chemical shift (varying by over 14 ppm) between two 19F resonances. Relaxation analyses of variable‐temperature and variable‐field 19F, 17O and 1H NMR spectroscopy experiments are reported, aided by identification of salient low‐energy conformers by using density functional theory. The study of fluorine relaxation rates, over a field range of 4.7 to 16.5 T allowed precise computation of the distance between the LnIII ion and the CF3 reporter group by using global fitting methods. The sensitivity benefits of using such paramagnetic fluorinated probes in 19F NMR spectroscopic studies are quantified in preliminary spectroscopic and imaging experiments with respect to a diamagnetic yttrium(III) analogue. 相似文献
962.
Alessandro Rodrigues Claudio Di Vitta José Eduardo Pandini Cardoso Filho Liliana Marzorati Mauro Alves Bueno Paulo Roberto Olivato 《Tetrahedron letters》2010,51(40):5344-3173
Increased diastereoisomeric excesses are obtained for the sulfanylation reactions of some 2-methylsulfinyl cyclanones under phase-transfer catalysis using the chiral catalyst QUIBEC instead of TEBA. The optically pure (SS,2S)-2-methylsulfinyl-2-methylsulfanylcyclohexanone thus prepared reacts with ethyl acetate lithium enolate affording, after hydrolysis, (R)-2-[(ethoxycarbonyl)methyl]-2-hydroxycyclohexanone in 60% ee. Density functional theory calculations (at the B3LYP/6-311++G(d,p) level) can successfully explain the origin of this result as the kinetically favored axial attack of the nucleophile to the carbonyl group of the most stable conformer of the cyclanone, in which the CH3SO and CH3S groups are at the equatorial and axial positions, respectively. 相似文献
963.
Vaccaro M Accardo A Tesauro D Mangiapia G Löf D Schillén K Söderman O Morelli G Paduano L 《Langmuir : the ACS journal of surfaces and colloids》2006,22(15):6635-6643
In this paper, we present the development of a new potential blood pool contrast agent for magnetic resonance imaging applications (MRA/MRI) based on gadolinium complexes containing amphiphilic supramolecular aggregates. A novel amphiphilic unimer, containing the DTPAGlu chelating agent covalently bound to two C18 alkylic chains, has been synthesized. DTPAGlu is a well-known chelating agent for a wide number of ions such as the paramagnetic metal ion Gd3+ used as contrast agent in MRA/MRI. The wide aggregation behavior of this surfactant, as free base or as gadolinium complex, has been studied and compared by means of dynamic light scattering, small-angle neutron scattering and cryogenic transmission electron microscopy techniques. Near neutral pH in both cases, the dominant aggregates are micelles.The high negative actual charge of the surfactant headgroup causes a strong headgroups repulsion, promoting the formation of large and high curvature aggregates. By decreasing pH and less markedly increasing the ionic strength, we observe a micelle-to-vesicle transition driven by a decreased electrostatic repulsion. A straightforward switch between different aggregation states can be particularly useful in the development of pH-responsive MRA/MRI contrast agents. 相似文献
964.
Missori M Mondelli C De Spirito M Castellano C Bicchieri M Schweins R Arcovito G Papi M Castellano AC 《Physical review letters》2006,97(23):238001
Paper is the main component of a huge quantity of cultural heritage. It is primarily composed of cellulose that undergoes significant degradation with the passage of time. By using small angle neutron scattering (SANS), we investigated cellulose's supramolecular structure, which allows access to degradation agents, in ancient and modern samples. For the first time, SANS data were interpreted in terms of water-filled pores, with their sizes increasing from 1.61 nm up to 1.97 nm in natural and artificially aged papers. The protective effect of gelatine sizing was also observed. 相似文献
965.
Scarabino C Lubritto C Proto A Rubino M Fiengo G Marzaioli F Passariello I Busiello G Fortunato A Alfano D Sabbarese C Rogalla D De Cesare N d'Onofrio A Terrasi F 《Isotopes in environmental and health studies》2006,42(2):151-158
Human bones recovered from the archaeological site of Pontecagnano (Salerno, Italy) have been studied to reconstruct the diet of an Etrurian population. Two different areas were investigated, named Library and Sant' Antonio, with a total of 44 tombs containing human skeletal remains, ranging in age from the 8th to the 3rd century B.C. This time span was confirmed by 14C dating obtained using Accelerator Mass Spectrometry (AMS) on one bone sample from each site.Atomic Absorption Spectrometry (AAS) was used to extract information about the concentration of Sr, Zn, Ca elements in the bone inorganic fraction, whilst stable isotope ratio measurements (IRMS) were carried out on bone collagen to obtain the delta13C and delta15N. A reliable technique has been used to extract and separate the inorganic and organic fractions of the bone remains.Both IRMS and AAS results suggest a mixed diet including C3 plant food and herbivore animals, consistent with archaeological indications. 相似文献
966.
We give the name Hausdorff to those ultrafilters that provide ultrapowers whose natural topology (-topology) is Hausdorff, e.g. selective ultrafilters are Hausdorff. Here we give necessary and sufficient conditions for product ultrafilters to be Hausdorff. Moreover we show that no regular ultrafilter over the ``small' uncountable cardinal can be Hausdorff. ( is the least size of an ultrafilter basis on .) We focus on countably incomplete ultrafilters, but our main results also hold for -complete ultrafilters.
967.
Any physical transformation that equally distributes quantum information over a large number M of users can be approximated by a classical broadcasting of measurement outcomes. The accuracy of the approximation is at least of the order O(M(-1)). In particular, quantum cloning of pure and mixed states can be approximated via quantum state estimation. As an example, for optimal qubit cloning with 10 output copies, a single user has an error probability p(err) > or = 0.45 in distinguishing classical from quantum output, a value close to the error probability of the random guess. 相似文献
968.
Cycle-to-cycle variation (CCV) limits how lean a spark-ignited (SI) internal combustion engine (ICE) can stably operate at, restricts efficiency, and increases emissions through incomplete combustion. Therefore, a way to cleaner, more efficient SI ICEs is to minimize the CCV. Current methods to study CCV include experimental investigations and CFD-based numerical simulations. This study, in contrast, investigates the ability of neural networks to accurately model the indicated mean effective pressure (IMEP) and its coefficient of variation (COV of IMEP). Experimental data from a previous study of spark-ignited propane/air combustion in the TCC-III engine was used to train and evaluate a neural network. An optimized network was generated that utilizes 109 experimental inputs and is operated with 15 neurons in one hidden layer to determine IMEP for 18 engine operating conditions, with 625 individual consecutive engine cycles for each condition. The impact of training set size and the number of input parameters was also investigated. The average deviation for IMEP from the experimental measurements is 0.7–2.2% for the training data set and less than 12% for the entire predicted range of operating conditions. Data sets consisted of tests under rich, lean, and stoichiometric conditions without and with 9% nitrogen dilution. Predicted COV of IMEP strongly correlates with experimental data (R2?=?0.8453). However, a systematic over prediction of COV of IMEP for low COVs was observed while higher COVs were under-predicted by the neural network. The cause for this systematic behavior has not yet been identified but histograms of the predicted IMEP data indicate that this could be related to missing physical parameters that have a significant impact on combustion variability. 相似文献
969.
Mauro Sergio Ferreira Santos Thiago Gomes Cordeiro Zuzana Cieslarova Ivano Gebhardt Rolf Gutz Carlos D. Garcia 《Electrophoresis》2019,40(18-19):2256-2262
1‐propanol is a primary alcohol extensively used in the pharmaceutical, chemical, and food industries. It has been also found as a contaminant in the atmosphere and is considered a model compound to mimic the behavior and fate of aliphatic alcohols exposed to environmental conditions. In order to understand that role of relevant variables, this paper presents results obtained with a simple experimental set‐up to investigate the reactivity of 1‐propanol under mild oxidizing conditions. Coupling this system with CE‐C4D allowed the quantification of the carboxylic acids formed. For the described experiments, aqueous solutions of 1‐propanol were placed inside a photoreactor and oxidized upon the addition of TiO2 and/or H2O2. According to the described results, the addition of H2O2 (0.1% w/w) was the most significant variable, roughly tripled the amount of carboxylic acids generated and led to the conversion of up to 70% of the initially available 1‐propanol (1 mmol/L). More importantly, the reaction yielded the formation (within 10 min) of propionate (50 µmol/L), acetate (400 µmol/L), formate (50 µmol/L), and malonate (200 µmol/L). The latter is critically important because it represents the first example of the photochemical oxidation of both terminal carbons of the C3‐chain of 1‐propanol under mild conditions, and opens new avenues for the production of this important chemical building block. 相似文献
970.
Andreea Ionescu Rossella Caligiuri Nicolas Godbert Angela Candreva Massimo LaDeda Emilia Furia Mauro Ghedini Iolinda Aiello 《化学:亚洲杂志》2019,14(17):3025-3034
A series of electropolymerizable cyclometallated IrIII complexes were synthesized and their electrochemical and photophysical properties studied. The triphenylamine electropolymerizable fragment was introduced by using triphenylamine‐2‐phenylpyridine and, respectively, triphenylamine‐benzothiazole as cyclometalated ligands. The coordination sphere was completed by two differently substituted β‐ketoiminate ligands deriving from the condensation of acetylacetone or hexafluoroacetylacetone with para‐bromoaniline. The influence of the ‐CH3/‐CF3 substitution to the electrochemical and photophysical properties was investigated. Both complexes with CH3 substituted β‐ketoiminate were emissive in solution and in solid state. Highly stable films were electrodeposited onto ITO coated glass substrates. Their emission was quenched by electron trapping within the polymeric network as proven by electrochemical studies. The ‐CF3 substitution of the β‐ketoiminate leads instead to the quenching of the emission and inhibits electropolymerization. 相似文献