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排序方式: 共有174条查询结果,搜索用时 906 毫秒
21.
Ambrosi G Formica M Fusi V Giorgi L Macedi E Micheloni M Paoli P Pontellini R Rossi P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(5):1670-1682
Binding properties of 24,29-dimethyl-6,7,15,16-tetraoxotetracyclo[19.5.5.0(5,8).0(14,17)]-1,4,9,13,18,21,24,29-octaazaenatriaconta-Δ(5,8),Δ(14,17)-diene ligand L towards Zn(II) and anions, such as the halide series and inorganic oxoanions (phosphate (Pi), sulfate, pyrophosphate (PPi), and others), were investigated in aqueous solution; in addition, the Zn(II)/L system was tested as a metal-ion-based receptor for the halide series. Ligand L is a cryptand receptor incorporating two squaramide functions in an over-structured chain that connects two opposite nitrogen atoms of the Me(2)[12]aneN(4) polyaza macrocyclic base. It binds Zn(II) to form mononuclear species in which the metal ion, coordinated by the Me(2)[12]aneN(4) moiety, lodges inside the three-dimensional cavity. Zn(II)-containing species are able to bind chloride and fluoride at the physiologically important pH value of 7.4; the anion is coordinated to the metal center but the squaramide units play the key role in stabilizing the anion through a hydrogen-bonding network; two crystal structures reported here clearly show this aspect. Free L is able to bind fluoride, chloride, bromide, sulfate, Pi, and PPi in aqueous solution. The halides are bound at acidic pH, whereas the oxoanions are bound in a wide range of pH values ranging from acidic to basic. The cryptand cavity, abundant in hydrogen-bonding sites at all pH values, allows excellent selectivity towards Pi to be achieved mainly at physiological pH 7.4. By joining amine and squaramide moieties and using this preorganized topology, it was possible, with preservation of the solubility of the receptor, to achieve a very wide pH range in which oxoanions can be bound. The good selectivity towards Pi allows its discrimination in a manner not easily obtainable with nonmetallic systems in aqueous environment. 相似文献
22.
Mauro M De Paoli G Otter M Donghi D D'Alfonso G De Cola L 《Dalton transactions (Cambridge, England : 2003)》2011,40(45):12106-12116
We describe a new class of water soluble metallosurfactant molecules based on luminescent neutral iridium(III) complexes. The compounds possess an alkyl chain terminated with a negatively charged group, a sulphate. Due to their amphiphilic nature they assemble in aggregates in water and their photophysical properties, as well as the morphological characterization of the assemblies are presented. In particular, UV-Vis absorption, steady-state and time-resolved emission spectroscopy, dynamic light scattering and scanning electron microscopy techniques have been employed towards the analysis of the assemblies in different media. Comparison with the single components shows that the aggregates have very different photophysical properties. Importantly, the change in colour upon self-assembly is a remarkable feature which could be used for the design of probes which can change properties in different environments. 相似文献
23.
Geis-Asteggiante L Lehotay SJ Fortis LL Paoli G Wijey C Heinzen H 《Analytical and bioanalytical chemistry》2011,401(8):2617-2630
Microcystins (MCs) are the most common cyanotoxins found worldwide in freshwater, brackish, and marine environments. The rapid
and accurate analysis of MCs and nodularin (Nod-R) in fish tissue is important for determining occurrence, following trends,
and monitoring exposure for risk assessment and other purposes. The aim of this study was to develop a streamlined and reliable
sample preparation method for eight MCs (MC-RR, MC-YR, MC-LR, MC-WR, MC-LA, MC-LY, MC-LW, and MC-LF) and Nod-R in fish, and
conduct a validation of the new method using liquid chromatography–tandem mass spectrometry (LC-MS/MS) for analysis and compare
the results with a commercial enzyme-linked immunosorbent assay (ELISA) kit. Different sample preparation methods were compared,
and a simple extraction protocol with acidified acetonitrile/water (3:1) followed by hexane partitioning cleanup was found
to be most effective. Thorough validation of the final method was conducted, and 90–115% recoveries were achieved for all
analytes except for MC-RR, which gave 130% average recovery (isotopically labeled internal standards were unavailable to correct
for possible biases). The use of electrospray ionization in the negative mode gave few interferences and minimal matrix effects
in the LC-MS/MS analysis overall. Precision was typically 10–20% RSD among multiple days in experiments, detection limits
were <10 ng/g in the fish tissue (catfish, basa, and swai filets), and no false-positives or false-negatives occurred in blind
analyses of many spiked samples. The ELISA was unable to distinguish between MCs but was found to correctly assess the presence
or absence of MCs and Nod-R in the blind-fortified fish tissues. The capability of these approaches to measure covalently
bound MCs was not assessed. 相似文献
24.
M. Paoli 《Journal of Graph Theory》1988,12(1):85-94
Let G be a 2-edge connected graph with at least 5 vertices. For any given vertices a, b, c, and d in G with a ≠ b, there exists in G3 a hamiltonian path with endpoints a and b avoiding the edge cd, and there exists in G3 ∪ {cd} a hamiltonian path with endpoints a and b and containing the edge cd. Also, after removal of two edges or one edge and one vertex from G3, the resulting graph is still hamiltonian. 相似文献
25.
26.
O. Civitarese A. L. De Paoli M. de Llano A. Plastino 《Zeitschrift für Physik A Hadrons and Nuclei》1982,307(4):323-331
Symmetric nuclear matter at finite temperature is studied, within the Thermal Hartree Fock framework, employing lattice density waves and density dependent forces of the Skyrme type. The disappearance of clusters at finite temperature is described and its characteristics are quantiatively determined. 相似文献
27.
The influence of temperature-dependent effects on nuclear level densities is investigated. The explicit treatment of thermal degrees of freedom, within the Darwin-Fowler method, shows that the level-density parameter strongly differs from a constant value at low temperatures. The formalism is presented both for normal and superfluid systems. 相似文献
28.
We present herein the composition of bacterial communities occurring in ground chicken and the changes which arise in these
populations based upon nonselective partitioning by commercially-available Dynal anti-Salmonella and anti-E. coli O157 immunomagnetic beads (IMB). Our enumeration and colony selection protocol was based upon a 6 × 6 drop plate method (n = 18 for each 25-g sub-sampling) using a dilution which resulted in ca. 4–8 colonies per drop. An average of 82 ± 13 colonies
were selected from three 25-g ground chicken subsamplings per batch, each of which was repeated seasonally for one year. DNA
was extracted from each colony and the composition of Eubacteria in each of these harvests was determined by sequence-based
identification of 16S rDNA amplicons. The Gram-positive bacteria Brochothrix thermosphacta and Carnobacterium maltaromticum were the most commonly found organisms in both the total chicken wash (PBS) and in the IMB-bound (PBS-washed) fractions.
The remaining background organisms which also adhered to varying degrees to commercial IMBs were: Pseudomonas oleovorans, Acinetobacter lwoffi, Serratia spp., and one Rahnella spp. A large number of the organisms were also cladistically evaluated based on rDNA basepair disparities: all Brochothrices
were monophyletic; twelve different Pseudomonads were found along with eight Carnobacteria, seven Acinetobacteres, four Serratiae,
and two Rahnellae. Carnobacterium alone showed an IMB-based concentration enhancement (ca. two to sixfold).
Any reference to a brand or firm name does not constitute endorsement of the US Department of Agriculture over others of a
similar nature not mentioned 相似文献
29.
Let X be a Banach space and a strongly continuous group of linear operators on X. Set and where is the unit circle and denotes the spectrum of T(t). The main result of this paper is: is uniformly continuous if and only if is non-meager. Similar characterizations in terms of the approximate point spectrum and essential spectra are also derived.
Received: 14 June 2006, Revised: 27 September 2007 相似文献
30.
Roy MD Herzing AA De Paoli Lacerda SH Becker ML 《Chemical communications (Cambridge, England)》2008,(18):2106-2108
Water soluble CdSe/ZnS nanoparticles with emission maxima from 511 nm to 596 nm and quantum efficiencies ranging from 11% to 28% are synthesized in a facile two-step method in ambient atmospheric conditions using a commercially available microwave reactor. 相似文献