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排序方式: 共有120条查询结果,搜索用时 15 毫秒
71.
Gerhardt WW Zucchero AJ South CR Bunz UH Weck M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(16):4467-4474
A straightforward methodology towards the supramolecular synthesis of novel organometallic polymers with attractive optical properties is presented. By coordinating bifunctional fluorescent cruciform molecules through ditopic metalated pincer complexes (Pd or Pt), we have synthesized a new class of well-defined coordination polymers that have controllable and tunable physical and photophysical properties. The formation of these new materials by employing metal coordination was monitored by (1)H NMR spectroscopy, the association strength of the metal-ligand interaction was measured by isothermal titration calorimetry, the solution polymeric properties were evaluated by viscometry, and the optical properties were measured and observed by fluorescence spectroscopy. The fast and quantitative synthesis of a wide range of prefabricated monomeric cruciform and metalated-pincer-complex components will allow for the rapid generation, growth, and optimization of this new class of functional polymers, which have potential electronic and optical applications. 相似文献
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73.
Fructose was converted into C-1 diastereomeric carbocyclic building blocks resembling mannose using ruthenium-catalysed ring-closing metathesis as a key step. The potential use of the compounds in the synthesis of valienamine pseudodisaccharides is demonstrated using Mitsunobu coupling chemistry directly between a carbohydrate sulfonamide and the carbasugar C-1 alcohols. 相似文献
74.
Nonlinear Dynamics - We investigate a (2+1)-dimensional coupled nonlinear Schrödinger equation with spatially modulated nonlinearity and transverse modulation, and derive analytical vector... 相似文献
75.
A new dynamical system based on Thomas' system is described with infinitely many strange attractors on a 3-D spatial lattice. The mechanism for this multistability is associated with the disturbed offset boosting of sinusoidal functions with different spatial periods. Therefore, the initial condition for offset boosting can trigger a bifurcation, and consequently infinitely many attractors emerge simultaneously. One parameter of the sinusoidal nonlinearity can increase the frequency of the second order derivative of the variables rather than the first order and therefore increase the Lyapunov exponents accordingly. We show examples where the lattice is periodic and where it is quasiperiodic, that latter of which has an infinite variety of attractor types. 相似文献
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We define two types of bipartite graphs, chordal bipartite graphs and perfect elimination bipartite graphs, and prove theorems analogous to those of Dirac and Rose for chordal graphs (rigid circuit graphs, triangulated graphs). Our results are applicable to Gaussian elimination on sparse matrices where a sequence of pivots preserving zeros is sought. Our work removes the constraint imposed by Haskins and Rose that pivots must be along the main diagonal. 相似文献
79.
Anthony J. Midey Amanda CamachoJayanthi Sampathkumaran Clinton A. KruegerMark A. Osgood Ching Wu 《Analytica chimica acta》2013
High-performance ion mobility spectrometry (HPIMS) with an electrospray ionization (ESI) source detected a series of food contaminants and additive compounds identified as critical to monitoring the safety of food samples. These compounds included twelve phthalate plasticizers, legal and illegal food and cosmetic dyes, and artificial sweeteners that were all denoted as detection priorities. HPIMS separated and detected the range of compounds with a resolving power better than 60 in both positive and negative ion modes, comparable to the commonly used high-performance liquid chromatography (HPLC) methods, but with most acquisition times under a minute. The reduced mobilities, K0, have been determined, as have the linear response ranges for ESI-HPIMS, which are 1.5–2 orders of magnitude for concentrations down to sub-ng μL−1 levels. At least one unique mobility peak was seen for two subsets of the phthalates grouped by the country where they were banned. Furthermore, ESI-HPIMS successfully detected low nanogram levels of a phthalate at up to 30 times lower concentration than international detection levels in both a cola matrix and a soy-based bubble tea beverage using only a simplified sample treatment. A newly developed direct ESI source (Directspray) was combined with HPIMS to detect food-grade dyes and industrial dye adulterants, as well as the sweeteners sodium saccharin and sodium cyclamate, with the same good performance as with the phthalates. However, the Directspray method eliminated sources of carryover and decreased the time between sample runs. Limits-of-detection (LOD) for the analyte standards were estimated to be sub-ng μL−1 levels without extensive sample handling or preparation. 相似文献
80.
South CR Higley MN Leung KC Lanari D Nelson A Grubbs RH Stoddart JF Weck M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(14):3789-3797
Poly(norbornene)-based block copolymers containing side chains of palladated pincer complexes/dibenzo[24]crown-8 or palladated pincer complexes/dibenzylammonium salts were synthesized. Noncovalent functionalization was accomplished with their corresponding recognition units through simple 1:1 addition with association constants (Ka) greater than 10(5) m(-1). The self-assembly processes were monitored by using both 1H NMR spectroscopy and isothermal titration calorimetry. In all cases, we found that the self-assembly of the recognition units along each polymer block does not preclude the self-assembly processes along the other block. 相似文献