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131.
2-Hydroxy-2-methylbut-3-yn-4-ylbenzenes, readily available from bromobenzenes, are efficiently cleaved by the water-miscible reagents sodium 2-propoxide in 2-propanol, or potassium hydroxide in dioxan, which facilitates isolation of volatile ethynylbenzenes. 相似文献
132.
133.
Ana C.F. Ribeiro Victor M.M. Lobo Hugh D. Burrows Artur J.M. Valente Ana M. Amado Abílio J.F.N. Sobral Ana S.N. Teles Cecília I.A.V. Santos Miguel A. Esteso 《Journal of Molecular Liquids》2008,140(1-3):73-77
Numerical values for the mean distance of closest approach of ions, “a”, for lithium salts in aqueous solutions are presented and discussed. These values were obtained from both experimental activity and diffusion coefficients, and estimated by using different theoretical approaches. 相似文献
134.
Roberto E. Di Paolo Dr. João Seixas de Melo Prof. João Pina Hugh D. Burrows Prof. Jorge Morgado Prof. António L. Maçanita Prof. 《Chemphyschem》2007,8(18):2657-2664
Two p‐phenylenevinylene (PV) trimers, containing 3′‐methylbutyloxyl (in MBOPV3) and 2′‐ethylhexyloxyl (in EHOPV3) side chains, are used as model compounds of PV‐based conjugated polymers (PPV) with the purpose of clarifying the origin of fast (picosecond time) components observed in the fluorescence decays of poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐p‐phenylenevinylene] (MEH‐PPV). The fluorescence decays of MBOPV3 and EHOPV3 reveal the presence of similar fast components, which are assigned to excited‐state conformational relaxation of the initial population of non‐planar trimer conformers to lower‐energy, more planar conformers. The rate constant of conformational relaxation kCR is dependent on solvent viscosity and temperature, according to the empirical relationship kCR=aηo?α?exp(?αEη/RT), where aηo?α is the frequency factor, ηo is the pre‐exponential coefficient of viscosity, Eη is the activation energy of viscous flow. The empirical parameter α, relating the solvent microscopic friction involved in the conformational change to the macroscopic solvent friction (α=1), depends on the side chain. The fast component in the fluorescence decays of MEH‐PPV polymers (PPVs), is assigned to resonance energy transfer from short to longer polymer segments. The present results call for revising this assignment/interpretation to account for the occurrence of conformational relaxation, concurrently with energy transfer, in PPVs. 相似文献
135.
Christopher A. Lukey Michaela Tymichova Hugh R. Brown 《Journal of polymer science. Part A, Polymer chemistry》2007,45(7):1282-1286
A novel route to styrene/p‐aminostyrene copolymers is described that involves the introduction of amino functionality into the structure of pure monodisperse polystyrene. The simple two‐step synthesis involves the introduction of a bromo group into the aromatic ring by electrophilic substitution and then a palladium‐catalyzed reaction with LiN(SiMe3)2 followed by an acid and base treatment to release the free amine. All reactions are carried out at room temperature. This approach avoids the difficulties often associated with the preparation of copolymers from incompatible monomers. The technique also gives a product with a precisely known molecular weight and polydispersity, important parameters governing many physical properties. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1282–1286, 2007 相似文献
136.
Effecting an increase in the use of inquiry-based learning pedagogies in mathematics and science at a large scale across Europe has been promoted within the European education policy space. The primary goal is greater numbers of young people having more positive dispositions towards future careers in science, engineering and technology (Rocard in EUR22845—science education now: a renewed pedagogy for the future of Europe, http://www.eesc.europa.eu/resources/docs/rapportrocardfinal.pdf, 2007). We report on policy research as part of a European funded project that aims to support professional development that might bring about such changes. Our analysis points to policy activity that, to a greater or lesser degree, appears to be ineffective in meeting the desired outcomes in respect of teacher change. We identify why, although there is much policy activity, initiatives struggle to make an impact on teaching practices and learners’ experiences. Overall we point to misalignment in what policy defines in terms of input to learning, what is measured and valued in terms of outcomes, and what is desired in the teaching process. We also point to how policy fails to support development of the individual teacher and the teaching profession as a whole in ways that might effect the desired change. 相似文献
137.
Ostrowska KM Malkin A Meade A O'Leary J Martin C Spillane C Byrne HJ Lyng FM 《The Analyst》2010,135(12):3087-3093
The main aetiology of cervical cancer is infection with high-risk human papillomavirus (HPV). Cervical cancer is almost 100% curable if detected in the early stages. Thus, information about the presence and levels of HPV in patient samples has high clinical value. As current screening methods, such as the Pap smear test, are highly subjective and in many cases show low sensitivity and specificity, new supportive techniques are desirable to improve the quality of cervical cancer screening. In this study, vibrational spectroscopic techniques (Raman and Fourier Transform Infra Red absorption) have been applied to the investigation of four cervical cancer cell lines: HPV negative C33A, HPV-18 positive HeLa with 20-50 integrated HPV copies per cell, HPV-16 positive SiHa with 1-2 integrated HPV strands per cell and HPV-16 positive CaSki containing 60-600 integrated HPV copies per cell. Results show that vibrational spectroscopic techniques can discriminate between the cell lines and elucidate cellular differences originating from proteins, nucleic acids and lipids. Similarities between C33A and SiHa cells were exhibited in the Raman and infrared spectra and were confirmed by Principal Component Analysis (PCA). Analysis of the biochemical composition of the investigated cells, with the aid of PCA, showed a clear discrimination between the C33A-SiHa group and HeLa and CaSki cell lines indicating the potential of vibrational spectroscopic techniques as a support to current methods for cervical cancer screening. 相似文献
138.
Toy AA Chaffey-Millar H Davis TP Stenzel MH Izgorodina EI Coote ML Barner-Kowollik C 《Chemical communications (Cambridge, England)》2006,(8):835-837
Thioketones are demonstrated to be suitable agents for controlling free radical polymerization processes: the polymerizations carry (pseudo) living characteristics indicating that the control process is induced by a persistent radical effect. 相似文献
139.
Much of our knowledge about molybdenum enzymes has originated from EXAFS spectroscopy. This technique provides excellent bond-length accuracy but has only limited bond-length resolution. We have used EXAFS spectroscopy with an extended data range in an attempt to improve bond-length resolution for the molybdenum enzyme sulfite oxidase. The Mo site of sulfite oxidase has two oxygen and three Mo-S ligands (two from cofactor dithiolene plus a cysteine). For the oxidized (Mo(VI)) enzyme, we find that the three Mo-S bond lengths are very similar (within 0.05 A) at 2.41 A, as are the Mo=O ligands at 1.72 A. Density functional theory shows that this is consistent with the proposed active-site structure. The reduced (Mo(IV)) enzyme shows two Mo-S bond lengths at 2.35 A and one at 2.41 A (assigned to cofactor dithiolene and cysteine, respectively, from DFT), together with one Mo=O at 1.72 A and one Mo-OH(2) at 2.30 A. 相似文献
140.
W. Hugh Woodin 《Annals of Pure and Applied Logic》2006,140(1-3):161
The results of this paper concern the effective cardinal structure of the subsets of [ω1]<ω1, the set of all countable subsets of ω1. The main results include dichotomy theorems and theorems which show that the effective cardinal structure is complicated. 相似文献