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Solvent Dependence (solvent + dependence)
Selected AbstractsSystematic Studies on Photoluminescence of Oligo(arylene-ethynylene)s: Tunability of Excited States and Derivatization as Luminescent Labeling Probes for ProteinsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2006Yong-Gang Zhi Abstract Functionalized oligo(phenylene-ethynylene)s (OPEs) with different conjugation lengths, p -X(C6H4C,C)nSiMe3 (n = 1,4; X = NH2, NMe2, H) were synthesized by Sonogashira coupling of (phenylene-ethynylene)s and 1-iodo-4-(trimethylsilylethynyl)benzene, followed by desilylation of the p -substituted (trimethylsilylethynyl)benzenes with potassium hydroxide. The photoluminescent properties for the OPE series with different chain lengths and their solvatochromic responses were examined. The absorption maxima were red-shifted with increasing numbers of ,(C6H4C,C), units (n), and a linear plot of the absorption energy maxima vs. 1/n was obtained for each series. The emission spectra in dichloromethane showed a broad and structureless band, the energies of which (in wavenumbers) also fit linearly with 1/n. Both the absorption and emission wavelength maxima of the NH2 - and NMe2 -substituted OPEs exhibited significant solvent dependence, whereas the parent OPEs (X = H) showed only minor shifts of the ,max values in different solvents. Substituent effects upon the photoluminescent characteristics of the OPEs and the tunability of the excited states were examined with the p -X(C6H4C,C)nSiMe3 (n = 2, 3; X = NH2, NMe2, H, SMe, OMe, OH, and F) series. The H- and F-substituted counterparts exhibited high-energy vibronically structured emissions attributed to the 3(,,*) excited states of the (arylene-ethynylene) backbone. For compounds bearing NH2 and NMe2 groups, a broad red-shifted emission with a remarkable Stokes shift from the respective absorption maximum was observed, which can be assigned to an n , ,* transition. The n , ,* assignment was supported by MO calculations on the model compounds p -X(C6H4C,C)2SiH3 (X = NH2, H). Functionalization of the oligo(arylene-ethynylene)s with the N -hydroxysuccinimidyl (NHS) moiety enabled covalent attachment of the fluorophore to HSA protein molecules. A series of fluorescent labels, namely p -X(C6H4C,C)nC6H4NHS, (n = 1, X = NH2, NMe2, SMe, OMe, OH, F; n = 2, X = NH2, NMe2) and p -Me2NC6H4C,C(C4H2S)C,CC6H4NHS were synthesized, and their conjugates with HSA (human serum albumin) were characterized by MALDI-TOF mass spectrometry, UV/Vis absorption spectroscopy, and gel electrophoresis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Mechanistic studies of intramolecular CH insertion reaction of arylnitrenes: isotope effect, configurational purity and radical clock studiesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 1 2005Shigeru Murata Abstract In order to reveal the mechanism of the intramolecular CH insertion of arylnitrenes, three experiments were carried out: measurement of isotope effects, determination of the extent of configurational retention and radical clock studies. Irradiation of the deuterium-substituted azide 4 - d in an inert solvent exclusively afforded the indolines 5 - h and 5 - d, in which the kinetic isotope effect kH/kD on the intramolecular CH insertion of the nitrene was evaluated as 12.6,14.7 at room temperature. A chiral chromatographic analysis of the indoline 11 obtained from the optically active azide (S)- 6 revealed that the enantiomeric purity of the starting azide was almost completely lost during the intramolecular CH insertion of the photolytically generated nitrene (enantiomeric excess <10%). The thermolysis of the azide 7 at 180°C mainly gave a mixture of the cyclopropyl ring-opened products 20,22, together with the intramolecular CH insertion product with an intact cyclopropyl ring 19. On the basis of these observations, we concluded that the intramolecular CH insertion of the nitrene proceeds primarily by the hydrogen abstraction,recombination mechanism. We propose, however, a small contribution of the concerted mechanism to the intramolecular CH insertion, based on the solvent dependence of the isotope effect and the extent of the configurational retention. Copyright © 2004 John Wiley & Sons, Ltd. [source] Role of hydrogen bonding in the oxidation potential of enolsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2003Mukul Lal Abstract Three stable ,,,-dimesityl enols with heteroaromatic rings in the ,-position were synthesized to study the effect of OH···N hydrogen bonding on the oxidation potentials of enols. In contrast to its solid-state structure, enol E1 exists predominantly as intramolecularly hydrogen-bonded species in solution. For enol E2 an intermolecular hydrogen bond and for E3 a partial proton transfer were established based on NMR, dilution experiments, solvent dependence and UV,visible spectroscopic studies. Cyclic voltammetric investigations revealed that OH···N hydrogen bonding may shift the oxidation potentials of enols by up to 510,mV cathodically. Copyright © 2003 John Wiley & Sons, Ltd. [source] Microwave-Assisted Free Radical Copolymerizations of Styrene and Methyl MethacrylateMACROMOLECULAR RAPID COMMUNICATIONS, Issue 4 2007Heiner Stange Abstract Free radical copolymerizations of styrene and MMA were performed in toluene and DMF as solvents using different peroxide initiators with and without microwave irradiation. A general trend showed significant solvent dependence of monomer conversion rate only for copolymerizations initiated by tert -butyl perbenzoate in DMF compared to toluene but nearly no impact for copolymerizations initiated by dicumyl peroxide and dibenzoyl peroxide. Significant variations in copolymer composition were not observed for reactions under conventional heating compared to microwave irradiation. It was concluded that enhanced initiator decomposition under microwave irradiation in DMF accelerate polymerization of styrene and MMA by formation of larger amount of initiator radicals. [source] Solvent Effect on Optical Rotation: A Case Study of Methyloxirane in WaterCHEMPHYSCHEM, Issue 12 2006Parag Mukhopadhyay Explicit solute,solvent interactions: MD simulations and TD-DFT are used to determine the solvent dependence of the optical rotatory dispersion (ORD) for methyloxirane in water (see figure). The inclusion of explicit solute,solvent interactions is essential to describe the influence of the solvent on the OR of the system and the MD simulations provide a suitable means to analyze and predict chiroptical solvation effects. [source] | ||||||||||