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Dipole Coupling (dipole + coupling)
Selected AbstractsSelf-Organization of Dipolar 4,4,-Disubstituted 2,2,-Bipyridine Metal Complexes into Luminescent Lamellar Liquid CrystalsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2003Daniela Pucci Abstract Mononuclear cis -dichloro complexes, [LnMCl2], with different metal centres (PtII, NiII, and ZnII) and a series of palladium and platinum derivatives, [L2MX2], in which chloride groups are replaced with iodide, bromide, and azide ligands, have been synthesized from 4,4,-disubstituted-2,2,-bipyridines. Upon complexation of these non-mesogenic ligands, the peculiar structural arrangement, characterized by intermolecular associations of the new derivatives, induces mesomorphism in most [L2MX2] complexes, confirming the importance of coordination chemistry in metal-mediated formation of liquid crystals. Single crystal X-ray structures have been determined for dihexadecyl 2,2,-bipyridyl-4,4,-dicarboxylatopalladium and -zinc dichloride derivatives. Both the metal centres and the ancillary ligands have been varied to use dipole coupling as a tool to control molecular architecture: thermal, as well as spectroscopic properties, depend strongly upon molecular dipolar interactions. Tunable red and blue emitters based on PdII and PtII, both in solution and in the solid state, have been obtained. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Understanding the Nature of the States Responsible for the Green Emission in Oxidized Poly(9,9-dialkylfluorene)s: Photophysics and Structural Studies of Linear Dialkylfluorene/Fluorenone Model CompoundsADVANCED FUNCTIONAL MATERIALS, Issue 13 2009Khai Leok Chan Abstract Here, the optical properties of a series of structurally well-defined model compounds for oxidatively degraded poly(dialkylfluorenes) (PFs) are reported. Specifically, linear compounds comprising one, two, or four dihexylfluorene (F) moieties together with one fluorenone (O) moiety placed either at the end or in the center of each chain (i.e., FO, FFO, FOF, FFOFF) are studied. The results support the recent observation that the photophysics of the fluorenone-centered "pentamer" (FFOFF) is most similar to that of oxidized PFs. They further demonstrate that molecule,molecule interaction is essential to activate the green emission band. Investigations by X-ray diffraction (XRD) identify the solid-state structure of a representative member of this class of compounds and reveal inter-molecular interaction through dipole,dipole coupling between neighboring fluorenone moieties. [source] Collagen structure: The molecular source of the tendon magic angle effectJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 2 2007Gary D. Fullerton PhD Abstract This review of tendon/collagen structure shows that the orientational variation in MRI signals from tendon, which is referred to as the "magic angle" (MA) effect, is caused by irreducible separation of charges on the main chain of the collagen molecule. These charges are held apart in a vacuum by stereotactic restriction of protein folding due in large part to a high concentration of hydroxyproline ring residues in the amino acids of mammalian collagen. The elevated protein electrostatic energy is reduced in water by the large dielectric constant of the highly polar solvent (, , 80). The water molecules serve as dielectric molecules that are bound by an energy that is nearly equivalent to the electrostatic energy between the neighboring positive and negative charge pairs in a vacuum. These highly immobilized water molecules and secondary molecules in the hydrogen-bonded water network are confined to the transverse plane of the tendon. Orientational restriction causes residual dipole coupling, which is directly responsible for the frequency and phase shifts observed in orientational MRI (OMRI) described by the MA effect. Reference to a wide range of biophysical measurements shows that native hydration is a monolayer on collagen hm = 1.6 g/g, which divides into two components consisting of primary hydration on polar surfaces hpp = 0.8 g/g and secondary hydration hs = 0.8 g/g bridging over hydrophobic surface regions. Primary hydration further divides into side-chain hydration hpsc = 0.54 g/g and main-chain hydration hpmc = 0.263 g/g. The main-chain fraction consists of water that bridges between charges on the main chain and is responsible for almost all of the enthalpy of melting ,H = 70 J/g-dry mass. Main-chain water bridges consist of one extremely immobilized Ramachandran water bridge per tripeptide hRa = 0.0658 g/g and one double water bridge per tripeptide hdwb = 0.1974 g/g, with three water molecules that are sufficiently slowed to act as the spin-lattice relaxation sink for the entire tendon. J. Magn. Reson. Imaging 2007. © 2007 Wiley-Liss, Inc. [source] Studies on fluorescence resonance energy transfer between dyes and water-soluble quantum dotsLUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 4-5 2005Qidan Chen Abstract In this work, donor,acceptor complexes were formed based on antibody,antigen interactions. Immunoglobulin antigen (mouse-IgG) was effectively conjugated to mercaptopropyl acid-modified CdTe quantum dot synthesized in aqueous solution via electrostatic interaction, while organic dyes,tetramethylrhodamine isothiocyanate (TRITC) were attached to the corresponding antibody (anti-mouse IgG). The mutual affinity of the antigen and antibody brought the CdTe quantum dot and TRITC sufficiently close together to allow the resonance dipole,dipole coupling required for fluorescence resonance energy transfer to occur. The formation of immunocomplexes resulted in fluorescence resonance energy transfer from the CdTe quantum dot donors to the TRITC acceptors. Copyright © 2005 John Wiley & Sons, Ltd. [source] An EPR and ENDOR Investigation of a Series of Diazabutadiene,Group 13 ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2005Robert J. Baker Dr. Abstract Paramagnetic diazabutadienegallium(II or III) complexes, [(Ar-DAB)2Ga] and [{(Ar-DAB.)GaX}2] (X=Br or I; Ar-DAB={N(Ar)C(H)}2, Ar=2,6-diisopropylphenyl), have been prepared by reactions of an anionic gallium N-heterocyclic carbene analogue, [K(tmeda)][:Ga(Ar-DAB)], with either "GaI" or [MoBr2(CO)2(PPh3)2]. A related InIII complex, [(Ar-DAB.)InCl2(thf)], has also been prepared. These compounds were characterised by X-ray crystallography and EPR/ENDOR spectroscopy. The EPR spectra of all metal(III) complexes incorporating the Ar-DAB ligand, [(Ar-DAB.)MX2(thf)n] (M=Al, Ga or In; X=Cl or I; n=0 or 1) and [(Ar-DAB)2Ga], confirmed that the unpaired spin density is primarily ligand centred, with weak hyperfine couplings to Al (a=2.85 G), Ga (a=17,25 G) or In (a=26.1 G) nuclei. Changing the N substituents of the diazabutadiene ligand to tert -butyl groups in the gallium complex, [(tBu-DAB.)GaI2] (tBu-DAB={N(tBu)C(H)}2), changes the unpaired electron spin distribution producing 1H and 14N couplings of 1.4 G and 8.62 G, while the aryl-substituted complex, [(Ar-DAB.)GaI2], produces couplings of about 5.0 G. These variations were also manifested in the gallium couplings, namely aGa ,1.4 G for [(tBu-DAB.)GaI2] and aGa ,25 G for [(Ar-DAB.)GaI2]. The EPR spectra of the gallium(II) and indium(II) diradical complexes, [{(Ar-DAB.)GaBr}2], [{(Ar-DAB.)GaI}2], [{(tBu-DAB.)GaI}2] and [{(Ar-DAB.)InCl}2], revealed doublet ground states, indicating that the GaGa and InIn bonds prevent dipole,dipole coupling of the two unpaired electrons. The EPR spectrum of the previously reported complex, [(Ar-BIAN.)GaI2] (Ar-BIAN=bis(2,6-diisopropylphenylimino)acenaphthene) is also described. The hyperfine tensors for the imine protons, and the aryl and tert -butyl protons were obtained by ENDOR spectroscopy. In [(Ar-DAB.)GaI2], gallium hyperfine and quadrupolar couplings were detected for the first time. [source] Tailoring 13C labeling for triple-resonance solid-state NMR experiments on aligned samples of proteinsMAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2007Neeraj Sinha Abstract In order to develop triple-resonance solid-state NMR spectroscopy of membrane proteins, we have implemented several different 13C labeling schemes with the purpose of overcoming the interfering effects of 13C13C dipole,dipole couplings in stationary samples. The membrane-bound form of the major coat protein of the filamentous bacteriophage Pf1 was used as an example of a well-characterized helical membrane protein. Aligned protein samples randomly enriched to 35% 13C in all sites and metabolically labeled from bacterial growth on media containing [2- 13C]-glycerol or [1,3- 13C]-glycerol enables direct 13C detection in solid-state NMR experiments without the need for homonuclear 13C13C dipole,dipole decoupling. The 13C-detected NMR spectra of Pf1 coat protein show a substantial increase in sensitivity compared to the equivalent 15N-detected spectra. The isotopic labeling pattern was analyzed for [2- 13C]-glycerol and [1,3- 13C]-glycerol as metabolic precursors by solution-state NMR of micelle samples. Polarization inversion spin exchange at the magic angle (PISEMA) and other solid-state NMR experiments work well on 35% random fractionally and metabolically tailored 13C-labeled samples, in contrast to their failure with conventional 100% uniformly 13C-labeled samples. Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||