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  • 1
    Electronic Resource
    Electronic Resource
    Spectroscopic Study of the Hydration Equilibria and Water Exchange Dynamics of Lanthanide(III) Complexes of 1,7-Bis(carboxymethyl)-1,4,7,10-tetraazacyclododecane (DO2A) (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 1001-1006 
    Details
    ISSN: 1434-1948
    Keywords: Imaging agents ; Lanthanides ; NMR spectroscopy ; DNA cleavage ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hydration state of a series of [Ln(DO2A)(H2O)n]+ complexes in aqueous solution at pH = 6.4-7.0 was studied by measuring the lanthanide-induced 17O shifts (LIS) of water [Ln includes elements from Ce to Yb; DO2A = 1,7-bis(carboxymethyl)-1,4,7,10-tetraazacyclododecane]. Their contact contribution, obtained from Reilley plots, indicated a decrease in the inner-sphere water coordination number of the [Ln(DO2A)(H2O)n]+ complexes from n = 3 (Ce-Eu), to n = 2 (Tb-Yb). A temperature-dependent UV/Vis absorption study of the 578-582 nm 7F0 → 5D0 transition band of [Eu(DO2A)(H2O)n]+ in aqueous solution showed that this complex is present in an equilibrium between eight- and nine-coordinate species with n = 2 and n = 3, respectively. The hydration equilibrium parameters (2 ↔ 3), K2-3298 = 4.0 ± 0.2, ΔH2-30 = -12.1 ± 1 kJ mol-1 and ΔS2-30 = -28.9 ± 3 J mol-1 K-1,correspond to an average hydration number of 2.65-2.85 in the temperature range 273-363 K. A variable temperature, multiple field 17O NMR study combined with direct EPR measurements of the transverse electronic relaxation rates has been used to obtain the parameters characterizing water exchange, rotation and electronic relaxation, all influencing the proton relaxivity of [Gd(DO2A)(H2O)2-3]+. The small increase in the water exchange rate of [Gd(DO2A)(H2O)2-3]+ (kex298 = (10 ± 5) × 106s-1) relative to that of[Gd(DOTA)(H2O)]- (4.8 × 106 s-1) is a consequence of an unfavorable interplay of charge and hydration equilibria. The value of τR298 = 40 ± 1 ps is short, and the electronic relaxation rate (1/T2e ≍ 1.2 × 1010 s-1) is fast relative to [Gd(DOTA)(H2O)]- (1.3-2.4 × 109 s-1 for B = 0.34 T). These parameters negate to some extent the expected increase in proton relaxivity of the [Gd(DO2A)(H2O)2-3]+ complex.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99338_s.pdf or from the author.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Interactions Between Cyclodextrins and TmIII Chelates of Polyazamacrocycles as Studied by NMR in Aqueous Solution (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 287-293 
    Details
    ISSN: 1434-1948
    Keywords: MRI contrast agents ; Macrocyclic ligands ; Cyclodextrins ; Host-guest chemistry ; Lanthanides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interactions between α-, β-, and γ-CD and the TmIII chelates of the macrocyclic polyaminopolycarboxylates DOTA and NOTA were studied with the use of 1H- and 13C-NMR shift and relaxation rate measurements. Interactions were only observed between Tm(DOTA)- and γ-CD. The structure and the stability of the concerning supramolecular structures was elucidated by fitting of the NMR titration curves to a theoretical model. It appears that an inclusion compound is formed, where the hydrophobic macrocyclic part of the chelate sits in the γ-CD cavity. This inclusion compound binds a second Tm(DOTA)- molecule at the outside lower rim of the CD cone. The binding occurs probably via hydrogen bonds between non-chelated carboxylate oxygen atoms of the concerning Tm(DOTA)- and CH2OH groups of the γ-CD molecule, which are in a favorable position due to opening of the γ-CD cone angle as a result of the inclusion of the first γ-CD.
    Additional Material: 3 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Study of Copper(II) Polyazamacrocyclic Complexes by Electronic Absorption Spectrophotometry and EPR Spectroscopy (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 559-565 
    Details
    ISSN: 1434-1948
    Keywords: Macrocyclic ligands ; Copper ; EPR spectroscopy ; Electronic spectrophotometry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copper(II) mononuclear complexes with the polyazamacrocyclic ligands NOTA (1,4,7-triazacyclononane-N,N′,N″triacetate), DOTA (1,4,7,10-tetraazacyclo-dodecane-N,N′,N″,N″′-tetraacetate), NOTP [1,4,7-triazacyclononane-N,N′,N″-tris(methylenephosphonate)] and DOTP [1,4,7,10tetraazacyclododecane-N,N′,N″,N‴-tetrakis(methylenephosphonate)] were characterised in aqueous solution by electronic absorption spectrophotometry and electron paramagnetic resonance (EPR) spectroscopy. While two isomeric species were detected by EPR spectroscopy in frozen samples of the polycarboxylate complexes, only one complex form was found for the poly(methylenephosphonate) systems. The results obtained are in accordance with a six-coordinate pattern for the metal centre, yielding tetragonally distorted complexes in solution, in agreement with previously reported studies on CuII complexes, both in solution and in the solid state.
    Additional Material: 3 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Nuclear magnetic resonance study of the configurational equilibria of ranitidine in solution (1987)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 25 (1987), S. 203-207 
    Details
    ISSN: 0749-1581
    Keywords: 13C NMR ; 1H NMR ; Ranitidine ; E/Z isomerization ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The E/Z configurational equilibrium of the nitroethylenic moiety of the antiulcer agent ranitidine was studied in aqueous solution and in DMSO-d6 and CDCl3 using 1H and 13C NMR spectroscopy. In aqueous solution the room temperature E/Z isomerization of the unprotonated nitroketenediamine moiety is fast on the NMR time scale, but becomes slow for the species protonated at this moiety owing to intramolecular hydrogen bonding between the nitro group and a neighbouring NH2R+ group. In DMSO-d6 a free energy of activation of the order of 70 kJ mol-1 was estimated for the E/Z isomerization of the unprotonated moiety of ranitidine, in good agreement with values previously found for 2,2-disubstituted nitroethylene model compounds.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260250305
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  • 5
    Electronic Resource
    Electronic Resource
    NMR study of the inclusion complex formed between γ-cyclodextrin and TmDOTP5- (1994)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 32 (1994), S. 361-365 
    Details
    ISSN: 0749-1581
    Keywords: Lanthanide-induced NMR shifts ; 1H NMR ; Host-guest complex ; γ-Cyclodextrin-paramagnetic anion complex ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The host-guest complex formed in aqueous solution between γ-cyclodextrin (γ-CD) and the macrocyclic paramagnetic shift reagent TmDOTP5- was examined by NMR spectroscopy. Paramagnetic lanthanide-induced shifts (LIS) and spin-lattice relaxation rate enhancements in the proton resonances of γ-CD on binding of TmDOTP5- were used to define the position of the guest anion within the host cavity. A proportionality constant which relates pseudo-contact shifts induced by TmDOTP5- to the geometrical position of each ligand nucleus (previously determined from a LIS study of the TmDOTP5- complex) was used to determine a fully bound LIS value for each γ-CD proton. These values, in combination with experimental LIS data from TmDOTP5- titrations at constant γ-CD concentration, were then used to obtain the association constant for the host-guest complex (3.9-4.5 mol l-1). These constants were indicative of a weak host-guest interaction and consistent with the location of the TmDOTP5- binding site reported by the LIS values well above the center of the γ-CD cavity.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260320610
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