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Hotze ACG, van der Geer EPL, Caspers SE, Kooijman H, Spek AL, Haasnoot JG, Reedijk J. Coordination of 9-Ethylguanine to the Mixed-Ligand Compound α-[Ru(azpy)(bpy)Cl2] (azpy = 2-Phenylazopyridine and bpy = 2,2‘-Bipyridine). An Unprecedented Ligand Positional Shift, Correlated to the Cytotoxicity of This Type of [RuL2Cl2] (with L = azpy or bpy) Complex. Inorg Chem 2004; 43:4935-43. [PMID: 15285670 DOI: 10.1021/ic035390f] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The striking difference in cytotoxic activity between the inactive cis-[Ru(bpy)(2)Cl(2)] and the recently reported highly cytotoxic alpha-[Ru(azpy)(2)Cl(2)] (alpha indicating the isomer in which the coordinating Cl atoms, pyridine nitrogens, and azo nitrogens are in mutual cis, trans, cis orientation) encouraged the synthesis of the mixed-ligand compound cis-[Ru(azpy)(bpy)Cl(2)]. The synthesis and characterization of the only occurring isomer, i.e., alpha-[Ru(azpy)(bpy)Cl(2)], 1 (alpha denoting the isomer in which the Cl ligands are cis related to each other and the pyridine ring of azpy is trans to the pyridine ring of bpy), are described. The solid-state structure of 1 has been determined by X-ray structure analysis. The IC(50) values obtained for several human tumor cell lines have indicated that compound 1 shows mostly a low to moderate cytotoxicity. The binding of the DNA model base 9-ethylguanine (9-EtGua) to the hydrolyzed species of 1 has been studied and compared to DNA model base binding studies of cis-[Ru(bpy)(2)Cl(2)] and alpha-[Ru(azpy)(2)Cl(2)]. The completely hydrolyzed species of 1, i.e., alpha-[Ru(azpy)(bpy)(H(2)O)(2)](2+), has been reacted with 9-EtGua in water at room temperature for 24 h. This resulted in the monofunctional binding of only one 9-EtGua, coordinated via the N7 atom. The product has been isolated as alpha-[Ru(azpy)(bpy)(9-EtGua)(H(2)O)](PF(6))(2), 2, and characterized by 2D NOESY NMR spectroscopy. The NOE data show that the 9-EtGua coordinates (under these conditions) at the position trans to the azo nitrogen atom. Surprisingly, time-dependent (1)H NMR data of the 9-EtGua adduct 2 in acetone-d(6) show an unprecedented positional shift of the 9-EtGua from the position trans to the azo nitrogen to the position trans to the bpy nitrogen atom, resulting in the adduct alpha'-[Ru(azpy)(bpy)(9-EtGua)(H(2)O)](PF(6))(2) (alpha' indicating 9-EtGua is trans to the bpy nitrogen). This positional isomerization of 9-EtGua is correlated to the cytotoxicity of 1 in comparison to both the cytotoxicity and 9-EtGua coordination of cis-[Ru(bpy)(2)Cl(2)], alpha-[Ru(azpy)(2)Cl(2)], and beta-[Ru(azpy)(2)Cl(2)]. This positional isomerization process is unprecedented in model base metal chemistry and could be of considerable biological significance.
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Sprengers JW, Agerbeek MJ, Elsevier CJ, Kooijman H, Spek AL. Synthesis and Crystal Structures of Zerovalent Platinum η2-Fumarate Bis(norbornene) Complexes and Their Application as Hydrosilylation Catalysts. Organometallics 2004. [DOI: 10.1021/om049913i] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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78
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Hogenbirk M, Schat G, de Kanter F, Akkerman O, Bickelhaupt F, Kooijman H, Spek A. Investigations on the Reactivity of Bis(bromomagnesio)trimethylsilylmethane − Molecular Structure of a Tebbe‐Type Spiro‐Organomagnesium Compound. Eur J Inorg Chem 2004. [DOI: 10.1002/ejic.200300836] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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79
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van den Broeke J, Heeringa JJH, Chuchuryukin AV, Kooijman H, Mills AM, Spek AL, van Lenthe JH, Ruttink PJA, Deelman BJ, van Koten G. Role of Cation−Anion Interactions in Ionic Complexes Containing [Pd{C6H3(CH2NMe2)2-2,6}(OH2)]+ and [{Pd(C6H3(CH2NMe2)2-2,6)}2(μ-Cl)]+ Cations. Organometallics 2004. [DOI: 10.1021/om0303698] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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80
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Hotze ACG, Caspers SE, de Vos D, Kooijman H, Spek AL, Flamigni A, Bacac M, Sava G, Haasnoot JG, Reedijk J. Structure-dependent in vitro cytotoxicity of the isomeric complexes [Ru(L)2Cl2] (L=o-tolylazopyridine and 4-methyl-2-phenylazopyridine) in comparison to [Ru(azpy)2Cl2]. J Biol Inorg Chem 2004; 9:354-64. [PMID: 15034769 DOI: 10.1007/s00775-004-0531-6] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2003] [Accepted: 02/14/2004] [Indexed: 10/26/2022]
Abstract
The dichlorobis(2-phenylazopyridine)ruthenium(II) complexes, [Ru(azpy)(2)Cl(2)], are under renewed investigation due to their potential anticancer activity. The three most common isomers alpha-, beta- and gamma-[RuL(2)Cl(2)] with L= o-tolylazopyridine (tazpy) and 4-methyl-2-phenylazopyridine (mazpy) (alpha indicating the coordinating Cl, N(pyridine) and Nazo atoms in mutual cis, trans, cis positions, beta indicating the coordinating Cl, N(pyridine) and Nazo atoms in mutual cis, cis, cis positions, and gamma indicating the coordinating Cl, N(pyridine) and Nazo atoms in mutual trans, cis, cis positions) are synthesized and characterized by NMR spectroscopy. The molecular structures of gamma-[Ru(tazpy)(2)Cl(2)] and alpha-[Ru(mazpy)(2)Cl(2)] are determined by X-ray diffraction analysis. The IC(50) values of the geometrically isomeric [Ru(tazpy)(2)Cl(2)] and [Ru(mazpy)(2)Cl(2)] complexes compared with those of the parent [Ru(azpy)(2)Cl(2)] complexes are determined in a series of human tumour cell lines (MCF-7, EVSA-T, WIDR, IGROV, M19, A498 and H266). These data unambiguously show for all complexes the following trend: the alpha isomer shows a very high cytotoxicity, whereas the beta isomer is a factor 10 less cytotoxic. The gamma isomers of [Ru(tazpy)(2)Cl(2)] and [Ru(mazpy)(2)Cl(2)] display a very high cytotoxicity comparable to that of the gamma isomer of the parent compound [Ru(azpy)(2)Cl(2)] and to that of the alpha isomer. These biological data are of the utmost importance for a better understanding of the structure-activity relationships for the isomeric [RuL(2)Cl(2)] complexes.
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81
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Habermann CR, Cramer MC, Graessner J, Kooijman H, Weiss F, Ußmüller J, Adam G. Fast and Ultra Fast MR-Sialography: Comparison of 1.5 T and 3 T. ROFO-FORTSCHR RONTG 2004. [DOI: 10.1055/s-2004-820830] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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82
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Hogenbirk M, Schat G, Akkerman O, Bickelhaupt F, Schottek J, Albrecht M, Fröhlich R, Kehr G, Erker G, Kooijman H, Spek A. (μ‐Methylene)bis(methylzirconocene): Preparation, Molecular Structure, and Thermal Disproportionation. Eur J Inorg Chem 2004. [DOI: 10.1002/ejic.200300754] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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83
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Mulder A, Juković A, van Leeuwen FWB, Kooijman H, Spek AL, Huskens J, Reinhoudt DN. Cover Picture: Photocontrolled Release and Uptake of a Porphyrin Guest by Dithienylethene-Tetheredβ-Cyclodextrin Host Dimers (Chem. Eur. J. 5/2004). Chemistry 2004. [DOI: 10.1002/chem.200490013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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84
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ten Cate AT, Kooijman H, Spek AL, Sijbesma RP, Meijer EW. Conformational Control in the Cyclization of Hydrogen-Bonded Supramolecular Polymers. J Am Chem Soc 2004; 126:3801-8. [PMID: 15038734 DOI: 10.1021/ja039408x] [Citation(s) in RCA: 123] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Bifunctional 2-ureido-4[1H]-pyrimidinone (UPy) derivatives can form small cyclic oligomers as well as long supramolecular polymers in chloroform solutions using the quadruple hydrogen-bonding motif. Ring-chain equilibria of a set of supramolecular monomers containing methyl-substituted alkyl linkers between the hydrogen-bonding UPy moieties were investigated by (1)H NMR spectroscopy and viscometry. The data were characterized in terms of critical concentration (CC, denoting the onset of polymerization) and equilibrium cyclic dimer concentration (EDC, representing preorganization of the monomer toward selective formation of cyclic dimer). Methyl substituents in the monomer were found to promote conformations favorable for cyclic dimerization, leading to an increase in both the EDC and the CC with respect to unsubstituted monomer. Furthermore, we observed an odd-even effect in the CC and EDC with increasing length of the linker between the hydrogen-bonding units. The combined results allow tuning of the critical concentration over a broad range and offer detailed information on the correlation between monomer structure, conformation, and polymerizability which may provide new insights for the study and design of other ring-chain equilibria or helix-random coil transitions.
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van der Vlugt J, Ackerstaff J, Dijkstra T, Mills A, Kooijman H, Spek A, Meetsma A, Abbenhuis H, Vogt D. Versatile Phosphite Ligands Based on Silsesquioxane Backbones. Adv Synth Catal 2004. [DOI: 10.1002/adsc.200303186] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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86
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de Cires-Mejias C, Tanase S, Reedijk J, González-Vı́lchez F, Vilaplana R, Mills AM, Kooijman H, Spek AL. Extended structures based on hydrogen bonding and π–π interactions: synthesis and characterization of two zinc complexes: [Zn(dap)Cl2] and [Zn(dap)2Cl2]. Inorganica Chim Acta 2004. [DOI: 10.1016/j.ica.2003.11.035] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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87
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Kooijman H, Spek AL, van Albada GA, Gamez P, Reedijk J. Bis[bis(pyrimidin-2-yl-kappaN)amine](dicyanamido-kappaN1)(trifluoromethanesulfonato-kappaO)copper(II) ethanol hemisolvate forms a hydrogen-bonded chain. Acta Crystallogr C 2004; 60:m51-4. [PMID: 14767111 DOI: 10.1107/s0108270103028385] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2003] [Accepted: 12/09/2003] [Indexed: 11/10/2022] Open
Abstract
In the crystal structure of [Cu(CF(3)SO(3))(C(2)N(3))(C(8)H(7)N(5))(2)].0.5C(2)H(6)O, the Cu(II) atom adopts a distorted octahedral geometry, with the basal plane formed by two N atoms of one dipyrimidinylamine ligand, one N atom of the second pyrimidine ligand and a nitrile N atom of the dicyanamide anion [Cu-N = 1.972 (2)-2.021 (2) A]. The apical positions are occupied by an N atom of the second ligand [Cu-N = 2.208 (2) A], and an O atom of the trifluoromethanesulfonate anion [Cu-O = 2.747 (2) A] at a semi-coordination distance. Pairs of inversion-related N-H.N hydrogen bonds of the so-called Watson-Crick type, augmented by two C-H.N contacts, link adjacent complexes into an infinite one-dimensional chain running in the [101] direction.
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Velders AH, van der Schilden K, Hotze ACG, Reedijk J, Kooijman H, Spek AL. Dichlorobis(2-phenylazopyridine)ruthenium(II) complexes: characterisation, spectroscopic and structural properties of four isomers. Dalton Trans 2004:448-55. [PMID: 15252553 DOI: 10.1039/b313182c] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The didentate ligand 2-phenylazopyridine (azpy) can--in theory--give rise to five different isomeric complexes of the type [Ru(azpy)2Cl2], of which three have been known since 1980. The molecular structures of the cis-dichlorobis(2-phenylazopyridine) ruthenium(II) complexes alpha-[Ru(azpy)2Cl2] and beta-[Ru(azpy)2Cl2](in which the coordinating pyridine nitrogen atoms are in mutually trans and cis positions, respectively, whilst the azo nitrogen atoms are in mutually cis positions) were unambiguously determined in the early 1980s. The third isomer, gamma-[Ru(azpy)2Cl2], has for two decades, erroneously, been assumed to be the all-trans isomer. In a recent communication we have proven that for this gamma isomer the chloride ions are indeed in a trans geometry, but the pyridine nitrogen and azo nitrogen atoms of the two azpy ligands are in mutually cis geometries. In this paper the isolation of a fourth isomer is presented, the hitherto unknown delta-[Ru(azpy)2Cl2]. The isomeric structure of delta-[Ru(azpy)2Cl2] has been determined by 1H-NMR spectroscopy and single-crystal X-ray diffraction analysis, and is the all-trans isomer. The bis(azpy)-ruthenium(II) isomers are of interest because of the pronounced cytotoxicity they exhibit against tumour cell lines and could be very useful in the search for structure-activity relationships of antitumour-active ruthenium complexes, as among the isomers there is a significant difference in activity. It is of paramount importance to have a good understanding of the structural and spectroscopic properties of these complexes, which in this paper are compared and discussed, with a particular emphasis on 1D and 2D 1H NMR spectroscopies.
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Hotze ACG, Kooijman H, Spek AL, Haasnoot JG, Reedijk J. Synthesis and characterization of ruthenium(ii) complexes with the new ligand 2-phenylazopyridine-5-sulfonic acid (Hsazpy): in search for new anticancer agents. NEW J CHEM 2004. [DOI: 10.1039/b313746e] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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90
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Walter C, Philippi G, Westerhausen R, Kooijman H, Hoffmannn HG, Busch HP. Hochauflösende 3D-MR-Angiographie (MRA) der Nierenarterien unter Verwendung der SENSE-Technik. ROFO-FORTSCHR RONTG 2004. [DOI: 10.1055/s-2004-827832] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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91
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Kooijman H. MRT – mit Sicherheit. ROFO-FORTSCHR RONTG 2004. [DOI: 10.1055/s-2004-828234] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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92
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Cramer M, Habermann CR, Reitmeier F, Graessner J, Kooijman H, Weiss F, Aldefeld D, Adam G. Schnelle und ultraschnelle MR-Sialographie: 1.5 T und 3 T im Vergleich. ROFO-FORTSCHR RONTG 2004. [DOI: 10.1055/s-2004-828114] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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93
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Kronenburg C, Rijnberg E, Jastrzebski J, Kooijman H, Spek A, van Koten G. Stereochemical Aspects of Enantiopure and Racemic Organolithium Aggregates Li4Ar4 {Ar = C6H4[CH(Me)NMe2]-2}. European J Org Chem 2004. [DOI: 10.1002/ejoc.200300550] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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94
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Kerckhoffs JMCA, van Leeuwen FWB, Spek AL, Kooijman H, Crego-Calama M, Reinhoudt DN. Cover Picture: Regulatory Strategies in the Complexation and Release of a Noncovalent Guest Trimer by a Self-Assembled Molecular Cage (Angew. Chem. Int. Ed. 46/2003). Angew Chem Int Ed Engl 2003. [DOI: 10.1002/anie.200390622] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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95
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Kerckhoffs JMCA, van Leeuwen FWB, Spek AL, Kooijman H, Crego-Calama M, Reinhoudt DN. Titelbild: Regulatory Strategies in the Complexation and Release of a Noncovalent Guest Trimer by a Self-Assembled Molecular Cage (Angew. Chem. 46/2003). Angew Chem Int Ed Engl 2003. [DOI: 10.1002/ange.200390649] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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96
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Kerckhoffs JMCA, van Leeuwen FWB, Spek AL, Kooijman H, Crego-Calama M, Reinhoudt DN. Regulatory Strategies in the Complexation and Release of a Noncovalent Guest Trimer by a Self-Assembled Molecular Cage. Angew Chem Int Ed Engl 2003. [DOI: 10.1002/ange.200352733] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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97
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van der Vlugt J, Grutters M, Mills A, Kooijman H, Spek A, Vogt D. New Diphosphane Ligands Based on Bisphenol A Backbones− Synthesis and Coordination Chemistry. Eur J Inorg Chem 2003. [DOI: 10.1002/ejic.200300419] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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98
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Kerckhoffs JMCA, van Leeuwen FWB, Spek AL, Kooijman H, Crego-Calama M, Reinhoudt DN. Regulatory Strategies in the Complexation and Release of a Noncovalent Guest Trimer by a Self-Assembled Molecular Cage. Angew Chem Int Ed Engl 2003; 42:5717-22. [PMID: 14661204 DOI: 10.1002/anie.200352733] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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99
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Walter C, Philippi G, Westerhausen R, Kooijman H, Hoffmann HG, Busch HP. [High resolution contrast-enhanced 3D MR-angiography of renal arteries using parallel imaging (SENSE)]. ROFO-FORTSCHR RONTG 2003; 175:1244-50. [PMID: 12964081 DOI: 10.1055/s-2003-41937] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
PURPOSE To compare three dimensional contrast enhanced MR angiography with parallel imaging technique (sensitivity encoding) to standard MR angiography technique. MATERIAL AND METHODS CE-3D MRA of renal arteries was performed in 22 patients (23 examinations) on a 1.5 T MR- scanner (Gyroscan Intera, Philips, Netherlands). For contrast enhanced MRA a single dose of Gd-DTPA (0.1 mmol/kg b.w.) was administered. Group I: The following standard 3D gradient echo (GE) sequence was performed in 9 of the 22 patients: TR: 4.3 ms, TE: 1.5 ms, flip angle: 40, 40 slices, scan duration: 19 seconds. A spatial resolution of 1.96 x 1.76 x 3.0 mm (3) (1.76 x 1.76 x 1.5 mm (3) interpolated) was obtained. Group II: 14 examinations were acquired in 13 patients: TR, TE and flip angle were equal compared to the first protocol. The k-space lines were acquired with CENTRA (contrast-enhanced time robust angiography) and parallel imaging technique (SENSE). 60 slices were acquired, scan duration was 24 seconds. The spatial resolution of this sequence was 1.19 x 1.08 x 2.0 mm (3) (0,84 x 0,84 x 1,0 mm (3) interpolated). Original images and calculated maximum intensity projection (MIP) images were analysed by two radiologists. Image quality and the visibility of renal arteries were rated on a four-point scale. RESULTS In the first group the image quality was rated "good" in 8/9 patients. The renal arteries were detected in all cases and rated "good". The anterior and posterior segments were rated "good" in only 5/9 and the lobar arteries were detectable only in 3 of 9 cases. The interlobar arteries could not be seen in these patients. In the second group the image quality was rated excellent in 5 examinations and good in 9 of 14 examinations. The rating for the renal arteries was excellent in all examinations (14/14). The results of the anterior and posterior segment were as followed: excellent 5/14, good 7/14, insufficient 2/14; the lobar arteries: good 6/14, insufficient 6/14 and not detectable 2/14. Interlobar arteries could be seen in 7/14 examinations, but the quality was insufficient. In 7/14 the interlobar arteries could not be detected. CONCLUSION The use of parallel imaging technique improves image quality and the delineation of small vessels in renal MRA.
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ten Cate AT, Dankers PYW, Kooijman H, Spek AL, Sijbesma RP, Meijer EW. Enantioselective cyclization of racemic supramolecular polymers. J Am Chem Soc 2003; 125:6860-1. [PMID: 12783526 DOI: 10.1021/ja034273g] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Homochiral hydrogen-bonded cyclic assemblies are formed in dilute solutions of racemic supramolecular polymers based on the quadruple hydrogen bonding 2-ureido-4[1H]-pyrimidinone unit, as observed by 1H NMR and SEC experiments. Preorganization of the monomers and the combined binding strength of the eight hydrogen bonds result in a very high stability of the cyclic aggregates with pronounced selectivity between homochiral and heterochiral cyclic species, usually only observed in crystalline or liquid crystalline phases.
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