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Avedano S, Botta M, Haigh JS, Longo D, Woods M. Coupling fast water exchange to slow molecular tumbling in Gd3+ chelates: why faster is not always better. Inorg Chem 2013; 52:8436-50. [PMID: 23841587 PMCID: PMC3769110 DOI: 10.1021/ic400308a] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The influence of dynamics on solution state structure is a widely overlooked consideration in chemistry. Variations in Gd(3+) chelate hydration with changing coordination geometry and dissociative water exchange kinetics substantially impact the effectiveness (or relaxivity) of monohydrated Gd(3+) chelates as T1-shortening contrast agents for MRI. Theory shows that relaxivity is highly dependent upon the Gd(3+)-water proton distance (rGdH), and yet this distance is almost never considered as a variable in assessing the relaxivity of a Gd(3+) chelate as a potential contrast agent. The consequence of this omission can be seen when considering the relaxivity of isomeric Gd(3+) chelates that exhibit different dissociative water exchange kinetics. The results described herein show that the relaxivity of a chelate with "optimal" dissociative water exchange kinetics is actually lower than that of an isomeric chelate with "suboptimal" dissociative water exchange. When the rate of molecular tumbling of these chelates is slowed, an approach that has long been understood to increase relaxivity, the observed difference in relaxivity is increased with the more rapidly exchanging ("optimal") chelate exhibiting lower relaxivity than the "suboptimally" exchanging isomer. The difference between the chelates arises from a non-field-dependent parameter: either the hydration number (q) or rGdH. For solution state Gd(3+) chelates, changes in the values of q and rGdH are indistinguishable. These parametric expressions simply describe the hydration state of the chelate--i.e., the number and position of closely associating water molecules. The hydration state (q/rGdH(6)) of a chelate is intrinsically linked to its dissociative water exchange rate kex, and the interrelation of these parameters must be considered when examining the relaxivity of Gd(3+) chelates. The data presented herein indicate that the changes in the hydration parameter (q/rGdH(6)) associated with changing dissociative water exchange kinetics has a profound effect on relaxivity and suggest that achieving the highest relaxivities in monohydrated Gd(3+) chelates is more complicated than simply "optimizing" dissociative water exchange kinetics.
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Affiliation(s)
- Stefano Avedano
- Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale “Amedeo Avogadro”, Viale T. Michel 11, I-15121 Alessandria, Italy
| | - Mauro Botta
- Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale “Amedeo Avogadro”, Viale T. Michel 11, I-15121 Alessandria, Italy
| | - Julian S. Haigh
- Department of Chemistry, Portland State University, 1719 SW 10th Ave, Portland, OR 97201, USA
| | - Dario Longo
- Dipartimento di Biotecnologie Molecolari e Scienze della Salute and Molecular Imaging Center, Università di Torino, Via Nizza 52, I-10126 Torino, Italy
| | - Mark Woods
- Department of Chemistry, Portland State University, 1719 SW 10th Ave, Portland, OR 97201, USA
- Advanced Imaging Research Center, Oregon Health & Science University, 3181 S.W. Sam Jackson Park Road, Portland, OR 97239, USA
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Botta M, Avedano S, Giovenzana GB, Lombardi A, Longo D, Cassino C, Tei L, Aime S. Relaxometric Study of a Series of Monoaqua GdIII Complexes of Rigidified EGTA-Like Chelators and Their Noncovalent Interaction with Human Serum Albumin. Eur J Inorg Chem 2011. [DOI: 10.1002/ejic.201001103] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Tei L, Gugliotta G, Avedano S, Giovenzana GB, Botta M. Application of the Ugi four-component reaction to the synthesis of ditopic bifunctional chelating agents. Org Biomol Chem 2009; 7:4406-14. [PMID: 19830289 DOI: 10.1039/b907932g] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The Ugi four-component reaction (Ugi 4CR) was exploited for the first time to obtain in a single synthetic step bifunctional ditopic chelators by using DOTA monoamide (DOTAMA) derivatives as amino and acid components. A number of ditopic systems in which the two DOTAMA units are connected by a central alpha-acylaminoamide group were synthesized by reacting different aldehydes, isocyanides and two DOTAMA chelates containing amino and acid functionalities. Variation of the components allows the insertion of another functional group into the alpha-acylaminoamide skeleton for further conjugation to biomolecules. The optimal reaction conditions were found by using methanol as solvent and ultrasound irradiation at a power of 60 W (20 kHz) for 3 h. The Gd(III) complexes of the dimeric ligands L1 and L2 (bearing a cyclohexyl ring and an octadecyl chain on the central alpha-acylaminoamide moiety, respectively) were fully characterized in aqueous media by relaxometric techniques with varying temperature and magnetic field strength. The relaxivity of Gd(2)L1 and Gd(2)L2 (in the aggregated form), at 20 MHz and 310 K, are 5.6 and 20.0 mM(-1) s(-1), respectively. The enhanced value found for Gd(2)L2 indicates that this lipophilic complex forms micelles at concentrations <0.1 mM. Finally, the binding of Gd(2)L2 to human serum albumin (HSA) was investigated by proton relaxometry, and the affinity constant of the complex and the relaxivity of the macromolecular adduct (r(1p)(b) = 38.1 mM(-1) s(-1); 20 MHz and 310 K) derived.
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Affiliation(s)
- Lorenzo Tei
- Dipartimento di Scienze dell'Ambiente e della Vita, Università degli Studi del Piemonte Orientale Amedeo Avogadro, Viale T. Michel 11, I-15100, Alessandria, Italy
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Werner EJ, Kozhukh J, Botta M, Moore EG, Avedano S, Aime S, Raymond KN. 1,2-hydroxypyridonate/terephthalamide complexes of gadolinium(III): synthesis, stability, relaxivity, and water exchange properties. Inorg Chem 2009; 48:277-86. [PMID: 19032045 DOI: 10.1021/ic801730u] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Four new Gd(III) complexes based on the 1,2-hydroxypyridinone chelator have been synthesized and evaluated as potential magentic resonance imaging contrast agents. Previously reported work examining Gd-TREN-1,2-HOPO (3; HOPO = hydroxypyridinone) suggests that the 1,2-HOPO unit binds strongly and selectively to Gd(III), encouraging further study of the stability and relaxivity properties of this class of compounds. Among the new complexes presented in this paper are the homopodal Gd-Ser-TREN-1,2-HOPO (Gd-5) and three heteropodal bis-1,2-HOPO-TAM complexes (Gd-6, Gd-7, and Gd-8; TAM = terephthalamide). Conditional stability constants were determined, and all pGd values are in the range of 18.5-19.7, comparable to other analogous HOPO complexes and currently used commercial contrast agents. Relaxivities for all complexes are about twice those of commercial agents, ranging from 7.8 to 10.5 mM(-1) s(-1) (20 MHz; 25 degrees C), and suggest two innersphere water molecules in fast exchange. Luminescent measurements were used to verify the number of coordinated waters for Gd-5, and VT (17)O NMR experiments were employed for the highly soluble Gd-TREN-bis-1,2-HOPO-TAM-N3 (Gd-8) complex to measure a fast water exchange rate, (298)k(ex) = 1/tau(M), of 5.1 (+/-0.4) x 10(8) s(-1) ((298)tau(M) approximately 2 ns).
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Affiliation(s)
- Eric J Werner
- Department of Chemistry, University of California, Berkeley, California 94720-1460, USA
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Arrais A, Botta M, Avedano S, Giovenzana GB, Gianolio E, Boccaleri E, Stanghellini PL, Aime S. Carbon coated microshells containing nanosized Gd(iii) oxidic phases for multiple bio-medical applications. Chem Commun (Camb) 2008:5936-8. [DOI: 10.1039/b811554k] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Jocher CJ, Moore EG, Xu J, Avedano S, Botta M, Aime S, Raymond KN. 1,2-hydroxypyridonates as contrast agents for magnetic resonance imaging: TREN-1,2-HOPO. Inorg Chem 2007; 46:9182-91. [PMID: 17914808 DOI: 10.1021/ic700985j] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
1,2-Hydroxypyridinones (1,2-HOPO) form very stable lanthanide complexes that may be useful as contrast agents for magnetic resonance imaging (MRI). X-ray diffraction of single crystals established that the solid-state structures of the Eu(III) and the previously reported [Inorg. Chem. 2004, 43, 5452] Gd(III) complex are identical. The recently discovered sensitizing properties of 1,2-HOPO chelates for Eu(III) luminescence [J. Am. Chem. Soc. 2006, 128, 10 067] allow for direct measurement of the number of water molecules coordinated to the metal center. Fluorescence measurements of the Eu(III) complex corroborate that, in solution, two water molecules coordinate the lanthanide (q = 2) as proposed from the analysis of NMRD profiles. In addition, fluorescence measurements have verified the anion binding interactions of lanthanide TREN-1,2-HOPO complexes in solution, studied by relaxivity, revealing only very weak oxalate binding (KA = 82.7 +/- 6.5 M-1). Solution thermodynamic studies of the metal complex and free ligand have been carried out using potentiometry, spectrophotometry, and fluorescence spectroscopy. The metal ion selectivity of TREN-1,2-HOPO supports the feasibility of using 1,2-HOPO ligands for selective lanthanide binding [pGd = 19.3 (2), pZn = 15.2 (2), pCa = 8.8 (3)].
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Affiliation(s)
- Christoph J Jocher
- Department of Chemistry, University of California, Berkeley, CA 94720-1460, USA
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Jocher CJ, Botta M, Avedano S, Moore EG, Xu J, Aime S, Raymond KN. Optimized relaxivity and stability of [Gd(H(2,2)-1,2-HOPO)(H2O)]- for use as an MRI contrast agent. Inorg Chem 2007; 46:4796-8. [PMID: 17497773 PMCID: PMC3188310 DOI: 10.1021/ic700399p] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Relaxometry and solution thermodynamic measurements show that Gd(H(2,2)-1,2-HOPO) is a good candidate as a contrast agent for magnetic resonance imaging (MRI-CA). Acidic, octadentate H(2,2)-1,2-HOPO forms a very stable Gd(III) complex [pGd=21.2(2)]. The coordination sphere at the Gd(III) center is completed by one water molecule that is not replaced by common physiological anions. In addition, this ligand is highly selective for Gd(III) binding in the presence of Zn(II) or Ca(II). The symmetric charge distribution of the 1,2-HOPO chelates is associated with favorably long electronic relaxation time T1,2e comparable to those of GdDOTA. This, in addition to the fast water exchange rate typical of HOPO chelates, improves the relaxivity to r1p=8.2 mM-1 s-1 (0.47 T). This remarkably high value is unprecedented for small-molecule, q=1 MRI-CA.
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Affiliation(s)
| | - Mauro Botta
- Dipartimento di Scienze dell´Ambiente e della Vita, Università del Piemonte Orientale “A. Avogadro”, Via Bellini 25/G, I-15100 Alessandria, Italy
| | - Stefano Avedano
- Dipartimento di Scienze dell´Ambiente e della Vita, Università del Piemonte Orientale “A. Avogadro”, Via Bellini 25/G, I-15100 Alessandria, Italy
| | - Evan G. Moore
- Department of Chemistry, University of California, Berkeley, CA 94720-1460
| | - Jide Xu
- Department of Chemistry, University of California, Berkeley, CA 94720-1460
| | - Silvio Aime
- Dipartimento di Chimica I. F. M., Università di Torino, Via P. Giuria 7, I-10125 Torino, Italy
| | - Kenneth N. Raymond
- Department of Chemistry, University of California, Berkeley, CA 94720-1460
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Werner EJ, Avedano S, Botta M, Hay BP, Moore EG, Aime S, Raymond KN. Highly soluble tris-hydroxypyridonate Gd(III) complexes with increased hydration number, fast water exchange, slow electronic relaxation, and high relaxivity. J Am Chem Soc 2007; 129:1870-1. [PMID: 17260995 PMCID: PMC3188311 DOI: 10.1021/ja068026z] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The design, synthesis, and relaxivity properties of highly soluble TACN-capped trishydroxypyridonate-Gd(III) complexes are presented. Molecular mechanics modeling was used to help design a complex capable of possessing three water molecules in the inner metal coordination sphere, an attractive property for high-relaxivity MRI contrast agents. The measured relaxivities of 13.1 and 12.5 mM-1 s-1 (20 MHz, 298 K) for two TACN-capped complexes are among the highest known relaxivities of low-molecular weight Gd complexes and are consistent with three coordinated waters, an extremely fast water exchange rate, and long electronic relaxation time. Luminescence measurements to confirm the number of coordinated water molecules for the first time in the HOPO series are also discussed.
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Affiliation(s)
- Eric J Werner
- College of Chemistry, University of California, Berkeley, California 94720-1460, USA
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Avedano S, Tei L, Lombardi A, Giovenzana GB, Aime S, Longo D, Botta M. Maximizing the relaxivity of HSA-bound gadolinium complexes by simultaneous optimization of rotation and water exchange. Chem Commun (Camb) 2007:4726-8. [DOI: 10.1039/b714438e] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Abstract
Two tripodal, hexadentate pyrone-based chelators have been prepared. These ligands form stable, soluble complexes with gadolinium(III). The complexes show aqueous stability comparable to that of [Gd(DTPA)]2- at pH 7.4. Evaluation by relaxometry shows that these complexes have two inner-sphere water molecules and a very fast water exchange rate. The solution behavior of these complexes suggests that they may be attractive as high relaxivity, next-generation magnetic resonance imaging contrast agents.
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Affiliation(s)
- David T Puerta
- Department of Chemistry and Biochemistry, University of California-San Diego, La Jolla, CA 92093, USA
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Thompson AL, Parker D, Fulton DA, Howard JAK, Pandya SU, Puschmann H, Senanayake K, Stenson PA, Badari A, Botta M, Avedano S, Aime S. On the role of the counter-ion in defining water structure and dynamics: order, structure and dynamics in hydrophilic and hydrophobic gadolinium salt complexes. Dalton Trans 2006:5605-16. [PMID: 17225897 DOI: 10.1039/b606206g] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The crystal structures of the hydrated salts of [Gd.DOTAM]3+ and its more hydrophobic derivative [Gd.]3+, bearing 4 alpha-phenylethyl groups, (both Gd and Yb salts) are reported and compared. The nature of the anion determines the degree of ordering in the lattice and the extent of hydration. These effects are correlated with the results of 17O and 1H NMR measurements of water exchange dynamics in solution. With [Gd.DOTAM]3+, structural ordering or the extent of hydration in the hydrated lattice follows the sequence Cl->Br->I- and this order also defines the water exchange rate in solution: 7.3, 19.5, 33.3x10(4) s-1 (298 K), respectively. For [Gd.]3+ salts, the measured relaxivity is determined purely by the outer sphere term and the water exchange rate at 298 K is very similar (typically 1x10(4) s-1) for chloride, bromide, iodide, acetate, triflate and nitrate salts, notwithstanding the different nature and extent of hydration found in the crystalline lattice.
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Affiliation(s)
- Amber L Thompson
- Department of Chemistry, University of Durham, South Road, Durham, DH13LE, UK
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Woods M, Botta M, Avedano S, Wang J, Sherry AD. Towards the rational design of MRI contrast agents: a practical approach to the synthesis of gadolinium complexes that exhibit optimal water exchange. Dalton Trans 2005:3829-37. [PMID: 16311635 PMCID: PMC2725757 DOI: 10.1039/b510778d] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The gadolinium(iii) complex of S-SSSS-NO(2)BnDOTMA exhibits water exchange kinetics that are optimal for use in high relaxivity or targeted contrast agents. However, the synthesis of this ligand is hampered by the steric encumbrance imparted upon the cyclen ring by the nitrobenzyl substituent. A relatively simple modification has been used to enable the synthesis of larger quantities of a bifunctional ligand that retains similar fast water exchange properties. The gadolinium complex of S-SSS-NO(2)BnDO3MA-1A is shown to retain the rapid water exchange kinetics characteristic of a twisted square antiprismatic (TSAP) coordination geometry (tau(M)= 6 +/- 0.4 ns).
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Affiliation(s)
- Mark Woods
- Macrocyclics, 2110 Research Row, Suite 425, Dallas, Texas 75235, USA.
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