- The amide oxygen as a donor group. Metal ion complexing properties of tetra-N-acetamide substituted cyclen: A crystallographic, NMR, molecular mechanics, and thermodynamic study
-
The syntheses of the octadentate ligand DOTAM (1,4,7,10-tetrakis(acetamido)-1,4,7,10-cyclododecane) and its complexes with Zn(II), Cd(II), and Ca(II) are described. Crystal structures of [Cd(DOTAM)](ClO4)2 · 1.5H2O (1), [Ca(DOTAM)](ClO4)2 · 2.5H2O (2), and [Zn(DOTAM)](ClO4)2 · H2O (3) are reported. Crystal data: (1) monoclinic, space group Cc, a = 11.908(2) A?, b = 21.237(3) A?, c = 11.445(2) A?, β= 102.15(1)° (2) monoclinic, P21/c, a = 14.031(9) A?, b = 11.469(8) A?, c = 17.448 A?, β = 92.10(1)°; (3) triclinic, space group P1, a = 9.490(1) A?, b = 12.464(2) A?, c = 12.998(2) A?, α = 99.070(1)°, β= 107.67(1)°, and γ = 108.24(1)°. There is an unusual distortion in the coordination geometry of the complexes. There are two sets of metal-to-oxygen bond lengths for each complex; Zn(II) has two oxygens, placed opposite each other in the approximately square arrangement defined by the four oxygen donor atoms at about 2.19 A? and two at 3.23 A, Cd(II) has two at 2.34 and two at 2.64 A?, and Ca(II) has two at 2.40 A? and two at 2.42 A?. Molecular mechanics calculations suggest the Cd(II) and Zn(II) structures represent six coordination of four nitrogens and two of the oxygens, while the two long bonds represent van der Waals contacts with a possible electrostatic component. Approach of the oxygen donors to the metal ion is controlled by the van der Waals radii of the oxygens. 13C NMR studies give rates of helicity interchange of the complexes Zn(II) > Hg(II) > Cd(II) > Ca(II) ? Pb(II). This order is discussed in terms of the difference in bond lengths between the two sets of oxygen donors. A stability constant study gave logK1 values in 0.1 M NaNO3 and 25 °C: Cu(II), 16.3; Zn(II), 10.47; Ca(II), 7.54; Sr(II), 6.67; Ba(II), 5.35; Hg(II), 14.53; La(III), 10.35; Gd(III), 10.05. For Cd(II) and Pb(II), the complexes were fully formed even at pH 0.3, and only a lower limit of 19 for logK1 could be set. Selectivity of DOTAM for metal ions is discussed in terms of coordinating properties of the amide oxygen donor and geometric requirements of the DOTAM ligand.
- Maumela, Hulisani,Hancock, Robert D.,Carlton, Laurence,Reibenspies, Joseph H.,Wainwright, Kevin P.
-
-
Read Online
- Including and Declaring Structural Fluctuations in the Study of Lanthanide(III) Coordination Chemistry in Solution
-
The physicochemical properties of lanthanide(III) ions are directly linked to the structure of the surrounding ligands. Rapid ligand exchange prohibits direct structure-property relationships from being formed for simple complexes in solution because the property measured will be an average over several structures. For kinetically inert lanthanide(III) complexes, the simpler speciation may alleviate the problem, yet the archetypical complexes formed by ligands derived from cyclen are known to have at least four different forms in solution - each with a variation in the crystal field that gives rise to significantly different properties. Slow interchange between forms has been engineered, so that a single complex geometry can be studied, but fast or intermediate interchange between forms is much more commonly observed. The rapid structural fluctuation can report on the changing chemical environment and can be disregarded if a specific property of a lanthanide(III) complex is exploited in an application. However, if we are to understand the chemistry of the lanthanide(III) ions in solution, we must include the structural fluctuation that takes place even in kinetically inert lanthanide(III) complexes in our studies. Here, we have scrutinized the processes that determine the speciation of lanthanide(III) complexes of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (DOTA)-like ligands, in particular the processes that enable exchange between forms that have different physicochemical properties, exemplified by the exchange between the diastereomeric capped square-antiprismatic (cSAP) and capped twisted-square-antiprismatic (cTSAP) forms of DOTA-like lanthanide(III) complexes. In the characterization of a kinetically inert f-element complex, understanding the structural fluctuation in the system is critical because a single observed property can arise from a weighted average, from all forms present, or from a single form with a dominating contribution. Further, the experimental condition will influence both the distribution of lanthanide(III) species in solution and the rates of the processes that change the coordination sphere of the lanthanide(III) ions. This is highlighted using data from a series of cyclen-derived ligands with different pendant arms and different denticity. The data were obtained in experiments that take place on different time scales to show that the rate of the process that results in a structural change must be considered against the time of the experiment. We conclude that the structural fluctuations must be taken into account and that they cannot be predicted from the ligand structure. Thus, an estimate of the exchange rates between forms, the relative concentrations of the specific forms, and the effect of the specific structure of each form of the complex must be included in the description of the solution properties of f-element chelates.
- Nielsen, Lea Gundorff,S?rensen, Thomas Just
-
-
Read Online
- DOTA-Branched Organic Frameworks as Giant and Potent Metal Chelators
-
Multinuclear complexes as metallo-agents for clinical use have caught extensive attention. In this paper, using 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) as both a functioning unit and a constructing junction, we build a series of DOTA-branched organic frameworks with multiple chelating holes by organizing DOTA layer by layer. These giant chelators are well characterized, which reveals their nanosized and soft structures. Further experiments demonstrate that they could efficiently hold abundant metal ions with much higher kinetic stabilities than the conventional small DOTA chelator. Their corresponding polynuclear complexes containing Gd3+, Tb3+, or both show superior imaging properties, excellent feasibility for peripheral modification, and unusual kinetic stability. This work can be easily extended to the fabrication of diverse homomultinuclear complexes and core/shell heteromultinuclear complexes with multifunctional properties. We expect that this new type of giant molecules and the ligand-branching strategy would open up a new avenue for the design and construction of next-generation polymetallic agents with high performance and stabilities for biomedical applications.
- Sun, Chengjie,Lin, Hongyu,Gong, Xuanqing,Yang, Zhaoxuan,Mo, Yan,Chen, Xiaoyuan,Gao, Jinhao
-
-
Read Online
- Exploring Inner-Sphere Water Interactions of Fe(II) and Co(II) Complexes of 12-Membered Macrocycles to Develop CEST MRI Probes
-
Several paramagnetic Co(II) and Fe(II) macrocyclic complexes were prepared with the goal of introducing a bound water ligand to produce paramagnetically shifted water 1H resonances and for paramagnetic chemical exchange saturation transfer (par
- Bond, Christopher J.,Sokolow, Gregory E.,Crawley, Matthew R.,Burns, Patrick J.,Cox, Jordan M.,Mayilmurugan, Ramasamy,Morrow, Janet R.
-
-
Read Online
- Stability Enhancement of Heavy-metal-Macrocycle Complexes via Pendant Amide Coordination
-
Formation of the pendant-arm macrocyclic ligand 1,4,7,10-tetrakis(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane L and subsequent generation of its cadmium(II) complex indicates very significant stabilisation of the complex, compared to that observed for related macrocyclic cadmium(II) complexes, which either lack pendant donors altogether, or have other types of neutral oxygen donors attached to the macrocycle, and compared to complexes of L with lighter metal ions.
- Carlton, Laurence,Hancock, Robert D.,Maumela, Hulisani,Wainwright, Kevin P.
-
-
Read Online
- MACROCYCLES, COBALT AND IRON COMPLEXES OF SAME, AND METHODS OF MAKING AND USING SAME
-
Provided are macrocyclic compounds and iron or cobalt coordinated macrocyclic compounds. The compounds can be used as MRI contrast agents. Certain compounds are redox active and can be used to assess the biological redox status of a sample.
- -
-
Page/Page column 51; 52
(2015/03/28)
-
- Modulation of the lifetime of water bound to lanthanide metal ions in complexes with ligands derived from 1,4,7,10-tetraazacyclododecane tetraacetate (DOTA)
-
A series of di- and tetraamide derivatives of DOTA were synthesized, and their lanthanide(III) complexes were examined by multinuclear 1H-, 13C-, and 17O-NMR spectroscopy, and compared with literature data of similar, know
- Zhang, Shanrong,Jiang, Xiuyan,Sherry, A. Dean
-
p. 923 - 935
(2007/10/03)
-
