A mononuclear Mn2+ complex based on a novel tris-(ethyl acetate) pendant-armed tetraazamacrocycle: Effect of pyridine on self-assembly and weak interactions

Wen, Jinghan; Geng, Zhirong; Yin, Yu; Wang, Zhilin

doi:10.1016/j.inoche.2012.03.042

Cited by 16 publications

(11 citation statements)

References 45 publications

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“…The relaxivity of the [Mn(PCTA)] − and [Mn(ODO3A)] − complexes are indeed very similar to that of the [Mn(DO3A)] − suggesting the absence of metal bound water molecules in these complexes as well. In fact, the X-ray crystal structure of the Mn(II) chelate formed with tris(ethyl ester) of PCTA confirms the absence of the metal bound solvent molecule in the [Mn(PCTA-OEt 3 )] 2+ complex (Wen et al, 2012 ) suggesting that this is also true for the PCTA complex. The Mn(II) complexes of amide derivatives show even lower relaxivity, which can be explained by weaker second and outer sphere contributions (for example, X-ray crystallography has shown that [Mn(DO3AM H )] 2+ does not have an inner sphere water molecule) (Wang and Westmoreland, 2009 ) whereas increased second and outer sphere effects are likely responsible for the slight increase in the relaxivities observed for [Mn(DOTP)] 6− and [Mn(DO3P)] 4− in the pH ranges of 10.0–11.0 and 8.5–9.3, respectively, where the deprotonated complex exists in solution.…”

Section: Resultsmentioning

confidence: 87%

Effect of the Nature of Donor Atoms on the Thermodynamic, Kinetic and Relaxation Properties of Mn(II) Complexes Formed With Some Trisubstituted 12-Membered Macrocyclic Ligands

et al. 2018

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During the past few years increasing attention has been devoted to Mn(II) complexes as possible substitutes for Gd(III) complexes as contrast agents in MRI. Equilibrium (log KMnL or pMn value), kinetic parameters (rates and half-lives of dissociation) and relaxivity of the Mn(II) complexes formed with 12-membered macrocyclic ligands were studied. The ligands were selected in a way to gain information on how the ligand rigidity, the nature of the donor atoms in the macrocycle (pyridine N, amine N, and etheric O atom), the nature of the pendant arms (carboxylates, phosphonates, primary, secondary and tertiary amides) affect the physicochemical parameters of the Mn(II) complexes. As expected, decreasing the denticity of DOTA (to afford DO3A) resulted in a drop in the stability and inertness of [Mn(DO3A)]− compared to [Mn(DOTA)]2−. This decrease can be compensated partially by incorporating the fourth nitrogen atom into a pyridine ring (e.g., PCTA) or by replacement with an etheric oxygen atom (ODO3A). Moreover, the substitution of primary amides for acetates resulted in a noticeable drop in the stability constant (PC3AMH), but it increased as the primary amides (PC3AMH) were replaced by secondary (PC3AMGly) or tertiary amide (PC3AMPip) pendants. The inertness of the Mn(II) complexes behaved alike as the rates of acid catalyzed dissociation increased going from DOTA (k1 = 0.040 M−1s−1) to DO3A (k1 = 0.45 M−1s−1). However, the rates of acid catalyzed dissociation decreased from 0.112 M−1s−1 observed for the anionic Mn(II) complex of PCTA to 0.0107 M−1s−1 and 0.00458 M−1s−1 for the cationic Mn(II) complexes of PC3AMH and PC3AMPip ligands, respectively. In spite of its lower denticity (as compared to DOTA) the sterically more hindered amide complex ([Mn(PC3AMPip)]2+) displays surprisingly high conditional stability (pMn = 8.86 vs. pMn = 9.74 for [Mn(PCTA)]−) and excellent kinetic inertness. The substitution of phosphonates for the acetate pendant arms (DOTP and DO3P), however, resulted in a noticeable drop in the conditional stability as well as dissociation kinetic parameters of the corresponding Mn(II) complexes ([Mn(DOTP)]6− and [Mn(DO3P)]4−) underlining that the phosphonate pedant should not be considered as a suitable building block for further ligand design while the tertiary amide moiety will likely have some implications in this respect in the future.

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Section: Resultsmentioning

confidence: 87%

Effect of the Nature of Donor Atoms on the Thermodynamic, Kinetic and Relaxation Properties of Mn(II) Complexes Formed With Some Trisubstituted 12-Membered Macrocyclic Ligands

et al. 2018

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“…Concerning the Mn-N bonds, the strongest coordination in the 3,6-PC2A complex is provided by the N atom of the pyridine group (Mn-N1 = 2.342 Å), as also observed in the X-ray crystal structures of Mn(II) complexes formed with pyclen derivatives [Mn(6-PC1A)Cl] (2.199 Å ) 28 and [Mn(PCTA-(OEt)3)] 2+ (2.165 Å). 36 In these structures, the nitrogen atom of the macrocycle located trans to the pyridine nitrogen coordinates rather weakly to the Mn(II) ion, as evidenced by rather long Mn-N bond lengths (corresponding bond lengths are 2.349 Å and 2.431 Å in [Mn(6-PC1A)] + and [Mn(PCTA-(OEt)3)] 2+ complexes, respectively. Similarly, the calculated structure of the 3,6-PC2A complex presents a relatively long Mn-N3 distance (2.362 Å).…”

Section: Resultsmentioning

confidence: 92%

Complexation of Mn(II) by Rigid Pyclen Diacetates: Equilibrium, Kinetic, Relaxometric, Density Functional Theory, and Superoxide Dismutase Activity Studies

Garda¹,

Molnár²,

Hamon

et al. 2020

Inorg. Chem.

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We report the Mn(II) complexes with two pyclen-based ligands (pyclen = 3,6,9,15tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene) functionalized with acetate pendant arms either at positions 3,6 (3,6-PC2A) or 3,9 (3,9-PC2A) of the macrocyclic fragment. The 3,6-PC2A ligand was synthesized in five steps from pyclenoxalate by protecting one of the secondary amine groups of pyclen using Alloc protecting chemistry. The complex with 3,9-PC2A is characterized by a higher thermodynamic stability (logKMnL = 17.09(2) than the 3,6-PC2A analogue (logKMnL = 15.53(1), 0.15 M NaCl). Both complexes contain a water molecule coordinated to the metal ion, which results in relatively high 1 H relaxivities (r1p = 2.72 and 2.91 mM -1 s -1 for the complexes with 3,6-and 3,9-PC2A, respectively, 25 ºC, 0.49 T). The coordinated water molecule displays fast exchange kinetics with the bulk in both cases; the rates (kex 298 ) are 14010 6 and 12610 6 s -1 for [Mn(3,6-PC2A)(H2O)] and [Mn(3,9-PC2A)(H2O)], respectively. The two complexes were found to be remarkably inert with respect to their dissociation, with half-lives of 63 and 21 h, respectively, at pH 7.4 in the presence of excess Cu(II). The r1p values recorded in blood serum remain constant at least over a period of 120 h. Cyclic voltammetry experiments show irreversible oxidation features shifted to higher potentials with respect to [Mn(EDTA)(H2O)] 2and [Mn(PhDTA)(H2O)] 2-, indicating that the PC2A complexes reported here have a lower tendency to stabilize Mn(III). The superoxide dismutase activity of the Mn(II) complexes was tested using the xanthine/xanthine oxidase/NBT assay at pH 7.8. The Mn(II) complexes of 3,6-PC2A and 3,9-PC2A are capable to assist the decomposition of superoxide anion radical. The kinetic rate constant of the complex of 3,9-PC2A is smaller by one order of magnitude than that of 3,6-PC2A.

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“…24 The Me 3 -TPADP was characterized by electrospray ionization mass spectrometry (ESI-MS) and 1 H and 13 C nuclear magnetic resonance (NMR) methods (see the SI, Experimental Section).…”

Section: Resultsmentioning

confidence: 99%

Reactivity of a Cobalt(III)–Hydroperoxo Complex in Electrophilic Reactions

et al. 2016

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The reactivity of mononuclear metal-hydroperoxo adducts has fascinated researchers in many areas due to their diverse biological and catalytic processes. In this study, a mononuclear cobalt(III)-peroxo complex bearing a tetradentate macrocyclic ligand, [CoIII(Me3-TPADP)(O2)]+ (Me3-TPADP = 3,6,9-trimethyl-3,6,9-triaza-1(2,6)-pyridinacyclodecaphane), was prepared by reacting [CoII(Me3-TPADP)(CH3CN)2]2+ with H2O2 in the presence of triethylamine. Upon protonation, the cobalt(III)-peroxo intermediate was converted into a cobalt(III)-hydroperoxo complex, [CoIII(Me3-TPADP)(O2H)(CH3CN)]2+. The mononuclear cobalt(III)-peroxo and -hydroperoxo intermediates were characterized by a variety of physicochemical methods. Results of electrospray ionization mass spectrometry clearly show the transformation of the intermediates: the peak at m/z 339.2 assignable to the cobalt(III)-peroxo species disappears with concomitant growth of the peak at m/z 190.7 corresponding to the cobalt(III)-hydroperoxo complex (with bound CH3CN). Isotope labeling experiments further support the existence of the cobalt(III)-peroxo and -hydroperoxo complexes. In particular, the O-O bond stretching frequency of the cobalt(III)-hydroperoxo complex was determined to be 851 cm−1 for 16O2H samples (803 cm−1 for 18O2H samples) and its Co-O vibrational energy was observed at 571 cm−1 for 16O2H samples (551 cm−1 for 18O2H samples; 568 cm−1 for 16O22H samples) by resonance Raman spectroscopy. Reactivity studies performed with the cobalt(III)-peroxo and -hydroperoxo complexes in organic functionalizations reveal that the latter is capable of conducting oxygen atom transfer with an electrophilic character, whereas the former exhibits no oxygen atom transfer reactivity under the same reaction conditions. Alternatively, the cobalt(III)-hydroperoxo complex does not perform hydrogen atom transfer reactions, while analogous low-spin Fe(III)-hydroperoxo complexes are capable of this reactivity. Density function theory calculations indicate that this lack of reactivity is due to the high free energy cost of O-O bond homolysis that would be required to produce the hypothetical Co(IV)-oxo product.

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A mononuclear Mn2+ complex based on a novel tris-(ethyl acetate) pendant-armed tetraazamacrocycle: Effect of pyridine on self-assembly and weak interactions

Cited by 16 publications

References 45 publications

Effect of the Nature of Donor Atoms on the Thermodynamic, Kinetic and Relaxation Properties of Mn(II) Complexes Formed With Some Trisubstituted 12-Membered Macrocyclic Ligands

Effect of the Nature of Donor Atoms on the Thermodynamic, Kinetic and Relaxation Properties of Mn(II) Complexes Formed With Some Trisubstituted 12-Membered Macrocyclic Ligands

Complexation of Mn(II) by Rigid Pyclen Diacetates: Equilibrium, Kinetic, Relaxometric, Density Functional Theory, and Superoxide Dismutase Activity Studies

Reactivity of a Cobalt(III)–Hydroperoxo Complex in Electrophilic Reactions

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