Synthesis, characterization and reactivity of copper(I) imidazole complexes based on a cavitand ligand design†

Voo, Janis K.; Lam, Kwok L.; Rheingold, Arnold L.; Riordan, Charles G.

doi:10.1039/b102480a

Cited by 28 publications

(20 citation statements)

References 18 publications

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“…The syntheses of the calixarene receptors 4a and 5a [23] and the tripodal benzene 2 [11] have been reported previously. The derivatives 3a and 1a were obtained from a similar reaction of 1,3,5-tris(bromomethyl)benzene [24] and 1,3-bis(bromomethyl)-2,4,6-triethylbenzene [25] with 1-methylimidazoles in 89 and 72 % yields, respectively. Compounds 1a-5a were subsequently subjected to anion exchange with a saturated solution of NH 4 PF 6 to afford anion receptors 1b-4b in 81-85 % yields and 5b in 93 % yield.…”

Section: Resultsmentioning

confidence: 99%

Influence of the Number and Geometry of Binding Sites on Host–Guest Affinity: Imidazolium‐Substituted Receptor Molecules for Small Inorganic Anions

Fahlbusch¹,

Frank²,

Schatz³

et al. 2006

Eur J Org Chem

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Section: Resultsmentioning

confidence: 99%

Influence of the Number and Geometry of Binding Sites on Host–Guest Affinity: Imidazolium‐Substituted Receptor Molecules for Small Inorganic Anions

Fahlbusch¹,

Frank²,

Schatz³

et al. 2006

Eur J Org Chem

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“…[11] The data also conform to the structures identified previously in our Cu I (His) 2 dipeptide complexes, in which intramolecular binding of the imidazole moieties of the dipeptide affords tight, linear CuÀN two-coordinate geometry. [6] Further results obtained for Cu I -Ab (6)(7)(8)(9)(10)(11)(12)(13)(14) firmly demonstrate the propensity for Cu I to adopt near-linear twocoordinate geometry: EXAFS spectroscopic analysis of solid Cu I -Ab(6-14) indicated formation of the same structure, despite the presence of a third potential histidine ligand. For Cu I -Ab (6)(7)(8)(9)(10)(11)(12)(13)(14), the Fourier Transform with fit is shown in Figure 2.…”

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confidence: 79%

“…For these solid samples, X-ray absorption spectroscopy (XAS) was used as a powerful (yet unexploited, in the case of Cu-Ab complexes) tool for the determination of oxidation state, coordination environment, and bond lengths in the derived metal complexes. [9,10] For both Ab (6)(7)(8)(9)(10)(11)(12)(13)(14) and Ab (10)(11)(12)(13)(14) complexes, the occurrence of the 1s!4p transition at 8983-84 eV (Figure 2) definitively indicated that copper was in the + 1 oxidation state. Extended X-ray absorption fine structure (EXAFS) spectroscopic data fits for the Cu I -Ab(10-14) complex, with only two histidine residues (Figure 1), indicated two nitrogen ligands from imidazole donors, as further supported by back-scattering from the ring carbons and nitrogen.…”

mentioning

confidence: 96%

“…Structural information was obtained by spectroscopic techniques for both solid and solution states (see below). Solid samples of Cu I -Ab (6)(7)(8)(9)(10)(11)(12)(13)(14) and Cu I -Ab (10)(11)(12)(13)(14) were prepared by incubating stoichiometric amounts of the respective peptides with a [Cu I (CH 3 CN) 4 ] + salt in DMF and isolated by precipitation with diethyl ether, filtration, and drying under reduced pressure. Their formulation was confirmed using ESI-MS. [8] Mishandled samples turned deep blue, indicating oxidation to Cu II , whereas the Cu I complexes remained white-to-gray when air was excluded, indicating reduced metal-peptide complexes.…”

mentioning

confidence: 99%

“…Results indicated that the 2N imid structure persists in solution, even for the three-His-containing complex Cu I -Ab (6)(7)(8)(9)(10)(11)(12)(13)(14). CO complexes were formed for each of the three peptides [ Figure 1: Ab (6)(7)(8)(9)(10)(11)(12)(13)(14) and Ab(10-14), discussed above, and the tripeptide FHH, discussed in more detail below] in 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffered (pH 7.4) D 2 O and characterized using FTIR spectroscopy. The stretching frequency of copper(I)bound CO is diagnostic for the overall coordination number in cationic copper(I) species, [6, 11e, 12] and has been noted in cuprous enzymes.…”

mentioning

confidence: 99%

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Structural Studies of Copper(I) Complexes of Amyloid‐β Peptide Fragments: Formation of Two‐Coordinate Bis(histidine) Complexes

Himes

Park

Siluvai³

et al. 2008

Angew Chem Int Ed

143

146

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Extensive evidence points to oxidative stress as a key event in the pathogenesis and exacerbation of Alzheimer's Disease (AD).[1] Transition metals, such as Zn, Fe, and Cu, are present in elevated concentrations in AD brain deposits, composed primarily of 40-or 42-mer amyloid beta (Aβ) peptides. The redox-active copper(II) ion binds to the unstructured, hydrophilic N terminus of Aβ; [1g,2] and the ability of copper to promote the formation of reactive oxygen species (ROS) and cause neuronal death by interaction with Aβ has been demonstrated in vitro. [1a,c,3,4] ROS formation is proposed to occur by interaction of reduced Cu I -Aβ with O 2 or H 2 O 2 . However, few direct studies of Cu I binding or reactivity with Aβ peptides or fragments have been reported. [5,6] We have studied the interactions of the hydrophilic N-terminal region of the Aβ peptide with Cu I . An understanding of the full redox competency of Cu-Aβ, leading to ROS formation and oxidative stress (that is, to cause events associated with the onset of AD), is incomplete without elucidation of the structure/function relationships of the reduced (active) copper(I)-peptide complexes. We report herein studies on the interaction of Cu I ions with small portions of the Aβ peptide incorporating specific metal-binding (His6, His13, His14) or potentially redoxactive (Tyr10) residues (Figure 1). Of considerable interest are the contiguous His13 and His14 residues. We have previously reported studies on Cu I complexes of modified (by end-capping and/or regiospecific N ε -or N δ -alkylation) His-His dipeptides which, significantly, adopt a two-coordinate, near-linear N His -Cu I -N His environment. [6] In this report, we demonstrate that Cu I complexes of longer Aβ peptide fragments adopt the same apparent two-coordinate structure in the solid state and aqueous solution. Preliminary reactivity investigations, described here, indicate that the His13-Cu I -His14 moiety is the active part of the structure, responsible for copper-Aβ reactivity.A range of peptides ( Figure 1) were synthesized and purified by reverse-phase (RP) HPLC to a single peak. Their identity and purity were confirmed by ESI mass spectrometry. The peptides

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The First Water‐Soluble Copper( I ) Calix[6]arene Complex Presenting a Hydrophobic Ligand Binding Pocket: A Remarkable Model for Active Sites in Metalloenzymes

2002

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Because of the unique properties of water, the synthesis of biomimetic complexes that are soluble and stable under physiological conditions is an attractive goal. Paradoxically, most metalloenzyme models have been developed in organic solvents. [1] The first reason is that the ligands used to mimic the biological active site often lead to water-insoluble complexes, and their solubilization through synthetic procedures is not an easy task. For instance, tris(pyrazolyl)borate, which is the basis for countless biomimetic complexes, [2] is sensitive to hydrolysis, and hydrophilic derivatives would not survive in aqueous solvent. [3] The second reason is that biologically relevant species are often reactive to water and must be protected and/or stabilized. In the specific case of copper, few water-soluble cuprous complexes have been described, [3,4] and to the best of our knowledge none of them can be considered biomimetic. Indeed, it is well known that Cu I centers are thermodynamically unstable in water and disproportionate in the absence of an appropriate coordinating environment. Another major difficulty stems from the fact that metalloenzyme model complexes must present a vacant or a labile site on the metal center to allow the coordination and/or activation of a guest.In the course of modeling type 2 active sites of copper enzymes, we have been interested in developing a supramolecular system that can stabilize a copper(i) center within a biomimetic environment. [5±7] We have now extended our previous work to demonstrate a possible route to transform the calix[6]arene derivatives soluble in organic solvents into compounds soluble in water. Here, we describe the synthesis of the first water-soluble biomimetic cuprous complex.The selectively functionalized calix[6]arene derivative 1 [8] was first O-alkylated with three imidazole arms to yield compound 2 (Scheme 1). [6] The next step consisted of the ipso sulfonation of the three anisole rings by treating 2 with concentrated sulfuric acid. The resulting triacid [3] ¥ H 3 was neutralized with sodium hydroxide, giving rise to the trisodium salt [3] ¥ Na 3 . This new ligand is highly soluble in water and, to a lesser extent, in methanol, ethanol, and 2-propanol. further purification. All glassware used in the following procedures were cleaned in a bath of freshly prepared 3:1 HCl:HNO 3 (aqua regia) and rinsed thoroughly in milli-Q grade water prior to use. The Ag nanoparticles were prepared by sodium citrate reduction of AgNO 3 : [9] AgNO 3 (18 mg) was dissolved in H 2 O (100 mL) and brought to reflux. A solution of 1 % trisodium citrate (2 ml) was added and the solution was kept at reflux for about 1 h. The final volume was adjusted to 500 mL. The Ag sols prepared were greenish yellow. The Ag plasmon absorbance maxima was at approximately 440 nm.In a typical synthesis, as-prepared Ag sols (5 mL) was diluted with water (5 mL), then a freshly prepared plating solution of 0.02 m NH 2 OH (0.10 mL) and 0.1 % HAuCl 4 (0.25 mL) was added with stirring. The solution was t...

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Synthesis, characterization and reactivity of copper(I) imidazole complexes based on a cavitand ligand design†

Cited by 28 publications

References 18 publications

Influence of the Number and Geometry of Binding Sites on Host–Guest Affinity: Imidazolium‐Substituted Receptor Molecules for Small Inorganic Anions

Influence of the Number and Geometry of Binding Sites on Host–Guest Affinity: Imidazolium‐Substituted Receptor Molecules for Small Inorganic Anions

Structural Studies of Copper(I) Complexes of Amyloid‐β Peptide Fragments: Formation of Two‐Coordinate Bis(histidine) Complexes

The First Water‐Soluble Copper( I ) Calix[6]arene Complex Presenting a Hydrophobic Ligand Binding Pocket: A Remarkable Model for Active Sites in Metalloenzymes

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