- A CuII2 Paramagnetic Chemical Exchange Saturation Transfer Contrast Agent Enabled by Magnetic Exchange Coupling
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The ability of magnetic exchange coupling to enable observation of paramagnetic chemical exchange saturation transfer (PARACEST) in transition metal ions with long electronic relaxation times (s) is demonstrated. Metalation of the dinucleating, tetra(carboxamide) ligand HL with Cu2+ in the presence of pyrophosphate (P2O7)4- affords the complex [LCuII2(P2O7)]-. Solution-phase variable-temperature magnetic susceptibility data reveal weak ferromagnetic superexchange coupling between the two S = 1/2 CuII centers, with a coupling constant of J = +2.69(5) cm-1, to give an S = 1 ground state. This coupling results in a sharpened NMR line width relative to a GaCu analogue, indicative of a shortening of s. Presaturation of the amide protons in the Cu2 complex at 37 °C leads to a 14% intensity decrease in the bulk water 1H NMR signal through the CEST effect. Conversely, no CEST effect is observed in the GaCu complex. These results provide the first example of a Cu-based PARACEST magnetic resonance contrast agent and demonstrate the potential to expand the metal ion toolbox for PARACEST agents through introduction of magnetic exchange coupling.
- Du, Kang,Harris, T. David
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- New polyaminocarboxylate macrocycles containing phenolate binding units: synthesis, luminescent and relaxometric properties of their lanthanide complexes
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The synthesis of two new polyaminocarboxylate macrocycles incorporating one or two intracyclic phenol units (H4L1 and H8L2, respectively) is described. The 12-membered H4L1 macrocycle leads to soluble and stable mononuclear LnIII complexes of [(L1)Ln(H2O)2]- composition (Ln = Eu, Tb and Gd) in aqueous solutions. In Tris buffer (pH 7.4), the [(L1)Tb(H2O)2]- complex displays a suitable efficiency for sensitized emission (ηsens = 48%) and a high luminescence quantum yield (Φ = 22%), which is worthy of note for a bis-hydrated terbium complex. Besides, luminescence experiments show that bidentate endogenous anions (citrate, carbonate, and phosphate) do not displace the two inner-sphere water molecules of this complex. In contrast, the possible presence of LMCT states causes the europium complex to be weakly luminescent. The [(L1)Gd(H2O)2]- complex is characterized by high relaxivity (r298 K1 = 7.2 s-1 mM-1 at 20 MHz) and a very short water residence time of the coordinated water molecules (τ298 KM = 9 ns), promising values for the realisation of macromolecular systems with high relaxivities. Thus, the Tb and Gd complexes of the H4L1 macrocycle exhibit several improvements in terms of luminescent (lower excitation energy, higher brightness) and relaxometric (shorter τM) properties compared to the corresponding LnPCTA complexes, where a phenol moiety substitutes a pyridine ring. On the other hand, the 24-membered H8L2 macrocycle including two phenol units in its structure leads to dinuclear complexes of [(L2)Ln2]2- composition. Its terbium complex shows a long luminescence lifetime (2 ms) and a high quantum yield (43%) in aqueous solutions, making this compound a new promising candidate for time-resolved applications.
- Enel, Morgane,Leygue, Nadine,Balayssac, Stéphane,Laurent, Sophie,Galaup, Chantal,Vander Elst, Luce,Picard, Claude
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- CALIXARENE COMPOUNDS AND USES THEREOF
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Compounds of general Formula (I) wherein the elements A, L, R1 and R2 have a defined meaning, and their medical and non-medical use.
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Page/Page column 54
(2021/01/22)
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- PROPARGYL-FUNCTIONALIZED MACROCYCLIC COMPOUNDS
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Propargyl-functionalized macrocyclic compounds can include non-aggregating compounds having at least one phthalocyanine (Pc), azaphthalocyanine (AzaPc), or naphthalocyanine (Nc) unit. The compounds can be metal-free or metal-complexed. The metal-complexed
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Paragraph 0058; 0060; 0094
(2020/04/24)
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- Electronic Effects of Ligand Substitution in a Family of CoII2 PARACEST pH Probes
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We report three new Co2-based paramagnetic chemical exchange saturation transfer (PARACEST) probes with the ability to ratiometrically quantitate pH. A CoII2 complex, [LCo2(etidronate)]-, featuring tetra(carboxamide) and OH-substituted etidronate ligands with opposing pH-dependent CEST peak intensities, was previously shown to exhibit a linear correlation between log(CESTOH/CESTNH) and pH in the pH range 6.5-7.6 that provided a sensitivity of 0.99(7) pH unit-1 at 37 °C. Here, we demonstrate through a series of CF3-functionalized CoII2 complexes [(XL′)Co2(etidronate)]- (X = NO2, F, Me), that modest changes in the electronic structure of CoII centers through remote ligand substitution can significantly affect the NMR and CEST properties of Co2-based PARACEST probes. Variable-pH NMR and CEST analyses reveal that the chemical shifts of the ligand protons are highly affected by the nature of the X substituent. The ratios of OH and NH CEST peak intensities at 115 and 88, 93 and 79, and 88 and 76 ppm for X = NO2, F, and Me, respectively, afford pH calibration curves with remarkably high sensitivities of 1.49(9), 1.48(7), and 2.04(5) pH unit-1 across the series. The 1.5-2-fold enhancement in pH sensitivity for the CF3-functionalized Co2 probes stems from the complete separation of the OH and NH CEST peaks. Furthermore, incorporation of electron-withdrawing CF3 groups shifts the detection window to a more acidic range of pH 6.2-7.4. Finally, the CoII2 complexes are found to be extremely robust toward substitution and oxidation in aqueous solutions. Taken together, these results highlight the unique ability of transition metal-based PARACEST probes to provide a highly sensitive concentration-independent measure of pH and demonstrate that modest ligand modifications can be a powerful tool for optimizing the pH sensing performance of these probes.
- Thorarinsdottir, Agnes E.,Tatro, Scott M.,Harris, T. David
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p. 11252 - 11263
(2018/09/14)
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- Highly enantioselective asymmetric reactions involving zinc ions promoted by chiral aziridine alcohols
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Enantiomerically pure, chiral secondary and tertiary aziridine alcohols (including the aziridine analogue of ProPhenol—AziPhenol) have proven to be highly effective catalysts for enantioselective asymmetric reactions in the presence of zinc ions, including arylation of aromatic aldehydes, epoxidation of chalcone and addition of diethylzinc to aldehydes, leading to the desired chiral products in high chemical yields (up to 90%) and with ee's up to 90%. A higher catalytic activity of Prophenol-type bis(aziridine alcohol) in the aforementioned asymmetric transformations has been demonstrated.
- Jarzyński, Szymon,Utecht, Greta,Le?niak, Stanis?aw,Rachwalski, Micha?
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p. 1774 - 1779
(2017/11/16)
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- Catalytic compositions and methods for asymmetric aldol reactions
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Methods and compositions are provided for the direct catalytic asymmetric aldol reaction of aldehydes with donor molecules selected from ketones and nitroalkyl compounds. The reactions employ as catalyst a Group 2A or Group 2B metal complex of a ligand of formula I, as defined further herein.
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- Effect of ligand structure on the zinc-catalyzed Henry reaction. Asymmetric syntheses of (-)-denopamine and (-)-arbutamine
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(Matrix presented) Syntheses of variously modified ligands for the dinuclear zinc catalysts for the asymmetric aldol and nitroaldol (Henry) reactions are reported. Catalytic enantioselective nitroaldol reactions promoted by these modified ligands led to efficient syntheses of the β-preceptor agonists (-)-denopamine and (-)-arbutamine.
- Trost, Barry M.,Yeh, Vince S. C.,Ito, Hisanako,Bremeyer, Nadine
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p. 2621 - 2623
(2007/10/03)
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- Alkyl- and aryl-oxygen bond activation in solution by rhodium(I), palladium(II), and nickel(II). Transition-metal-based selectivity
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Reaction of [RhCl(C8H14)2]2 (C8H14 = cyclooctene) with 2 equiv of the aryl methyl ether phosphine 1 in C6D6 results in an unprecedented metal insertion into the strong sp2-sp3 aryl-O bond. This remarkable reaction proceeds even at room temperature and occurs directly, with no intermediacy of C-H activation or insertion into the adjacent weaker ArO-CH3 bond. Two new phenoxy complexes (8 and 9), which are analogous to the product of insertion into the ArO-CH3 bond (had it taken place) were prepared and shown not to be intermediates in the Ar-OCH3 bond cleavage process. Thus, aryl-O bond activation by the nucleophilic Rh(I) is kinetically preferred over activation of the alkyl-O bond. The phenoxy Rh(I)-η1-N2 complex (8) is in equilibrium with the crystallographically characterized Rh(I)-μ-N2-Rh(I) dimer(12). Reaction of [RhClC8H14)2]2 with 2 equiv of the aryl methyl ether phosphine 2, PPh3, and excess HSiR3 (R = OCH2CH3, CH2CH3) results also in selective metal insertion into the aryl-O bond and formation of (CH3O)SiR3. Thus, transfer of a OCH3 group from carbon to silicon was accomplished, showing that hydrosilation of an unstrained aryl-O single bond by a primary silane is possible. The selectivity of C-O bond activation is markedly dependent on the transition-metal complex and the alkyl group involved, allowing direction of the C-O bond activation process at either the aryl-O or alkyl-O bond. Thus, contrary to the reactivity of the rhodium complex, reaction of NiI2 or Pd(CF3CO2)2 with 1 equiv of 1 in ethanol or C6D6 at elevated temperatures results in exclusive activation of the sp3-sp3 ArO-CH3 bond, while reaction of the analogous aryl ethyl ether 4 and Pd(CF3CO2)2 results in both sp3-sp3 and sp2-sp3 C-O bond activation. The resulting phenoxy Pd(II) complex (18) is fully characterized by X-ray analysis. Heating the latter under mild dihydrogen pressure results in hydrodeoxygenation to afford an aryl-Pd(II) complex (19).
- Van Der Boom, Milko E.,Liou, Shyh-Yeon,Ben-David, Yehoshoa,Shimon, Linda J. W.,Milstein, David
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p. 6531 - 6541
(2007/10/03)
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