The ligand 2-anilino-4,6-di-tert-butylphenol and its 2-(3,5-dichloroanilino)-4,6-di-tert-butylphenol analogue react in CH(3)CN or CH(3)OH solutions with divalent transition metal ions in the presence of air and triethylamine. Depending on the metal:ligand ratio (1:1, 1:2, or 1:3) and the presence (or absence) of the cyclic amine 1,4-dimethyl-1,4,7-triazacyclononane (dmtacn), the following complexes have been isolated as crystalline solids: [Co(III)(L(ISQ))(3)] (1); [Cu(II)(dmtacn)(L(ISQ))]PF(6) (2); [Cu(II)(L(ISQ))(2)] (3); [Ni(II)(L(ISQ))(2)] (4a); [Ni(II)((Cl)L(ISQ))(2)] (4b); [Pd(II)(L(ISQ))(2)] (5). (L(ISQ))(-) represents the monoanionic o-iminobenzosemiquinonate radical (S(rad) = (1)/(2)). Compounds 1-5 have been characterized by single-crystal X-ray crystallography at 100(2) K. For all complexes it is unambiguously established that the O,N-coordinated o-iminobenzosemiquinonato(1-) ligand is present. Complexes 3, 4b, and 5 are square planar molecules which possess an S(t) = (1)/(2), 0, and 0 ground state, respectively, as was established by (1)H NMR and EPR spectroscopies and variable-temperature magnetic susceptibility measurements. Complex 2 possesses an S(t) = 1 ground state which is attained via strong intramolecular ferromagnetic coupling (J = +195 cm(-1)) between the d(x)2-(y)2 magnetic orbital of the Cu(II) ion and the pi-orbital of the ligand radical. Complex 1 contains three mutually orthogonal (L(ISQ))(-*) ligands and has an S(t) = (3)/(2) ground state. It is shown that the electronic structure of 4a and 5 is adequately described as singlet diradical containing a divalent, diamagnetic d(8) configurated central metal ion and two strongly antiferromagnetically coupled (L(ISQ))(-) radical ligands. It is concluded that the same electronic structure prevails in the classic bis(o-diiminobenzosemiquinonato)- and bis(o-benzosemiquinonato)metal complexes of Ni(II), Pd(II), and Pt(II). The electrochemistry of all complexes has been investigated in detail. For 3, 4a, and 5 a series of reversible one-electron-transfer waves leads to the formation of the anions and cations [M(L)(2)](2-),(1-),(1+),(2+) which have been characterized spectroelectrochemically. All redox processes are shown to be ligand-based.
The development of efficient water oxidation catalysts based on inexpensive and Earth-abundant materials is a prerequisite to enabling water splitting as a feasible source of alternative energy. In this work, we report the synthesis of ternary cobalt manganese phosphide nanoparticles from the solution-phase reaction of manganese and cobalt carbonyl complexes with trioctylphosphine. The CoMnP nanoparticles (ca. 5 nm in diameter) are nearly monodisperse and homogeneous in nature. These CoMnP nanoparticles are capable of catalyzing water oxidation at an overpotential of 0.33 V with a 96% Faradaic efficiency when deposited as an ink with carbon black and Nafion. A slight decrease in activity is observed after 500 cycles, which is ascribed to the etching of P into solution, as well as the oxidation of the surface of the nanoparticles. Manganese-based ternary phosphides represent a promising new system to explore for water oxidation catalysis.
The coordination chemistry of the ligands 2-anilino-4,6-di-tert-butylphenol, H[L(AP)], and N,N"'-bis[2-(4,6-di-tert-butylphenol]diethylenetriamine, H(2)[(L(AP))N(L(AP))], has been studied with the first-row transition metal ions V, Cr, Fe, and Co. The ligands are noninnocent in the sense that the aminophenolato parts, [L(AP)](-) and [L(AP)-H](2)(-), can be readily oxidized to their o-iminobenzosemiquinonato, [L(ISQ)](-), and o-iminobenzoquinone, [L(ISB)], forms. The following neutral octahedral complexes have been isolated as crystalline materials, and their crystal structures have been determined by X-ray crystallography at 100 K: [Cr(III)(L(ISQ))(3)] (1), [Fe(III)(L(ISQ))(3)] (2), [Co(III)(L(ISQ))(3)] (3), [V(V)(L(ISQ))(L(AP)-H)(2)] (4), [V(V)(L(AP)-H)(2)(L(AP))] (5), and [V(V)O[(L(AP))N(L(AP)-H)]] (6). From variable-temperature magnetic susceptibility measurements and X-band EPR spectroscopy it has been established that they possess the ground states: 1, S = 0; 2, S = 1; 3, S = (3)/(2); 4, S = (1)/(2); 5, S = 0; 6, S = 0. The o-iminobenzosemiquinonato radicals (S(rad) = (1)/(2)) couple strongly intramolecularly antiferromagnetically to singly occupied orbitals of the t(2g) subshell at the respective metal ion but ferromagnetically to each other in 3 containing a Co(III) ion with a filled t(2g)(6) subshell. It is demonstrated that the oxidation level of the ligands and metal ions can be unequivocally determined by high-quality X-ray crystallography in conjunction with EPR, UV-vis, and Mössbauer spectroscopies. The spectro- and electrochemistry of these complexes have also been studied in detail. Metal- and ligand-based redox chemistry has been observed. The molecular and electronic structures are compared with those of their o-semiquinonato analogues.
Species 1-6 are [M(III)(L)2]ClO4 complexes formed with the PhO--CH=N-CH2-Py imines, (L(I))- and (L(tBuI))-, and PhO--CH2-NH-CH2-Py amines, (L(A))- and (L(tBuA))-, in which PhO- is a phenolate ring and Py is a pyridine ring and the prefix tBu indicates the presence of tertiary butyl groups occupying the positions 4 and 6 of the phenol ring. Monometallic species with d5 high-spin iron (1, 2, 3, 4) and d10 gallium (5, 6) were synthesized and characterized to assess the influence of the ligand rigidity and the presence of tertiary butyl-substituted phenol rings on their steric, electronic, and redox behavior. Characterization by elemental analysis, mass spectrometry, IR, UV-visible, and EPR spectroscopies, and electrochemistry has been performed, and complexes [FeIII(L(tBuI))2]ClO4 (2), [FeIII(L(tBuA))2]ClO4 (4), and [Ga(III)(L(tBuI))2]ClO4 (5) have been characterized by X-ray crystallography. The crystal structures show the imine ligands meridionally coordinated to the metal centers, whereas the amine ligands are coordinate in a facial mode. Cyclic voltammetry shows that the complexes with the ligands (L(tBuI))- and (L(tBuA))- were able to generate ligand-based phenoxyl radicals, whereas unsubstituted ligands displayed ill-defined redox processes. EPR spectroscopy supports high-spin configurations for the iron complexes. UV-visible spectra are dominated by charge-transfer phenomena, and imine compounds exhibit dramatic hyperchromism when compared to equivalent amines. The tertiary butyl groups on the phenolate ring enhance this trend. Detailed B3LYP/6-31G(d)-level calculations have been used to account for the results observed.
Selective 20S proteasomal inhibition and apoptosis induction were observed when several lines of cancer cells were treated with a series of copper complexes described as [Cu((2), and [Cu(HL I )(L I )]OAc (3), where HL I is the ligand 2,4-diiodo-6-((pyridine-2-ylmethylamino) methyl)phenol. These complexes were synthesized, characterized by means of ESI spectrometry, infrared, UV-visible and EPR spectroscopies, and X-ray diffraction when possible. After full characterization species 1-3 were evaluated for their ability to function as proteasome inhibitors and apoptosis inducers in C4-2B and PC-3 human prostate cancer cells and MCF-10A normal cells. With distinct stoichiometries and protonation states, this series suggests the assignment of species [CuL I ] + as the minimal pharmacophore needed for proteasomal chymotryspin-like activity inhibition and permits some initial inference of mechanistic information.Three well characterized discrete copper complexes with asymmetric phenol-substituted ligands are able to inhibit the proteolytic activity of the 20s proteasome. Evidence for a minimal pharmacophore suggests a potential basis for new cancer therapies with tunable and cost-effective metallodrugs.
Owing to their topology, three iminosemiquinone radical ligands couple in a ferromagnetic fashion, mediated by a low-spin Co(iii) ion.
The investigation of metal-based complexes with potential antitumor activity has been of paramount importance in recent years due to the successful use of cisplatin against various cancers. Gallium(III) and subsequently developed gallium(III)-containing complexes have shown promising antineoplastic effects when tested in a host of malignancies, specifically in lymphomas and bladder cancer. However, the molecular mechanism responsible for their anticancer effect is yet to be fully understood. We report here for the first time that the proteasome is a molecular target for gallium complexes in a variety of prostate cancer cell lines and in human prostate cancer xenografts. We tested five gallium complexes (1-5) in which the gallium ion is bound to an NN ¶O asymmetrical ligand containing pyridine and substituted phenolate moieties in a 1:2 (M/L) ratio. We found that complex 5 showed superior proteasome inhibitory activity against both 26S proteasome (IC 50 , 17 Mmol/L) and purified 20S (IC 50 , 16 Mmol/L) proteasome. Consistently, this effect was associated with apoptosis induction in prostate cancer cells. Additionally, complex 5 was able to exert the same effect in vivo by inhibiting growth of PC-3 xenografts in mice (66%), which was associated with proteasome inhibition and apoptosis induction. Our results strongly suggest that gallium complexes, acting as potent proteasome inhibitors, have a great potential to be developed into novel anticancer drugs.
Rectification consists of an asymmetric flow of electric current. In a macroscopic electrical circuitry, rectifiers, such as vacuum tubes or solid-state diodes, control the mobility of current, enabling it to flow in one direction and preventing reversibility. This directionality is fundamental to the conversion of alternating into direct current. Molecular rectification, which was proposed in the celebrated Aviram-Ratner ansatz, [1] anticipates the feasibility of a current flow in one direction that takes place in an electrode j molecule j electrode junction. Central to this paradigm is the existence of asymmetric molecules that incorporate electron-donor and electron-acceptor moieties, [DA], with an excited state] of higher, but accessible, energy.[2] Usually, donor and acceptor are separated by a s-or p-bridge to decrease electronic coupling, [3] and if the requirements are fulfilled, rectification occurs with contributions from Schottky, asymmetric, and/or unimolecular mechanisms. Schottky rectification is based on interfacial dipoles from electrode contact or on covalent bonding between the molecule and the electrode.[4] Asymmetric and unimolecular mechanisms rely on the use of frontier molecular orbitals of the molecule; whereas the former relies on an asymmetric placement of the HOMO or the LUMO in the electrode j molecule j electrode assembly, the latter is based on small HOMO-LUMO gaps that allow for through-molecule current flow. [4a, 5] Although experimental distinction between asymmetric and unimolecular contributions can be ambiguous, there is consensus that electroactive molecules with local low symmetry [6] constitute good candidates for this enterprise, and welldocumented cases of molecular rectification heavily rely on the formation of high-quality Langmuir-Blodgett (LB) films. [7] Although it has been shown that self-assembled monolayers of polypyridine-cobalt(II) complexes in octahedral environments [8] can act as single-electron transistors and induce increased resistance (Coulomb blockade) at cryogenic temperatures, the incorporation of transition-metal complexes into electrode j molecule junctions has generally employed symmetric molecules and has been rather slow in development. Examples involve assemblies based on metalloporphyrins, [9] terpyridine-ruthenium(II) complexes, [10] as well as trivalent cobalt [11] and rhodium [12] azo-containing species in octahedral environments that are capable of the symmetric conductance that is relevant for memory-switching devices. An example of rectification based on an octahedral bipyridine/acac-ruthenium(II) system has been reported (acac = acetylacetonate), [13] but the effect of lowering global symmetries around the metal center is yet to be tested.Our group is engaged in an effort to integrate bioinspired asymmetry principles into new molecular materials, with the aim of developing redox-responsive metallosurfactants with topologies that display unique structural, spectroscopic, and surface patterning behavior. We recently reported on the red...
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