The study of the structures and properties of atomically precise gold nanoclusters is the object of active research worldwide. Recently, research has been also focusing on the doping of metal ...nanoclusters through introduction of noble metals, such as platinum, and less noble metals, such as cadmium and mercury. Previous studies, which relied extensively on the use of mass spectrometry and single-crystal X-ray crystallography, led to the assignment of the location of each of these foreign-metal atoms. Our study provides new insights into this topic and, particularly, compelling evidence about the actual position of the selected metal atoms M = Pt, Pd, Hg, and Cd in the structure of Au24M(SR)18 0. To make sure that the results were not dependent on the thiolate, for SR we used both butanethiolate and phenylethanethiolate. The clusters were prepared according to different literature procedures that were supposed to lead to different doping positions. Use of NMR spectroscopy and isotope effects, with the support of mass spectrometry, electrochemistry, and single-crystal X-ray crystallography, led us to confirm that noble metals indeed dope the cluster at its central position, whereas no matter how the doping reaction is conducted and the nature of the ligand, the position of both Cd and Hg is always on the icosahedron shell, rather than at the central or staple position, as often reported. Our results not only provide a reassessment of previous conclusions, but also highlight the importance of NMR spectroscopy studies and cast doubts on drawing conclusions mostly based on single-crystal X-ray crystallography.
The new 3-monosubstituted acetylacetone ligands, 3-(phenyl(1
-pyrazol-1-yl)methyl)pentane-2,4-dione (HL
) and 3-((3,5-dimethyl-1
-pyrazol-1-yl)(phenyl)methyl)pentane-2,4-dione (HL
), were synthesized ...and used as supporting ligands for new copper(II) and copper(I) phosphane complexes of the general formulae Cu(HL
)
(L
)
and Cu(PPh
)
(HL
)PF
(X = Pz (pyrazole) or PzMe (3,5-dimethylpyrazole)), respectively. In the syntheses of the Cu(I) complexes, the triphenylphosphine coligand (PPh
) was used to stabilize copper in the +1 oxidation state, avoiding oxidation to Cu(II). All compounds were characterized by CHN analysis,
H-NMR,
C-NMR, FT-IR spectroscopy, and electrospray ionization mass spectrometry (ESI-MS). The ligands HL
(
) and HL
(
) and the copper complex Cu(PPh
)
(HL
)PF
(
) were also characterized by X-ray crystallography. The reactivity of these new compounds was investigated and the new compounds 4-phenyl-4-(1
-pyrazol-1-yl)butan-2-one (
) and 4-(3,5-dimethyl-1
-pyrazol-1-yl)-4-phenylbutan-2-one (
) were obtained in basic conditions via the retro-Claisen reaction of related 3-monosubstituted acetylacetone, providing efficient access to synthetically useful ketone compounds. Compound
was also characterized by X-ray crystallography.
A new dimeric copper(II) bromide complex, Cu(LOHex)Br(μ-Br)2 (1), was prepared by a reaction of CuBr2 with the hexyl bis(pyrazol-1-yl)acetate ligand (LOHex) in acetonitrile solution and fully ...characterized in the solid state and in solution. The crystal structure of 1 was also determined: the complex is interlinked by two bridging bromide ligands and possesses terminal bromide ligands on each copper atom. The two pyrazolyl ligands in 1 coordinate with the nitrogen atoms to complete the Cu coordination sphere, resulting in a five-coordinated geometry—away from idealized trigonal bipyramidal and square pyramidal geometries—which can better be described as distorted square pyramidal, as measured by the τ and χ structural parameters. The pendant hexyloxy chain is disordered over two arrangements, with final site occupancies refined to 0.705 and 0.295. The newly synthesized complex was evaluated as a catalyst in copper-catalyzed C–H oxidation for allylic functionalization through a Kharasch–Sosnovsky reaction without any external reducing agent. Using 0.5 mol% of this catalyst, and tert-butyl peroxybenzoate (Luperox) as an oxidant, allylic benzoates were obtained with up to 90% yield. The general reaction time was only slightly decreased to 24 h but a very significant decrease in the alkene:Luperox ratio to 3:1 was achieved. These factors show relevant improvements with respect to classical Kharasch–Sosnovsky reactions in terms of rate and amount of reagents. The present study highlights the potential of copper(II) complexes containing functionalized bis(pyrazol-1-yl)acetate ligands as efficient catalysts for allylic oxidations.
The knowledge on element 43 (Tc) of the periodic table, built over the years through the contributions given by the close relationship between chemistry and nuclear medicine, allowed the development ...of new and increasingly effective radiopharmaceuticals useful both as perfusion and target specific imaging agents for SPECT (single photon emission tomography). Among the manifold Tc-compounds, Tc(V) nitrido complexes played a relevant role in the search for new technetium-99m radiopharmaceuticals, providing efficient labeling procedures that can be conveniently exploited for the design and synthesis of agents, also incorporating small organic molecules or peptides having defined structural features. With this work, we present an overview of four decades of research on the chemistry and on the nuclear medicine applications of Tc(V) nitrido complexes.
Three new 6-methyl-2-oxo-1,2-dihydroquinoline-3-carbaldehyde-thiosemicarbazones-N-4-substituted pro-ligands and their Cu(II) complexes (
, -NH
;
, -NHMe;
, -NHEt) have been prepared and ...characterized. In both the X-ray structures of
and
, two crystallographically independent complex molecules were found that differ either in the nature of weakly metal-binding species (water in
and nitrate in
) or in the co-ligand (water in
and methanol in
). Electron Paramagnetic Resonance (EPR) measurements carried out on complexes
and
confirmed the presence of such different species in the solution. The electrochemical behavior of the pro-ligands and of the complexes was investigated, as well as their biological activity. Complexes
and
exhibited a high cytotoxicity against human tumor cells and 3D spheroids derived from solid tumors, related to the high cellular uptake. Complexes
and
also showed a high selectivity towards cancerous cell lines with respect to non-cancerous cell lines and were able to circumvent cisplatin resistance. Via the Transmission Electron Microscopy (TEM) imaging technique, preliminary insights into the biological activity of copper complexes were obtained.
An exhaustive study dealing with the kinetic and mechanistic behavior of alkyl- and arylpalladium complexes bearing pyridyl−thioethers (NS−R) and quinoline−phosphines (NP) as ancillary ligands when ...reacting with 2,6-dimethyl isocyanide (DIC) and tosylmethyl isocyanide (TosMIC) was undertaken. In these reactions some differently substituted isocyanides insert into the palladium−carbon bond of alkyl and aryl complexes bearing mixed (NS or NP) ligands. The reactions were carried out under equimolecular conditions since such a restrictive approach allows the determination of the rate constants related to the isocyanide insertion attack. Reactions carried out under nonstoichiometric conditions were also taken into account and the reaction products characterized. Usually the formation of an inserted bis-substituted isocyanide halide derivative of palladium(II) was observed. In a particular case the formation of an imidoyl dimer was detected. The structures of the monoinserted Pd(NSt-Bu)(C(Tol)NR2)I (NSt-Bu = 2-(tert-butylthiomethyl)pyridine) and of the dimer Pd(CNR2)(C(NR2)Me)Cl2 (R2 = 2,6-Me2C6H3) were reported.
The knowledge on element 43 (Tc) of the periodic table, built over the years through the contributions given by the close relationship between chemistry and nuclear medicine, allowed the development ...of new and increasingly effective radiopharmaceuticals useful both as perfusion and target specific imaging agents for SPECT (single photon emission tomography). Among the manifold Tc-compounds, Tc(V) nitrido complexes played a relevant role in the search for new technetium-99m radiopharmaceuticals, providing efficient labeling procedures that can be conveniently exploited for the design and synthesis of agents, also incorporating small organic molecules or peptides having defined structural features. With this work, we present an overview of four decades of research on the chemistry and on the nuclear medicine applications of Tc(V) nitrido complexes.
Tetrahedral copper(I) TpCuP complexes 1–15, where Tp is a N,N,N-tris(azolyl)borate and P is a tertiary phosphine, have been synthesized and characterized by means of NMR, ESI-MS, and XAS-EXAFS, and ...X-ray diffraction analyses on the representative complexes 1 and 10, respectively. All copper(I) complexes were evaluated for their antiproliferative activity against a panel of human cancer cell lines (including cisplatin and multidrug-resistant sublines). The two most effective complexes HB(pz)3Cu(PCN), 1, and HB(pz)3Cu(PTA), 2, showed selectivity toward tumor vs normal cells, inhibition of 26S proteasome activity associated with endoplasmic reticulum (ER) stress, and unfolded protein response (UPR) activation. No biochemical hallmarks of apoptosis were detected, and morphology studies revealed an extensive cytoplasmic vacuolization coherently with a paraptosis-like cell death mechanism. Finally, the antitumor efficacy of complex 1 was validated in the murine Lewis Lung Carcinoma (LLC) model.
Novel tetrahedral copper(I) mixed-ligand complexes of the type Cu(X)(N∩N)(PCN), 3–10, where X = Cl or Br, N∩N = 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen), 5,6-dimethyl-1,10-phenanthroline ...(dmp), and dipyrido-3,2-d:2′,3′-f-quinoxaline (dpq), and PCN = tris-(2-cyanoethyl)phosphine, have been synthetized and characterized by NMR, ESI-MS, and X-ray diffraction on two representative examples, CuCl(phen)(PCN)·DMF (5·DMF) and CuBr(dpq)(PCN)·2DMF (10·2DMF). Cu(I) complexes were evaluated for their in vitro antitumor properties against a panel of human cancer cell lines, including cisplatin- and multidrug-resistant sublines. The most effective complex, CuCl(dpq)(PCN) (9), exhibited nanomolar cytotoxicity toward both sensitive and resistant cancer cells, but it significantly inhibited the growth of cultured normal cells. In vitro DNA assays and single cell gel electrophoresis revealed that 9 induced DNA fragmentation resulting in cell apoptosis. In parallel, fluorescence in situ hybridization (FISH) micronucleus assay attested high levels of genotoxicity following treatment of peripheral blood lymphocytes with complex 9, suggesting that the potential risk posed by diimine metal complexes should be carefully reconsidered.
A library of homoleptic mononuclear Ga(III) complexes of the general formula Ga(DTC)
, where DTC is an alicyclic or a linear dithiocarbamate chelator, is reported. The complexes were prepared in high ...yields starting from Ga(NO
)
·6H
O and fully characterized by elemental analysis and IR and NMR spectroscopy. Crystals of five of these complexes were obtained. The antitumor activity of the newly synthesized compounds against a panel of human cancer cell lines was evaluated. The chemical nature of the DTC does not have a marked impact on the structural features of the final compound. X-ray crystal structure analyses revealed that all these complexes have a trigonal prismatic geometry with three identical chelating DTCs coordinating the Ga(III) ion. It is noteworthy that in complex 22, Ga(NHEt)
(NHEt =
-ethyldithiocarbamate), the asymmetric unit is formed by two independent and structurally different molecules. Cellular studies showed that all the synthesized Ga-DTC complexes exhibit marked cytotoxic activity, even against human colon cancer cells that are less sensitive to cisplatin. Among the tested compounds, 6 (Ga(CEPipDTC)
, CEPipDTC = (ethoxycarbonyl)-piperidinedithiocarbamate) and 21 (Ga(Pr-13)
, PR13 = 4 and
-(2-ethoxy-2-oxoethyl)-
-methyldithiocarbamate) are very promising derivatives, but they have no selectivity towards cancer cells. Nevertheless, the obtained data provide a foundation for developing gallium-dithiocarbamate complexes as anticancer agents.
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