196,100 research outputs found
Self-assembly of polyoxoselenitopalladate nanostars [Pd15(μ3-SeO3)10(μ3-O)10Na]9- and their supramolecular pairing in the solid state
No full textAn anionic Pd15-oxo-cluster [Pd15(l3-SeO3)10(l3-O)10Na]9- has
been synthesized. It is the result of an unprecedented selfassembly
of Pd2+ and Na+ cations, SeO3
2- and oxo anions.
It has been found for the first time, that selenito groups can
give rise to supramolecular interactions in the solid state with
palladium atoms, through the selenium electron lone pairs
Oxidative Addition of Iodomethane to Charge-Tuned Rhodium(I) Complexes
No full textThe zwitterionic Rh(I) monocarbonyl complex [Rh(EtSNS)(CO)] (1, EtSNS =EtNC(S)Ph(2)P=NPPh(2)C(S)NEt(-)) was reacted with iodomethane in dichloromethane, yielding the stable acetyl-Rh(III) complex [Rh(EtSNS)(COCH(3))I] (4). Complex 4 was characterized in solution and in the solid state by X-ray diffraction analysis.. The rate constant of the reaction [5.48 (7) x 10(-2) M(-1) s(-1) at 25 degrees C CH(2)Cl(2)] and the activation parameters Delta H(double dagger) [28(3) kJ mol(-1)] and Delta S(double dagger)[-173(10) J mol(-1) K(-1)] were determined, confirming a nucleophilic addition mechanism. The rate constant was obtained by monitoring the acetylic product by (1)H NMR, under second-order conditions ([Rh]/[CH(3)I]=1). Complex 1 can be mono- and biprotonated with HX (X=PF(6), OTf, NO(3)), forming [Rh(HEtSNS)(CO)]X (2 center dot X) and [Rh(H(2)EtSNS)(CO)]X(2) (3 center dot X(2)), respectively. A decrease of the calculated DFT Mulliken atomic population on the Rh atom is observed along the series 1 > 2 > 3 in accordance with the variation of the coordinated CO stretching frequency. Compounds 2 center dot X were also reacted with iodomethane, forming complexes [Rh(HEtSNS)(COCH(3))I]X (5 center dot X), stable in solution for a short time, that transform by deprotonation into 4 and into unidentified decomposition products. The rate constants were determined under pseudo-first-order conditions due to the lower reactivity [2 center dot NO(3)=24.6 (6) x 10(-5) M(-1) s(-1); 2 center dot OTf=12.7 (3) x 10(-5) M(-1) s(-1); 2 center dot PF(6)=2.50 (6) x 10(-5) M(-1) s(-1)]. The activation parameters for 2 center dot PF(6) were also determined. The influence of the counterion could be explained assuming that the different non-metal-coordinated anions form hydrogen bonding with the NH group of 2 center dot X, which in turn causes a variation of the electron density on the Rh center. A good correlation between the CO stretching frequencies and the rate constants was observed. The experimental rate constant for complex 1 is 1 order of magnitude higher than the one calculated using the linear regression function obtained for the 2 center dot X series (experimental=5.48 x 10(-2) M(-1) s(-1); calculated=1.29 x 10(-3) M(-1) s-(1)), pointing out that the monoprotonated complexes react more slowly than expected. Both steric and electronic effects were examined and held responsible for this reduced reactivity. Complexes 3 center dot X(2) reacted too slowly, yielding complex 4 and unidentified decomposition products, hindering the determination of the rate constants
Oral escalating dose of cyclosporine-a combined with 4-epidoxorubicin in advanced colorectal-cancer - a phase-I study.
No full textMultidrug resistance, a major factor in the resistance to drugs, can be reversed by cyclosporin A. It is generally given by intravenous route. The aim of the present study was to assess the possibility of achieving useful plasma levels, giving cyclosporin A orally in advanced colorectal cancer patients treated with 4-epidoxorubicin. Cyclosporin A was given orally twice a day, for four days. The starting study dose was 5 mg/kg. Dose in cohorts of 3 patients was escalated to 10, 15, 20, 30, 40 mg/kg if the previous dose was not able to determine the target blood level (2,000 ng/ml). Cyclosporin A blood levels were analyzed by a specific fluorescence polarization immunoassay method (TDx; Abbot Laboratoires, North Chigaco, IL). 4-epidoxorubicin was given at a fixed dose of 75 mg/m(2), every 3 weeks. None of the dose levels of cyclosporin A given orally produced the target blood level. Only two patients, receiving cyclosporin at a dose of 30 mg/kg, and two after a CsA dose of 40 mg/kg, presented blood levels higher than 1,000 ng/ml, but however, lower than 1,500 ng/ml. In conclusion, the oral route of administration of cyclosporin does not seem recommendable in order to reverse multidrug resistance because it is not able to produce sufficient plasma levels
Reactivity of the zwitterionic ligand EtNHC(S)Ph2PNPPh 2C(S)NEt towards [Ru3(CO)12]. Sulfur transfer and ligand fragmentation leading to the methideylamide [-N(Et)-CH(R)-] μ3-bridging moiety
No full textThe reaction of EtNHC(S)Ph2PNP+Ph2C(S) N-Et (HEtSNS) with [Ru3(CO)12] has been carried out under two different experimental conditions: in the first case [Ru 3(CO)12], previously turned into the labile intermediate [Ru3(CO)10(CH3CN)2], afforded, at room temperature in dichloromethane, the trinuclear clusters [Ru 3(CO)11(CNEt)] (1), {Ru3(CO) 9(μ-H)[(μ-S:κ-P)Ph2PNPPh2C(S)NEt]} (2), {Ru3(CO)9(μ-H)[(μ-S:κ-P)Ph 2PNP(S)Ph2]} (3) and {Ru3(CO) 10[(μ-κ2P)Ph2PNHPPh2]} (4). Ligand fragmentation occurs via loss of EtNC or EtNCS, without sulfur transfer to the cluster core. In the second case, [Ru3(CO)12] reacted with HEtSNS in toluene at 70 °C, giving the trinuclear clusters 4, {Ru3(CO)7(CNEt)(μ3-S)[(μ2-N: η1-C:κ1-P)Ph2PNPPh 2C(H)NEt]} (5), {Ru3(CO)8)(μ3-S) [(μ2-N:η-C:κ-P)Ph2PNPPh2C(H)NEt]} (6) and {Ru3(CO)6(μ3-CO)(μ3-S) (EtNC)[(μ-κ2P) Ph2PNHPPh2]} (7). The last three compounds derive from ligand fragmentation and sulfur transfer to the metal cluster. All compounds were characterized by spectroscopy (NMR, IR) and the molecular structures of 2, 5 and 7 were determined by single-crystal X-ray diffraction. Cluster 2 preserves the original Ru3 triangular core in which an edge is bridged by a hydride ligand and by the sulfur atom of the Ph2PNPPh2C(S)NEt ligand. Cluster 5 shows an open triangle of Ru atoms capped by a μ3-sulfide and by the unprecedented methideylamide -N(Et)CH(R)-μ3-bridging moiety of the Ph 2PNPPh2C(H)NEt ligand. It formally derives from cluster 6 by substitution of ethyl isonitrile with one CO molecule. Finally, cluster 7 displays a Ru3(μ3-S)(μ3-CO) trigonal bipyramidal core. © 2009 The Royal Society of Chemistry
Suppression of β-Hydride Chain Transfer in Nickel(II)-Catalyzed Ethylene Polymerization via Weak Fluorocarbon Ligand–Product Interactions
No full textThe synthesis and characterization of two neutrally charged Ni(II) ethylene polymerization catalysts, [2-tert-butyl-
6-((2,6-(3,5-dimethylphenyl)phenylimino)methyl)phenolato]nickel(II) methyl trimethylphosphine ((CH3)FI-Ni) and [2-tertbutyl-
6-((2,6-(3,5-bis(trifluoromethyl)phenyl)phenylimino)methyl)phenolato]nickel(II) methyl trimethylphosphine ((CF3)FINi)
are reported. In the presence of a Ni(COD)2 cocatalyst, these catalysts produce markedly different polyethylenes: densely
branched oligomers with Mw = 1.4 × 103 g mol−1 for (CH3)FI-Ni vs lightly branched polyethylenes with Mw = 92 × 103 g mol−1 for
(CF3)FI-Ni and with ∼6.5× the polymerization activity and with much greater performance thermal stability. HOESY 2D 19F,1H
NMR spectra of a model Ni-ethyl compound, [2-tert-butyl-6-((2,6-(3,5-bis(trifluoromethyl)phenyl)phenylimino)methyl)phenolato]-
nickel(II) ethyl 2,4-lutidine ((CF3)FI-Ni-Et), indicate non-negligible Cβ−Hβ···F3C through-space dipolar interactions, and molecular
modeling reveals that Cβ−Hβ···F(C) distances can be as small as ∼2.61 Å during the polymerization process. Furthermore, there is no
structural or spectroscopic evidence for fluorocarbon inductive effects on the structure, bonding, and reactivity of these complexes, and
a catalyst with CF3 introduced β to the imino N produces only low-Mw oligomers with low activity. These results argue that weak
(ligand)C−F···H−C(polymer) interactions can significantly influence the chain transfer characteristics of these catalysts
Synthesis, Structural Characterization, and Magnetic Properties of the Heteroleptic Dinuclear Nickel Selenite Complex [{Ni(TMEDA)SeO3}2]
No full textCoordination properties of the multifunctional S,N,S zwitterionic ligand EtNHC(S)Ph2P=NPPh2C(S)NEt
No full textThe reaction of trialkylphoshanes and amino-phosphanes with isothiocyanates yields adducts containing
the zwitterionic thioamidyl-phosphonium P+C(S)N− functional group. Ligands containing this group were
not previously studied, probably due to their instability towards dissociation, in the presence of metal
species able to coordinate the P atom. The ligand EtNHC(S)Ph2P NPPh2C(S)NEt (HEtSNS) was obtained
by reaction of Ph2PNHPPh2 with ethylisothiocyanate and proved to be very versatile: it can be protonated
giving cation H2EtSNS+ and deprotonated forming the dianion–cation EtSNS−. HEtSNS and its derivatives
behave as ligands showing five possible coordination fashions, S,N,S tridentate and S,S-bidentate (with a
bite-angle varying from 180◦ to 90◦), S-monodentate, S,S bridging andN,N,Ninteraction. Here we describe
the coordination chemistry of HEtSNS, in particular towards Rh, Cu, Ag and Au, and some properties of
its complexes which are still the only examples containing the P+C(S)N− zwitterionic grou
A Neutrally Charged Trimethylmanganese(III) Complex: Synthesis, Characterization, and Disproportionation Chemistry
No full textDr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
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