Ligand Transfer Research Articles

Reduction of Nitriles to Amines with H2 Catalyzed by Nonclassical Ruthenium Hydrides – Water‐Promoted Selectivity for Primary Amines and Mechanistic Investigations

AbstractCatalytic hydrogenation of nitriles to amines by nonclassical ruthenium hydride complexes derived from PNP pincer ligands is described. Aromatic as well as aliphatic nitriles are reduced to the corresponding primary amines. Hydrogen pressure influences the selectivity for the primary amines. The mechanism of nitrile reduction with nonclassical ruthenium hydride pincer complexes is investigated by DFT calculations. A catalytic cycle involving the coordination of nitrile trans to the pincer backbone after an initial hydride rearrangement at the ruthenium center, and the subsequent first transfer of the hydride ligand to the carbon center of the nitrile ligand is suggested as a possible reaction mechanism. Interestingly, the use of water as additive increases the selectivity for the primary amines and the rate of the reactions.

An open aperture z-scan study of Sr 2CeO 4 blue phosphor

Sr 2CeO 4 blue phosphor has been prepared by the solid-state reaction method. The X-ray diffraction (XRD) study confirms the structure of the system to be orthorhombic. High resolution electron transmission microscopy reveals that Sr 2CeO 4 prepared by the solid state reaction method is composed of elongated spherical structures of length ∼0.2–0.6 μm and width ∼90–150 nm. The excitation spectrum shows a broad band which peaks at 275 nm. The emission spectrum shows a broad band which peaks at 467 nm when excited at 275 nm. The emission band is assigned to the energy transfer between the molecular orbital of the ligand and charge transfer (CT) state of the Ce 4+ ion. The Commission International de l’Eclairage (CIE) co-ordinates are x = 0.15, and y = 0.23. The nonlinear absorption behavior of Sr 2CeO 4 has been investigated using the open aperture z-scan technique. The calculated effective two-photon absorption coefficient shows that the Sr 2CeO 4 blue phosphor is a promising optical limiting material.

A new synthetic pathway of Sr 2CeO 4 phosphor and its characterization

A blue–white emitting Sr 2CeO 4 phosphor was synthesized via a simple sol–gel poly vinyl alcohol (PVA)-complexing process using strontium nitrate and cerium nitrate as raw materials. The samples were characterized by TG/DTA, XRD, FTIR, SEM and photoluminescence spectroscopy. The X-ray diffraction study confirms the structure of the system to be orthorhombic. The emission spectra when excited at 267 nm peaks at ∼470 nm. The emission band is assigned to the energy transfer between the molecular orbital of the ligand and charge transfer state of the Ce 4+ ion. The Commission International de l'Eclairage (CIE) co-ordinates for the Sr 2CeO 4 sample were also calculated.

Interaction of enterocyte FABPs with phospholipid membranes: Clues for specific physiological roles

Intestinal and liver fatty acid binding proteins (IFABP and LFABP, respectively) are cytosolic soluble proteins with the capacity to bind and transport hydrophobic ligands between different sub-cellular compartments. Their functions are still not clear but they are supposed to be involved in lipid trafficking and metabolism, cell growth, and regulation of several other processes, like cell differentiation. Here we investigated the interaction of these proteins with different models of phospholipid membrane vesicles in order to achieve further insight into their specificity within the enterocyte. A combination of biophysical and biochemical techniques allowed us to determine affinities of these proteins to membranes, the way phospholipid composition and vesicle size and curvature modulate such interaction, as well as the effect of protein binding on the integrity of the membrane structure. We demonstrate here that, besides their apparently opposite ligand transfer mechanisms, both LFABP and IFABP are able to interact with phospholipid membranes, but the factors that modulate such interactions are different for each protein, further implying different roles for IFABP and LFABP in the intracellular context. These results contribute to the proposed central role of intestinal FABPs in the lipid traffic within enterocytes as well as in the regulation of more complex cellular processes.

Cyanide and Carbon Monoxide Ligand Formation in Hydrogenase Biosynthesis

AbstractThe inside cover picture shows a schematic representation of [FeFe]‐hydrogenase maturation in a microbial community in a geothermal hot spring of Yellowstone National Park, USA. In the stepwise formation of the active site H‐cluster (lower right) of the [FeFe]‐hydrogenase, carbon monoxide and cyanide ligands are synthesized from tyrosine through a radical SAM reaction catalyzed by HydG (lower left, shown here as a ribbon diagram based on a homology model). The synthesis and transfer of these diatomic ligands to the H‐cluster during hydrogenase maturation is discussed in detail in the Microrevierw by John W. Peters, Joan B. Broderick et al. (p. 935 ff ). Photograph and superimposed artwork by courtesy of Kevin Swanson.

Improved Immunological Tolerance Following Combination Therapy with CTLA-4/Ig and AAV-Mediated PD-L1/2 Muscle Gene Transfer

Initially thought as being non-immunogenic, recombinant AAVs have emerged as efficient vector candidates for treating monogenic diseases. It is now clear however that they induce potent immune responses against transgene products which can lead to destruction of transduced cells. Therefore, developing strategies to circumvent these immune responses and facilitate long-term expression of transgenic therapeutic proteins is a main challenge in gene therapy. We evaluated herein a strategy to inhibit the undesirable immune activation that follows muscle gene transfer by administration of CTLA-4/Ig to block the costimulatory signals required early during immune priming and by using gene transfer of PD-1 ligands to inhibit T cell functions at the tissue sites. We provide the proof of principle that this combination immunoregulatory therapy targeting two non-redundant checkpoints of the immune response, i.e., priming and effector functions, can improve persistence of transduced cells in experimental settings where cytotoxic T cells escape initial blockade. Therefore, CTLA-4/Ig plus PD-L1/2 combination therapy represents a candidate approach to circumvent the bottleneck of immune responses directed toward transgene products.

Organomercury(ii) and tellurium(ii) compounds with the “pincer” ligand 2,6-[O(CH2CH2)2NCH2]2C6H3– stabilization of an unusual organotellurium(ii) cationic species

The reaction of RH (1) with Hg(OAc)(2), in EtOH, gave the acetate RHgOAc (2) [R = 2,6-[O(CH(2)CH(2))(2)NCH(2)](2)C(6)H(3)]. The corresponding RHgCl (3) was obtained from 2 and LiCl. The reaction of 3 with TeCl(4) (1:1 molar ratio), in anhydrous 1,4-dioxane, resulted in the transfer of the organic ligand from mercury to tellurium and the isolation of the unexpected ionic compounds [RTe](2)[Hg(2)Cl(6)] (4) and [RH(3)][HgCl(4)] (5). The molecular structures of 1-4 and 5·H(2)O were established by single-crystal X-ray diffraction. The acetate 2 and the chloride 3 are monomeric in solid state. In both mercury and tellurium organometallic compounds the organic group acts as an (N,C,N) "pincer" ligand. This coordination pattern provided stability for the rare [RTe](+) cation. Weak cation-anion interactions [Te···Cl 3.869(3) Å] are present between [RTe](+) and the dinuclear anion [Hg(2)Cl(6)](2-) in the crystal of 4. Theoretical calculations with DFT methods were performed for models of 3 and 4. The results show that in the cation of 4 the coordination of the nitrogen atoms play an important role for the stabilization of the structure found in the crystal whereas in 3 the coordination of the nitrogen atoms to the metal centre stabilizes to a less extent the structure found in solid state.

Metal–ligand bifunctional activation and transfer of N–H bonds

The concept of metal-ligand bifunctionality can be employed for an efficient activation of N-H bonds by well-defined ruthenium amido complexes. An enantioselective catalytic aza-Michael reaction was developed on the basis of this process, which gives rise to indoline β-amino acids.

Transition metal complexes of the pentacyanocyclopentadienide anion

The ready formation of a range of transition metal complexes of the pentacyanocyclopentadienide anion via ligand transfer reactions employing Na[C(5)(CN)(5)] indicates that the [C(5)(CN)(5)](-) anion has an extensive transition metal coordination chemistry and is not such a weakly coordinating anion.

The Contribution of Surface Residues to Membrane Binding and Ligand Transfer by the α-Tocopherol Transfer Protein (α-TTP)

Previous work has shown that the α-tocopherol transfer protein (α-TTP) can bind to vesicular or immobilized phospholipid membranes. Revealing the molecular mechanisms by which α-TTP associates with membranes is thought to be critical to understanding its function and role in the secretion of tocopherol from hepatocytes into the circulation. Calculations presented in the Orientations of Proteins in Membranes database have provided a testable model for the spatial arrangement of α-TTP and other CRAL–TRIO family proteins with respect to the lipid bilayer. These calculations predicted that a hydrophobic surface mediates the interaction of α-TTP with lipid membranes. To test the validity of these predictions, we used site-directed mutagenesis and examined the substituted mutants with regard to intermembrane ligand transfer, association with lipid layers and biological activity in cultured hepatocytes. Substitution of residues in helices A8 (F165A and F169A) and A10 (I202A, V206A and M209A) decreased the rate of intermembrane ligand transfer as well as protein adsorption to phospholipid bilayers. The largest impairment was observed upon mutation of residues that are predicted to be fully immersed in the lipid bilayer in both apo (open) and holo (closed) conformations such as Phe165 and Phe169. Mutation F169A, and especially F169D, significantly impaired α-TTP-assisted secretion of α-tocopherol outside cultured hepatocytes. Mutation of selected basic residues (R192H, K211A, and K217A) had little effect on transfer rates, indicating no significant involvement of nonspecific electrostatic interactions with membranes.

Platinum Complex Catalyzed Decomposition of Formic Acid

AbstractThe decomposition of formic acid catalyzed by a cationic hydridoplatinum tetradentate phosphane complex was studied by NMR spectroscopy, isotope labeling and DFT calculations. In the initial step dihydrogen is formed by the reaction of the formic acid with the hydrido ligand yielding a platinum formate cation. The formato ligand is then transformed to CO2 by a β‐H transfer of the formate C–H bond to the Pt center revealing the initial cationic Pt–H complex. The reaction sequence was illuminated by deuterium and C‐13 isotope labeling revealing the cationic Pt–D complex as only Pt complex product if a deuterated formate ligand was used. The transfer of the hydrido ligand to an ensuing coordination site at the Pt center is assisted by the labile bonding character of the phosphane ligand. The activation energy was calculated to be +110 kJ/mol above the initial formate complex. The decomposition reaction was observed to be completely reversible yielding formic acid from CO2 and H2 at a pressure of around 40 bar. Thus, this reaction provides an excellent example for dihydrogen storage and release on demand using a Pt complex as catalyst.

Divergent reactivity of [(κ 3-L)ThCl 2(dme)] with Grignard reagents: Alkylation, ancillary ligand transfer to magnesium, and halide exchange caught in the act

Reaction of [(BDPP)ThCl 2(dme)] ( 1) with 2 equivalents of MeMgBr in OEt 2, followed by filtration and layering a toluene solution with hexanes at −30 °C yielded a single large crystal of [{(BDPP)ThX(μ-X) 2Mg(OEt 2)(μ-Me)} 2]·2 toluene (X = Br 0.73–0.87/Cl 0.13–0.27; 3·2 toluene). This product is the result of halide exchange to form a partially brominated neutral thorium species, which is adducted with MeMgX(OEt 2). The complex is then tetrametallic as a result of Mg–Me–Mg bridges. The structure of complex 3 provides direct insight into the process by which halide exchange takes place between electrophilic metal halide complexes and Grignard reagents. This reactivity stands in stark contrast to the reactions of 1 and [(XA 2)ThCl 2(dme)] ( 2) with PhCH 2MgCl. In these cases the expected dialkyl products, [LTh(CH 2Ph) 2] [L = BDPP ( 4) and XA 2 ( 5)], were formed under most conditions. However, addition of a PhCH 2MgCl solution to 2 at −78 °C and warming to room temperature after 5 minutes gave [(XA 2)Mg(dme)] ( 6), the product of ancillary ligand transfer from thorium to magnesium, in 30–50% yield.

Anti-tumor activity of gene transfer of the membrane-stable CD40L mutant into lung cancer cells

Gene transfer of CD40 ligand (CD40L) holds promise as a novel therapy for lymphoid malignancies and a number of solid carcinomas because of its multiple anti-tumor activities. However, membrane-bound CD40L can be cleaved into a soluble form, sCD40L, which contributes to systemic inflammatory and cardiovascular diseases, and induces survival signals in the absence of protein synthesis block, suggesting a deleterious side effect of CD40L gene therapy. We generated a plasmid encoding non-cleavable human CD40L mutant (pcDNA3.1+-CD40L-M) to determine the direct anti-proliferative and pro-apoptotic effects in CD40-positive lung adenocarcinoma cell line A549, to verify activation of immature dentritic cells (DCs) by co-cultivation with the transfected A549 cells and to evaluate the lower expression of sCD40L relative to that of wild-type CD40L (CD40L-WT) transfectant in cell-free supernatants. These studies suggest that gene transfer of the membrane-stable CD40L mutant into CD40-positive cells may provide an efficient and safe method to treat non-small cell lung cancer.

ChemInform Abstract: Clusters Containing Carbene Ligands. Novel Example of Carbene Ligand Transfer from a Metal Atom to a Carbon Atom.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Bionanoprobes with Excellent Two‐Photon‐Sensitized Eu3+ Luminescence Properties for Live Cell Imaging

Bioimaging or bioanalysis based on nanoprobes encapsulating Eu 3 + complexes with excellent two-photon-sensitized (TPS) luminescence properties combines the advantages of deep penetration, high sensitivity, high signal-to-noise ratio, stable signals during long term observation, low photodamage to biological samples, and desirable target recognizability. The TPS luminescence of lanthanide complexes is produced through the two-photon excitation (TPE) of a lightharvesting antenna ligand and subsequent excitation energy transfer (EET) to the metal ions, which provides a promising manner for extending the excitation windows of lanthanide complexes to the near-infrared (NIR) light wavelength region. In the last two decades, remarkable progress has been achieved in the design and synthesis of two-photonsensitized luminescent lanthanide complexes. [1] Several lanthanide complexes have been applied to the multiphoton-excited bioimaging of cells. [2–4] Due to the characteristic luminescence properties of Eu 3 + complexes, such as the characteristic narrow-line emission in the red-light wavelength region with acceptable transparence for many biosamples, high luminescence quantum yields, large Stokes shifts, and long luminescence lifetime (millisecond order), the TPS Eu 3 + luminescence is of significance for developing bioanal

Natural ligand binding and transfer from liver fatty acid binding protein (LFABP) to membranes

Liver fatty acid-binding protein (LFABP) is distinctive among fatty acid-binding proteins because it binds more than one molecule of long-chain fatty acid and a variety of diverse ligands. Also, the transfer of fluorescent fatty acid analogues to model membranes under physiological ionic strength follows a different mechanism compared to most of the members of this family of intracellular lipid binding proteins. Tryptophan insertion mutants sensitive to ligand binding have allowed us to directly measure the binding affinity, ligand partitioning and transfer to model membranes of natural ligands. Binding of fatty acids shows a cooperative mechanism, while acyl-CoAs binding presents a hyperbolic behavior. Saturated fatty acids seem to have a stronger partition to protein vs. membranes, compared to unsaturated fatty acids. Natural ligand transfer rates are more than 200-fold higher compared to fluorescently-labeled analogues. Interestingly, oleoyl-CoA presents a markedly different transfer behavior compared to the rest of the ligands tested, probably indicating the possibility of specific targeting of ligands to different metabolic fates.

Copper(I) Iodide Polyphosphine Adducts at Low Loading for Sonogashira Alkynylation of Demanding Halide Substrates: Ligand Exchange Study between Copper and Palladium

The prestabilization of copper iodide with a multidentate ferrocenyl phosphine ligand promotes the palladium-catalyzed cross-coupling of demanding halides with phenylacetylene in a selective way. Novel CuI-triphosphine adducts are described in the solid state and in solution. Their use allowed the introduction of the copper iodide cocatalyst in unprecedented low amounts (0.4 to 0.1 mol %) in systems also employing low amounts of “ligand-free” [PdII(η3-allyl)Cl]2 precursor (0.2 to 0.05 mol %). The scope of substrates is reported, and electronically or sterically deactivated bromides were efficiently coupled. Concerning aryl chlorides, electron-poor activated substrates were also coupled using this innovative low-metal-content catalytic system. Some rarely tackled mechanistic aspects are discussed herein. In particular, the transfer of ligand from copper to palladium monitored by NMR was found to be different depending on the polyphosphine ligand. The inhibition of diyne formation was also an interesting fe...

Roles of the Distinct Electronic Structures of the {Fe(NO)2}9 and {Fe(NO)2}10 Dinitrosyliron Complexes in Modulating Nitrite Binding Modes and Nitrite Activation Pathways

Nitrosylation of [PPN](2)[(ONO)(2)Fe(eta(2)-ONO)(2)] [1; PPN = bis(triphenylphosphoranylidene)ammonium] yields the nitrite-containing {Fe(NO)}(7) mononitrosyliron complex (MNIC) [PPN](2)[(NO)Fe(ONO)(3)(eta(2)-ONO)] (2). At 4 K, complex 2 exhibits an S = (3)/(2) axial EPR spectrum with principal g values of g( perpendicular) = 3.971 and g( parallel) = 2.000, suggestive of the {Fe(III)(NO(-))}(7) electronic structure. Addition of 1 equiv of PPh(3) to complex 2 triggers O-atom transfer of the chelating nitrito ligand under mild conditions to yield the {Fe(NO)(2)}(9) dinitrosyliron complex (DNIC) [PPN][(ONO)(2)Fe(NO)(2)] (3). These results demonstrate that both electronic structure [{Fe(III)(NO(-))}(7), S = (3)/(2)] and redox-active ligands ([RS](-) for [(RS)(3)Fe(NO)](-) and [NO(-)] for complex 2) are required for the transformation of {Fe(NO)}(7) MNICs into {Fe(NO)(2)}(9) DNICs. In comparison with the PPh(3)-triggered O-atom abstraction of the chelating nitrito ligand of the {Fe(NO)(2)}(9) DNIC [(1-MeIm)(2)(eta(2)-ONO)Fe(NO)(2)] (5; 1-MeIm = 1-methylimidazole) to generate the {Fe(NO)(2)}(10) DNIC [(1-MeIm)(PPh(3))Fe(NO)(2)] (6), glacial acetic acid protonation of the N-bound nitro ligand in the {Fe(NO)(2)}(10) DNIC [PPN][(eta(1)-NO(2))(PPh(3))Fe(NO)(2)] (7) produced the {Fe(NO)(2)}(9) DNIC [PPN][(OAc)(2)Fe(NO)(2)] (8), nitric oxide, and H(2)O. These results demonstrate that the distinct electronic structures of {Fe(NO)(2)}(9/10) motifs [{Fe(NO)(2)}(9) vs {Fe(NO)(2)}(10)] play crucial roles in modulating nitrite binding modes (O-bound chelating/monodentate nitrito for {Fe(NO)(2)}(9) DNICs vs N-bound nitro as a pi acceptor for {Fe(NO)(2)}(10) DNICs) and regulating nitrite activation pathways (O-atom abstraction by PPh(3) leading to the intermediate with a nitroxyl-coordinated ligand vs protonation accompanied by dehydration leading to the intermediate with a nitrosonium-coordinated ligand). That is, the redox shuttling between the {Fe(NO)(2)}(9) and {Fe(NO)(2)}(10) DNICs modulates the nitrite binding modes and then triggers nitrite activation to generate nitric oxide.

Platinum Complexes with Picoline-functionalized Benzimidazolin-2-ylidene Ligands

The dicarbene platinum complexes of the type [Pt(L)2]Br2 [5]Br2 - [8]Br2 (L = N-alkyl-N´- picolylbenzimidazolin-2-ylidene) have been prepared by two different methods. The in situ deprotonation of picoline-functionalized benzimidazolium salts 1 - 4 with platinum acetylacetonate gave the platinum complexes [5]Br2 - [8]Br2 in good yields. Complex [8]Br2 has also been obtained by a ligand transfer reaction from the silver dicarbene complex [9][AgBr2]. Attempts to cystallize [8]Br2 obtained from the carbene transfer reaction led to the isolation of the previously undetected monocarbene complex [Pt(Cl)2L] (10) which contains only one picoline-functionalized carbene ligand coordinating in a chelating fashion to the metal center

Synthesis and Structure of Magnesium and Group 13 Metal Bis(thiophosphinoyl)methanediide Complexes

Metalations of bis(diphenylthiophosphinoyl)methane, CH2(PPh2═S)2, with equimolar BunLi or Bun2Mg in THF afforded [Li{(S═PPh2)2CH}(THF)(Et2O)] (1) and [MgC(PPh2═S)2(THF)]2 (2), respectively. Compound 1 with a group 13 metal chloride MCl3 (M = Al, Ga, In) gave the methanediide complex [MCl{C(PPh2═S)2}]2 (M = Al (3), Ga (4), In (5)). Compounds 3−5 are believed to be formed by ligand transfer reaction followed by dehydrochlorination. X-ray structures of 1−5 have been determined. It was found that the magnesium complex 2 has a similar structure to the group 13 metal analogues 3−5.