Ligand Coupling Research Articles

P–C and C–C Coupling Processes in the Reactions of the Phosphinidene-Bridged Complex [Fe2(η5-C5H5)2(μ-PCy)(μ-CO)(CO)2] with Alkynes

The title complex reacts with excess HC≡C(p-tol) at room temperature to give selectively the complex [Fe2Cp{μ–η5:κ1-C5H4PCyCHCH(p-tol)}(CO)3] (Fe–Fe = 2.6930(7) Å), which displays a bridging (cyclopentadienylidene)(alkenyl)phosphine ligand resulting from an unprecedented coupling of the phosphinidene ligand to both the alkyne and one of the cyclopentadienyl (Cp) groups. At 348 K, however, a mixture is obtained of the above compound and two isomers of the phosphide-acyl complex [Fe2Cp2{μ–κ1:κ1,η1-CyPCHC(p-tol)C(O)}(μ-CO)(CO)] differing in the relative orientation of the Cp rings with respect to the Fe2P plane (Fe–Fe = 2.6069(8) Å in the cis isomer). The latter complex is decarbonylated photochemically to give the dicarbonyl derivative [Fe2Cp2{μ–η3:η1-PCyCHC(p-tol)}(μ-CO)(CO)], which displays a rare four-electron donor phosphaallyl ligand bridging the dimetal center. The stoichiometric reaction with dimethyl acetylenedicarboxylate proceeded analogously to yield the complexes [Fe2Cp{μ–η5:κ1-C5H4PCyC(CO2Me)CH(CO2Me)}(CO)3] and [Fe2Cp2{μ–κ1:κ1,η1-CyP(CO2Me)C(CO2Me)C(O)}(μ-CO)(CO)]. However, the reaction with 2 equiv of alkyne at 273 K gave selectively the dicarbonyl complex [Fe2Cp2{μ–κ1:η2-PCy(CCO2Me)4}(μ-CO)2] with a four-electron-donor phosphole ligand bridging the metal atoms derived from the coupling of the phosphinidene ligand with two alkyne molecules. The reactions with methyl propiolate turned out to be particularly complex since several compounds were formed in significant amounts depending on the reaction conditions. The (cyclopentadienylidene)(alkenyl)phosphine complex [Fe2Cp{μ–η5:κ1-C5H4PCyCHCH(CO2Me)}(CO)3] was selectively formed in the reaction with 2 equiv of alkyne in toluene at 348 K, whereas the slow addition of a dichloromethane solution of the title complex to a solution of 2 equiv of alkyne in the same solvent at 273 K led to the exclusive formation of the (alkenyl)(alkynyl)phosphine complex [Fe2Cp2(μ-CO)2(CO){κ1-PCy(C2H2CO2Me)(C2CO2Me)}] (Fe–Fe = 2.5246(8) Å in the cis isomer). All these products seem to follow from of a common zwitterionic intermediate resulting from the nucleophilic attack of the pyramidal phosphinidene ligand of the title complex to the less protected α carbon of the alkyne, which then evolves differently depending on the alkyne and experimental conditions.

Chemical cross-linking of HIV-1 Env for direct TLR7/8 ligand conjugation compromises recognition of conserved antigenic determinants

Covalent conjugation of immune-stimulatory compounds to protein antigens is a potential means to self-adjuvant non-replicating subunit vaccines. Previously, it was demonstrated that covalent coupling of a Toll-like receptor (TLR) ligand to the exterior HIV-1 envelope glycoprotein, gp120, enhanced its immunogenicity. However, the consequences of chemical conjugation to gp120 on broadly neutralizing antibody (bNAb) epitopes were so far not examined. Here, we conjugated a TLR7/8 ligand to lysine residues on gp120 using NHS-PEO8-maleimide linkers and investigated if this affected Ab recognition of the CD4 binding site (CD4bs), a highly conserved target for bNAbs. We demonstrate that the recognition of the CD4bs was reduced following coupling, especially at a higher coupling ratio. These results have implications for the coupling of ligands to vaccine antigens where elicitation of humoral immune responses to specific neutralizing determinants is desired.

Synthesis and characterization of biomimetic nanogels for immunorecognition

Biomimetic nanoparticles are promising materials for biomedical and biotechnological applications. Cationic poly(N-isopropylacrylamide) (PNIPAM) nanogels containing charged amine groups brought by addition of 2-aminoethylmethacrylate hydrochloride (AEMH) or N-(3-aminopropyl) methacrylamide hydrochloride (APMH) as co-monomers were prepared by surfactant-free precipitation polymerization. The influence of the relative amount and mode of addition of the co-monomer on both the size and the amine group density of the nanogel particles was studied. Two nanogels, one prepared using APMH (1%mol/mol NIPAM, in batch) and another with AEMH (2%mol/mol NIPAM, by shot addition) as co-monomers, were selected for the covalent coupling of a Protein L-mimic ligand to free amine groups on the particles. The ability of the synthesized biomimetic nanoparticles for recognizing and binding human IgG (hIgG) molecules was assessed and the selectivity toward immunoglobulin molecules evaluated.

Subunit Variation to Uncover Properties of Polyazine-Bridged Ru(II), Pt(II) Supramolecules with Low Lying Charge Separated States Providing Insight into the Functioning as H2O Reduction Photocatalysts to Produce H2

Two new structurally diverse polyazine-bridged Ru(II),Pt(II) tetrametallic complexes, [{(Ph2phen)2Ru(dpp)}2Ru(dpp)PtCl2](PF6)6 (1a) and [{(Ph2phen)2Ru(dpp)}2Ru(dpq)PtCl2](PF6)6 (2a) (Ph2phen = 4,7-diphenyl-1,10-phenanthroline, dpp = 2,3-bis(2-pyridyl)pyrazine, dpq = 2,3-bis(2-pyridyl)quinoxaline), as well as their trimetallic precursors have been synthesized to provide a comparison for detailed analysis to elucidate component effects in the previously reported photocatalyst [{(phen)2Ru(dpp)}2Ru(dpq)PtCl2](PF6)6 (4a) (phen = 1,10-phenanthroline). Electrochemistry shows terminal Ru based highest occupied molecular orbitals (HOMOs) with remote BL' (BL' = bridging ligand coupling central Ru and cis-PtCl2 moiety) based lowest unoccupied molecular orbitals (LUMOs). Population of a lowest-lying charge separated ((3)CS) excited state with oxidized terminal Ru and reduced remote BL' via intramolecular electron transfer is predicted by electrochemical analysis and is observed through steady-state and time-resolved emission studies as well as emission excitation profiles which display unusual nonunity population of the lowest lying emissive Ru→dpp (3)MLCT (metal-to-ligand charge transfer) state. Each tetrametallic complex is an active photocatalyst for H2 production from H2O with 2a showing the highest activity (94 TON (turnover number) in 10 h, where TON = mol H2/mol catalyst). The nature of the bridging ligand coupling the trimetallic light absorber to the cis-PtCl2 moiety has a significant impact on the catalyst activity, correlated to the degree of population of the (3)CS excited state. The choice of terminal ligand affects visible light absorption and has a minor influence on photocatalytic H2 production from H2O. Evidence that an intact supramolecule functions as the photocatalyst includes a strong dependence of the photocatalysis on the identity of BL', an insensitivity to Hg(l), no detectable H2 production from the systems with the trimetallic synthons and cis-[PtCl2(DMSO)2] as well as spectroscopic analysis of the photocatalytic system.

Reactions of the σ,π-furyl complex [Fe2(CO)6(μ-Fu)(μ-PFu2)] (Fu = C4H3O) with phosphines: Carbonyl substitution, migratory carbonyl insertion and cyclometallation-induced furan elimination

The reactivity of the σ,π-furyl complex [Fe2(CO)6(μ-Fu)(μ-PFu2)] (1) towards PPh3 and a range of bidentate phosphines has been studied and a number of different reaction products have been identified. With PPh3, carbonyl substitution affords [Fe2(CO)5(PPh3)(μ-Fu)(μ-PFu2)] (2) in which the new phosphine is coordinated to the iron center that is σ-coordinated by the bridging furyl moiety. With small bite-angle diphosphines – bis(diphenylphosphino)methane (dppm) and 1,8-bis(diphenylphosphino)naphthalene (dppn) – carbonyl substitution and migratory carbonyl insertion result to give the furyl–acyl complexes with bridging, [Fe2(CO)4(μ-dppm)(μ-OCFu)(μ-PFu2)] (3), or chelating, [Fe2(CO)4(κ2-dppn)(μ-OC–Fu)(μ-PFu2)] (4), diphosphines, respectively. With the more flexible diphosphines Ph2P(CH2)nPPh2 (n = 2, dppe, n = 3, dppp), the cyclometallated products [Fe2(CO)5{μ,κ2-C6H4PPh(CH2)nPPh2}(μ-PFu2)] (n = 2, 5; n = 3, 6) are isolated as a result of carbonyl substitution and furan elimination, and a similar complex [Fe2(CO)5{μ,κ2-C6H4PPh(C6H4)PPh2}(μ-PFu2)] (7) is generated from the more rigid diphosphine bis(diphenylphosphino)benzene (dppb). With bis(diphenylphosphino)-1,1-binaphthalene (1,1-BINAP) the novel tridentate phosphine complex [Fe2(CO)5{μ,κ3-C6H4P(C20H12PPh2)C6H4PFu}] (8) results from the putative coupling of cyclometallated diphosphine and difurylphosphido ligands, following elimination of two equivalents of furan. The crystal structures of 2, 3, 5 and 8 have been determined and allow a detailed insight into the overall reaction profile.

Polyethylenimines for siRNA and miRNA delivery in vivo

The discovery of RNA interference (RNAi) as a naturally occurring mechanism for gene knockdown has attracted considerable attention toward the use of small interfering RNAs (siRNAs) for therapeutic purposes. Likewise, microRNAs (miRNAs) have emerged as important cellular regulators of gene expression, and their pathological underexpression allows for novel therapeutic strategies ('miRNA replacement therapy'). To address issues related to the instability, charge, and molecular weight of small RNA molecules, nanoparticle formulations have been explored for their in vivo application. Polyethylenimines (PEIs) are positively charged, linear, or branched polymers that are able to form nanoscale complexes with small RNAs, leading to RNA protection, cellular delivery, and intracellular release. This review highlights the important properties of various PEIs with regard to their use for in vivo RNA delivery. PEI modifications for increased efficacy, altered pharmacokinetic properties, improved biocompatibility and, upon covalent coupling of ligands, targeted delivery are described. An overview of various modified PEIs and a comprehensive list of representative studies using PEI-based siRNA or miRNA delivery in vivo are given.

Coupling of C-amino aza-substituted heterocycles with an isocyanide ligand in palladium(ii) complex

The reaction of cis-dichlorobis(2,6-xylylisocyanide)palladium(ii) with 2-aminopyrazine affords a binuclear palladium complex, in which one of the metal atoms is involved in the palladacyclic ligand. In the contrast, the coupling of isocyanide ligands in cis-dichlorobis-(2,6-xylylisocyanide)palladium(ii) with another C-amino aza-substituted heterocycle, viz.,4-acetyl-3-amino-5-methylpyrazole, gives a mononuclear cationic palladium diaminocarbene complex. Both compounds were characterized by elemental analysis, IR spectroscopy, 1H, 13C{1H}, DEPT90/DEPT135, and 1H,13C-HSQC/1H,13C-HMBC NMR spectroscopy, high-resolution electrospray ionization mass spectrometry, and X-ray diffraction.

Radiative and Nonradiative Lifetime Engineering of Quantum Dots in Multiple Solvents by Surface Atom Stoichiometry and Ligands

CdTe quantum dots have unique characteristics that are promising for applications in photoluminescence, photovoltaics or optoelectronics. However, wide variations of the reported quantum yields exist and the influence of ligand-surface interactions that are expected to control the excited state relaxation processes remains unknown. It is important to thoroughly understand the fundamental principles underlying these relaxation processes to tailor the QDs properties to their application. Here, we systematically investigate the roles of the surface atoms, ligand functional groups and solvent on the radiative and non-radiative relaxation rates. Combining a systematic synthetic approach with X-ray photoelectron, quantitative FT-IR and time-resolved visible spectroscopies, we find that CdTe QDs can be engineered with average radiative lifetimes ranging from nanoseconds up to microseconds. The non-radiative lifetimes are anticorrelated to the radiative lifetimes, although they show much less variation. The density, nature and orientation of the ligand functional groups and the dielectric constant of the solvent play major roles in determining charge carrier trapping and excitonic relaxation pathways. These results are used to propose a coupled dependence between hole-trapping on Te atoms and strong ligand coupling, primarily via Cd atoms, that can be used to engineer both the radiative and non-radiative lifetimes.

A Molecular and Thermodynamic View of the Assembly of Gold Nanoparticles in Nematic Liquid Crystal

The molecular interactions driving the assembly of gold nanoparticles (AuNPs) in a nematic liquid crystal (LC) are directly detected by nuclear magnetic resonance (NMR) spectroscopy and thermodynamically analyzed. The orientational orders of the selectively deuterated LC matrix and AuNP ligands, each separately followed by variable temperature (2)H NMR as a function of particle concentration, were observed to be strongly correlated. The mechanism of the reversible formation of long-range, quasi-periodic nanoparticle structures is attributed to the coupling of the AuNP ligands to the LC matrix, inducing an isotropic-nematic biphasic state. Experimentally validated thermodynamic modeling shows that, in contrast to colloidal nematics that are dominated by elastic forces, nematic dispersions of nanoparticles self-organize through a subtle balance of entropic forces and excluded volume, interface-mediated mesogen and nanoparticle molecular interactions, and couplings between conserved and nonconserved order parameters. Fine-tuning of these interactions through ligand and mesogen chemistry, together with mesoscale modeling, provides a route for materials innovations by merging structured fluid physics and nanoscience.

Evaluation of immunoglobulin adsorption on the hydrophobic charge-induction resins with different ligand densities and pore sizes

Hydrophobic charge-induction chromatography (HCIC) is a novel technology for antibody purification. The ligand densities and pore properties of HCIC resins have significant effects on the separation behavior of protein, however, the understandings are quite limited. In the present work, new HCIC ligand, 2-mercapto-1-methylimidazole (MMI) was coupled to three agarose matrices with different pore sizes. A series of MMI resins with different ligand density and pore size was prepared by the control of ligand coupling. The adsorption isotherms and kinetics on the series of MMI resins were investigated with bovine serum immunoglobulin as the model IgG, and the effects of salt addition were studied. The Langmuir equation and pore diffusion model were used to fit the experimental data, and the influences of ligand density, pore size and salt addition on the saturated adsorption capacity, the dissociation constant and the effective diffusivity were discussed. It was found that the adsorption capacities and the effective pore diffusion coefficient increased with the increase of ligand density and pore size. The effects of salt addition on the adsorption behaviors were dependent on the ligand density. For low ligand density the IgG adsorption was salt-promoted, while the resins with high ligand density showed a salt-independent property. The results indicated that for a given protein the ligand density and pore size of HCIC resins should be optimized for improving the protein adsorption.

The impact of crystal symmetry on the electronic structure and functional properties of complex lanthanum chromium oxides

Complex oxides exhibit a wide range of crystal structures, chemical compositions and physical properties. The underlying drivers determining the complicated structure–composition–property phase diagrams are the relative positions and orbital overlaps between the metal cations and the oxygen anions. Here we report a combined experimental and theoretical investigation of the structure and bonding in a series of lanthanum chromium oxides prepared by molecular beam epitaxy. Of particular interest is the charge state and local coordination of the Cr. We have stabilized LaCrO3, LaCrO4 and La2CrO6 films by controlling the three elemental fluxes during deposition, and have carried out X-ray diffraction, X-ray photoemission, and X-ray absorption spectroscopy, as well as first-principles calculations, to determine structure, charge state, chemical bonding, and electronic structure. Significant changes in bonding character and orbital interaction are revealed with decreasing ligand symmetry from octahedral to tetrahedral Cr coordination. Both LaCrO4 and La2CrO6 with tetrahedrally coordinated Cr show strong pre-edge features in the Cr K-edge near-edge structure whereas LaCrO3 with octahedrally coordinated Cr exhibits very weak pre-edge features. The origin of these pre-edge features is discussed based on various selection rules and ligand symmetry. We also demonstrate an increase in cation–anion orbital hybridization and a decrease in long-range ligand coupling induced by this symmetry reduction. These in turn result in dramatic modifications of the macroscopic optical and magnetic properties.

Reversible Intramolecular Coupling of the Terminal Borylene and a Carbonyl Ligand of [Cp(CO)2MnBtBu

Cyclic complex 2 with bridging carbonyl ligands was synthesized from a facile and reversible intermolecular carbonyl-borylene ligand coupling reaction at room temperature. Complex 2 exhibits an unprecedented coordination mode for boron-metal complexes, which is also reflected in its remarkable (11)B NMR chemical shift of -57.2 ppm. Findings from spectroscopic, X-ray, and computational studies are presented, along with a proposed mechanism.

Effect of affinity Sorbent on proteomic profiling of isatin-binding proteins of mouse brain

Use of small molecules for isolation of particular sub-proteomes is often complicated by the need for chemical modification of a parent compound for affinity sorbent preparation. Isatin (indoledione-2,3) is an endogenous indole that exhibits a wide spectrum of biological activities. Using 5-aminocaproylisatin for proteomic profiling of fractionated rodent brain homogenates, we previously identified more than sixty individual proteins. However, proteins tested in an optical biosensor study for validation of their isatin-binding capacity demonstrated different affinity for immobilized 5-aminocaproylisatin and 5-aminoisatin. In this study, we comparatively evaluated proteomic profiles of isatin-binding proteins separated using both isatin analogs as the affinity ligands. The total number of identified proteins was higher with the shorter isatin analog (88 versus 66), and only 22 proteins were identical in the two proteomic profiles. Thus, proteomic profiling of brain isatin-binding proteins is significantly influenced by the length of the spacer between the amino group used for affinity ligand coupling to Sepharose and the isatin moiety. This suggests that the actual number of brain proteins interacting with endogenous (unmodified) isatin still remains underestimated due to different affinity of proteins for the isatin analogs used for the affinity-based proteomic profiling.

Bis-o-semiquinonato complexes of transition metals with 5,7-di-tert-butyl-2-(pyridine-2-yl)benzoxazole

New cobalt(II) (1), iron(II) (2) and manganese(II) (3) complexes of M(3,6-SQ)2L type containing 3,6-di-tert-butyl-o-benzosemiquinonato ligands (3,6-SQ) and 5,7-di-tert-butyl-2-(pyridine-2-yl)benzoxazole (L) were synthesized and characterized in details. Magnetic susceptibility measurements and spectroscopic studies have shown that all complexes include metal(II) in the high-spin state and two radical-anionic o-semiquinonato ligands. The antiferromagnetic ligand–ligand coupling in cobalt(II) and iron(II) complexes takes place, while manganese(II) complex demonstrates metal–ligand antiferromagnetic interactions. Molecular structure of Co(3,6-SQ)2L was determined by X-ray analysis. Cobalt(II) atom has a distorted trigonal prismatic environment.

Diverse C–C Bond-Forming Reactions of Bis(carbene)platinum(II) Complexes

The platinum(0) complex Pt(PPh_3)_4 catalyzes coupling of the carbene ligands of (CO)_5Cr{C(OMe)(p-MeOC_6H_4)} (1). The stable bis(carbene)platinum(II) complexes Cl_2Pt{C(OMe)(Me)}_2 (3), Br_2Pt{C(OMe)(Me)}_2 (4), and Cl_2Pt{C(O^iPr)(Me)}_2 (5) can be induced to undergo C–C coupling reactions by several means. Reduction of 3–5 to platinum(0) with cobaltocene results in formation of internal olefins, (E/Z)-2,3-dimethoxybut-2-ene (6) or (E/Z)-2,3-diisopropoxybut-2-ene (7). Reaction of 3–5 with PPh3 yields terminal olefins, 2,3-dimethoxybut-1-ene (13) or 2,3-diisopropoxybut-1-ene (15), along with Cl_2Pt(PPh_3)_2 (12) or Br_2Pt(PPh_3)_2 (14). In contrast, addition of pyridine to 3–5 does not effect C–C coupling; instead, the acyl complexes cis-Cl(py)Pt(COMe){C(OMe)(Me)} (8), cis-Br(py)Pt(COMe){C(OMe)(Me)} (9), and cis-Cl(py)Pt(COMe){C(O^iPr)(Me)} (10) are obtained, with concomitant formation of alkyl halide. Possible mechanistic pathways for C–C bond formation are discussed, as well as explanations for the different reactivities observed for pyridine and PPh_3.

Influence of Second Coordination Sphere Hydroxyl Groups on the Reactivity of Copper(I) Complexes

We report the enhanced reactivity of hydroxyl substituted CuN(3)(+) derivatives, where N(3) = tris(picolinyl)methane (tripic) and related derivatives, upon deprotonation of the O-H functionality. The work capitalizes on new methodology for incorporating hydroxyl groups into the second coordination sphere of copper centers. The key synthetic methodology relies on Pd-catalyzed coupling reactions of dilithiated 6-methyl-2-pyridone with bromopyridyl derivatives. These building blocks allow the preparation of tridentate N(3) ligands with OH and OMe substituents flanking the fourth coordination site of a tetrahedral complex. Coupling of these tridendate ligands gives the corresponding hydroxy- and methoxy-functionalized bistripodal ligands. [Cu[bis(2-methylpyrid-6-yl)(2-hydroxypyrid-6-yl)methane](NCMe)](+) ([Cu(2H)(NCMe)](+)) oxidizes readily in air to afford the mixed valence Cu(1.5) dimer ([Cu(2)(2)(2)](+)). Formation of [Cu(2)(2)(2)](+) is accelerated in the presence of base and can be reversed with a combination of decamethylferrocene and acid. The reactivity of [Cu(2H)(NCMe)](+) with dioxygen requires deprotonation of the hydroxyl substituent: neither [Cu(tripic)(NCMe)](+) nor the methoxy-derivatives displayed comparable reactivity. A related mixed valence dimer formed upon oxidation of the dicopper(I) complex of a tetrahydroxy bis(tridentate) ligand, [Cu(2)(6H(4))(NCMe)(2)](2+). The dicopper(I) complex of the analogous tetramethoxy N(6)-ligand, [Cu(2)(5)(NCMe)(2)](2+), instead reversibly binds O(2). Deprotonation of [Cu(2H)(CO)](+) and [Cu(2H)(NCMe)](+) afforded the neutral derivatives Cu(2)(CO) and Cu(2)(2)(2), respectively. The dicopper(I) derivative Cu(2)(2)(2) can be reoxidized, reprotonated, and carbonylated. The silver(I) complex, [Ag(2H)(NCMe)]BF(4), forms an analogous neutral dimer (Ag(2)(2)(2)) upon deprotonation of the hydroxyl group. The structures of ligand 2H, [Cu(2)(5)(NCMe)(2)](+), [Cu(2)(2)(2)](+), [Cu(2)(6H(2))](+), [Ag(2H)(NCMe)]BF(4), and Ag(2)(2)(2) were confirmed by single crystal X-ray diffraction.

Theoretical investigation of optical spectra and covalent effect of Cr4+ in Y2Ti2O7 and Y2Sn2O7

In this work, the complete matrix of optical spectral levels in trigonal symmetry of 3d2 (3d8) ions are established on basis of strong field coupling mechanism by using two spin–orbit coupling parameters model. The contribution of the spin–orbit coupling of ligand to the optical spectra has been included in these formulas. As an application, the optical spectra of Cr4+ in Y2Ti2O7 and Y2Sn2O7 have been studied by the complete diagonalization (energy matrix) method. The covalent effect has been studied and the difficulty about Dq parameter in explanation of optical spectra of Cr-doped Y2Ti2O7 and Y2Sn2O7 is removed. The theoretical results are in good agreement with observed data.

Studies into the Mechanism of CO-Induced N2 Cleavage Promoted by an Ansa-Hafnocene Complex and C–C Bond Formation from an Observed Intermediate

Carbonylation of the hafnocene dinitrogen complex, [Me(2)Si(η(5)-C(5)Me(4))(η(5)-C(5)H(3)-(t)Bu)Hf](2)(μ(2), η(2), η(2)-N(2)), yields the corresponding hafnocene oxamidide compound, arising from N(2) cleavage with concomitant C-C and C-N bond formation. Monitoring the addition of 4 atm of CO by NMR spectroscopy allowed observation of an intermediate hafnocene complex with terminal and bridging isocyanates and a terminal carbonyl. (13)C labeling studies revealed that the carbonyl is the most substitutionally labile ligand in the intermediate and that N-C bond formation in the bridging isocyanate is reversible. No exchange was observed with the terminal isocyanate. Kinetic data established that the conversion of the intermediate to the hafnocene oxamidide was not appreciably inhibited by carbon monoxide and support a pathway involving rate-determining C-C coupling of the isocyanate ligands. Addition of methyl iodide to the intermediate hafnocene resulted in additional carbon-carbon bond formation arising from CO homologation following nitrogen methylation. Similar reactivity with (t)BuNCO was observed where C-C coupling occurred upon cycloaddition of the heterocumulene. By contrast, treatment of the intermediate hafnocene with CO(2) resulted in formation of a μ-oxo hafnocene with two terminal isocyanate ligands.

Immobilization of hydrophobic peptidic ligands to hydrophilic chromatographic matrix: A preconcentration approach

This study presents a methodology for covalent attachment of hydrophobic peptidic ligands to hydrophilic chromatographic matrices with improved coupling efficiency. Preconcentration was introduced through the use of polyethylene glycol (PEG)-based crosslinkers. Immobilization of model hydrophobic peptide pep12 (ITLISSEGYVSS) to hydrophilic silica–amine matrix was investigated in the absence/presence of PEG-based linker. The effect of linker densities 14.2, 27.6, and 56.4μmol/g beads on coupling efficiency was investigated. Whereas a ligand coupling efficiency of 67% was obtained in the absence of the linker, incorporating PEG-based linker at low densities allowed a 30% increase in the coupling efficiency. Although the heterobifunctional crosslinker, maleimide–PEG–NHS (N-hydroxysuccinimide) ester, can be used to couple thiol-bearing ligands to amine-functionalized matrices, no method is available for quenching free amine moieties on the matrix after ligand immobilization. The efficacy of acylating agents, acetyl chloride and oxalyl chloride, in blocking free amine groups when immobilizing the model peptide pep14 (CITLISSEGYVSSK) to silica–amine matrix using maleimide–PEG–NHS ester crosslinker was investigated. Because oxalyl chloride was nonreactive to maleimides, it allowed successful coupling of pep14 to the maleimide termini of the linkers. Adsorption studies between pep14-immobilized microspheres and human immunoglobulin M (hIgM) suggested retention of ligand activity and a 95% decrease in nonspecific binding of proteins to the matrix.

NC Coupling of NO Ligands with β-Carbon Atoms in Aliphatic Tertiary Amines on Nitrosylruthenium Complexes Accompanying Oxidative Dehydrogenation of Amines and CH Activation

NC Coupling of NO Ligands with β-Carbon Atoms in Aliphatic Tertiary Amines on Nitrosylruthenium Complexes Accompanying Oxidative Dehydrogenation of Amines and CH Activation