Investigation of uranyl nitrate ion pairs complexed with amide ligands using electrospray ionization ion trap mass spectrometry and density functional theory

Ion populations formed from electrospray of uranyl nitrate solutions containing different amides vary depending on ligand nucleophilicity and steric crowding at the metal center. The most abundant species were ion pair complexes having the general formula [UO(2)(NO(3))(amide)(n=2,3)](+); however, singly charged complexes containing the amide conjugate base and reduced uranyl UO(2)(+) were also formed as were several doubly charged species. The formamide experiment produced the greatest diversity of species resulting from weaker amide binding, leading to dissociation and subsequent solvent coordination or metal reduction. Experiments using methyl formamide, dimethyl formamide, acetamide, and methyl acetamide produced ion pair and doubly charged complexes that were more abundant and less abundant complexes containing solvent or reduced uranyl. This pattern is reversed in the dimethylacetamide experiment, which displayed lower abundance doubly charged complexes, but augmented reduced uranyl complexes. DFT investigations of the tris-amide ion pair complexes showed that interligand repulsion distorts the amide ligands out of the uranyl equatorial plane and that complex stabilities do not increase with increasing amide nucleophilicity. Elimination of an amide ligand largely relieves the interligand repulsion, and the remaining amide ligands become closely aligned with the equatorial plane in the structures of the bis-amide ligands. The studies show that the phenomenological distribution of coordination complexes in a metal-ligand electrospray experiment is a function of both ligand nucleophilicity and interligand repulsion and that the latter factor begins exerting influence even in the case of relatively small ligands like the substituted methyl-formamide and methyl-acetamide ligands.     

The Influence of the Amide Linkage in the FeIII‐Binding Properties of Catechol‐Modified Rosamine Derivatives

The two new fluorescent ligands RosCat1 and RosCat2 contain catechol receptors connected to rosamine platforms through an amide linkage and were synthesized by using microwave‐assisted coupling reactions of carboxyl‐ or amine‐substituted rosamines with the corresponding catechol units and subsequent deprotection. RosCat1 possesses a reverse amide, whereas RosCat2 has the usual oriented amide bond (HNCO vs. CONH, respectively). The ligands were characterized by means of NMR spectroscopy, mass‐spectrometry, and DFT calculations and X‐ray crystallography studies for RosCat1 . The influence of the amide linkage on the photophysical properties of the fluorescent ligands was assessed in different solvents and showed a higher fluorescence quantum yield for RosCat1 . The coordination chemistry of these ligands with a Fe^III center has been rationalized by mass‐spectrometric analysis and semiempirical calculations. Octahedral Fe^III complexes were obtained by the chelation of three RosCat1 or RosCat2 ligands. Interestingly, the unconventional amide connectivity in RosCat1 imposes the formation of an eight‐membered ring on the chelate complex through a “salicylate‐type” mode of coordination.     

Unprecedented reversible migration of amide to schiff base ligands attached to tin: latent single-site initiators for lactide polymerization

In an unprecedented transformation, amide ligands are found to attack the imine carbon centers of tridentate Schiff base ligands attached to tin. The process is reversible, and the resultant (masked) amide species can be exploited as latent single-site initiators for the controlled polymerization of rac-lactide.     

Synthesis of homochiral pentadentate sulfonamide-based ligands

A two-step synthesis of pentadentate, tetraionic ligands based on sulfonamide, amide, and pyridyl groups is reported. These ligands are easily accessible in good to excellent yield from commercially available materials.     

Phenylenedioxydiacetamide—End group effect

A series of neutral ligands featuring ether and amide groups were prepared. The complexation studies suggest a strong participation of the extra terminal amide group.Taken in part from the Master's Thesis of Antonio Paulo Altoé, Instituto Militar de Engenharia, Rio de Janeiro, Brasil (1979).     

catena‐Poly[[bis(nicotinamide‐κN1)copper(I)]‐μ‐thiocyanato‐κ2N:S]

The Cu^I cations in the title compound, [Cu(NCS)(C₆H₆N₂O)₂]_n, are coordinated by N atoms from each of two mirror‐related nicotin­amide ligands, as well as by one N atom of one thio­cyanate ligand and one S atom of a symmetry‐related thio­cyanate ligand, within a slightly distorted tetrahedron. The Cu^I cations and the thio­cyanate anions are located on a crystallographic mirror plane and the nicotin­amide ligands occupy general positions. The Cu^I cations are connected by the thio­cyanate anions to form chains in the direction of the crystallographic a axis. These chains are connected by hydrogen bonds between the amide H atoms and the O atoms of adjacent nicotin­amide ligands, to give a three‐dimensional structure.     

A series of tripodal cysteine derivatives as water-soluble chelators that are highly selective for copper(I)

A series of tripodal ligands derived from nitrilotriacetic acid and extended by three converging, metal-binding, cysteine chains was synthesised. Their ability to bind soft metal ions thanks to their three thiolate functions was investigated by means of complementary analytical and spectroscopic methods. Three ligands that differ by the nature of the carbonyl group next to the coordinating thiolate functions were studied: L(1) (ester), L(2) (amide) and L(3) (carboxylate). The negatively charged derivative L(3), which bears three carboxylate functions close to the metal binding site, gives polynuclear copper(I) complexes of low stability. In contrast, the ester and amide derivatives L(1) and L(2) are efficient Cu(I) chelators with very high affinities, close to that reported for the metal-sequestering metallothioneins (log K≈19). Interestingly, these two ligands form mononuclear copper complexes with a unique MS(3) coordination in water solution. An intramolecular hydrogen-bond network involving the amide functions in the upper cavity of the tripodal ligands stabilises these mononuclear complexes and was evidenced by the very low chemical-shift temperature coefficient of the secondary amide protons. Moreover, L(1) and L(2) display large selectivities for the targeted metal ion that is, Cu(I), with respect to bioavailable Zn(II). Therefore the two sulfur-based tripods L(1) and L(2) are of potential interest for intracellular copper detoxication in vivo, without altering the homeostasis of the essential metal ion Zn(II).     

Stable functionalized PEGylated quantum dots micelles with a controlled stoichiometry

Here we report the synthesis of monofunctional PEGylated amide ligands that were used to prepare bioactivable quantum dots of a 20 nm diameter with a controlled mean number of the covalently grafted ligands. They are stable in aqueous medium of high salinity including a large pH domain.     

Atropisomeric amides as chiral ligands: using (-)-sparteine-directed enantioselective silylation to control the conformation of a stereogenic axis

An enantiomerically pure (1-trimethylsilyl)ethyl group, constructed by a (-)-sparteine-directed enantioselective quench of a laterally lithiated tertiary aromatic amide, exerts powerful thermodynamic control over the conformation of the adjacent tertiary amide substituent. Ortholithiation and functionalization of the amide in the 6-position allows the single amide conformer to be trapped as an enantiomerically and diastereoisomerically pure amide atropisomer. Protodesilylation of the amide gives functionalized atropisomeric amides with a stereogenic axis of single absolute configuration, whose barriers to racemization have been determined by polarimetry. Enantiomerically pure amides bearing phosphine substituents are effective ligands in a Pd-catalyzed allylic substitution reaction-the first use of a nonbiaryl atropisomer as a chiral ligand-and give products with 90% ee. The rate of racemization of the phosphine-substituted amide is powerfully influenced by the presence of palladium.     

Pyroglutamate-derived hydroxyamide ligands: synthesis and application to asymmetric catalysis

The synthesis of a series of chiral hydroxy amide ligands is described. These ligands were used in a ruthenium-catalysed transfer hydrogenation reaction where one ligand gave the product in 72% ee. The ligands were also used in two titanium-catalysed reactions, an alkylation where ee’s of up to 74% were achieved and a phenyl acetylene addition where more modest selectivities were observed.     

Amide‐Substituted Titanocenes in Hydrogen‐Atom Transfer Catalysis

Two new catalytic systems for hydrogen‐atom transfer (HAT) catalysis involving the N?H bonds of titanocene(III) complexes with pendant amide ligands are reported. In a monometallic system, a bifunctional catalyst for radical generation and reduction through HAT catalysis depending on the coordination of the amide ligand is employed. The pendant amide ligand is used to activate Crabtree's catalyst to yield an efficient bimetallic system for radical generation and HAT catalysis.     

Recent developments in the non-cyclopentadienyl organometallic and related chemistry of scandium

Up to the early to mid 1990s the organometallic chemistry of scandium was dominated by cyclopentadienyl derivatives. This present article highlights advances in the synthesis and reactivity of non-cyclopentadienyl organometallic and related compounds of scandium. These include: compounds containing arene and other eta(x)-CxRx ligands; compounds with macrocyclic and fac-L3 ligands; compounds with polydentate ligands that incorporate amide donors; compounds with bidentate, monoanionic N,N' donor ligands; and compounds with iminophenolate, bis(phenoxide) and some other anionic O-donor ligands.     

Biarylpyrimidines: a new class of ligand for high-order DNA recognition

Biarylpyrimidines bearing omega-aminoalkyl substituents have been designed as ligands for high-order DNA structures: spectrophotometric, thermal and competition equilibrium dialysis assays showed that changing the functional group for substituent attachment from thioether to amide switches the structural binding preference from triplex to tetraplex DNA; the novel ligands are non-toxic and moderate inhibitors of human telomerase.     

Efficient stabilization of copper(III) in tetraaza pseudo-macrocyclic oxime-and-hydrazide ligands with adjustable cavity size

Substitution of the amide donors in open-chain {2N(oxime), 2N(amide)} ligands by hydrazide donors gives new pseudo-macrocyclic copper complexes that show a significant decrease of the Cu(3+/2+) redox potentials in both mono- and polynuclear systems, thus demonstrating a pronounced capacity of such ligand systems to efficiently stabilize the trivalent copper.     

Synthesis of C3-symmetric tris(beta-hydroxy amide) ligands and their Ti(IV) complex-catalyzed enantioselective alkynylation of aldehydes

[reaction: see text]. A series of new chiral C3-symmetric tris(beta-hydroxy amide) ligands have been synthesized via the reaction of 1,3,5-benzenetricarboxylic chloride and optically pure amino alcohols (up to 96% yield). The asymmetric catalytic alkynylation of aldehydes with these new C3-symmetric chiral tris(beta-hydroxy amide) ligands and Ti (O(i)'Pr)4 was investigated. Ligand 4c synthesized from (1R,2S)-(-)-2-amino-1,2-diphenylethanol is effective for the enantioselective alkynylation of various aldehydes, and high enantioselectivity was obtained with aromatic aldehydes and alpha,beta-unsaturated aldehyde (up to 92% ee).     

Synthesis of new C2-symmetric bis(β-hydroxy amide) ligands and their applications in the enantioselective addition of alkynylzinc to aldehydes

A series of chiral C₂-symmetric bis(β-hydroxy amide) ligands was synthesized via the reaction of isophthaloyl dichloride and amino alcohols derived from l-amino acid. The titanium(IV) complex of C₂-symmetric chiral ligand 3b was effective for the asymmetric alkynylation of aldehydes and the propargyl alcohols were obtained in high yields (up to 94%) and high enantiomeric excesses (up to 98%) under optimized conditions. The results obtained using ligand 3h support that the two β-hydroxy amide moieties in these ligands behave as two independent ligands in the catalytic system.     

The preparation and properties of neutral diamide ionophores for group IIa metal cations

The preparation of a series of neutral ligands featuring ether and N-methyl-N-carbethoxypentylamide groups is described. These ligands as well as related ones bearing other diamide groups are shown to selectively chelate Group IIA cations by picrate extraction from water to methylene chloride. The changes in UV absorption of aromatic rings and amide groups in the ligands upon titration with metal salts in methanol allow the estimation of the stoichiometry of complexation and the ordering of cation binding. The observed selectivity sequences of cation extraction and binding are briefly discussed. Preliminary proton and ¹³C NMR studies on the effect of addition of Group IIA cation salts to several of the ligands in methanol suggest that most of the complexation occurs at the central ether and amide groups. ¹³C NMR T₁ changes by the Inversion Recovery Fourier Transform method are in agreement with the cation-induced shift data.     

Diarylethynyl amides that recognize the parallel conformation of genomic promoter DNA G-quadruplexes

We report bis-phenylethynyl amide derivatives as a potent G-quadruplex binding small molecule scaffold. The amide derivatives were efficiently prepared in 3 steps by employing Sonogashira coupling, ester hydrolysis and a chemoselective amide coupling. Ligand-quadruplex recognition has been evaluated using a fluorescence resonance energy transfer (FRET) melting assay, surface plasmon resonance (SPR), circular dichroism (CD) and (1)H nuclear magnetic resonance (NMR) spectroscopy. While most of the G-quadruplex ligands reported so far comprise a planar, aromatic core designed to stack on the terminal tetrads of a G-quadruplex, these compounds are neither polycyclic, nor macrocyclic and have free rotation around the triple bond enabling conformational flexibility. Such molecules show very good binding affinity, excellent quadruplex:duplex selectivity and also promising discrimination between intramolecular promoter quadruplexes. Our results indicate that the recognition of the c-kit2 quadruplex by these ligands is achieved through groove binding, which favors the formation of a parallel conformation.     

Structural aspects of metal–amide complexes

An exhaustive survey of crystal structure data on simple amides and metal complexes containing monodentate amide ligands has been performed. Statistical analysis of structural features are reported as a function of the degree of alkylation of the amide functional group, the type of metal ion in the amide complex, and the type of binding to the metal ion. Average values are reported for bond lengths, bond angles, and torsional angles. Orientational preferences of the coordinated amide ligand are discussed in terms of M–O–C bond angles and M–O–C–N torsion angles.     

Complexation of lanthanides(III), americium(III), and uranium(VI) with bitopic N,O ligands: an experimental and theoretical study

New functionalized terpyridine-diamide ligands were recently developed for the group actinide separation by solvent extraction. In order to acquire a better understanding of their coordination mode in solution, protonation and complexation of lanthanides(III), americium(III), and uranium(VI) with these bitopic N,O-bearing ligands were studied in homogeneous methanol/water conditions by experimental and theoretical approaches. UV-visible spectrophotometry was used to determine the protonation and stability constants of te-tpyda and dedp-tpyda. The conformations of free and protonated forms of te-tpyda were investigated using NMR and theoretical calculations. The introduction of amide functional groups on the terpyridine moiety improved the extracting properties of these new ligands by lowering their basicity and enhancing the stability of the corresponding 1:1 complexes with lanthanides(III). Coordination of these ligands was studied by density functional theory and molecular dynamics calculations, especially to evaluate potential participation of hard oxygen and soft nitrogen atoms in actinide coordination and to correlate with their affinity and selectivity. Two predominant inner-sphere coordination modes were found from the calculations: one mode where the cation is coordinated by the nitrogen atoms of the cavity and by the amide oxygen atoms and the other mode where the cation is only coordinated by the two amide oxygen atoms and by solvent molecules. Further simulations and analysis of UV-visible spectra using both coordination modes indicate that inner-sphere coordination with direct complexation of the three nitrogen and two oxygen atoms to the cation leads to the most likely species in a methanol/water solution.