Monofunctional Ligands Research Articles

Potassium Hexamethyldisilazide (KHMDS): Solvent-Dependent Solution Structures.

Solution structures of potassium hexamethyldisilazide [KHMDS] and labeled [15N]KHMDS were examined using a number of analytical methods including 29Si NMR spectroscopy and density functional theory computations. A combination of 15N-29Si couplings, 29Si chemical shifts, and the method of continuous variations reveals dimers, monomers, and ion pairs. Weakly coordinating monofunctional ligands such as toluene, N,N-dimethylethylamine, and Et3N afford exclusively dimers. 1,3-Dioxolane, THF, dimethoxyethane, hexamethylphosphoramide, and diglyme provide dimers at low ligand concentrations and monomers at high ligand concentrations. N,N,N',N'-Tetramethylethylenediamine and N,N,N',N'-tetramethylcyclohexanediamine provide exclusively dimers at all ligand concentrations at ambient temperatures and significant monomer at -80 °C. Studies of 12-crown-4 ran into technical problems. Equimolar 15-crown-5 forms a dimer, whereas excess 15-crown-5 affords a putative ion pair. Whereas equimolar 18-crown-6 also affords a dimer, an excess provides a monomer rather than a solvent-separated ion pair. [2.2.2]cryptand affords what is believed to be a contact-ion-paired cryptate. Solvation was probed using largely density functional theory (DFT) computations. Thermally corrected energies are consistent with lower aggregates and higher solvates at low temperatures, but the magnitudes of the computed temperature dependencies were substantially larger than the experimentally derived data.

Effects of Mono- and Bifunctional Surface Ligands of Cu-In-Se Quantum Dots on Photoelectrochemical Hydrogen Production.

Semiconductor nanocrystal quantum dots (QDs) are promising materials for solar energy conversion because of their bandgap tunability, high absorption coefficient, and improved hot-carrier generation. CuInSe2 (CISe)-based QDs have attracted attention because of their low toxicity and wide light-absorption range, spanning visible to near-infrared light. In this work, we study the effects of the surface ligands of colloidal CISe QDs on the photoelectrochemical characteristics of QD-photoanodes. Colloidal CISe QDs with mono- and bifunctional surface ligands are prepared and used in the fabrication of type-II heterojunction photoanodes by adsorbing QDs on mesoporous TiO2. QDs with monofunctional ligands are directly attached on TiO2 through partial ligand detachment, which is beneficial for electron transfer between QDs and TiO2. In contrast, bifunctional ligands bridge QDs and TiO2, increasing the amount of QD adsorption. Finally, photoanodes fabricated with oleylamine-passivated QDs show a current density of ~8.2 mA/cm2, while those fabricated with mercaptopropionic-acid-passivated QDs demonstrate a current density of ~6.7 mA/cm2 (at 0.6 VRHE under one sun illumination). Our study provides important information for the preparation of QD photoelectrodes for efficient photoelectrochemical hydrogen generation.

Unique transport behaviour of Am(III)/Eu(III) ions across a supported liquid membrane containing a TREN-based diglycolamide dendrimer ligand

Abstract Appropriately functionalized dendrimers are exotic ligands and are expected to give rise to better extraction/transport results than the corresponding monofunctional ones. Diglycolamide- (DGA) based dendrimers and their transport studies are rarely reported. Transport of Am(III) and Eu(III) was studied across a PTFE- (polytetrafluoroethylene) based flat sheet supported liquid membrane containing a tris(2-aminoethyl)amine (TREN) dendrimer ligand containing six DGA pendent arms (termed as TREN-G1-DGA) in 5% isodecanol modified n-dodecane. The transport results were compared with those of the monofunctional ligand TODGA (N,N,N′,N′-tetra-n-octyl diglycolamide). In case of a 5.75 × 10−4 M TREN-G1-DGA solution, Am(III) transport was slower than that of Eu(III) under identical conditions. In case of TREN-G1-DGA the role of acid on the metal ion transport was less important than that while using TODGA as a carrier. However, a nitric acid medium is much more suitable for metal ion transport than a mixture containing sodium nitrate as the major component. Insight into the extraction and transport of the Eu(III) complexes was obtained from luminescence spectroscopic studies.

Unique Eu(III) transport selectivity seen using a supported liquid membrane containing a diglycolamide dendrimer ligand

ABSTRACT Dendrimers are exotic multi-functional ligands and are expected to give rise to better extraction/transport results as compared to the mono-functional ligands. Diglycolamide (DGA) based dendrimers are scarcely reported and literature on their transport studies are very limited. Transport of Am(III) and Eu(III) across a PTFE (polytetrafluoroethylene) based flat sheet supported liquid membrane containing a generation 1 dendrimer of tris(2-aminoethyl)amine (TREN), containing six diglycolamide (DGA) pendent arms (termed as TREN-G1-DenDGA) was investigated from nitric acid feed solutions. The transport studies involved 5.75 × 10−4 M ligand solution in 5% isodecanol modified n-dodecane. Am(III) transport was slower than that of Eu(III) under identical conditions. The transport of both Am(III) and Eu(III) increased with increasing nitric acid concentration from 1 to 6 M HNO3 suggesting a solvation extraction mechanism with nitrate ions playing a significant role. A unique preferential Eu(III) transport over Am(III) was seen at 3 M HNO3 with a transport selectivity factor (ratio of permeability coefficient values) of 6.2 which decreased upon changing the acid concentration. Carrier ligand concentration also played a significant role in transport selectivity. Membrane parameters such as permeability coefficient and effective diffusion coefficient (D eff) values were determined experimentally. The liquid membrane stability studies were also carried out.

Synthesis, spectroscopic characterization, DFT calculations, and antimicrobial activities of N-arylsalicylaldiminate derivatives of diorganotin(IV)

Equimolar reaction of di-n-butyltin(IV) complexes of bidentate Schiff bases of the type [(n-Bu)2Sn(sb)Cl] with sodium salt of mono-functional bidentate ligands in THF-benzene solution afforded structurally interesting complexes of the type [(n-Bu)2Sn(sb)(L)] (1–6) [where sbH = Schiff bases: N-salicylidene-2-aminopyridine (sapH) I, N-salicylidene-2-methylaminobenzene (o-smabH) II, and N-salicylidene-4-methylaminobenzene (p-smabH) III; LH = mono-functional bidentate ligands, acetylacetone (acacH), ethanolamine (eaH)]. All these colored solid complexes were soluble in common organic solvents and characterized by elemental (C, H, N, and Sn) analysis, spectroscopic techniques [IR, (1H, 13C, and 119Sn) NMR] and mass spectrometry. Thermogravimetric analysis of complexes shows thermal behavior and stability of complexes. Computational studies of the synthesized Schiff bases and their organotin(IV) complexes were carried out using DFT which validate the structure of complexes proposed on the basis of spectroscopic data. The mixed-ligand complexes of diorganotin(IV) and Schiff bases were screened for their antibacterial and antifungal activities.

Chiral Bifunctional Phosphine‐Carboxylate Ligands for Palladium(0)‐Catalyzed Enantioselective C−H Arylation

AbstractPrevious enantioselective Pd0‐catalyzed C−H activation reactions proceeding via the concerted metalation‐deprotonation mechanism employed either a chiral ancillary ligand, a chiral base, or a bimolecular mixture thereof. This study describes the development of new chiral bifunctional ligands based on a binaphthyl scaffold which incorporates both a phosphine and a carboxylic acid moiety. The optimal ligand provided high yields and enantioselectivities for a desymmetrizing C(sp2)−H arylation leading to 5,6‐dihydrophenanthridines, whereas the corresponding monofunctional ligands showed low enantioselectivities. The bifunctional system proved applicable to a range of substituted dihydrophenanthridines, and allowed the parallel kinetic resolution of racemic substrates.

Chiral Bifunctional Phosphine‐Carboxylate Ligands for Palladium(0)‐Catalyzed Enantioselective C−H Arylation

Previous enantioselective Pd0 -catalyzed C-H activation reactions proceeding via the concerted metalation-deprotonation mechanism employed either a chiral ancillary ligand, a chiral base, or a bimolecular mixture thereof. This study describes the development of new chiral bifunctional ligands based on a binaphthyl scaffold which incorporates both a phosphine and a carboxylic acid moiety. The optimal ligand provided high yields and enantioselectivities for a desymmetrizing C(sp2 )-H arylation leading to 5,6-dihydrophenanthridines, whereas the corresponding monofunctional ligands showed low enantioselectivities. The bifunctional system proved applicable to a range of substituted dihydrophenanthridines, and allowed the parallel kinetic resolution of racemic substrates.

DFT studies of the interactions between the [Ca(H2O)5]2+ cation and monofunctional oxo, aza, sulfur and phosphorous ligands

Quantum chemical calculations using the B3LYP/6-311++G(d,p) method were performed to determine the affinity of the [Ca(H2O)5]2+ cation for several monofunctional ligands. Four sets of ligands were studied: with oxygen binding atom (phosphoryl, amide, carboxylic acid, ketone, aldehyde, ether, alcohol, enol), nitrogen (imine, thiocyanic acid, nitrile, amine and ammonia), sulfur (thiocarbonyl, thioether and thioalcohol) and phosphorous (phosphine) binding atom. Compounds that bind via a double bonded oxygen atom have the strongest metal–ligand interaction, followed by compounds binding via nitrogen, singly bonded oxygen atom, sulfur and phosphine. The ligand with the strongest interaction, phosphine oxide, has an ionic resonance form with a negative charge on the binding oxygen atom that highly contributes to the hybrid geometry, what favors the interaction. The Energy Decomposition Analysis (EDA) of the interaction energy between the [Ca(H2O)5]2+ cation and the ligand shows that the electrostatic term is the major component of the interaction and represents at least 43.66% of the total interaction energy. The covalent component represents at least 28.09% of the total interaction energy. Along the set of compounds studied, the electrostatic component varies more than twice the covalent term. The repulsive and the dispersion components are roughly constant in all complexes.

First principles investigations on the electronic structure of anchor groups on ZnO nanowires and surfaces

We report on density functional theory investigations of the electronic properties of monofunctional ligands adsorbed on ZnO-(1010) surfaces and ZnO nanowires using semi-local and hybrid exchange-correlation functionals. We consider three anchor groups, namely thiol, amino, and carboxyl groups. Our results indicate that neither the carboxyl nor the amino group modify the transport and conductivity properties of ZnO. In contrast, the modification of the ZnO surface and nanostructure with thiol leads to insertion of molecular states in the band gap, thus suggesting that functionalization with this moiety may customize the optical properties of ZnO nanomaterials.

Stabilizing catalytically active nanoparticles by ligand linking: toward three-dimensional networks with high catalytic surface area.

A general approach for the linking of Pt nanoparticles (NPs) with bifunctional amine ligands (organic molecules with two amine groups) is presented that allows for the preparation of NP catalysts without inorganic supports and high densities of the catalytically active metal. Advantage was taken of the use of "unprotected" NPs, which enables us to prepare different ligand-functionalized NPs from the same particle batch and thus to relate changes of the resulting material properties exclusively to the influence of the ligand. Three bifunctional ligands with similar functional groups (amines) but different hydrocarbon skeletons were used and compared to monofunctional ligands of similar molecular structures (alkyl and aryl amines) showing significantly different material properties. Monofunctional molecules with minor steric demand cover almost completely the NP surface and lead to two-dimensional assembling of the NPs. In contrast, the use of bifunctional amine ligands leads to the formation of porous, three-dimensional NP networks (ligand-linked NPs) with a high density of ligand free surface atoms, thus enabling for the application as catalytic materials. The stabilizing effect of bifunctional ligands serves as an alternative to the use of inorganic support materials and enables for catalytic applications of ligand-linked NP networks.

Atom transfer radical polymerization of methyl methacrylate with a thermo-responsive ligand: construction of thermoregulated phase-transfer catalysis in an aqueous–organic biphasic system

The concept of thermoregulated phase-transfer catalysis (TRPTC) for an aqueous–organic biphasic system was applied in Cu(II)-mediated atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). Herein, activators generated by electron transfer (AGET) ATRP was used to establish the TRPTC ATRP system using 2-cyanoprop-2-yl 1-dithionaphthalate (CPDN) as an alkyl pseudohalide initiator, CuBr2 as the catalyst and ascorbic acid (AsAc) as the reducing agent. It used a thermo-responsive monofunctional ligand including the dipyridyl group (MPEG-DPA), which enabled the transfer of the catalyst complex into the organic phase from the aqueous phase upon heating, thus achieving homogeneous polymerization; and the catalyst complex could retransfer into the aqueous phase from the organic phase thereby realizing the separation and recycling of the catalyst complex upon cooling. Well-defined PMMA with controlled molecular weight and narrow molecular weight distribution could be obtained by TRPTC ATRP. Furthermore, the polymerization of MMA could be successfully carried out even when the amount of catalyst was reduced to the ppm level. The features of controlled/“living” radical polymerization of MMA were verified by chain end analysis and chain-extension experiments.

Synthesis, characterization, antimicrobial, pesticidal and DNA cleavage activity of germanium(IV) derivatives of 3-(2-methyl-2,3-dihydro-benzthiazo-2-yl)-chromen-2-one and N′-[1-2-oxo-2H-chrome-3yl-ethylidene]-hydrazinecarbodithionic acid benzyl ester ligands

Abstract The new ligands 3-(2-methyl-2,3-dihydro-benzthiazo-2-yl)-chromen-2one (AcBzH) and N′-[1-2-oxo-2H-chrome-3yl-ethylidene]-hydrazinecarbodithionic acid benzyl ester (AcBDTZH) were prepared by the reaction of 3-acetyl-2H-chromen-2-one with 2-aminothiophenol and S-benzyl dithiocarbazate, respectively. The germanium(IV) complexes have been prepared by reacting Ph3GeCl and Me3GeCl in 1:1 molar ratio with these monofunctional bidentate AcBzH and AcBDTZH ligands by using microwave as well as conventional heating methods for comparison purposes. All the synthesized compounds were characterized by elemental analyses, melting point, IR, 1H-NMR 13C-NMR, mass and X-ray powder diffraction techniques. These studies showed that the ligands coordinated to the germanium atom in a monobasic bidentate manner and trigonal bipyramidal environment around the germanium atom have been established for the complexes. To evaluate the effect of metal ion upon chelation, both ligands and their complexes have been screened for their antimicrobial activity against the various pathogenic bacterial and fungal strains. The metal complexes have shown antimicrobial activity as compared to the free ligands. The pesticidal activity and DNA cleavage activity of both ligands and their metal complexes have been tested and discussed.

Shape controlled synthesis of superhydrophobic zinc coordination polymers particles and their calcination to superhydrophobic ZnO

In this paper, superhydrophobic Zinc-CPPs (coordination polymer particles) with controllable shapes were synthesized by an in situ ligand generating reaction in combination with monofunctional ligands as capping reagents. The as-synthesized samples were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), energy-dispersion X-ray (EDX) spectroscopy, and Brunauer–Emmett–Teller (BET) analysis. The Zn–CPPs exhibit superhydrophobicity. Crystalline ZnO particles were formed from the calcination of Zn–CPPs, exhibiting superhydrophobicity and good photocatalytic activity.

Conformational isomerism and hydrogen-bonded motifs of anion assisted supramolecular self-assemblies using Cu II/Co II salts and pyridine-4-acetamide

Six novel metal–organic complex assemblies constructed from a conformation-flexible ligand – pyridine-4-acetamide (PAT) and inorganic Cu II and Co II salts have been synthesized and structurally characterized by single crystal X-ray diffraction analysis. Crystal structure analysis reveals five types of architectures by variation of metal salts. In {[Cu(PAT) 2Cl 2]} n ( 1) and {[Co(PAT) 2Cl 2]} n ( 3), PAT ligands bridge metal centers to form one-dimensional chains. The chains are extended to three dimensions with the aid of two types of hydrogen bonded motifs ( R 4 2 ( 8 ) ) and R 2 2 (12)). {[Cu(PAT) 2(NO 3)](NO 3)(THF)} n ( 5) which exhibits two-dimensional coordinating layers forms open channels filled with solvent molecules. In [Cu(PAT) 2Cl 2] ( 2), [Co(PAT) 2Cl 2] ( 4) and [Co(PAT) 4(H 2O) 2](NO 3) 2(THF) 2 ( 6), PAT is observed as a monofunctional ligand. Complex 2 forms one-dimensional hydrogen bonded chains. Crystal structure of complex 4 has a two-dimensional infinite hydrogen-bonded network with R 4 2 ( 8 ) and R 2 2 ( 8 ) motifs formed by complementary amide–amide hydrogen bonds. [Co(PAT) 4(H 2O) 2](NO 3) 2(THF) 2 ( 6) crystallizes in centrosymmetric I4 1/ a space group. Complex 6 forms chiral channels which are filled with twisted solvent helices and anion helices. Within each channel the solvent helix and the anion helix have the same handedness; and adjacent channels have opposite handedness. Complexes 1, 2 and complexes 3, 4 illustrate examples of conformational supramolecular isomerism in {[Cu(PAT) 2Cl 2]} ∞ and {[Co(PAT) 2Cl 2]} ∞ , respectively. In these complexes, changes of PAT conformations and coordination geometry of metal center induced the structural versatility.

Structural Studies with Antimicrobial and Antifertility Activity of a Monofunctional Bidentate Ligand with its Boron(III), Palladium(II), and Platinum(II) Complexes

The reaction of the sulfur donor Schiff base ligand, 7-nitro-3-(indolin-2-one) hydrazinecarbo-thioamide, with phenyldihydroxyboron in benzene, palladium(II)chloride, and platinum(II) chloride, in ethanol, gave the mononuclear tetracoordinated and hexacoordinated complexes. The Schiff base ligand coordinated to the boron atom in 1:1 and 1:2 molar ratios and to the palladium and platinum metals in only 1:2 molar ratios in the presence of an acidic and basic medium. Tentative structural conclusions are drawn for reaction products based upon elemental analysis, electrical conductance, and spectral (electronic, infrared, 1 H NMR, 13 C NMR, and 11 B NMR) data. The antifertility activity of the ligand and its nonmetal/metal complexes are discussed with a comparative study in an effective manner.

Amplification of Bifunctional Ligands for Calmodulin from a Dynamic Combinatorial Library

A well known strategy to prepare high affinity ligands for a biological receptor is to link together low affinity ligands. DCC (dynamic combinatorial chemistry) was used to select bifunctional protein ligands with high affinity relative to the corresponding monofunctional ligands. Thiol to disulfide linkage generated a small dynamic library of bifunctional ligands in the presence of calmodulin, a protein with two independently mobile domains. The binding constant of the bifunctional ligand (disulfide) most amplified by the presence of calmodulin is nearly two orders of magnitude higher than that of the corresponding monofunctional ligand (thiol).

Enhanced Ligand Affinity for Receptors in which Components of the Binding Site Are Independently Mobile

Using calmodulin antagonism as a model, it is demonstrated that, under circumstances in which binding sites are motionally independent, it is possible to create bifunctional ligands that bind with significant affinity enhancement over their monofunctional counterparts. Suitable head groups were identified by using a semiquantitative screen of monofunctional tryptophan analogs. Two bifunctional ligands, which contained two copies of the highest-affinity head group tethered by rigid linkers, were synthesized. The bifunctional ligands bound to calmodulin with a stoichiometry of 1:1 and with an affinity enhancement over their monofunctional counterparts; the latter bound with a stoichiometry of 2:1 ligand:protein. A lower limit to the effective concentrations of the domains of calmodulin relative to each other (0.2-2 mM) was determined. A comparable effective concentration was achieved for bifunctional ligands based on higher-affinity naphthalene sulphonamide derivatives.

Synthesis And Characterization of Some New Diphenylbismuth(III) Complexes of Ν, Ο and S Donor Monofunctional Tridentate Ligands

Synthesis And Characterization of Some New Diphenylbismuth(III) Complexes of Ν, Ο and S Donor Monofunctional Tridentate Ligands

FKBP ligands as novel therapeutics for neurological disorders.

Given their clinical importance for the treatment of acute and chronic neurodegenerative diseases in humans including nerve injuries (e.g. Alzheimer's disease, Parkinson's disease, diabetic neuropathy) a number of different approaches were pursued to obtain selectively acting FK506-binding protein (FKBP) ligands: computational methods and target-oriented screening of natural compound and synthetic product libraries. The resulting monofunctional ligands, which inhibit the peptidyl prolyl cis/trans isomerase activity of FKBPs, highlight the role of these enzymes in neuronal signaling. The exploration of the mechanisms of neuroregenerative and neuroprotective action of some of these compounds is the main focus of ongoing neuropharmaceutical research.

DNA triple helix stabilisation by a naphthylquinoline dimer

We have used DNase I footprinting to examine the effect of a novel naphthylquinoline dimer, designed as a triplex-specific bis-intercalator, on the stability of intermolecular DNA triplexes. We find that this compound efficiently promotes triplex formation between the 9-mer oligonucleotide 5′-TTTTTTCTT and its oligopurine duplex target at concentrations as low as 0.1 μM, enhancing the triplex stability by at least 1000-fold. This compound, which is the first reported example of a triplex bis-intercalator, is about 30 times more potent than the simple monofunctional ligand.