Donor Ability Research Articles

Uranyl(VI) Mixed-ligand complex synthesis and characterization using 4-acylhydrazone-5-pyrazolone and 4-acylpyrazolone: Covalency, crystal assay, DFT study and Hirshfeld analysis

Newly prepared bidentate HLA and tridentate Bz-HLA ligands were used to synthesize the novel uranyl mixed ligand [UO2(HLA)(Bz-HLA)] complex with pentagonal bipyramidal geometry. HLA ligand was prepared via the common acylation method, and the Bz-HLA ligand was prepared using the Schiff base reaction of HLA with a benzohydrazide molecule. FTIR, 1H and 13C NMR, SCXRD, molar conductance, and TG-DTA were mainly implemented to examine the structure of produced compounds. The combined covalency effect of complex due to both ligands has been studied, which was discovered to be influenced by the average bond length values on the pentagonal plane, uranyl axial bond lengths, ligand coordination, and donor ability of various atoms. To demonstrate that solvents have no impact on the covalency of the synthesised complex, Sinha's covalency parameters were computed using UV–vis data. DFT calculations were performed in order to validate experimental findings in comparison to theoretical findings, and theoretical bond characteristics were also investigated through the recognition of global index values. Hirshfeld surface analysis was used to examine the crystal strength, energy characteristics and non-covalent surface interactions. Analysis using cyclic voltammetry(CV) shows that the complex is irreversibly reducing. Understanding the Schiff base of acylpyrazolones and their covalency in uranyl complexes allow for the investigation of a wide range of chemical properties and applications.

Probing the Impact of Solvent on the Strength of Lewis Acids via Fluorescent Lewis Adducts.

Various methods have been developed to measure the strength of a Lewis acid. A major challenge for these measurements lies in the complexity that arises from variable solvent interactions and perturbations of Lewis acids as their reaction environment changes. Herein, we investigate the impact of solvent effects on Lewis acids for the first time as measured by the fluorescent Lewis adduct (FLA) method. The binding of a Lewis acid in various solvents reveals a measurable dichotomy between both polarity and donor ability of the solvent. While not strictly separable, we observe that the influence of solvent polarity on Lewis acid unit (LAU) values is distinctly opposite to the influence of donor ability. This dichotomy was confirmed by titration data, illustrating that solvation effects can be appropriately and precisely gauged by the FLA method.

Charge Manipulation in a Series of π-Stacked Pillared-Layer Frameworks by Tuning Electron Donation Ability of Building Blocks

One advantage of charge-transfer metal–organic frameworks comprising electron-donor (D) and electron-acceptor (A) units is their controllable electronic state. Herein, a new charge-ordered state with the formula Z+[D+D0A2–]− was revealed in π-stacked pillared-layer frameworks (π-PLFs), [FeCp*2][{Ru2(RxPhCO2)4}2(TCNQ)]·n(solv) (RxPhCO2– = R-substituted benzoate with R = m-F (1), and 3,5-F2 (2); [FeCp*2]+ = decamethylferrocenium; TCNQ = 7,7,8,8-tetracyano-p-quinodimethane; solv = interstitial crystallization solvents), where [FeCp*2]+ (Z+) acts as a pillar connecting the two-dimensional [D2A]− layers of [{Ru2(RxPhCO2)4}2(TCNQ)]− in the π-stacking mode. The prototype π-PLF with R = 2,3,5,6-F4 (0) had another charge-ordered state Z+[D02A–], whereas the Z+[D+D0A2–]−-type charge-ordered state in 1 and 2 was achieved by significantly enhancing the electron-donating ability of the [Ru2] units compared to that in 0, inducing electron transfer from [Ru2II,II] to TCNQ•– to produce a set of [Ru2II,III]+ and TCNQ2– in the layer. Compounds 1 and 2 were paramagnetic because of the isolation of paramagnetic species [Ru2II,II] (S = 1), [Ru2II,III]+ (S = 3/2), and [FeCp*2]+ (S = 1/2) shielded by diamagnetic TCNQ2– linkers. This work demonstrates the feasibility of charge manipulation, even in the π-PLF system, by controlling the electron-donating ability of the [Ru2] unit.

4Fe–4S]-Mediated Proton-Coupled Electron Transfer Enables the Efficient Degradation of Chloroalkenes by Reductive Dehalogenases

Reductive dehalogenases (RDases) are key enzymes involved in the degradation of organohalide compounds. Despite extensive experimental and computational studies, the catalytic mechanism of RDases remains unclear. We show here that the proximal [4Fe–4S]1+ cluster of the reductive dehalogenase PceA can mediate a proton-coupled electron transfer (PCET) process to quench the substrate radical. Such a [4Fe–4S]1+-mediated PCET process is enhanced by both exchange and super-exchange interactions. The participation of [4Fe–4S]1+ in mediating a PCET process in RDases is unexpected, although well known in reducing Co(II). In addition, in RDases, the Arg305 residue acts as an efficient proton donor for the PCET reactions. The deprotonated Tyr246 serves to maintain the favorable conformation of Arg305 during catalysis and sustains its proton donation ability, which is requested during the PCET reaction. Such a novel mechanism enables the efficient detoxification of chloroalkene pollutants by the reductive dehalogenase PceA, which also rationalizes the selective dechlorination of trichloroethene to form cis-1,2-dichloroethylene. These results highlight the critical role of the proximal [4Fe–4S].

Chalcogen-substituted carbenes: a density functional study of structure, stability, and donor ability.

Chalcogen-substituted carbenes are examined computationally using density functional theory. Several approaches are used to assess the stability and reactivity of chalcogenazol-2-ylidene carbenes (NEHCs; E = O, S, Se, Te). The known unsaturated species 1,3-dimethylimidazol-2-ylidene is studied at the same level of theory as the NEHC molecules, as a reference. Electronic structures, stability towards dimerization, and ligand properties are discussed. The results highlight the NEHCs as potentially valuable ancillary ligands for stabilizing low-valent metals or paramagnetic main group molecules. A simple, effective computational method for evaluating σ donor ability and π acidity of carbenes is presented.

Exploration of advanced cellulosic material for membrane filtration with outstanding antifouling property.

Membranes, at times, have issues due to membrane fouling. The membrane fouling leads to performance deterioration and poses a potential to clog the membrane. Here we present experimental works carried out with emphasis on the antifouling properties, chlorine resistance, and mechanical properties of cellulose triacetate (CTA) and cellulose esters. We present that antifouling performance of cellulose esters evaluated by means of the VCG theory decreases with increasing carbon number in the substituent because of the high electron-donating nature of short aliphatic ester groups. When a long aliphatic ester group is required in terms of other properties such as resistance to chlorine, introducing it together with another substituent with an electron-donating nature such as an ethylene glycol moiety may strike a balance between antifouling and other performances.

Partner effect in accelerating pincer-co catalyzed nitrile hydroboration reactions.

The pincer-Co catalyzed nitrile hydroboration of nitrile has been presented as an elegant strategy to afford amine synthesis; however, ligand engineering is required. We show here a strategy to tune the catalytic behavior of the organometallic catalyst, as an alternative approach to ligand engineering, by means of computational investigations to understand the effect of partners such as (18-crown-6)K+, W(CO)3 and W(PMe3)3 on the reactivity of the pincer-Co catalyzed nitrile hydroboration reaction through π-coordination to the ligand aromatic ring. The extra additives bind the central phenyl ring of the ligand by either dispersion or chemical bonding. The electron-richness of the cobalt center is tuned by the partner, and follows the order (18-crown-6)K+ > W(PMe3)3 > no partner > W(CO)3. While the influence of the covalent W-containing partners parallels the electron-richness of the W, the non-covalent partner, (18-crown-6)K+, surprisingly increases the donor ability of the pincer ligand through the polarization effect. All the elementary steps involved in the nitrile hydroboration reaction are influenced by the partner, and the overall barrier is lowered by a surprisingly large amount of 4.9 kcal mol-1 in the presence of (18-crown-6)K+, suggesting a notable partner effect to be explored by experimentalists so that the reactivity of a catalyst can be tuned without ligand modification.

Selective binding of oxalate by a tris-ureido calix[6]tube in a protic environment.

Due to their significant role in industry and biological systems, the interest in selectively recognizing and detecting small dicarboxylates has grown in recent years. In this study, we report on the binding properties of a family of tubular-shaped heterotritopic receptors based on bis-calix[6]arenes, which contain three (thio)urea bridges (C3U and C3TU) or six urea bridges (C6U), toward dicarboxylates. While poor binding properties were observed by NMR for the newly synthesized C6U, receptors C3U and C3TU exhibited a unique ability to cooperatively complex a dicarboxylate anion sandwiched between two ammonium ions. The three ions are complexed in contact and aligned within the tubular shape of the receptor, forming cascade complexes that are stable even in a competitive environment. The different binding properties between the receptors were rationalized in terms of size, flexibility, H-bond donor ability, and intramolecular H-bonding within the anion binding pocket between the calixarene cavities. With C3U, a rare selectivity for oxalate over other small dicarboxylates and various bicharged anions was observed. Molecular modeling of the cascade complex indicated that the oxalate anion is stabilized by an array of hydrogen bonds with the urea bridges of the receptor and both propylammonium cations nested within the calixarene cavities.

Quantification of the hydride donor abilities of NADH, NADPH, and BH3CN- in water.

The nucleophilic reactivities of the hydride donors NADH, NADPH, and BH3CN- in water were quantified using kinetic measurements with benzhydrylium ions as reference electrophiles. All three hydride donors were found to possess almost identical nucleophilic reactivities, providing a potential explanation for why they are involved in similar transformations in biochemistry and organic synthesis, respectively.

Ligands containing 7-azaindole functionality for inner-sphere hydrogen bonding: Structural and photophysical investigations

The synthesis, structural analysis and spectroscopic characterisation of three new 7-azaindole ligands is reported, alongside a novel 7-azaindole derived coordination polymer, with the aim of identifying new bridging ligands containing inner-sphere hydrogen bond donor functionality. Structural characterisation shows that the 7-azaindole hydrogen bond donor ability is significantly stronger in the hydrazone and imine species 1 and 2 compared to the amine 3, with the opposite trend evident in their hydrogen bond acceptor character. These findings are mirrored by the fluorescence spectroscopy results which show bimodal emission, characteristic of multiple emissive species related by proton transfer, is only evident in the amine species and not the more acidic imines. The polymeric copper(II) complex of the hydrazone ligand 1 shows the anticipated inner-sphere hydrogen bonding with a similar donor strength to that observed in the free ligand, which leads to deformation in the remainder of the coordination sphere. These results show the untapped versatility of the 7-azaindole functional group as a building block for ligands in coordination polymers and other multinuclear assemblies, with the potential for both stabilisation through hydrogen bonding and interesting photophysical properties.

Cyclic alkyl(amino)iminates (CAAIs) as strong 2σ,4π-electron donor ligands for the stabilisation of boranes and diboranes(4): a synthetic and computational study.

Singly and doubly cyclic alkyl(amino)iminate (CAAI)-substituted boranes and diboranes(4) were synthesised by halosilane elimination between a silylimine and halo(di)borane precursors. 11B NMR-spectroscopic studies show that the CAAI ligand is a much stronger electron donor than amino ligands. X-ray crystallographic analyses reveal that the degree of B-NCAAI double bonding increases with the electron-withdrawing capacity of the other substituents at boron. The C-N-B bond angle displays a great flexibility, ranging from 131° to near-linear 176°, the narrowest angles being observed for NMe2-substituted derivatives and the widest angles for highly sterically demanding substituents. Density functional theory (DFT) calculations on the electronic structures of the anionic CAAI ligand compared to unsaturated and saturated N-heterocyclic iminate (NHI) ligands show that the former is the best σ donor of the three but less π-donating than the unsaturated NHI. Nevertheless, the linear (CAAI)BH2 complex displays somewhat stronger C-N and N-B π bonding than the corresponding ((S)NHI)BH2 complexes.

Skeletally substituted aluminium and gallium carbenoids: a computational exploration.

Comprehensive computational investigations were carried out to understand the electronic and ligand properties of skeletally substituted β-diketiminate stabilized Al(I) and Ga(I) carbenoids as well as to probe their potential in small molecule activation. All of the proposed group 13 carbenoids possess a stable singlet ground state, and the majority of them have a significantly enhanced electron donation ability compared to the experimentally reported systems. The evaluation of the energetics associated with the splitting of various strong bonds such as H-H, N-H, C-F, and B-H by these carbenoids indicates that many of the proposed Al and Ga carbenoids may be considered as suitable candidates for small molecule activation.

η6 -Metalated Aryl Iodides in Diels-Alder Cycloaddition Reactions: Mode of Activation and Catalysis.

The potential application of η6 -metalated aryl iodides as organocatalyst has been explored by means of computational methods. It is found that the enhanced halogen bonding donor ability of these species, in comparison with their demetalated counterparts, translates into a significant acceleration of the Diels-Alder cycloaddition reaction involving cyclohexadiene and methyl vinyl ketone. The factors behind this acceleration, the endo-exo selectivity of the process and the influence of the nature of the transition metal fragment in the activity of these species are quantitatively explored in detail by means of the combination of the Activation Strain Model of reaction and the Energy Decomposition Analysis methods.

D 6 h Symmetric Radical Donor–Acceptor Nanographene Modulated Interfacial Carrier Transfer for High-Performance Perovskite Solar Cells

<i>D</i> ^{6 <i>h</i>} Symmetric Radical Donor–Acceptor Nanographene Modulated Interfacial Carrier Transfer for High-Performance Perovskite Solar Cells

Study of structure of nonaqueous reverse micelles with o-nitroaniline and methyl orange as molecular probes: comparison with an aqueous reverse micelles

Abstract Instead of water reversed micelles can also be formed with polar organic solvents possessed with high dielectric constant and very low solubility in oil phase. Nonaqueous reverse micelles or microemulsions represent an interesting microreactors for various reactions, especially for reactions, where reagents can react with water. Study of localization places of molecular probes in organic polar pockets of reverse micelles is topical. The solvatochromic behavior of optical probes ortho-nitroaniline (o-NA) and methyl orange (MO) was studied in nonaqueous reverse micelles on the basis of surfactants sodium bis (2-ethylhexyl) sulfosuccinate (AOT) and polyoxyethylene (4) lauryl ether (C12E4) and polar organic solvents (acetonitrile, dimethylformamide, glacial acetic acid, etc.) insoluble in oil phase hexane. The strength of binding of o-NA and MO to AOT and C12E4 reversed micelles was assesssed via binding constant (K b ) and association degree (α) respectively. Donor, acceptor, or dipole-dipole interactions ability of the solvent to the head groups of surfactant was taken into account in order to explain results obtained with UV–visible spectroscopic method. The binding constants of o-NA with reverse AOT micelles in the presence of various solvents in the pockets of reversed micelles increase in the following row water &lt; glacial acetic acid &lt; acetonitrile &lt; dimethylformamide &lt; dimethyl sulfoxide, but this sequence is reversed when o-NA binds to C12E4 reverse micelles. The high value of the proton donor or acidity parameter in the water molecule (x d = 0.37) determines the weak binding of o-NA to the head AOT groups (K b = 20.8) in case of aqueous reverse micelles. The high value of the dipole parameter in the dimethylformamide molecule (x n = 0.40) promotes its strong interaction with nonionic polyoxyethylene groups of C12E4, which results in low value of binding constant (K b = 26.5) in case of optical probe o-NA and low value of association degree (α = 0.60) using MO as absorption probe. The results of this article will contribute to the improvement of the concept of interfacial processes, viz.: (i) some issues of supramolecular chemistry, (ii) revealing the contribution of parameters of donor, acceptor or dipole-dipole interaction in a polar organic solvent at the surfactant/nonpolar organic solvent interface, and (iii) features of the dissolution of optical probes in non-aqueous reverse micelles.

Insights into Lewis/Brønsted acidity of metal chlorides and solvent effect of alcohols for synthesis of γ-valerolactone by combining molecular dynamics simulations and experiments

The synthesis of biofuel γ-valerolactone (GVL) from furfural is a multistep process that entails the regulation of Lewis/Brønsted (L/B) acidity of catalyst and the hydrogen donation ability of alcohols. In this study, experiments and molecular dynamics (MD) simulations were combined to get insights into the role of catalysts and solvents during the conversion of furfural to GVL. The capacities of various metal chlorides (divalent to hexavalent metal elements) and alcohols (primary and secondary alcohols) were comparatively investigated. The results showed that chlorides of Group IVB metals (ZrCl4 and HfCl4) exhibited excellent catalytic performance and achieved GVL yields of 61.88 % and 68.13 %, respectively. By preliminary statistical assessment, the intervals in which high isopropyl levulinate (IPL) yields and high GVL yields were found corresponded to different L/B acidity (3.5 < N < 4.8, −2 < Z < 1 and N < 5.7, Z > 1.5) (Z: Lewis acid strength. N: number of molecules in the shell). Secondary alcohols displayed the lower reduction potential but the higher interaction energy with reactants than that of primary alcohols. The distribution of Hf4+ around the reactants was tendentious, whereas the distribution of C3H7OH2+ was more homogeneous. The investigation of reaction mechanism proposed new understandings of the reacted sites of reactants and the hydrogen transfer of solvent to reactants. The hypothesis that IPL was capable of hydrogen/deuterium (H/D) exchange was developed.

Diverse Hydrogen-Bonded Structural Motifs in 1,4-Diazabicyclo[2.2.2]octane N,N’-Dioxide Salts with Oxoanions

Four new hybrid inorganic–organic salts of 1,4-diazabicyclo[2.2.2]octane N,N’-dioxide (odabco) with the formulae odabco·2HNO3 (1), odabco·HClO4 (2), odabco·H2SO4 (3) and odabco·2H2SO4 (4) were synthesized and characterized by single-crystal x-ray diffraction (XRD), powder XRD and infrared spectroscopy. Compound 1 is based on the isolated (H2odabco)2+ fragments, representing 0D structure. 2 is based on cationic 1D {Hodabco}nn+ hydrogen-bonded chains. Compound 3 comprising a strongly coordinated sulfate anion consists of two-component hydrogen-bonded {-H2odabco-SO4−} fragments forming uncharged 1D helical chains. 4 contains both {-HSO4-}nn– and {-HSO4-H2odabco-HSO4−} hydrogen bonding motifs, resulting in a 3D polymeric network. A comparative structural analysis of both the obtained and the previously reported cognate structures was performed to rationalize the impact of the degree of odabco protonation and the anion donor ability on the structural features and dimensionalities of odabco-based hydrogen-bonded lattices.

Controlled Access to Four- and Six-Membered Palladacycles via Modifying Donor Abilities of β-Ketiminato Ligands ("NacAcs").

The synthesis of Pd complexes of the type [PdBr(iPr2-bimy)(NacAc)] (NacAc = β-ketiminate, iPr2-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene) was attempted, in a continuing effort to quantify donor abilities of chelating β-ketiminate ligands using the Huynh electronic parameter for bidentate donors (HEP2). Subtle variation of N-substituents on the NacAc backbone was discovered to induce a drastic change in the preferred chelating mode, in that the commonly encountered κ2-N,O-six-membered palladacycles were observed with R = Me and Et, while the unusual κ2-C,N-four-membered palladacycles were isolated with R = iPr, Cy, and tBu. Computational studies subsequently corroborated these findings, in the form of an overall exergonic six-to-four-membered ring contraction process and a lower associated activation energy for the three more electron-donating alkyl moieties. This trend in the established energy profiles can be attributed to a reduced HOMO-LUMO gap in the corresponding optimized structures of the six-membered ring complexes.

An Intracellular Metabolic Signature as a Potential Donor-Independent Marker of the Osteogenic Differentiation of Adipose Tissue Mesenchymal Stem Cells

This paper describes an untargeted NMR metabolomics study to identify potential intracellular donor-dependent and donor-independent metabolic markers of proliferation and osteogenic differentiation of human adipose mesenchymal stem cells (hAMSCs). The hAMSCs of two donors with distinct proliferating/osteogenic characteristics were fully characterized regarding their polar endometabolome during proliferation and osteogenesis. An 18-metabolites signature (including changes in alanine, aspartate, proline, tyrosine, ATP, and ADP, among others) was suggested to be potentially descriptive of cell proliferation, independently of the donor. In addition, a set of 11 metabolites was proposed to compose a possible donor-independent signature of osteogenesis, mostly involving changes in taurine, glutathione, methylguanidine, adenosine, inosine, uridine, and creatine/phosphocreatine, choline/phosphocholine and ethanolamine/phosphocholine ratios. The proposed signatures were validated for a third donor, although they require further validation in a larger donor cohort. We believe that this proof of concept paves the way to exploit metabolic markers to monitor (and potentially predict) cell proliferation and the osteogenic ability of different donors.

Mesoionic N-Heterocyclic Imines as Super Nucleophiles in Catalytic Couplings of Amides with CO2.

An extended class of stable mesoionic N-heterocyclic imines (mNHIs), containing a highly polarized exocyclic imine moiety, were synthesized. The calculated proton affinities (PA) and experimentally determined Tolman electronic parameters (TEPs) reveal that these synthesized mNHIs have the highest basicity and donor ability among NHIs reported so far. The superior nucleophilicity of newly designed mNHIs was utilized in devising a strategy to incorporate CO2 as a bridging unit under reductive conditions to couple inert primary amides. This strategy was further extended to hetero-couplings between amide and amine using CO2 . These hitherto unknown catalytic transformations were introduced in the diversification of various biologically active drug molecules under metal-free conditions. The underlying mechanism was explored by performing a series of control experiments, characterizing key intermediates using spectroscopic and crystallographic techniques.