Tuning the lanthanide binding tags for preferential actinide chelation: an all atom molecular dynamics study.

The present study focuses on designing mutant peptides derived from the lanthanide binding tag (LBT) to enhance selectivity for trivalent actinide (An) ions over lanthanide (Ln) metal ions (M). The LBT is a short peptide consisting of only 17 amino acids, and is known for its high affinity towards Ln. LBT was modified by substituting hard-donor ligands like asparagine (ASN or N) and aspartic acid (ASP or D) with softer ligand cysteine (CYS or C) to create four mutant peptides: M-LBT (wild-type), M-N103C, M-D105C, and M-N103C-D105C.

Synthesis, Structure, and Redox Reactivity of Ni Complexes Bearing a Redox and Acid-Base Non-innocent Ligand with Ni, Ni, and Ni Formal Oxidation States.

A series of Ni complexes bearing a redox and acid-base noninnocent tetraamido macrocyclic ligand, H-(TAML-4) {H-(TAML-4) = 15,15-dimethyl-5,8,13,17-tetrahydro-5,8,13,17-tetraaza-dibenzo[]cyclotridecene-6,7,14,16-tetraone}, with formal oxidation states of Ni, Ni, and Ni were synthesized and characterized structurally and spectroscopically. The X-ray crystallographic analysis of the Ni complexes revealed a square planar geometry, and the [Ni(TAML-4)] complex with the formal oxidation state of Ni was characterized to be [Ni(TAML-4)] with the oxidation state of the Ni ion and the one-electron oxidized TAML-4 ligand, TAML-4. The Ni oxidation state and the TAML-4 radical cation ligand, TAML-4, were supported by X-ray absorption spectroscopy and density functional theory calculations.

Manifold Fluorescence Enhancement of a Styryl(pyridinium)-chromene Hybrid Dye upon Binding with an Elongated β-Cyclodextrin Cavity.

The interaction of a styryl(pyridinium)-chromene hybrid dye (DSP-C) with the 2-hydroxypropyl-β-cyclodextrin (HPβCD) macrocycle leads to a remarkably large increase (∼310-fold) in its fluorescence intensity, in contrast to the relatively smaller (∼45-fold) enhancement observed with native β-cyclodextrin (βCD). Both macrocycles (βCD and HPβCD) bind with the styryl(pyridinium) as well as the chromene fragments of the hybrid dye, with the simultaneous formation of 1:1 and 2:1 host:guest complexes. However, the binding constant (K) is more than an order of magnitude higher for HPβCD than for βCD.

Direct observation of arene⋯sulphur dioxide interaction: role of metal ions in electronic modulation for binding and activation.

In the quest to understand biologically relevant interactions of environmentally detrimental SO with host molecules to modulate the electronic properties of the binding sites, we have directly observed the lone pair⋯π interaction between the aromatic ring and nucleophilic O of SO (3.11 Å), for the first time to the best of our knowledge, in addition to the interaction between electrophilic S of SO and metal-bound thiolate (2.63 Å).

Thorium Complexation with Aliphatic and Aromatic Hydroxycarboxylates: A Combined Experimental and Theoretical Study.

Hydroxycarboxylic acids, viz., α-hydroxyisobutyric acid (HIBA) and mandelic acid (MA), have been widely employed as eluents for inner transition metal separation studies. Both extractants have identical functional groups (OH and COOH) with different side-chains.

Identification, Characterization, and Electronic Structures of Interconvertible Cobalt-Oxygen TAML Intermediates.

The reaction of Li[(TAML)Co]·3HO (TAML = tetraamido macrocyclic tetraanionic ligand) with iodosylbenzene at 253 K in acetone in the presence of redox-innocent metal ions (Sc(OTf) and Y(OTf)) or triflic acid affords a blue species , which is converted reversibly to a green species upon cooling to 193 K. The electronic structures of and have been determined by combining advanced spectroscopic techniques (X-band electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), X-ray absorption spectroscopy/extended X-ray absorption fine structure (XAS/EXAFS), and magnetic circular dichroism (MCD)) with theoretical studies. Complex is best represented as an = 1/2 [(Sol)(TAML)Co---OH(LA)] species (LA = Lewis/Brønsted acid and Sol = solvent), where an = 1 Co(III) center is antiferromagnetically coupled to = 1/2 TAML, which represents a one-electron oxidized TAML ligand.

Remarkably High Separation of Neodymium from Praseodymium by Selective Dissolution from their Oxide Mixture using an Ionic Liquid Containing aβ-Diketone.

A simple, efficient, direct and economical method for the mutual separation of Nd and Pr was developed by the selective dissolution of NdO from their oxide mixtures in an ionic liquid containing 2-thenoyltrifluoroacetone (HTTA) resulting in an unprecedented separation factor (β)>500, which is 277 times more than the thus far reported β values. The proposed mechanism was supported by DFT computations.

Late-stage Ligand Modification After Coordination Strengthens Stereoselectively Self-Assembled Hemiaminal Ether Complexes.

Fragile hemiaminal ether linkages present in the backbone of koneramines (L OR'), tridentate ligands, bound to copper(II) in stereoselectively self-assembled syn-[Cu(L OR')X ] complexes were transformed into sturdy methylene linkages to make corresponding rac-[Cu(L H)Cl ] complexes by late-stage ligand modification after coordination with the retention of coordination sphere. The generality of stereoselective self-assembly of koneramine complexes is shown by utilising a number of metal ions, anions, amines, alcohols and thiols with complete characterisations.

Redox Potentials of Uranyl Ions in Macrocyclic Complexes: Quantifying the Role of Counter-Ions.

Several uranyl ions strapped with Schiff-base ligands in the presence of redox-innocent metal ions are synthesized, and their reduction potentials are recently estimated. The change in Lewis acidity of the redox-innocent metal ions contributes to ∼60 mV/p unit quantified which is intriguing. Upon increasing the Lewis acidity of metal ions, the number of triflate molecules found near the metal ions also increases whose contributions toward the redox potentials remain poorly understood and not quantified until now.

A six-coordinate high-spin FeO species of cucurbit[5]uril: a highly potent catalyst for C-H hydroxylation of methane, if synthesised.

DFT and DLPNO-CCSD(T) calculations predict a stable = 2 six-coordinate FeO species with cucurbit[5]uril (CB[5]) as a ligand ([(CB[5])FeO(HO)](1)). The strong oxidising capability of far exceeds even that of metalloenzymes such as sMMOs in activating inert substrates such as methane, setting the stage for a new generation of biomimetic catalysts.

Stimuli Responsive Confinement of a Molecular Rotor Based BODIPY Dye inside a Cucurbit[7]uril Nanocavity.

Present study reports the interaction of a molecular rotor based BODIPY dye, 8-anilino-BODIPY (ABP), with a versatile macrocyclic molecule, cucurbit[7]uril (CB7), investigated through various techniques such as ground-state absorption, steady-state fluorescence, time-resolve emission, proton NMR, and quantum chemical studies. Although BODIPY dyes have widespread applications due to their intriguing photochemical properties, studies on their noncovalent interactions with different macrocyclic hosts, especially regarding their supramolecularly induced modulations in photophysical properties are very limited. The investigated BODIPY dye, especially its protonated ABPH form (pH ∼ 1), shows a large fluorescence enhancement on its interaction with the CB7 host, due to large reduction in the structural flexibility for the bound dye, causing a suppression in its nonradiative de-excitation process in the excited state.

Near-Infrared Fluorescent Probe Activated by Nitroreductase for and Hypoxic Tumor Detection.

Tumor hypoxia is correlated with increased resistance to chemotherapy and poor overall prognoses across a number of cancer types. We present here a cancer cell-selective and hypoxia-responsive probe () designed on the basis of density functional theory (DFT)-optimized quantum chemical calculations. The probe was found to provide a rapid fluorescence "off-on" response to hypoxia relative to controls, which lack the folate or nitro-benzyl moieties.

MD simulation reveals differential binding of Cm(III) and Th(IV) with serum transferrin at acidic pH.

The iron carrier human serum transferrin (sTf) is known to transport other metals, including some actinides (An). Radiotoxic An are routinely involved in the nuclear fuel cycle and the possibility of their accidental exposure cannot be ruled out. Understanding An interaction with sTf assumes a greater significance for the development of safe and efficacious chelators for their removal from the blood stream.

Molecular dynamics simulations of plutonium binding and its decorporation from the binding-cleft of human serum transferrin.

The possibility of plutonium (Pu) intake by radiation workers can not be ruled out. Transportation of Pu(IV) to various organs/cells is mainly carried through iron-carrying protein, serum transferrin (sTf), by receptor-mediated endocytosis. Understanding the Pu-sTf interaction is a primary step toward future design of its decorporating agents.

Regioselective Oxidation of C-H Bonds in Unactivated Alkanes by a Vanadium Superoxo Catalyst Bound to a Supramolecular Host.

A vanadyl ion bound to a cucurbituril (CB) host was reported to oxidize pentane to 2-pentanol in the presence of an oxidizer. DFT calculations suggest that the catalyst selectively reacts with stronger C-H bonds in pentane over weaker C-H bonds in cyclohexane due to size exclusion by the CB host. The active catalyst is an unprecedented vanadium superoxo species bound to the host, and the selectivity toward secondary over the primary C-H bond is the result of a higher degree of charge transfer from the secondary compared to the primary position.

Correction: A comparative study of Ir(iii) complexes with pyrazino[2,3-f][1,10]phenanthroline and pyrazino[2,3-f][4,7]phenanthroline ligands in light-emitting electrochemical cells (LECs).

Correction for 'A comparative study of Ir(iii) complexes with pyrazino[2,3-f][1,10]phenanthroline and pyrazino[2,3-f][4,7]phenanthroline ligands in light-emitting electrochemical cells (LECs)' by Iván González et al., Dalton Trans., 2015, 44, 14771-14781.

Design and Optimization of Catalysts Based on Mechanistic Insights Derived from Quantum Chemical Reaction Modeling.

Until recently, computational tools were mainly used to explain chemical reactions after experimental results were obtained. With the rapid development of software and hardware technologies to make computational modeling tools more reliable, they can now provide valuable insights and even become predictive. In this review, we highlighted several studies involving computational predictions of unexpected reactivities or providing mechanistic insights for organic and organometallic reactions that led to improved experimental results.

Stabilizing Terminal Ni(III)-Hydroxide Complex Using NNN-Pincer Ligands: Synthesis and Characterization.

The reaction of [Ni(COD)] (COD; cyclooctadiene) in THF with the NNN-pincer ligand bis(imino)pyridyl (L) reveals a susceptibility to oxidation in an inert atmosphere ([O] level <0.5 ppm), resulting in a transient Ni:dioxygen adduct. This reactive intermediate abstracts a hydrogen atom from THF and stabilizes an uncommon Ni(III) complex.

Maximizing Property Tuning of Phosphorus Corrole Photocatalysts through a Trifluoromethylation Approach.

An eight-member series of CF-substituted difluorophosphorus corroles was prepared for establishing a structure-activity profile of these high-potential photosensitizers. It consisted of preparing all four possible isomers of the monosubstituted corrole and complexes with 2-, 3-, 4-, and 5-CF groups on the macrocycle's periphery. The synthetic pathway to these CF-substituted derivatives, beginning with (tpfc)PF, involves two different initial routes: (i) direct electrophilic CF incorporation using FSOCFCOMe and copper iodide, or (ii) bromination to achieve the 2,3,8,17,18-pentabrominated compound using excess bromine in methanol.

Binding of Cm(III) and Th(IV) with Human Transferrin at Serum pH: Combined QM and MD Investigations.

Human serum transferrin (sTf) can also function as a noniron metal transporter since only 30% of it is typically saturated with a ferric ion. While this function of sTf can be fruitfully utilized for targeted delivery of certain metal therapeutics, it also runs the risk of trafficking the lethal radionuclides into cells. A large number of actinide (An) ions are known to bind to the iron sites of sTf although molecular-level understanding of their binding is unclear.

Strong influence of weak hydrogen bonding on actinide-phosphonate complexation: accurate predictions from DFT followed by experimental validation.

Among the varied classes of weak hydrogen bond, the CHO type is one of immense interest as it governs the finer structures of biological and chemical molecules, hence determining their functionalities. In the present work, this weak hydrogen bond has been shown to strongly influence the complexation behaviour of uranyl nitrate [UO2(NO3)2] with diamyl-H-phosphonate (DAHP) and its branched isomer disecamyl-H-phosphonate (DsAHP). The structures of the bare ligands and complexes have been optimized by density functional theory (DFT) calculations.

Are cucurbiturils better drug carriers for bent metallocenes? Insights from theory.

Bent metallocenes (BM) have anti-tumor properties but they face a serious drug efficacy problem due to poor aqueous solubility and rapid hydrolysis under physiological conditions. These two problems can be fixed by encapsulating them in host molecules such as cyclodextrin (CD), cucurbituril (CB) etc. Experimentally, CD-BM, CB-BM host-guest complexes have been investigated to check the efficiency of the drug delivery and efficiency of the encapsulated drug.

Remarkable structural effects on the complexation of actinides with H-phosphonates: a combined experimental and quantum chemical study.

The structural effects of the carbon chain on the extraction of actinides by organo-phosphorus extractants have been examined experimentally and by computation. Branched butyl H-phosphonates and their linear chain isomer, n-butyl H-phosphonate (DBHP), were synthesised and characterised using IR, NMR and GC-MS techniques. Their physical properties viz.

A new series of tetrahedral Co(ii) complexes [CoLX] (X = NCS, Cl, Br, I) manifesting single-ion magnet features.

A series of tetrahedral Co complexes [CoLX] (X = NCS (1), Cl (2), Br (3) and I (4); L = 9,9-dimethyl-4,5-bis(diphenylphosphino) xanthene) based on a P-donor ligand has been prepared to investigate the influence of terminal ligand field strength on the anisotropy of Co single-ion magnets. It has been observed that heavier and softer terminal ligands are able to decrease the anisotropy of the tetrahedral Co centers. Thorough analyses of experimental and theoretical studies show that all complexes have an easy-axis type magnetic anisotropy and slow relaxation behaviors of tetrahedral Co centers.