Modulation of Metallophilic and π–π Interactions in Platinum Cyclometalated Luminophores with Halogen Bonding

Luminescent cyclometalated complexes [M(C^N^N)CN] (M=Pt, Pd; HC^N^N=pyridinyl- (M=Pt 1 , Pd 5 ), benzyltriazolyl- (M=Pt 2 ), indazolyl- (M=Pt 3 , Pd 6 ), pyrazolyl-phenylpyridine (M=Pt 4 )) decorated with cyanide ligand, have been explored as nucleophilic building blocks for the construction of halogen-bonded (XB) adducts using IC₆F₅ as an XB donor. The negative electrostatic potential of the CN group afforded CN⋅⋅⋅I noncovalent interactions for platinum complexes 1 – 3 ; the energies of XB contacts are comparable to those of metallophilic bonding according to QTAIM analysis. Embedding the chromophore units into XB adducts 1 – 3 ⋅⋅⋅IC₆F₅ has little effect on the charge distribution, but strongly affects Pt⋅⋅⋅Pt bonding and π-stacking, which lead to excited states of MMLCT (metal–metal-to-ligand charge transfer) origin. The energies of these states and the photoemissive properties of the crystalline materials are primarily determined by the degree of aggregation of the luminophores via metal–metal interactions. The adduct formation depends on the nature of the metal and the structure of the metalated ligand, the variation of which can yield dynamic XB-supported systems, exemplified by thermally regulated transition 3 ↔ 3 ⋅⋅⋅IC₆F₅.     

Reaction of trimethylene–bisadenine with d10 divalent cations

The synthesis, spectroscopic characterisation and X-ray structure determination of Ade₂(CH₂)₃ 1, [(H-Ade)₂(CH₂)₃]Cl₂⋅H₂O 2 and the outer sphere complex [(H-Ade)₂(CH₂)₃]₂[Cd₂Cl₈(H₂O)₂]⋅4H₂O 3 are reported (Ade=adenine). An important change of conformation appears when trimethylene–bisadenine is protonated. The eclipsed and anti conformation between the two adenine moieties of 1 varies to a gauche and syn conformation for the corresponding Cl⁻ 2 and [Cd₂Cl₈(H₂O)₂]⁴⁻ 3 salts. Compound 3 presents a new dimeric [Cd₂Cl₈(H₂O)₂]⁴⁻ anion in which cadmium(II) has a distorted-octahedral co-ordination with two cis chlorine atoms bridging two cadmium atoms. The corresponding Zn(II) and Hg(II) salts have been obtained by similar procedures.     

Interactions of HCl with 1-Butanol and Group Additivity Analysis for the HCl–Alcohol Interactions

An electromotive force (emf) method was used to determine thermodynamic parameters of interaction of HCl with normal 1-butanol (n-BuOH) in water between 5 and 45°C. A comparison of pair interaction parameters for HCl–n-BuOH with those for HCl–t-BuOH (tert butyl alcohol) showed that there is an obvious difference between them. This was interpreted in terms of steric structure of their carbon chains. The group Gibbs free energy parameters ( and ) for the HCl–alcohol–water systems were derived according to the Savage–Wood group additivity principle. These group parameters can be used to evaluate pair interaction parameters of HCl with alcohol molecules.     

Synthesis,Structure, and Bonding of d3 Molybdenum–Oxo Complexes

Reduction of d² metal–oxo ions of the form [MO(PP)₂Cl]⁺ (M=Mo, W; PP=chelating diphosphine) produces d³ MO(PP)₂Cl complexes, which include the first isolated examples in group 6. The stability and reactivity of the MO(PP)₂Cl compounds are found to depend upon the steric bulk of the phosphine ligands: derivatives with bulky phosphines that shield the oxo ligand are stable enough to be isolated, whereas those with phosphines that leave the oxo ligand exposed are more reactive and observed transiently. Magnetic measurements and DFT calculations on MoO(dppe)₂Cl indicate the d³ compounds are low spin with a ²[(d_xy)²(π*(MoO))¹] configuration. X-ray crystallographic and vibrational-spectroscopic studies on d² and d³ [MoO(dppe)₂Cl]^0/+ establish that the d³ compound possesses a reduced M−O bond order and significantly longer Mo−O bond, accounting for its greater reactivity. These results indicate that the oxo-centered reactivity of d³ complexes may be controlled through ligand variation.     

Anion Binding Properties of Alkynylplatinum(II) Complexes with Amide-Functionalized Terpyridine: Host–Guest Interactions and Fluoride Ion-Induced Deprotonation

Molecular sensors able to detect ions are of interest due to their potential application in areas such as pollutant sequestration. Alkynylplatinum(II) terpyridine complexes with an amide-based receptor moiety have been synthesized and characterized. Their anion binding properties based on host–guest interactions have been examined with the use of UV-vis absorption and emission spectral titration studies. Spectral changes were observed for both complexes upon the addition of spherical and nonspherical anions. Their titration profiles were shown to be in good agreement with theoretical results predicting a 1:1 binding model, and the binding constants were determined from the experimental data. Drastic color changes from yellow to orange–red were observed for one of the complexes upon titration with fluoride (F⁻) ion in acetone. These changes were ascribed to the deprotonation of the amide functionalities induced by F⁻ ion, and this was confirmed by the restoration of spectral changes upon addition of trifluoroacetic acid to the F⁻ ion–complex mixture as well as by electrospray ionization mass spectrometry (ESI-MS) data.     

Binding Site Switch by Dispersion Interactions: Rotational Signatures of Fenchone–Phenol and Fenchone–Benzene Complexes

Non-covalent interactions between molecules determine molecular recognition and the outcome of chemical and biological processes. Characterising how non-covalent interactions influence binding preferences is of crucial importance in advancing our understanding of these events. Here, we analyse the interactions involved in smell and specifically the effect of changing the balance between hydrogen-bonding and dispersion interactions by examining the complexes of the common odorant fenchone with phenol and benzene, mimics of tyrosine and phenylalanine residues, respectively. Using rotational spectroscopy and quantum chemistry, two isomers of each complex have been identified. Our results show that the increased weight of dispersion interactions in these complexes changes the preferred binding site in fenchone and sets the basis for a better understanding of the effect of different residues in molecular recognition and binding events.     

Concentration-Dependent Interactions of Amphiphilic PiB Derivative Metal Complexes with Amyloid Peptides Aβ and Amylin**

Metal chelates targeted to amyloid peptides are widely explored as diagnostic tools or therapeutic agents. The attachment of a metal complex to amyloid recognition units typically leads to a decrease in peptide affinity. We show here that by separating a macrocyclic GdL chelate and a PiB targeting unit with a long hydrophobic C10 linker, it is possible to attain nanomolar affinities for both Aβ_1-40 (K_d=4.4 nm ) and amylin (K_d=4.5 nm ), implicated, respectively in Alzheimer's disease and diabetes. The Scatchard analysis of surface plasmon resonance data obtained for a series of amphiphilic, PiB derivative GdL complexes indicate that their Aβ_1-40 or amylin binding affinity varies with their concentration, thus micellar aggregation state. The GdL chelates also affect peptide aggregation kinetics, as probed by thioflavin-T fluorescence assays. A 2D NMR study allowed identifying that the hydrophilic region of Aβ_1-40 is involved in the interaction between the monomer peptide and the Gd³⁺ complex. Finally, ex vivo biodistribution experiments were conducted in healthy mice by using ¹¹¹In labeled analogues. Their pancreatic uptake, ∼3 %ID g⁻¹, is promising to envisage amylin imaging in diabetic animals.     

Interactions of γ-Cyclodextrin with the Mixed Micelles of Anionic Surfactants and Their Inclusion Complexes Formation

Interactions of γ-cyclodextrin (γ-CD) with the single and mixed micelles of sodium dodecyl sulfate (SDS) and sodium lauroyl sarcosine (SLAS) have been studied at different concentrations of γ-CD by using conductivity measurements. From conductivity data, the pure and mixed critical micellar concentration (cmc), the equivalent ionic conductivities of the monomeric species (Λ _m), the associated species (Λ _assc) and the micelle (Λ _mic), the degree of counterion dissociation (χ) in the presence of γ-CD have been evaluated from the slope of the conductivity versus concentration plots for the pure and binary mixture of surfactants. From the dependence of cmc of the surfactantson γ-CD concentration, we have deduced the association constant (K) of surfactant-γ-CD inclusion complexes assuming 2:1 stoichiometry. Theories of Clint, regular solution, and Motomura's have been used for the evaluation of ideality or nonideality of the mixed system. Mixed micelles were found to be rich in SDS content in the presence and the absence of γ-CD. The cmc values have been used to evaluate the transfer of standard free energy of micelles (ΔG⁰ _M,tr) from the aqueous medium to additive medium.     

Synthesis, Characterization and Structure of 3d Metal Nitrate Complexes with 1,8-Naphthyridine-N-Oxide

The complexes of 3d metal(Cr, Mn, Fe, Co, Ni, Cu, Zn) nitrates with 1 , 8-naphthyridine-N-oxide (NAPYO) were synthesized. The melting points and solubilities of the new complexes were determined and all the complexes were characterized by elemental analyses, IR spectra, UV spectra and molar conductance. The structures of both nickel complex and copper complex were determined by X-ray single crystal diffraction analyses.     

Tri- and tetrasubstituted α-fluorocyclohexanones with enantiomeric excesses in the range of 97–100%

The α-fluorinated trisubstituted ketones (2S,5R)-(−)-7-Ia, (2R,5R)-(+)-7-IIe, (2S,5R)-(−)-8-Ia and (2R,5R)-(+)-8-IIe were synthesised from (+)-dihydrocarvone (99% (R)-configuration at C-5) and fully characterised. α-Fluorinated tetrasubstituted ketones (−)-9-Ia, (+)-9-Ia, (+)-9-IIa and (+)-10-Ia having e.e.s of ≥97% were synthesised as racemates from 3-methyl cyclohexenone then resolved into the pure enantiomers using chiral HPLC and fully characterised.     

Structures and Magnetic Properties of Three Heterobimetallic 3d–4f Hexanuclear Complexes

Three butterfly heterhexanuclear 3d–4f clusters have been prepared under solvothermal conditions and structurally characterized by IR spectroscopy, elemental analyses, thermal analyses, and single-crystal X-ray diffraction. Each of hexanuclear clusters was built from butterfly Co ₂ ^III Ln ₂ ^III clusters and two Ln^III ions by the bridging of pivalate. Variable-temperature magnetic susceptibilities measurements of the complexes in the temperature range 2–300 K indicate dominant antiferromagnetic exchange interactions.     

New Silver(I) Complexes of Pyridyl Dithioether Ligands with Ag–Ag Interactions: Effects of Anions and Ligand Spacers on the Framework Formations of Complexes

Three new silver(I) complexes existing Ag–Ag interactions, a trinuclear cluster complex [Ag₃(L ¹)₂(NO₃)₂](NO₃) 1, a dinuclear complex [Ag₂(L ¹)₂](PF₆)₂ 2 and a one-dimensional chain complex [Ag₂ L ²(NO₃)₂] 3, where L ¹ and L ² are two structurally related pyridyl dithioether ligands, bis(2-pyridylthio)methane (L ¹) and 1,3-bis(2-pyridylthio)-propane (L ²), have been synthesized and their structures were determined by single-crystal X-ray diffraction analysis. The striking structural differences of 1 and 2 suggest that counter anions have a profound effect upon the framework formations of silver complexes with pyridyl dithioether ligands, and the differences of 1 and 3 indicate that the subtle changes of the space groups have great influence on the coordination modes of the terminal pyridylsulfanyl groups and the geometries of Ag^I ion and therefore greatly influence the structures of their complexes. The weak AgO interactions in the trinuclear complex 1 and the one-dimensinoal chain complex 3 extend them into quasi two-dimensional networks, and the AgS weak interactions in the dinuclear complex 2 into one-dimensinoal chains, and such weak interactions further stabilized these complexes.     

Tetranuclear copper complexes with new β-diketone and β-iminoketone-containing ligands

Novel tetranuclear copper complexes, Cu4(OH)2(ClO4)3 (HA)·H2O (1) and Cu4(ClO4)5(H3B)·3H2O (2), were synthesized by reacting 1,5-bis(1-phenyl-3-methyl-5-pyrazolone-4)-1 ,5-pentanedione with 1,3-propanediamine and 2-hydroxyl-1,3-propanediamine in the presence of a template reagent copper ion. New [2+2] type open cyclic multidentate ligands are also obtained from the reaction (H4A and H6B stand for new compounds from 1,3-propanediamine and 2-hydroxyl-1,3-propanediamine, respectively). They each contain five C = O, three C = N and one NH2 groups. The complexes were characterized by elemental analyses, conductivity, FT-i.r. (micro-i.r., deconvolution technique), FAB-MS, e.s.r., electronic spectra and extended X-ray absorption fine structure (EXAFS). Copper ions in (1) are basically four coordinate with tetragonal geometry. The average coordination bond distances of Cu–N and Cu–O are 1.91 Å and 2.05 Å. In (2), copper ions are primarily five coordinate with square-based pyramidal geometry. The average coordination bond distances of Cu–N and Cu–O are 1.93Å and 2.08Å. Four copper atoms in molecules may be arranged tetragonally. Both the ligand field and the coordination bonds in complex (1) are stronger than those in (2). Investigations on variable temperature susceptibilities show that some antiferromagnetic exchange interaction exist in the complexes. The plots of –1 versus T obey the Curie-Weiss law only at low temperature. Preliminary results of a bioassay indicate that the two complexes have some antitumour activity in vitro.     

Tricoordinate Coinage Metal Complexes with a Redox-Active Tris-(Ferrocenyl)triazine Backbone Feature Triazine–Metal Interactions

2,4,6-Tris(1-diphenylphosphanyl-1’-ferrocenylene)-1,3,5-triazine ( 1 ) coordinates all three coinage metal(I) ions in a 1:1 tridentate coordination mode. The C₃-symmetric coordination in both solid state and solution is stabilised by an uncommon cation–π interaction between the triazine core and the metal cation. Intramolecular dynamic behaviour was observed by variable-temperature NMR spectroscopy. The borane adduct of 1 , 1BH₃ , displays four accessible oxidation states, suggesting complexes of 1 to be intriguing candidates for redox-switchable catalysis. Complexes 1Cu , 1Ag , and 1Au display a more complicated electrochemical behaviour, and the electrochemical mechanism was studied by temperature-resolved UV/Vis spectroelectrochemistry and chemical oxidation.     

Synthesis, Structure and Noncovalent Interactions of Palladium(II) Complexes with N-Benzoyl-β-phenylalaninate Dianion and Aromatic Diimine

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Micromolar Affinity and Higher: Synthetic Host–Guest Complexes with High Stabilities

The design of high-affinity synthetic host–guest complexes is of paramount importance because they are key elements in constructing unprecedented supramolecular assemblies, functional materials, molecular probes, artificial signal transduction events, and interfaces with the biological world. The present review article collects recent achievements in the design of 1 : 1 host–guest complexes with outstanding stabilities, i.e., exceeding 10⁶ M⁻¹. The relationships between the measured thermodynamic constants and the structural parameters of the interacting species are analyzed. The design features of high-affinity hosts are discussed in light of their binding properties. Different solvents and different types of noncovalent interactions are considered for the stabilization of the complexes. Finally, some hints are provided for the design of future synthetic receptors displaying high affinity and selectivity.     

nES GEMMA Analysis of Lectins and Their Interactions with Glycoproteins – Separation,Detection, and Sampling of Noncovalent Biospecific Complexes

In order to better understand biological events, lectin–glycoprotein interactions are of interest. The possibility to gather more information than the mere positive or negative response for interactions brought mass spectrometry into the center of many research fields. The presented work shows the potential of a nano-electrospray gas-phase electrophoretic mobility molecular analyzer (nES GEMMA) to detect weak, noncovalent, biospecific interactions besides still unbound glycoproteins and unreacted lectins without prior liquid phase separation. First results for Sambucus nigra agglutinin, concanavalin A, and wheat germ agglutinin and their retained noncovalent interactions with glycoproteins in the gas phase are presented. Electrophoretic mobility diameters (EMDs) were obtained by nES GEMMA for all interaction partners correlating very well with molecular masses determined by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) of the individual molecules. Moreover, EMDs measured for the lectin–glycoprotein complexes were in good accordance with theoretically calculated mass values. Special focus was laid on complex formation for different lectin concentrations and binding specificities to evaluate the method with respect to results obtained in the liquid phase. The latter was addressed by capillary electrophoresis on-a-chip (CE-on-a-chip). Of exceptional interest was the fact that the formed complexes could be sampled according to their size onto nitrocellulose membranes after gas-phase separation. Subsequent immunological investigation further proved that the collected complex actually retained its native structure throughout nES GEMMA analysis and sampling.

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Graphical Abstract ?

     

Selective Activation of Ar–Cl and Ar–C Bonds with Iron(II) Complexes

The electrophilic iron–carbene chelate complexes 1 and 2 react with alkoxides RO⁻ to give the neutral chelate complex 3 and the carbene complex 4 , respectively. Depending on the nature of the chelating ortho substituent, selective activation of the Ar–Cl or Ar–C bond occurs; these processes are promoted by the chelation.