Novel route in the synthesis of ψ[CH2NH] amide bond surrogate

An alternative method for the synthesis of pseudopeptides containing a ψ[CH₂NH] amide bond surrogate is reported. The synthetic approach is based on a nucleophilic displacement of the chiral N-protected β-iodoamines with conveniently protected amino acid esters. The compatibility of this method with both conventional and microwave-assisted peptide synthesis should increase the potentiality of the ψ[CH₂NH] peptide bond isostere in peptide chemistry.     

Hydrosilylation of epoxides catalyzed by a cationic η1-silane iridium(III) complex

Cationic silane complex 2, catalyzes the hydrosilylation of epoxides and cyclic ethers to give the silyl-protected alcohols, regioselectively. A mechanistic study shows that the epoxide undergoes isomerization to the ketone, followed by hydrosilylation.     

Insertion of arynes into the carbon–oxygen double bond of amides and its application into the sequential reactions

The reaction of arynes, generated from ortho-(trimethylsilyl)aryl triflates, with the CO bond of formamides gave salicylaldehyde derivatives via the formation of formal [2+2] adducts. The sequential transformation of arynes into ortho-disubstituted arenes, o-aminoalkylphenols or o-hydroxyalkylphenols, was achieved by one-pot procedure using dialkylzincs.     

Effects of fluorine substituent on properties of cyclometalated iridium(III) complexes with a 2,2′-bipyridine ancillary ligand

Cationic cyclometalated Ir(III) complexes (Ir1-Ir5) with fluorine-substituted 2-phenylpyridine (ppy) derivatives as C^N cyclometalating ligands and 2,2′-bipyridine (bpy) as the ancillary ligand, have been synthesized and fully characterized. The influences of the number and the position of fluorine atoms at the cyclometalating ligands on the photophysical, electrochemical and oxygen sensing properties of the Ir(III) complexes have been investigated systematically. The introduction of fluorine on the C^N cyclometalating ligands of the complexes results in blue-shifts of the maximum emission wavelengths, and increases in the photoluminescence quantum yields (Φ_PL), phosphorescence lifetimes and energy gaps, compared to the non-fluorinated [Ir(ppy)₂(bpy)]⁺PF₆^? (Ir0). Among them, 2-(2,4-difluorophenyl)pyridine-derived Ir4 shows the maximum blue-shift (514 nm vs. 575 nm for Ir0) and the highest Φ_PL (50.8% vs. 6.5% for Ir0). The complex Ir3 with 2-(4-fluorophenyl)-5-fluoropyridine as C^N ligand exhibits the highest oxygen sensitivity and excellent operational stability in 10 cycles within 4000 s.     

Solid-state electrochemiluminescence of a novel iridium(Ⅲ) complex

The sofid-state ECL behavior of a water-insoluble bis-cyclometalated (pq)2Ir(N-phMA) complex is presented, in which pq is a 2-phenylquinoline anion and N-phMA is N-phenyl methacrylamide, a monoanionic bidentate ligand. The MWNTs/(pq)2Ir(N-phMA) film, MWNTs/Ru(bpy)32+ film and (pq)2Ir(N-phMA) directly modified glassy carbon electrode were fabricated; only the MWNTs/(pq)2Ir(N-phMA) film can produce steady ECL in the presence of tri-n-propylamine as a coreactant.     

Synthesis of dipyrrolo[2,3-a:1′,2′,3′-fg]acridin-12(1H)-ones

Acylation reactions of 4,6-dimethoxyindoles with glyoxyloyl chlorides were achieved by the use of graphite powder in 1,2-dichloroethane at reflux. The products were monoketones as a result of decarbonylation, rather than the expected 1,2-diketones. Treatment of these monoketones with base led to their cyclisation and elimination of methanol to afford the novel dipyrrolo[2.3-a:1′,2′,3′-fg]acridin-12(1H)-ones.     

Synthesis and characterization of a trianionic pincer supported Mo-alkylidene anion and alkyne insertion into a Mo(IV)-Cpincer bond to form metallocyclopropene(η-vinyl) complexes

This report describes two approaches to form complexes featuring Mo-C multiple bonds and a trianionic pincer ligand. Treating the trianionic pincer ligand precursor [^tBuOCO]H₃ (1) with MeLi provides the corresponding dilithio salt [^tBuOCHO]Li₂(THF)₃ (6) in situ, which further reacts with Mo(NAr) (CHCMe₂Ph)(OTf)₂(DME) to provide the terphenyl diphenolate complex [^tBuOCHO]Mo(NAr)CHCMe₂Ph (5). Complex 5 is characterized by ¹H, ¹³C{¹H} NMR spectroscopy, combustion analysis, and single crystal X-ray diffraction. The solid state structure of 5 reveals a distorted trigonal pyramidal geometry for the Mo(VI) ion. Treating 5 with one equiv. of phosphorane in toluene converts the diphenolate ligand into a trianionic pincer ligand by deprotonation of the pincer C_ipso-H proton to give the alkylidene salt {[^tBuOCHO]Mo(NAr)(CHCMe₂Ph)}{Ph₃PCH₃} (7). Treating [^tBuOCO]MoNMe₂(NHMe₂)₂ (2), containing a d² Mo(IV) ion, with terminal alkynes (H-C≡CR, R = Ph, 3,5-F₂C₆H₃, 3,5-(CF₃)₂C₆H₃ and SiMe₃) produces in excellent yield the corresponding metallocyclopropylidene complexes 10-R (R H, F, CF₃) and 11 (R = SiMe₃). X-ray diffraction studies on single crystals of 10-H and 11 reveal three important features: 1) a highly distorted hexacoordinate Mo(VI) center, 2) a metallocyclopropene(η²-vinyl) fragment, and 3) a highly distorted CH group in the metallocyclopropene unit. A single point calculation and an NBO analysis performed on 10-H′ confirms the multiple bond between Mo1 and C28. The highest occupied Kohn-Sham molecular orbital (HOMO) represents a π-combination between d_yz of Mo1 and the p_y orbital of C28, and the corresponding π∗-combination of those orbitals constitutes the lowest unoccupied molecular orbital (LUMO).     

Facile synthesis of σ-π conjugated organosilicon polymers via Click polymerization

Poly[silylene-(1,2,3-triazol-4-yl)-1,4-phenylene]s have been prepared via Cu(I)-catalyzed Azides and Alkynes Cycloaddition (CuAAC) polymerization from diethynylsilanes and 1,4-diazidobenzene. The organosilicon units contribute to electronic transitions between the π-conjugated units, as well as improving the solubility and processability of the polymers. Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (NMR) have been utilized to confirm the structure of these polymers. The UV-visible spectra of polymers show almost identical absorption at around 270 nm. The fluorescence emission in CHCl₃ solutions were observed as similar broad band in visible blue region (ca. 430 nm). The quantum yields (Φ) were ranged from 0.19 to 0.37. The optical properties support the σ-π conjugation of the silylene and aromatic heterocycle groups, and the substituents on silicon atoms have negligible effect on the photoproperties.     

Syntheses and characterization of η 5-pentamethylcyclopentadienyl rhodium(III) and iridium(III) complexes containing polypyridyls

Reaction of [(η ⁵-C₅Me₅)M(μ-Cl)Cl]₂ {M?=?Rh (1), Ir (2)} and [(η ⁵-C₅Me₅)MCl₂(DBT)] (DBT?=?dibenzothiophene) {M?=?Rh (3), Ir (4)} with polypyridyl ligands 2,3-bis(2-pyridyl)pyrazine (bpp), 2,3-bis(2-pyridyl)quinoxaline (bpq), 1,3,5-tris(2-pyridyl)-2,4,6-triazine (tptz), 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) and 4′-pyridyl-2,2′:6′,2′′-terpyridine (py-terpy) results in the formation of mononuclear cationic complexes, [(η ⁵-C₅Me₅)MCl(poly-py)]⁺ (poly-py?=?polypyridyl ligand). The complexes were isolated as hexafluorophosphate salts and characterized by IR and NMR spectroscopy.     

Atomic and vacancy ordering in carbide ζ-Ta4C3−x (0.28?x?0.40) and phase equilibria in the Ta-C system

The structure of nonstoichiometric carbide phase ζ-Ta₄C_3−x formed in the tantalum-carbon (Ta-C) system is studied by X-ray and neutron powder diffraction and metallography. Investigated carbide ζ-TaC_0.67 crystallizes in a trigonal (rhombohedral) space group with cell parameters a_tr=1.0180(1) nm, α_tr=17.64° (or a_h=0.31216(2) nm, c_h=3.0058(1) nm in hexagonal axes). The closely packed metal sublattice in carbide ζ-Ta₄C_3−x consists of alternating blocks where metal atoms are located in the same manner as on the FCC sublattice of the cubic carbide TaC_y and the HCP sublattice of the hexagonal carbide Ta₂C_y. This metal sublattice represents a transition sublattice between these FCC and HCP sublattices. An ordered distribution of atoms C and structural vacancies in carbide ζ-Ta₄C_3−x is revealed and the distribution function of atoms C is calculated for nonmetal sublattice sites, on which ordering takes place. It is shown that one long-range order parameter η describes the ordering of ζ-carbide and the η value in the investigated ζ-Ta₄C_3−x phase does not exceed 0.7. Carbide ζ-Ta₄C_3−x is stable in bulk and powdered states over a wide temperature interval of 300 to ∼2400 K and has a narrow homogeneity interval from TaC_0.65 to TaC_0.68. Microhardness of disordered and ordered tantalum carbide TaC_y with the basic B1 structure and trigonal carbide ζ-Ta₄C_3−x is measured. The phase diagram of the Ta-C system is refined considering data obtained for the ζ-Ta₄C_3−x phase.     

DFT analysis of the activation and breaking of the Mo-N bond in a (mu-nitrido)dimolybdenum complex: is molybdenum tris(thiolate) an elusive intermediate?

The electronic structure, conformation, synthesis, and thermal decomposition pathways of the recently characterized dimolybdenum mu-nitrido complex (AdS)(3)Mo(mu-N)Mo(N[(t)Bu]Ph)(3) (1exp, Ad = adamantyl) are investigated by means of DFT calculations carried out on the model system (HS)(3)Mo(mu-N)Mo(NH(2))(3) (1). The observed asymmetry of the Mo(mu-N)Mo core is reproduced in the optimal conformation of 1 and assigned to the tendency for the electron density of the metal atoms to be preferably accommodated in the pi orbitals of Mo(thiolate). The balance in the metal-ligand and ligand-ligand interactions conditioning the flow of the electron density along the Mo-(mu-N)-Mo framework, and eventually the relative activation of the molybdenum-nitrido bonds, appears very sensitive to the nature of the ancillary substituents on both the thiolate and the amido sides. On one hand, replacing HS by AdS in 1 increases the calculated value of Delta(mu-N-Mo) from 0.053 to 0.094 A, close to the experimental value of 0.111 A. The mu-nitrido complex with bulky thiolates 1a is also less stable than 1 by 7.3 kcal x mol(-1) with respect to its monometallic constituents. On the other hand, substituting the bulky N[(t)Bu]Ph for NH(2) in the model complex 1b induces an important charge transfer toward the thiolate moiety resulting in structural and energetic consequences of similar magnitude. Even though these substitutional effects are not likely to be fully additive in the real complex, both should contribute to an increase of the mu-N-Mo(thiolate) bond activation in 1exp. The importance of this activation conditions the feasibility of the thermal decomposition of 1exp promoted by benzonitrile which eventually yields the molybdenum thiolate dimer (RS)(3)Mo [triple bond] Mo(SR)(3). The energy profile calculated for this reaction with model complex1 in the presence of one or two molecules of acetonitrile shows that the axial fixation of the promoter on one or both molecular ends forms intermediates in which the mu-N-Mo(thiolate) bond is further activated with respect to the original complex. The consequence is an important, but still insufficient, decrease of the barrier to Mo-N bond breaking, from 53 to 37 kcal x mol(-1). Furthermore, the thermodynamic balance of the reaction leading from the acetonitrile adducts of 1 to (HS)(3)Mo [triple bond] Mo(SH)(3) remains endothermic by 6.5 kcal x mol(-1) for the monoadduct, and more for the diadduct. It therefore appears that bulky substituents on both ends of the dinuclear complex are essential to the completion of the reaction, from both the thermodynamic and the kinetic viewpoints.     

In vitro hydrolytic degradation of poly(?-caprolactone) grafted dextran fibers and films

We studied the hydrolytic degradation of poly(?-caprolactone) grafted dextran (PGD) fibers and films (matrices) prepared by electrospinning and solvent evaporation methods, respectively. In vitro degradation and erosion experiments were carried out in phosphate buffered saline (pH 7.4 ± 0.1) at 37 ± 1 °C for 150 days. Changes in molecular weights and morphologies of the PGD matrices were monitored as a function of degradation time. The extent of degradation was measured by physical weight loss, scanning electron microscopic (SEM) observations, Fourier transform-infrared (FT-IR) spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). During the progress of hydrolysis, GPC chromatograms appeared bi modal for fibers and bi and trimodal for the films. The crystallization temperature (T_c) and heat of fusion were significantly increased in both matrices; this indicated preferential hydrolytic degradation in amorphous regions followed by cleavage-induced crystallization. The biodegradation rates were faster for the films (28%) than fibers (23%). After 150 days of degradation, the pH was steady at 5.8 ± 0.3 for fibers and 6.1 ± 0.3 for films. The faster degradation of the films could be probably due to autocatalysis in the interior of the films and the degraded oligomers are hard to diffuse out into the surrounding solution due to its compact physical geometry. Thus, our preliminary results about the degradation of matrices suggested that PGD nanofibers could be excellent matrices in tissue engineering over the films.     

Efficient two-photon-sensitized luminescence of a novel europium(III) β-diketonate complex and application in biological imaging

A novel europium(III) β-diketonate complex exhibiting bright two-photon-sensitized luminescence is synthesized and applied as a two-photon-sensitized luminescent probe to stain DNA in live cells.     

Synthesis and structural characterization of η-allyl(α-diimine)nickel(II) complexes bearing trimethylsilyl groups

A set of isomeric para- and meta-trimethylsilylphenyl ortho-substituted N,N-phenyl α-diimine ligands [(Ar-NC(Me)-(Me)CN-Ar) Ar=2,6-di(4-trimethylsilylphenyl)phenyl (16); Ar=2,6-di(3-trimethylsilylphenyl)phenyl (17)] have been synthesized through a two-step procedure. The palladium-catalysed cross-coupling reaction between 2,6-dibromophenylamine (7) and 4-trimethylsilylphenylboronic acid (8), 3-trimethylsilylphenylboronic acid (9) was used to prepare 4,4^′-bis(trimethylsilyl)-[1,1^′;3^′,1″]terphenyl-2^′-ylamine (10) and 3,3^′-bis(trimethylsilyl)-[1,1^′;3^′,1″]terphenyl-2^′-ylamine (11). The di-1-adamantylphosphine oxide Ad₂P(O)H (13) and di-tert-butyl-trimethylsilylanylmethylphosphine tert-Bu₂P-CH₂-SiMe₃ (14) were used for the first time as ligands for the Suzuki coupling. The condensation of 2,2,3,3-tetramethoxybutane (15) with anilines 10 and 11 afforded α-diimines 16 and 17. The reaction of π-allylnickel chloride dimer (18), α-diimines (16), (17) and sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BAF) (19) or silver hexafluoroantimonate (20) led to two sets of isomeric complexes [η³-allyl(Ar-NC(Me)-(Me)CN-Ar)Ni]⁺ X⁻, [Ar=2,6-di(4-trimethylsilylphenyl)phenyl, X=BAF (3), X=SbF₆ (4); Ar=2,6-di(3-trimethylsilylphenyl)phenyl, X=BAF (5), X=SbF₆ (6)]. The steric repulsion of closely positioned trimethylsilyl groups in 4 caused the distortion of the nickel square planar coordination by 17.6° according to X-ray analysis.     

α- to β-[C6H4(NH3)2]2Bi2I10 reversible solid-state transition, thermochromic and optical studies in the p-phenylenediamine-based iodobismuthate(III) material

α-[C₆H₄(NH₃)₂]₂Bi₂I₁₀, which is a new material containing low-dimensional iodobismuthate anions, was synthesized and through its single crystal X-ray diffraction measurements, was proven to crystallize at room temperature in the centrosymmetric space group P2₁/c. It consists of a p-phenylenediammonium dication and a discrete (0-D) anion built up of edge-sharing bioctahedron. Due to the hydrogen bonds and the interatomic distances (Bi-I, I?I and π-π) changes, α-phase was transformed into the corresponding centrosymmetric β-phase, β-[C₆H₄(NH₃)₂]₂Bi₂I₁₀, through a single-crystal to single-crystal transformation occurring upon cooling to −28/−26 °C. Below the transition temperature, β-[C₆H₄(NH₃)₂]₂Bi₂I₁₀ crystallizes in the monoclinic system, centrosymmetric space group P2₁/n. Besides, the optical transmission measurements on α-[C₆H₄(NH₃)₂]₂Bi₂I₁₀ thin films have revealed two absorption bands at 2.47 and 3.01 eV. Finally, two room temperature photoluminescence emissions attributed to excitons radiative recombinations confined within the bioctahedra Bi₂I₁₀⁴⁻, were observed in the red spectral range at 1.9 and 2.05 eV energy.     

Properties of η-pentamethylcyclopentadienyl rhodium(III) and iridium(III) complexes with quinolin-8-ol and their cytostatic activity

Reaction of dimers [M(η⁵-C₅Me₅)Cl₂]₂ (M-Rh, Ir) with quinolin-8-ol in molar ratio 1:2 leads to formation of monomer complexes [Rh(η⁵-C₅Me₅)Cl(qol)] (1) and [Ir(η⁵-C₅Me₅)Cl(qol)] (2) (qol = quinolin-8-olate). Compounds 1 and 2 have been characterized with elemental analysis and spectroscopic methods. ¹H NMR spectra revealed that quinolin-8-olate is coordinated via oxygen and nitrogen atoms. The ¹H NMR and ¹³C NMR spectra showed that carbon and hydrogen atoms of pentamethylcyclopentadienyl ligand are equivalent. The structure of rhodium complex has been calculated using DFT B3LYP method. The calculated geometry of complex 1 agrees very well with data found for rhodium complexes containing Cl, C₅Me₅ and qol ligands. Both complexes are active antitumor and antibacterial agents.     

Investigating the inclusion of the Ag(I)-nimesulide complex into β-cyclodextrin: studies in solution and in the solid state

The present work describes the preparation and characterization of inclusion systems involving β-CD and the silver(I) nimesulide coordination complex (Ag-NMS), prepared by kneading (K) and co-evaporation (CE) methods. Solid state characterization by DSC, XRD and IR vibrational spectroscopic measurements provided remarkable evidences of the formation of true inclusion systems. Solution measurements provided information about the inclusion mode. The UV–Vis spectroscopy was used to obtain the association constants by the Scatchard method, and the value obtained was 370 ± 2 L mol^?1. The ¹H NMR spectroscopic measurements indicate a total inclusion of the guest into the cavity. A 2D NOESY experiment was carried out for the inclusion complex. The spectrum shows that hydrogens 3–6 of the cyclodextrin clearly correlate with the protons of the phenoxy ring of nimesulide in the Ag-NMS coordination compound, which confirms the formation of the inclusion complex. The antibacterial activities of the Ag-NMS and CE-[(Ag-NMS)·β-CD] inclusion system were evaluated by the well diffusion method over Escherichia coli and Pseudomonas aeruginosa (Gram-negative) and Staphylococcus aureus (Gram-positive) pathogenic bacterial strains. The observed data shows the significant antibacterial activity of the Ag-NMS coordination complex, and no activity for the inclusion complex under the same considered conditions.