Soluble and thermally stable polyamides bearing 1,1′-thiobis(2-naphthoxy) groups

A new-type of sulfide containing diacid (1,1′-thiobis(2-naphthoxy acetic acid)) was synthesized from 2-naphthol in three steps. Reaction of 2-naphthol with sulfur dichloride afforded 1,1′-thiobis(2-naphthol) (TBN). 1,1′-Thiobis(2-naphthoxy acetic ester) (TBNAE) was successfully synthesized by refluxing the TBN with methylcholoroacetate in the presence of potassium carbonate. The related diacid was synthesized by basic solution reduction of TBNAE. The obtained diacid was fully characterized and used to prepare novel thermally stable poly(sulfide ether amide)s via polyphosphorylation reaction with different aromatic diamines. The properties of these new polyamides were investigated and compared with similar polyamides. These polyamides showed inherent viscosities in the range of 0.39-0.87 dL g⁻¹ in N,N-dimethylacetamide (DMAc) at 30 °C and at a concentration of 0.5 g dL⁻¹. All the polyamides were readily soluble in a variety of polar solvents such as DMAc and tetrahydrofuran (THF). These polyamides showed glass transition temperature (T_g) between 241-268 °C. Thermogravimetric analysis measurement revealed the decomposition temperature at 10% weight loss (T₁₀) ranging from 441- 479 °C in argon atmosphere.     

Enzyme assay for chitinase catalyzed hydrolysis of tetra-N-acetylchitotetraose by isothermal titration calorimetry

Isothermal titration calorimetry (ITC) has been used to observe the chitinase-catalyzed hydrolysis of tetra-N-acetylchitotetraose. Enzymatic hydrolysis of tetra-N-acetylchitotetraose by chitinase B from Serratia marcescens produces exclusively two molecules of di-N-acetylchitobiose allowing for the determination of a single glycosidic bond hydrolysis heat that was used to monitor the rate of the enzymatic reaction. The change in heat rate with respect to time (dQ/dt) was translated to the reaction rate, and the total heat produced was related to substrate concentration throughout the reaction. Reaction rates versus substrates concentration were fit to Michaelis-Menten plots, yielding a k_cat of 40.9 ± 0.5 s⁻¹ and a K_m of 54 ± 2 μM.     

Chemistry of diazocarbonyl compounds: XXVIII. Reaction of acyclic N-arylsulfonylacetamides with Rh(II)-carbenoids as a new synthetic route to alkyl acetimidoates

A new procedure was proposed for the synthesis of alkyl acetimidoates via alkylation of the carbonyl group in N-arylsulfonylacetamides with Rh(II)-carbenoids. The procedure ensures preparation in good yield of acetimidoates having a polyfunctionalized O-alkyl group. The obtained alkyl acetimidoates in crystal exist as E isomers with respect to the C=N bond and as s-cis conformers relative to the C-OCHRR’ bond. Alkyl N-arylsulfonylacetimidoates react with ammonia and hydrazine hydrate to give in good yield the corresponding carboximidamides(hydrazides) via replacement of the O-alkyl group. Unlike structurally related compounds having simple alkyl or aryl groups on the nitrogen atom, N-arylsulfonylacetimidoates readily undergo hydrolysis in the presence of moisture and traces of acids.     

Fluorometric determination of fluoride ion by reagent tablets containing 3-hydroxy-2'-sulfoflavone and zirconium(IV) ethylenediamine tetraacetate

A reagent tablet for determination of fluoride ion has been prepared using ethylenediamine-N,N,N′,N′-tetraacetate complex of zirconium (Zr-EDTA), 3-hydroxy-2′-flavone (FS) and an appropriate pH buffer. Dissolving of the tablet into water exhibits an intense blue fluorescence (λ_max = 460 nm) upon excitation at 377 nm and the fluorescence intensity decreases with the presence of fluoride ion. Hence, a simple fluorescent detection procedure for fluoride ion in aqueous media was successfully constructed with this tablet. The principle of this detection system is the ligand exchange reaction of FS bound to Zr-EDTA with fluoride ion. The present system provides an easy, rapid and selective determination method of fluoride ion ranging from 5 × 10⁻⁶ to 1 × 10⁻³ mol dm⁻³. The measurement of real samples with this tablet showed the similar results as those by the common method with the Alfusone reagent.     

AlCl3 induced C-N bond formation followed by Pd/C-Cu mediated coupling-cyclization strategy: synthesis of pyrrolo[2,3-b]quinoxalines as anticancer agents

AlCl₃ facilitated C-N bond forming reaction between 2,3-dichloroquinoxaline and anilines affording a convenient method for the preparation of N-aryl substituted 3-chloroquinoxalin-2-amines. A related N-benzyl derivative, however, was prepared via a conventional method. These N-alkyl/aryl substituted 3-chloroquinoxalin-2-amines on coupling with terminal alkynes in toluene under Pd/C-Cu catalysis afforded a range of 1,2-disubstituted pyrrolo[2,3-b]quinoxalines within 3-5 h in good to excellent yields. Some of the compounds synthesized showed promising anti-proliferative properties when tested in vitro against two cancer cell lines. Docking studies indicated that these molecules interact well with human Akt in silico.     

Stereodynamics of 1,3,5-tris(trifluoromethylsulfonyl)-1,3,5-triazinane: experimental and theoretical analysis

Dynamic NMR of 1,3,5-tris(trifluoromethylsulfonyl)-1,3,5-triazinane reveals two dynamic processes: ring inversion leading to equilibrium between two degenerate rotamers of C_s symmetry (ΔG^≠ = 13.5 kcal/mol), and rotation about the S-N bond leading to equilibrium between the C_s (more stable) and C_3v (2.12 kcal/mol less stable) rotamers (ΔG^≠ = 13.0 kcal/mol).     

Synthesis and characterization of new poly(azomethine ester)s having phenylthiourea units

New polyesters having azomethine and phenylthiourea groups in the polymer backbone were synthesized by interfacial polycondensation method. The dihydroxy monomer N-(4-hydroxy-3-methoxybenzal) N′-(4′-hydroxyphenyl)thiourea was condensed with six diacid chlorides: terephthaloyl, isophthaloyl, azeloyl, suberoyl, pimeloyl and adipolyl chlorides. The resulting polyesters were characterized by viscosity, IR, NMR and TGA analysis. The wholly aromatic poly(azomethine ester) derived from terephthaloyl chloride when blended with polyaniline/NH₄OH, polyaniline/HCl and pure polyaniline shows conductance in the range 3.2 × 10⁻³-0.91 × 10⁻¹ S cm⁻¹.     

Alkylation of acylmetalates with alkyl halides to prepare Fischer carbene complexes: an improved protocol

Alkoxy Fischer carbene complexes have been synthesized by alkylation of lithium acylmetalates with alkyl halides in the presence of catalytic amount (5-10 mol %) of n-tetrabutylammonium bromide (n-Bu₄NBr) restricting the temperature below 55 °C to minimize decomposition of the product. The reaction occurs in a biphasic condition involving water and alkyl halide. The effect of cesium on this alkylation reaction has been studied. The presence of a radical quencher, di-tert-butyl phenol, neither affects the yield nor leads to the formation of dimer of di-tert-butyl phenol, which rules out the possibility of radical pathway mechanism. The kinetic study and the ¹H NMR spectra of products suggest an S_N2 pathway particularly involving alkyl halides.     

Titanium and zirconium ketimide complexes: synthesis and ethylene polymerisation catalysis

The syntheses of ketimide titanium complexes of the type Ti(NC^tBu₂)₃X (X = Cl, Cp, Ind), Ti(NC^tBu₂)₄ and the zirconium complex CpZr(NC^tBu₂)₂Cl are described. When activated by MAO, all compounds are ethylene polymerisation catalysts. In the conditions studied, the most active catalyst is CpZr(NC^tBu₂)₂Cl, with an activity of 2.7 × 10⁵ kg/(molZr [E] h). Titanium complexes are less active by about two orders of magnitude. The polyethylene produced is linear, as determined by NMR spectroscopy. Molecular structures of Ti(NC^tBu₂)₃X (X = Cl, Cp, Ind) and Ti(NC^tBu₂)₄ were determined by X-ray single crystal diffraction.     

Towards understanding monomer coordination in atom transfer radical polymerization: synthesis of [Cu(PMDETA)(π-M)][BPh4] (M = methyl acrylate, styrene, 1-octene, and methyl methacrylate) and structural studies by FT-IR and H NMR spectroscopy and X-ray crystallography

Cu^I complexes of the form [Cu^I(PMDETA)(π-M)][BPh₄] (where PMDETA = N,N,N′,N″,N″-pentamethyldiethylenetriamine, and M = vinyl monomer) were synthesized and isolated from solution as crystals with methyl acrylate (MA), styrene (Sty), and 1-octene (Oct). The interaction of the CC double bond of the vinyl monomer with Cu^I was characterized via FT-IR and ¹H NMR spectroscopy and single crystal X-ray crystallography. A fourth complex with methyl methacrylate (MMA) was synthesized and characterized spectroscopically, but no crystals suitable for X-ray structure analysis could be obtained. In all complexes, PMDETA acts as a tridentate ligand, while the pseudotetrahedral coordination geometry around Cu^I is completed by a π-interaction with the CC double bond of M in the presence of a non-coordinating counter-ion. A decrease in CC IR stretching frequencies of Δν(CC) = −110, −80, −109, and −127 cm⁻¹ for complexes with MA, Sty, Oct, and MMA, respectively, was observed upon coordination. No significant change in CC bond length was seen in the crystal structure for complexes with MA and Oct while a slight lengthening was observed for the Sty complex. The upfield shift of the vinyl proton resonances indicated the presence of significant π-back-bonding.     

Synthesis, characterization, antibacterial and cytotoxic activity of new palladium(II) complexes with dithiocarbamate ligands: X-ray structure of bis(dibenzyl-1-S:S′-dithiocarbamato)Pd(II)

Six palladium(II) dithiocarbamates of general formula Pd(AmDTC)₂, where HAmDTC = aminedithiocarbamic acid, [Pd(II) piperidinedithiocarbamate (1), Pd(II) 4-methylpiperidinedithiocarbamate (2), Pd(II) N-methylbenzyldithiocarbamate (3), Pd(II) dibenzyldithiocarbamate (4), Pd(II) dicyclohexyldithiocarbamate (5), Pd(II) N-cyclohexyl-N-methyldithiocarbamate (6)] have been synthesized and characterized by elemental analyses, FT-IR, ¹H and ¹³C NMR. The X-ray structure of Pd(II), compounds 3 and 4, showed that the ligands are chelated by both sulfur atoms with bond angles S1-Pd-S4 = 179.24(2)° and S2-Pd-S3 = 179.09(5)°, with a distorted square planar geometry around Pd. All these complexes were screened for cytotoxic and antibacterial effects and showed significant antibacterial activity and no substantial in vitro cytotoxicity indicating specificity of the compounds.     

One-dimensional and two-dimensional coordination polymers constructed from copper(II) nodes and polycarboxylato spacers: Synthesis,crystal structures and magnetic properties

Four new coordination polymers were obtained by employing polycarboxylato spacers and cationic copper(II) complexes as nodes: ^∞₂[Cu₃(trim)₂(NH₃)₆(H₂O)₃] (1); ^∞₁[Cu(tmen)(dhtp)] (2), ^∞₁[Cu(tmen)(hitp)(H₂O)] (3), ^∞₁[Cu(tmen)(nitp)] (4). (H₃trim = trimesic acid, H₂dhtp = 2,5-dihydroxy-terephthalic acid; H₂hitp = 5-hydroxy-isophthalic acid, H₂nitp = 5-nitro-isophthalic acid; tmen = N,N,N′,N′-tetramethyl-ethylenediamine). The crystal structures of the four compounds have been solved. Compound 1 consists of 2D coordination polymers with heart-shaped meshes, while compounds 2–4 contain infinite zigzag chains. The role of the hydrogen bond interactions in sustaining the supramolecular solid-state architectures in compounds 1 and 3 is discussed. The cryomagnetic investigation of compounds 1, 2, and 4 reveals antiferromagnetic interactions between the copper ions.     

Sensitive fluorimetric flow injection analysis for fluoride ion with a novel reagent, 2',7'-dichlorofluorescein di-tert-butyldimethylsilyl ether

A novel reagent, 2′,7′-dichlorofluorescein di-tert-butyldimethylsilyl ether (FCl₂TBS), was synthesized for fluoride ion and used for a sensitive fluorimetric flow injection analysis by detecting the recovery of fluorescence due to cleavage of Si-O bond. Four kinds of fluorescein di-tert-butyldimethylsilyl ether (FTBS) analogues were synthesized and FCl₂TBS was the best. By introducing chlorine to FTBS, stability of the reagent, reactivity and the baseline signals were improved. The FIA system was three lines. The sample solution (aqua medium) was injected in the carrier solution (water) and merged with the reagent solution (2.0 × 10⁻⁵ M FCl₂TBS acetone solution), then mixed with phosphate buffer solution (pH 7.5). The fluorescence intensities were measured at λ_ex 503 nm and λ_em 527 nm. The calibration graph had linear relationship between (1.0-50.0) × 10⁻⁶ M and the determinable limit was 1.0 × 10⁻⁶ M. The relative standard deviation of 12 measurements with 1.0 × 10⁻⁵ M F⁻ solution was 1.0% and the sample throughput was 13 h⁻¹. The developed method was successfully applied to river and tap water samples.     

Chelating ionic versus bridged molecular structures of group 13 metal complexes with bidentate ligands

Complexes of aluminum and gallium trihalides with ethylenediamine (en) and N,N,N′,N′-tetramethylethylenediamine (tmen) of 2:1 composition have been synthesized and structurally characterized by single crystal X-ray diffraction analysis. In contrast to known molecular complexes of hydrido and methyl-substituted analogs, these solid complexes adopt ionic structures of the general type [M¹X₂LL]⁺[M²X₄]⁻ (X = Br, I; M¹, M² = Al or Ga; LL = en, tmen).     

Preparation, structure and photoluminescence properties of Eu and Ce-doped SrYSi4N7

Undoped and Eu²⁺ or Ce³⁺-doped SrYSi₄N₇ were synthesized by solid-state reaction method at 1400-1660 °C under nitrogen/hydrogen atmosphere. The crystal structure was refined from the X-ray powder diffraction data by the Rietveld method. SrYSi₄N₇ and EuYSi₄N₇, being isotypic with the family of compounds MYbSi₄N₇ (M=Sr, Eu, Ba) and BaYSi₄N_7, crystallize with the hexagonal symmetry: space group P6₃mc (No. 186), Z=2, a=6.0160 (1) Å, c=9.7894 (1) Å, V=306.83(3) Å³; and a=6.0123 (1) Å, c=9.7869 (1) Å, V=306.37(1) Å³, respectively. Photoluminescence properties have been studied for Sr_1−xEu_xYSi₄N₇ (x=0-1) and SrY_1−xCe_xSi₄N₇ (x=0-0.03) at room temperature. Eu²⁺-doped SrYSi₄N₇ shows a broad yellow emission band peaking around 548-570 nm, while Ce³⁺-doped SrYSi₄N₇ exhibits a blue emission band with a maximum at about 450 nm. SrYSi₄N₇:Eu²⁺ can be very well excited by 390 nm radiation, which makes this material attractive as conversion phosphor for LED lighting applications.     

Synthesis and reactivity towards carbon monoxide of an optically active endo five-membered ortho-cyclopalladated imine: X-ray molecular structure of trans-(μ-Cl)2[Pd(κ-C,N-(R)-C6H4-CHN-CHMe-Ph)]2

(R)-1-Phenylethyl-benzylidene-amine (1) reacted with Pd(OAc)₂ in acetic acid at 60 °C under nitrogen affording the acetato-bridged dinuclear endo five-membered ortho-cyclopalladated compound (μ-OAc)₂[Pd(κ²-C,N-(R)-C₆H₄-CHN-CHMe-Ph)]₂ (2) in 65% yield. Compound 2 was converted by a metathesis reaction with LiCl into the corresponding chloro-bridged dinuclear cyclopalladated compound (μ-Cl)₂[Pd(κ²-C,N-(R)-C₆H₄-CHN-CHMe-Ph)]₂ (3). ¹H NMR of CDCl₃ solutions of compounds 2 and 3 treated separately with py-d₅, (R)-1-phenylethylamine and racemic 1-phenylethylamine were consistent with the endo cyclopalladated structure and the R absolute configuration of the chiral carbon atoms of compounds 2 and 3. Compounds 2 and 3 reacted with carbon monoxide in methanol affording, as major compounds, methyl 2-formylbenzoate (91% chemical yield) and the epimers of 3-methoxy-2-[(R)-1-phenylethyl]isoindolin-1-one (64% chemical yield) in ca. 20% diastereomeric excess, respectively. The trans isomer of compound 3 crystallized in the P2₁ monoclinic space group with a = 10.430(4) Å, b = 12.082(8) Å, c = 11.168(4) Å and β = 95.20(3)° and presented C-H?Cl intramolecular and C-H?Pd intermolecular non-conventional hydrogen bonds.     

The synthesis, structural characterization and in vitro anti-cancer activity of novel N-(3-ferrocenyl-2-naphthoyl) dipeptide ethyl esters and novel N-(6-ferrocenyl-2-naphthoyl) dipeptide ethyl esters

N-(3-ferrocenyl-2-naphthoyl) dipeptide esters (5-7) and N-(6-ferrocenyl-2-naphthoyl) dipeptide esters (8-10) were prepared by coupling either 3-ferrocenylnaphthalene-2-carboxylic acid 2 or 6-ferrocenylnaphthalene-2-carboxylic acid 4 to the dipeptide ethyl esters GlyAla(OEt) (5, 8), AlaGly(OEt) (6, 9), and AlaAla(OEt) (7, 10) using the standard N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC), 1-hydroxybenzotriazole (HOBt) protocol. All the compounds were fully characterized using a combination of ¹H NMR, ¹³C NMR, DEPT-135 and ¹H-¹³C COSY (HMQC) spectroscopy, electrospray ionization mass spectrometry (ESI-MS) and cyclic voltammetry (CV). In vitro, the cytotoxic effects of compounds 5-10 show improvements over the corresponding N-(ferrocenyl)benzoyl derivatives, with IC₅₀ values against the H1299 lung cancer cells ranging from 1.2 μM to 8.0 μM. N-(6-ferrocenyl-2-naphthoyl)-glycine-l-alanine ethyl ester 8 was found to be the most active derivative of the naphthoyl series so far, displaying an IC₅₀ value of 1.3 ± 0.1 μM. This value is slightly lower than that found for the clinically employed anti-cancer drug cisplatin (IC₅₀ = 1.5 ± 0.1 μM against H1299).     

Synthesis, structure and dynamic stereochemistry of (O → Si)-chelate N-(trifluorosilylmethyl)-[N-(S)-(1-phenylethyl)]acetamide and 1-(trifluorosilylmethyl)-2-oxoperhydroazepine: Retention of the O → Si coordination in the adduct with KF and 18-crown-6

The novel compounds, N-(trifluorosilylmethyl)-[N-(S)-(1-phenylethyl)]-acetamide (1a) and 1-(trifluorosilylmethyl)-2-oxoperhydroazepine (1b) have been prepared from the corresponding NH-compounds using ClCH₂SiCl₃/Et₃N or ClCH₂SiCl₃/(Me₃Si)₂NH followed by methanolysis or hydrolysis of the reaction mixture in the presence of Lewis bases, and then BF₃ etherate. Potassium-(18-crown-6)-(2-oxoperhydroazepinomethyl)tetrafluorosilicate (2) was synthesized by reaction of the trifluoride (1b) with KF in the presence of 18-crown-6. Using ¹⁹F, ²⁹Si NMR and X-ray diffraction techniques it was established that the silicon atom is pentacoordinate in the trifluorides (1a, b) and hexacoordinate in the adduct 2. Thus the internal coordination of the O → Si bond present in the trifluoride (1b) is retained in the adduct 2.The stereochemical non-rigidity of the trifluorides (1a, b) and the N-(trifluorosilylmethyl)-N-methylacetamide (1c) was investigated using dynamic ¹⁹F NMR spectroscopy. The activation barriers for permutational isomerization are in the range 9.5-10 kcal mol⁻¹. Lower values of ΔG^# for permutation of trifluorides (1a-c) compared to the monofluorides with the coordination core OSiC₃F together with small negative values for the activation entropy implies a non-dissociative mechanism. Quantum-chemical analysis suggests a mechanism involving a turnstile rotation.     

Organoboron compounds as Lewis acid receptors of fluoride ions in polymeric membranes

Newly synthesized organoboron compounds – 4-octyloxyphenylboronic acid (OPBA) and pinacol ester of 2,4,6-trifluorophenylboronic acid (PE-PBA) – were applied as Lewis acid receptors of fluoride anions. Despite enhanced selectivity, the polymer membrane electrodes containing the lipophilic receptor OPBA exhibited non-Nernstian slopes of the responses toward fluoride ions in acidic conditions. Such behavior was explained by the lability of the B–O bond in the boronic acids, and the OH⁻/F⁻ exchange at higher fluoride content in the sample solution. In consequence, the stoichiometry of the OPBA–fluoride complexes in the membrane could vary during the calibration, changing the equilibrium concentration of the primary anion in membrane and providing super-Nernstian responses. The proposed mechanism was supported by ¹⁹F NMR studies, which indicated that the fluoride complexation proceeds more effectively in acidic solution leading mainly to PhBF₃⁻ species. Finally, the performances of the membranes based on the phenylboronic acid pinacol ester, with a more stable B–O bond, were tested. As it was expected, Nernstian fluoride responses were recorded for such membranes with worsened fluoride selectivity.     

Structure and magnetic properties of the cubic oxide fluoride BaFeO2F

Fluorination of the parent oxide, BaFeO_3−δ, with polyvinylidine fluoride gives rise to a cubic compound with a=4.0603(4) Å at 298 K. ⁵⁷Fe Mössbauer spectra confirmed that all the iron is present as Fe³⁺. Neutron diffraction data showed complete occupancy of the anion sites, indicating a composition BaFeO₂F, with a large displacement of the iron off-site. The magnetic ordering temperature was determined as T_N=645±5 K. Neutron diffraction data at 4.2 K established G-type antiferromagnetism with a magnetic moment per Fe³⁺ ion of 3.95 μ_B. However, magnetisation measurements indicated the presence of a weak ferromagnetic moment that is assigned to the canting of the antiferromagnetic structure. ⁵⁷Fe Mössbauer spectra in the temperature range 10-300 K were fitted with a model of fluoride ion distribution that retains charge neutrality of the perovskite unit cell.