Compared properties of related aromatic poly(1,3,4-oxadiazole-amide)s

Two series of aromatic poly(1,3,4-oxadiazole-amide)s have been synthesized by low-temperature solution polycondensation reaction of equimolar amounts of aromatic diamines containing preformed oxadiazole rings with diacid chlorides having silicon or hexafluoroisopropylidene groups. These polymers are soluble in polar aprotic solvents and show high thermal stability with decomposition temperature being above 400 °C and glass transition temperature in the range of 250-350 °C. The polyoxadiazole-amides have weight- and number-average molecular weights in the range of 207 000-330 000 and 77 000-131 000, respectively. Conformational parameters of these polymers were calculated by Monte Carlo method with allowance for hindered rotation and discussed in relation with thermal properties. Polymer solutions in NMP were processed into thin free-standing films that showed good mechanical properties with tensile strength in the range of 50-100 MPa, tensile modulus in the range of 2.25-3.56 GPa and elongation to break in the range of 1.65-8.58%.     

Surface-modified CdSe quantum dots as luminescent probes for cyanide determination

Luminescent surface-modified CdSe semiconductor quantum dots (QDs), with nanoparticle (NP) size distribution in the order of 2-7 nm, have been synthesized for optical determination of cyanide ions. The nanoparticles have been functionalised with tert-butyl-N-(2-mercaptoethyl)-carbamate (BMC) groups and exhibit a strong fluorescent emission at about 580 nm with rather long fluorescence lifetimes (several hundred nanoseconds) in aerated methanolic solution. The observed luminescence emitted by the synthesized nanocrystals was tremendously increased by photo-activation under sunlight exposure. The functionalised QDs turned out to exhibit excellent long-term stability when stored in the dark (no significant changes in QDs luminescence emission intensity was observed even after two months from synthesis). The functionalisation of the NPs with carbamate ligand allowed a highly sensitive determination of free cyanide via analyte-induced changes in the photoluminescence (fluorescence quenching of intensity at 580 nm and lifetime changes) of the modified quantum dots (excited at 400 nm). A detection limit of 1.1 × 10⁻⁷ M (2.9 μg l⁻¹) of cyanide ions was obtained, while the interfering effect of other inorganic anions (including NO₃⁻, Cl⁻ or SCN⁻) was negligible even at 200-fold level concentrations in excess of cyanide.     

An improved procedure for the diastereoselective addition of triorganozincates to N-(tert-butanesulfinyl)imines: use of catalytic dialkylzinc

The addition of triorganozincates to (R)-N-(tert-butanesulfinyl)benzaldimine has been performed with very good results by using a catalytic amount of Me₂Zn (0.15 equiv) to generate the organozincate. Yields and/or diastereoselectivities of the formed α-branched sulfinamides improve in comparison with the values obtained in the same reactions carried out with an excess of a previously formed triorganozincate. On the other hand, the transfer of the two alkyl groups of a dialkylzinc reagent to the imine has been achieved by using 0.5 equiv of dialkylzinc and 1.5 equiv of MeMgBr to generate the trialkylzincate. In both methods, good to excellent yields and diastereomeric ratios (up to 98:2) have been obtained.     

Effect of a perfluorocyclopentene core unit on the structures and photoluminescence of fluorene- and anthracene-based compounds

A novel series of blue luminescent compounds, in which three identical functional groups, such as fluorene, anthracene, and spiro-bifluorene, are linked distortedly around a perfluorocyclopentene core, have been synthesized and characterized. The introduction of a perfluorocyclopentene linkage into the molecular framework leads to an enhancement of the photoluminescence (PL) efficiency and thermal stability. All compounds exhibit intense blue photoluminescence, which has been attributed to fluorene- or anthracene-based π→π* transitions. The maximum emission wavelengths of all compounds at room temperature are in the region of 420-480 nm, with higher PL quantum efficiencies than in 9,10-diphenylanthracene. The electroluminescent (EL) properties of compound 4, 1,2-bis(9,9′-spirobifluoren-2-yl)-3,3,4,4,5,5-hexafluorocyclopentene, were investigated. A multilayer EL device with the configuration of ITO/2TNATA(60 nm)/NPB(20 nm)/ADN:2%-compound-4(35 nm)/Alq₃(20 nm)/LiF(2 nm)/Al has been successfully fabricated.     

Complex formation equilibria between Ag(I) and thioureas in n-propanol

Complex formation equilibria between Ag(I) and thiourea or N-alkyl-substituted thioureas have been investigated in n-propanol by potentiometry at 10 °C intervals from 5 to 50 °C. Stepwise formation of tris-coordinated AgL_n (n = 1-3) complexes has been found for the majority of the ligands. ΔH and ΔS values for the complex formation reactions have been evaluated from the dependence of ln β_n on temperature. The alkyl-substituents affect the ligand affinities in different ways in relation with the coordination level n.The reactions are exothermic with few exceptions. Enthalpy favoured complex formation with negative dependence of ΔG on temperature (ΔS > 0) have been found.The enthalpy and entropy changes for the stepwise complex formation equilibria are correlated by two linear compensative relationships with the same isoequilibrium temperature 50-51 °C.     

Synthesis, characterization and luminescence study of dialkyl[1-arylmethyleneimino-2-naphthonato]gallium complexes: Crystal structure of dimethyl[1-(2-pridyl) methyleneimino-2-naphthonato]gallium

Eight dialkylgallium complexes of type R₂GaL [(M = Me, L = 1-(2-pyridyl)methyleneimino-2-naphthonato (1), M = Et, L = 1-(2-pyridyl)methyleneimino-2-naphthonato (2), M = Me, L = 1-phenylmethyleneimino-2-naphthonato (3), M = Et, L = 1-phenylmethyleneimino-2-naphthonato (4), M = Me, L = 1-(p-methoxylphenyl)methyleneimino-2-naphthonato (5), M = Me, L = 1-(3,4-dimethoxylphenyl)methyleneimino-2-naphthonato (6), M = Me, L = 1-naphthylmethyleneimino-2-naphthonato (7), M = Me, L = 1-naphthylmethyleneimino-2-naphthonato (8)) have been synthesized by reaction of trialkylgallium with appropriate 1-arylmethyleneimino-2-naphthols. The complexes have been characterized by elemental analysis, ¹H NMR, IR and mass spectrometry. Structure of dimethyl[1-(2-pyridyl)methyleneimino-2-naphthonato]gallium (1) has been determined by X-ray single crystal analysis. Ga atom is five coordinate in the structure. Photoluminescent properties have been measured. The maximum emission wavelengths are in the range of 358 and 412 nm with the intensity of 13-325 a.u. The electroluminescent properties of 3, 5, 7 and 8 have been measured. The maximum emission wavelengths are in the range of 450 and 480 nm.     

Electrospinning nanosuspensions loaded with passivated Au nanoparticles

Aqueous polyethylene oxide (PEO) solutions (2 MDa, 2-5 wt %) with or without citrate passivated Au nanoparticles (5.7×10⁻⁷ wt %) have been electrospun, producing fibres with diameters from 290 μm to 55 nm. The incorporation of nanoparticles suppresses the diameter of the fibres and increases the degree of crystallinity. Such nanocomposite fibres are of interest as self-assembled templates for bottom-up fabrication methodologies.     

Preparation of an efficient sorbent by washing then pyrolysis of olive wood for simultaneous solid phase extraction of chloro-phenols and nitro-phenols from water

Simultaneous preconcentration of phenol, 2-chlorophenol, 3-chlorophenol, 4-chlorophenol, 2-nitrophenol, 4-nitrophenol, and 2,4-dinitrophenol was improved by using olive wood (OW) washed with ethanol then pyrolyzed at 200 °C as preconcentrating sorbent. Various OW sorbents were prepared by either washing OW (with ethanol, ether, dichloromethane, tetrahydrofuran or n-hexane); or by pyrolysis (at 100, 150, 200, 250 or 300 °C); or by combined pyrolysis/washing. The adsorbents were characterized by elemental analysis, total acidity/basicity, methylene blue relative surface area, point of zero charge, distribution coefficients of the phenols, and sample loading flow rate. It seems that washing and pyrolysis have removed compounds covering the OW pores, which improved the OW porosity and exposed more acidic groups on the OW surface. The pores and the surface acidic groups seem to play major role in phenols sorption. Ethanol-washed OW then pyrolyzed at 200 °C gave the best preconcentration performance towards phenols (300 mg sorbent, 150 mL of the sample (pH 7), and elution with 3 mL of acetonitrile). The method was linear up to 100 μg L⁻¹; limit of quantification: 0.20-0.48 μg L⁻¹. The method could detect phenol and 2,4-dinitrophenol in industrial wastewater with spiked recovery range from 80.2% to 91.4% (±1.1 to 5.5%RSD) for all the phenols.     

Kinetic determination of cysteine and thiosulphate by inhibition of Hg(II) catalyzed ligand substitution reaction

The sulphur containing inhibitors (I), cysteine (Cys) and sodium thiosulphate (THS), have been found to inhibit Hg(II) catalyzed exchange of cyanide in hexacyanoferrate(II) by nitroso-R-salt (NRS). The inhibitory effect of both the ligands are attributed to their binding tendencies with Hg(II) leading to the formation of catalyst-inhibitor (C-I) complex. The reactions have been followed spectrophotometrically in aqueous medium at 720 nm by noting the increase in absorbance of the green colour product, [Fe(CN)₅NRS]³⁻ at pH 6.50 ± 0.02, temp 25.0 ± 0.1 °C and ionic strength (μ) 0.1 M (KNO₃). A most plausible mechanistic scheme involving the role of analytes (inhibitors) has been proposed. The values of equilibrium constants for complex formation between catalyst-inhibitor (K_CI), catalyst-substrate (K_S) and Mechaelis-Menton constant (K_m) have been computed from the kinetic data. The linear calibration curves have been established between absorbance and inhibitor concentrations under specified conditions. Cys and THS have been determined in the range 1-5 × 10^− 7 M and 4.9-16.9 × 10^− 7 M respectively. The detection limits have been computed to be 1 × 10^− 7 M and 4.9 × 10^− 7 M for Cys and THS, respectively.     

Functionalized semiconductor nanocrystals for ultrasensitive detection of peptides

Semiconductor CdS nanoparticle have been prepared and modified with thiovanic acid. The functionalized nanoparticles are water-soluble. They were used as the fluorescence probes in the ultrasensitive detection of peptides. This method is based on the fluorescence enhancement of functionalized nano-CdS in the presence of peptide with mercapto groups (GN-9) and the fluorescence quenching of functionalized nano-CdS in the presence of peptide (GA-8 and MT-25). Excitation and emission wavelengths were 360 and 530 nm, respectively. Under optimum conditions, the calibration graphs are linear over the range of 0.15-3.5, 0.2-4.0, and 0.2-3.8 μg ml⁻¹ for GN-9, GA-8 and MT-25, respectively. The corresponding detection limits were 0.010 μg ml⁻¹ for GN-9, 0.018 μg ml⁻¹ for GA-8 and 0.022 μg ml⁻¹ for MT-25, respectively. This method has been proved to be a simple, rapid and sensitive method.     

Synthesis and optical properties of fluorene and p-phenylenevinylene copolymers containing non-conjugated spacer

A series of alternating fluorene and p-phenylenevinylene copolymers containing non-conjugated spacer have been synthesized through the Wittig polycondensation reaction. These amorphous copolymers are highly soluble in common organic solvents and can be spin-cast to obtain transparent films. The effects of non-conjugated spacers in the main chain and the methoxyl groups on the side chain on the thermal behavior, photoluminescence (PL) and electroluminescence (EL) properties of these copolymers have been investigated in detail. Single-layered light-emitting diodes (LEDs) have been fabricated in the configuration of ITO/PEDOT/copolymer/Ca/Al and emitted blue light in the range of 456-492 nm. The measurements of current vs voltage show turn-on voltages at 6.2-12.4 V. Among the LEDs based on the six copolymers, the maximum EL brightness and efficiency of the LED based on P1 containing 4CH₂ aliphatic segment length in the main chain and without methoxyl groups on side chain are reached 3936 cd/m² and 0.70 cd/A, respectively.     

Heat capacity and Raman spectra of Cr(C5H7O2)3 at low temperature

The heat capacity of Cr(C₅H₇O₂)₃ has been measured by the adiabatic method within the temperature range 5-320 K. An anomaly with a maximum at ∼60 K has been discovered which points to the phase transformation of the compound. Anomalous contributions to entropy and enthalpy have been revealed. The thermodynamic functions (entropy, enthalpy and reduced Gibbs energy) at 298.15 K have been calculated using the obtained experimental heat capacity data. The Raman spectra have been measured in the frequency range 60-400 cm⁻¹ and in the temperature range 5-220 K. It has been discovered that a new line (109 cm⁻¹) appears at ∼60 K. The nature of these peculiarities in heat capacity and in Raman spectra is discussed.     

Preparation and properties of covalently cross-linked sulfonated copolyimide membranes containing benzimidazole groups

A series of sulfonated copolyimides containing benzimidazole groups (SPIs) were synthesized by random copolymerization of 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), 2-(4-aminophenyl)-5-aminobenzimidazole (APABI), 4,4′-diaminodiphenyl ether-2,2′-disulfonic acid (ODADS) and 9,9-bis(4-aminophenyl)fluorene (BAPF) in m-cresol in the presence of benzoic acid and triethylamine at 180 °C for 20 h. Membranes with good mechanical properties were prepared by solution cast method. Proton exchange treatment resulted in ionic cross-linking and the membranes were further covalently cross-linked by treating them in polyphosphoric acid (PPA) at 180 °C for 6 h. The covalently cross-linked membranes displayed slightly lower ion exchange capacities (IECs) and proton conductivities than the corresponding covalently uncross-linked ones because small part of the sulfonic acid groups had been consumed during the cross-linking process. Fenton’s test (3% H₂O₂ + 3 ppm FeSO₄, 80 °C) revealed that benzimidazole groups played an important role in the radical oxidative stability of the membranes, while the cooperative effect of benzimidazole groups and covalent cross-linking led to much more significant enhancements in the radical oxidative stability of the membranes than each alone. The membrane 4 (ODADS/APABI/BAPF = 2/1/1, by mol), for example, after covalent cross-linking could maintain membrane form within 8 h measurement, which was much longer than that (3 h) before covalent cross-linking under the same conditions. The membrane 5 (ODADS/BAPF = 3/1, by mol) without benzimidazole groups, however, after covalent cross-linking started to break into pieces after 85 min measurement, which was only slightly longer than that (60 min) before cross-linking under the same conditions.     

Synthesis and solid-state spectroscopic investigation of some novel diorganotin(IV) complexes of tetraazamacrocyclic ligands

The tetradendate macrocyclic ligands, [H₂L-1 = 5,12-dioxa-7,14-dimethyl-1,4,8,11-tetraazacyclotetradeca-1,8-diene] and [H₂L-2 = 6,14-dioxa-8,16-dimethyl-1,5,9,13-tetraazacyclohexadeca-1,9-diene] have been prepared by the condensation reaction of 1,2-diaminoethane and 1,3-diaminopropane, respectively, with ethyl acetoacetate in methanol at room temperature. The diorganotin(IV) complexes of general formula [R₂Sn(L-1)/R₂Sn(L-2)] (R = Me, n-Bu and Ph) have been synthesized by template condensation reaction of 1,2-diaminoethane or 1,3-diaminopropane and ethyl acetoacetate with R₂SnCl₂ (R = Me or Ph) or n-Bu₂SnO in 2:2:1 molar ratio at ambient temperature (35 ± 2 °C) in methanol. The solid-state characterization of resulting complexes have been carried out by elemental analysis, IR, recently developed DART-mass, solid-state ¹³C NMR, ^119mSn Mössbauer spectroscopic studies. These studies suggest that in all of the studied complexes, the macrocyclic ligands act as tetradentate coordinating through four nitrogen atoms giving a skew-trapezoidal bipyramidal environment around tin center. Since, the studied diorganotin(IV) macrocyclic complexes are insoluble in common organic solvents, hence good crystals could not be grown for single crystal X-ray crystallographic studies. Thermal studies of all of the studied complexes have also been carried out in the temperature range 0-1000 °C using TG, DTG and DTA techniques. The end product of pyrolysis is SnO₂ confirmed by XRD analysis.     

Novel potentiometric and optical silver ion-selective sensors with subnanomolar detection limits

Ten Ag⁺-selective ionophores have been characterized in terms of their potentiometric selectivities and complex formation constants in solvent polymeric membranes. The compounds with π-coordination show much weaker interactions than those with thioether or thiocarbamate groups as the coordinating sites. Long-term studies with the best ionophores show that the lower detection limit of the best Ag⁺ sensors can be maintained in the subnanomolar range for at least 1 month. The best ionophores have also been characterized in fluorescent microspheres. The so far best lower detection limits of 3 × 10⁻¹¹ M (potentiometrically) and 2 × 10⁻¹¹ M Ag⁺ (optically) are found with bridged thiacalixarenes.     

Syntheses, crystal structures, magnetic properties of two new lanthanide-nitronyl nitroxide complexes (Ln = Gd, Nd)

Two new complexes based on lanthanide ions and nitronyl nitroxide radical, Ln(hfac)₃(NITPh-p-Cl)₂ (Ln = Gd(1), Nd(2); hfac = hexafluoroacetylacetonate; NITPh-p-Cl = 2-(4′-chlorphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) have been synthesized and characterized by single-crystal X-ray diffraction. The single-crystal structures show that two complexes have similar structures, which consist of radical-Ln-radical isolated molecules. The Ln(III) ions are eight-coordinated in slightly distorted dodecahedral geometry. NITPh-p-Cl molecules act as monodentate ligands linking two Ln(III) ions through the oxygen atoms of the N-O groups. The magnetic studies show that the spin coupling between the Gd(III) ion and the radicals in the complex 1 is weak ferromagnetic (J = 0.38 cm⁻¹), while complex 2 exhibits antiferromagnetic interactions (zJ′ = −0.36 cm⁻¹) between Nd(III) ion and radicals.     

Catalytic transfer hydrogenation of ketones catalyzed by orthometalated ruthenium(III) 2-(arylazo)phenolate complexes containing triphenylarsine

Air-stable, mononuclear orthometalated ruthenium(III) 2-(arylazo)phenolate complexes of the general composition [RuX(AsPh₃)₂(L)] (X = Cl or Br; L = CNO donor of the 2-(arylazo)phenolate ligands) have been synthesized and characterized by IR, UV-vis, and EPR as well as by elemental analysis. One of the complexes [RuBr(AsPh₃)₂(azo-OMe)] was structurally characterized by X-ray analysis and was found to be an efficient catalyst for the transfer hydrogenation of ketones with excellent conversion in the presence of isopropanol at 80 °C in 1 h.     

Catalytic adsorptive stripping voltammetric measurements of trace vanadium at bismuth film electrodes

Bismuth-coated glassy carbon electrodes have been successfully applied for catalytic adsorptive stripping voltammetric measurements of low levels of vanadium(V) in the presence of chloranilic acid (CAA) and bromate ion. The new protocol is based on the accumulation of the vanadium-chloranilic acid complex from an acetate buffer (pH 5.5) solution at a preplated bismuth film electrode held at −0.35 V (versus Ag/AgCl), followed by a square-wave voltammetric scan. Factors influencing the adsorptive stripping performance, including the CAA and bromate concentrations, solution pH, and accumulation potential or time have been optimized. The response compares favorably with that observed at mercury film electrodes. A linear response is observed over the 5-25 μg/L concentration range (2 min accumulation), along with a detection limit of 0.20 μg/L vanadium (10 min accumulation). High stability is indicated from the reproducible response of a 50 μg/L vanadium solution (n = 25; R.S.D. = 3.1%). Applicability to a groundwater sample is illustrated.     

Syntheses, structures and properties of dinickel(II) macrocyclic complexes with two 2-thiophenoethyl pendant arms

Three dinickel(II) macrocyclic complexes [Ni₂L(μ-OAc)]ClO₄•X (L = L¹, L² and L³) with two 2-thiophenoethyl pendant arms, have been synthesized by cyclocondensation between N,N-bis(3-aminopropyl)-2-thiophenoethylamine and 2,6-diformyl-4-R-phenol (where R = Me, Cl and F and X = MeOH, 2MeCN and H₂O, respectively), in the presence of nickel(II) ions. The complexes were characterized by elemental analysis, spectroscopic methods and X-ray diffraction techniques. The geometry around both of the Ni(II) ions in each molecule is a slightly distorted octahedral and the thiopheno groups do not coordinate to the Ni(II) ions, resulting that the complexes display contorted saddle-form configurations. The distances between the Ni?Ni centers for the complexes are 3.145, 3.171 and 3.155 Å, respectively. The influences of the substituted groups R in the benzene rings of the macrocyclic units on the structure, electrochemistry, magnetism, cleavage and antibacterial property to DNA have been investigated. The ES-MS results of the complexes confirm that [Ni₂L]²⁺ species in methanol solution are very stable because all the peaks in ES-MS spectra contain this kind of units. The reduction potentials of the complexes shift towards anode upon increasing the drawing electronic ability of substituted groups. Magnetic measurements in the 2-300 K range indicate weak antiferromagnetism for the dinuclear Ni(II) complexes and the magnetic exchange interactions enhance with the decrease of the Ni-Ni distances. These complexes exhibit cleavage activities towards plasmid pBR322 DNA and antibacterial activities.     

Comparison of direct solid sampling and slurry sampling for the determination of cadmium in wheat flour by electrothermal atomic absorption spectrometry

Two analytical methods for the determination of cadmium in wheat flour by electrothermal atomic absorption spectrometry without prior sample digestion have been compared: direct solid sampling analysis (SS) and slurry sampling (SlS). Besides the conventional modifier mixture of palladium and magnesium nitrates (10 μg Pd + 3 μg Mg), 0.05% (v/v) Triton X-100 has been added to improve the penetration of the modifier solution into the solid sample, and 0.1% H₂O₂ in order to promote an in situ digestion for SS. For SlS, 30 μg Pd, 12 μg Mg and 0.05% (v/v) Triton X-100 have been used as the modifier mixture. Under these conditions, and using a pyrolysis temperature of 800 °C, essentially no background absorption was observed with an atomization temperature of 1600 °C. About 2 mg of sample have been typically used for SS, although as much as 3-5 mg could have been introduced. In the case of SlS multiple injections had to be used to achieve the sensitivity required for this determination. Calibration against aqueous standards was feasible for both methods. The characteristic mass obtained with SS was 0.6 pg, and that with SlS was 1.0 pg. The limits of detection were 0.4 and 0.7 ng g⁻¹, the limits of quantification were 1.3 and 2.3 ng g⁻¹ and the relative standard deviation (n = 5) was 6-16% and 9-23% for SS and SlS, respectively. The accuracy was confirmed by the analysis of certified reference materials. The two methods were applied for the determination of cadmium in six wheat flour samples acquired in supermarkets of different Brazilian cities. The cadmium content varied between 8.9 ± 0.5 and 13 ± 2 ng g⁻¹ (n = 5). Direct SS gave results similar to those obtained with SlS using multi-injections; the values of both techniques showed no statistically significant difference at the 95% confidence level. Direct SS was finally adopted as the method of choice, due to its greater simplicity, the faster speed of analysis and the better figures of merit.