Copper-free and amine-free Sonogashira coupling in air in a mixed aqueous medium by palladium complexes of N/O-functionalized N-heterocyclic carbenes

Highly convenient copper-free and amine-free Sonogashira coupling of aryl bromides and iodides with terminal acetylenes under amenable conditions in air and in a mixed aqueous medium are reported using several new, user friendly and robust palladium precatalysts (1–5) of N/O-functionalized N-heterocyclic carbenes (NHCs). In particular, the precatalysts, 1 and 2, were synthesized from the imidazolium chloride salts by the treatment with PdCl₂ in pyridine in presence of K₂CO₃ as a base while the precatalysts, 3–5, were synthesized from the respective silver complexes by the treatment with (COD)PdCl₂. The DFT studies carried out on the 1–5 complexes suggest the presence of strong NHC–Pd σ-interactions arising out of deeply buried NHC–Pd σ-bonding molecular orbitals (MOs) that account for the inert nature of the metal–carbene bonds and also provide insights into the exceptional stability of these precatalysts.     

Side chain functionalized η-tetramethyl cyclopentadienyl complexes of Rh and Ir with a pendant primary amine group

Conversion of 2-(2,3,4,5-tetramethylcyclopentadien)ethylamine tautomere C₅Me₄H₂(CHCH₂)NH₂ (1) with MCl₃ · n H₂O (M = Rh, Ir) under acidic conditions gives the respective μ-chloro-bridged chelates [(η⁵-Me₄Cp(CH₂)₂NH₃)RhCl₂]₂Cl₂ (2) and [(η⁵-Me₄Cp(CH₂)₂NH₃)IrCl₂]₂Cl₂ (3). The dimeric complexes are received as ammonium salts and thus display good solubility in strong donor solvents such as water and DMSO. Addition of triphenyl phosphine converts Rh-dimer 2 into the mononuclear phosphine complex 4. Under basic conditions, no intramolecular coordination of the pendant NH₂ is observed and thus the primary amino group of 4 reacts selectively with succinic anhydride by formation of a peptide bond. Hence, the electrophilic metal center and the latent nucleophilic nitrogen, which represent complementary functionalities, can be addressed separately under the appropriate reaction conditions.     

C18, C8, and perfluoro reversed phases on diamond for solid-phase extraction

In spite of advances in solid-phase extraction (SPE) technology there are certain disadvantages to current SPE silica-based, column packings. The pH range over which extraction can occur is limited and each column is generally only used once. New diamond-based reversed SPE phases (C₁₈, C₈, and perfluorinated) were developed in our laboratories. Studies were done which show that these phases do not have the same limitations as traditional silica-based stationary phases. The synthesis and properties of these diamond-based phases are presented, and the stability, percent recovery, and column capacity are given for the C₁₈ phase.     

Fabrication and characterization of hexahistidine-tagged protein functionalized multi-walled carbon nanotubes for selective solid-phase extraction of Cu and Ni

Hexahistidine-tagged protein functionalized multi-walled carbon nanotubes (MWCNTs/6His-tagged protein) were prepared and characterized by ultraviolet-visible spectrophotometry and atomic force microscopy. Both static and dynamical adsorption experiments showed that the MWCNTs/6His-tagged protein served as good sorbent for the solid-phase extraction of Cu²⁺ and Ni²⁺. Effective on-line sorption of Cu²⁺ and Ni²⁺ on the MWCNTs/6His-tagged protein packed microcolumn was achieved in a pH range of 3.0-4.5 and 4.5-6.0, respectively. The retained Cu²⁺ and Ni²⁺ were efficiently eluted with 0.2 mol L⁻¹ imidazole-HCl solution for on-line flame atomic absorption spectrometric determination. The MWCNTs/6His-tagged protein exhibited fairly fast kinetics for the sorption of Cu²⁺ and Ni²⁺, and offered up to 20,000 and 1800 times improvement in the tolerable concentrations of co-existing ions over the MWCNTs for solid-phase extraction of Cu²⁺ and Ni²⁺, respectively. On-line solid-phase extraction at a flow rate of 5.0 mL min⁻¹ for 60 s gave an enhancement factor of 29 for Cu²⁺ and 28 for Ni²⁺, a sample throughput of 45 h⁻¹, and a detection limit (3s) of 0.31 μg L⁻¹ for Cu²⁺ and 0.63 μg L⁻¹ for Ni²⁺. The precision for 11 replicate measurements was 2.4% for 10 μg L⁻¹ Cu²⁺, and 2.5% for 15 μg L⁻¹ Ni²⁺.     

Novel fluorescent pH sensor based on 5-(4-carboxy-phenyl)-10,15,20-tris(phenyl)-porphyrin

A novel fluorescent pH sensor based on 5-(4-carboxy-phenyl)-10,15,20-tris(phenyl)-porphyrin, as sensing agent, has been developed. The carboxyl functionalized asymmetric porphyrin has been synthesized and characterized by high performance liquid chromatography (HPLC), thin layer chromatography (TLC), proton nuclear magnetic resonance (¹H NMR), Fourier transform infrared spectroscopy (FT-IR), ultraviolet–visible (UV–vis), emission, excitation and mass spectrometry (MS) spectra. Optical and fluorescence behaviors were investigated in relationship with variation of acid concentration in the range of acid pH from 1.5 to 5.5. Upon increasing the acidity of the solution, the decrease of the fluorescence intensity was noticed, as a linear function of pH. Different metal ions were tested to put into evidence the changes regarding the fluorescence intensity, but the fluorescence obtained results revealed no significant interference on pH determination. The conclusion is that the proposed fluorescent sensor can measure pH in acid range in the presence of different metal ions making this sensor a proper one for pH determinations in leaching solutions of the recyclable processes of valuable metals.     

Tuning retention and selectivity in reversed-phase liquid chromatography by using functionalized multi-walled carbon nanotubes

Aim of this work was to explore the possibility of retention and selectivity tuning in reversed-phase liquid chromatography by means of chemically modified multi-walled carbon nanotubes (MWCNTs). These were synthesized by derivatizing pristine MWCNTs with amino-terminated alkyl chains containing polar embedded groups. A novel hybrid material based on functionalized MWCNTs (MWCNTs-R-NH₂) was prepared, characterized and tested. The idea was to design a mixed-mode separation medium basing its sorption properties on the peculiar characteristics of MWCNTs combined with the chemical interactions provided by the functional chains introduced on the nanotube skeleton. MWCNTs-R-NH₂ were easily grafted to silica microspheres by gamma radiation (using a ⁶⁰Co source) in the presence of polybutadiene as the linking agent. The composite was characterized by scanning electron microscopy (SEM) and Brunauer, Emmett and Teller (BET) analysis in terms of structural morphology, surface area and porosity. The MWCNTs-R-NH₂ sorbent was tested as stationary phase. The reversed-phase behaviour was first proved by analysis of alkylbenzenes, while the key role of CNT derivatization in addressing the selectivity/affinity towards the solutes was evidenced by testing three classes of analytes, viz. barbiturates, steroid hormones and alkaloids. These compounds, with different molecular structure and polarity, were here analysed for the first time on CNT-based LC stationary phases. The behaviour of the novel sorbent was compared in terms of retention capability and resolution with that observed using unmodified MWCNTs, pointing out the mixed-mode characteristics of the MWCNTs-R-NH₂ material. The same test mixtures were analysed also on a conventional mono-modal separation sorbent (C18) to highlight the particular behaviour of the (derivatized)MWCNTs-based stationary phases. The novel material showed better performance in separation of polar compounds, i.e. barbiturates and alkaloids, than the unmodified MWCNTs and than the C18 column. Results showed that MWCNT functionalization is powerful to modulate retention/selectivity in reversed-phase liquid chromatography.     

Rheological characterization and modeling of end-functionalized polybutadienes

The rheological characterization and modeling of a series of polybutadienes obtained by anionic solution polymerization is presented in this work. The polybutadienes are synthesized using two different initiators: R,R′,R′′-silyloxyalkyllithium (F1) and R,R′,R′′-silylalkyllithium (F3). In addition, a polybutadiene obtained with a conventional alkyllithium initiator (n-butyllithium) is used as a reference. The rheological characterization is carried out under small amplitude oscillatory shear in the stress-controlled mode. Microstructure, molecular weight, and molecular weight distribution are determined by FTIR and GPC. The vinyl content of the polybutadienes synthesized using the functionalized initiators is similar to that obtained with n-butyllithium (8–11%). Materials obtained with F1 show a relatively low polydispersity within a narrow molecular weight range (250,000–300,000 g/mol), while samples obtained with F3 cover a wider range of molecular weights (65,000–670,000 g/mol) and display higher values of polydispersity. In all cases, a parallel reaction using propylene oxide in the termination step is done to place a functional group at the chain ends. The effect of this group on the rheological behavior appears to be negligible. Three rheological models are used and their predictions of the experimental data are compared. The models include the Doi and Edwards reptation model, expressions using a discrete spectrum of relaxation times based in the rubber-like liquid constitutive equation and the fractional Maxwell equation in which a given analytical relaxation-spectrum is used. Relevant relations are obtained between the models' parameters and the molecular properties of these systems, which in turn are related to the presence of functional groups at the polymer chain ends.     

功能化聚丙烯腈纳米纤维膜同时高效萃取莠去津及其毒性代谢物

研制了一种新型固相萃取(SPE)介质,用于同时高效萃取莠去津(ATZ)及其两种毒性代谢产物脱乙基莠去津(DEA)和脱异丙基莠去津(DIA),为全面客观地评价ATZ的水污染状况提供基础.以聚丙烯腈纳米纤维(PAN NFs)膜为基底膜,制备了3种功能化的NFs膜.吸附容量和吸附效率实验结果表明,羧基修饰的PAN NFs(COOH-PAN NFs)膜对3种目标物的静态和动态吸附容量分别为2.00和0.19 mg/g,动态吸附流出率低于30.0％,显著优于其它3种NFs膜,且对极性较大的目标物保留最强,表明其为同时高效吸附ATZ、 DIA和DEA的优势SPE介质,且主要通过羧基基团与目标物之间形成的氢键进行目标物吸附.采用基于COOH-PAN NFs膜的SPE,结合高效液相色谱-二极管阵列检测器(HPLC-DAD),建立了同时检测水样中ATZ、 DIA和DEA的方法,方法回收率为81.4％～120.3％, DIA检出限(LOD, S/N=3)为0.12 ng/mL,DEA和ATZ的检出限为0.09 ng/mL,可应用于实际水样监测.     

Synthesis and Applications of Hajos–Parrish Ketone Isomers

Numerous natural products possess ring systems and functionality for which Hajos–Parrish ketone isomers with a transposed methyl group (termed “iso‐Hajos–Parrish ketones”) would be of value. However, such building blocks have not been exploited to the same degree as the more typical Hajos–Parrish hydrindane. An efficient three‐step synthesis of such materials was fueled by a simple method for the rapid preparation of highly functionalized cyclopentenones, several of which are new chemical entities that would be challenging to access through other approaches. Furthermore, one iso‐Hajos–Parrish ketone was converted into two distinct natural product analogues and one natural product. As one indication of the value of these new building blocks, that latter target was obtained in 10 steps, having previously been accessed in 18 steps using the Hajos–Parrish ketone.