Interfacial behavior and film patterning of redox-active cationic copper(II)-containing surfactants

Herein, we describe the synthesis and characterization of a novel series of single-tail amphiphiles LPyCn (Py=pyridine, Cn=C18, C16, C14, C10) and their copper(II)-containing complexes, which are of relevance for patterned films. The N-(pyridine-2-ylmethyl)alkyl-1-amine ligands and their complexes [CuIICl2(LPyC18)] (1), [CuIICl2(LPyC16)] (2), [CuIICl2(LPyC14)] (3), [CuIIBr2(LPyC18)] (4), [CuIIBr2(LPyC16)] (5), and [CuIIBr2(LPyC10)] (6) were synthesized, isolated, and characterized by means of mass spectrometry, IR and NMR spectroscopies, and elemental analysis. Complexes 1, 2, 3, and 6 had their molecular structure solved by X-ray diffraction methods, which showed that the local geometry around the metal center is distorted square planar. With the aim of using these species as precursors for redox-responsive films, an assessment of their electrochemical properties involved cyclic voltammetry in different solvents, with different supporting electrolytes and scan rates. Density functional theory calculations of relevant species in bulk and at interfaces were used to evaluate their electronic structure and dipole moments. The morphology and order of the resulting films at the air/water interface were studied by isothermal compression and Brewster angle microscopy. Biphasic patterned Langmuir films were observed for all complexes except 3 and 6, and dependence on the chain length and the nature of the halogen coligand determine the characteristics of the isotherms and their intricate topology. Complexes 3 and 6, which have shorter chain lengths, failed to exhibit organization. These results exemplify the first comprehensive study of the behavior of single-tail metallosurfactants, which are likely to lead to high-end technological applications based on their patterned films.     

Ethylene/1,3-Cyclohexadiene Copolymerization by Means of Methylaluminoxane Activated Half-Sandwich Complexes

Ethylene copolymerization with 1,3-cyclohexadiene (CHD) was investigated by using methylaluminoxane (MAO) activated single-site catalysts including bridged and non-bridged titanium half-sandwich and bimetallic cobalt(I) complexes. MAO activated CpTiCl₂[NP(^tBu)₃] (Cp = cyclopentadienyl, ^tBu = tert-butyl) gave high molecular weight CHD copolymers without encountering catalyst activity losses. According to the NMR microstructure investigation the resulting copolymers are highly regioregular.     

Hydration of ionic species studied by the reference interaction site model with a repulsive bridge correction

We have tested the reference interaction site model (RISM) for the case of the hypernetted chain (HNC) and the partially linearized hypernetted chain (PLHNC) closures improved by a repulsive bridge correction (RBC) for ionic hydrated species. We have analyzed the efficiency of the RISM/HNC+RBC and RISM/PLHNC+RBC techniques for decomposition of the electrostatic and the nonpolar hydration energies on the energetic and the enthalpic parts for polyatomic ions when the repulsive bridge correction is treated as a thermodynamic perturbation, and investigate the repulsive bridge effect on the electrostatic potential induced by solvent on solute atoms. For a number of univalent and bivalent atomic ions, molecular cations, and anions, the method provides hydration energies deviating only by several percents from the experimental data. In most cases, the enthalpic contributions to the free energies are also close to the experimental results. The above models are able to satisfactory predict the hydration energies as well as the electrostatic potential around the ionic species. For univalent atomic ions, they also provide qualitative estimates of the Samoilov activation energies.     

A chemometric approach to the investigation of major and minor ion chemistry in Lake Como (Lombardia, Northern Italy

A chemometric approach based on Principal Component Analysis (PCA) has been proposed, in order to study chemical features (major and minor ions, total alkalinity, dissolved silica) of surface and deep waters of Lake Como (Northern Italy). The method allowed us to investigate the correlations between the analyzed ions in an easy-to-see way, using bi-dimensional graphs. In wintertime, the ionic composition of Lake Como waters seems to be mainly related to the geological composition of the lake basin, with a crystalline bedrock on the northern side and a sedimentary cover in the southern part. The presence of contaminants such as bromide and nitrite in water columns is also evidenced and discussed.     

MSPD procedure for determining buprofezin,tetradifon, vinclozolin,and bifenthrin residues in propolis by gas chromatography–mass spectrometry

A simple and effective extraction method based on matrix solid-phase dispersion (MSPD) was developed to determine bifenthrin, buprofezin, tetradifon, and vinclozolin in propolis using gas chromatography–mass spectrometry in selected ion monitoring mode (GC–MS, SIM). Different method conditions were evaluated, for example type of solid phase (C₁₈, alumina, silica, and Florisil), the amount of solid phase and eluent (n-hexane, dichloromethane, dichloromethane–n-hexane (8:2 and 1:1, v/v) and dichloromethane–ethyl acetate (9:1, 8:2 and 7:3, v/v)). The best results were obtained using 0.5 g propolis, 1.0 g silica as dispersant sorbent, 1.0 g Florisil as clean-up sorbent, and dichloromethane–ethyl acetate (9:1, v/v) as eluting solvent. The method was validated by analysis of propolis samples fortified at different concentration levels (0.25 to 1.0 mg kg⁻¹). Average recoveries (four replicates) ranged from 67% to 175% with relative standard deviation between 5.6% and 12.1%. Detection and quantification limits ranged from 0.05 to 0.10 mg kg⁻¹ and 0.15 to 0.25 mg kg⁻¹ propolis, respectively.     

Stabilizing and destabilizing effects of phenylalanine --> F5-phenylalanine mutations on the folding of a small protein

We report a systematic evaluation of phenylalanine-to-pentafluorophenylalanine (Phe --> F5-Phe) mutants for the 35-residue chicken villin headpiece subdomain (c-VHP), the hydrophobic core of which features a cluster of three Phe side chains (residues 6, 10, and 17). Phe --> F5-Phe mutations are interesting because aryl-perfluoroaryl interactions of optimal geometry are intrinsically more favorable than aryl-aryl interactions and because perfluoroaryl units are more hydrophobic than are analogous aryl units. One mutant, Phe-10 --> F5-Phe, provides enhanced tertiary structural stability relative to the native sequence. The other six mutants analyzed caused a decrease in stability.     

Synthesis of (Z)-tributylstannyl enynes: systematic studies of Sonogashira cross-coupling reactions between (E)-1-iodovinyl-1-tributylstannanes and terminal acetylenes using amines or tetrabutylammonium hydroxide (TBAOH) as activator

Sonogashira cross-coupling reactions involving (E)-iodo vinyl stannanes and terminal acetylenes were carried out in the presence of Pd(PPh₃)₄, CuI and several amines, affording (Z)-tributylstannyl enynes in moderate to good yields (62-91%). Utilizing the catalytic system containing Pd(PPh₃)₄ (5%), CuI (10%), and TBAOH (40% in aqueous media) as activator, better yields (72-91%) and lower reaction times were achieved.     

Integrated NMR and computational study of push-pull NLO probes: interplay of solvent and structural effects

In this study we combined QM calculations and NMR measurements to understand at a detailed level the complex interplay of structural/electronic properties with the effects of the solvent in the NLO activity of push-pull systems, quantified in terms of variations of the static hyperpolarizability. Different parameters (bond lengths and bond length alternation, vibrational frequencies, electronic charge distribution) are introduced and tested to rationalize both the solvent sensitivity of three molecular systems (namely, p-nitroaniline, ethyl 4-ammino benzoate, and 5-nitro-1H-indole) and the differences among them. This analysis has finally allowed us to establish a clear correlation between the charge transfer behavior of the systems, their NLO properties, and NMR parameters also validating simplified but effective chemical analyses based on resonance limit forms.