Novel dithiolene complexes incorporating conjugated electroactive ligands

A series of new metal (M) dithiolene complexes bearing terthiophene (3, 12, M = Ni; 4, M = Pd; 5, 6, M = Au) and 2,5-bis(para-methoxyphenyl)thiophene units (14, M = Ni; 15, 16, M = Au; 17, M = Pd) have been synthesised in 38-99% yield. The electrochemical properties of the materials have been characterised by cyclic voltammetry and UV-vis spectroelectrochemistry. The nickel complexes possess low oxidation potentials (-0.12 to -0.25 V vs Ag/AgCl) due to the electron-rich dithiolene centres and all complexes display ligand-based redox activity. The terthiophene derivatives have been polymerised by electrochemical oxidation to give stable films with, in the case of poly(3), broad absorption characteristics. Charge transfer materials have been isolated from 14 and 16 with conductivities in the range 9 x 10(-6) to 7 x 10(-8) S cm(-1).     

Receptors for organochlorine pesticides based on calixarenes

The water soluble 4-sulfocalix[n]arenes (with n?=?4,6,8) have been investigated as potential synthetic receptors for cyclodiene organochlorine pesticides. Steady state fluorescence experiments in ethanol solution have shown that only the cavitands with n equal to 6 and 8 form complexes, of comparable stability, with heptachlor. Electrochemical data, obtained in water solution, confirmed the ability of 4-sulfocalix[6]arene to bind the heptachlor, unlike the smaller calixarene. Moreover, a significant increase in the stability constant is observed in water solutions. This stability is caused by the sterical hindrance of pesticides with respect to the cavity dimension of the calixarene. This results in a selective interaction of this molecule with other organochlorine pesticides. Binding experiments, carried out with endosulfan have shown that, despite of chemical similarity, 4-sulfocalix[6]arene and 4-sulfocalix[8]arene behave in a very different way: the former is unable to bind this pesticide, while the latter shows a binding constant of 4.7?×?10⁵ with endosulfan. To investigate the molecular features of the interactions, molecular dynamic simulations of 4-sulfocalix[6]arene in presence of heptachlor in water solution have been performed. These simulations show that different configurations of heptachlor inside the calixarene cavity are equally populated and easily interconverting, suggesting that a non specific hydrophobic interaction plays a key role in the complex stability. These studies have permitted to individuate versatile synthetic receptors for organochlorine pesticides.     

On the investigation of the bilayer functionalities of 1,2-di-oleoyl-sn-glycero-3-phosphatidylcholine (DOPC) large unilamellar vesicles using cationic hemicyanines as optical probes: a wavelength-selective fluorescence approach

The behavior of the cationic hemicyanines trans-4-[4-(dimethylamino)-styryl]-1-methylpyridinium iodide (HC) and 4,(4-(dihexadecylamino)styryl-N-methyl-pyridinium iodide (DIA) were studied in large unilamellar vesicles (LUV) of 1,2-di-oleoyl-sn-glycero-3-phosphatidylcholine (DOPC) using absorption, emission, depolarization and time resolved spectroscopies. Also, thorough spectroscopic studies were performed in homogeneous media to investigate the different interactions that the dyes can experience with its microenvironment. These results help us to comprehend the dye performance under different media and, consequently find interesting features of the DOPC membrane properties. The studies in homogeneous media analyzed by the Kamlet and Taft's solvatochromic comparison method demonstrate, for the first time, that the cationic hemycianines undergo specific interactions with the medium through the solvents ability to donate an electron pair as measured by the beta parameter. Thus, the absorption bands shifts bathochromically with beta while, the emission band shifts hypsochromically. In addition, for the relaxed hemicyanines the 00 energy, nu00, is invariant with the solvent properties. The results in LUV of DOPC show that, DIA undergoes a strong association with the vesicle bilayer while HC partitions between the water and the bilayer pseudophases. To monitor directly the microenvironment and dynamics around HC and DIA inside the DOPC bilayer, we use the wavelength-selective fluorescence approach, which is based on the red edge effect in fluorescence spectroscopy, in addition with the nu00 energy of the hemicyanines. The results show that the fluid state of the DOPC bilayer resembles the microenvironment of sodium bis (2-ethylhexyl) sulfosuccinate (AOT) reverse micelles at W=[H2O]/[AOT] below 10 where there is no free water forming the water pool. Moreover, it is demonstrated for the first time, that the region of the bilayer close to the polar head of DOPC is a powerful electron donor environment.     

Effect of temperature and pH on the aggregation and the surface hydrophobicity of bovine κ-casein

κ-Casein (κ-CN) aggregation by heating has been studied at pH 7.2 and 5.2 using UV-visible spectrophotometry, sodium dodecyl sulfate polyacrylamide gel electrophoresis, spectrofluorometric study of the 1–8 aniline naphtalene sulfonate (ANS)–κ-CN binding and circular dichroism (CD) spectroscopy. The aggregation process to form aggregates like micelles or submicelles and the structural characteristics of these aggregates were pH dependent. Far-UV CD showed that the aggregates obtained by heating presented changes in the κ-CN secondary structure. Near-UV CD spectra showed a certain degree of tertiary organization in the Tyr environment for the protein heated or unheated, only at pH 5.2. ANS binding at both pH was quite different and depends on the self-association process. Heating produced exposition of hydrophobic binding sites only at pH 7.2, including those in the neighborhood of the κ-CN Trp residue.     

Kinetics of reactions catalyzed by enzymes in solutions of surfactants

The effect of surfactants, both in water-in-oil microemulsions (hydrated reverse micelles) and aqueous solutions upon enzymatic processes is reviewed, with special emphasis on the effect of the surfactant upon the kinetic parameters of the process. Differences and similarities between processes taking place in aqueous and organic solvents are highlighted, and the main models currently employed to interpret the results are briefly discussed.     

Direct Identification of Protein–Protein Interactions by Single‐Molecule Force Spectroscopy

Single‐molecule force spectroscopy based on atomic force microscopy (AFM‐SMFS) has allowed the measurement of the intermolecular forces involved in protein‐protein interactions at the molecular level. While intramolecular interactions are routinely identified directly by the use of polyprotein fingerprinting, there is a lack of a general method to directly identify single‐molecule intermolecular unbinding events. Here, we have developed an internally controlled strategy to measure protein–protein interactions by AFM‐SMFS that allows the direct identification of dissociation force peaks while ensuring single‐molecule conditions. Single‐molecule identification is assured by polyprotein fingerprinting while the intermolecular interaction is reported by a characteristic increase in contour length released after bond rupture. The latter is due to the exposure to force of a third protein that covalently connects the interacting pair. We demonstrate this strategy with a cohesin–dockerin interaction.     

On the possibility that cyclodextrins' chiral cavities can be available on AOT n-heptane reverse micelles. A UV-visible and induced circular dichroism study

The formation of reverse micelles (RMs) of sodium 1,4-bis(2-ethylhexyl)sulfosuccinate (AOT) in n-heptane including two different beta-cyclodextrin (beta-CD) derivatives (hydroxypropyl-beta-CD, hp-beta-CD, and decenyl succinyl-beta-CD, Mod-beta-CD) is reported. Both cyclodextrins can be incorporated into AOT RMs in different zones within the aggregate, while beta-CD cannot. Using UV-vis and induced circular dichroism (ICD) spectroscopy and different achiral molecular probes (some azo dyes, p-nitroaniline and ferrocene), it was possible to determine that Mod-beta-CD is located with its cavity at the oil side of the AOT RM interface, while for hp-beta-CD the cavity is inside the RM water pool. Among the molecular probes used, methyl orange (MO) was the only one which gave the ICD signal when dissolved in the AOT RMs with hp-beta-CD, so a detailed study of MO behavior in homogeneous media was also performed to compare with the microheterogeneous media. The solvatochromic behavior of the dye depends not only on the polarity of the media but also on other specific solvent properties. A Kamlet-Taft analysis shows that the MO absorption spectrum shifts to longer wavelength with an increase in the solvent polarity-polarizability (pi*) and the hydrogen donor ability (alpha) of the medium. MO appears to be almost 3 times more sensitive to the pi* parameter than to the alpha parameter. In addition, from the MO absorption spectral changes with the hp-beta-CD concentration, the association equilibrium constants in pure water (K11W) and inside the RMs (K11RM) were computed. The results show that K11W is almost 10 times larger than the value inside the RMs. The latter can be explained considering that MO resides anchored to the RM interface through hydrogen bond interaction with the hydration bound water. This study shows for the first time that the cyclodextrin chiral cavity is available for a guest in an organic medium such as the RMs; therefore, we have created a potentially powerful nanoreactor with two different confined regions in the same aggregate: the polar core of the RMs and the chiral hydrophobic cavity of cyclodextrin.     

“Living” Free Radical Polymerization in Tubular Reactors. I. Modeling of the Complete Molecular Weight Distribution Using Probability Generating Functions

This is the first of a series of works aiming at developing a tool for designing “living” free radical polymerization processes in tubular reactors, in order to achieve tailor‐made MWDs. A mathematical model of the nitroxide‐mediated controlled free radical polymerization is built and implemented to predict the complete MWD. It is shown that this objective may be achieved accurately and efficiently by means of the probability generating function (pgf) transformation. Comparison with experimental data is good. The potential of the resulting model for optimization activities involving the complete MWD is also shown.

     

Preparation, characterization, and Zn(2+) adsorption behavior of chemically modified MCM-41 with 5-mercapto-1-methyltetrazole

A mesoporous silica (MCM-41) has been chemically modified with 5-mercapto-1-methyltetrazole using the homogeneous route. This synthetic route involved the reaction of 5-mercapto-1-methyltetrazole with 3-chloropropyltriethoxysilane prior to immobilization on the support. The resulting material (MTTZ-MCM-41) has been characterized by powder X-ray diffraction, nitrogen gas sorption, FT-IR and MAS NMR spectroscopy, thermogravimetry, and elemental analysis. The solid was employed as a Zn(II) adsorbent from aqueous solutions at room temperature. The effect of several variables (stirring time, pH, metal concentration, addition of ethanol, presence of other metals in the medium) has been studied using batch and column techniques. Flame atomic absorption spectrometry was used to determine the Zn(II) concentration in the filtrate or in the eluted solution after the adsorption process. Results obtained indicate that under the optimum conditions (pH 8 and 2 h stirring time), the maximum adsorption value for Zn(II) was 1.59+/-0.01 mmol/g, whereas the adsorption capacity of the unmodified mesoporous silica was about 0.010+/-0.001 mmol/g. On the other hand, the Zn(II) adsorption on the MTTZ-MCM-41 was independent of the presence of ethanol and other metals (Cu(II), Mn(II), Ca(II), and Mg(II)) in the medium. Finally, experiments carried out in order to study the regeneration capacity of the MTTZ-MCM-41 revealed that the adsorption capacity of this material was maintained after 3 cycles of the adsorption/desorption process.     

Synthesis, structural characterization and reactivity of new tin bridged ansa-bis(cyclopentadiene) compounds: X-ray crystal structures of Me2Sn(C5Me4R-1)2 (R = H, SiMe3)

The organo-tin compounds, Me₂Sn(C₅H₄R-1)₂ (R = Me (1), Prⁱ (2), Bu^t (3), SiMe₃ (4)) and Me₂Sn(C₅Me₄R-1)₂ (R = H (5), SiMe₃ (6)), were prepared by the reaction of Me₂SnCl₂ with the lithium or sodium derivative of the corresponding cyclopentadiene. Compounds 1-6 have been characterized by multinuclear NMR spectroscopy (¹H, ¹³C, ¹¹⁹Sn). In addition the molecular structures of 5 and 6 were determined by single crystal X-ray diffraction studies. The transmetalation reaction of 1-6 with ZrCl₄ or [NbCl₄(THF)₂] gave the corresponding metallocene complexes in high yields.