Nanotexturing of polystyrene surface in fluorocarbon plasmas: from sticky to slippery superhydrophobicity

In this work plasma etching processes have been studied to roughen and fluorinate polystyrene surface as an easy method to achieve a superhydrophobic slippery character. Radiofrequency discharges have been fed with CF(4)/O(2) mixtures and the effect of the O(2):CF(4) ratio, the input power, and the treatment duration have been investigated in terms of wettability, with focus on sliding performances. For this purpose, surface morphological variations, evaluated by means of scanning electron microscopy and atomic force microscopy, together with the chemical assessment by X-ray photoelectron spectroscopy, have been correlated with water contact angle hysteresis and volume resolved sliding angle measurements. Results indicate that by increasing the height and decreasing the density of the structures formed by etching, within a tailored range, a transition from sticky to slippery superhydrophobicity occurs. A short treatment time (5 min) is sufficient to obtain such an effect, provided that a high power input is utilized. Optimized surfaces show a unaltered transparency to visible light according to the low roughness produced.     

Assessment of water-soluble pi-extended squaraines as one- and two-photon singlet oxygen photosensitizers: design, synthesis, and characterization

Singlet oxygen sensitization by organic molecules is a topic of major interest in the development of both efficient photodynamic therapy (PDT) and aerobic oxidations under complete green chemistry conditions. We report on the design, synthesis, biology, and complete spectroscopic characterization (vis-NIR linear and two-photon absorption spectroscopy, singlet oxygen generation efficiencies for both one- and two-photon excitation, electrochemistry, intrinsic dark toxicity, cellular uptake, and subcellular localization) of three classes of innovative singlet oxygen sensitizers pertaining to the family of symmetric squaraine derivatives originating from pi-excessive heterocycles. The main advantage of pi-extended squaraine photosensitizers over the large number of other known photosensitizers is their exceedingly strong two-photon absorption enabling, together with sizable singlet oxygen sensitization capabilities, for their use at the clinical application relevant wavelength of 806 nm. We finally show encouraging results about the dark toxicity and cellular uptake capabilities of water-soluble squaraine photosensitizers, opening the way for clinical small animal PDT trials.     

Multifunctional nanostructures based on inorganic nanoparticles and oligothiophenes and their exploitation for cellular studies

The combination of materials that possess different properties (such as, for instance, fluorescence and magnetism) into one single object of nanoscale size represents an attractive challenge for biotechnology, especially for their potential relevance in biomedical applications. We report here the preparation of novel bifunctional conjugates based on the linkage of inorganic nanoparticles to organic oligothiophene fluorophores (OTFs). In comparison to the organic dyes commonly used in bioimaging and more similarly to colloidal quantum dots, OTFs have broad optical absorption spectra, and therefore OTF fluorophores emitting at different colors can be excited with a single excitation source, allowing for easier multiplexing analysis. In this work we show the preparation of OTF-nanoparticle conjugates based on gold and iron oxide nanoparticles and their characterization using different techniques such as gel electrophoresis, photoluminescence spectroscopy, dynamic light scattering, and so on. In addition, by performing an in vitro study on human tumor cells we show that OTF-nanoparticle conjugates emitting at different colors can be used for multiplexing detection. Also, in the case of iron oxide-OTF conjugates, once uptaken by the cells, we show that they preserve both their fluorescent and their magnetic properties.     

Effect of ortho-SR groups on O-H bond strength and H-atom donating ability of phenols: a possible role for the Tyr-Cys link in galactose oxidase active site?

Rotation about the Ar-S bond in ortho-(alkylthio)phenols strongly affects the bond dissociation enthalpy (BDE) and the reactivity of the OH group. Newly synthesized sulfur containing heterocycles 3 and 4, where the -SR group is almost coplanar with the phenolic ring, are characterized by unusually low BDE(O-H) values (79.6 and 79.2 kcal/mol, respectively) and by much higher reactivities toward peroxyl radicals than the ortho-methylthio derivative 1 (82.0 kcal/mol). The importance of the intramolecular hydrogen bond (IHB) in determining the BDE(O-H) was demonstrated by FT-IR experiments, which showed that in heterocycles 3 and 4 the IHB between the phenolic OH group and the S atom is much weaker than that present in 1. Since the IHB can be formed only if the -SR group adopts an out-of-plane geometry, this interaction is possible only in the methylthio derivative 1 and not in 3 and 4. The additive contribution to the phenolic BDE(O-H) of the -SR substituent therefore varies from -3.1 to +2.8 kcal/mol for the in-plane and out-of-plane conformations, respectively. These results may be relevant to understanding the role of the tyrosine-cysteine link in the active site of galactose oxidase, an important enzyme that catalyzes the two-electron aerobic oxidation of primary alcohols to aldehydes. The switching of the ortho -SR substituent between perpendicular and planar conformations may account for the catalytic efficiency of this enzyme.     

Synthesis and intramolecular and interionic structural characterization of half-sandwich (arene)ruthenium(II) derivatives of bis(pyrazolyl)alkanes

Arene ruthenium(II) complexes containing bis(pyrazolyl)methane ligands have been prepared by reacting the ligands L' (L' in general; specifically L(1) = H(2)C(pz)(2), L(2) = H(2)C(pz(Me2))(2), L(3) = H(2)C(pz(4Me))(2), L(4) = Me(2)C(pz)(2) and L(5) = Et(2)C(pz)(2) where pz = pyrazole) with [(arene)RuCl(mu-Cl)](2) dimers (arene = p-cymene or benzene). When the reaction was carried out in methanol solution, complexes of the type [(arene)Ru(L')Cl]Cl were obtained. When L(1), L(2), L(3), and L(5) ligands reacted with excess [(arene)RuCl(mu-Cl)](2), [(arene)Ru(L')Cl][(arene)RuCl(3)] species have been obtained, whereas by using the L(4) ligand under the same reaction conditions the unexpected [(p-cymene)Ru(pzH)(2)Cl]Cl complex was recovered. The reaction of 1 equiv of [(p-cymene)Ru(L')Cl]Cl and of [(p-cymene)Ru(pzH)(2)Cl]Cl with 1 equiv of AgX (X = O(3)SCF(3) or BF(4)) in methanol afforded the complexes [(p-cymene)Ru(L')Cl](O(3)SCF(3)) (L' = L(1) or L(2)) and [(p-cymene)Ru(pzH)(2)Cl]BF(4), respectively. [(p-cymene)Ru(L(1))(H(2)O)][PF(6)](2) formed when [(p-cymene)Ru(L(1))Cl]Cl reacts with an excess of AgPF(6). The solid-state structures of the three complexes, [(p-cymene)Ru{H(2)C(pz)(2)}Cl]Cl, [(p-cymene)Ru{H(2)Cpz(4Me))(2)}Cl]Cl, and [(p-cymene)Ru{H(2)C(pz)(2)}Cl](O(3)SCF(3)), were determined by X-ray crystallographic studies. The interionic structure of [(p-cymene)Ru(L(1))Cl](O(3)SCF(3)) and [(p-cymene)Ru(L')Cl][(p-cymene)RuCl(3)] (L' = L(1) or L(2)) was investigated through an integrated experimental approach based on NOE and pulsed field gradient spin-echo (PGSE) NMR experiments in CD(2)Cl(2) as a function of the concentration. PGSE NMR measurements indicate the predominance of ion pairs in solution. NOE measurements suggest that (O(3)SCF(3))(-) approaches the cation orienting itself toward the CH(2) moiety of the L(1) (H(2)C(pz)(2)) ligand as found in the solid state. Selected Ru species have been preliminarily investigated as catalysts toward styrene oxidation by dihydrogen peroxide, [(p-cymene)Ru(L(1))(H(2)O)][PF(6)](2) being the most active species.     

Experimental and theoretical charge density distribution of the colossal magnetoresistive transition metal sulfide FeCr2S4

The total charge density distribution rho(r) of the colossal magnetoresistive transition metal sulfide FeCr(2)S(4) was evaluated through a multipole formalism from a set of structure factors obtained both experimentally, by means of single crystal high-quality x-ray diffraction data collected at T=23 K, and theoretically, with an extended-basis unrestricted Hartree-Fock periodic calculation on the experimental geometry. A full topological analysis, followed by the calculation of local energy density values and net atomic charges, was performed using the quantum theory of atoms in molecules. The experimental and theoretical results were compared. Good agreement was found for the topological properties of the system, as well as for the atomic net charges and the nature of the chemical bonds. An analysis of the electron density rho(r), its Laplacian nabla(2)[rho(r)], and the total energy density H(r) at the bond critical points was employed to classify all the interactions that resulted as predominantly closed shell (ionic) in nature. The topological indicators of the bonded interactions for Fe are distinct from those for Cr. The Fe-S bond distances were found to be 0.145 A shorter than the ideal values computed on the basis of Shannon's crystal radii, much shorter than the Cr-S distances with respect to their ideal Shannon lengths. Concomitantly, rho(r) and |H(r)| at the bond critical points are greater for Fe-S interactions, indicating that the local concentration of charge density in the internuclear region is larger for the tetrahedrally coordinated iron than for the octahedrally coordinated chromium. The isosurface in the real space for nabla(2)[rho(r)]=0 was plotted for both iron and chromium, pointing out the local zones of valence shell charge concentration and relating them to the partial d-orbital occupancy of the two transition metal atoms.     

Acidification of three-dimensional emeraldine polymers: Search for minimum energy paths from base to salt

We present a numerical simulation of the HCl acidification process of a three-dimensional semiconducting emeraldine base (EB) polymer leading to the corresponding metallic emeraldine salt form. We have searched minimum energy paths connecting the initial configuration, composed of two EB polymer chains per cell each one attached by two HCl molecules, with the Pc2a polaronic configuration which is the final state of the acidification process. For this aim, the variational nudged elastic band method has been adopted. We provide a pictorial representation of the acidification process at T=0 K, monitoring the EB protonation and the evolution of the polymeric chains and of the positions of the Cl(-) counterions on the lowest potential energy surface. To include also temperature effects, we have explored the potential energy surface around the final equilibrium configuration, heating the system and following its dynamics by the Car-Parrinello procedure.     

Monitoring ssDNA Binding to the DnaB Helicase from Helicobacter pylori by Solid‐State NMR Spectroscopy

DnaB helicases are bacterial, ATP‐driven enzymes that unwind double‐stranded DNA during DNA replication. Herein, we study the sequential binding of the “non‐hydrolysable” ATP analogue AMP‐PNP and of single‐stranded (ss) DNA to the dodecameric DnaB helicase from Helicobacter pylori using solid‐state NMR. Phosphorus cross‐polarization experiments monitor the binding of AMP‐PNP and DNA to the helicase. ¹³C chemical‐shift perturbations (CSPs) are used to detect conformational changes in the protein upon binding. The helicase switches upon AMP‐PNP addition into a conformation apt for ssDNA binding, and AMP‐PNP is hydrolyzed and released upon binding of ssDNA. Our study sheds light on the conformational changes which are triggered by the interaction with AMP‐PNP and are needed for ssDNA binding of H. pylori DnaB in vitro. They also demonstrate the level of detail solid‐state NMR can provide for the characterization of protein–DNA interactions and the interplay with ATP or its analogues.     

Synthesis of 3-substituted 2-fluoro- and 2,2-difluoroaziridines

A new route for the synthesis of stable 3-alkyl- and 3-aryl-2(,2)-(di)fluoroaziridines was developed by hydride reduction of novel alpha-bromo- and alpha-chloro-alpha(,alpha)-(di)fluoroketimines and subsequent ring closure of beta-fluorinated beta-chloro- and beta-bromoamines. This is the first report on the synthesis of 2,2-difluoroaziridines sensu stricto.     

Free volume from molecular dynamics simulations and its relationships to the positron annihilation lifetime spectroscopy

The free volume micro-structural properties of propylene glycol obtained by means of molecular dynamics simulations have been investigated and compared with the experimental data from positron annihilation lifetime spectroscopy (PALS). The results are also compared to those recently obtained on glycerol. The bulk microstructures of the samples have been analyzed in the temperature range 100–350 K with a probe-based procedure for exploring the free volume cavities of the microstructures. The basic free volume property, i.e., mean cavity volume, is compared with the hole volume data from PALS. A comparison between calculated and experimental data suggests the existence of a threshold volume for the smallest cavity detectable by PALS, which may be ascribed to fast local motions of the matrix constituents. At high temperatures the cavity analysis reveals the formation of an infinite cavity, i.e., percolation phenomenon. The onset temperatures of the percolation process in propylene glycol and glycerol are found to be close to the characteristic PALS temperature \(T^{\rm L}_{\rm b2}\) , where a pronounced change in the PALS response occurs, as well as to the characteristic dynamic Schönhals temperature \(T^{\rm SCH}_{\rm B}\) , and Stickel’s temperature \(T^{\rm ST}_{\rm B}\) , marking a dramatic change in the primary α properties.