Massimiliano Lanzi

Extracellular production of tellurium nanoparticles by the photosynthetic bacterium Rhodobacter capsulatus.

The toxic oxyanion tellurite (TeO3(2-)) is acquired by cells of Rhodobacter capsulatus grown anaerobically in the light, via acetate permease ActP2 and then reduced to Te(0) in the cytoplasm as needle-like black precipitates. Interestingly, photosynthetic cultures of R. capsulatus can also generate Te(0) nanoprecipitates (TeNPs) outside the cells upon addition of the redox mediator lawsone (2-hydroxy-1,4-naphtoquinone). TeNPs generation kinetics were monitored to define the optimal conditions to produce TeNPs as a function of various carbon sources and lawsone concentration. We report that growing cultures over a 10 days period with daily additions of 1mM tellurite led to the accumulation in the growth medium of TeNPs with dimensions from 200 up to 600-700 nm in length as determined by atomic force microscopy (AFM). This result suggests that nucleation of TeNPs takes place over the entire cell growth period although the addition of new tellurium Te(0) to pre-formed TeNPs is the main strategy used by R. capsulatus to generate TeNPs outside the cells. Finally, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) analysis of TeNPs indicate they are coated with an organic material which keeps the particles in solution in aqueous solvents.

Comparison between Inorganic Geomimetic Chrysotile and Multiwalled Carbon Nanotubes in the Preparation of One-dimensional Conducting Polymer Nanocomposites

The aim of this study was to examine the role of the nanofillers spatial arrangement in the electrical properties of hybrid organic-inorganic fibers. In this paper, we have presented experimental results for preparation of fibers with a nanometric diameter based on a polyaniline/poly(ethylene oxide) doped blend and geomimetic chrysotile nanotubes. The nanostructured material was prepared using electrospinning techniques. Electrospun fibers made by pristine polymers and by the same blend loaded with carbon nanotubes were used as reference materials to compare the structural, and electrical properties of the novel organic-inorganic material. Generally, electrical properties were improved by the addition of materials that have high conductivity. Electrospun fibers filled with a traditional insulator like chrysotile have shown higher electrical conductivity than the pristine materials. In order to fully understand how structural variations impact upon the electrical conductivity the materials were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (RS), differential scanning calorimetry (DSC) and four-point probe method. The results suggest that the occurred electrical conductivity gain could be attributed to parallel orientation of the chrysotile nanotubes and higher crystallinity induced by the one-dimensional nanostructured filler materials. The obtained results bring us one step closer to using intrinsically conducting polymers (ICPs) in the creation of functionalized polymeric nanocomposites for nanotechnology.

Escherichia coli DnaE Polymerase Couples Pyrophosphatase Activity to DNA Replication

DNA Polymerases generate pyrophosphate every time they catalyze a step of DNA elongation. This elongation reaction is generally believed as thermodynamically favoured by the hydrolysis of pyrophosphate, catalyzed by inorganic pyrophosphatases. However, the specific action of inorganic pyrophosphatases coupled to DNA replication in vivo was never demonstrated. Here we show that the Polymerase-Histidinol-Phosphatase (PHP) domain of Escherichia coli DNA Polymerase III α subunit features pyrophosphatase activity. We also show that this activity is inhibited by fluoride, as commonly observed for inorganic pyrophosphatases, and we identified 3 amino acids of the PHP active site. Remarkably, E. coli cells expressing variants of these catalytic residues of α subunit feature aberrant phenotypes, poor viability, and are subject to high mutation frequencies. Our findings indicate that DNA Polymerases can couple DNA elongation and pyrophosphate hydrolysis, providing a mechanism for the control of DNA extension rate, and suggest a promising target for novel antibiotics.

Electrodeposition of PEDOT perchlorate as an alternative route to PEDOT:PSS for the development of bulk heterojunction solar cells

Bulk heterojunction (BHJ) solar cells were fabricated employing different poly(3,4-ethylenedioxythiophene) (PEDOT) buffers: one deposited by electrochemical potentiostatic synthesis (perchlorate as counterion) and the other by casting a commercial polymer (polystyrene sulfonate, PSS, as counterion) on indium tin oxide (ITO) electrodes. The experimental conditions to electrosynthesize the PEDOT film and control its thickness were successfully investigated. [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) was used as electron acceptor in the blend. As electron donor, either the regioregular poly(3-hexylthiophene) (P3HT) or a polythiophene copolymer, functionalized with a porphyrin derivative to improve the absorption of the layer in the visible range, was employed. The morphologies of the PEDOT and the photoactive layers were extensively investigated by atomic force microscopy. The performances of all devices were tested evaluating the power conversion efficiencies which resulted comparable when either PEDOT:ClO4 or PEDOT:PSS was used as buffer layer. That proves electrochemical deposition of PEDOT can represent a good alternative to casting for the production of solar cells, since it is less expensive and permits an excellent control of the layer thickness.

Synthesis and characterization of conjugated polymers for the obtainment of conductive patterns through laser tracing

This article describes the preparation of thin films of conjugated polymers which can enhance their specific electrical conductivity by several orders of magnitude by changing their state from insulating to conducting materials. The examined polymers, i.e., a polyacetylenic and a polythiophenic derivative, are functionalized with thioalkylic side chains and are soluble in common organic solvents from which they lead to thick homogeneous films. The films can be deposited on different substrates, either rigid or flexible, and can be easily exposed to laser radiation to make them conductive. The process is irreversible, and the final conductivity is stable over time, even in the presence of high temperatures (up to 180xa0°C), moisture, and air. The high stability of treated samples, easy polymer synthesis and quick and inexpensive suitably tailored laser tracing procedure make these materials very promising for applications in organic electronics and in the development of new electronic circuitry.

Electrospun Polyaniline-Based Composite Nanofibers: Tuning the Electrical Conductivity by Tailoring the Structure of Thiol-Protected Metal Nanoparticles

Composite nanofibers made of a polyaniline-based polymer blend and different thiol-capped metal nanoparticles were prepared using ex situ synthesis and electrospinning technique. The effects of the nanoparticle composition and chemical structure on the electrical properties of the nanocomposites were investigated. This study confirmed that Brust’s procedure is an effective method for the synthesis of sub-10u2009nm silver, gold, and silver-gold alloy nanoparticles protected with different types of thiols. Electron microscopy results demonstrated that electrospinning is a valuable technique for the production of composite nanofibers with similar morphology and revealed that nanofillers are well-dispersed into the polymer matrix. X-ray diffraction tests proved the lack of a significant influence of the nanoparticle chemical structure on the polyaniline chain arrangement. However, the introduction of conductive nanofillers in the polymer matrix influences the charge transport noticeably improving electrical conductivity. The enhancement of electrical properties is mediated by the nanoparticle capping layer structure. The metal nanoparticle core composition is a key parameter, which exerted a significant influence on the conductivity of the nanocomposites. These results prove that the proposed method can be used to tune the electrical properties of nanocomposites.

Π-Stacking Signature in NMR Solution Spectra of Thiophene-Based Conjugated Polymers

Studies on conjugated polymers seldom report on their NMR characterization in solution. This paper shows how NMR experiments, both 1H NMR and routine 2D NMR spectra, can help in gaining a further insight into the aggregation behavior of conjugated polymers and could be used to flank the more employed solid-state NMR and other spectroscopy and microscopy techniques in the understanding of the aggregation processes. NMR spectroscopy allows distinguishing, within the class of poorly solvatochromic conjugated polymers, those highly prone to form π-stacked aggregates from the ones that have a low tendency toward π-stacking.

Chirality on Amorphous High-Tg Polymeric Nanofilms: Optical Activity Amplification by Thermal Annealing

The chiroptical properties of amorphous chiral polymers functionalized with conjugated trans-azoaromatic chromophore linked to the backbone through a chiral cyclic pyrrolidine moiety of one single configuration at the solid state, as thin films, were investigated. For the first time nanometric thin films of amorphous polymers (not liquid crystals) showed a remarkable chiral amplification upon thermal treatment at a temperature close to their Tg. The side-chain azobenzene chromophores rearrangement driven by the enhanced chain mobility seems to favor the formation of nanodomains of conformationally ordered macromolecular chains with one prevailing helical handedness whose optical activity depends on the configuration of the intrinsic chirality of the monomeric units and which as a result are stable at room temperature for a long time.

Effects of polar additives on the anionic polymerization of 1,3-butadiene and styrene

The homopolymerization of butadiene and copolymerization of styrene with butadiene were performed using n-butyllithium as the initiator, cyclohexane as a solvent and some new ethers (σ-ligands) as active centers modifiers. The modifiers were synthesized using an elegant synthetic route starting from a commercial precursor, and high yields were obtained. Their addition in the homopolymerization of butadiene strongly influences the vinyl content and reduces the polydispersity of the obtained polymer. The modifiers are also able to change the reactivity ratios in the styrene-butadiene copolymerization, leading to an appreciable randomizing effect. The modifiers also show a high activity, since their addition in a very low amount is able to strongly modify the progress in the reaction of anionic polymerization.