Nanoremediation of As and metals polluted soils by means of graphene oxide nanoparticles.

The capacity of graphene oxide nanoparticles (nGOx) to reduce or increase As and metals availability in polluted soils was compared with that of zero valent iron nanoparticles (nZVI). The nanomaterials used in this study were characterized by X-ray techniques, CHNS-O analysis, dynamic light scattering, and microscopy procedures such as atomic force microscopy. To assess the capacity of these materials to immobilize pollutants, field samples of two soils were treated with nZVI and nGOx at a range of doses (0.2%, 1% and 5%). Availability tests were then performed. nGOx effectively immobilized Cu, Pb and Cd, but mobilized As and P (even at low doses), in the latter case irrespective of the simultaneous presence of high concentrations of metals. In turn, nZVI promoted notable immobilization results for As and Pb, a poorer result for Cd, and an increased availability for Cu. Soil pH and EC have been slightly affected by nGOx. On the whole, nGOx emerges as a promising option for mobilization/immobilization strategies for soil nanoremediation when combined with other techniques such as phytoremediation.

Oligomers of cyclopentadithiophene-vinylene in aromatic and quinoidal versions and redox species with intermediate forms.

A new series of π-conjugated oligomers based on the 4,4 dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene vinylene repeating unit has been prepared and characterized by X-ray, electrochemical, spectroscopic (UV-Vis absorption, emission and Raman) and density functional theory methods. The oligomers in their neutral, oxidized and reduced forms have been investigated. The neutral compounds show a longer mean conjugation length than oligothiophenes and oligothiophene-vinylenes and display very rich redox chemistry with the stabilization of polycationic states of which the radical cations and dications are strong NIR absorbers, the latter displaying singlet diradicaloid character. An interesting complementarity between the sequence of aromatic-quinoidal structural segments in the radical cations and dications has been described and interpreted. Two derivatives with the 4,4 dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene vinylene unit, disubstituted either with electron donor, bis(triaryl amino) groups, or acceptors bis(dicyano-methylene) caps enforcing a quinoidal structure in the dithiophene-vinylene bridge, have been also synthesized and characterized. The radical cation of the triarylamine compound and the radical anion of the tetracyano compound similarly display hole and electron charge localization, or confinement, in the nitrogen and dicyano surrounding parts, or class II mixed valence systems, while their dication and dianion species, conversely, are open-shell diradical (i.e., polaron pair) and closed-shell (i.e., bipolaron), respectively. The preparation of these new π-conjugated oligomers gives way to the realization of compounds with new electronic properties and unique structures potentially exploitable in organic electronics.

Regioselective preparation of a bis-pyrazolinofullerene by a macrocyclization reaction.

A single isomer of a pyrazolinofullerene bis-adduct was prepared by tether-directed remote functionalization. Specifically, a macrocyclization reaction between C60 and a bis-hydrazone reagent has been carried out to generate a regioisomerically pure fullerene bis-adduct which presents a lower LUMO than pristine C60.

Metal-mediated aggregation of DNA comprising 2,2'-bipyridine nucleoside, an asymmetrically substituted chiral bidentate ligand.

The incorporation of an artificial 5-methyl-2,2'-bipyridine nucleoside at the 5' terminus of an otherwise self-complementary oligonucleotide sequence opens up the opportunity of metal-mediated aggregation of DNA double helices triggered by the addition of the respective metal ions. Interestingly, two-dimensional aggregates (DNA monolayers) are formed in the presence of nickel(ii), whereas copper(ii) leads to the formation of three-dimensional disc-shaped structures. With iron(ii), a coexistence of both types of aggregates had been observed previously. Models are proposed in which these observations are explained based on geometrical considerations. The artificial nucleoside itself represents a rare example for a C(1)-symmetric chiral derivative of 2,2'-bipyridine, enabling the formation of four isomeric octahedral complexes.

Single layers of a multifunctional laminar Cu(I,II) coordination polymer.

A multifunctional bidimensional mixed-valence copper coordination polymer [Cu2Br(IN)2]n (IN = isonicotinato) has been characterized in crystal phase and isolated on graphite surface as single sheets.

Highly conductive self-assembled nanoribbons of coordination polymers.

Organic molecules can self-assemble into well-ordered structures, but the conductance of these structures is limited, which is a disadvantage for applications in molecular electronics. Conductivity can be improved by using coordination polymers-in which metal centres are incorporated into a molecular backbone-and such structures have been used as molecular wires by self-assembling them into ordered films on metal surfaces. Here, we report electrically conductive nanoribbons of the coordination polymer [Pt(2)I(S(2)CCH(3))(4)](n) self-assembled on an insulating substrate by direct sublimation of polymer crystals. Conductance atomic force microscopy is used to probe the electrical characteristics of a few polymer chains ( approximately 10) within the nanoribbons. The observed currents exceed those previously sustained in organic and metal-organic molecules assembled on surfaces by several orders of magnitude and over much longer distances. These results, and the results of theoretical calculations based on density functional theory, confirm coordination polymers as candidate materials for applications in molecular electronics.

Synthesis of designed conductive one-dimensional coordination polymers of Ni(II) with 6-mercaptopurine and 6-thioguanine.

Calculations performed with the goal of designing suitable electrical conductive [M(6-MP)(2)](n) (M = transition metal, 6-MP = 6-mercaptopurinato) one-dimensional coordination polymers suggested that metal ions such as Ni(II) could provide suitable materials. In this work, direct hydrothermal reactions between 6-mercaptopurine (6-MPH) and the analogous 6-thioguanine (6-ThioGH) with NiSO(4).6H(2)O yield the compounds [Ni(6-MP)(2)](n).2nH(2)O [1] and [Ni(6-ThioG)(2)](n).2nH(2)O [2]. The X-ray structures confirm that both compounds present similar structures based on one-dimensional chains in which the deprotonated nucleobases act as the bridging ligands connecting the metal ions by short distances. Electrical measurements at room temperature confirm the conductor character of both coordination polymers. The small differences found in these measurements have been rationalized with the help of density functional theory calculations. Preliminary adsorption studies on surfaces for 1 have allowed characterization of single chains on mica and graphite. The results obtained suggest the potential use of coordination polymers on nanomaterials for molecular electronics.

Dependence of the single walled carbon nanotube length with growth temperature and catalyst density by chemical vapor deposition.

We report the growth of isolated single walled carbon nanotubes (SWCNTs) on a silicon surface by chemical vapor deposition, in the temperature range from 800 to 950 degrees C using two different iron catalyst precursors, Fe(NO3)3 x 9H2O and Fe(CO)5. The results show that while for the first catalyst precursor temperature is the key factor in determining nanotube length, for the second it is the density of catalyst precursor on the surface. Solutions of Fe(CO)5 adsorbed on silicon oxide result in a suitable catalyst precursor to obtain SWCNTs of controllable diameter and with clean surfaces.

Direct evidence of nanowires formation from a Cu(I) coordination polymer.

In this work we present both spectroscopic and morphological evidence showing one-dimensional organization of [CuBr(HIN)]n (HIN=isonicotinic acid) on surfaces.

Covalent deposition of ferritin nanoparticles onto gold surfaces.

Ferritin nanoparticles have been deposited immobilized onto a properly modified gold surface by specific covalent bonding through lysine rests at the ferritin external surface. Atomic force microscopy (AFM) images confirmed the existence of a single ferritin monolayer. This is an easy and flexible route to form stable ferritin networks, which are covalently fixed to a gold substrate.

Time-dependence structures of coordination network wires in solution.

We present a mechanochemistry-based procedure to isolate individual chains on surfaces of a ruthenium MMX polymer. After sonication of solutions containing the two building blocks of the mentioned MMX polymer, time-depending structures are formed in the solution. The architecture of the different structures obtained in this process, as a function of the time, is monitored using atomic force microscopy. The resulting structures exhibit uniform subnanometer diameters over microns length, in agreement with the expected diameter for an individual polymer chain. From the atomic force microscope images, we infer a long persistence length for the linear structures. Finally, the effect of the temperature solution in the formation of the different structures is also addressed.