Local and global aromaticity in a molecular carbon nanobelt: insights from magnetic response properties in neutral and charged species.

The formation of carbon nanobelt made exclusively from fused benzene rings has recently been achieved. Our results reveal an interesting shift from a local aromatic character constrained in each of the six aromatic Clar sextets (6π-electron circuit) to a global aromatic character in charged species (+2 and -2) involving the overall π-circuit from the molecular nanobelt. This demonstrates the suppression of the local aromatic character in favor of a global aromaticity by selecting the oxidation state of the carbon nanobelt, giving rise to a shielding cone extended within the structure.

Aromatic and antiaromatic spherical structures: use of long-range magnetic behavior as an aromatic indicator for bare icosahedral [Al@Al12]- and [Si12]2- clusters.

The long-range characteristics of the induced magnetic field in the bare icosahedral [Al@Al12]- and [Si12]2- clusters reveal inherent characteristics for spherical aromatic and antiaromatic systems. Here, we extend the shielding cone property to these highly symmetrical inorganic examples to achieve a suitable indicator for aromaticity as a reliable method for evaluating the aromaticity of clusters containing interstitial atoms.

Magnetic Response of Aromatic Rings Under Rotation: Aromatic Shielding Cone of Benzene Upon Different Orientations of the Magnetic Field.

The induced shielding cone is one of the most characteristic aspects of aromatic species. Herein, we explore its behavior under different orientations of the applied magnetic field by evaluating the overall and dissected π- and σ-electron contributions. Our results shed light onto the orientation dependence behavior of the shielding cone, unraveling a characteristic pattern upon rotation of the aromatic ring. This pattern decreases the long range of the magnetic response, such that it resembles the behavior under constant molecular tumbling in solution.

Magnetic response properties of gaudiene - a cavernous and aromatic carbocage.

A spherical and cavernous carbocage molecule exhibiting faces with larger ring sizes than regular fullerenes is a suitable species for investigating how molecular magnetic properties depend on the structure of the molecular framework. The studied all-carbon gaudiene (C72) is a highly symmetrical molecule with three- and four-fold faces formed by twelve membered rings. Here, we attempt to unravel the magnetic response properties of C72 by performing magnetic shielding and current density calculations with the external magnetic field applied in different directions. The obtained results indicate that the induced current density flows mainly along the chemical bonds that are largely perpendicular to the magnetic field direction. However, the overall current strength for different directions of the magnetic field is nearly isotropic differing by only 10% indicating that C72 can to some extent be considered to be a spherical aromatic molecule, whose current density and magnetic shielding are ideally completely isotropic. The induced magnetic field is found to exhibit long-range shielding cones in the field direction with a small deshielding region located perpendicularly to the field outside the molecule. The magnetic shielding is isotropic inside the molecular framework of C72, whereas an orientation-dependent magnetic response appears mainly at the exterior of the molecular cage.

The impact of endohedral atoms on the electronic and optical properties of Au25(SR)18 and Au38(SR)24.

An understanding of the rational modification of the optical properties of gold nanoparticles allows us to explore their versatility as molecular-sized materials. We show from theoretical relativistic calculations that such properties can be tuned efficiently by varying the architecture of the central core from endohedral to hollow structures in thiolate-protected clusters derived from two prototypical gold clusters, namely, Au25(SR)18 and Au38(SR)24. Our results estimate the feasible variation of the absorption spectrum driven by the modification of frontier levels due to the removal of the endohedral atom, leading to smaller gaps between occupied and low-lying unoccupied levels. This reveals a characteristic consequence for hollow counterparts given by a red-shift in energy of the optical properties. Hence, the formation of hollow derivatives can be a useful strategy for the fine-tuning of such properties. Future work will extend this observation to larger clusters, and allow gleaning knowledge of the electronic and optical properties in the case of higher order multilayer core nanoparticles.

Alternation of aromatic-nonaromatic rings in belt-like structures. The behavior of [6.8](3)cyclacene in magnetic fields.

[6.8]3Cyclacene is an interesting belt-like structure displaying aromatic-non-aromatic alternation, which is useful to gain an understanding of the intramolecular and intermolecular interactions between the anisotropic cones in the magnetic behavior of such rings. From the analysis of certain components in an induced magnetic field and (13)C-NMR shielding under its own principal axis system (PAS), the individual and overall magnetic behavior of each respective aromatic and non-aromatic fragments can be clearly described. Interestingly, the magnetic response of [6.8]3cyclacene suggests a characteristic behavior given by its confinement into a belt-like structure.

Axis-dependent magnetic behavior of C60 and C60(10+). consequences of spherical aromatic character.

The magnetic response of C60 has been studied and compared to its spherical aromatic counterpart C60(10+), focusing on the overall and local shielding tensors. A high axis dependence behavior at the outside region of the structure is characterized, unravelling a characteristic pattern of the local chemical shift anisotropy as a consequence of the spherical aromatic behavior.

Assessing cellular DNA damage from a helium plasma needle.

The aim of the present study is to determine the deoxyribonucleic acid (DNA) damage by cells exposed to atmospheric pressure non-thermal plasma (APNTP). Mouse leukocytes embedded in agarose were exposed to the plasma at two different distances from a helium plasma needle outlet and during three different exposure periods. Damage was assessed by the single cell gel electrophoresis assay. The results indicate that, at 0.1 cm from the plasma needle, the exposure caused complete DNA fragmentation determined by the presence of so called "clouds". Samples exposed at 0.5 cm from the slide sample surface presented damage proportional to the exposure periods in terms of tail intensity, tail moment and "clouds" frequency. Studies performed with alkaline single cell gel electrophoresis assay to determine DNA breaks and alkali-labile sites, indicates that DNA damage produced by exposure to APNTP was caused mainly by oxidative radicals, rather than by UV light which causes cyclobutane pyrimidine dimers. These results allow us to conclude that plasma needle induced DNA breaks in mice leukocytes proportionally to exposure time.

Inactivation of Escherichia coli in water by pulsed dielectric barrier discharge in coaxial reactor.

An experimental study of ATCC (American Type Culture Collection) 8739 Escherichia coli bacteria inactivation in water by means of pulsed dielectric barrier discharge (PDBD) atmospheric pressure plasmas is presented. Plasma is generated by an adjustable power source capable of supplying high voltage 25 kV pulses, ∼30 µs long and at a 500 Hz frequency. The process was conducted in a ∼152 cm(3) cylindrical stainless steel coaxial reactor, endowed with a straight central electrode and a gas inlet. The bacterial concentration in water was varied from 10(3) up to 10(8) E. coli cells per millilitre. The inactivation was achieved without gas flow in the order of 82% at 10(8) colony-forming units per millilitre (CFU mL(-1)) concentrations in 600 s. In addition, oxygen was added to the gas supply in order to increase the ozone content in the process, raising the inactivation percentage to the order of 90% in the same treatment time. In order to reach a higher efficiency however, oxygen injection modulation is applied, leading to inactivation percentages above 99.99%. These results are similarly valid for lower bacterial concentrations.

Spin-orbit effects on electronic delocalization. Aromaticity in a discrete square tetrapalladium sandwich complex.

In this article, we report the relativistic electronic structure, including spin-orbit interaction, employing all-electron density functional theory calculations on the multimetallic sandwich compound [(CNT)Pd(4)(COT)](1+) (1), which can be considered as a [Pd(4)](2+) fragment flanked by two ring-ligands, namely, cyclononatetraenyl (CNT(1-)) and cyclooctatetraene (COT), as well as the dimer of 1, hereafter 2. The calculations suggest that the Pd(4)-ligand interaction is mainly electrostatic, being the main responsible term for the stabilization of the almost fully occupied 4d shell [Pd(4)](2+) fragment. The ring currents and electronic delocalization estimated via the nuclear independent chemical shifts indices and electron localization function, allow us to describe a significant sigma-aromaticity at the center of the Pd(4) square in 1, which in conjunction with the aromaticity arising from the ligands induce considerable aromatic character inside of the multimetallic metallocene.

Electronic delocalization, energetics, and optical properties of tripalladium ditropylium halides, [Pd(3)(C(7)H(7))(2)X(3)](1-) (X = Cl(-), Br(-), and I(-)).

Here we report relativistic electronic structure calculations employing all-electron density functional theory (DFT) including scalar and spin-orbit interaction, on the multimetallic sandwich compound [Pd(3)(C(7)H(7))(2)X(3)](1-) (X = Cl(-) (1), Br(-) (2), and I(-) (3)), which can be considered as a [Pd(3)X(3)](3-) fragment flanked by two ring-ligands [(C(7)H(7))(2)](2+). The calculations suggest that the [Pd(3)X(3)](3-)-ligand interaction is mainly arising from electrostatic contributions, where the formally zerovalent Pd atoms allows backdonation of charge from the halide X(1-) atoms to the [(C(7)H(7))(2)](2+) ligands, resulting in a net charge of about +0.4 for each Pd atoms that decreases from 1 to 3. The electronic delocalization estimated via the NICS indexes and the ELF function allows us to describe a significant stabilizing sigma-aromaticity at the center of the Pd(3) triangle, which decreases from [Pd(3)Cl(3)](3-) to [Pd(3)I(3)](3-) (1 to 3) due to the softer character of the iodine counterpart, that donates extra charge to the ligands. The calculated electronic transitions via TD-DFT are in reasonable agreement with the experimental data obtained in CH(2)Cl(2) solution, indicating that the most intense transition involves a core-centered [Pd(3)X(3)](3) transition toward the [(C(7)H(7))(2)](2+) ligands, with mainly X(1-) character in the former molecular spinor that is responsible for the variation of the observed lambda(max) according to the variation of X(1-).