Ottorino Ori

Topological lattice descriptors of graphene sheets with fullerene-like nanostructures

Polynomial behaviour of the Wiener index for infinite chemical graphs is subject here to a generalisation to structures with topological dimensionality d T>1. This allows a pure topological analysis of relative chemical stability of graphite lattice portions and fullerene fragments (nanocones) built around a pentagonal face. The Wiener index of the graph acts as a lattice topological potential subject to a minimum principle that is able to discriminate topological structures made of hexagons with different connectivity. A new indicator of graph topological efficiency has been applied in the infinite lattice limit to allow a complete ranking of graph chemical stability. A certain grade of reactivity of the pentagonal ring at the centre of nanocones is also predicted. Our considerations are mainly performed in the dual topological space.

Ozone reaction with C60 fullerene. A study on the antiozonant activity of C60 fullerene in dienic rubber

Abstract The reaction between C 60 fullerene and O 3 has been studied in CCl 4 . The ozonization reaction has been followed by UV-VIS spectroscopy and the formation of fullerene oxides C 60 O n ( n = 1,2…5) observed in the early stages of reaction as indicated by the growth of a new band at 485 nm. These oxides are formed after the scission of intermediate ozonides presumably formed. At the end of ozonization, yellowish to brown fluffy gels, insoluble in carbon tetrachloride but soluble in absolute ethanol or acetone, are recovered. They are composed of polymeric ozonides of C 60 . The UV spectrum of these substances in ethanol shows only a broad maximum at 220 nm. The dried substance examined by FT-IR spectroscopy shows extensive oxidation and fullerene cage breakdown. The tarry products are rich in keto, aldehydic and carboxylic groups. The possible antiozonant activity of C 60 fullerene has been estimated in cis-1,4-polyisoprene. The study was conducted by measuring the viscosity change undergone by a standard solution of cis -1,4-polyisoprene in CCl 4 in the presence of C 60 without any protection, or in the presence of a commercial antiozonant ( p -phenylenediamine-based). Contrary to expectations, the results show that cis -1,4-polyisoprene acts as an ozone scavenger and protects C 60 from ozone attack.

A topological study of the structure of the C76 fullerene

Abstract A detailed topological study regarding the C 76 isomers has been done. The main result is the definition of a method for calculating the features, number of lines and relative intensities, of the 13 C NMR theoretical spectrum of a given isomer. We found also a set of molecules with touching pentagons that are able to fit the experimental resonance data and that appear to be of some interest in order to explain the C 76 properties. The current theoretical approach is completely general and fully applicable to other C n fullerenes with no restrictions on the number of carbon atoms n .

Topological Ranking of C28 Fullerenes Reactivity

We derive topological indications about relative stability of C28 molecules. We compute the Wiener index for each molecular structure to determine topologically independent sites predicting a certain grade of reactivity of the fullerenic carbon atoms. Also, the number of 13C NMR resonance peaks and their relative intensities are derived. Our considerations are performed in both topological spaces, the dual and the direct one.

The mathematics and topology of fullerenes

Harry KROTO: Foreword.- 1. Ali Reza ASHRAFI/Mircea DIUDEA/Ante GRAOVAC: Omega Polynomials of Fullerenes and Nanotubes.- 2. Ali Reza ASHRAFI: Wiener Index of Nanotubes, Toroidal Fullerenes and Nanostars.- 3. Mircea DIUDEA/A. E. Vizitiu: C60 Structural Relatives. An Omega-aided Topological Study.- 4. Istvan LASZLO/Reti TAMAS/Ante GRAOVAC: Local Combinatorial Characterization of Fullerenes.- 5. Ali IRANMANESH: Computation of some Topological Indices of C60 and C80 Fullerenes by GAP Program.- 6. Mathieu Dutour SIKIRIC/Michel DEZA: 4-Regular and Self-Dual Analogs of Fullerenes.- 7. Helena DODZIUK: Endohedral fullerene complexes and in- out isomerism in perhydrogenated fullerenes. Why the carbon cages cannot be used as the hydrogen containers?.- 8. Damir VUKICEVIC/Milan RANDIC: Detailed Atlas of Kekule Structures of the Buckminsterfullerene.- 9. Ernesto ESTRADA: A Graph Theoretic Approach to Atomic Displacements in Fullerenes.- 10.E.C. KIRBY/R.B. MALLION/P. POLLAK: Counting Spanning Trees in Toroidal Fullerenes.- 11. O.ORI, F.CATALDO, A.GRAOVAC: Topological Determination of 13C-NMR Spectra of C66 Fullerenes.- 12. Giorgio BENEDEK: The Topological Background of Schwarzite Physics.- 13. Haruo HOSOYA: High pi-Electronic Stability of Soccer Ball Fullerene C60 and Truncated Octahedron C24 among Spherically Polyhedral Networks.- 14. Patrick W. FOWLER/A.GRAOVAC: The Estrada Index and Fullerene Isomerism.

Topological Anisotropy of Stone-Wales Waves in Graphenic Fragments

Stone-Wales operators interchange four adjacent hexagons with two pentagon-heptagon 5|7 pairs that, graphically, may be iteratively propagated in the graphene layer, originating a new interesting structural defect called here Stone-Wales wave. By minimization, the Wiener index topological invariant evidences a marked anisotropy of the Stone-Wales defects that, topologically, are in fact preferably generated and propagated along the diagonal of the graphenic fragments, including carbon nanotubes and graphene nanoribbons. This peculiar edge-effect is shown in this paper having a predominant topological origin, leaving to future experimental investigations the task of verifying the occurrence in nature of wave-like defects similar to the ones proposed here. Graph-theoretical tools used in this paper for the generation and the propagation of the Stone-Wales defects waves are applicable to investigate isomeric modifications of chemical structures with various dimensionality like fullerenes, nanotubes, graphenic layers, schwarzites, zeolites.

Generalized Stone-Wales Transformations

Abstract We introduce a large class of transformations allowing rearrangements of the fullerene surface. We call this set of rearrangements generalized Stone-Wales transformations (gSW) because the well-known Stone-Wales (or pyracylene) flip may be seen as the simplest representative of the novel gSW family. The interconversion between the two C28 fullerene isomers is presented as a simple example of gSW application. Further examples involving the complete generation of C 60 and C 70 isomer spaces are provided. In both cases, just one fullerene molecule is used as seed data. Some considerations on gSW energetics are also reported.

Bondonic Effects in Group-IV Honeycomb Nanoribbons with Stone-Wales Topological Defects

This work advances the modeling of bondonic effects on graphenic and honeycomb structures, with an original two-fold generalization: (i) by employing the fourth order path integral bondonic formalism in considering the high order derivatives of the Wiener topological potential of those 1D systems; and (ii) by modeling a class of honeycomb defective structures starting from graphene, the carbon-based reference case, and then generalizing the treatment to Si (silicene), Ge (germanene), Sn (stannene) by using the fermionic two-degenerate statistical states function in terms of electronegativity. The honeycomb nanostructures present η-sized Stone-Wales topological defects, the isomeric dislocation dipoles originally called by authors Stone-Wales wave or SWw. For these defective nanoribbons the bondonic formalism foresees a specific phase-transition whose critical behavior shows typical bondonic fast critical time and bonding energies. The quantum transition of the ideal-to-defect structural transformations is fully described by computing the caloric capacities for nanostructures triggered by η-sized topological isomerisations. Present model may be easily applied to hetero-combinations of Group-IV elements like C-Si, C-Ge, C-Sn, Si-Ge, Si-Sn, Ge-Sn.

Parabolic Reactivity “Coloring” Molecular Topology: Application to Carcinogenic PAHs

The ability to derive colored representations of widely employed distance-based topological indices from chemical reactivity electronegativity and chemical hardness has been developed in the novel theoretical tool presented in this work to provide novel, mean- ingful topo-reactive or structure-reactivity indices with application to polycyclic aromatic hydrocarbons (PAHs). The model, which com- bines topological and ab initio molecular structural information, relies on the so-called Timisoara-Parma rule for assigning the axial dis- tribution of electronegativity and chemical hardness to a given molecular structure based on a compact finite-difference (CFD) hierarchy, which involves ordering nine forms of electronegativity and chemical hardness derivative-based definitions within conceptual density functional theory (DFT). The results are in good agreement with theoretical and experimental properties improving the predictive power of standard topological indices. The proposed method is suitable for molecular structures with delocalized electrons.

Compression ratio of Wiener index in 2-d rectangular and polygonal lattices

In this paper, we establish leading coefficient of Wiener index for open and closed 2-dimensional rectangular lattices, for various open and closed polygonal lattices, and for open and closed multidimensional cubes. These results enable us to establish compression ratio of Wiener index when number of rows and columns in the lattice tends to infinity.