Franco Cataldo

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.

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.

Far- and mid-infrared spectroscopy of complex organic matter of astrochemical interest: coal, heavy petroleum fractions and asphaltenes

The coexistence of a large variety of molecular species (i.e., aromatic, cycloaliphatic and aliphatic) in several astrophysical environments suggests that unidentified IR emission (UIE) occurs from small solid particles containing a mix of aromatic and aliphatic structures (e.g., coal, petroleum, etc.), renewing the astronomical interest on this type of materials. A series of heavy petroleum fractions namely DAE, RAE, BQ-1, and asphaltenes derived from BQ-1 were used together with anthracite coal and bitumen as model compounds in matching the band pattern of the emission features of proto-planetary nebulae (PPNe). All the model materials were examined in the mid-infrared (2.5-16.7 um) and for the first time in the far-infrared (16.7-200 um), and the IR bands were compared with the UIE from PPNe. The best match of the PPNe band pattern is offered by the BQ-1 heavy aromatic oil fraction and by its asphaltenes fraction. Particularly interesting is the ability of BQ-1 to match the band pattern of the aromatic-aliphatic C-H stretching bands of certain PPNe, a result which is not achieved neither by the coal model nor by the other petroleum fractions considered here. This study shows that a new interesting molecular model of the emission features of PPNe are asphaltene molecules which are composed by an aromatic core containing 3-4 condensed aromatic rings surrounded by cycloaliphatic (naphtenic) and aliphatic alkyl chains. It is instead shown the weakness of the model involving a mixture of PAHs for modeling the aromatic IR emission bands. The laboratory spectra of these complex organic compounds represent a unique data set of high value for the astronomical community; e.g., they may be compared with the Herschel Space Observatory spectra (~51-220 um) of several astrophysical environments such as (proto-) PNe, H II regions, reflection nebulae, star forming galaxies, and young stellar objects.

Infrared spectroscopy of fullerene C60/anthracene adducts

Recent Spitzer Space Telescope observations of several astrophysical environments such as Planetary Nebulae, Reflection Nebulae, and R Coronae Borealis stars show the simultaneous presence of mid-infrared features attributed to neutral fullerene molecules (i.e., C60) and polycyclic aromatic hydrocarbons (PAHs). If C60 fullerenes and PAHs coexist in fullerene-rich space environments, then C60 may easily form adducts with a number of different PAH molecules; at least with catacondensed PAHs. Here we present the laboratory infrared spectra (�2 25 µm) of C60 fullerene and anthracene Dies-Alder mono- and bis-adducts as produced by sonochemical synthesis. We find that C60/anthracene Diels-Alder adducts display spectral features strikingly similar to those from C60 (and C70) fullerenes and other unidentified infrared emission features. Thus, fullerene-adducts - if formed under astrophysical conditions and stable/abundant enough - may contribute to the infrared emission features observed in fullerene-containing circumstellar/interstellar environments.

Determination of the Chemical Structure of Poly-β (-)-pinene by NMR Spectroscopy

This paper is dedicated to the memory of our friend and colleague Annalaura Segre. The chemical structure of a series of β (-)-pinene polymers (PBP) obtained by radiation-induced polymerization, free radical initiation, cationic polymerization over a Friedel-Craft catalyst and by coordinative polymerization over a Ziegler-Natta catalyst has been fully elucidated by 1H and 13C-NMR spectroscopy. 2D NMR techniques have been applied in order to assign all the NMR resonances to the structures of the PBP investigated. The NMR spectra show that the most regular PBP structure is obtained by radiation-induced polymerization followed by the free radical initiated polymerization. The most defective structure has been observed in the case of PBP prepared by cationic mechanism over a Friedel-Crafts catalyst. The discussion accounts for different types of defects and cross-links present in the PBPs investigated whose fundamental structure is based on the p-menthene repeating unit. NMR self-diffusion measurements have been performed to evaluate the molecular weight of all the PBP investigated. The highest molecular weight (2600 Dalton) was found in the case of PBP prepared by Ziegler-Natta catalyst, while the lowest molecular weight was found in the case of PBP prepared by radiation-induced polymerization (about 1000 Dalton).

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.

RAMAN SPECTRA AND THERMAL ANALYSIS ON POLYYNE AND POLYENE-YNE CHAIN SEGMENTS

Chlorinated paraffin and its derivative, dehydrohalogenated paraffin were studied by laser-Raman spectroscopy. It is shown that the dehydrohalogenation reaction leads to almost complete elimination of chlorine from the chain backbone with formation of polyyne segments of 3 to 10 acetylenic units as can be deduced from the triple bond stretching band at 2170 cm−1 for the sample having shorter polyyne segments and 2095 cm−1 for the sample with longer polyyne segments. The presence of polyene segments is underlined by the intense band at 1500 cm−1 in both samples studied. The thermogravimetric analysis of dehydrohalogenated paraffin as well as the differential thermal analysis has been performed in comparison to carbyne and graphite samples used as references.

On the radiopolymerization of carbon disulfide

Abstract Liquid carbon disulfide was irradiated under nitrogen with 1 MGy dose of γ-rays at room temperature. The chemical structure of the resulting radiopolymer was studied by electronic and FT–IR spectroscopy and was found to be that of the CS2-polymer obtained by UV irradiation, ultrasound or high pressure treatment. It consists of a mixture of a linear polymer (CS2)X and a ladder polymer (C3S2)X derived from carbon subsulfide (SCCCS). The mechanism of reaction is discussed and is suggested to be similar to that of photopolymerization, involving the formation of carbon monosulfide CS and sulfur in the early reaction step. The implications of CS2 photopolymerization and radiopolymerization in the cosmochemistry of molecular clouds, planetary atmospheres and comets and meteorites are discussed.

Silver and Copper Polyynides: A Study with HPLC, FT‐IR and XPS Spectroscopy

Abstract The transformation of dicopper acetylide (Cu2C2) into Cu‐polyynides has been studied carefully under different conditions. The conditions necessary and sufficient to produce Cu‐polyynides involve the oxidation and the consequent Glaser coupling reaction of Cu2C2. The acid hydrolysis of unoxidized Cu2C2 does not yield polyynes as it happens for the oxidized derivative. Similarly, the acid hydrolysis of disilver acetylide (Ag2C2) does not produce polyynes. It is shown how to produce Ag‐polyynides whose acid hydrolysis yield a mixture of polyynes. The liquid chromatographic analysis (HPLC) of the polyynes released both from Cu‐polyynides and from Ag‐polyynides are always dominated by the presence of C8H2 as the main product (>70% by mol) followed by C10H2 in terms of abundance. The chemical structure of Cu‐polyynides and Ag‐polyynides has been investigated by FT‐IR and XPS spectroscopy. The spectra suggest a rather complex polymeric structure for Cu‐polyynides, which appear depleted in Cu content with respect to the theoretical at the XPS spectra with a C/Cu ratio of 5.7, although not far from the expected value of 4. On the other hand, for Ag‐polyynides the spectral analysis suggests a more regular structure and indeed the XPS spectra suggest a C/Ag ratio of 4.5 in excellent agreement with the expected value of 4 deduced from the HPLC analysis of the hydrolysis products.