Roberto Salcedo

Universidad Nacional Autónoma de México, Ciudad de México, The Federal District, Mexico

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Publications (96)138.37 Total impact

  • Computational and Theoretical Chemistry. 01/2014;
  • Citlalli Rios, Roberto Salcedo
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    ABSTRACT: A number of hexaarylbenzene compounds were studied theoretically, in order to compare energy changes as a result of the toroidal delocalization effect that is characteristic of all these species. The energy was studied taking advantage of locally designed isodesmic reactions. Results indicate that the amount of aromaticity manifested by each substituent is a factor that should be considered when assessing the quantity of energy dissipated from each aromatic center. The influence of different substituents on electronic delocalization is also analyzed, as well as the role played by their frontier molecular orbitals.
    Molecules 01/2014; 19(3):3274-3296. · 2.43 Impact Factor
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    ABSTRACT: We describe herein the first synthesis of a new class of anti-aromatic planar cyclooctatetraenes: the azatrioxa[8]circulenes. This was achieved by treating a suitably functionalised 3,6-dihydroxycarbazole with 1,4-benzoquinones or a 1,4-naphthoquinone. We fully characterised the azatrioxa[8]circulenes by using optical, electrochemical and computational techniques as well as by single-crystal X-ray crystallography. The results of a computational study (NICS) suggest that the central planar cyclooctatetraene is anti-aromatic when the molecules are in neutral or oxidised states (2+), and that the corresponding dianions are aromatic. We discuss the aromatic/anti-aromatic nature of the planar cyclooctatetraenes and compare them with the isoelectronic tetraoxa[8]circulenes.
    Chemistry 03/2013; 19(12):3898-904. · 5.93 Impact Factor
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    ABSTRACT: In this article, the antioxidant activity of fullerene is theoretically studied by applying the density functional theory (DFT) method in terms of its protective effects against the derivatives of estrone that constitute species known to exhibit carcinogenic activity. Several reactions involving fullerene C60 in different possible reactive centres of estradiol and epoxidised estradiol were studied. Surprisingly, the ring that supports the epoxide group is able to react with fullerene by means of a 2+2 cycloaddition, forming a very stable compound. This new compound has the potential to avoid known reactions between the epoxidised molecule and DNA fragments causing the mutagenic process of breast cancer. Therefore, fullerene C60 represents the possibility of a new agent for combating this disease.
    Molecular Simulation 01/2013; 39(8). · 1.06 Impact Factor
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    ABSTRACT: Recently synthesized π-extended symmetrical tetraoxa[8]circulenes that exhibit electroluminescent properties were calculated at the density functional theory (DFT) level using the quantum theory of atoms in molecules (QTAIM) approach to electron density distribution analysis. Nucleus-independent chemical shift (NICS) indices were used to characterize the aromaticity of the studied molecules. The tetraoxa[8]circulene molecules were found to consist of two antiaromatic perimeters (according to the Hückel "4n" antiaromaticity rule) that include 8 and 24 π-electrons. Conversely, NICS calculations demonstrated the existence of a common π-extended system (distributed like a flat ribbon) in the studied tetraoxa[8]circulene molecules. Thus, these symmetrical tetraoxa[8]circulene molecules provide examples of diatropic systems characterized by the presence of induced diatropic ring currents.
    Journal of Molecular Modeling 10/2012; · 1.98 Impact Factor
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    ABSTRACT: The phenomenon of formation of two isomers, yellow and orange, of the cyclometalated Ru(II) complex, [Ru(o-C₆H₄-py)(MeCN)₄]⁺, was investigated by EELS spectroscopy and theoretical calculations. Both forms show very similar structures and spectroscopic properties, but slight differences in X-ray data and absorption between them were noted. No double minimum on the potential energy surface was found and thus these two forms cannot be considered as bond stretching isomers. However, the DFT study revealed the change in the hybridization of the carbon in trans-position of one of acetonitrile ligands. This effect can be responsible for the difference in colour. The results of the theoretical modelling coincide well with the experimental EELS data.
    Molecules 01/2012; 17(1):34-47. · 2.43 Impact Factor
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    Delia Soto, Roberto Salcedo
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    ABSTRACT: The different coordination modes in fullerene organometallic complexes are reviewed. The main modes are η2 and η5, but there are some interesting studies about the other four, all of them are revised in order to show which is the state of art of this kind of compounds with the respect of the hapticity.
    Molecules 01/2012; 17(6):7151-68. · 2.43 Impact Factor
  • Citlalli Rios, Roberto Salcedo
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    ABSTRACT: C(80) is a fullerene species which appears in different isomeric configurations. A general homodesmotic reaction previously designed to study the energy of fullerenes was implemented, in order to analyze the energy of this family of isomers. These results concur with some of the experimental data, but energy differences referring to all the configurations yield novel propositions about their particular behavior. The corresponding lanthanum complexes are also analyzed here and a new isodesmic reaction was designed for this particular case.
    Molecules 01/2012; 17(12):14588-14601. · 2.43 Impact Factor
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    ABSTRACT: Density functional theory calculations and theoretical representations of the density of states (DOS) were undertaken in order to understand the electronic properties of silicon nanocrystals (Si-nc), when partially passivated with Cl and F. Effects relating to cluster size (Si29, Si35, and Si87), type, and percentages of halogen surface passivant, concerning both the cluster gap and electron-donor–acceptor capabilities, were analyzed. These calculations indicate that as the percentage of Cl and F substitution increases, the energy of the LUMO decreases, and consequently, the HOMO–LUMO gap decreases. Correspondingly, we found that the high-electronegativity substituent Cl and F atoms produce the appearance of shoulders in the DOS band edges, thus reducing the band gap. These results explain the photoluminescent experimental data reported for Si-nc. The evaluation of the electrodonating and electroaccepting powers of Si-nc partially passivated with Cl and F indicates that Si-nc have potential applications for bulk heterojunction solar cells and electroluminescent devices.
    The Journal of Physical Chemistry 01/2012; 116:3988-3994.
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    ABSTRACT: This study analyzes the aromatic nature of cyanuric acid (hexahydrotriazine) and some of its derivatives, in terms of aromatic stabilization energy (ASE) and electronic behavior. The simplest molecule (C(3)N(3)O(3)H(3)) is the most aromatic item out of the entire set, but some of the others also display aromatic character. The structure of all the rings is analyzed considering their molecular orbitals as well as studying the inductive effect.
    Journal of Molecular Modeling 06/2011; 17(6):1311-5. · 1.98 Impact Factor
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    ABSTRACT: The theoretical study of the interaction between CH(2) and fullerene (C(60)) suggests the existence of an addition reaction mechanism; this feature is studied by applying an analysis of electronic properties. Several different effects are evident in this interaction as a consequence of the particular electronic transfer which occurs during the procedure. The addition or insertion of the methylene group results in a process, where the inclusion of CH(2) into a fullerene bond produces the formation of several geometric deformations. A simulation of these procedures was carried out, taking advantage of the dynamic semi-classical Born-Oppenheimer approximation. Dynamic aspects were analyzed at different speeds, for the interaction between the CH(2) group and the two bonds: CC (6, 6) and CC (6, 5) respectively on the fullerene (C(60)) rings. All calculations which involved electrons employed DFT as well as exchange and functional correlation. The results indicate a tendency for the CH(2) fragment to attack the CC (6, 5) bond.
    Journal of Molecular Modeling 05/2011; 17(5):1035-40. · 1.98 Impact Factor
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    ABSTRACT: Novel organometallic complexes of fullerene C₈₀ and aryl ligands were simulated. The nature and characteristics of this family of complexes involving π coordination between the fullerene and a metal centre have been studied from a theoretical point of view. We are particularly interested in complexes where η⁶ coordination is present, this being the strangest manifestation of known coordinations, and thus we have studied several known and simulated compounds of this kind in order to understand the lack of examples. The presence of other η⁶ or η⁵ ligands on the opposite side seems to be an important element aiding the stabilization of these complexes, also inducing the conductive and semiconductive behaviour of the studied species.
    Molecules 01/2011; 16(6):4652-9. · 2.43 Impact Factor
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    Roberto Salcedo, Lioudmila Fomina
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    ABSTRACT: Astronomical observations have revealed diffuse interstellar bands ranging from blue in the visible spectrum to the near IR. It has been suggested that these bands exist, owing to the presence of polyaromatic hydrocarbons or fullerene in the vicinity of certain stars, and constitute residual material from stellar explosions. The intention here is to study the relative stability of these species, when exposed to extreme conditions. The aromaticity of polycarbon molecules is an important aspect of this explanation.
    Structural Chemistry 01/2011; · 1.77 Impact Factor
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    ABSTRACT: The electronic structure of small (1 nm) silicon nanocrystals passivated with nitrogen and chlorine is explored using density funcional theory calculations. The HOMO−LUMO gap of 3.2 and 3.3 eV, calculated for the fully nitrogen [Si35(NH2)36] and chlorine passivated (Si35Cl36) nanocrystals, respectively, correlate quite well with experimental observations describing the blue and/or white photoluminescence and electroluminescence of silicon nanocrystals, embedded in chlorinated silicon nitride films. On the other hand, the ionization energy and the electron affinity allow us to study the electron transfer properties of these systems. The charge-transfer capacity of these nanocrystals is modified in opposite directions with respect to hydrogen-passivated nanocrystals, becoming good electron acceptors with Cl passivation and good electron donors with NH2 passivation.
    Journal of Physical Chemistry C - J PHYS CHEM C. 07/2010; 114(29):12427-12431.
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    ABSTRACT: A systematic study was undertaken of the EPR of sodium hydroxide solutions of Benzoin, Anisoin and Thenoin in both ethanol and DMSO as well as their corresponding ionised species of varying colours. In all cases, the EPR consist of symmetric spectra, resulting from the generation of a free radical-anion. Furthermore, theoretical DFT methods were applied in order to study the radical anions, revealing the reason for the colour change in the solutions and in the case of benzoin, found to be related to the interaction between the cis and trans-isomers with the molecules in the two solvents. We have defined the structure of the cis-isomer and for the first time we have described how the adduct between the cis-isomer and the solvent molecule, results in a stable conformer. This corresponds with the EPR results which indicated a significant difference between the cis and trans-isomers. Both the theoretical and experimental results inspired similar descriptions of the significant differences between the cis and trans-isomers in solution.
    Journal of Molecular Structure 01/2010; 963:115-121. · 1.40 Impact Factor
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    ABSTRACT: Theoretical calculations were performed on 2,5-aromatic substituted pyrroles which have a nitro-benzene or a cyano-benzene link to the nitrogen atom of the pyrrole fragment. The molecules manifested interesting semiconductor behavior that was confirmed when thin films were prepared and their corresponding electrical characterization was undertaken. The reason for this behavior is discussed, with reference to the electron-withdrawing feature of the substituents in the benzene chain.
    Materials Chemistry and Physics - MATER CHEM PHYS. 01/2010; 124(1):257-263.
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    ABSTRACT: The study of trimeric mixed-metal complexes is of great importance for their potential use in sensor devices and nanoparticle design, due to the fascinating luminescent and catalytic activity properties. The goal of this work is to understand the Au(I)–Ag(I) closed-shell metallophilic attraction and phosphorescent character in the representative Au–Ag complexes [Au2(carb)2Ag(μ-3,5-Ph2pz)] (1) and [Au(im)CH3(pz)Ag2(μ-3,5-H2pz)2] (2) through ab initio and DFT techniques. The metal–metal intramolecular interactions are ruled by a Au 5d and Ag 4d mixing, while the intermolecular attractions are governed by a Au 6s and Ag 5s mixing, by π-stacking attractions coming from pz groups and dispersion interactions in complex 2. The phosphorescence reported experimentally may be addressed to MLCT transitions, with intrametallic contributions, where a distortion of the lowest-energy excited state geometry of the monomer and dimer are also involved.
    Journal of Molecular Structure THEOCHEM 05/2009; 901(s 1–3):232–242. · 1.37 Impact Factor
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    ABSTRACT: The prediction of the series of complexes [Au(3)Cl(3)M(2)] with M = Li, Na, K, Rb and Cs, has been achieved at the ab initio level of theory. All geometries were fully optimized at the MP2 level of theory; the central Au(3) cluster is capped by chlorine atoms and the alkaline metals lie above and below the plane of the central ring; aurophilic interactions were found on the metal cluster, and also a strong aromatic character coming from the delocalized d-electrons of the Au atoms according to nuclear independent chemical shift calculations. On the other hand, the chemical hardness parameter was used to test the stability of the series of complexes, and the Fukui indexes of electrophilic and nucleophilic attack were employed to explore possible sites where chemical reactivity may play a role.
    Journal of Molecular Modeling 03/2009; 15(10):1165-73. · 1.98 Impact Factor
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    ABSTRACT: The interaction between alcohol molecules and platinum (Pt) was studied using molecular dynamics (MD; Born-Oppenheimer method). Alcohol molecules like ethanol and methanol present a similar molecular structure, with a methyl group (CH(3)) at one end and a fragment of hydroxyl (OH) at the other. This fact generates two orientations that are considered in the interaction with Pt. The MD calculation results for these two orientations indicate a preferential orientation due to energy interactions. A plausible reaction mechanism that takes into account the interaction between Pt and alcohol is presented. The charge transference obtained from the Pt-alcohol interaction was also analyzed. The energy for the two orientations was calculated by indicating the preferential orientation. The methyl and hydroxyl groups are involved in heterolytic breakage of hydrogen bonds, joined to a carbon atom in the former and to an oxygen atom in the latter; however, the methyl group reaction seems to be the most important.
    Journal of Molecular Modeling 01/2009; 15(5):447-51. · 1.98 Impact Factor

Publication Stats

98 Citations
138.37 Total Impact Points

Institutions

  • 1993–2014
    • Universidad Nacional Autónoma de México
      • • Materials Research Institute (IIM-UNAM)
      • • Institute of Materials Research
      Ciudad de México, The Federal District, Mexico
  • 2012
    • Хмельницький національний університет
      Kamelnitskiy, Khmel’nyts’ka Oblast’, Ukraine
  • 2001–2005
    • Instituto Mexicano del Petroleo
      Villa Gustavo A. Madero, The Federal District, Mexico