Millennium Nucleus
Molecular Engineering for Catalysis and Biosensors

What we learned...


Synthesis of CdTe QDs/single-walled aluminosilicate nanotubes hybrid compound and their antimicrobial activity on bacteria
Daniela A. Geraldo, Nicolás Arancibia-Miranda, Nicolás A. Villagra, Guido C. Mora, Ramiro Arratia-Perez
J. Nanopart. Res. 2012, 14:1286 [0.000, 0]
DOI:   10.1007/s11051-012-1286-6
The use of molecular conjugates of quantum dots (nanocrystalline fluorophores) for biological purposes have received much attention due to their improved biological activity. However, relatively, little is known about the synthesis and application of aluminosilicate nanotubes decorated with quantum dots (QDs) for imaging and treatment of pathogenic bacteria. This paper describes for a first time, the use of single-walled aluminosilicate nanotubes (SWNT) (imogolite) as a one-dimensional template for the in situ growth of mercaptopropionic acid-capped CdTe QDs. This new nanohybrid hydrogel was synthesized by a simple reaction pathway and their enhanced optical properties were monitored by fluorescence and UV–Vis spectroscopy, confirming that the use of these nanotubes favors the confinement effects of net CdTe QDs. In addition, studies of FT-IR spectroscopy and transmission electron microscopy confirmed the non-covalent functionalization of SWNT. Finally, the antimicrobial activity of SWNT coated with CdTe QDs toward three opportunistic multi-resistant pathogens such as Salmonella typhimurium, Acinetobacter baumannii, and Pseudomonas aeruginosa were tested. Growth inhibition tests were conducted by exposing growing bacteria to CdTe QDs/SWNT hybrid compound showing that the new nano-structured composite is a potential antimicrobial agent for heavy metal-resistant bacteria.

Bonding, energetic, electronic delocalization and optical properties of MCp3 complexes, where M = Sc, Y, La, Ac, Lu, Ce, Yb and Th
Franklin Ferraro and Ramiro Arratia-Perez
Chem. Phys. Lett. 2012, 554, 219-224 [0.000, 0]
DOI:   10.1016/j.cplett.2012.10.020
In this work we evaluated the bonding nature and electronic properties of a series of metal-cyclopentadienyl MCp3 complexes. The Morokuma–Ziegler analysis show a covalent character increase of the metal–ligand bond in the following order: transition-metals > actinide > lanthanide containing molecules. NBO and frequency analysis shows a similar behavior. TD-DFT calculation shows a red shift for the aa transition, which is common to all the complexes. The NICSzz values and ELF analysis show a ring electron delocalization change due to a combined effect between the more external metal orbitals ‘nd’ and the interaction with the hydrogens of the neighboring ring.

Theoretical study on electronic spectra and interaction in [Au3]-L-[Au3] (L = C6F6,Ag+) complexes
Fernando Mendizabal and Richard Salazar
J. Mol. Model. 2012 [0.000, 0]
DOI:   10.1007/s00894-012-1570-5
The electronic structure and spectroscopic properties of [Au3(μ-C(OEt) = NC6H4CH3)3]n-(C6F6)m and [Au3(μ-C2,N3-bzim)3]n-(Ag+)m were studied at the B3LYP, PBE and TPSS levels. The interaction between the [Au3] cluster and L (C6F6, Ag+) was analyzed. Grimme’s dispersion correction is used for those functionals. Weak π-interactions (Au-C6F6) were found to be the main contribution short-range stability in the models; while in the models with Ag+, an ionic interaction is obtained. The absorption spectra of these models at the PBE level agree with the experimental spectra.

Quantum Dynamical Simulations as a Tool for Predicting Photoinjection Mechanisms in Dye-Sensitized TiO2 Solar Cells
M. Belén Oviedo, Ximena Zarate, Christian F. A. Negre, Eduardo Schott, Ramiro Arratia-Pérez, and Cristián G. Sánchez
J. Phys. Chem. Lett. 2012, 3, 2548?2555 [0.000, 0]
DOI:   10.1021/jz300880d
On the basis of a time-dependent self-consistent density functional tight-binding (TD-DFTB) approach, we present a novel method able to capture the differences between direct and indirect photoinjection mechanisms in a fully atomistic picture. A model anatase TiO2 nanoparticle (NP) functionalized with different dyes has been chosen as the object of study. We show that a linear dependence of the rate of electron injection with respect to the square of the applied field intensity can be viewed as a signature of a direct electron injection mechanism. In addition, we show that the nature of the photoabsorption process can be understood in terms of orbital population dynamics occurring during photoabsorption. Dyes involved in both direct (type-I) and indirect (type-II) mechanisms were studied to test the predictive power of this method.

Survey Of Long d10–d10 Metallophilic Contacts in Four-Membered Rings of Ag(I) and Au(I) Supported by Carbene–Pyrazole Mixed Ligands
Raul Guajardo Maturana, Miguel Ponce Vargas, and Alvaro Muñoz-Castro
J. Phys. Chem. A 2012, 116, 8737-8743 [0.000, 0]
DOI:   10.1021/jp304928k
The interesting case of long intramolecular d10–d10 contacts has been studied through [Ag4L2]2+ and [Au4L2]2+ (L = 3,5-bis((N-methylimidazolyl)methyl)pyrazole) systems, showing interesting features gained by analysis of the electronic structure and the overall shielding tensor in the molecular domain, in terms of its components. The long intramolecular closed-shell separations are attributed to the population of the bonding, nonbonding, and antibonding combinations of the ns atomic shells in the [M4]4+ core, contrasting with that observed in systems with shorter d10–d10 distances. This point allows to concludeb that separations shorter then the sum of the van der Waals radii (3.4 Å for Ag–Ag, and 3.2 Å for Au–Au) of the nucleus involved requires a net bonding population between ns and np atomic shells of the d10 closed-shell centers. Moreover, [Au4L2]2+ exhibits an increased covalency observed for the enhanced charge-donation due to the stabilization of the ns and destabilization of the (n – 1)d driven by the relativistic effects. The magnetic response denotes a slight interaction between the closed-shell centers at distances in the range of their sum of van der Waals radii because the observed remote effect (or anisotropic effect) caused by each d10 nucleus does not influence considerably the neighbor center. The analysis of ? in terms of its components allows to conclude that the [Au4L2]2+ system exhibits an increased magnetic response due to the increase in the number of the inner-electrons in comparison to [Ag4L2]2+.

A TD-DFT basis set and density functional assessment for the calculation of electronic excitation energies of fluorene
Cristina Aparecida Barboza, Pedro Antonio Muniz Vazquez, Desmond Mac-Leod Carey, and Ramiro Arratia-Perez
International Journal of Quantum Chemistry 2012, 112, 3434–3438 [0.000, 0]
DOI:   10.1002/qua.24300
Conjugated organic materials are the subject of intensive research for a range of optoelectronic applications. A model for such molecules is fluorene, which consists of rigid planar biphenyl units of C2v symmetry. A low energy experimental absorption spectrum in the gas phase is composed of A1 and B2 transitions. The aim of this work is to evaluate the performance of the basis sets cc-pVXZ (X = D and T), aug-cc-pVDZ, 6-31G**, 6-31++G**, 6-311G**, 6-311++G**, Sadlej-pVTZ, Z2Pol, Z3Pol, and pSBKJC and of the functionals B3LYP, B3LYP/CS00, CAM-B3LYP, PBE0, and LB94 in predicting the electronic transitions obtained taking linear response-coupled cluster singles and doubles (LR-CCSD) results as the theoretical reference. Our findings suggest that the time-dependent density functional theory singles method is not able to correctly assign the predicted spectrum while LR-CCSD always correctly describes the experimental data. Among the studied density functionals, the best performance was achieved by the CAMB3LYP. For transitions above 5 eV, diffuse functions are required to properly predict the observed transitions.

Ceria(100) Nanotubes with Negative Strain Energy: A First-Principles Prediction
José J. Plata, Igor Ruiz-Tagle, Antonio M. Márquez, and Javier Fdez. Sanz
J. Phys. Chem. Lett. 2012, 3, 2092-2096 [0.000, 0]
DOI:   10.1021/jz300731n
Over the past decade, one-dimensional (1D) ceria nanotubes (NTs) have been synthesized and reported as promising candidates for catalysis. Here, for first time, we address the structural and electronic properties of a family of ceria single-walled NTs by means of state-of-the-art periodic density functional theory (DFT) calculations using a hybrid functional. Strain energies were found to be negative in almost the whole diameter range for the (0,N) series, indicating the stability of these NTs relative to the ceria flat layer. Both O2p-Ce4f and O2p-Ce5d band gaps are found to widen with respect to the bulk values. Gold atoms have been deposited on both the outer and inner surfaces of a prototypical NT, the interaction energy being of -1.4 eV. These surfaces appear to be easily reducible with the formation of cationic Au+ species, which make them especially attractive for catalytic purposes.

Magnetic Response Properties of Coinage Metal Macrocyles. Insights into the Induced Magnetic Field through the Analysis of [Cu5(Mes)5], [Ag4(Mes)4], and [Au5(Mes)5] (Mes = 2,4,6-Me3C6H2)
Alvaro Muñoz-Castro
J. Phys. Chem. C, 2012, 116 (32), 17197–17203 [0.000, 0]
DOI:   10.1021/jp3012443
The complexity of the magnetic response of coinage metal macrocycles supporting closed-shell d10–d10 interaction has been studied through the analysis of [Cu5(Mes)5], [Ag4(Mes)4], and [Au5(Mes)5] (Mes = 2,4,6-Me3C6H2) by means of relativistic DFT methods. Our effort relies on the description of the overall shielding tensor (?) surrounding the molecular space in terms of its components (?ij, i, j = x, y, z) by using chemical shift tensor maps to unravel the magnetic complexity of such molecular arrays. Additionally, the diamagnetic, paramagnetic, and spin–orbit contributions to the through the space chemical shift tensor are depicted for the first time in order to gain more insight into the variation of the magnetic response according to the atomic number (Z) of the metallic core involved. Our results show a strong axis-dependent (orientation-dependent) behavior of the coinage macrocycles indicating that the magneto-responsive properties increase according to Z with the core electrons mainly contributing to diamagnetic term of the shielding tensor.

[Ge9{Si(SiMe3)3}3{SnPh3}]: A Tetrasubstituted and Neutral Deltahedral Nine-Atom Cluster
Feng Li, Alvaro Muñoz-Castro, and Slavi C. Sevov
Angew. Chem. Int. Ed. 2012, 51, 8581 –8584 [0.000, 0]
DOI:   10.1002/anie.201202906
Reaching neutral territory: The title compound, the first tetrasubstituted deltahedral Zintl cluster, is no longer an ion (see picture; Ge green, Si purple, Sn blue). It is a neutral molecule formed by a reaction of the trisilylated anion with Ph3SnCl

The aromaticity of the [Re3(μ-X)3X9]3− clusters, X = Cl, Br, I
Leonor Alvarado-Soto, Eduardo Schott, Ximena Zarate, Ramiro Arratia-Pérez, Rodrigo Ramirez-Tagle
Chemical Physics Letters 2012, 545, 50–53 [0.000, 0]
DOI:   10.1016/j.cplett.2012.07.033
The results of this Letter reveals that the [Re3(μ-Cl)3Cl9]3−, [Re3(μ-Br)3Br9]3−, [Re3(μ-I)3I9]3− clusters exhibit aromaticity and that spin–orbit effect decreases the aromaticity due to the fact that the 5d3/2 spinors are more contracted than the scalar 5d orbitals. The [Re3(μ-I)3I9]3− and [Re3(μ-Br)3Br9]3− clusters are the most aromatic clusters. This can be explained by the np1/2 and np3/2 spinors radial expectation (<r>) values which follows the Cl < Br < I sequence. Thus, the most extended spinors correspond to I and Br ligands, as indicated in the ELF plots. Furthermore we carried out TDDFT calculations which agrees with the fact that [Re3(μ-I)3I9]3− should show the highest value of aromaticity.

A. Carreño, S. Ladeira, A. Castel, A. Vega and I. Chavez
Acta Cryst. 2012, E68, o2507-o2508 [0.000, 0]
DOI:   10.1107/S1600536812032060
In the title compound, C20H27N3O, the hydroxy group forms an intramolecular O-H…N hydrogen bond with the imino N atom. The dihedral angle between the aromatic rings is 33.09 (9)°. In the crystal, molecules form centrosymmetric dimers via pairs of N-H…N hydrogen bonds involving aminopyridine fragments.

Methylation and the system-size effect over the structural, electronic, magnetic (NICS) and reactive properties of pentalene derivatives
Cristina A. Barboza, Ezequiel Barboza, Ramiro Arratia-Perez, Desmond MacLeod Carey
Chemical Physics Letters 2012, 545, 88-94 [0.000, 0]
DOI:   10.1016/j.cplett.2012.07.031
The effects of increasing size and tetra-methylation over dimerization, electronic and magnetic properties of the pentalene, s-indacene, dicyclopenta-[b,g]-naphthalene and dicyclopenta-[b,i]-anthracene series, were studied. Potential energy surfaces were evaluated using the hybrid-density functionals BHandH and LC-wPBE. Our results suggest a linear scaling of the dimers stabilization and interaction energies. NICS values indicate that, there are no effects over the five member rings antiaromaticity, however the central rings are slightly aromatic for the largest molecules. The presence of methyl groups has a small effect over the reactivity of the molecules, while the increasing of system-size increases the reactivity of the five membered-rings.

Enhancement of the Catalytic Activity of Fe Phthalocyanine for the Reduction of O2 Anchored to Au(111) via Conjugated Self-Assembled Monolayers of Aromatic Thiols As Compared to Cu Phthalocyanine
Ingrid Ponce, J. Francisco Silva, Ruben Oñate, Marcos Caroli Rezende, Maritza A. Paez, José H. Zagal, Jorge Pavez, Fernando Mendizabal and Sebastián Miranda-Rojas, Alvaro Muñoz-Castro and Ramiro Arratia-Pérez
J. Phys. Chem. C, 2012, 116 (29), 15329–15341 [0.000, 0]
DOI:   10.1021/jp301093q
We have prepared self-assembled monolayers (SAMs) of 4-aminothiophenol (4-ATP) and 1-(4-mercaptophenyl)-2,6-diphenyl-4-(4-pyridyl)pyridinium tetrafluoroborate (MDPP) functionalized with iron phthalocyanine (FePc) and copper phthalocyanine (CuPc) adsorbed on gold (111) electrodes. The catalytic activity of these SAMs/MPc was examined for the reduction of O2 in aqueous solutions and compared to that of bare gold and with gold coated directly with preadsorbed MPc molecules. Scanning tunneling microscopy (STM) studies confirm the functionalization of the 4-ATP by MPc. STM images reveal that iron phthalocyanine molecules are chemically anchored to 4-aminothiophenol organic monolayers, probably having an “umbrella” type orientation with regards to the surface. The electrocatalytic studies carried out with Au/4-ATP/FePc and Au/MDPP/FePc electrodes show that the O2 reduction takes place by the transfer of 4-electron to give water in contrast to a 2-electron transfer process observed for the bare gold. The modified electrode obtained by simple adsorption of FePc directly to the Au(111) surface still promotes the 4-electron reduction process, but it shows a lower activity than the electrodes involving SAMs with FePc molecules positioned at the outmost portion of the self-assembled monolayers. The activity of the electrodes increases as follow: Au < Au/FePc < Au/4-ATP/FePc < Au/MDPP/FePc with the highest activity when FePc molecules are more separated from the Au surface. In contrast, the less active CuPc shows almost the same activity in all three configurations. Theoretical calculations suggest the importance of the back-bonding into the adduct formation, showing the relevance of the supporting gold surface on the electron-transfer process mediated by anchoring ligands.

Substituents Effects on Two Related Families of Dyes for Dye Sensitized Solar Cells: [Ru(4,4´-R,R-2,2´-bpy)3]2+ and [Ru(4,4´-COOH-2,2´-bpy)(4,4´-R,R-2,2´-bpy)2]2+
Eduardo Schott, Ximena Zarate, and Ramiro Arratia-Perez
J. Phys. Chem. A, 2012, 116 (27), 7436-7442 [0.000, 0]
DOI:   10.1021/jp303497h
We studied the influence of the substituents over the composition of the molecular orbitals, electronic transitions, and reactivity of several ruthenium derivatives. We found a good agreement with the previously reported experimental data. In these theoretical calculations including spin–orbit coupling, we study several ruthenium-tris-(2,2?-bipyridine) substituted dyes, which do or do not have an anchoring group to get attached to the semiconductor surface. It was observed that the complexes that have electron-donor substituents might be more efficient to donate electrons if they are anchored to a semiconductor than those complexes that have electron-acceptor substituents. Therefore, the results suggest that these dyes with electron-donor substituents will give better yields in photocurrent generation. Also, the localization of the lowest unoccupied molecular orbital over the ligand that has the anchoring will help to improve electron injections into the TiO2 nanoparticles. We propose here several not yet synthetized dyes, which could be used in this kind of device, due to their interesting molecular properties.

A new method to radical anions derived from s-Indacene organobimetallic complexes, their ESR characterization
D. MacLeod Carey, C. Adams, A. Muñoz-Castro, C. Morales-Verdejo, J.F. Araneda, I. Chavez, J.M. Manríquez, A. Castel, P. Rivière, M. Rivière-Baudet, D. Matioszek, R. Septelean, I. Martinez, R. Arratia-Pérez
Inorg. Chim. Acta 2012, 392, 154–159 [0.000, 0]
DOI:   10.1016/j.ica.2012.05.033
The following organobimetallic radical anions derived from 2,6-diethyl-4,8-dimethyl-s-indacene (s-Ic′): [CODRh(s-Ic′)RhCOD]radical dot (IIa), [CpRu(s-Ic′)RuCp]radical dot (IIb), [CpRu(s-Ic′)RhCOD] radical dot (IIc), [CpRu(s-Ic′)NiCp]radical dot (IId) [(CO)3Mn(s-Ic′)NiCp]radical dot (IIe) and [CpFe(s-Ic′)NiCp]radical dot (IIf) (COD = 1,5-cyclooctadiene; Cp = pentamethylcyclopentadienyl) were prepared by reduction of the parent complexes using a monoelectronic transfer from an electron rich olefin. The radical anions were fully characterized by ESR spectroscopy which usually gave a well resolved hyperfine coupling structure, indicating that the spin distribution in the symmetrical radical anions (IIa, IIb) affects mainly the organic spacer whereas in the unsymmetrical ones (IIcf) it is displaced towards the most electronegative metal center and its ligands. This effect is most pronounced in IId, IIe and IIf. The calculated g tensor values of the radical anions are in good agreement with the experimental values. In heterobimetallic radical anions, the dissymmetric spin distribution shows that the two metals present different electrophile properties leading to potentially different catalytic activities.

Computational Studies of the Metal-Binding Site of the Wild-Type and the H46R Mutant of the Copper, Zinc Superoxide Dismutase
Raúl Mera-Adasme, Fernando Mendizábal, Mauricio Gonzalez, Sebastián Miranda-Rojas, Claudio Olea-Azar, and Dage Sundholm
Inorg. Chem., 2012, 51 (10), 5561-5568 [0.000, 0]
DOI:   10.1021/ic202416d
Impairment of the Zn(II)-binding site of the copper, zinc superoxide dismutase (CuZnSOD) protein is involved in a number of hypotheses and explanations for the still unknown toxic gain of function mutant varieties of CuZnSOD that are associated with familial forms of amyotrophic lateral sclerosis (ALS). In this work, computational chemistry methods have been used for studying models of the metal-binding site of the ALS-linked H46R mutant of CuZnSOD and of the wild-type variety of the enzyme. By comparing the energy and electronic structure of these models, a plausible explanation for the effect of the H46R mutation on the zinc site is obtained. The computational study clarifies the role of the D124 and D125 residues for keeping the structural integrity of the Zn(II)-binding site, which was known to exist but its mechanism has not been explained. Earlier results suggest that the explanation for the impairment of the Zn(II)-site proposed in this work may be useful for understanding the mechanism of action of the ALS-linked mutations in CuZnSOD in general.

Oxygen reduction reaction using N4-metallomacrocyclic catalysts: fundamentals on rational catalyst design
Justus Masa, Kenneth Ozoemena, Wolfgang Schuhmann, and José H. Zagal
J. Porphyrins Phthalocyanines 2012; 16: 761–784 [0.000, 0]
DOI:   10.1142/S1088424612300091
In this review, we describe and discuss the developments in the use of metalloporphyrins and metallophthalocyanines as catalysts for oxygen reduction in aqueous electrolytes. The main goal of most researchers in this field has been to design catalysts which can achieve facile reduction of oxygen by the four-electron transfer pathway at the lowest overpotential possible. With this in mind, the primary objective of this review was to bring to light the research frontiers uncovering important milestones towards the synthesis and design of promising N4-metallomacrocyclic catalysts which accomplish the four-electron reduction of oxygen, and, based on literature, to draw attention to the fundamental requirements for synthesis of improved catalysts operating at low overpotentials. Our emphasis was not to make parallel comparisons between individual classes of N4-metallomacrocyclic complexes with respect to their activity, but rather to focus on the commonalities of the fundamental properties that govern their reactivities and how these may be aptly manipulated to develop better catalysts. Therefore, besides discussion of the progress attained with regard to synthesis and design of catalysts with high selectivity towards four-electron reduction of O2, a major part of the review highlights quantitative structure-activity relationships (QSAR) which govern the activity and stability of these complexes, which when well understood, refined and carefully implemented should constitute a fundamental gateway for rational design of better catalysts.

Carbon nanotubes and metalloporphyrins and metallophthalocyanines-based materials for electroanalysis
José H. Zagal, Sophie Griveau, Mireya Santander-Nelli, Silvia Gutierrez Granados and Fethi Bedioui
J. Porphyrins Phthalocyanines 2012; 16: 713–740 [0.000, 0]
DOI:   10.1142/S1088424612300054
We discuss here the state of the art on hybrid materials made from single (SWCNT) or multi (MWCNT) walled carbon nanotubes and MN4 complexes such as metalloporphyrins and metallophthalocyanines. The hybrid materials have been characterized by several methods such as cyclic voltammetry (CV), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and scanning electrochemical microscropy (SECM). The materials are employed for electrocatalysis of reactions such as oxygen and hydrogen peroxide reduction, nitric oxide oxidation, oxidation of thiols and other pollutants.

Relativistic effects in bonding and isomerization energy of the superheavy roentgenium (111Rg) cyanide
Alvaro Muñoz-Castro, Desmond Mac-Leod Carey, Ramiro Arratia-Perez, Gulzari L. Malli
Polyhedron 2012, 39 (1), 113-117 [0.000, 0]
DOI:   10.1016/j.poly.2012.03.032
The cyanide and isocyanides of the superheavy roentgenium (111Rg) element are investigated using relativistic 4-component Dirac–Fock (DF) and 2-component Density-Functional Theory (DFT) with ZORA Hamiltonian. The relativistic effects in bonding and energetics allow us to conclude that these complexes could be synthesized in a linear conformation with a preference for the RgCN isomer. The relativistic effects (RE) lead to an increase in the covalent character of the Rg(I)–ligand interaction, resulting in a higher charge transfer from the ligand to the metal by an enhanced acceptor character of Rg(I), mainly due to the relativistic stabilization of the 7s shell. The inclusion of the spin–orbit interaction modifies the bonding picture leading to a decrease of about 40 kcal/mol in the bonding interaction in both isomers. In conclusion, our calculations at several levels of theory suggest that it is possible to develop an exotic chemistry of complexes involving Rg(I) and the CN ligand.

1,1′:4′,1′′-Terphenyl-2′,5′-dicarb­oxy­lic acid dimethyl sulfoxide-d6 disolvate
Lucian C. Pop, Marcelo Preite, Juan Manuel Manriquez, Andrés Vega, and Ivonne Chavez
Acta Cryst. 2012. E68, o1192 [0.000, 0]
DOI:   10.1107/S1600536812012056
The asymmetric unit of the title solvate, C20H14O4·2C2D6OS, contains half of the substituted terephthalic acid mol­ecule and one solvent mol­ecule. The centroid of the central benzene ring in the acid mol­ecule is coincident with a crystallographic inversion center. Neither the carboxyl nor the phenyl substituents are coplanar with the central aromatic ring, showing dihedral angles of 53.18 (11) and 47.83 (11)°, respectively. The dimethyl sulfoxide solvent mol­ecules are hydrogen bonded to the carb­oxy­lic acid groups.

Theoretical study of 3,3′ substitution of 9,9,9′,9′-tetramethyl-fluorene-dimers
Cristina A. Barboza, Ramiro Arratia-Pérez, Desmond MacLeod Carey
Chemical Physics Letters 2012, 538, 67-71 [0.000, 0]
DOI:   10.1016/j.cplett.2012.03.075
The effect of the 3,3′ substitution in 9,9,9′,9′-tetramethyl-fluorene-dimers with electron donor and withdrawing groups was analyzed. Ground state potential energy surfaces were obtained at DFT level using B3LYP/6-31+G(d,p). All studied dimers are nonplanar at their electronic ground states. The electronic transitions were investigated through the time-dependent-DFT method at their optimized ground states. The chemical potential (?) as well as the HOMO and LUMO eigenvalues were plotted against the Hammet parameters, showing a good linear correlation, giving us insights about the modulation of the electronic properties, e.g. HOMO–LUMO gap, by means of the functionalization of fluorene dimers at strategical positions.

Reinterpreting the Role of the Catalyst Formal Potential. The case of Thiocyanate Electrooxidation Catalyzed by CoN4-Macrocyclic Complexes
C. Linares-Flores, D. Mac-Leod Carey, A. Muñoz-Castro, J. H. Zagal, J. Pavez, D. Pino-Riffo, and R. Arratia-Pérez
J. Phys. Chem. C, 2012, 116 (12), 7091-7098 [0.000, 0]
DOI:   10.1021/jp300764n
We report on the interaction of the thiocyanate ion (SCN) with Co macrocyclics. In order to modulate the electron density located on the metal center, we used several phthalocyanine and macrocyclic molecules with electron-donating or electron-withdrawing groups located on the phthalocyanine ligand. We studied the following substituted Cobalt-macrocycles (CoPc’s): cobalt-tetraamino-phthalocyanine (4β(NH2)CoPc), cobalt-phthalocyanine (CoPc), cobalt-octahydroxyethylthio-phthalocyanine (8β(SC2H4OH)CoPc), cobalt-tetrapentylopyrrol-phthalocyanine (4β(PenPyr)CoPc), cobalt-tetrapyridino-phorphyrazine (4β(Pyr)CoPc), cobalt-octaethylhexyloxy-phthalocyanine (8β(EH)CoPc), cobalt-octamethoxyphthalocyanine (8β(OCH3)CoPc), and cobalt-hexadecafluorophthalocyanine (16(F)CoPc). Our results for the formation of a CoPc-SCN adduct indicate that the electron-withdrawing groups favors the formation of an adduct between thiocyanate and the Co center, with an increase of the thiocyanate-binding energy. When the adducts are formed, they exhibit an increasing chemical potential, thus indicating the feasibility to produce the catalysis once the adducts are formed. The molecular hardness values suggest that the CoPc’s with electron-withdrawing substituents will show low catalytic activity while those with electron-donor substituents will show an enhanced catalytic activity. The functionalized Co-phthalocyanine shows the highest catalytic activity for the thiocyanate electroxidation, which presents an appropriate energy gap (HOMOSCN — LUMOCoPc's) for the adduct formation and the subsequent electronic transfer.

Reactivity of Dipyridyl Ditellurides with (Diphosphine)Pt0 and 2-Pyridyltellurolates with (Diphosphine)PtCl2 and Isolation of Different Structural Motifs of Platinum(II) Complexes
Rohit Singh Chauhan, G. Kedarnath, Amey Wadawale, Arnold L. Rheingold, Alvaro Muñoz-Castro, Ramiro Arratia-Perez, and Vimal K. Jain
Organometallics, 2012, 31 (5), 1743-1750 [0.000, 0]
DOI:   10.1021/om2010589
Oxidative addition reaction of dipyridyl ditellurides to [Pt2(dppm)3] gave two types of complexes, [Pt{2-Te-C5H3(3-R)N}2(dppm)] (1) and [Pt{PPh2C(TeC5H3(3-R)N)2PPh2}2] (2) (R = H or Me), in ˜65 and ˜20% yield, respectively. Both these complexes are also formed in the substitution reaction between [PtCl2(dppm)] and NaTeC5H3(3-R)N. Treatment of [Pt(dppe)2] with dipyridyl ditellurides yielded an oxidative addition product, [Pt{2-Te-C5H3(3-R)N}2 (dppe)] (3) (R = H or Me), exclusively. In a substitution reaction of [PtCl2(dppe)] with NaTeC5H3(3-Me)N a complex of composition Pt{TeC5H3(3-Me)N}(dppe)Cl (4) wasformed. The reaction between either [Pt(dppp)2] and Te2(C5H3(3-Me)N)2or [PtCl2(dppp)] and NaTeC5H3(3-R)N afforded a mixture of [Pt{2-Te-C5H3(3-Me)N}2(dppp)] (5) and [Pt3Te2(dppp)3]2+ (6), which were separated by column chromatography. All the complexes were characterized by elemental analyses and NMR (1H, 31P, 195Pt) spectroscopy. The molecular structures of [Pt{PPh2C(TeC5H4N)2PPh2}2] and [Pt2{TeC5H3(3-Me)N}2(dppe)2][BPh4]2 were established by single-crystal X-ray diffraction analyses. The bonding, charge transfer, and geometry of compounds [Pt{2-Te-C5H3(3-R)N}2(dppm)] (1), [Pt{PPh2C(TeC5H3(3-R)N)2PPh2}2] (2), and [Pt3Te2(dppp)3]2+ (6) have been analyzed through relativistic density functional calculations.

Electronic structure and molecular properties of paramagnetic hexanuclear Tantalum [Ta6X12Y6]3− (X and Y = F, Cl, Br, I) cluster compounds
Eduardo Schott, Ximena Zarate, Ramiro Arratia-Pérez
Polyhedron, 2012, 36 (1), 127-132 [0.000, 0]
DOI:   10.1016/j.poly.2012.02.011
Relativistic density functional calculations were carried out on several Tantalum cluster of the general formula [Ta6X12Y6]3−, with the aim to characterize and analyze their molecular structure and electronic properties, in order to gain more insights into their stability and reactivity. Herein are reported the geometrical parameters, electronic structures, excitation energies and magnetic properties, of a series of clusters that have been and have not been yet synthesized. The calculated Δg tensor shows that as the halide capping ligand become heavier the Δg tensor values increases due to spin–orbit effects. Through the use of the reactivity indexes it is shown that when the axial ligand is iodine it becomes the most reactive and labile ligand. The TD-DFT calculations on the complete [Ta6X12Y6]3− cluster family show good agreement with the available experimental data

Tri-metallic deltahedral Zintl ions: experimental and theoretical studies of the novel dimer [(Sn6Ge2Bi)2]4-
Miriam M. Gillett-Kunnath , Alvaro Muñoz-Castro and Slavi C. Sevov
Chem. Commun., 2012, 48, 3524-3526 [0.000, 0]
DOI:   10.1039/C2CC30459G
We report the synthesis, characterization, and computational rationalization of the first trimetallic deltahedral Zintl ions. The novel nine-atom clusters were structurally characterized as dimers of [(Sn6Ge2Bi)2]4? with Ge–Ge intercluster bonds. They are synthesized either by reacting bimetallic clusters (Sn9?xGex)4? with BiPh3 or by direct extraction from precursors with nominal composition K4Ge4Sn4Bi

Photophysical properties of [Cu(binap)2]+ and [Pd(binap)2] complexes: A theoretical study
Ximena Zarate, Eduardo Schott, Rodrigo Ramirez-Tagle, Desmond MacLeod-Carey, Ramiro Arratia-Pérez
Polyhedron 2012, 37 (1), 54-59 [0.000, 0]
DOI:   10.1016/j.poly.2012.02.009
A theoretical study of the electronic and molecular structure of [Cu(binap)2]+ (1) and [Pd(binap)2] (2) complexes (binap = 2,20-bis(diphenylphosphino)-1,10-binaphthyl) was performed. We examined the ground states and the lowest excited states (S1 and T1) in order to get insights about the luminescence processes of these systems. Geometry optimizations were performed at density functional theory DFT (PW91 functional) employing Slater type orbitals (STO) including two polarization functions (TZ2P) and scalar relativistic corrections via the ZORA Hamiltonian. The UV–Vis absorption spectra were simulated employing time-dependent density functional theory (TD-DFT) and solvent effects were estimated using the COSMO model. The calculated excitation energies are in good agreement with experimental data, which is reflected by the calculated UV–Vis spectra. The results suggest that the lowest-energy excited state in each compound corresponds to a ML-LCT (metal–ligand to ligand charge transfer) state. We constructed Jablonsky diagrams for the luminescence phenom. In (1), this process consists of flourescence originated from the S1 state and the phosphorescence from the T1 state. In (2) the emission energy only results in phosphorescence. We found mainly differences in the geometrical parameters that envolve the Pd metal. The structural changes observed in the calculated geometries of the first excited states respect to those of the ground state have significative relevance in the values of the calculated Stokes shifts showed by the complexes in their UV–Vis/emission spectra.

The paramagnetic and luminescent [Re6Se8I6]3- cluster. Its potential use as an antitumoral and biomarker agent
Cesar Echeverría, Alvaro Becerra, Felipe Nuñez-Villena, Alvaro Muñoz-Castro, Jimmy Stehberg, Zhiping Zheng, Ramiro Arratia-Perez, Felipe Simon and Rodrigo Ramírez-Tagle
New J. Chem., 2012, 36, 927-932 [0.000, 0]
DOI:   10.1039/C2NJ21016A
Success in cancer chemotherapy is based on the selectivity of some drugs to induce tumor cell death without affecting normal cells. In that respect, some metal-based drugs appear to be promising in the development of efficient anticancer agents. Here, we evaluate the efficacy of the anionic hexa-iodo rhenium selenide cluster, Re6Se8I63?, which was predicted some years ago to be luminescent, to selectively increase tumor cell death, leaving non-tumoral cells unaffected. Thus, here we explore its intracellular localization by taking advantage of its revealed luminescence. Comparative studies of the cytotoxic effects of the Re6Se8I63? cluster when exposed to the tumorigenic cell line HepG2, endothelial cell-derived cell line (EA cells) and non-tumor primary endothelial cells (HUVEC) revealed that the cytotoxicity was highest for HepG2 and lowest for HUVEC. In addition, cells tend to uptake the cluster into their nuclei, where we found significant evidence of direct non-intercalating DNA binding. Finally, DNA laddering experiments suggested that the cluster induced apoptotic-like cell death. Our results suggest that the Re6Se8I63? cluster could be useful for the development of novel and efficient metal-based antitumor drugs for the diagnosis and treatment of cancers. The findings reported here represent the first attempts of a new and exciting field of research of inorganic multinuclear clusters in cancer research