Polyradical character and spin frustration in fullerene molecules: An ab initio non-collinear Hartree--Fock study

Most {\em ab initio} calculations on fullerene molecules have been carried out based on the paradigm of the H\"uckel model. This is consistent with the restricted nature of the independent-particle model underlying such calculations, even in single-reference-based correlated approaches. On the other hand, previous works on some of these molecules using model Hamiltonians have clearly indicated the importance of short-range inter-atomic spin-spin correlations. In this work, we consider {\em ab initio} non-collinear Hartree--Fock (HF) solutions for representative fullerene systems: the bowl, cage, ring, and pentagon isomers of C$_{20}$, and the larger C$_{30}$, C$_{36}$, C$_{60}$, C$_{70}$, and C$_{84}$ fullerene cages. In all cases but the ring we find that the HF minimum corresponds to a truly non-collinear solution with a torsional spin density wave. Optimized geometries at the generalized HF (GHF) level lead to fully symmetric structures, even in those cases where Jahn-Teller distortions have been previously considered. The nature of the GHF solutions is consistent with the $\pi$-electron space becoming polyradical in nature: each $p$-orbital remains effectively singly occupied. The spin frustration, induced by the pentagon rings in an otherwise anti-ferromagnetic background, is minimized at the HF level by aligning the spins in non-collinear arrangements. The long-range magnetic ordering observed is reminiscent of the character of broken symmetry HF solutions in polyacene systems.Comment: 16 figure

Multi-reference symmetry-projected variational approximation for the ground state of the doped one-dimensional Hubbard model

A multi-reference configuration mixing scheme is used to describe the ground state, characterized by well defined spin and space group symmetry quantum numbers as well as doping fractions $N_{e}/N_{sites}$, of one dimensional Hubbard lattices with nearest-neighbor hopping and periodic boundary conditions. Within this scheme, each ground state is expanded in a given number of nonorthogonal and variationally determined symmetry-projected configurations. The results obtained for the ground state and correlation energies of half-filled and doped lattices with 30, 34 and 50 sites, compare well with the exact Lieb-Wu solutions as well as with the ones obtained with other state-of-the-art approximations. The structure of the intrinsic symmetry-broken determinants resulting from the variational procedure is interpreted in terms of solitons whose translational and breathing motions can be regarded as basic units of quantum fluctuations. It is also shown that in the case of doped 1D lattices, a part of such fluctuations can also be interpreted in terms of polarons. In addition to momentum distributions, both spin-spin and density-density correlation functions are studied as functions of doping. The spectral functions and density of states, computed with an ansatz whose quality can be well-controlled by the number of symmetry-projected configurations used to approximate the $N_{e} \pm 1$ electron systems, display features beyond a simple quasiparticle distribution, as well as spin-charge separation trends.Comment: 16 pages, 11 figure

Multi-component symmetry-projected approach for molecular ground state correlations

The symmetry-projected Hartree--Fock ansatz for the electronic structure problem can efficiently account for static correlation in molecules, yet it is often unable to describe dynamic correlation in a balanced manner. Here, we consider a multi-component, systematically-improvable approach, that accounts for all ground state correlations. Our approach is based on linear combinations of symmetry-projected configurations built out of a set of non-orthogonal, variationally optimized determinants. The resulting wavefunction preserves the symmetries of the original Hamiltonian even though it is written as a superposition of deformed (broken-symmetry) determinants. We show how short expansions of this kind can provide a very accurate description of the electronic structure of simple chemical systems such as the nitrogen and the water molecules, along the entire dissociation profile. In addition, we apply this multi-component symmetry-projected approach to provide an accurate interconversion profile among the peroxo and bis($\mu$-oxo) forms of [Cu$_2$O$_2$]$^{2+}$, comparable to other state-of-the-art quantum chemical methods

Excited electronic states from a variational approach based on symmetry-projected Hartree--Fock configurations

Recent work from our research group has demonstrated that symmetry-projected Hartree--Fock (HF) methods provide a compact representation of molecular ground state wavefunctions based on a superposition of non-orthogonal Slater determinants. The symmetry-projected ansatz can account for static correlations in a computationally efficient way. Here we present a variational extension of this methodology applicable to excited states of the same symmetry as the ground state. Benchmark calculations on the C$_2$ dimer with a modest basis set, which allows comparison with full configuration interaction results, indicate that this extension provides a high quality description of the low-lying spectrum for the entire dissociation profile. We apply the same methodology to obtain the full low-lying vertical excitation spectrum of formaldehyde, in good agreement with available theoretical and experimental data, as well as to a challenging model $C_{2v}$ insertion pathway for BeH$_2$. The variational excited state methodology developed in this work has two remarkable traits: it is fully black-box and will be applicable to fairly large systems thanks to its mean-field computational cost

Evaluación del potencial oncolítico del rotavirus en la línea celular Sp2/0-Ag14 de mieloma de ratón

Introduction: Cancer is the second leading cause of death in the United States, surpassed only by cardiovascular disease. However, cancer has now overtaken cardiovascular disease as the main cause of death in 12 countries in Western Europe. The burden of cancer is posing a major challenge to health care systems worldwide and demanding improvements in methods for cancer prevention, diagnosis, and treatment. Alternative and complementary strategies for orthodox surgery, radiotherapy, and chemotherapy need to be developed.Objective: To determine the oncolytic potential of tumor cell-adapted rotavirus in terms of their ability to infect and lysate murine myeloma Sp2/0-Ag14 cells.Materials and methods: We inoculated rotaviruses Wt1-5, WWM, TRUYO, ECwt-O, and WTEW in Sp2/0-Ag14 cells and we examined their infectious effects by immunocytochemistry, immunofluorescence, flow cytometry, and DNA fragmentation assays.Results: Rotavirus infection involved the participation of some heat shock proteins, of protein disulfide isomerase (PDI), and integrin β3. We detected the accumulation of viral antigens within the virus-inoculated cells and in the culture medium in all the rotavirus isolates examined. The rotavirus-induced cell death mechanism in Sp2/0-Ag14 cells involved changes in cell membrane permeability, chromatin condensation, and DNA fragmentation, which were compatible with cytotoxicity and apoptosis.Conclusions: The ability of the rotavirus isolates Wt1-5, WWM, TRUYO, ECwt-O, and WTEW to infect and cause cell death of Sp2/0-Ag14 cells through mechanisms that are compatible with virus-induced apoptosis makes them potential candidates as oncolytic agents.Introducción. El cáncer es la segunda causa de muerte en los Estados Unidos, solamente superado por la enfermedad cardiovascular. Sin embargo, el cáncer aventaja a la enfermedad cardiovascular como primera causa de muerte en doce países de Europa occidental. Se requieren mejores métodos de prevención, diagnóstico y tratamiento para afrontar el gran desafío que el cáncer representa mundialmente para los sistemas de salud, y se necesita desarrollar estrategias alternativas y complementarias a la cirugía, la radioterapia y la quimioterapia convencionales.Objetivo. Evaluar el potencial oncolítico de rotavirus adaptados a células tumorales por su capacidad para infectar y lisar células Sp2/0-Ag14 de mieloma de ratón.Materiales and métodos. Los aislamientos de rotavirus Wt1-5, WWM, TRUYO, ECwt-O y WTEW se inocularon en células Sp2/0-Ag14 y se examinaron sus efectos infecciosos mediante inmunocitoquímica, inmunofluorescencia, citometría de flujo y ensayos de fragmentación del ADN.Resultados. La infección con los rotavirus Wt1-5, WWM, TRUYO, ECwt-O y WTEW implicó la participación de algunas proteínas de choque térmico, la proteína disulfuro isomerasa y la integrina β3. La acumulación de antígenos virales intracelulares y extracelulares se detectó en todos los virus utilizados. Los mecanismos de muerte inducidos por los rotavirus en células Sp2/0-Ag14 indujeron cambios en la permeabilidad de la membrana celular, la condensación de cromatina y la fragmentación de ADN, los cuales fueron compatibles con citotoxicidad y apoptosis.Conclusiones. La capacidad de los rotavirus estudiados para infectar y causar la muerte de células Sp2/0-Ag14 mediante mecanismos compatibles con la apoptosis inducida viralmente los convierte en candidatos potenciales para ser utilizados como agentes oncolíticos

High resistance against clindamycin, metronidazole and amoxicillin in Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans isolates of periodontal disease

Objectives: To test the antimicrobial sensitivity of two periodontal pathogens to a panel of five orally administrable antibiotics in periodontal disease. Study design: A total of 69 isolates of Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis were processed using culture and biochemical tests. Selected colonies of A. actinomycetemcomitans and P. gingivalis were used to evaluate the antibacterial activity of clindamycin, metronidazole, amoxicillin, moxifloxacin and amoxicillin/clavulanic acid. Results: Susceptibility testing revealed a sensitivity of 100% of A. actinomycetemcomitans and P. gingivalis to moxifloxacin and amoxicillin/clavulanic acid but moderate susceptibilities were found for the rest of antibiotics agents evaluated. Conclusions: The widespread use of antibiotics is reflected in the level of resistance of A. actinomycetemcomitans and P. gingivalis in patients with periodontal infections. This suggests that antibiotic susceptibility testing is necessary to determine efficacy of antimicrobial agents. Clinical studies with antibiotics should take these differences into account

Televisión, visibilidad y exclusión: un estudio de caso (Presa de Arcediano)

El presente estudio analiza aquello que la televisión invisibiliza o expone de acuerdo a su lógica comercial o su agenda política. Se refiere a lo que aun considerado como de beneficio o interés público, se encuentra sujeto al control de ciertas élites dominantes y que conforme al criterio del medio, no corresponde a otros grupos o sujetos informarse. Se aborda el caso del ex poblado de Arcediano, situado en la barranca de Huentitán y reducido a escombros por iniciativas gubernamentales a efecto de construir una presa. Los habitantes de esta región manifestaron inconformidad porque la televisora local, dependiente del corporativo de televisión y radio más grande del país, en lugar de prestarse para hacer del conocimiento público lo favorable y sobretodo lo desfavorable del proyecto, se inclinó por apoyar su realización, lo que dejó entrever que el medio hizo la voluntad de aquellos en el poder. Esta tesis estudia las consecuencias que conlleva para la sociedad la correlación de intereses que mantiene la televisión con el Estado, al igual que con algunos grupos que ejercen poder económico e ideológico, y qué estrategias se han empleado por parte de los excluidos de las pantallas.Universidad de Guadalajar

Calculation of molecular g-tensors by sampling spin orientations of generalised Hartree-Fock states

The variational inclusion of spin-orbit coupling in self-consistent field (SCF) calculations requires a generalised two-component framework, which permits the single-determinant wave function to completely break spin symmetry. The individual components of the molecular g-tensor are commonly obtained from separate SCF solutions that align the magnetic moment along one of the three principal tensor axes. However, this strategy raises the question if energy differences between solutions are relevant, or how convergence is achieved if the principal axis system is not determined by molecular symmetry. The present work resolves these issues by a simple two-step procedure akin to the generator coordinate method (GCM). First, a few generalised Hartree Fock (GHF) solutions are converged, applying, where needed, a constraint to the orientation of the magnetic-moment or spin vector. Then, superpositions of GHF determinants are formed through non-orthogonal configuration interaction. This procedure yields a Kramers doublet for the calculation of the complete g-tensor. Alternatively, for systems with weak spin-orbit effects, diagonalisation in a basis spanned by spin rotations of a single GHF determinant affords qualitatively correct g-tensors by eliminating errors related to spin contamination. For small first-row molecules, these approaches are evaluated against experimental data and full configuration interaction results. It is further demonstrated for two systems (a fictitious tetrahedral CH4+ species, and a CuF4(2-) complex) that a GCM strategy, in contrast to alternative mean-field methods, can correctly describe the spin-orbit splitting of orbitally-degenerate ground states, which causes large g-shifts and may lead to negative g-values.Comment: 33 pages, 5 figur

In vivo Neutralization of Pro-inflammatory Cytokines During Secondary Streptococcus pneumoniae Infection Post Influenza A Virus Infection

An overt pro-inflammatory immune response is a key factor contributing to lethal pneumococcal infection in an influenza pre-infected host and represents a potential target for therapeutic intervention. However, there is a paucity of knowledge about the level of contribution of individual cytokines. Based on the predictions of our previous mathematical modeling approach, the potential benefit of IFN-γ- and/or IL-6-specific antibody-mediated cytokine neutralization was explored in C57BL/6 mice infected with the influenza A/PR/8/34 strain, which were subsequently infected with the Streptococcus pneumoniae strain TIGR4 on day 7 post influenza. While single IL-6 neutralization had no effect on respiratory bacterial clearance, single IFN-γ neutralization enhanced local bacterial clearance in the lungs. Concomitant neutralization of IFN-γ and IL-6 significantly reduced the degree of pneumonia as well as bacteremia compared to the control group, indicating a positive effect for the host during secondary bacterial infection. The results of our model-driven experimental study reveal that the predicted therapeutic value of IFN-γ and IL-6 neutralization in secondary pneumococcal infection following influenza infection is tightly dependent on the experimental protocol while at the same time paving the way toward the development of effective immune therapies