Emergence of complexity in hierarchically organized chiral particles

The structural complexity of composite biomaterials and biomineralized particles arises from the hierarchical ordering of inorganic building blocks over multiple scales. Although empirical observations of complex nanoassemblies are abundant, the physicochemical mechanisms leading to their geometrical complexity are still puzzling, especially for nonuniformly sized components. We report the self-assembly of hierarchically organized particles (HOPs) from polydisperse gold thiolate nanoplatelets with cysteine surface ligands. Graph theory methods indicate that these HOPs, which feature twisted spikes and other morphologies, display higher complexity than their biological counterparts. Their intricate organization emerges from competing chirality-dependent assembly restrictions that render assembly pathways primarily dependent on nanoparticle symmetry rather than size. These findings and HOP phase diagrams open a pathway to a large family of colloids with complex architectures and unusual chiroptical and chemical properties

Estudo sobre a estrutura eletrônica de ftalocianinas metaladas para aplicação em células solares sensibilizadas por corante

The electronic properties of push-pull substituted, zinc(II) (ZnPc), aluminum(III) (AlPc), and ruthenium(II) (RuPc), metal-phthalocyanine derivatives, presenting two electron donating groups (diethylamine) and two electron withdrawing groups (carboxylic) was studied using the Density Functional Theory (DFT) with B3LYP exchange-correlation functional in the vacuum and under the presence of solvent (DMSO), aiming their application in dye-sensitized solar cells (DSSC). For the excited states, the time-dependent approach of DFT (TD-DFT) was applied. In the transition for the excited state it was evidenced a charge transfer from donor to acceptor groups which results in large electronic rearrangement inducing the bathochromism when adding DMSO (a polar solvent). This electronic transfer is directed to the acceptor groups (benzoic groups), mainly in RuPc molecule, which enables bigger probability in the electronic injection into the semiconductor s conduction band. HOMO s energy to the ZnPc and AlPc are sufficiently below the redox potential of the electrolyte and LUMO s energy, in all compounds, is above the conduction band of the oxide. Those push-pull molecules present panchromism, important for the application of these compounds in DSSC since they can absorb photons in a large range of energies. NBO analysis suggests that the ruthenium presents strong coordination with the nitrogen atoms of the macrocycle, which allows a larger participation of this metal in the electronic transition. The ionization energy and electron affinity were calculated aiming to quantify the energetic barrier in the electron gain / loss.Fundação de Amparo a Pesquisa do Estado de Minas GeraisMestre em QuímicaAs propriedades eletrônicas de derivados de ftalocianinas metaladas push-pull de zinco(II) (FtZn), alumínio(III) (FtAl) e rutênio(II) (FtRu) apresentando dois grupos doadores de elétrons (N,N-dietilanilina) e dois grupos retiradores de elétrons (ácido benzóico), foram estudadas usando a teoria do funcional de densidade (DFT) com o funcional híbrido B3LYP na presença do solvente (DMSO) e no vácuo, visando sua aplicação em células solares sensibilizadas por corante (CSSC). Para a descrição dos estados excitados usou-se a extensão dependente do tempo da DFT (TD-DFT). Na transição para o estado excitado destes compostos há uma transferência de carga dos grupos doadores para os grupos aceptores, que resulta em rearranjo eletrônico induzindo o efeito batocrômico observado com a adição de DMSO. Essa transferência eletrônica está direcionada para o grupo aceptor (grupo benzóico), principalmente na FtRu, que possibilita uma maior probabilidade na injeção eletrônica na banda de condução do semicondutor. A energia do HOMO para a FtZn e FtAl estão suficientemente abaixo do potencial redox do eletrólito e o LUMO, em todos os compostos, está acima da banda de condução do TiO2. Essas moléculas push-pull apresentam pancromismo, importante para a aplicação destes compostos em CSSC uma vez que podem absorver fótons de diferentes energias. Análises NBO sugerem que o rutênio apresenta forte coordenação com os nitrogênios do macrociclo que possibilita grande participação deste metal nestas transições eletrônicas. As energias de ionização e eletroafinidades foram calculadas com o objetivo de quantificar a barreira energética no ganho/perda de um elétron

Themis: A Software to Assess Association Free Energies via Direct Estimative of Partition Functions

We present the program Themis - a computer implementation of a standard statistical mechanics framework to compute free energies, average energies and entropic contributions for association processes of two atom-based structures. The partition functions are computed analytically using a discrete grid in the phase space, whose size and degree of coarseness can be controlled to allow efficient calculations and to achieve the desired level of accuracy. With this strategy, applications ranging from molecular recognition, chiral discrimination, surface adsorption and even the interactions involving molecules in electronic excited states can be handled.</div

The bimolecular sensitization of nitric oxide release from weak interacting ruthenium units

This work reports on the bimolecular sensitization of nitric oxide release from cis-[Ru(bpy)(2)(iso)-NO](PF(6))(3) (1) (iso = isoquinoline and bpy = 2,2`- bipyridine) by irradiating the MLCT transition of the chloro analog cis-[Ru(bpy) 2(iso) Cl] PF6 (2). The compounds displayed peaks in the ESI-MS spectra at m/z 749.1 and m/z 578.1 ascribed, respectively, to ([1(NO(o))-2PF(6)center dot CH(3)OH](2+)) and ([2-PF(6)](+)). In the cyclic voltammograms, the nitrosyl complex presented two redox waves related to the NO ligand at 0.48 and -0.37 V (versus Ag/AgCl, NO(+/0/-1) processes), while the sensitizer showed two reversible waves at 0.79 and -1.46 V (versus Ag/AgCl, Ru(2+/3+) and bpy(0/-1), respectively). The most important feature of this system is that the nitrosyl compound does not have significant absorption in the visible region, while the sensitizer has an intense band centered at 496 nm. The irradiation of an equimolar mixture of the two compounds in an ethanol: water solution (v: v) with light of lambda > 500 nm leads to NO release, as probed by amperometric measurements. The variational method was applied, showing that the two compounds self-assembly in solution with a 1: 1 stoichiometry. Fluorescence spectra acquired at 77 K provided the E(0-0) for the system and, from the thermodynamic cycle it was estimated that the photoinduced electron transfer between the species has a Delta G value of -1.59 eV. (C) 2011 Elsevier B. V. All rights reserved.FAPESPFAPEMIGCAPESCNP

Nean Oju Obá: enfrentamentos e aquilombamento de estudantes negras(os) da Universidade Federal da Paraíba

Este artículo presenta las articulaciones de estudiantes y graduados negros de los cursos de Antropología y Ciencias Sociales, así como del programa de posgrado en Antropología de la Universidad Federal de Paraíba y discute las relaciones étnico-raciales, el racismo, la identidad y sus efectos en la dinámica del campo científico de la antropología. El debate se basa en el trabajo del Colectivo Nean Oju Obá para garantizar la admisión de candidatos negros en el programa de postgrado en Antropología a través del curso Negritudes na Pós En definitiva, el Colectivo constituye un espacio de resistencia y quilombo, en la defensa de los derechos y la lucha contra el racismo, especialmente el racismo institucional.Este artigo apresenta as articulações de estudantes e egressos negros(as) dos cursos de Antropologia e Ciências Sociais, assim como da pós-graduação em Antropologia da Universidade Federal da Paraíba e discute as relações étnico-raciais, racismos, identidade e seus efeitos sobre a dinâmica do campo científico da antropologia. O debate parte da atuação do coletivo Nean Oju Obá para garantir o ingresso de candidates negres na Pós-Graduação em Antropologia por meio do Curso Negritudes na Pós. Em suma, o Coletivo forma um espaço de resistência e aquilombamento, na defesa de direitos e combate aos racismos, sobretudo, o racismo institucional.This article presents the articulations of black students and graduates of the courses of Anthropology and Social Sciences, as well as the post-graduate program in Anthropology at the Federal University of Paraíba and discusses ethnic-racial relations, racism, identity and its effects on the dynamics of the scientific field of anthropology. The debate is based on the work of the Nean Oju Obá collective to guarantee the admission of black candidates to the post-graduate program in Anthropology through the course Negritudes na Pós In short, the Collective forms a space of resistance and quilombo-making, in the defense of rights and the fight against racism, especially institutional racism

Synthesis and Spectroscopic Characterization of Two Tetrasubstituted Cationic Porphyrin Derivatives

An imidazolium tetrasubstituted cationic porphyrin derivative (the free base and its Zn(II) complex) with five-membered heterocyclic groups in the meso-positions were synthesized using microwave irradiation, and the compounds obtained characterized by 1H-NMR and mass spectrometry. We observed that under microwave irradiation the yield is similar to when the synthesis is performed under conventional heating, however, the time required to prepare the porphyrins decreases enormously. In order to investigate the electronic state of these compounds, we employed UV-Vis and fluorescence spectroscopy combined with quantum chemical calculations. The results reveal the presence, in both compounds, of a large number of electronic states involving the association between the Soret and a blue-shifted band. The Soret band in both compounds also shows a considerable solvent dependence. As for emission, these compounds present low quantum yield at room temperature and no solvent influence on the fluorescence spectra was observed

Nat. Nanotechnol.

Optoelectronic effects differentiating absorption of right and left circularly polarized photons in thin films of chiral materials are typically prohibitively small for their direct photocurrent observation. Chiral metasurfaces increase the electronic sensitivity to circular polarization, but their out-of-plane architecture entails manufacturing and performance tradeoffs. Here, we show that nanoporous thin films of chiral nanoparticles enable high sensitivity to circular polarization due to light-induced polarization-dependent ion accumulation at nanoparticle interfaces. Self-assembled multilayers of gold nanoparticles modified with L-phenylalanine generate a photocurrent under righthanded circularly polarized light as high as 2.41 times higher than under left-handed circularly polarized light. The strong plasmonic coupling between the multiple nanoparticles producing planar chiroplasmonic modes facilitates the ejection of electrons. Concomitantly, a thick layer of enantiopure phenylalanine facilitates their subsequent entrapment at the membrane-electrolyte interface. Demonstrated detection of light ellipticity with equal sensitivity at all incident angles mimics phenomenological aspects of polarization vision in marine animals. The simplicity of self-assembly 2 and sensitivity of polarization detection found in optoionic membranes opens the door to a family of miniaturized fluidic devices for chiral photonics

Study of the spectroscopic properties and first hyperpolarizabilities of disperse azo dyes derived from 2-amino-5-nitrothiazole

The solvatochromism and other spectroscopic and photophysical characteristics of four azo disperse dyes, derived from 2-amino-5-nitrothiazole, were evaluated and interpreted with the aid of experimental data and quantum mechanical calculations. For the non-substituted compound two conformers, E and Z, were proposed for the isolated molecules, being the second one considerably less stable. The optimization of these structures in combination with a SCRF methodology (IEFPCM, Simulating the molecules in a continuum dielectric with characteristics of methanol), suggests that the Z form is not stable in solution. This same behaviour is expected for the substituted compounds, which is corroborated by experimental data presented in previous investigations [A.E.H. Machado, L.M. Rodrigues, S. Gupta, A.M.F. Oliveira-Campos, A.M.S. Silva, J. Mol. Struct. 738 (2005) 239-245]. For the substituted compounds, two forms derived from E conformer (A and R) are possible. Quantum mechanical data suggest for the isolated molecules, that the low energy absorption hand of the E conformers involve at least two close electronic states. having the low-lying excited state a (1)(n,pi*) nature, and being the S-2 state attributed to a (1)(pi,pi*) transition. The data also suggest a small energy gap between the absorption peaks of A and B, related to the easy conversion between these forms. For the structures optimized in combination with the applied SCRF methodology, an states inversion is observed for the Substituted compounds, with a considerable diminish of the energy gap between A and B absorption peaks. The electronic spectra of these compounds are quite sensitive to changes in the solvent polarity. The positive solvatochromism is more evident in aprotic solvents, probably due to the polarization induced by the solute. These compounds do not fluoresce at 298 K, but present a small but perceptible fluorescence at 77 K, which seems to be favoured by the nature of the group in the 2 `-position of the phenyl ring. Moreover, such compounds present expressive values for first hyperpolarizability, which implies in good non-linear optics (NLO) responses and photoswitching capability. (C) 2008 Elsevier B.V. All rights reserved.Universidade do MinhoUniversidade do MinhoFCT-Portugal[POCTI-SFA-3-686]Fundação para a Ciência e a Tecnologia de Portugal (FCT)Radim Hrdina[VZ MSM 0021627501]Radim HrdinaFundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG)FAPEMIG (PRONEX)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPqCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)CAPE