Surfactant-tail control of CsPbBr3 nanocrystal morphology.

CsPbBr3 nanocrystals (NCs) are promising optoelectronic and catalytic materials. Manipulating their morphology can improve their properties and stability. In this work, an alkene-derived zwitterionic ligand was used to control the morphology of CsPbBr3 NCs to yield the highly unusual rhombicuboctahedron morphology, showcasing the first example of a surfactant-tail controlled growth.

Mono-Dendronized ß-Cyclodextrin Derivatives as Multitasking Containers for Curcumin. Impacting Its Solubility, Loading, and Tautomeric Form.

In this study, three mono-dendronized ß-cyclodextrin (ßCD) derivatives (ßCD-1G, ßCD-2G, and ßCD-3G) were used as multitasking containers of curcumin (CUR) to influence its aqueous solubility and tautomerism, both of which are related to its biological activity. We evaluated the relevant physicochemical properties of these containers associated with their potential hosting capacity. All mono-dendronized derivatives exhibited enhanced solubility in different solvents, including water, in comparison with native ßCD. Gas-phase geometry optimizations by density functional theory (DFT) confirmed that none of the dendrons blocked the passage of CUR into the ßCD cavity, and depending on the generation, different preorganization scenarios were promoted before complexation. Phase solubility diagrams showed that all the dendronized containers have superior performance for solubilizing CUR compared to native ßCD. We proved that coprecipitation is most efficient than lyophilization for forming inclusion complexes (ICs) with dendronized containers. Even though ßCD-3G with the largest 3G dendron exhibited the highest CUR loading, the complexation of CUR with ßCD-2G provided the supramolecular system that contains CUR preferentially in its diketo tautomer, which is known for its antioxidant activity.

Interaction of graphene with antipsychotic drugs: Is there any charge transfer process?

Antipsychotics represent an effective therapy for schizophrenia (a chronic mental disorder). Their benefits are related to the interaction of the drugs with dopamine D2 receptor (D2R). Antipsychotics are classified as agonists or antagonists. One of the working hypotheses is that there is a charge transfer process between the drugs and the receptors, which is different for agonists and antagonists. To have more insight into the nature of the interaction of these molecules and the differences between agonists and antagonists, we analyze the interaction of graphene with three molecules: dopamine, pramipexole (an agonist of dopamine), and risperidone (an antagonist of dopamine). The idea is to use graphene as a simple model to analyze the charge transfer process of these three drugs. Optimized structures, atomic charges, and Density of States results indicate that global charges of dopamine and pramipexole are similar, while for risperidone, it is more than double. Pramipexole is an agonist, and the charge transfer process is similar to that of dopamine. Risperidone is an antagonist, and the charge transfer process is different from dopamine. The charge transfer is more significant with risperidone than with dopamine, and this could be related to the mechanism of action. This is in agreement with the working hypotheses that establish that it is possible to distinguish between agonists and antagonists since they have different capacity to transfer charge.

Do weak interactions affect the biological behavior of DNA? A DFT study of CpG island-like chains.

The origin, stability, and contribution to the formation of noncovalent interactions, such as hydrogen bonds and π - π stacking, have been already widely discussed. However, there are few discussions about the relevance of these weak interactions in DNA performance. In this work, we seek to shed light on the effect of hydrogen bonds and π - π stacking interactions on the biological behavior of DNA through the description of these intermolecular forces in CpG island-like (GC-rich) chains. Furthermore, we made some comparisons with TATA box-like (TA-rich) chains in order to describe hydrogen bond and π - π stacking interactions as a function of the DNA sequence. For hydrogen bonds, we found that there is not a significant effect related to the number of base pairs. Whereas for π - π stacking interactions, the energy tended to decrease as the number of base pairs increased. We observed anticooperative effects for both hydrogen bonds and π - π stacking interactions. These results are in contrast with those of TATA box-like chains since cooperative and additive effects were found for both hydrogen bonds and π - π stacking, respectively. Based on the chemical hardness and density of states, we can conclude that proteins may interact easier with GC-rich chains. We conclude that regardless of the chain length, a protein could interact more easily with these genomics regions because the π - π stacking energies did not increase as a function of the number of base pairs, making, for the first time, a first approximation of the influence of noncovalent interaction on DNA behavior. We did all this work by means of DFT framework included in the DMol3 code (M06-L/DNP). Graphical Abstract Cartoon representation of how nocovalent interactions affect the interaction of DNA with a protein, i.e., how hydrogen bond and π - π stacking interactions influence the biological behavior of DNA.

Erratum: Del Castillo, R.M., et al. Electronic Peculiarities of a Self-Assembled M12L24 Nanoball (M = Pd+2, Cr, or Mo). Molecules 2019, 24, 771.

The author wishes to make the following correction to this paper [...].

Electronic Peculiarities of a Self-Assembled M12L24 Nanoball (M = Pd+2, Cr, or Mo).

We use molecular mechanics and DFT calculations to analyze the particular electronic behavior of a giant nanoball. This nanoball is a self-assembled M12L24 nanoball; with M equal to Pd+2; Cr; and Mo. These systems present an extraordinarily large cavity; similar to biological giant hollow structures. Consequently, it is possible to use these nanoballs to trap smaller species that may also become activated. Molecular orbitals, molecular hardness, and Molecular Electrostatic Potential enable us to define their potential chemical properties. Their hardness conveys that the Mo system is less reactive than the Cr system. Eigenvalues indicate that electron transfer from the system with Cr to other molecules is more favorable than from the system with Mo. Molecular Electrostatic Potential can be either positive or negative. This means that good electron donor molecules have a high possibility of reacting with positive regions of the nanoball. Each of these nanoballs can trap 12 molecules, such as CO. The nanoball that we are studying has large pores and presents electronic properties that make it an apposite target of study.

Cycloaddition reactions of pristine and endohedral fullerene molecules: possible anticancer activity.

Epoxide of oestradiol is one of the main risk factors for the genesis and evolution of breast cancer; hence, in recent years there has been considerable interest in the investigation of new inhibitors capable of reducing its carcinogenic activity. The aim of this article is to study the [2 + 2] cycloaddition reaction of epoxide of oestradiol in different pristine (C76 and D5h-C80) and endohedral metallofullerene (C72@Sc2C2, C76@Sc2 and C80@Sc2) by means of molecular electrostatic potential (MEP) topological analysis. Different from other molecular scalar fields, MEP topology enables to find minima related to lone pairs and π electrons, therefore, this molecular scalar field is appropriate to identify the most reactive sites. In consonance with our results, it was found that C80 was the best candidate to carry out the epoxide of oestradiol cycloaddition since more stable adducts were obtained. Furthermore, it is expected that more than one oestradiol epoxide molecule will be added to C80, forasmuch as C80 reactivity is enhanced once the adduct is formed. The study was carried through DFT framework included in the Gaussian 09 package (MPWB95/6-31G(d,p)).

Electronic properties of DNA: Description of weak interactions in TATA-box-like chains.

DNA is one of the most important biomolecules since it contains all the genetic information about an organism. The tridimensional structure of DNA is a determinant factor that influences the physiological and biochemical mechanisms by which this molecule carries out its biological functions. It is believed that hydrogen bonds and π-π stacking are the most relevant non-covalent interactions regarding DNA stability. Due to its importance, several theoretical works have been made to describe these interactions, however, most of them often consider only the presence of two nitrogenous bases, having a limited overview of the participation of these in B-DNA stabilization. Furthermore, due to the complexity of the system, there are discrepancies between which involved interaction is more important in duplex stability. Therefore, in this project we describe these interactions considering the effect of chain length on the energy related to both hydrogen bonds and π-π stacking, using as model TATA-box-like chains with n base pairs (n=1 to 14) and taking into consideration two different models: ideal and optimized B-DNA. We have found that there is a cooperative effect on hydrogen bond and π-π stacking mean energies when the presence of other base pairs is considered. In addition, it was found that hydrogen bonds contribute more importantly than π-π stacking to B-DNA stability; nevertheless, the participation of π-π stacking is not negligible: when B-DNA looks for a conformation of lower energy, π-π stacking interaction are the first to be optimized. All work was realized under the framework of DFT using the DMol3 code (M06-L/DNP).

A Direct Bandgap Copper-Antimony Halide Perovskite.

Since the establishment of perovskite solar cells (PSCs), there has been an intense search for alternative materials to replace lead and improve their stability toward moisture and light. As single-metal perovskite structures have yielded unsatisfactory performances, an alternative is the use of double perovskites that incorporate a combination of metals. To this day, only a handful of these compounds have been synthesized, but most of them have indirect bandgaps and/or do not have bandgaps energies well-suited for photovoltaic applications. Here we report the synthesis and characterization of a unique mixed metal ⟨111⟩-oriented layered perovskite, Cs4CuSb2Cl12 (1), that incorporates Cu2+ and Sb3+ into layers that are three octahedra thick (n = 3). In addition to being made of abundant and nontoxic elements, we show that this material behaves as a semiconductor with a direct bandgap of 1.0 eV and its conductivity is 1 order of magnitude greater than that of MAPbI3 (MA = methylammonium). Furthermore, 1 has high photo- and thermal-stability and is tolerant to humidity. We conclude that 1 is a promising material for photovoltaic applications and represents a new type of layered perovskite structure that incorporates metals in 2+ and 3+ oxidation states, thus significantly widening the possible combinations of metals to replace lead in PSCs.

Surface chemistry and density distribution influence on visible luminescence of silicon quantum dots: an experimental and theoretical approach.

The impact of the surface reconstruction of the density distribution and photoluminescence of silicon quantum dots (QDs) embedded in a silicon oxide matrix (SiOx) has been studied. Annealing treatments carried out on the as-deposited samples provoked the effusion of hydrogen species. Moreover, depending on the surrounding density and coalescence of QDs, they resulted in a change in the average size of the particles depending on the initial local environment. The shift in the luminescence spectra all over the visible region (blue, green and red) shows a strong dependence on the resultant change in the size and/or the passivation environment of QDs. Density functional theoretical (DFT) calculations support this fact and explain the possible electronic transitions (HOMO-LUMO gap) involved. Passivation in the presence of oxygen species lowers the band gap of Si29 and Si35 nanoclusters up to 1.7 eV, whereas, surface passivation in the environment of hydrogen species increases the band gap up to 4.4 eV. These results show a good agreement with the quantum confinement model described in this work and explain the shift in the luminescence all over the visible region. The results reported here offer vital insight into the mechanism of emission from silicon quantum dots which has been one of the most debated topics in the last two decades. QDs with multiple size distribution in different local environments (band gap) observed in this work could be used for the fabrication of light emission diodes (LEDs) or shift-conversion thin films in third generation efficient tandem solar cells for the maximum absorption of the solar spectrum in different wavelength regions.

Which Is The Best Sandwich Compound? Hexaphenylbenzene Substituted By Sandwich Compounds Bearing Sc, Cr, and Fe.

The electronic properties of nine different hexaarylbenzene molecules substituted by sandwich compounds have been studied by applying density functional theory. Different structures and the particular electron donor power of these systems have been considered in order to analyze their oxidant capacity, using bis(ciclopentadienyl) scandium, ferrocene, and bis(benzene)chromium as sandwich compounds. Both monometallic and bimetallic combinations are investigated. According to the ionization energies and electron affinities, compounds with Cr are nucleophiles and represent the best electron donors, whereas compounds with Sc are electrophiles and represent the best electron acceptors. The worse electron donor or acceptor is hexakis(4-ferrocenyl phenyl) benzene. This is very significant, as it implies that the very well-known electronic properties of hexakis(4-ferrocenyl phenyl) benzene can be improved by substituting with other metals, such as Sc and Cr. This suggests several possible applications for these compounds.

Gold as an intruder in ZnO nanowires.

Several techniques for obtaining ZnO nanowires (ZnO NWs) have been reported in the literature. In particular, vapour-liquid-solid (VLS) with Au as a catalyst is widely used. During this process, Au impurities in the ZnO NWs can be incorporated accidentally, and for this reason we named these impurities as intruders. It is thought that these intruders may produce interesting alterations in the electronic characteristics of nanowires. In the experiment, it is not easy to detect either Au atoms in these nanowires, or the modification that intruders produce in different electrical, optical and other properties. For this reason, in this density functional theory investigation, the effect of Au intruders on ZnO NWs is analysed. Au extended (thread) and point defects (atoms replacing Zn or O, or Au interstitials) are used to simulate the presence of gold atoms. Optimised geometries, band-gaps and density of states indicate that the presence of small amounts of Au drastically modifies the electronic states of ZnO NWs. The results reported here clearly indicate that small amounts of Au have a strong impact on the electronic properties of ZnO NWs, introducing states in the band edges that may promote transitions in the visible spectral region. The presence of Au as an intruder in ZnO NWs enhances the potential use of this system for photonic and photovoltaic applications.

Symmetric nested complexes of fullerenes.

Large fullerenes such as C180 and C116 can be used as hosts for other molecules of the same family. Based on this idea, two complexes were designed, one in which C180 accepts a C60 molecule as a guest and the other in which C20 was placed inside C116. The behavior of these new assemblies was closer to that of a large endohedral complex rather than onion-like. There were marked differences between the systems. In the first system, there was minor interaction between the two cages but the association resulted in a more stable thermodynamic state. In the second system, there was strong electronic interchange between the cages, and the thermodynamic results suggest that such a combination might be useful for forming stable C20.

Computational simulation of the effects of oxygen on the electronic states of hydrogenated 3C-porous SiC.

A computational study of the dependence of the electronic band structure and density of states on the chemical surface passivation of cubic porous silicon carbide (pSiC) was performed using ab initio density functional theory and the supercell method. The effects of the porosity and the surface chemistry composition on the energetic stability of pSiC were also investigated. The porous structures were modeled by removing atoms in the [001] direction to produce two different surface chemistries: one fully composed of silicon atoms and one composed of only carbon atoms. The changes in the electronic states of the porous structures as a function of the oxygen (O) content at the surface were studied. Specifically, the oxygen content was increased by replacing pairs of hydrogen (H) atoms on the pore surface with O atoms attached to the surface via either a double bond (X = O) or a bridge bond (X-O-X, X = Si or C). The calculations show that for the fully H-passivated surfaces, the forbidden energy band is larger for the C-rich phase than for the Si-rich phase. For the partially oxygenated Si-rich surfaces, the band gap behavior depends on the O bond type. The energy gap increases as the number of O atoms increases in the supercell if the O atoms are bridge-bonded, whereas the band gap energy does not exhibit a clear trend if O is double-bonded to the surface. In all cases, the gradual oxygenation decreases the band gap of the C-rich surface due to the presence of trap-like states.

Donor-acceptor tubular nanoaggregates of cyclic oligothiophenes. A theoretical study.

The geometries of neutral, monooxidized, and monoreduced donor-acceptor tubular aggregates of cyclo[8]thiophene, cyclo[8](3,4-dicyanothiophene), and the corresponding donor-acceptor tubular nanoaggregates containing up to 4 repeating units were fully optimized at MPWB1K/3-21G* level of theory. The binding energies between macrocycles in neutral donor-acceptor tubular aggregates (77-84 kcal/mol) were found to be much higher compared to donor (43-45 kcal/mol) or acceptor (27-28 kcal/mol) aggregates. The oxidation or the reduction of the donor-acceptor tubular aggregates lead to a decrement in the binding energy. However, the reduction increases the binding in acceptor aggregates and decreases in donor ones, whereas the oxidation causes the opposite effect. In spite of a decrease in the binding energy in donor-acceptor aggregates in oxidized or reduced states, they remain the most thermodynamically stable formations. Donor-acceptor aggregates possess the lowest band gap among all studied systems (1.31 eV for the tetramer) and the photoexcitation of donor-acceptor aggregates results in almost complete electron transfer from donor to acceptor fragment, thus showing a very strong charge separation in the excited-state, which is highly desirable in materials with potential application in photovoltaic devices. Polaron cations are localized at donor fragments, whereas polaron anions are located at acceptor units.

Tubular aggregates of cyclic oligothiophenes. A theoretical study.

The geometries of neutral, mono-, and dioxidized tubular aggregates of cyclo[8]thiophenes containing up to 5 repeating units were fully optimized at the MPWB1K/3-21G* level of theory. Calculated interplane distances between macrocycles were found to be close to 3.1 A for neutral and charged aggregates. The binding energies between macrocycles in neutral intermediates were in the range of 40-45 kcal/mol, increasing for monocations and dropping strongly for dicationic species due to electrostatic repulsion between polarons. It was established that there exists a noticeable interaction between pi-orbitals of individual macrocycles in tubular aggregates as follows from decreasing of the band gap with a number of repeating units in aggregates and the polaron delocalization toward tube axes in oxidized species. A polaron pair is the most stable dicationic state for all studied molecules according to the calculations. A singlet polaron pair is more stable than a triplet one. The energy difference between singlet and triplet states is growing smaller with the size of the system, becoming zero for the pentamer corresponding to a completely dissociated bipolaron.

Terapeutica grupal nos transtornos psicopatologicos

As reacoes individuais frente aos estimulos vivenciais quando destoantes da expectativa humana, de forma geral caracterizam o disturbio mental, do ponto de vista psicologico. Aos doentes mentais muito empenho se tem despendido no sentido de serem formuladas proposicoes dos mais variados planos de acao para o seu restabelecimento. Muitas variaveis, como o espaco fisico e equipe especializada, algumas vezes se tornam impossiveis de ser controladas na pratica, como requerem estas proposicoes, e por isso alguns planejamentos fantasticos apresentam resultados aquem do esperado. Por conhecermos as limitacoes que naturalmente nos seriam impostas, por trabalharmos em um hospital de modelo classico, procuramos adequar nossos anseios a realidade e partimos entao para uma concreta e possivel proposta de trabalho: nao modificariamos o ambiente fisico, nao requisitariamos cursos de treinamento dos funcionarios em contato constante com as pacientes e nem almejariamos um programa ideal de trabalho, mas procurariamos contar, acima de tudo, com a colaboracao das proprias doentes mentais. Fez-se o esquema: uma equipe com psiquiatra, psicologa e assistente social, reunioes semanais fornecendo explicacoes de nossas finalidades, palestras com temas socio-educativos, discussoes de grupo e ensaios comportamentais. Embasando tudo: a nossa crenca no potencial humano e o respaldo das tecnicas de modificacoes de comportamento. Ao fim de uma fase intensa de empenho, o resultado: muitas pacientes se tornaram mais bem preparadas para o convivio social, com remissao dos comportamentos que lhes exacerbavam os quadros da doenca mental e nos permitiam supor, inicialmente, maior gravidade e cronicidade dos disturbios. Comportamentos de higiene, responsabilidade, honestidade, sociabilidade e muitos outros passaram a integrar seus repertorios, e o que a nosso ver e mais fantastico: as mesmas doentes antes repulsivas a muitos, passaram a naturalmente fornecer modelos de conduta adequados, facilitando-nos assim a continuidade do programa e o treinamento da equipe de funcionarios. Como vimos, a simples atuacao de uma restrita equipe de trabalho, aliada ao potencial inerente do ser humano, mesmo quando adoecido, e a formulacao de um plano racional de trabalho, pode levar a recompensadores resultados. Isso e possivel.