Where are the Excess Electrons in Subvalent Compounds? The Case of Ag7Pt2O7.

Subvalent compounds raise the question of where those valence electrons not belonging to chemical bonds are. In the limiting case of Ag7Pt2O7, there is just one-electron excess in the chemical formula requiring the presence of Ag atoms with oxidation states below +1, assuming conventional Pt4+ and O2- ions. Such a situation challenges the understanding of the semiconducting and diamagnetic behavior observed in this oxide. Previous explanations that localize pairwise the electron excess in tetrahedral Ag4 interstices do not suffice in this case, since there are six silver tetrahedral voids and only an excess of nine electrons in the unit cell. Here, we provide an alternative explanation for the subvalent nature of this compound by combining interatomic distances, electron density-based descriptors, and orbital energetic analysis criteria. As a result, Ag atoms that do not participate in their valence electron are revealed. We identify excess electrons located in isolated subvalent silver clusters with electron-deficient multicenter bonds resembling pieces of metallic bonding in fcc-Ag and Ag7Pt2 alloy. Our analysis of the electronic band structure also supports the multicenter bonding picture. This combined approach from the real and reciprocal spaces reconciles existing discrepancies and is key to understanding the new chemistry of silver subvalent compounds.

Externally driven molecular ratchets on a periodic potential surface: a rate equations approach.

The long time dynamics of molecular ratchets on a 1D periodic potential energy surface (PES) subjected to an external stimulus is studied using the rate equation method. The PES consisting of repeated waveforms made of two peaks is considered as an example of a spatially symmetric or asymmetric PES. This PES may, for example, correspond to diffusion of a bipedal molecule that moves along an atomic track via an inchworm walk mechanism [Raval et al., Angew. Chem., Int. Ed., 2015, 54, 7101]. Generalisation to a PES consisting of an arbitrary number of peaks of various heights is straightforward. Assuming the validity of the transition state theory (TST) for the calculation of the transition rates between neighbouring potential wells, the probability of occupying each type of potential well on the PES is obtained analytically, and then the net current for the molecules to move preferentially in a particular direction under application of external fields over a long time is derived. Note that different to methods based on solving numerically the corresponding Fokker-Plank equation, our method is entirely analytical in the limit of weak external fields. The results of the analytical calculations are compared with the exact numerical solution of the derived rate equations. The following external stimuli are considered: constant, sinusoidal and shifted sinusoidal fields due to either a spatially uniform thermal gradient or an electrostatic field. The possible applications of the method for extracting energy from the Brownian motion under load and separating molecules of different chiralities on the surface are also discussed.

Effects of the CO2 Guest Molecule on the sI Clathrate Hydrate Structure.

This paper analyzes the structural, energetic and mechanical properties of carbon dioxide hydrate clathrates calculated using finite cluster and periodic ab initio density-functional theory methodologies. Intermolecular interactions are described by the exchange-hole dipole moment method. The stability, gas saturation energetics, guest-host interactions, cage deformations, vibrational frequencies, and equation of state parameters for the low-pressure sI cubic phase of the CO2@H2O clathrate hydrate are presented. Our results reveal that: (i) the gas saturation process energetically favors complete filling; (ii) carbon dioxide molecules prefer to occupy the larger of the two cages in the sI structure; (iii) blue shifts occur in both the symmetric and antisymmetric stretching frequencies of CO2 upon encapsulation; and (iv) free rotation of guest molecules is restricted to a plane parallel to the hexagonal faces of the large cages. In addition, we calculate the librational frequency of the hindered rotation of the guest molecule in the plane perpendicular to the hexagonal faces. Our calculated spectroscopic data can be used as signatures for the detection of clathrate hydrates in planetary environments.

A novel crystalline SiCO compound.

Ab initio evolutionary structural searches have been performed on SixCyO2(x+y) compounds. A novel structure, with SiC2O6 stoichiometry and the P21/c space group is calculated to be stable against decomposition within a wide pressure window from 7.2 to 41 GPa, and metastable under ambient conditions. It consists of CO3 units, linked to SiO6 octahedra, supporting previous experimental studies. The evolution of the carbon environment towards tetrahedral CO4 units, thus resembling the crystal chemistry of silicon, is predicted at higher pressures.

From ELF to compressibility in solids.

Understanding the electronic nature of materials' compressibility has always been a major issue behind tabulation and rationalization of bulk moduli. This is especially because this understanding is one of the main approaches to the design and proposal of new materials with a desired (e.g., ultralow) compressibility. It is well recognized that the softest part of the solid will be the one responsible for its compression at the first place. In chemical terms, this means that the valence will suffer the main consequences of pressurization.It is desirable to understand this response to pressure in terms of the valence properties(charge, volume, etc.). One of the possible approaches is to consider models of electronic separability, such as the bond charge model (BCM), which provides insight into the cohesion of covalent crystals in analogy with the classical ionic model. However, this model relies on empirical parametrization of bond and lone pair properties. In this contribution, we have coupled electron localization function (ELF) ab initio data with the bond charge model developed by Parr in order to analyze solid state compressibility from first principles and moreover, to derive general trends and shed light upon superhard behavior.

[Factors related to refuse antiretroviral therapy in prison]. / Factores relacionados con rehusar el tratamiento antirretroviral en prisión.

INTRODUCTION: Despite the benefits of highly-active antiretroviral therapy (HAART) on morbidity and mortality, some seropositive patients refuse to accept this treatment. Prisons provide easier access to this population. OBJECTIVE: To determine the psychosocial characteristics of prisoners who refuse HAART. METHODS: We performed a cross-sectional study in 580 seropositive prisoners in 3 hospitals in Andalusia (Spain). The dependent variable was being under treatment or refusal to be so. The independent variables were sociodemographic and psychosocial factors related to the prison environment and clinical factors related to health status and drug addiction. A logistic regression analysis was performed to determine which factors were related with refusal to accept HAART. RESULTS: HAART was recommended to 73.1% of seropositive prisoners. This treatment was refused by 23.1% of these prisoners and was accepted by 76.9%. The factors related to refusal to accept HAART were high viral load, worse self-perceived health status, a greater number of stays in prison, and being visited by persons other than relatives. CONCLUSIONS: There is a group of prisoners with specific characteristics that refuse HAART. Specific interventions should be performed in these prisoners to make them aware of the effects of their decision on the course of their disease.

Factores relacionados con rehusar el tratamiento antirretroviral en prisión / Factors related to refuse antiretroviral therapy in prison

Introducción: A pesar de los beneficios sobre la morbilidad y la mortalidad que tiene el tratamiento antirretroviral de gran actividad, hay pacientes seropositivos que rehúsan tomarlo. Las prisiones nos permiten acceder con más facilidad a esta población. Objetivo: Determinar las características psicosociales de los reclusos que rehúsan el tratamiento antirretroviral. Metodología: Estudio transversal realizado a 580 reclusos seropositivos de 3 cárceles andaluzas. Como variable dependiente se estableció estar en tratamiento o rehusarlo. Las variables independientes fueron: sociodemográficas, psicosociales, relacionadas con el medio penitenciario, clínicas, y relacionadas con el estado de salud y con las drogodependencias. Se realizó un análisis de regresión logística para determinar qué factores se relacionaban con rehusar el tratamiento antirretroviral. Resultados: Al 73,1% de los reclusos seropositivos se les recomendaba el tratamiento con antirretrovirales. De éstos, el 23,1% rechazaba tomarlo, mientras el 76,9% lo tomaba. Los factores relacionados con los reclusos que rehusaban el tratamiento antirretroviral fueron una carga viral elevada, una peor salud autopercibida, un mayor número de entradas en la cárcel y ser visitados por personas diferentes a los familiares. Conclusiones: Hay un grupo de reclusos con características propias que rechazan el tratamiento antirretroviral, sobre el que deben realizarse intervenciones específicas encaminadas a que conozcan las consecuencias de su decisión sobre la evolución de su enfermedad (AU)

Introduction: Despite the benefits of highly-active antiretroviral therapy (HAART) on morbidity and mortality, some seropositive patients refuse to accept this treatment. Prisons provide easier access to this population. Objective: To determine the psychosocial characteristics of prisoners who refuse HAART. Methods: We performed a cross-sectional study in 580 seropositive prisoners in 3 hospitals in Andalusia (Spain). The dependent variable was being under treatment or refusal to be so. The independent variables were sociodemographic and psychosocial factors related to the prison environment and clinical factors related to health status and drug addiction. A logistic regression analysis was performed to determine which factors were related with refusal to accept HAART. Results: HAART was recommended to 73.1% of seropositive prisoners. This treatment was refused by 23.1% of these prisoners and was accepted by 76.9%. The factors related to refusal to accept HAART were high viral load, worse self-perceived health status, a greater number of stays in prison, and being visited by persons other than relatives. Conclusions: There is a group of prisoners with specific characteristics that refuse HAART. Specific interventions should be performed in these prisoners to make them aware of the effects of their decision on the course of their disease (AU)

Adherence to antiretroviral treatment in prisons.

The effectiveness of antiretroviral drugs is closely linked to the degree of adherence. The prison environment has specific characteristics that may affect adherence in HIV-positive patients, so that it may not be possible to extrapolate factors associated with nonadherence in HIV+ patients outside prison. The objective was to analyze the prevalence of nonadherence to antiretroviral treatment in three Spanish prisons, and to examine the relation between a large group of factors and nonadherence to the medication. A cross-sectional study of all patients receiving antiretroviral treatment was done. Adherence was evaluated using a validated questionnaire (SMAQ). The prevalence of nonadherence was 54.8%, and the factors independently associated with nonadherence were having difficulties in taking the medication, feeling completely or largely unable to follow the medication, classifying the food as "bad", mentioning not having anyone concerned for them outside prison, suffering anxiety or depression in the last week, and having the flexibility of the prison staff opening their cell in the event of them forgetting their medication.