Electronic and electrocatalytic properties of PbTiO3: unveiling the effect of strain and oxygen vacancy.

First-principles calculations based on density-functional theory have been used to investigate the effect of biaxial strain and oxygen vacancy on the electronic, photocatalytic, and electrocatalytic properties of PbTiO3 oxide. Our results show that PbTiO3 has a high exciton binding energy and a band gap that can be easily moderated with different strain regimes. From a reactivity viewpoint, the highly exothermic adsorption of hydrogen atoms in both pristine and strained PbTiO3 structures does not make it a potential electrocatalyst for the hydrogen evolution reaction. Fortunately, the presence of oxygen vacancies on the PbTiO3 surface induces moderate adsorption energies, making the reduced PbTiO3 suitable for hydrogen evolution reaction processes.

The role of polymers in cross-kingdom bioadhesion.

The secretion of extracellular polymeric substances provides an evolutionary advantage found in many organisms that can adhere to surfaces and cover themselves in a protective matrix. This ability is found in prokaryotes, archaea and eukaryotes, all of which use functionally similar polysaccharides, proteins and nucleic acids to form extracellular matrices, mucus and bioadhesive substances. These macromolecules have been investigated from the perspective of polymer biophysics, and theories to help understand adhesion, viscosity and gelling have been developed. These properties can be measured experimentally using straightforward methods such as cell counting as well as more advanced techniques such as atomic force microscopy and rheometry. An integrated understanding of the properties and uses of adhesive macromolecules across kingdoms is also important and can provide the basis for a range of biotechnological and medical applications. This article is part of the theme issue 'Transdisciplinary approaches to the study of adhesion and adhesives in biological systems'.

Computer simulations of 3C-SiC under hydrostatic and non-hydrostatic stresses.

The response of 3C-SiC to hydrostatic pressure and to several uni- and bi-axial stress conditions is thoroughly investigated using first principles calculations. A topological interpretation of the chemical bonding reveals that the so-called non-covalent interactions enhance only at high pressure while the nature of the covalent Si-C bonding network keeps essentially with the same pattern. The calculated low compressibility agrees well with experimental values and is in concordance with the high structural stability of this polymorph under hydrostatic pressure. Under uniaxial [001] stress, the c/a ratio shows a noticeable drop inducing a closure of the band gap and the emergence of a metallic state around 40 GPa. This behavior correlates with a plateau of the electron localization function exhibiting a roughly constant and non-negligible value surrounding CSi4 and SiC4 covalent bonded units.

First-principles calculations and electron density topological analysis of covellite (CuS).

Covellite (CuS) is an important mineral sulfide that can be used in many technological applications. It has a simple formula but a complex structure consisting of alternating layers of planar CuS3 triangles and CuS4 tetrahedrons with S-S bonds. Accurate first-principles calculations are performed for covellite structure (CuS), aiming to provide insights about its structural, mechanical and electronic properties and to unveil the nature of its chemical bonding. DFT and DFT+U methods have been used and showed to be sensitive to the correlation treatment (U value). Although it is not possible to extract a universal value of the U, this study indicates that U = 5 eV is an adequate value. The electronic structure analysis shows a significant metallic character due to p(S)-d(Cu) orbital interactions up to Fermi level. The projected density of states indicates that most of the contribution comes from the atomic orbitals in the [001] plane of the covellite, explaining the conductivity anisotropy observed experimentally. Topological analysis of the electron density was performed by means of quantum theory of atoms in molecules (QTAIM). Two different topological charges in Cu and S were calculated, confirming an ionic model with mix-charges. This mineral presents ionic degree of ∼ 32%. On the basis of the QTAIM analysis, the covalent character of S-S bond is confirmed, and the favored cleavage of CuS at the [001] surface might be at the Cu-S bond. The S atoms occupy most of the cell volume, and their contributions dominate the crystal compressibility: κ(S) ≈ κ(CuS).

Structural phase transitions on AgCuS stromeyerite mineral under compression.

The structural behavior of mineral Stromeyerite, AgCuS, has been studied by means of angle-dispersive X-ray diffraction measurements up to 13 GPa and ab initio total-energy calculations. Two high-pressure phase transitions are found at 1.4 and 5.7 GPa, from the initial distorted Ni(2)In-type phase (AuRbS-type, RP, space group Cmc2(1)) through an anti-PbClF-type phase (HP1, space group P4/nmm) to a monoclinic distortion of this latter phase (HP2, space group P2(1)/m). The collapse of the metal-metal interatomic distances at the RP-HP1 transition suggests a stronger metallic behavior of the high-pressure phase. The compressibility of the lattice parameters and the equation of state of the first pressure-induced phase have been experimentally determined. First-principles calculations present an overall agreement with the experimental results in terms of the high-pressure sequence and provide chemical insight into the AgCuS behavior under hydrostatic pressure.

DFT+U calculations of crystal lattice, electronic structure, and phase stability under pressure of TiO2 polymorphs.

This work investigates crystal lattice, electronic structure, relative stability, and high pressure behavior of TiO(2) polymorphs (anatase, rutile, and columbite) using the density functional theory (DFT) improved by an on-site Coulomb self-interaction potential (DFT+U). For the latter the effect of the U parameter value (0 < U < 10 eV) is analyzed within the local density approximation (LDA+U) and the generalized gradient approximation (GGA+U). Results are compared to those of conventional DFT and Heyd-Scuseria-Ernzehorf screened hybrid functional (HSE06). For the investigation of the individual polymorphs (crystal and electronic structures), the GGA+U/LDA+U method and the HSE06 functional are in better agreement with experiments compared to the conventional GGA or LDA. Within the DFT+U the reproduction of the experimental band-gap of rutile/anatase is achieved with a U value of 10/8 eV, whereas a better description of the crystal and electronic structures is obtained for U < 5 eV. Conventional GGA∕LDA and HSE06 fail to reproduce phase stability at ambient pressure, rendering the anatase form lower in energy than the rutile phase. The LDA+U excessively stabilizes the columbite form. The GGA+U method corrects these deficiencies; U values between 5 and 8 eV are required to get an energetic sequence consistent with experiments (E(rutile) < E(anatase) < E(columbite)). The computed phase stability under pressure within the GGA+U is also consistent with experimental results. The best agreement between experimental and computed transition pressures is reached for U ≈ 5 eV.

[Dispositional optimism in patients on chronic haemodialysis and its possible influence on their clinical course]. / Optimismo disposicional en pacientes en hemodiálisis y su influencia en el curso de la enfermedad.

INTRODUCTION: Dispositional optimism is a personality trait significantly associated with the use of positive adaptive coping strategies as well as with perceived psychological and physical well-being, and it appears to be an important predictor of illness. OBJECTIVES: To analyse if dispositional optimism is significantly associated with the number of hospital admissions of our chronic haemodialysis patients, as well as its relationship with perceived state of health. METHODS: We studied 239 patients on chronic haemodialysis. Patients were categorised into two groups according to the variables: hospital admissions/no. of admissions in the last year and dispositional optimism (DO). We used the following variables and questionnaires: 1) Dispositional O/P using the Spanish-validated cross-cultural adaptation of the revised version of the Life Orientation Test (LOT-R) (Scheier, 1994): higher scores mean a higher degree of dispositional optimism. 2) Health-related quality of life (HRQoL) using the different aspects of the COOP/WONCA (CW) charts and its total score. In this case higher scores mean lower HRQoL. 3) Modified Charlson Comorbidity Index (mCCI). 4) Age, gender, and time on dialysis. RESULTS: Mean age was 64.8 ± 14.3 years; median time on dialysis 2.9 years (range: 0-32); and median LOT-R 21 (range 6-30). Patients considered DO had a lower risk of hospital admissions than pessimists (DP) (OR: 0.55; IC 95%: 0.32-0.94; P<.05). PD Patients that were admitted in the last year showed a significantly lower score on LOT-R (they were more pessimistic) than those that had no hospital admissions (19.4 ± 5.7 vs 22.3 ± 4.6; P=.001). We found no significant differences between admitted and not admitted patients in age, gender, time on haemodialysis and comorbidity. Admitted patients showed worse HRQoL (higher scores in total CW) than those that were not (Total CW: 22.37 vs 19.42; P<.001). PD patients had significantly higher scores than OD patients in all COOP-WONCA aspects except in aspect 1 (physical fitness) and 5 (change in health). CONCLUSIONS: Pessimistic personality trait is significantly associated with hospital admissions in chronic haemodialysis patients, regardless of age, gender and comorbidity. Optimistic patients perceived a better state of health.

[Strongyloides stercoralis infection in renal transplant recipients]. / Infección por Strongyloides stercoralis en pacientes trasplantados renales.

We present two cases of strongyloides stercoralis infection in renal transplant recipients in our centre. We describe clinical presentation characteristics, treatment and resolution.

[Analysis of variability in determining intact parathyroid hormone (iPTH) according to the method used to process the sample]. / Análisis de la variabilidad en la determinación de la hormona paratiroidea (PTH-i) según el método empleado para procesar la muestra.

BACKGROUND: The measurement of i-PTH circulating is not easy due to its analytical variablity. Variability that appears in the process that goes from the sample collection to the final result determination. There are several important aspects that can influence within the pre-test variability: type of sample (serum o plasma), temperature, time elapses from blood extraction to freezing and from freezing to i-PTH quantification. Blood coming from centres far from our laboratory do not always meet the required processing conditions. Our aim was to study the stability of i-PTH with varying conditions of temperature and time until freezing in patients with chronic kidney disease (CKD). METHODS: We have analyzed 294 blood samples of 49 patients with chronic kidney disease (18 transplantated patients (36.7%) and 31 patients in haemodyalisis (63.3%)). The blood samples were collected using tubes treated with ethylenediaminotetraacetic acid (EDTA); these samples were subjected to different conditions of temperature and time before they were frozen, constituting 6 groups: blood centrifuged and plasma immediately frozen (group A or reference group); blood maintained 1 hour at room temperature and plasma stored at 2-8 masculineC during 0, 8 and 24 hours (groups B,C,D); blood maintained 3 hours at room temperature and plasma stored at 2-8 masculineC during 0 and 8 hours (groups E,F). The intact PTH (i-PTH) was measured using the immunoradiometric assay (IRMA Total Intact Scantibodies assay). We have analyzed the differences between the PTH-i mean values in the referenced groud and the others. We have applied the tests of homogeneity variance and normality and we have perform a comparation by pairs with the t-test including the Bonferroni correction. RESULTS: The mean value of intact-PTH in the referente Group was 202.5+/-199.72 pg/ml. The means values of intact-PTH in the other groups were 196 +/- 203.23 pg/ml, 202.8 +/- 200.2 pg/ml, 200.06 +/- 194.87 pg/ml, 204.08 +/- 204.073 pg/ml, 197.94 +/- 182.31 pg/ml. The results were practically identical for each group. We did not find important differences with respect to the reference group (p = 0.87, p = 0,99, p = 0,95, p = 0,96, p = 0,90 when comparing with groups 2a, 2b, 2c, 3a y 3b). CONCLUSIONS: The use of EDTA maintain the PTH stability during a longer period without the necessity of freezing the samples immediately. These results can help to state strategies to management the samples in patients with ERC.

Induction treatment with low-dose thymoglobulin or basiliximab in renal transplants from older donors.

Transplantation of kidneys from older donors is followed by an increase in delayed graft function (DGF) and acute rejection episodes (ARE). In these circumstances, induction treatment, whether with antithymocyte globulin or with interleukin-2 receptor blockers, may delay the introduction of calcineurin inhibitors (CNI) with effective prevention of ARE. We examined the efficacy and safety of induction treatment with 2 low doses of thymoglobulin compared with 2 doses of basiliximab. A group of 27 patients were treated with thymoglobulin and another 36 with basiliximab. CNI introduction was delayed until day 3 posttransplantation. The thymoglobulin group received 2 doses of 1.25 mg/kg on alternate days and the basiliximab group 2 doses of 20 mg. A trend to a lower incidence of DGF was observed in the thymoglobulin group (33% vs 55.6%; P = .08), with lower levels of serum creatinine on days 7 (P = .02) and 14 (P = .02) posttransplantation. No patient in the thymoglobulin group experienced ARE, but 11 patients (30.6%) in the basiliximab group did (P < .001), and 5 needed rescue treatment with thymoglobulin. We found no differences in the incidence of cytomegalovirus (CMV) disease (P = .945), admission due to infections (P = .274), or neoplasia (P = .340), or differences in graft (P = .69) and patient (P = .21) survivals at 1 and 3 years. Low-dose thymoglobulin was more effective at preventing DGF and ARE in renal transplant recipients of organs from older donors, with no differences in infectious complications or graft and patient survivals.

[Pharmacokinetic variations in anticonvulsants in Mexican epileptic women during different stages of the postpartum period]. / Variaciones farmacocinéticas de anticonvulsivantes en mujeres epilépticas mexicanas durante las diferentes etapas del postparto.

During pregnancy, there are several physiological changes that influence the kinetics of medication administrated during this time. These physiological changes are not reestablished immediately during delivery; so, its concentration in biologic fluids is different when is administered immediately after delivery, than several weeks after. The purpose in this work was to identify the changes of pharmacocinetics constants for fenitoin and carbamacepine, in epileptic patients. When the same dose is maintained, during different times of postpartum. In 20 Mexican epileptic women, the plasma and milk concentrations of fenitoina during 60 day postpartum and in 14 carbamacepine was determined. In all the patients pharmakocinetics of anticonvulsivant, in each study period (5, 15, 30, 45 y 60 days postpartum). Excretion index of maternal milk was determined. Maximal plasmatic concentration of fentoine had no variation; however, carbamacepine was higher during the late period. There were no differences in the areas under curve and life all the middle of elimination and in excretion index.

Variaciones farmacocinéticas de anticonvulsivantes en mujeres epilépticas mexicanas durante las diferentes etapas del postparto / Pharmakocinetic variation of anticonvulsants in Mexican epileptic women during different parts of puerperium

Durante el embarazo existen una serie de cambios fisiológicos que influyen en la cinética de los medicamentos administrativos durante esta etapa: Estos cambios fisiológicos no se restauran inmediatamente en el parto, de tal manera que su concentración en los fluidos biológicos es diferente cuando se administra inmediatamente después del parto que varias semanas posterior al mismo. El presente trabajo tiene como propósito identificar los cambios en las constantes farmacocinéticas de fenitoína y carbamacepina, en pacientes epilépticas cuando se mantiene una misma dosis durante diferentes etapas del postparto. En 20 mujeres mexicanas epilépticas se determinó la concentración en plasma y leche de fenitoína durante 60 días postparto y en 14 se determinó carbamacepina. A todas las pacientes se les realizó la farmacocinética de los anticonvulsivantes en cada periodo de estudio (5, 15, 30, 45 y 60 días posparto) y se determinó el índice de excreción en leche materna. Las concentraciones plasmáticas de fenitoína no presentaron variaciones, sin embargo la carbanacepina fue más alta en el periodo tardió, también se observaron diferencias en las áreas bajo la curva y vida media de eliminación y en los índices de excreción