Phase Transition, Dielectric Properties, and Ionic Transport in the [(CH3)2NH2]PbI3 Organic-Inorganic Hybrid with 2H-Hexagonal Perovskite Structure.

In this work, we focus on [(CH3)2NH2]PbI3, a member of the [AmineH]PbI3 series of hybrid organic-inorganic compounds, reporting a very easy mechanosynthesis route for its preparation at room temperature. We report that this [(CH3)2NH2]PbI3 compound with 2H-perovskite structure experiences a first-order transition at ≈250 K from hexagonal symmetry P63/mmc (HT phase) to monoclinic symmetry P21/c (LT phase), which involves two cooperative processes: an off-center shift of the Pb2+ cations and an order-disorder process of the N atoms of the DMA cations. Very interestingly, this compound shows a dielectric anomaly associated with the structural phase transition. Additionally, this compound displays very large values of the dielectric constant at room temperature because of the appearance of a certain conductivity and the activation of extrinsic contributions, as demonstrated by impedance spectroscopy. The large optical band gap displayed by this material (Eg = 2.59 eV) rules out the possibility that the observed conductivity can be electronic and points to ionic conductivity, as confirmed by density functional theory calculations that indicate that the lowest activation energy of 0.68 eV corresponds to the iodine anions, and suggests the most favorable diffusion paths for these anions. The obtained results thus indicate that [(CH3)2NH2]PbI3 is an electronic insulator and an ionic conductor, where the electronic conductivity is disfavored because of the low dimensionality of the [(CH3)2NH2]PbI3 structure.

Liquid self-diffusion of H2O and DMF molecules in Co-MOF-74: molecular dynamics simulations and dielectric spectroscopy studies.

In this work we use molecular dynamics simulations to study the diffusion of N,N-dimethylformamide (DMF) and H2O as a function of temperature within the well-known metal-organic framework Co2(dobdc)·[G] (G = 2DMF·1H2O), also known as Co-MOF-74. The molecular dynamics simulations show that the diffusivity of guest molecules, which is almost negligible at low temperatures (T < 200 K), increases in the range of 200 < T (K) < 400 up to 3 and 4 orders of magnitude for DMF and H2O, respectively. This molecular diffusion can be easily detected by dielectric spectroscopy as it gives rise to extrinsic interfacial polarization effects that result in an apparent "colossal" dielectric constant at room temperature, εr' ∼ 42 000 (T = 300 K, ν = 10 Hz). Furthermore, the measured dielectric constant exhibits a thermal dependence similar to that of the diffusion coefficient, revealing the parallelism of the dielectric response and the molecular diffusion as a function of temperature. These results highlight: (a) the great utility of the fast and non-destructive dielectric and impedance spectroscopy techniques for the study and detection of the molecular transport of small polar molecules within porous metal-organic frameworks and related materials; (b) the peculiarity and uniqueness of MOF materials with "medium" size nanopores containing guest molecules as they are solid materials in which the guest molecules display a liquid state-like behaviour close to room temperature; and

[Pleuropericarditis as the only manifestation of Legionella pneumophila infection]. / Pleuropericarditis como manifestación única de infección por Legionella pneumophila.

Pleural effusion caused by Legionella is seen fairly frequently but is hardly ever of great clinical significance. Pericardial involvement has been described only rarely. We present a case of pleuropericarditis as the only sign of infection by Legionella pneumophila in a 66-years-old man with no prior history of disease. The patient came to the hospital with chest pain suggestive of pleurisy, low-grade fever, dry cough and dyspnea. The etiology was not suspected and the diagnosis was made retrospectively based on indirect immunofluorescence. After 3 weeks of treatment with high dose of erythromycin the patient recovered and remains asymptomatic to date. We conclude that infection by Legionella pneumophila should be suspected in patients with pleurisy or pericarditis of unknown cause.

Low serum levels of alpha-interferon, gamma-interferon, and interleukin-2 in alcoholic cirrhosis.

The existence of cellular immune deficit in alcoholic cirrhosis, together with the role of alpha- and gamma-interferon and interleukin-2 in the immune system, led us to compare serum levels of these immune system mediators in a group of 40 patients with alcoholic cirrhosis classified according to Child-Pugh's grade of severity of liver disease and 23 healthy volunteers. Serum levels of alpha-IFN, gamma-IFN, and IL-2 were significantly depressed in alcoholic cirrhotics, with no significant differences between the different degrees of hepatic damage. The results suggest a profound alteration in the immune system of alcoholic cirrhotics, which may contribute to the development of the disease and the accompanying immune system deficit.

[Zinc in patients with ascites]. / Cinc en pacientes con ascitis.

The concentrations of zinc (Zn) in blood and ascitic fluid (AF) in 48 patients with ascites (alcoholic liver cirrhosis: 32; liver carcinoma associated to cirrhosis: 7; different malignant neoplasias: 9). In addition, total protein, albumin and alpha 2-globulin as well as zinc, were determined in ascitic fluid. There was a decrease of zinc levels in serum, total protein, albumin and alpha 2-globulin in ascitic fluid of cirrhotic patients compared to neoplastic patients. The zinc concentration in ascitic fluid was related to the concentration of total protein, albumin, alpha 2-globulin. There is a parallel correlation between seric zinc and AF zinc.

[The incidence of consumption coagulopathy in liver cirrhosis]. / Incidencia de la coagulopatía de consumo en la cirrosis hepática.

DIC in patients affected by cirrhosis, accompanied by portal hypertension and splenomegaly, has been suspected in the past. The main aim of this study is to ascertain the incidence of this phenomenon. We carried out coagulation and fibrinolytic tests in 113 cirrhotic patients and 20 healthy control persons. We found chronic consumption coagulopathy at analysis level in 28 cases (24.8%) with a decrease of fibrinogen, factor V, kallikrein, platelets, prothrombin complex activity, increase of PDF, partial thromboplastic time and euglobulin lysis. 25 cases had active cirrhosis, with ascites, variceal bleeding and/or hepatic encephalopathy; 3 were non-active cirrhosis. Only 7 patients had clinical DIC. We observed that coagulation disorders increased with more active cirrhosis.

[Beta-endorphin in acute focal cerebral infarct]. / Betaendorfina en el infarto cerebral focal agudo.

Experimental studies in animal models suggest that the endorphin system may be implicated in the pathogenetic mechanism of cerebral ischemic lesions. Naloxone has been shown to possess a beneficial effect on the neurologic deficit associated with cerebral ischemia in animal experiments, probably because of its endorphin antagonist properties. By contrast, the results of clinical trials are contradictory. Moreover, the true significance of high plasma levels of beta-endorphin in patients with acute focal cerebral infarct (AFCI) has not yet been elucidated. We have evaluated 23 patients with established AFCI, in whom plasma levels of beta-endorphin and corticotropin (ACTH) were simultaneously measured during the first 48 hours after the onset of the disease. The results were compared with those from a control group. In a subgroup of 9 cases new measurements were made after 7 days. In the patients with AFCI, significantly lower levels of beta-endorphin and ACTH than in the control group were found. One week later, a moderate nonsignificant increase in the plasma level of beta-endorphin was found. The localization and estimated size of the infarct area were not relevant. Probably, the plasma levels of beta-endorphin will need to be considered before naloxone therapy is indicated, and only if it is confirmed that the plasma levels of beta-endorphin reflect changes at the cerebral level, as the pathophysiological role of these opioids in AFCI has not yet been established.