RESUMO
We find significant differences between degradation and healing at the surface or in the bulk for each of the different APbBr3 single crystals (A = CH3NH3+, methylammonium (MA); HC(NH2)2+, formamidinium (FA); and cesium, Cs+). Using 1- and 2-photon microscopy and photobleaching we conclude that kinetics dominate the surface and thermodynamics the bulk stability. Fluorescence-lifetime imaging microscopy, as well as results from several other methods, relate the (damaged) state of the halide perovskite (HaP) after photobleaching to its modified optical and electronic properties. The A cation type strongly influences both the kinetics and the thermodynamics of recovery and degradation: FA heals best the bulk material with faster self-healing; Cs+ protects the surface best, being the least volatile of the A cations and possibly through O-passivation; MA passivates defects via methylamine from photo-dissociation, which binds to Pb2+. DFT simulations provide insight into the passivating role of MA, and also indicate the importance of the Br3- defect as well as predicts its stability. The occurrence and rate of self-healing are suggested to explain the low effective defect density in the HaPs and through this, their excellent performance. These results rationalize the use of mixed A-cation materials for optimizing both solar cell stability and overall performance of HaP-based devices, and provide a basis for designing new HaP variants.
RESUMO
Anemia is a major clinical symptom of a wide variety of pathological conditions a common related to reduced erythropoiesis. Whereas erythropoietin treatment showed an improvement in the patients' condition, it revealed increased risks of thromboembolic and cardiovascular events. Herein we describe stimulation of erythropoiesis by the multifunctional 1-(butyryloxy)ethyl-5-amino-4-oxopentanoate, (AlaAcBu), a 5-aminolevulinic-acid (ALA) derivative, which undergoes metabolic hydrolysis yielding two erythroid differentiation inducers, ALA and butyric acid (BA), each acting through a different mechanism. ALA, the first precursor in the heme biosynthesis, accelerates heme synthesis and BA, a histone deacetylase inhibitor (HDACI) that activates the transcription of globin mRNA. Our results show that the AlaAcBu mutual prodrug is a potent chemical differentiation inducer of K562 human erythroleukemia cells manifested by augmentation of heme and globin synthesis and assembly of hemoglobin. Exposure of K-562 cells to AlaAcBu resulted in an increase in heme synthesis and globin expression. Stimulation of the heme pathway was evident by the over-expression of porphobilinogen deaminase (PBGD) and ferrochelatase. AlaAcBu promoted cellular erythroid differentiation depicted by the expression of the marker glycophorin A and cellular maturation characterized by cytoplasm hemoglobinization, polar arrangement of mitochondria and a developed central vacuolar system preceding nuclear extrusion. The ability of AlaAcBu to promote differentiation along the erythroid lineage and to dramatically induce hemoglobin synthesis presented in this report.
Assuntos
Ácido Aminolevulínico/análogos & derivados , Ácido Aminolevulínico/farmacologia , Diferenciação Celular/efeitos dos fármacos , Células Eritroides/efeitos dos fármacos , Células Eritroides/patologia , Leucemia Eritroblástica Aguda/patologia , Ácidos Levulínicos/farmacologia , Ácido Aminolevulínico/metabolismo , Ácido Butírico/metabolismo , Proliferação de Células/efeitos dos fármacos , Eritropoese/efeitos dos fármacos , Eritropoese/genética , Eritropoetina/genética , Eritropoetina/metabolismo , Ferroquelatase/genética , Ferroquelatase/metabolismo , Glicoforinas/genética , Glicoforinas/metabolismo , Heme/biossíntese , Heme/metabolismo , Hemoglobinas/biossíntese , Hemoglobinas/metabolismo , Humanos , Hidrólise/efeitos dos fármacos , Hidroximetilbilano Sintase/genética , Hidroximetilbilano Sintase/metabolismo , Células K562 , Leucemia Eritroblástica Aguda/tratamento farmacológico , Leucemia Eritroblástica Aguda/genética , Leucemia Eritroblástica Aguda/metabolismo , Pró-Fármacos/farmacologia , RNA Mensageiro/genética , alfa-Globinas/biossíntese , alfa-Globinas/genética , alfa-Globinas/metabolismoAssuntos
Absenteísmo , Sistemas Homem-Máquina , Hostilidade , Humanos , Masculino , Moral , Alienação SocialRESUMO
The prevalence of epilepsy among children in the third grade in Multnomah County, Oregon, was investigated by use of a questionnaire similar to that used by Rose et al. (1973). Of the 7,039 potential respondents, 5,317 (75.5%) responded to the questionnaire. A stratified random sample of 161 children was drawn from the respondents, and of these 129 (80%) underwent physical and EEG examinations. This replication of the study by Rose et al. (1973) yielded prevalence estimates which were somewhat lower than those reported by Rose et al. for Washington County, Maryland. Our findings suggest that the questionnaire method of estimating the prevalence of epilepsy has promise; further investigation of the method is in progress.