RESUMO
In this work, to probe the charge transfer mechanism of methylammonium lead triiodide (CH3NH3PbI3), we have used density functional theory (DFT) and time-dependent density functional theory (TDDFT). We investigate ground and excited states optimized geometry, UV-vis spectrum and vibrational frequencies of CH3NH3PbI3 molecule. It is observed that in an excited state, the structural change is mostly localized in PbI3 part of the molecule. Mulliken charge analysis shows that lead (Pb) atom acquires a maximum positive charge and all iodine atoms get a negative charge. In addition to this, all the hydrogen atoms donate their charge to iodine atoms. Therefore, electron transfer from lead (Pb) and hydrogen atoms to the iodine atoms can be considered as a significant charge transfer mechanism. Vibrational frequencies are obtained and assigned with the help of hessian calculations. Vibrational mode at 225 cm-1 is identified as the NH3-I stretching.
RESUMO
The inhibition of transcriptional elongation plays an important role in gene regulation in metazoans, including C. elegans. Here, we combine genomic and biochemical approaches to dissect a role of ZFP-1, the C. elegans AF10 homolog, in transcriptional control. We show that ZFP-1 and its interacting partner DOT-1.1 have a global role in negatively modulating the level of polymerase II (Pol II) transcription on essential widely expressed genes. Moreover, the ZFP-1/DOT-1.1 complex contributes to progressive Pol II pausing on essential genes during development and to rapid Pol II pausing during stress response. The slowing down of Pol II transcription by ZFP-1/DOT-1.1 is associated with an increase in H3K79 methylation and a decrease in H2B monoubiquitination, which promotes transcription. We propose a model wherein the recruitment of ZFP-1/DOT-1.1 and deposition of H3K79 methylation at highly expressed genes initiates a negative feedback mechanism for the modulation of their expression.
