Biochemical and structural characterization of mycobacterial aspartyl-tRNA synthetase AspS, a promising TB drug target.

The human pathogen Mycobacterium tuberculosis is the causative agent of pulmonary tuberculosis (TB), a disease with high worldwide mortality rates. Current treatment programs are under significant threat from multi-drug and extensively-drug resistant strains of M. tuberculosis, and it is essential to identify new inhibitors and their targets. We generated spontaneous resistant mutants in Mycobacterium bovis BCG in the presence of 10× the minimum inhibitory concentration (MIC) of compound 1, a previously identified potent inhibitor of mycobacterial growth in culture. Whole genome sequencing of two resistant mutants revealed in one case a single nucleotide polymorphism in the gene aspS at 535GAC>535AAC (D179N), while in the second mutant a single nucleotide polymorphism was identified upstream of the aspS promoter region. We probed whole cell target engagement by overexpressing either M. bovis BCG aspS or Mycobacterium smegmatis aspS, which resulted in a ten-fold and greater than ten-fold increase, respectively, of the MIC against compound 1. To analyse the impact of inhibitor 1 on M. tuberculosis AspS (Mt-AspS) activity we over-expressed, purified and characterised the kinetics of this enzyme using a robust tRNA-independent assay adapted to a high-throughput screening format. Finally, to aid hit-to-lead optimization, the crystal structure of apo M. smegmatis AspS was determined to a resolution of 2.4 Å

Polarization of line radiation in the presence of external electric quadrupole and uniform magnetic fields: II. Arbitrary orientation of magnetic field

In continuation of our earlier investigation (referred to hereafter as part I) where we considered the mathematically simple case of magnetic field orientation along the Z-axis of the principal axes frame (PAF) of the electric quadrupole field, we take up here the general problem of arbitrary orientation of the magnetic field with respect to the PAF, and investigate the nature of polarized line spectra of an atom making a transition from an upper level with spin Ju to a lower level with spin Jl. Explicit formulae for the emitted Stokes parameters are obtained and we discuss their physical significance by computing numerically the cases of transitions Ju=1→Jl=0 and Ju=32→Jl=12. Specific features or signatures of the polarized line spectra are discussed as functions of the relevant physical parameters. The Stokes parameters are also analyzed in terms of the Zeeman term contributions and the cross-term contributions (which arise due to quantum interference)

Polarization of line radiation in the presence of external electric quadrupole and uniform magnetic fields: II. Arbitrary orientation of magnetic field

In continuation of our earlier investigation (referred to hereafter as part I) where we considered the mathematically simple case of magnetic field orientation along the Z-axis of the principal axes frame (PAF) of the electric quadrupole field, we take up here the general problem of arbitrary orientation of the magnetic field with respect to the PAF, and investigate the nature of polarized line spectra of an atom making a transition from an upper level with spin Ju to a lower level with spin Jl. Explicit formulae for the emitted Stokes parameters are obtained and we discuss their physical significance by computing numerically the cases of transitions Ju=1→Jl=0 and Ju=32→Jl=12. Specific features or signatures of the polarized line spectra are discussed as functions of the relevant physical parameters. The Stokes parameters are also analyzed in terms of the Zeeman term contributions and the cross-term contributions (which arise due to quantum interference)

A Review on the Classifications of Organic/Inorganic/Carbonaceous Hole Transporting Materials for Perovskite Solar Cell Application

The rapid increase in the efficiency of perovskite solar cells (PSCs) in last few decades have made them very attractive to the photovoltaic (PV) community. However, the serious challenge is related to the stability under various conditions and toxicity issues. A huge number of articles have been published in PSCs in the recent years focusing these issues by employing different strategies in the synthesis of electron transport layer (ETL), active perovskite layer, hole transport layer (HTL) and back contact counter electrodes. This article tends to focus on the role and classification of different materials used as HTL in influencing long-term stability, in improving the photovoltaic parameters and thereby enhancing the device efficiency. Hole Transport Materials (HTMs) are categorized by dividing into three primary types, namely; organic, inorganic and carbonaceous HTMs. To analyze the role of HTM in detail, we further divide these primary type of HTMs into different subgroups. The organic-based HTMs are subdivided into three categories, namely; long polymer HTMs, small molecule HTMs and cross-linked polymers and the inorganic HTMs have been classified into nickel (Ni) derivatives and copper (Cu) derivatives based HTMs, p-type semiconductor based HTMs and transition metal based HTMs. We further analyze the dual role of carbonaceous materials as HTM and counter electrode in the perovskite devices. In addition, in this review, an overview of the preparation methods, and the influence of the thickness of the HTM layers on the performance and stability of the perovskite devices are also provided. We have carried out a detailed comparison about the various classification of HTMs based on their cost-effectiveness and considering their role on effective device performance. This review further discusses the critical challenges involved in the synthesis and device engineering of HTMs. This will provide the reader a better insight into the state of the art of perovskite solar devices