Search

Total reflection X-ray fluorescence (TXRF) spectroscopy has seen remarkable progress over the past years. Numerous applications in basic and applied sciences prove its importance. The large spectral background, which is a major detrimental factor in the conventional X-ray fluorescence technique, limits the element detection sensitivities of the technique to the µg g-1 (ppm) range. This spectral background is reduced to a great extent in the TXRF technique due to the low extinction depth of the primary incident X-ray beam. In synchrotron radiation (SR) based TXRF measurements the spectral background is reduced further because of the polarization of the synchrotron X-ray beam. Here, we show in detail the influence of synchrotron polarization on the spectral background in a fluorescence spectrum and its significance towards TXRF detection sensitivities. We have performed TXRF measurements on standard reference materials to show that one obtains approximately one order of magnitude enhancement in the spectral signal strength by utilizing the anisotropic nature of the scattered synchrotron radiation in the horizontal detection geometry. [ABSTRACT FROM AUTHOR]

Violacein is a naturally found pigment that is used by some gram negative bacteria to defend themselves from various gram positive bacteria. As a result, this molecule has caught attention for its potential biomedical applications and has already shown promising outcomes as an antiviral, an antibacterial, and an anti-tumor agent. Understanding the interaction of this molecule with a cellular membrane is an essential step to extend its use in the pharmaceutical paradigm. Here, the interaction of violacein with a lipid monolayer formed at the air–water interface is found to depend on electrostatic nature of lipids. In presence of violacein, the two dimensional (2D) pressure–area isotherms of lipids have exhibited changes in their phase transition pressure and in-plane elasticity. To gain insights into the out-of-plane structural organization of lipids in a membrane, X-ray reflectivity (XRR) study on a solid supported lipid monolayer on a hydrophilic substrate has been performed. It has revealed that the increase in membrane thickness is more pronounced in the zwitterionic and positively charged lipids compared to the negatively charged one. Further, the lipid molecules are observed to decrease their tilt angle made with the normal of lipid membrane along with an alteration in their in-plane ordering. This has been quantified by grazing incidence X-ray diffraction (GIXD) experiments on the multilayer membrane formed in an environment with controlled humidity. The structural reorganization of lipid molecules in presence of violacein can be utilized to provide a detailed mechanism of the interaction of this molecule with cellular membrane. [Display omitted] • Interaction of violacein with cellular membrane may control its activities. • Violacein can condense the in-plane organization of lipids in a cellular membrane. • Tilt angle of lipids in membranes changes due to the condensing effect of violacein. • Lipid membrane thickness increases as violacein penetrates into the membrane. [ABSTRACT FROM AUTHOR]