X-Ray Characterization of Ag Impurities in Na_1-xAg_xCl

Abstract

The alkali halide Na1-xAgxCl, with two different compositions (x = 0.03 and 0.10), was studied with regard to the Ag impurities in terms of the bonding and electron density distribution. X-ray single crystal data sets have been used for the purpose. The present analysis focused on the electron density distribution and hence the interaction between the atoms is clearly revealed by maximum entropy method (MEM) and multipole analyses. The bonding in these systems has been studied using two-dimensional MEM electron density maps on the (100) and (110) planes and onedimensional electron density profiles along the [100], [110] and [111] directions. The mid-bond electron densities between atoms in these systems are found to be 0.175 e/Å3 and 0.183 e/Å3, respectively, for Na0.97Ag0.03Cl and Na0.90Ag0.10Cl. Multipole analysis of the structure has been performed for these two systems, with respect to the expansion/contraction of the ion involved.

Structure and Function in Antimicrobial Piscidins: Histidine Position, Directionality of Membrane Insertion, and pH-Dependent Permeabilization

“…Compared to histidine, they have longer sidechains with delineated hydrophobic and charged regions, allowing them to snorkel to stabilize a deep insertion. 93 Several histidine-containing synthetic peptides that interact with membranes have been investigated under varying pH conditions, yielding results consistent with ours. For instance, Bechinger and colleagues designed histidine-rich cell-penetrating "LAH4" peptide analogs and used solution and solid-state NMR to show that pH is a key regulator of their membrane orientations.…”

“…92 Furthermore, neutral bulky aromatic sidechains can readily intercalate between the acyl chains of the lipids, resulting in enhanced membrane disruption. [93][94] Within a membrane environment, the neutral state of histidine could be achieved through proton transfer between the histidine sidechains and lipid headgroups. 95 Even with neutral histidines, piscidin remains cationic due to multiple arginine and lysine residues.…”