Determination of ICH-Q3D Elemental Impurity Leachables in Glass Vials by Inductively Coupled Plasma Mass Spectrometry.

Container closure systems that are used for packaging pharmaceutical products are required to satisfy numerous safety requirements. Maximum permitted limits on the concentrations of numerous toxic elemental impurities that potentially leach from the packaging are one such requirement. The implementation of ICH-Q3D Guideline for Elemental Impurities, in conjunction with the 2018 publication of USP <232> Elemental Impurities-Limits and USP <233> Elemental Impurities-Procedures, requires a critical risk assessment of all container closure systems to evaluate their contribution of certain elemental impurities to the enclosed drug product. ICH-Q3D has established limits for each specific elemental impurity that considers relevant toxicological data and administration route (oral, parenteral, or inhalation) and presents them as permitted daily exposures based on the maximum daily dosage of the final drug product. A study was undertaken to assess the degree of elemental impurity leaching from one type of pharmaceutical glass vial under specific, fixed environmental controls. Multiple buffer systems representing a broad spectrum of possible parenteral drug product formulations were used in the study. Resulting buffer solutions that had been in contact with a single type of glass vial under specific conditions were subsequently analyzed using an inductively coupled plasma mass spectrometry (ICP-MS) method developed and validated specifically for the purpose of quantifying elemental impurity leachables in a variety of parenteral formulations. Results indicated that the degree of elemental impurity leachables imparted by the specific type of glass vial evaluated during this study posed no risk to patient safety, regardless of the drug product buffer formulation. Following this evaluation, the ICP-MS method developed for the determination of elemental impurities leachables has been successfully applied to the assessment of elemental impurities in a number of different biological parenteral drug product formulations currently under development. These data can be leveraged for inclusion in elemental impurities component ICH-Q3D risk assessments to satisfy the container closure system contribution.

Revealing Conformational Variants of Solution-Phase Intrinsically Disordered Tau Protein at the Single-Molecule Level.

Intrinsically disordered proteins, such as tau protein, adopt a variety of conformations in solution, complicating solution-phase structural studies. We employed an anti-Brownian electrokinetic (ABEL) trap to prolong measurements of single tau proteins in solution. Once trapped, we recorded the fluorescence anisotropy to investigate the diversity of conformations sampled by the single molecules. A distribution of anisotropy values obtained from trapped tau protein is conspicuously bimodal while those obtained by trapping a globular protein or individual fluorophores are not. Time-resolved fluorescence anisotropy measurements were used to provide an explanation of the bimodal distribution as originating from a shift in the compaction of the two different families of conformations.

Tracking Lithium Ions via Widefield Fluorescence Microscopy for Battery Diagnostics.

Direct tracking of lithium ions with time and spatial resolution can provide an important diagnostic tool for understanding mechanisms in lithium ion batteries. A fluorescent indicator of lithium ions, 2-(2-hydroxyphenyl)naphthoxazole, was synthesized and used for real-time tracking of lithium ions via widefield fluorescence microscopy. The fluorophore can be excited with visible light and was shown to enable quantitative determination of the lithium ion diffusion constant in a microfluidic model system for a plasticized polymer electrolyte lithium battery. The use of widefield fluorescence microscopy for in situ tracking of lithium ions in batteries is discussed.

Allosteric tertiary interactions preorganize the c-di-GMP riboswitch and accelerate ligand binding.

Cyclic diguanylate (c-di-GMP) is a bacterial second messenger important for physiologic adaptation and virulence. Class-I c-di-GMP riboswitches are phylogenetically widespread and thought to mediate pleiotropic genetic responses to the second messenger. Previous studies suggest that the RNA aptamer domain switches from an extended free state to a compact, c-di-GMP-bound conformation in which two helical stacks dock side-by-side. Single molecule fluorescence resonance energy transfer (smFRET) experiments now reveal that the free RNA exists in four distinct populations that differ in dynamics in the extended and docked conformations. In the presence of c-di-GMP and Mg(2+), a stably docked population (>30 min) becomes predominant. smFRET mutant analysis demonstrates that tertiary interactions distal to the c-di-GMP binding site strongly modulate the RNA population structure, even in the absence of c-di-GMP. These allosteric interactions accelerate ligand recognition by preorganizing the RNA, favoring rapid c-di-GMP binding.