Photochemical degradation of trypan blue

Purpose To investigate the photochemical degradation of trypan blue (TB) and to identify decomposition products. Methods Defined solution samples of TB and a mixture with lutein/zeaxanthin were exposed to blue light. Thermal degradation processes were ruled out using controls not subjected to irradiation. All samples were analyzed using optical microscopy, UVNis spectroscopy, matrix assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry and nuclear magnetic resonance (NMR) spectrometry. Degradation kinetics were determined based on changes in absorbance; intermediates were identified by analyzing mass differences of characteristic fragment ion peaks within the fragmentation patterns, and assignments were verified by NMR. Results TB demonstrated a photochemical degradation, which can be triggered by lutein/zeaxanthin. Intermediates vary depending on the presence of lutein/zeaxanthin. The self-sensitized photodegradation of TB occurs under generation of dimethyl sulfate and presumed formation of phenol. In contrast, within the presence of lutein/zeaxanthin the decomposition of TB indicates the formation of methoxyamine and sulfonyl arin. Thermal degradation processes were not observed. Conclusions TB demonstrated a photodegradation that may be triggered by lutein/zeaxanthin and results in the formation of cytotoxic decomposition products. Our findings contribute to understand degradation mechanisms of TB and may elucidate previous clinical and experimental observations of cellular toxicity after TB application

Everything But the Merits: Analyzing the Procedural Aspects of the Healthcare Litigation

The role of States as Litigants in the Mandate Litigation Panel featured E. Duncan Getchell, Jr., Solicitor General of Virginia; William F. Brockman, Acting Solicitor General of Maryland; and William P. Marshall, the William Rand Kenan, Jr. Distinguished Professor of Law at the University of North Carolina School of Law. The Defining the Scope and Legal Effect of the Challenges to the Individual Mandate Panel featured Edward A. Hartnett, Richard J. Hughes Professor at the Seton Hall University School of Law; Tobias A. Dorsey, Special Counsel for the United States Sentencing Commission (USSC); and Kevin C. Walsh, Assistant Professor of Law at the University of Richmond School of Law The Situating the Mandate Litigation in the Broader Regulatory and Political Landscape Panel featured Bradley W. Joondeph, Santa Clara University School of Law, Creator of the ACA litigation blog; A. Christopher Bryant, Professor of Law at the University of Cincinnati College of Law; and Elizabeth Weeks Leonard, Associate Professor of Law at the University of Georgia Law School

The Range and Shielding of Dipole-Dipole Interactions in Phospholipid Bilayers

In molecular dynamics simulations of lipid bilayers, the structure is sensitive to the precise treatment of electrostatics. The dipole-dipole interactions between headgroup dipoles are not long-ranged, but the area per lipid and, through it, other properties of the bilayer are very sensitive to the detailed balance between the perpendicular and in-plane components of the headgroup dipoles. This is affected by the detailed properties of the cutoff scheme or if long-range interactions are included by Ewald or particle-mesh Ewald techniques. Interaction between the in-plane components of the headgroup dipoles is attractive and decays as the inverse sixth power of distance. The interaction is screened by the square of a dielectric permittivity close to the value for water. Interaction between the components perpendicular to the membrane plane is repulsive and decays as the inverse third power of distance. These interactions are screened by a dielectric permittivity of the order 10. Thus, despite the perpendicular components being much smaller in magnitude than the in-plane components, they will dominate the interaction energies at large distances