The timescale of spinodal dewetting at a polymer/polymer interface

We investigate the dynamics of spinodal dewetting in liquid-liquid polymer systems. Dewetting of poly(methyl-methacrylate) (PMMA) thin films on polystyrene (PS) “substrates” is followed in situ using neutron reflectivity. By following the development of roughness at the PS/PMMA interface and the PMMA surface we extract characteristic growth times for the dewetting process. These characteristic growth times are measured as a function of the molecular weight of the two polymers. By also carrying out experiments in the regime where the dynamics are independent of the PS molecular weight, we are able to use dewetting to probe the scaling of the PMMA thin film viscosity with temperature and molecular weight. We find that this scaling reflects bulk behaviour. However, absolute values are low compared to bulk viscosities, which we suggest may be due in part to slippage at the polymer/polymer interface. Received 25 June 2001 and Received in final form 5 December 2001     

A novel 14C-postlabeling assay using accelerator mass spectrometry for the detection of O6-methyldeoxy-guanosine adducts

Accelerator mass spectrometry (AMS) is currently one of the most sensitive methods available for the trace detection of DNA adducts and is particularly valuable for measuring adducts in humans or animal models. However, the standard approach requires administration of a radiolabeled compound. As an alternative, we have developed a preliminary 14C-postlabeling assay for detection of the highly mutagenic O6-methyldeoxyguanosine (O6-MedG), by AMS. Procedures were developed for derivatising O6-MedG using unlabeled acetic anhydride. Using conventional liquid chromatography/mass spectrometry (LC/MS) analysis, the limit of detection (LOD) for the major product, triacetylated O6-MedG, was 10 fmol. On reaction of O6-MedG with 14C-acetic anhydride, using a specially designed enclosed system, the predominant product was 14C-di-acetyl O6-MedG. This change in reaction profile was due to a modification of the reaction procedure, introduced as a necessary safety precaution. The LOD for 14C-di-acetyl O6-MedG by AMS was determined as 79 amol, approximately 18,000-fold lower than that achievable by liquid scintillation counting (LSC). Although the assay has so far only been carried out with labeled standards, the degree of sensitivity obtained illustrates the potential of this assay for measuring O6-MedG levels in humans.     

ESI‐MS/MS of expanded porphyrins: a look into their structure and aromaticity

Electrospray mass spectrometry/mass spectrometry was used to investigate the gas‐phase properties of protonated expanded porphyrins, in order to correlate those with their structure and conformation. We have selected five expanded meso‐pentafluorophenyl porphyrins, respectively, a pair of oxidized/reduced fused pentaphyrins (22 and 24 π electrons), a pair of oxidized/reduced regular hexaphyrins (26 and 28 π electrons) and a regular doubly N‐fused hexaphyrin (28 π electrons). The gas‐phase behavior of the protonated species of oxidized and reduced expanded porphyrins is different. The oxidized species (aromatic Hückel systems) fragment more extensively, mainly by the loss of two HF molecules. The reduced species (Möbius aromatic or Möbius‐like aromatic systems) fragment less than their oxidized counterparts because of their increased flexibility. The protonated regular doubly fused hexaphyrin (non‐aromatic Hückel system) shows the least fragmentation even at higher collision energies. In general, cyclization through losses of HF molecules decreases from the aromatic Hückel systems to Möbius aromatic or Möbius‐like aromatic systems to non‐aromatic Hückel systems and is related to an increase in conformational distortion. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis, photophysical, photochemical, and redox properties of nitrospiropyrans substituted with Ru or Os tris(bipyridine) complexes

Photochromic nitrospiropyrans substituted with 2,2'-bipyridine (bpy), [Ru(bpy)3]2+, and [Os(bpy)3]2+ groups were synthesized, and their photophysical, photochemical, and redox properties investigated. Substitution of the spiropyran with the metal complex moiety results in strongly decreased efficiency of the ring-opening process as a result of energy transfer from the excited spiropyran to the metal center. The lowest excited triplet state of the spiropyran in its open merocyanine form is lower in energy than the excited triplet MLCT level of the [Ru(bpy)3]2+ moiety but higher in energy than for [Os(bpy)3]2+, resulting in energy transfer from the excited ruthenium center to the spiropyran but inversely in the osmium case. The open merocyanine form reduces and oxidizes electrochemically more easily than the closed nitrospiropyran. Like photoexcitation, electrochemical activation also causes opening of the spiropyran ring by first reducing the closed form and subsequently reoxidizing the corresponding radical anion in two well-resolved anodic steps. Interestingly, the substitution of the spiropyran with a Ru or Os metal center does not affect the efficiency of this electrochemically induced ring-opening process, different from the photochemical path.