Probing the Saltwater Immersion Effect on Buried Interfacial Structures between a Sealant and Adhesion Promoter at the Molecular Level.

In this research, we used sum frequency generation vibrational spectroscopy to investigate the buried interface of a thiol-epoxy model aerospace sealant in contact with a silane-based adhesion promoter (6111) following exposures to 3% saltwater at elevated temperatures and elevated temperatures alone. The results suggest that the saltwater caused a change at the interface between the adhesion promoter and sealant, while an elevated temperature of 60 °C itself did not affect the interfacial structure noticeably. Model hydrolyzed and nonhydrolyzed silanes were also used in the study to compare with the adhesion promoter 6111 to understand the interfacial behavior of main silane components in 6111 as well as their potential role in adhesion. The amino silane in 6111 likely segregates more at the sealant/adhesion promoter interface and interacts with the sealant compared to the vinyl silane. The results imply that the saltwater immersion process led to the disordering of the adhesion promoter/sealant interface (caused by interfacial structural randomization), which could potentially have implications for adhesion.

Time-resolved EPR study of the photophysics and photochemistry of 1-(3-(methoxycarbonyl)propyl)-1-phenyl[6.6]C61.

Time-resolved (TR) EPR was used to study the photophysics and photochemistry of 1-(3-(methoxycarbonyl)propyl)-1-phenyl[6.6]C61 (M1). The CW TREPR spectra of M1 in the photoexcited triplet state, frozen in a rigid matrix and in liquid solution at room temperature, were compared with those of 3C60. The introduction of the substituent on C60 has a striking effect on the spectra of the triplets, which is attributed to the lifting of the orbital degeneracy by the reduction in symmetry. Fourier transform (FT) EPR was used in an investigation of electron-transfer reactions in liquid solutions mediated by 3M1. Of particular interest was the system of M1/chloranil (CA)/perylene (Pe). Photoexcitation of M1 is found to lead to the formation of the chloranil anion radical and the perylene cation radical. From the chemically induced dynamic electron polarization (CIDEP) patterns in the FTEPR spectra and the dependence of the reaction kinetics on reactant concentrations, it was deduced that CA- is formed by two competing pathways following photoexcitation of M1: (1) direct electron transfer from 3M1 to CA followed by electron transfer from Pe to M1+ and (2) energy transfer from 3M1 to Pe followed by oxidative quenching of 3Pe by CA. In both pathways, M1 acts as a light-energy harvester and mediator of electron-transfer reactions from Pe to CA without itself being consumed in the process, that is, as a photocatalyst. It is found that the functionalization of C60 makes its triplet state a worse electron donor and acceptor, but it has no significant effect on the triplet energy transfer reaction.

Cryogenic Charge Transport in Oxidized Purple Bacterial Light-Harvesting 1 Complexes.

We report on the analysis of the inter-bacteriochlorophyll a (BChla) charge-transport process that occurs in oxidized purple bacterial light-harvesting 1 (LH1) complexes. Experimentally, charge migration within oxidized LH1 is monitored by following the temperature-dependent changes of the BChla(•)(+) electron paramagnetic resonance (EPR) line-shape characteristics. At 6 K, a Gaussian-shaped spectrum with a 1.3-mT width is detected. These characteristics indicate that at extremely low temperatures charge transport is substantially slowed so that the unpaired electron is localized on one or two BChlas. At higher temperatures, the spectra exhibit non-Gaussian line shapes and decreased line widths. These characteristics are engendered by charge migration. We have analyzed the temperature dependence of the transport process through EPR spectral simulations. The simulations incorporated a nonadiabatic model for electron transfer. The temperature dependence could be adequately described on the basis of an electron-transfer model that accounts for the effects of slow medium relaxation, whereas a satisfactory description could not be obtained on the basis of conventional multimode models for transport. The results of our analysis are consistent with the notion that the protein functions as the primary solvent for the redox centers and are in accord with the view that the protein behaves as a frozen glass, even at room temperature, with respect to the low-frequency vibrational motions coupled to electron transfer.