Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy was used to study the nature of the dipalmitoylphosphatidylcholine (DPPC) aggregated structures adsorbed on TiO(2). DPPC molecules were assembled on TiO(2) using Langmuir-Blodgett (LB) deposition methods or by directly flowing the DPPC liposome solution across the TiO(2)-coated ATR crystal. We found that there is a direct correlation between the intensity and frequency position of the zwitterionic headgroup IR bands and the nature of LB films. Specifically, we have shown that the bands due to PO(2)(-) modes are sensitive to changes in the degree of hydration of the LB films and that the symmetric deformation vibrational mode (delta(s) (+)N-CH(3)) is sensitive to interaction with oppositely charged surface sites. Using this information, we found that the liposomes adsorbed on TiO(2) remain intact as vesicles and that the vesicles are stable and not removed in flowing water. We have also shown that the antisymmetric deformation vibrational (delta(as) (+)N-CH(3)) modes are sensitive to changes in lateral-lateral DPPC interactions. This information was used to show that there is a lateral interaction between each positively charged (+)N(CH(3))(3) headgroup and negatively charged PO(2)(-) headgroup of the adjacent DPPC molecule in the adsorbed vesicles and LB films. This study provides a framework for the use of this IR technique in studies of adsorption and transport of molecules across membrane interfaces.
Phosphorescence measurements with 5,8-dimethyl-1-tetralone (DMT) and 5,8-dimethyl-1-tetralone-d 8 (DMTd 8 ) in methylcyclohexane were carried out between 15 and 80 K to analyze their triplet-state hydrogen-and deuterium-transfer reactions. As expected for a decay process displaying a very large isotope effect, emission could be observed only for the deuterated compound. Phosphorescence intensities and decay measurements in the case of DMT-d 8 were analyzed to determine the rates of deuterium transfer which were used to build an Arrhenius plot where tunneling can be readily identified. A temperature-independent triplet state reaction rate (k D (QMT) ) (5 ( 1) × 10 2 s -1 ) below 40 K was assigned to quantum mechanical tunneling. Detection of the photoproduct after irradiation at 77 and 15 K was accomplished by fluorescence and by FTIR spectroscopy. Results obtained in this study are in excellent agreement with laser flash photolysis results reported by Al-Soufi et al. (Al-Soufi, W.; Grellmann, K. H. J. Phys. Chem. 1991, 95, 2022-2026.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.