Geothermal energy can provide answers to many of America’s essential energy questions. The United States has tremendous geothermal resources, as illustrated by the results of the DOE GeoVision analysis, but technical and non-technical barriers have historically stood in the way of widespread deployment of geothermal energy. The U.S. Department of Energy’s Geothermal Technologies Office within the Office of Energy Efficiency and Renewable Energy has invested more than $470 million in research and development (R&D) since 2015 to meet its three strategic goals: (1) unlock the potential of enhanced geothermal systems, (2) advance technologies to increase geothermal energy on the U.S. electricity grid, and (3) support R&D to expand geothermal energy opportunities throughout the United States. This paper describes many of those R&D initiatives and outlines future directions in geothermal research.
Surface-enhanced
Raman scattering (SERS) spectra contain information
on the chemical structure on nanoparticle surfaces through the position
and alignment of molecules with the electromagnetic near field. Time-dependent
density functional theory (TDDFT) can provide the Raman tensors needed
for a detailed interpretation of SERS spectra. Here, the impact of
molecular conformations on SERS spectra is considered. TDDFT calculations
of the surfactant cetyltrimethylammonium bromide with five conformers
produced more accurate unenhanced Raman spectra than a simple all-trans
structure. The calculations and measurements also demonstrated a loss
of structural information in the CH2/CH3 scissor
vibration band at 1450 cm–1 in the SERS spectra.
To study lipid bilayers, TDDFT calculations on conformers of methyl
phosphorylcholine and cis-5-decene served as models
for the symmetric choline stretch in the lipid headgroup and the CC
stretch in the acyl chains of 1,2-oleoyl-glycero-3-phosphocholine.
Conformer considerations enabled a measurement of the distribution
of double-bond orientations with an order parameter of S
CC = 0.53.
Small fluorescent molecules are widely used as probes of biomembranes. Different probes optically indicate membrane properties such as the lipid phase, thickness, viscosity, and electrical potential. The detailed molecular mechanisms behind probe signals are not well understood, in part due to the lack of tools to determine probe position and orientation in the membrane. Optical measurements on aligned biomembranes and lipid bilayers provide some degree of orientational information based on anisotropy in absorption, fluorescence, or nonlinear optical properties. These methods typically find the polar tilt angle between the membrane normal and the long axis of the molecule. Here we show that solution-phase surface enhanced Raman scattering (SERS) spectra of lipid membranes on gold nanorods can be used to determine molecular orientation of molecules within the membrane. The voltage sensitive dye 4-(2-(6-(dibutylamino)-2-naphthalenyl)ethenyl)-1-(3-sulfopropyl)-hydroxide, known as di-4-ANEPPS, is studied. Through the analysis of several peaks in the SERS spectrum, the polar angle from the membrane normal is found to be 63°, and the roll angle around the long axis of the molecule to be 305° from the original orientation. This structural analysis method could help elucidate the meaning of fluorescent membrane probe signals, and how they are affected by different lipid compositions.
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.