Atomic force microscopy has been used to study the distribution of ganglioside GM1 in model membranes composed of ternary lipid mixtures that mimic the composition of lipid rafts. The results demonstrate that addition of 1% GM1 to 1:1:1 sphingomyelin/dioleoylphosphatidylcholine/cholesterol monolayers leads to the formation of small ganglioside-rich microdomains (40-100 nm in size) that are localized preferentially in the more ordered sphingomyelin/cholesterol-rich phase. With 5% GM1 some GM1 microdomains are also detected in the dioleoylphosphatidylcholine-rich phase. A similar preferential localization of GM1 in the ordered phase is observed for bilayers with the same ternary lipid mixture in the upper leaflet. The small GM1-rich domains observed in these experiments are similar to the sizes for lipid rafts in natural membranes but considerably smaller than the ordered bilayer domains that have been shown to be enriched in GM1 in recent fluorescence microscopy studies of lipid bilayers. The combined data from a number of studies of model membranes indicate that lateral organization occurs on a variety of length scales and mimics many of the properties of natural membranes.
We report the development of a high-sensitivity time-resolved infrared and Raman spectrometer with exceptional experimental flexibility based on a 10-kHz synchronized dual-arm femtosecond and picosecond laser system. Ultrafast high-average-power titanium sapphire lasers and optical parametric amplifiers provide wavelength tuning from the ultraviolet (UV) to the mid-infrared region. Customized silicon, indium gallium arsenide, and mercury cadmium telluride linear array detectors are provided to monitor the probe laser intensity in the UV to mid-infrared wavelength range capable of measuring changes in sample absorbance of ΔOD ~ 10(-5) in 1 second. The system performance is demonstrated for the time-resolved infrared, two-dimensional (2D) infrared, and femtosecond stimulated Raman spectroscopy techniques with organometallic intermediates, organic excited states, and the dynamics of the tertiary structure of DNA.
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