Living molecular diffusion

Fluorescence Correlation Spectroscopy on Molecular Diffusion Inside and Outside a Single Living Cell 645... 

The nanosized detection area Ar or volume created by STED also extends the power of fluorescence correlation spectroscopy (FCS) and the detection of molecular diffusion [74,95]. For example, STED microscopy has probed the diffusion and interaction of single lipid molecules on the nanoscale in the membrane of a living cell (Fig. 19.6). The up to 70 times smaller detection areas created by STED (as compared to confocal microscopy) revealed marked differences between the diffusion of sphingo- and phospholipids [74]. While phospholipids exhibited a comparatively free diffusion, sphingolipids showed a transient ( 10 ms) cholesterol-mediated trapping taking place in a < 20-nm diameter area, which disappeared after cholesterol depletion. Hence, in an unperturbed cell putative cholesterol-mediated lipid membrane rafts should be similarly short-lived and smaller. 

Molecular diffusion in emulsions can be effectively slowed down by including in the dispersed phase a small amount of a component with lesser water solubility, in the case of a PFC emulsion, a secondary, higher MW ( heavier ) PFC.t This is the role of 7 in Fluosol and of 8 in Perftoran, however, at the cost of longer organ half-lives of 65 and 90 days, respectively. 

While there have been several studies on the synthesis of block copolymers and on the molecular weight evolution during solution as well as bulk polymerizations (initiated by iniferters), there have been only a few studies of the rate behavior and kinetic parameters of bulk polymerizations initiated by iniferters. In this paper, the kinetics and rate behavior of a two-component initiation system that produces an in situ living radical polymerization are discussed. Also, a model that incorporates the effect of diffusion limitations on the kinetic constants is proposed and used to enhance understanding of the living radical polymerization mechanism. 

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