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John W. Duggan M.S. Clifford J. Bruell Ph.D. David K. Ryan Ph.D. 《Soil & Sediment Contamination》1994,3(2):159-182
In this article the conditions that govern surfactant‐enhanced emulsification and mobilization of petroleum hydrocarbons in soil are reviewed. The effect of soil properties, groundwater constituents, and differing surfactant solutions on the emulsification process is discussed. A constant head soil flushing apparatus used to characterize surfactant‐enhanced mobilization of m‐xylene is described. Data showing the effect of surfactant‐enhanced mobilization on m‐xylene removal efficiency in washed sand is presented. Flushing solutions were used at concentrations from below to well above the critical micelle concentration (CMC) of the surfactants used. Removal efficiencies are shown to vary with surfactant concentration and with surfactant type. Flushing solutions of anionic, nonionic, and anionic/nonionic surfactant mixtures were evaluated. 相似文献
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D Porschke 《Biophysical journal》1996,71(6):3381-3391
The stationary electric dichroism of bacteriorhodopsin is in qualitative, but not quantitative, agreement with the orientation function for disks having a permanent dipole directed perpendicular to the plane and an induced dipole in the plane. Fits of the orientation function to data measured at low field strengths demonstrate: an increase of the permanent dipole moment mu with the square of the disk radius r2, whereas the polarizability alpha increases with r4; the ionic strength dependence is small for mu and clearly stronger for alpha; the permanent dipole moment is 4x10(6) D at r = 0.5 micron. According to the risetime constants, the induced dipole does not saturate and increases to 4x10(8) D at 40 kV/cm and r = 0.5 micron. The data indicate that the permanent dipole is not of some interfacial character but is due to a real assymetry of the charge distribution. The experimental dipole moment per protein monomer is approximately 55 D, whereas calculations based on the structure of Grigorieff et al. (Grigorieff, N., T.A. Ceska, K.H. Downing, J.M. Baldwin, and R. Henderson. 1996. Electron-crystallographic refinement of the structure of bacteriorhodopsin. J. Mol. Biol. 259:393-421) provide a dipole moment of approximately 570 D. The difference is probably due to a nonsymmetric distribution of charged lipid residues. It is concluded that experimental dipole moments reflect the mu-potential at the plane of shear for rotational diffusion, in analogy to the sigma-potential used for translational diffusion. It is suggested that the permanent dipole of bacteriorhodopsin supports proton transport by attraction of protons inside and repulsion of protons outside of the cell. Dichroism rise curves at field strengths between E = 150 and 800 V/cm reveal an exponential component with time constants tau 3r in the range between 1 and 40 ms, which is not found in Brownian dynamics simulations on a disk structure using hydrodynamic and electric parameters characteristic of bacteriorhodopsin disks. The experimental data suggest that this process reflects a cooperative change of the bacteriorhodopsin structure, which is induced already at a remarkably low field strength of approximately 150 V/cm. 相似文献
1000.
R. H.F. Hunter 《Molecular reproduction and development》1994,39(2):176-181
Studies on protein molecules in oviduct luminal fluid are viewed historically, and then in terms of more recent studies on a possible involvement of unique glycoproteins in embryonic development. As a caution, however, it is noted that incorporation of such molecules into the vitellus may be nonspecific. The question is raised as to whether oviduct glycoproteins could be acting primarily in a physical sense to stabilize differing chemical environments along the oviduct. Equally or more importantly, glycoproteins might be acting as carrier molecules to present cations and metabolic substrates at appropriate concentrations to the vitelline membrane. This latter possibility is examined in some detail and could be tested by manipulating the composition of the perivitelline fluid. Glycoproteins may also be critically involved in regulating the physiological competence of spermatozoa in the pre- and peri-ovulatory oviduct, in maintaining a coordinated pattern of cilial beat, and in immunosuppressive functions within the oviduct, not least in those associated with the masking of paternal antigens on both spermatozoa and embryos. © 1994 Wiley-Liss, Inc. 相似文献