Adsorption and conformational changes

A. Kondo and H. Fukuda, Effects of adsorption conditions on kinetics of protein adsorption and conformational changes at ultrafine silica particles, J. Colloid Interface Sci. 198, 34-41 (1998). 

Valenta, P., Sequaris, J.M., Koglin, E., and Numberg, H.W. (1982) Smdy of adsorption and conformational changes of nucleic acids by voltammetry and by surface-enhanced Raman-scattering. Journal of the Electrochemical Society, 129, C131-C131. 

Shamim N, Liang H, Hidajat K, Uddin MS (2008) Adsorption, desorption, and conformational changes of lysozyme from thermosensitive nanomagneetic particles. J Colloid Interface Sci 320 15-21... 

If kinetic processes of adsorption or desorption were observed in time scales t lOO tg, it is difficult to distinguish between impurity effects and specific effects of the surfactant system, such as electrostatic retardation, phase transitions in adsorption layers, conformational changes, structure formations etc. 

The helix-coil transition can be demonstrated by polarization of fluorescence techniques, and the results may be compared with spectroscopic measurements to correlate the change in the hydrodynamic properties of the molecule with the change of its conformational structure. It is clear that the hydrodynamic and conformational changes do not necessarily parallel one another. Ion adsorption, breaks in the helix, and changes in helical type can occur without being reflected in the optical rotation parameters. 

The conclusions that may be drawn so far are (1) that only a small portion of the protein molecule should enter the interface, so that the adsorption could proceed spontaneously, and (2) that the spreading and conformational changes in the protein molecule occur by movement of only small segments of the molecule, several amino acid residues each. 

Notice that quantum chemical calculations of the adsorption of a CO2 cluster onto a silicon surface using periodic boundary conditions showed that the density of the monolayer can be higher than the critical density of relatively rigid CO2 molecules. Consequently, the adsorption layer density of molecules such as TEA and DEA softer than CO2 can be relatively high. Thus, any strong interactions of adsorbates with the adsorbent surface cause compaction of, at least, the first adsorption monolayer (due to both orientation effects, e.g., for acetonitrile, and conformation changes, e.g., for DEA and TEA) that result in diminution of the effective surface area occupied by a molecule and an increase in the 5 bet,x/ bet,n2 value. 

Hence, dr/dtl+ varies linearly with d9/dll+. This definition of 0 holds for molecules that do not change their conformation when they adsorb. This is the case for small, rigid molecules. Polymers, including proteins, may show adsorption-induced conformational changes. The relation between T and 0 then usually is more intricate this is discussed in Section 15.1. 

Many polystyrene fractions are available as probe polymer in nonaqueous systems. For aqueous systems, we can use the dextran-oligosaccharide series and poly(ethy1ene oxide) - polyethylene glycol series (polymers that are substantially neutral and with which there will be little possibility of adsorption or conformational change due to the presence of electrolytes). For the latter polymers, the relations between the Stokes radius and molecular weight have been collected as in Fig. 6. 

As for polyelectrolytes, peptide binding to phospholipid membranes and surfaces is expected to decrease with decreasing peptide length as a result of the increased entropy penalty (per amino acid) on adsorption. For peptides displaying adsorption-induced conformational changes, there is also a decreased tendency to form ordered... 

The experimental test of the theoretical models describing polymer adsorption has been slow in developing. While the situation is far from satisfactory, a number of techniques, including ellipso-metry, infrared spectroscopy, viscosity, attenuated total reflection, and radiotracer rate studies have provided information on the adsorbed conformation and conformational changes. We will summarize the information provided by these techniques for polystyrene. 

W. H. Grant (National Bu/ieau o StandoAcU) No. Our objective in this study was to determine the effect of polymer conformation and conformational change on the adsorption process. We have generally, therefore, employed polymer solutions under theta conditions where the polymer conformation in solution is well characterized. Appreciable temperature changes would be necessary to precisely determine an activation energy in these systems. 

Michael, K. E., Vernekar, V. N., Keselowsky, B. G., Meredith, J. C., Latour, R. A., and Garcia, A. J. 2003. Adsorption-induced conformational changes in fibronectin due to interactions with well-defined surface chemistries. Langmuir, 19, 8033-8040. 

Uda, Y., Zepeda, S., Kaneko, F., Matsuura, Y., and Furukawa, Y. (2007) Adsorption-induced conformational changes of antifreeze glycoproteins at the ice/water interface. J. Phys. Chem. 

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