Chaotropic interaction

A variety of well-established macroscale SPE methods for nucleic acid extraction have been successfully transferred to microscale devices [10, 31-57]. Although the physical principles of these methods may be different (e.g., chaotropic interactions, electrostatic interactions, affinity interactions, etc.), micro-SPE protocols typically consist of three steps (1) selective adsorption of nucleic acids onto a solid phase (2) removal of contaminants by a washing step and (3) elution of the preconcentrated nucleic acids from the solid support using water or a low salt buffer [31]. Like their macroscale counterparts, micro-SPE devices possess a loading level of target material that is dependent upon the available surface area within the extraction bed and, thus, are manufactured either by packing the solid phase... 

In this report, we examine the effects of millimolar to molar levels of Cl" and of other anions on the electron transport activity of isolated PS2 particles. At a concentration approx, above 0.1 M) anions inactivate PS2 via chaotropic interactions that require neutralization of the negative particle charge by binding metal cations. Betaine is shown to protect the PS2 particles against anion-induced inactivation and removal of extrinsic proteins. Protection Is visualized to be due to a surface layer of betaine zwitterions, preferentially oriented with the positive end groups facing the particle surface. This dipole layer shields the PS2 particles against bulk phase anions both sterically and electrostatically-... 

Several conclusions can be drawn from this experiment. The most likely inactivation cause appears to be the disorganization of the particles, because of anion chaotropic interactions, since the inhibition magnitudes rank in the same order as the anion chaotropic potencies (5) ... 

Cook et al. [2] also proposed a new mechanism whereby equilibrium of the bound zwitterions with a mobile phase containing a suitable electrolyte causes the establishment of a charged layer created by the terminal sulfonate groups of the zwitterion, which acts as a Donnan membrane. The magnitude and polarity of the charge on this membrane depends on the nature of the mobile-phase ions. The Donnan membrane exerts weak electrostatic repulsion or attraction effects on analyte anions. A second component of the retention mechanism is chaotropic interaction of the analyte anion with the quaternary ammonium functional group of... 

Thus, aside from the covalently polymerized a-chain itself, the majority of protein structure is determined by weaker, noncovalent interactions that potentially can be disturbed by environmental changes. It is for this reason that protein structure can be easily disrupted or denatured by fluctuations in pH, temperature, or by substances that can alter the structure of water, such as detergents or chaotropes. 

The immobibzation of NAs onto these membranes is usually achieved through electrostatic interactions of the NA and surface under chaotropic conditions. However, chemical activation of the membrane by silanization is also possible and would allow covalent linkage of NAs to the support surface. 

Proteins interact with the membrane (support) by hydrophobic and charge-transfer forces and hydrogen bridges. The extent of these interactions depends on the accessibility of respective area of a protein. The accessibility is influenced, among other things, by the composition of the surrounding buffer, e.g., pH, ionic strength and/or chaotropic additives. 

Integral proteins are dissolved into the lipid bilayer of the membrane through interactions of the hydrophobic amino acid side chains and fatty acyl groups of phospholipids. In order to remove integral membrane proteins, the membrane must be disrupted by addition of detergents or other chaotropic reagents to solubilize the protein and to prevent aggregation and precipitation of the hydrophobic proteins upon their removal from the membrane. 

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