clays and binders

Metal oxide chemistry

Zirconium oxide is used by research scientists to isolate phosphopeptides. Aumina can do the job too. Zirchrom makes specialized columns for isolating phospho proteins. Lewis acids are chemicals that have empty orbitals and can accept electron pairs from Lewis Bases, which has a highly localized HOMO (The Highest Occupied Molecular Orbital) that can donate an electron pair to a Lewis acid.

Here we see a speckling of the zirconium atom already bound to water and hydroxide ions that has some vacancies for the electrons in our phosphate molecule. Wikipedia authors assembled a good piece on the isoelectric point defined as the pH at which a molecule has no net electrical charge.

Figure 4 from The Lewis acid sites on the surface of ZirChrom®-PBD allow for a tunable, multi-modal, selectivity.  Without the addition of any Lewis base modifiers in the mobile phase the surface of zirconia is positive at low pH, neutral at neutral pH and negative at high pH . The IEP table is from Wikipedia.

When I was working with kaolin we bound the DNA to the alumina groups at pH 3-4 and eluted at pH 9. Note the isolectric points of gamma and alpha alumina and very low isolectric point of silica.

Figure 5. Eluotropic Scale for Lewis Base Modifiers
The negative charge imparted on the surface (with phosphate or EDTPA a net negative charge is possible even at very low pH) coupled with the reversed phase character of the polymer coating and unparalleled thermal and chemical stability allows for a very unique multi-mode separation by cation exchange and reversed phase.  Furthermore by judiciously selecting the mobile phase modifier and separation pH, the extent each mode (SCX or RP) plays in the separations can be controlled.  This enables users to “tune” the separation, allowing for effortless optimization of the analysis.   It is exactly this feature of the ZirChrom-PBD phase that we put to full advantage in the method development for these aromatic amine isomers.

The following bentonite / montmorillonite structure is from Scott Labs. “Natural calcium bentonite has a high percentage of exchangeable calcium ions, very few exchangeable sodium ions. Calcium bentonite lattice structures open less but flocculate better, making them well-suited for clarification and lees compaction. Due to their less open lattice structure, calcium bentonites have a lower ability to bind proteins.” This is the link for the kaolin structure.

Kaolin with its sandwich of alumina and silca make it an appealing choice for DNA. In all honesty I found that alumina without the silica performed just as well. Yttria stabilized zirconia performed well. Is bentonite/montmorillonite really the best mineral to bind glyphosate? The water channels may make a good case for aflatoxins. Maybe.

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