Photo-response assisted enantiomer separations on an azobenzene-modified gamma-cyclodextrin stationary phase in micro-HPLC.
The photo-responses of the retention and enantioseparation of several optical isomers were evaluated using an azobenzene-modified gamma-cyclodextrin stationary phase (Az gamma-CDSP) in micro-HPLC. UV light irradiation induced a decrease in the retention and the chiral selectivity for N-(3,5-dinitrobenzoyl)-1-phenylethylamine (DNBPEA) and N-(3,5-dinitrobenzoyl)-1-(1-naphtylethyl)amine (DNBNEA), while an increase was induced for dansylphenylalanine (DnsPhe) using a mixture of methanol and aqueous phosphate buffer as the mobile phase. No changes in the retention and the enantiomer separation of benzoin were observed with UV light irradiation. The retention behaviors were recovered by visible-light irradiation. It was speculated that the main factor of the change in the retention behavior was a change in the pi-pi interaction due to the azobenzene moiety of the stationary phase with photo-irradiation. Comparing the retention behavior before and after UV light irradiation, a suitable condition for obtaining a better resolution and enantiomer separation would be chosen using Az gamma-CDSP.
Separation of proteins by polymeric adsorbents containing azobenzene moiety as a ligand
Polymeric adsorbents containing an azobenzene moiety as a ligand were prepared, and the photoinduced adsorption behavior of proteins to the adsorbent was studied. This method regulates by light the adsorption/desorption of proteins in hydrophobic chromatography. In the dark, the amount of protein adsorbed onto the adsorbent increased with increasing hydrophobicity of either adsorbent or protein. On irradiation with UV light, the amount of protein adsorbed decreased. Such a photoinduced change of the adsorption of protein was considered to be caused by the change of the hydrophobic interaction between the adsorbent and the protein due to the photoisomerization of the azobenzene moiety accompanying the polarity change of the adsorbent. It is also found that the desorption of protein was dependent on the balance of the hydrophobicity between the adsorbents and proteins. When column chromatography was carried out, the proteins were adsorbed in the dark and could be eluted after photoirradiation, with water as the single solvent. Furthermore, mixture of proteins could be separated by using a hydrophobic gradient column which was constituted by two polymeric adsorbents having different hydrophobicity.
Assessing student learning in higher education
Chapter 1. Introduction to the Text, Chapter 2. What is Assessment?, Chapter 3. Student Learning, Chapter 4. Methods and Strategies: An Overview, Chapter 5. Assessing Essays, Chapter 6. Multiple Choice Questions, Chapter 7. Assessing Practical Work, Chapter 8. Assessing Projects, Chapter 9. Assessing Problems, Chapter 10. Assessing Oral Communication, Chapter 11. Self and Peer Assessment, Chapter 12. Self Assessment: Related Approaches, Chapter 13. Using Computers in Assessment, Chapter 14. Changing Assessment, Chapter 15. Reliability, Validity and Examining, Chapter 16. Quality, Standards and Underlying Issues, Bibliography Notes and comments on activities Some further reading Appendix One: Examples of examination questions in Arts, Law and Social Sciences