TLS Online TPP Program

#Id: 2863

#Unit 13. Methods in Biology

The electronic transitions of the peptide bond occur in the far UV. The intense peak at 190 nm, and the weaker one at 210–220 nm is due to the p ® p* and n ® p* transitions.

TLS Online TPP Program

#Id: 2864

#Unit 13. Methods in Biology

A number of amino acids (Asp, Glu, Asn, Gln, Arg and His) have weak electronic transitions at around 210 nm Usually, these cannot be observed in proteins because they are masked by the more intense peptide bond absorption.

TLS Online TPP Program

#Id: 2865

#Unit 13. Methods in Biology

The most useful range for proteins is above 230 nm, where there are absorptions from aromatic side chains.

TLS Online TPP Program

#Id: 2866

#Unit 13. Methods in Biology

A very weak absorption maximum of phenylalanine occurs at 257 nm, tyrosine and tryptophan dominate the typical protein spectrum with their absorption maxima at 274nm and 280 nm, respectively.

TLS Online TPP Program

#Id: 2867

#Unit 13. Methods in Biology

Cystine (Cys2) possesses a weak absorption maximum of similar strength as phenylalanine at 250 nm.

TLS Online TPP Program

#Id: 2868

#Unit 13. Methods in Biology

The absorption of UV light by nucleic acids arises from n ® p* and p ® p* transitions of the purine and pyrimidine bases that occur between 260nm and 275 nm.