Free radical detection of biological species requires a highly sensitive instrument with rapid response. (Varian EPR Spectrometers will detect 2 x 10 11 A H free radicals [ 1 ( H molar concentrations] at a response time of 1 second). Magnet and cavity configuration plus a large choice of accessories make the Varian EPR system the most versatile spectrometer available for free radical studies. The scientist interested in producing free radicals by irradiation is practically unlimited in the source and techniques which may be selected. In addition, Varian's C-1024 time averaging computer can effectively enhance signal to noise and in many cases permit the scientists to directly observe free radical growth and decay and calculate the free radical life time. EPR spectra also provide additional information to aid in identifying the radical specie; i.e., mono-radical, biradical, or a triplet state.
EPR
IN THE W O R L D OF
BIOCHEMISTRY
EXCITED TRIPLET STATES IN AROMATIC AMINO ACIDS ON
OFF
TRYPTOPHAN 5 sec.
1450 GAUSS
ON
OFF
*~V- TYROSINE 5 sec.
1280 GAUSS
-V
PHENYL-ALANINE
1300 GAUSS
ON
^ _ ^ ^ 5 SeC
*
OFF
Phosphorescence of proteins was first observed as early as 1952. (1) This phosphorescence generally originates from the aromatic amino acids such as tyrosine and tryptophan. The triplet character of this phosphorescence has now been established by electron paramagnetic resonance. Dilute solutions of tryptophan, tyrosine and phenyl-alanine in 6N HC1 give rise to an excited triplet state when photolysed with ultraviolet light at 77°K. The EPR signal for these triplet states was detected at 1450, 1280 and 1300 gauss respectively for the three amino acids and is characteristic of the half field H 0 / 2 forbidden transitions ( A M S = ± 2 ) . The life times of the triplet states are measured directly when the exciting light is extinguished. Detailed studies of the spectral line shape and life times of these triplets can yield valuable information as to the orientation and geometry of the molecules. (1) P. Debye and J. 0. Edwards Science 116,143 (1952)
Additional information about this and other examples in this series is available upon request, or if you would like to see a demonstration of our EPR systems and their accessories, write the EPR Product Group, Palo Alto, for an appointment at one of our Applications Laboratories. They are located at Pittsburgh, Pennsylvania; Palo Alto, California; and Zurich, Switzerland. In Europe, contact Varian A. G., Zug, Switzerland.
^VARIAN
ASSOCIATES PALO ALTO 18, CALIF.
