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Antibiotics in biological materials, including tetracyclines, are determined usually be means of microbiological methods. Because of the low specificity and the time consuming procedure of the microbiological assays, we developed a fluorimetric method, which enables us to determine specifically the tetracyclines and to reduce the time for the assay down to 4 hours. Our method is based on the determination of tetracyclines published by Kohn (1961), which we modified for the determination of chlortetracycline in meat and bone. Tetracyclines are fluorescent compounds, whose quantum yields are very much enhanced in most cases by forming a complex with Ca2+ ions and by extracting it into an organic solvent. This transfer into acetic acid ethylester separates the chlortetracycline from interfering substances. The yield of chlortetracycline with the described method was about 80%, the sensitivity of the detection was about 0.5 ppm.

A procedure for developing =C NMR chemical shift additivity rules for all 136 polymethoxyxanthones and all 136 polyacetoxyxanthones, based on multiple linear regression analysis, is reported. The influence of steric interactions between the substhents on the chemical shifts of the carbon atoms in the xanthone ring system is discussed and induded in the calculations of the additivily rules for the polymethoxyxanthones. The derived chemical shift increments are implemented into the computer program SEOX 1. The extended program, SEOX 2, allows an automated structure elucidation of polyhydroxy-, polymethoxy-and polyacetoxyxanthones. The increments are tested lasing the leave-one-out method in conjunction with SEOX 2, and have been found to be very suitable for this purpose.

The 13C NMR chemical shifts of the C-1' carbon atom of fifteen para-substituted benzophenones correlate with the 9 and % substituent constants in a reversed manner.