Dean Burk

Recognition of cancer in vivo by nuclear magnetic resonance.

Pulsed nuclear magnetic resonance has been used to differentiate in vivo between normal mouse tail tissue and a malignant transplanted melanoma, S91, located on the tail. The tumor displayed a nuclear (proton) spin-lattice relaxation time of ∼0.7 second contrasted with the simultaneously measured normal tail tissue relaxation time of ∼0.3 second.

The quantum efficiency of photosynthesis

Abstract Photosynthesis is a unique endothermic photochemical reaction in which chemical energy is gained from visible light energy by the combined action of several quanta. Nothing similar is known in the nonliving world. It was first reported a quarter of a century ago 1 that in photosynthesis the greater part of the absorbed visible light energy could be converted into chemical energy under optimum conditions. Indeed, no more than four quanta of red light seemed to be necessary to produce one molecule of oxygen gas, which is close to the thermodynamic requirement of three quanta. It is easy to understand that this result, lacking any analogy, has sometimes been doubted by theoreticians, and it is a fact that certain investigators have raised methodological objections 2 . For this reason we have reinvestigated the question of the minimum quantum requirement of photosynthesis as measured by oxygen and carbon dioxide gas exchange. The present paper is a short summary of our findings by new and simplified methods.

An electrochemical demonstration of the energy cycle and maximum quantum yield in photosynthesis

Abstract 1. 1. The electrochemical method of Todt for the determination of oxygen gas has been applied to the measurement of (1) the quantum requirement of photosynthesis and (2) the course of the light reaction and the dark back-oxidation over very short time periods (seconds). 2. 2. With this new and independent, galvanometric method, the earlier results obtained by us with manometry have been confirmed, that is, attainment of a limiting quantum requirement of about 3 in the cycle of light and dark reactions. All significant objections raised regarding the time lag of manometry, as used by us, are thereby refuted. 3. 3. Quantum requirements with single illumination periods as short as 5 seconds have been reported, and much shorter periods are shown possible. 4. 4. The new electrochemical method opens up a field of investigation closed, on a time basis, to manometry. Nevertheless, manometry, with which the energetics of photosynthesis was discovered, can never be given up: for it alone of all methods gives information about both gases, oxygen and carbon dioxide.