Abstract— The redox dependence of the light‐induced electron paramagnetic resonance signal at g=2 in R. rubrum, R. spheroides and Chromatium chromatophore particles and quantasonie particles from spinach chloroplasts has been determined qualitatively over the range —0.3 to +0.6 V and quantatively over the range +0.3 to ±0.6 V. A light‐induced EPR signal has been titrated and demonstrated to have a midpoint potential of +0.44 v at pH 7 and 20°C. Concentration, ionic strength and pH dependence for this transition in R. rubrum chromatophores is reported. In addition to the dark signal which replaces the light signal, in chromatophore material another dark signal, occurring in the seine location as the light signal, has been demonstrated to occur at high potential. Selective chemical oxidation with K2lrCl6 of chromatophore particles from the three bacteria resulted in the removal of some 95 per cent of the absorbance in the near infrared and left the photoactive pigments. Two light‐induced EPR signals were found in quantasome particles by their dependence upon the redox level. Of particular interest is a signal observed at quite high potential (e.g. + 0.60 V). It was demonstrated that oxygen evolution by these quantasonie particles in the presence of K3Fe(cN)0 occurred at the same rate at +0.55 V as at +0.40 V.

The difficulties of interpretation that plagued previous nuclear magnetic resonance experiments in superconducting metals 1 ' 2 arose mainly because the samples contained widely varying particle sizes. Thus, a significant fraction of the sample remained in the normal state at temperatures < T c in the fields employed. Since the two different types of particles contributed resonance lines which overlapped, it was difficult to separate the part arising from the absorption in the superconducting material. In order to avoid this difficulty, a sample has been built up by evaporating, alternately, layers of tin and a dielectric (Nylon). The metal in the sample (approximately one gram) has the 0 tin structure, and is uniformly divided into small platelets with diameters, in the plane of the evaporated layers, of-140 A, and thickness ~40 A. The critical temperature is found to be 3.712 ±0.010°K, and the critical field atT = 0is25±3 kilogauss. Experiments have been performed with the sample in the superconducting state in fields up to 8.8 kilogauss.The resonance has an almost Gaussian shape, a width which varies linearly with the magnetic field, and, aside from the usual T~x variation of intensity, no observable temperature dependence. That is, to the accuracy of measurement (signal to noise ratio of £10 at 4.2°K), the line shape and width are the same above, in, and below the superconducting transition. Work on other tin samples containing somewhat larger particles indicates that the line width is also inversely proportional to particle size, and in the final sample it is -4.5 times the width for "bulk" tin (taken as V\\ -v ± ) s in the same field. These characteristics may be explained by considering, in conjunction with the theory of Bloembergen and Rowland, 3 that the conduction electrons near the surface of a piece of metal do not see the regular tin lattice symmetry. In the platelets in the sample, half or more of the atoms are within 10 A of the surface. The variety of the surface positions in relation to the crystal axes, and the effects of some sort of random particle-size distribution account for the shape of the line.The nuclear magnetic resonance shift in the evaporated metal at 4.2°K was found to be the same as the isotropic shift in "bulk" tin. But

One of the outstanding features, possibly a unique feature, of the process of photosynthesis as it occurs in nature today is the ability of the organism, either green plant or bacterium, to utilize a quantum of energy of the order of 38,000 calories for green plants and 40,000 for the bacteria to accomplish an ordered chemical transformation at room temperature with a relatively high degree of efficiency. The apparatus which accomplishes this, we must remember, is of labile organic construction, and the thermal reactions which can be performed by such a system rarely, if ever, involve energy changes higher than 10,000 or 15,000 calories; thus, manipulation of a package of energy two or three times that size without damage to the apparatus and in a highly directed and specific way is an impressive accom-.plishment indeed.The ultimate products of this energy transformation have long been known to us, in the form primarily of carbohydrate and oxygen but of course including all of the plant substances. In fact, it is currently possible to describe some more immediate products of this energy conversion process in terms of more transient, specific energy-storing materials. We have every reason to believe that two such energy-storing intermediates which can be used to produce the final, or more long-term, 23 NOVEMBER 1962 storage materials are reduced pyridine nucleotide and adenosine triphosphate. It may turn out that other transient energy-bearing chemical intermediates may be still closer to the energy transformation step itself. At this point it is perhaps worth while to define, as nearly as we can, the properties of the energy-bearing intermediate or intermediates which we consider to be the earliest form of chemical energy into which the electromagnetic quantum may be converted. Such a material would be the first chemically definable compound in thermal equilibrium with its environment, but, quite clearly, not in chemical equilibrium with it since, under such a definition, oxygen itself could not be evolved.We will consider the primary quantum conversion act, then, as that act, or sequence of events, that follows the absorption of the electromagnetic quantum and terminates with the appearance of the thermally relaxed, chemically defined individual which may then proceed, by direct thermal work-performing reactions, to produce the next transient and, finally, the ultimate products of photosynthesis.Under such a definition, an electronically excited state of a molecule, or array of molecules, such as might result from the primary absorption of a quantum of light would not be considered a chemical entity distinct from the parent material before light absorption. Only after the energy stored in this electronically excited state had been transformed into new chemical species which could then proceed to react, or interact, with their environment in accordance with thermodynamic principles would we consider the quantum conversion process accomplished. All succeeding reactions from these initial chemical species would...