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SynopsisThe inirinsic viscosity of soiiicated calf thymiis DNA (molecular weight 4-5 X lo5) increases and the sedimentation constant decreases, with increasing binding of proflavine at 0.2 ionic strength and at 25°C. The measiirements correspond to a linear increase in length of the almost rodlike DNA molecules with the amount of proflavine bonrid; independent calculations from viscosity and sedimentation measurements yield almost identical results. Over the range of r (moles of proflavine bound per moles of nricleotides) equal to zero to r = 0.13, the length increases by about 20%. This extension is compatible with the intercalation hypothesis proposed by Lerman. Density increments a t varioiis values of r, at constant chemical potential of diffusible solutes, were determined. I t was also forind that, in addition to the known isosbestic point of DNA-proflaviiie complexes at 455.5 mp, an additional ibosbestic point exists at 225.5 mp; this proved extremely ubefril for the evaluatioii of binding studies.

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By using the diffraction properties of waveguide arrays, we propose a scheme to produce structures with designed diffraction. We fabricated arrays with reduced, canceled, and even reversed diffraction. Results of experiments with such waveguides are presented and compared with the predictions made by coupled-mode theory.

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