CONCENTRATION QUENCHINGOF PROFLAVINE already been discussed. Vycor (Corning 7910) shows a sharp infrared absorption band at 3560 not at the position reported for Cabosil, i.e. 3750 cm-l. Asher, Goodman, and Gregg2’ reported that silica which had been calcined at 900” became “hydrophobic,” but it then became “hydrophilic” after a lengthy exposure to water vapor during the determination. This behavior is in agreement with the dynamic aspects of the present observations. Our results show quantitatively a high degree of reversibility after surface dehydration at 300, 500, and 800” and hydration taking place a t 60,80, 100, or 120”. After the 800” outgassing the silica networks need only more contact time to hydrate at 120” t o the same extent as for a 300” outgassing. Presumably, there are fewer nucleation sites present after the 800” treatment to initiate the reactions and this would require a greater energy of activation. The majority of adsorption isotherms of water vapor on silica have been measured at ambient temperatures. The present investigation demonstrates that the conditions for the chemisorption of water vapor are also the conditions for adsorption as the water molecule. The question had been raised-can a silica network be hydroxlyated without also adsorbing water vapor as HzO? The present measurements and the isochrone model suggest that both occur in rapid succession during the adsorption process. On the other hand, a desorp-
2727 tion process at a controlled higher temperature may fractionate the adsorbate and perhaps leave only silanol groups as suggested by many investigators using infrared absorption. The coverage of a silica network by water molecules can be calculated in one of several ways. If the rhombohedral structure of silica extends into the surface, and if only vicinal silanol groups are present where the silicon atoms are exposed, then compleJe coverage corresponds to a cross-sectional area of 20.7 A2per water molecule. For the geminal structure monolayer coverper molecule. Using the age corresponds to 10.3 i2 density of liquid water at 25”, the molecular area is 10.5 i2.28 Thus, any calculation of surface coverage by water molecules is seen to depend on the model adopted for the water-solid interaction. It is interesting, however, that one cannot distinguish between packing that corresponds to either liquid-like packing or interactions to form geminal bonds with the silica network.
Acknowledgment. This work was supported, in part, by Naval Air Systems Command. (26) W. Espe, “Materials of High Vacuum Technology,” Vol. 2, Pergamon Press, New York, N. Y., 1968, p 426. (27) R. C. Asher, J. F. Goodman, 8. J. Gregg, Proc. Brit. Ceram. SOC., 5, 125 (1965). (28) A. L. McClellan and H. F. Harnsberger, J . Colloid Interface Sei., 23, 577 (1967).
Concentration Quenching of Proflavine Hydrochloride in Dry Films of Sodium Deoxyribonucleate and Poly(viny1 alcoho1)l by G. Straws,* S. B. Broyde, and T. Kurucsev2 School of Chemistry, Rutgers University, The State University of New Jersey, New Brunswick, New Jersey (Receined April 6 , 1971)
08905
Publication costs assisted by University College, Rutgers University
Concentration quenching of proflavine hydrochloride was studied in dry films of sodium deoxyribonucleate (DNA) and poly(viny1 alcohol) (PVA) by measuring the decline of flash-induced triplet formation with increasing dye concentration. The quencher was identified as the dimeric species of proflavine. The quenching of the excited singlet state may be interpreted in terms of long-rang: Forster-type energy-transfer mechanism. Critical donor-acceptor distances were found to be 33.5 and 46.3 A in DNA and PVA, respectively; these differences may be explained by consideration of the polymer-dye interactions.
Introduction The well established biological activity of acridine dyes and other polycyclic hydrocarbons structurally related to these dyes has provided the motivation for numerous studies in recent years concerned particularly
with the structural aspects of the interaction of these materials with DXA and other polymer^.^-^ The (1) T+ work was supported by a grant from the Rutgers Research Council t o G. Strauss and by a grant (65/15799) from the Australian Research Grants Committee to T. Kurucsev. (2) On study leave from the University of Adelaide, South Australia.
The Journal of Physical Chemistry, Val. 76, N o . 18, 1971
2728 study of electronic energy transfer between acridine dyes bound to DNA and other polymers must be considered as complementary to such structural studies from this point of view since it is probable that the biochemical behavior of these molecules is related to their photophysical properties, Furthermore, since energy transfer between dye molecules is sensitive to their environment, such studies may provide alternative avenues for the elucidation of dye-polymer interactions. Energy-transfer studies confined to systems where the energy donor and the energy acceptor are different chemical species are relatively easy to interpret unambiguously since deactivation of the donor and/or excitation of the acceptor are easily recognized and differentiated from each other. However, in polymer-dye systems the simultaneous use of two dye species may lead to difficulties due to the possibility of competitive binding or to the formation of several types of polymerdye complexes. For these reasons our studies were restricted to a single cationic acridine dye, 3,6-diaminoacridine or proflavine hydrochloride (PF) dispersed in dry solid films of sodium deoxyribonucleate (DNA) and of poly(viny1 alcohol) (PVA). I n comparison with DNA, PVA lacks ionic groups and has a more flexible chain structure of much smaller diameter. Thus comparison of the results in the two media may provide information about the effect of these polymer characteristics on energy transfer. Energy transfer from dye donors under these conditions may be ascertained from the study of concentration quenching or self-quenching, terms used to describe the decrease in fluorescence, triplet formation, or phosphorescence with increasing concentration of a solute. We used a microbeam flash photolysis technique to measure triplet yields and triplet lifetimes of proflavine over a range of dye molarity, It is to be emphasized that C, of
