Raman Spectra of Phospholipid-Water Gels
from 346 to 344 K and finally, a shift in cls/k. from 26 to 27 K, which causes the well-depth ratio listed for neon in the last column of Table I1 to rise to 0.86. The change in ergs brings it into better agreement with the arithmetic mean prediction of 3.08 A, and the change in egs g'ives rise to a smoother variation in well-depth ratio with atomic size. However, the inclusion of the parallel variation in energy does not explain the observed deviations from the welldepth combining rules. Of the various possibilities left as a possible explanation of the values found for the well-depth ratio, it appears that the most likely one is that the gas-solid energy is not exactly equal to a pairwise sum of the gas-solid atom interactions. The presence of delocalized (conduction) electrons in the graphite planes lends some credence to this belief; furthermore, the fact that a large gas atom tends to "see" more of the surface than a small one might lead one to guess that nonlocal interactions would be more important. The quantum mechanical calculations required to test this hypothesis are not available. Even if such a computation shows that this argument is correct, it should be emphasized that the deviations are small, and that the results of the work presented here are a striking confirmation of the ability of the pairwise additive approximation combined with (12-6) atom-atom potentials to give a good representation of the main features of the rare gas-graphite interactions and of the observable quantities that are directly derivable from this energy.
Acknowledgment. This work was supported in part by a grant from the Petroleum Research Fund, administered by the American Chemical Society.
The Journal of Physical Chemistry, Vol. 82,No. 7, 7978 821
Supplementary Material Available: An Appendix containing values of BAS* for the various potentials (2 pages). Ordering information is available on any current masthead page. References and Notes N. N. Avgul and A. V. Kiselev in "Chemistry and Physics of Carbon", Vol. 6, Marcel Dekker, New York, N.Y., 1970. W. A. Steele in "The Gas-Solid Interface", Vol. I,E. A. Flood, Ed., Marcel Dekker, New York, N.Y., 1964. R. A. Pierotti and H. E. Thomas in "Surface and Colloid Science", Vol. IV, E. Matijevic, Ed., Wiley-Interscience, New York, N.Y., 1971. W. A. Steele and G. D. Halsev. Jr.. J. Chem. Phvs.. 22. 979 (1954). J. R. Sams, Jr., G. Constabari;, and G. D. Halsey, jr., J. Phys. Chem., 65 - - , 367 _ _ 11961\ R. Yaris and J. R. Sams, Jr., J . Chem. Phys., 37, 571 (1962). J. R. Sams, Jr., G. Constabaris, and G. D. Halsey, Jr., J. Phys. Chem., 64, 1689 (1960). S.Ross and J. P. Olivier, Adv. Chem. Ser., 33, 301 (1961); I.D. Morrison and S. Ross, Surface Sci., 39, 21 (1973). F. A. Putnam and T. Fort, Jr., J . Phys. Chem., 81, 2164 (1977). W. A. Steele, Surface Sci., 36, 317 (1973). See, for example, D. L. Freeman, J. Chem. Phys., 62, 4306 (1975); A. J. Bennett, Phys. Rev. B , 9, 7411 (1974); J. N. Schmit, Surface Sci., in press. For example, see, J. A. Venables and P. S.Schabes-Retchkiman, J . Phys., in press. F. A. Putnam and T. Fort, Jr., J. Phys. Chem., 79, 459 (1975). Proceedings of the International Conference on Two Dimensional Phases, Marseille, 1977, to appear in J . Phys. E. J. Derderian and W. A. Steele, J . Chem. Phys., 66, 2831 (1977). H. Taub, K. Carniero, J. K. Kjems, and L. Passell, Phys. Rev., submitted for publication. See W. A. Steele. "The Interaction of Gases with Solid Surfaces", Pergamon, New York, N.Y., 1974, section 2.8. See, for example, D. Henderson, Annu. Rev. Phys. Chem., 25, 461 (1974). C. H. Chen, P. E. Siska, and Y. T. Lee, J . Chem. Phys., 59, 601 (1973); C. Y. Ng, Y. T. Lee, and J. A. Barker, ibid., 61, 1996 (1974). See, for example, K. M. Smith, A. M. Rulis, G. Scoles, R. A. Aziz, and V. Nain, J. Chem. Phys., 67, 152 (1977). I . - -
I
Raman Spectroscopic Study of Chloroform and Carbon Tetrachloride in 69 % Dipalmitoyl Lecithin-31 YO Water Multilayers Bernard J. Bulkin" and Nehama Yellin Depadment of Chemistty, Polytechnic Institute of New York, Brooklyn, New York 1120 1 (Received July 5, 1977) Publication costs assisted by the Polytechnic Institute of New York
The Raman spectrum of 69% dipalmitoyl lecithin (DPL)-31% water multilayers has been studied as a function of addition of CHC13and CCl+ The results indicate that a phase transition analogous to that which is thermally induced takes place at constant temperatures below T, when solute is added. A substantial two phase region is found, although the molecular nature of this two phase region is unclear. The extent of this region is different for CHC13 and CC4. By using the solute Raman bands as an internal intensity standard, the intensity changes in various lipid bands, previously measured only as relative changes, can be put on a somewhat more absolute basis. The implications of this for order calculations are discussed.
Introduction The bilayer structure of phospholipid-water gels and the thermally induced phase transition (at temperature T,) of gel-liquid crystal of these systems are the subjects of a large number of studies (see, for example, ref 1-51, The gel-liquid crystalline transition exists between two structural states: (1)the rigid crystalline one, Lp' or Lp, in which the hydrocarbon chains of the phospholipid are in an all-trans extended conformation with some rotational disorder, and (2) the liquid crystalline one (La)in which the chains are fluid, having a liquidlike disorder. Recording, by spectroscopic or calorimetric techniques, thermally induced changes related to the chains in the 0022-3654/78/2082-0821$01 .OO/O
bilayer allows one to detect the phase transition of a given gel system. Small organic molecules can also lead to structural changes of the lipid chains in the bilayer (at constant temperature below T J . These perturbations, both hydrophobic and hydrogen bonding, have been studied mainly with anesthetic molecules.~gIt has been found that the effect of the anesthetic molecules is to reduce the order of the bilayer, by partial fluidization of the rigid lipid chains. The structural changes in the pure bilayers have been studied by most of the modern spectroscopic techniques, including Raman spectroscopy. The Raman spectrum of
0 1978 American
Chemical Society
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TABLE I: -
Frequency Changes with Phase Transition in 69%DPL-31% H,O Multilayers CCl, (26 C)
Onset cm-' 1094 1127 1294 2844 a
B. J. Bulkin and N. Yellin
The Journal of Physical Chemistry, Vol. 82, No. 7, 1978
End
Xa 0.45 0.50 0.45 0.40
cm-' 1086 1124 1298 2947
X 1.00 1.00 0.90 0.90
cm-' 1094 1127 1294 2844
X is the mole ratio of solute to DPL.
X 0.25 0.25 0.60 0.25
cm-' 1085 1124 1299 2848
69% DPL-31% H.OC
CCl, (30 'C)
CHC1, (26 a C) Onset End
X 1.35 1.35 1.40 1.35
Onset cm-' X 1094
