Langmuir 1988,4, 780-781
780
sites rather than the absence of charge. From this analysis one can conclude that, under physiological conditions,the unresponsive microspheres surface will have predominantly negative electron-donor sites whereas the responsive microspheres will have both negative donor sites, positive acceptor sites, and, in addition, sites containing adsorbed chloride ions. Both surfaces will also contain neutral “backbone” sites. Although the data presented are not definitive in determining why one batch of polystyrene microspheres is responsive to body fluids
while the other is not, it clearly shows that surface chemistry plays a key role in the biological activity of indicator particles and the power of electrophoretic fingerprinting in discerning the chemistry of biologically active versus nonactive surfaces. We believe that this simple technique can be an important analytical tool to help unravel the complexities surrounding biological activity of colloidal surfaces. Registry No. Polystyrene, 9003-53-6.
Notes Oxidation of Alcohol Monolayers by Chromic Acid
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Jamil Ahmad* and K. Brian Astin*
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Department of Chemistry, University of Bahrain, P.O. Box 1082, Bahrain
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Received December 8, 1987. In Final Form: January 28, 1988
Reactions in monolayer assemblies provide the opportunity to examine the reactivity of molecules constrained to the plane. This environment can produce novel effects; e.g., we recently reported that the cyclization of the monoterpenoid alcohol nerol could be controlled by compression of the alcohol fi1m.l Conformer selection could be induced, since the coiled conformers required for cyclization could not be formed in highly compressed films. In the present study we have examined the kinetics of the surface acid dichromate oxidation of 1-phenyl-l-hexadecanol (la) and its deuteriated analogue 1-[2H]-1phenyl-1-hexadecanol (lb) to 1-phenyl-1-hexadecanone(2) using high-performance liquid chromatography (HPLC) for analysis of reactant and product. As noted by Valenty? this provides more reliable kinetic data than measurements of surface pressure, surface potential, etc.
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The experiments were performed on a modified Langmuir trough, consisting of a thermostated multicompartmental PTFEtrough with a Wilhelmy plate balance? The subphases, water and acidified sodium dichromate solution (0.10 M in 2% H2S04), could be confined to different compartments and the monolayers transferred from one to the other with minimal mixing. In a typical experiment 20 pL of a 2 X M solution of the alcohol in hexane (la prepared by the sodium borohydride reduction of 2, lb by sodium borodeuteride reduction of 2, >99 atom % D) was spread on water and compressed to 18 mN m-l (for ex(1) Ahmad, J.; Astin, K. B. J. Am. Chem. SOC.1986, 108, 7434. (2) Valenty, S.J. J. Am. Chem. SOC.1979, 101, 1. (3) Fromherz, P.Rev. Sci. Instrum. 1976, 46, 1380.
0743-7463/88/2404-0780$01.50/0
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Figure 1. a-u isotherm measured at 25 O C with a Wilhelmy balance (initial f i i area 170 cm2,fiial area 80 cm2,compression rate 24 cm2 min-’).
panded films R was
