The atomic force microscope was used to investigate the interaction between 11-mercaptoundecanoic acid surfaces and 2-mercaptoethanesulfonic acid surfaces as a function of electrolyte and pH. The surface potential was found to peak at −80 mV at pH 6-8 in 0.1 mM 1:1 electrolyte. The Hamaker constant for the gold−gold interaction was found to be decreased from the value of 1 × 10-19 J in water to 4 × 10-20 J in ethanol. The dispersion interaction between gold surfaces following derivatization with 11-mercaptoundecanoic acid was drastically reduced. The terminal carboxyl groups did not ionize in ethanol. Even in water, extremely low degrees of ionization were observed, with just 1−2% of surface sites being ionized at pH 10. The force curves showed no jump-in nor adhesion above pH 7. We could not reconcile the ψafm−pH results with a simple diffuse layer model for the interface; however the ionization behavior could be explained with sodium ion binding to surface carboxyl groups with a binding constant pK Na = 6.3. The addition of micromolar amounts of Pb2+ caused almost complete neutralization of charged surface groups. These data could be modeled with K Pb = (1−4) × 10-10. An alternative modeling procedure based on incorporation of a zero-order Stern layer could only explain the experimental values if an extremely low value of the inner layer capacitance was assumed of 1−4 μF cm-2. However, this model may be able to explain the lack of jump-in in alkaline solution and the absence of adhesion at high pH.

A Photochemical Preparation of Indoles An organic chemistry experimentThe chemical literature is filled with a variety of organic laboratory photoreactions, which provide novel heterocycles, molecules of theoretical interest, and pharmaceutically valuable, naturally occurring materials. In industry, perhaps the most impressive photochemical process to date is the photooximation of cyclohexane, which produces f-caprolactam (the precursor to Nylon-6) on a 150,000 ton per year scale (7 ). The process was developed by Toyo Rayon of Japan and what is truly remarkable is that the photoreaction proceeds with a quantum yield of less than unity and the product sells for $l-$2/kg. Despite these documented achievements, a search through the many popular organic laboratory textbooks reveals that at best, a single photochemical experiment is included. Almost without exception, the experiment involves the sunlight initiated photoreduction of benzophenone to benzophenol. While the experiment is certainly convenient, it, unfortunately, demonstrates little of the synthetic value of modern organic