These conditions for oxidative coupling of terminal acetylenes were adopted from: D O'Krongly, S. R. Denmeade, M. Y. Chiang, R. Breslow, J Am. Chrm. S O L . 1985. 107. 5544. The molecular mass of compound 4. but not of 12, was determined by matrixassisted laser desorption time-of-flight mass spectrometry (MALD-TOF-MS) (9-nitroanthracene matrix). We are grateful to Armen Boldi and Prof. Dr. Franqois Diederich, ETH, Zurich. Structure determination of 4: Dlffractometer Nicolet R 3m/V, i(MoKI), graphite monochromator. Wyckoff scan, 3 I 2 0 2 50-, direct methods (SHELXTL-PLUS). Crystal dimensions 0.65 x 0.52 x 0.45 mm3, space group P2,:n, Z = 2. T = 200 K : cell dimensions: a = 6 053(2), h = 21.121(8), c =15 l61(4) A. 1 = 7 = 90', fl = 92.34(2)'. pEalCd = 1 . 3 6 g~m -~. 3397 Independent reflections, of which 2566 were considered observed (F" 2 4a(F)). 229 parameters for the structure refinement, all non-hydrogen atoms anisotropic, R = 0.047. R, = 0.047. Further details of the crystal structure investigation may he obtained from the Fachinformationsrentrum Karlsruhe, D-76344 Eggenstein-Leopoldshafen, on quoting the depository number CSD-400451, the names of the authors. and the journal citation.We recently described the preparation of new materials consisting of helical peptides arranged nearly vertically and unidirectionally from the surface of gold and of indium-tin oxide (ITO) glass."] These layers were produced by polymerization of the N-carbonic anhydride of amino acids, and although they are composed of essentially completely helical structures. the polypeptide chains appeared not to be monodisperse. We report here that these synthetic, oriented peptide layers can be manipulated enzymatically to clip selectively the longer peptide chains, providing a more uniform layer without concurrently destroying bulk material or adversely influencing the high levels of helicity of the layers. These results are significant from two perspectives. First, we have demonstrated that enzymes can be used to manipulate the macroscopic features of bulk materials, in this case resulting in the smoothing of an uneven polymer surface. Second, we have shown that bulk materials comprised of natural substrates for enzymes are resistant to natural enzymatic degradation when formed in a tightly organized array.Through the use of suitable starting "seeds" of different size, we have been able to define an area on the surface that is appropriate for the helical secondary structure of polyphenylalanine, polyethylglycine, and polyleucine on gold (as a thin layer on chromium-coated silicon) and of polyalanine on both I T 0 glass and gold (Fig. I).". Possible applications of these polypeptide Fig. 1. Schematic representation of a layer of helical polyalanine formed by polymerizarion of the N-carbonic anhydride starting with a monolayer of aminotrithiol 1 as a "seed" bound to a gold layer on silicon with an intervening layei ofchromium. For clarity, 1 is shown as a cylinder on the surface layers include waveguide optical switches based on nonlinear ...