Secondary structure “mask

Small peptides in solution are generally random coils however, above a certain critical length, the peptides will be able to have secondary structures distinctly different from the random coil. Thus, the critical length for a-helix formation is 7-9 amino acid residues (22). It is not generally possible to predict at what chain length two hydrophobic side-chains are able to interact, whereby the peptide becomes U-shaped, because this must depend on the actual position and nature of the side-chains. This hydrophobic interaction masks the side-chains, resulting in a reduction of the bitter taste. 

To summarize the model above At low DH-values, the majority of the hydrophobic side-chains are still masked and bitterness is low. At increasing DH-values more and more peptides will be too small to form proper secondary structures, the hydrophobic side-chains become exposed, and bitterness increases. At still higher DH-values, however, the peptides are so small that a significant fraction of hydrophobic amino acid will be either free or in terminal position and this will tend to reduce the bitter taste. 

Circular dichroism has been a useful servant to the biophysical chemist sinee it allows the non-invasive determination of secondary structure (a-helices and P-sheets) in dissolved biopolymers. Due to the dissymmetry of these structures (containing chiral centres) they are biaxial and show cireular birefringence. Circular dichroism is the Kramers-Kronig transformation of the resulting optical rotatory dispersion. The spectral window useful for distinguishing between a-helices and so on lies in the region 200-250 nm and henee is masked by certain salts. The method as usually applied is only semi-quantitative, since the measured optieal rotations also depend on the exact amino acid sequence. 

For this reason, we investigated the potential of a backside UV-exposure technique [52-54] to transfer the square structures given by the mask into taper-shaped posts. Thus we can create much slender pillars than predetermined by the mask (see Fig. 1). For this pvupose, we used a chemically amplified resist, SU8, where the polymerization of monomers is induced by a catalytic proton produced by the UV exposixre [55, 56]. The proton migration can be easily controlled by the pre-and post-bake procedixres for the resist and, as we will show here, leads to a new kind of secondary structuring for novel and promissing applications. 

The unique attributes of "catalyzed resins are that they eliminate the need for secondary (after molding) pre-plate activation or "seeding" operations common to conventional plating-on-plastics (POP) processes. For molded circuit board manufacture, catalytic resins are used in two-shot (two-component) molding processes which form highly complex 3D plastic structures which are capable of being selectively plated without the need for plating masks or resists. Polymers currently available in a "catalytic" composition include only amorphous sulfone and imide based systems. 

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