Gradation Masking

The success of future searches for photochromic compounds feasible for applications will be determined by the progress in studying the relationship between the structure of these compounds and their properties. 

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In chapter 7, special emphasis has been placed on the synthesis of representative polycyclic quinones and their photochromic behavior, including the spectral, kinetic, and fatigue characteristics of such systems. Potential applications are focused on recording and multiplication of images, optical memories, and gradation masking. 

It is clear that this volume is truly different from the preceding accounts. Photochemists will appreciate Volume 2 as a nice complement to Volume 1, although it can be read independently. Organic photochromic systems are known for their applications in variable-transmission optical materials, ophthalmic lenses, authentification devices (photochromic inks), and novelty items, but they also have great potential in any domain where reversible physical properties are desired (optical memories, gradation masking, optoelectronic systems, nonlinear optical devices, etc.). This book is thus strongly recommended to anyone interested in materials science. 

There is a gradation in the solubility of alcohols in water. The lower alcohols (methanol, ethanol and propan-l-ol) are miscible with water because they can hydrogen bond with water molecules. Heptan-l-ol and longer chain alcohols are insoluble in water. So, as the chain length increases, the solubility decreases because the long non-polar hydrocarbon part of the molecule masks the polar hydroxyl group. 

To summarize, the masking functions in a Merrifield synthesis should be selected in such a gradation of lability that the often repeated N-terminal deprotections endanger neither the C-terminal link to the support nor the masked side functions of the growing peptide. The type of anchoring used should allow us to liberate the peptide in an entirely protected form from its support, to allow further use of the sequence in fragment condensation reactions. 

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