Publisher Summary This chapter discusses the photoaffinity labeling which could be used as a method that allows to unleash the reagent at a particular time and place, when the chemical affinity labeling restricts it. The chapter notes that the possibility that a labile group of appropriate reactivity cannot be incorporated into the ligand molecule without excessive disturbance of the recognition process, there are two limitations to the affinity labeling approach. The first challenge; the range of chemical reactivity of groups that can be incorporated into the ligand is limited by the fact that these groups must not react so rapidly with water that they are destroyed hydrolytically before the ligand that carries them can reach the binding site. And secondly, it is becoming clear that some biological problems require a reagent whose reactivity remains masked until the experimenter chooses to activate it. Both of the two limitations of classical chemical affinity labeling discussed above can in principle be circumvented by the use of a photogenerated reagent.

[8] Photoaffinity labeling

Photogenerated reagents for biological receptor-site labeling

The application of chemical crosslinking for studies on cell membranes and the identification of surface reporters.

Nanoscale patterning by block copolymer self-assembly is one of the most promising “bottom-up” approaches for nanolithography, and has recently been introduced into large-scale manufacturing environments by IBM for the production of microelectronics based on Air Gap technology. [1] In contrast to conventional “top-down” photolithography, these materials can generate nanostructures in the sub-25 nm size regime by controlling the polymer molecular weight, architecture, polydispersity, and segmental interactions. [2–4] Combining the ability to create nanoscale structures with proven compatibility with current top-down lithographic processes, block copolymer thin films have the potential to become a critical feature of semiconductor manufacturing. [3–16]

Facile Routes to Patterned Surface Neutralization Layers for Block Copolymer Lithography

This first technical session is further developing the technological dimensions of technology transfer, with three illustrations of successful and representative industrial applications. It covers the cases of embedded autonomy in spacecraft applications, advanced avionics solutions for satellite communication and component hybridization for navigation.

Industrial applications

The transients in the flash photolysis of several aromatic azides are identified as triplet nitrenes by their spectra. Their half-lives are determined over a range of concentrations in hexane, ethanol and in several polymeric matrices (polystyrene, sucrose benzoate, polymethylmethacrylate) and are interpreted in terms of three processes : nitrene recombination, hydrogen abstraction from the solvent and reaction of the nitrene with an azido group. Recombination is diffusion-controlled (rate constant ∼109 1. mole–1 sec–1); the same applies to the reaction with an azido group. In contrast, hydrogen abstraction by an aromatic nitrene is a comparatively slow process, corresponding to a life-time (in ethanol) of about 2 × 10–4 sec. This value is corroborated by experiments in soft polystyrene matrices (half-life 10–3sec) and by the rate of intramolecular hydrogen abstraction in the cyclization of 2-nitrenobiphenyl to carbazole (half-life 8 × 10–4 sec). In hard polymeric matrices, hydrogen abstraction is considerably slower (half-lives from 0.1 to 2 sec). Here the rate-determining step is configurational diffusion of CH bonds towards the electron-deficient nitrogen.

Photolysis of aromatic azides. Part 4.—Lifetimes of aromatic nitrenes and absolute rates of some of their reactions

NITRENES have been postulated as intermediates in the decomposition of organic azides, iminoxides, nitro- and nitroso-compounds1–3. Most of the evidence in support of this is convincing but circumstantial4–9. Direct proof of the existence of nitrenes is based on the electron spin resonance spectra of triplet species in the photolysis products of several aromatic azides in a solid matrix at 77° K (ref. 10). Several alkyl-nitrenes have also been discovered in the even more extreme conditions of an organic matrix at 4° K (ref. 11). Recently we recorded the absorption spectra of several aromatic nitrenes12 produced by photolysis in organic glasses at 77° K and were able to detect the nitrene intermediate in the photo-cyclization of 2-azidobiphenyl13.

F. W. Willets

Papers

Photolysis of aromatic azides. Part 4.—Lifetimes of aromatic nitrenes and absolute rates of some of their reactions

Observation of the Nitrene in the Flash-photolysis of 1-Azidoanthracene