Focus Bleach

We bleach our clothes. We bleach our hair. We bleach our teeth. We bleach our skin. We bleach our food. We use bleaches to disinfect and deodorize. 

Some bleaches smell awful. Some, like lemon juice and sunshine, are refreshing. Here are a few things you should know about bleach. 

Colored substances contain molecules with chromophores, areas of the molecule that have double bonds between carbon atoms or oxygen atoms. A good example is beta-carotene, and that section goes into more detail on how molecules become colored. Bleaches attack these chromophores in one of two ways. 

oxidizing bleaches such as sodium hypochlorite break the molecules at the double bond. This results in either a shorter molecule that does not absorb visible light, or a molecule whose chromophore is either shorter or nonexistent. A shorter chro-mophore will absorb light of a shorter wavelength than visible light (such as ultraviolet light), and so does not appear colored. 

Second, reducing bleaches such as lemon juice (in combination with sunlight) or sulfur dioxide convert the double bonds in the chromophore into single bonds, eliminating its ability to absorb visible light. Sometimes the reaction is reversible, where oxygen in the air reacts with the molecule to repair the chromophore, and the stain returns. 

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The major advantage of TIRF is that fluorophores outside the evanescent wave (typically more than 200 nm away from the surface) are not excited. Hence, TIRF has an intrinsic sectioning capability. Of interest is that the section capability (z-resolution) is far better than for confocal microscopy systems, which typically have a z-resolution of about 1 /mi. In addition and in contrast to confocal microscopy, TIRF does not cause out-of-focus bleaching because only the molecules at the surface will sense the evanescent wave. However, in comparison with confocal microscopy, a clear limitation of TIRF is that only one z-plane can be imaged the molecules immediately adjacent to the surface. As a consequence,... 

One-photon excitation has lunitations due to the unwanted out-of-focus fliiorophore absorption and bleaching, and light scattering. These drawbacks can be circumvented if multiphoton excitation of the fliiorophore is used. Since it increases with the nth power of the photon density, significant absorption of the exciting light will only occur at the focal point of the objective where the required high photon density for absorption is reached. Consequently, only... 

Thus, multiphoton excitation eliminates unwanted out-of-focus excitation, lumecessary phototoxity and bleaching. However, efficient power sources are required and, since the efficiency of multiphoton excitation is usually low, the times needed to generate unages are mcreased. 

Figure 3-4 FRAP analysis of strain bearing Sui2-GFP PB, pre-bleached image B, bleached image R, recovered image. The bleached focus is marked with an arrow.

Previous production of pentachlorophenol, as well as the bleaching process in pulp and paper mills, has been shown to be a major source. Changes in industrial processes have resulted in a reduction of PCDD/PCDFs concentration in products. Whereas in the past the chemical industry and, to a lesser extent, the pulp and paper industry were considered to be the main sources of PCDD/PCDFs (and also the cause of many of today s contaminated sites in several industrialized countries), today s dioxin input is mainly due to thermal processes. There is still a considerable focus on waste incineration but, owing to requirements for dioxin reduction in stack gases set by several national authorities, the importance of this category has declined during the last years. Examples can be seen especially in the European emission inventories... 

The high photostability and acute fluorescence intensity are two major features of DDSNs compared to dye molecules in a bulk solution. The early DDSN studies have focused on these two properties [8, 13]. For example, Santra et al. studied the photostability of the Ru(bpy)32+ doped silica nanoparticles. In aqueous suspensions, the Ru(bpy)32+ doped silica nanoparticles exhibited a very good photostability. Irradiated by a 150 W Xenon lamp for an hour, there was no noticeable decrease in the fluorescence intensity of suspended Ru(bpy)32+ doped silica nanoparticles, while obvious photobleaching was observed for the pure Ru(bpy)32+ and R6G molecules. To eliminate the effect from Brownian motion, the authors doped both pure Ru(bpy)32+ and Ru(bpy)32+-doped silica nanoparticles into poly(methyl methacrylate). Under such conditions, both the pure Ru(bpy)32+ and Ru(bpy)32+ doped silica nanoparticles were bleached. However, the photobleaching of pure Ru(bpy)32+ was more severe than that of the Ru(bpy)32+ doped silica nanoparticles. 

Two-photon excitation provides intrinsic 3-D resolution in laser scanning fluorescence microscopy. The 3-D sectioning effect is comparable to that of confocal microscopy, but it offers two advantages with respect to the latter because the illumination is concentrated in both time and space, there is no out-of-focus photo-bleaching, and the excitation beam is not attenuated by out-of-focus absorption, which results in increased penetration depth of the excitation light. 

Fluorescence microphotolysis, or photobleaching, has been widely used to study translational mobility of lipids and proteins in membranes. An attenuated laser beam may be focused down to the diameter of a cell or less. Then the intensity can be suddenly increased by several orders of magnitude, bleaching any fluorescent material present. The return of fluorescent material by free diffusion from a neighboring region (fluorescence recovery after photobleaching) or by diffusion through a membrane into a cell can then be... 

If integral membrane proteins are free to diffuse in the membrane, we expect the same to be true of the individual phospholipid molecules that make up the bilayer. To study the dynamics of these motions, phospholipids were labeled with a fluorescent dye that decomposed irreversibly when it was illuminated by a strong laser. When a laser flash was focused to a small spot on the surface of a cell, the labeled phospholipids in this region abruptly ceased fluorescing (fig. 17.16). Fluorescence then rapidly reappeared as the bleached molecules diffused out of the illuminated region and fresh phospholipids diffused in from outside. 

Many modifications of this basic chemistry have been explored to tailor these resists to deep-UV radiation. For example, changes have been made in the sensitizer so that it bleaches in this wavelength region. Early work in this area was performed on diazo-Meldrum s acid (54) (see structure). This compound functioned as a deep-UV-bleachable dissolution inhibitor however, it was somewhat volatile and, consequently, could be depleted via evaporation during soft bake. More-recent studies have therefore focused on less-volatile sensitizers incorporating heteroatom substitution (55) and on increases in molecular weight (56). 

This article is organized first to examine the issues associated with pulp mill raw materials. It then focuses on chemical pulping, mechanical pulping, bleaching, and papermaking. It is designed to overview the major technical concerns associated with these technologies. 

Figure 9. Beads (similar to FISH spots) were excited every minute sequentially with a 488 nm and a 568 nm laser. The mean intensity of the bead was measured every minute for 3.3 hours (200 sample times). The pattern shows periodic fluctuations in intensity over time indicating an unstable system (6-11). The mean intensity also drops overtime, which implies that the sample is either going out of focus, is emitting less light or is bleaching and emitting less light. Newer microscopes have controls that can correct such a stage drift.

A considerable amount of recent work has focused on the oxidation of polymeric and monomeric carbohydrates in aqueous media. In the context of the biorefinery, these processes could be used for the preparation of oxidized carbohydrates as primary outputs of biomass deconstruction. Of particular interest are processes catalyzed with stable oxygen-centered radicals such as the nitroxyl radical TEMPO (2) (2,2,6,6-tetramethylpiperidi-noxyl) and using bleach as the stoichiometric oxidant. 

This chapter will focus on three important industries where peroxygens have had a significant impact, particularly with respect to environmental issues chemical purification, pulp and paper bleaching and hydrometallurgy and metal finishing. 

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