Substances light-sensitive

Tertiary stibines have been widely employed as ligands in a variety of transition metal complexes (99), and they appear to have numerous uses in synthetic organic chemistry (66), eg, for the olefination of carbonyl compounds (100). They have also been used for the formation of semiconductors by the metal—organic chemical vapor deposition process (101), as catalysts or cocatalysts for a number of polymerization reactions (102), as ingredients of light-sensitive substances (103), and for many other industrial purposes. 

Conjugation is crucial not only for the colors we see in organic molecules but also for the light-sensitive molecules on which our visual system is based. The key substance for vision is dietary /3-carotene, which is converted to vitamin A by enzymes in the liver, oxidized to an aldehyde called 11-frans-retinal, and then isomerized by a change in geometry of the C11-C12 double bond to produce 11-cis-retinal. 

The composition of the planetary atmospheres is fairly constant. This is indeed surprising in view of the fact that molecules such as methane, ammonia, and carbon dioxide are easily decomposed by the ultraviolet radiation from the sun. Presumably other reactions regenerate those substances that are light sensitive. 

For a protected development of light-sensitive substances, a specially designed cover, the Baron Protective Cover against Light for Development Chambo-s, provides auxiliaries. For various chamber sizes of different manufacturers, adjusted models are available. As a special option, a connection for protective gas can also be installed. 

Once treated effluent leaves the WWTP, further degradation of the residual PhC APIs may still occur in surface water bodies. In fact, as mentioned above, if a substance is light sensitive, photodecomposition may contribute to its further removal once in the environment. Phototransformation easily takes place in clear surface water, and the effectiveness of this process is strictly correlated to the intensity and frequency of available light [53, 70]. Nonetheless, this process may be affected by other parameters, specifically pH, water hardness, location, season and latitude [71, 72]. 

Q1B Stability Testing Photostability Testing of New Drug Substances and Products Basic testing protocol required to evaluate light sensitivity and stability of new drugs and products... 

Colloids are classified according to the phases of the substances involved (Table 15.10). A colloid that is a suspension of solids in a liquid is called a sol, and a suspension of one liquid in another is called an emulsion. For example, muddy water is a sol in which tiny flakes of clay are dispersed in water mayonnaise is an emulsion in which small droplets of water are suspended in vegetable oil. Photographic emulsions also contain solid colloidal particles of light-sensitive materials such as silver bromide. Foams are suspensions of a gas in a liquid or solid. Foam rubber, Styrofoam, soapsuds, and aerogels are foams. Zeolites (Box 13.4) are a type of solid foam in which the openings in the solid are comparable in size to molecules. 

Takacs M, Reisch J, Gergely-Zobin A, Giicer-Ekiz N. Light sensitivity investigations of some solid pharmaceutical substances. Sci Pharm 1990 58 ... 

There are several different types of P.O.P., salted paper, albumen, gelatino-chloride, and collodio-chloride, differing in the medium used to suspend the light-sensitive substance and if the sensitizer is applied in the salting solution (as in an emulsion) or as a second step. In the traditional salted paper process the silver is held by the fibers of the paper while albumen papers use egg whites as the binder. Gelatino-chloride papers suspend the silver in a gelatin layer and collodio-chloride uses a binder of cellulose nitrate. 

The basic light-sensitive substance used in all of these papers is silver chloride with an excess of silver nitrate. Once the image has been printed and toned, it is fixed, washed, dried, and preserved in much the same way as a silver print. Because the silver particles of printed out images are a much finer size than those of developed out prints, they are often more susceptible to deterioration. But with proper processing, they will stand the test of time as well as any process. Indeed, collodio-chloride is actually the most stable silver printing process because the nitrocellulose binder hermetically seals the silver from the harmful atmosphere that fades all silver base photographic prints. 

Reduction. Reduction of the reprecipitated dye with stannous chloride and hydrochloric acid produces a brown solution. Nothing separates out from the hot solution. The reduced solution is therefore electrolyzed directly and then evaporated somewhat. On cooling the solution, a light brown substance, rather sensitive to air, is obtained. This compound gives a condensation product with phenanthrenequi-none which has an absorption band at 611.0 m u in concentrated sulfuric acid solution. This phenanthrazine is identical with that from l-amino-y acid. Hence, in benzo light grey BL, acid-coupled y acid is present, undoubtedly as an end component since y acid couples only once. All other reactions also indicate that the reduction product is l-amino-y acid. 

Eisenbrand VJ. Protection of light-sensitive drugs. Pharm Ztg 1927 72(81) 1275-1276. (Scientific Communication, A method for the Testing of the Light Sensitivity of Drug Substances). CA 21,1689. 

Bilirubin is a light sensitive substance, samples should be stored in the dark. Range of measurement 0.5-12 mg/dl or 9-205 xmol/l. 

Special care is necessary in TLC when working with light-sensitive samples. As special precautions must be taken when dealing with these throughout all stages of the work from receipt of the material to the documentation of the chromatogram, a special chapter is devoted to sensitive samples (see Section 10.2 Substances Sensitive to TLC ). 

It may be assumed that when detection is performed using hght-induced reactions, light-sensitive substances are present in the samples, and therefore the entire operation as far as the reaction with hght should be performed in the absence of light. See also Section 10.2.3 Effect of Light . 

If 100 % decomposition occius after the 100 h, the storage time must be reduced. This can be as little as 10 min., e.g. in the case of light-sensitive substances. 

In many operating instructions referring to light-sensitive samples, the precautions that have to be taken are mentioned either simply in the form of footnotes or not at all. However, especially in these circumstances it is essential that the necessary advice on light-protected operation should be given clearly and emphatically at the start of the testing procedure. This is also the case if relatively insensitive substances in sohd form decompose rapidly when in solution. 

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