Photolabile molecule

First, an inert ligand is desirable because it allows the investigator to perform important preliminary experiments with ease. Binding measurements and assays of biological activity are straightforward and unusual experiments that might not be feasible with a chemically reactive molecule can be done. For example, photolabile molecules may be used as haptens for antibody production and the hapten-immunoglobulin interaction subsequently explored (Fleet et al., 1969). 

In resonance Raman experiments it is very important to consider the effect of the absorbed light on the sample composition. Raman scattering and absorption are independent events. Some photons are scattered, but a much larger number are absorbed. Cross sections for Raman scattering are on the order of 10" A /molecule, whereas cross sections for absorption are about 1 A /molecule. Thus, if photon absorption results in a photochemical transformation, as in the case of visual pigments, the effect of the photoalteration must be carefully considered. This situation has been analyzed in detail and rapid-flow methods devised that allow one to obtain resonance Raman spectra of even the most photolabile molecules without distortion of the sample composition. " ... 

Numerous photolabile molecules have been developed for the modification of bioactive cargos, which can be divided into four groups depending on the mechanism of photolysis ... 

Even if examination is limited to the molecular aspects, neglecting strictly photobiological (cellular) aspects, photochemistry has many interactions with biology, from understanding photochemical reactions occurring in nature to photomedicine. The various uses of photolabile molecules for... 

Using a rapid flow technique, where a jet of molecules solved in a liquid flows through a focused laser beam, it is possible to study also photolabile molecules, such as rhodopsin, by resonance Raman spectroscopy [14.32]. This allows investigation of the interesting problem about the molecular mechanisms and dynamics of visual excitation. Rhodopsin molecules act as photoreceptors in the retina of vertebrates. If the rhodopsin sample is rapidly flowed through the focused laser beam, the fraction of isomerized molecules within the illuminated region stays small. This allows measurement of the resonance... 

Intestinal bile-acid-binding protein (IBABP) is a small 14-15-kDa protein found in the cytoplasm of cells in the ileum that binds bile acids as they enter the cell. By using photolabile bile-acid derivative and immunoprecipitation, expression was primarily found in the soluble protein fraction of ileal enter-ocytes, although cholangiocytes do show a low level of expression. One molecule of IBABP binds two bile-acid molecules as shown in Figure 2.4. 

Loudwig, S., Specht, A. and Goeldner, M. (2002) Caged compounds, the photolabile precursors of bioactive molecules. Developments and prospects. Actualite Chimique, (1), 7-12. 

Table 2 lists atmospheric lifetimes for a range of anthropogenic molecules. As seen from Table 2 the lifetimes of pollutant molecules range from minutes or hours for photolabile compounds such as CF3I and HCHO to millennia for perfluoro compounds such as CP4 and SF6. There is discussion as to whether... 

Chromium hexacarbonyl is extremely photolabile (equation 6) therefore photochemical substitution is an efficient means of preparing derivatives. Oxidation of the Cr center requires nitric or sulfuric acid, or chlorine. Alternatively, some hgands induce complete carbonyl dissociation with concomitant oxidation, for example, acetylacetonate. Chemical reduction with alkali or alkaline-earth metals or electrochemical reduction proceeds in two-electron steps with loss of two CO molecules to first give [Cr2(CO)io]" and then [Cr(CO)s]. Nucleophilic attack at CO generates a number of stable (Nu = R) and unstable (Nu = N3, OH, H, NEt2) products. The stable [(OC)5CrCOR] ion is a carbene precursor. 

Of all sample forms, liquid solutions allow drug molecules to the greatest exposure to EMR. The consequence of this is that drugs tend to be more photolabile in solutions than in other sample forms such as solid tablets. This is particularly true for dilute solutions where the absorption and scattering by components in the solution other than drug molecules is minimized. A drug that is stable in powders or tablets may not be stable in liquid solutions. Conversely, a drug that is stable in liquid solution is likely to also be stable in powders and tablets. 

In the second part of the present work we have investigated the thermal and photochemical stabilities of the siliranes synthesized in the first part of the study. Photolysis experiments with the siliranes demonstrate that all of these molecules are photolabile. In general, the product mixtures were so complex that mostly only those compounds could be identified that were, in part, formed... 

A new and efficient route to endo-hirsutene has been described which uses, as the key step, the oxetane (11) from the intramolecular photocycloaddition of (12) (Rawal et ai), and 3-deoxy-D-arabino-2-heptulopyranosonic acids can be synthesised photochemically from Barton esters such as (13) (Barton and Liu). Interest in the development of photochemically removable protecting groups continues, and the irradiation of the 4-hydroxyphenacyl-protected system (14) is reported to release ATP with a quantum yield of 0.37 (Givens and Park). Benzoylbenzoate esters of primary and secondary alcohols undergo cleavage in the presence of electron donor molecules and it is proposed that such esters could be effective photolabile protecting groups for alcohols and that thiols can be similarly protected (Jones et al.). 

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