Chemical coupling

The determination of an analyte s concentration based on its absorption of ultraviolet or visible radiation is one of the most frequently encountered quantitative analytical methods. One reason for its popularity is that many organic and inorganic compounds have strong absorption bands in the UV/Vis region of the electromagnetic spectrum. In addition, analytes that do not absorb UV/Vis radiation, or that absorb such radiation only weakly, frequently can be chemically coupled to a species that does. For example, nonabsorbing solutions of Pb + can be reacted with dithizone to form the red Pb-dithizonate complex. An additional advantage to UV/Vis absorption is that in most cases it is relatively easy to adjust experimental and instrumental conditions so that Beer s law is obeyed. 

The ability of dyneins to effect mechano-chemical coupling—i.e., motion coupled with a chemical reaction—is also vitally important inside eukaryotic cells, which, as already noted, contain microtubule networks as part of the cytoskele-ton. The mechanisms of intracellular, microtubule-based transport of organelles and vesicles were first elucidated in studies of axons, the long pro-... 

An important chemical modification method is the chemical coupling method. This method improves the interfacial adhesion. The fiber surface is treated with a compound that forms a bridge of chemical bonds between fiber and matrix. 

For chromatographic sorbents it is necessary that the polymeric cover be uniformly distributed over the silica surface and chemically coupled to it. The appropriate introduction of the initiator is one of the decisive steps of this task. The first method (binding to the surface) increases the yield of grafted polymer. However in this case a large amount of homopolymer is formed. This disadvantage could be prevented by the application of hydroperoxide initiators in combination with the proper redox-agents [78-81],... 

BODIPY fluorophores are a class of probes based on the fused, multi-ring structure, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (Figure 9.27) (Invitrogen) (U.S. patent 4,774,339). This fundamental molecule can be modified, particularly at its 1, 3, 5, 7, and 8 carbon positions, to produce new fluorophores with different characteristics. The modifications cause spectral shifts in its excitation and emission wavelengths, and can provide sites for chemical coupling to label biomolecules. 

Axen, R., Porath, J., and Ernback, S. (1967) Chemical coupling of peptides and proteins to polysaccharides by means of cyanogen halides. Nature (London) 214, 1302-1304. 

A remaining crucial technological milestone to pass for an implanted device remains the stability of the biocatalytic fuel cell, which should be expressed in months or years rather than days or weeks. Recent reports on the use of BOD biocatalytic electrodes in serum have, for example, highlighted instabilities associated with the presence of 02, urate or metal ions [99, 100], and enzyme deactivation in its oxidized state [101]. Strategies to be considered include the use of new biocatalysts with improved thermal properties, or stability towards interferences and inhibitors, the use of nanostructured electrode surfaces and chemical coupling of films to such surfaces, to improve film stability, and the design of redox mediator libraries tailored towards both mediation and immobilization. 

Immobilized antibodies may be used as affinity adsorbents for the antigens that stimulated their production (Figure 6.15). Antibodies, like many other biomolecules, may be immobilized on a suitable support matrix by a variety of chemical coupling procedures. 

Chemical coupling of the dyes to the matrix is usually straightforward, often requiring no more than incubation under alkaline conditions at elevated temperature. The use of noxious coupling chemicals, such as cyanogen bromide, is avoided. 

By the mid-1950s, therefore, it had become clear that oxidation in the tricarboxylic acid cycle yielded ATP. The steps had also been identified in the electron transport chain where this apparently took place. Most biochemists expected oxidative phosphorylation would occur analogously to substrate level phosphorylation, a view that was tenaciously and acrimoniously defended. Most hypotheses entailed the formation of some high-energy intermediate X Y which, in the presence of ADP and P( would release X and Y and yield ATP. A formulation of the chemical coupling hypothesis was introduced by Slater in 1953,... 

The spatial separation between the components of the electron transport chain and the site of ATP synthesis was incompatible with simple interpretations of the chemical coupling hypothesis. In 1964, Paul Boyer suggested that conformational changes in components in the electron transport system consequent to electron transfer might be coupled to ATP formation, the conformational coupling hypothesis. No evidence for direct association has been forthcoming but conformational changes in the subunits of the FI particle are now included in the current mechanism for oxidative phosphorylation. 

Peracchia MT, Vauthier C, Puisieux F, Couvreur P (1997) Development of sterically stabilized poly(isobutyl 2-cyanoacrylate) nanoparticles by chemical coupling of poly(ethylene glycol). J Biomed Mater Res 34 317-326. 

Lu, J.Z., Wu, Q. and McNabb, H.S. (2000). Chemical coupling in wood fiber and polymer composites a review of coupling agents and treatments. Wood and Fiber Science, 32(1), 88-104. 

Alternatively, CO2 can be used as source of CO. Indeed, it is well known that low-valent transition metal complexes can catalyze the chemical or electrochemical reduction of CO2 into CO. This approach was used to generate the mixed nickel complex Ni°bpy(CO)2 by the electrochemical reduction of Nibpy in NMP or DMF in the presence of CO2. The reduced complex can react with alkyl, benzyl, and allylhalides to give the symmetrical ketone along with the regeneration of Nibpy ". A two-step method alternating electroreduction and chemical coupling leading to the ketone has thus been set up (Scheme 9) [126,127]. 

Initial studies of brain delivery based on the chimeric peptide strategy used the absorptive-mediated uptake of cationized albumin which was chemically coupled to the opioid peptide P-endorphin [80] or its metabohcaUy stabilized analogue [D-Ala ]P-endorphin. Tracer experiments in which the chimeric peptide was labelled in the endorphin moiety provided evidence of internalization by isolated brain capillaries and transport into brain tissue in vivo [81]. 

The substance to be assayed—e.g., the hormone thyroxine in a serum sample—is pipetted into a microtiter plate (1), the walls of which are coated with antibodies that specifically bind the hormone. At the same time, a small amount of thyroxine is added to the incubation to which an enzyme known as the "tracer" (1) has been chemically coupled. The tracer and the hormone being assayed compete for the small number of antibody binding sites available. After binding has taken place (2), all of the unbound molecules are rinsed out. The addition of a substrate solution for the enzyme (a chromogenic solution) then triggers an indicator reaction (3), the products of which can be assessed using photometry (4). 

And do you really believe this—No, no, my friend, Flamel is living still — neither he nor his vife are dead It is not above three years since I left both the one and the other in the Indies he is one of my best friends They have been living in various countries long after they had their own coffins buried (Barrett 43). Long-lived and wealthy, Flamel and Perrenelle make an exemplary, functional, childless chemical couple. 

---