Dye interaction technique

Carboxyl end group contents of poly(lactide) were determined by a dye interaction technique proposed by Palit and Mandal (21). A dilute solution of the polymer in benzene is reacted with a dilute benzene solution of a basic dye (e.g., Rhodamine 6G) in its unionized basic... 

The dye interaction technique was used to follow polymer degradations in in vivo and in vitro studies as well as to establish a viscosity-molecular weight relationship for racemic poly(lactide). In order to assure the presence of one carboxyl group per chain partially hydrolized polymers of high initial molecular weights were used in the latter case. The polymers were hydrolyzed with deionized water either in form of solid powder or in tetrahydrofuran or acetone solution with complete agreement of data obtained in both ways. 

Ghosh and co-workers [42] carried out end-group analysis of persulfate-initiated PS using a dye partition and a dye interaction technique. Sulfate and hydroxyl end groups are usually found to be incorporated in the polymer to an average total of 1.5 to 2.5 end groups per polymer chain. 

In dye-binding tests, milk is mixed with excess acidic dye solution where the protein binds the dye in a constant ratio and forms a precipitate. After the dye—protein interaction takes place, the mixture is centrifuged and the optical density of the supernatant is determined. Utilization of the dye is thus measured and from it the protein content determined. Several methods for appHcation of dye-binding techniques to milk are given (24,25). 

With a modified miniemulsion technique using the encapsulated dye and preformed PS(Mw = 50,000gmor ) as hydrophobic costabilizer, the dyes solvent green, solvent yellow, solvent blue, and solvent red could be encapsulated in a PMMA matrix [27, 28], Depending on the concentration and the dye, phase separation occurred during the generation of the composite particles to form dye crystallites enclosed by a polymeric shell [27]. In the dispersed state, the dyes interact with the polymeric matrix, which is manifested by a small but significant bathochromic shift of the absorption maxima [28]. 

There are several other techniques Uke the fluorescent dye displacement assays, footprinting, Fourier transform infrared spectroscopy. X-ray crystallography, electron microscopy, confocal microscopy, atomic force microscopy, surface plasmon resonance etc used for hgand-DNA interactions that are not discussed here. 

One of the most popular applications of molecular rotors is the quantitative determination of solvent viscosity (for some examples, see references [18, 23-27] and Sect. 5). Viscosity refers to a bulk property, but molecular rotors change their behavior under the influence of the solvent on the molecular scale. Most commonly, the diffusivity of a fluorophore is related to bulk viscosity through the Debye-Stokes-Einstein relationship where the diffusion constant D is inversely proportional to bulk viscosity rj. Established techniques such as fluorescent recovery after photobleaching (FRAP) and fluorescence anisotropy build on the diffusivity of a fluorophore. However, the relationship between diffusivity on a molecular scale and bulk viscosity is always an approximation, because it does not consider molecular-scale effects such as size differences between fluorophore and solvent, electrostatic interactions, hydrogen bond formation, or a possible anisotropy of the environment. Nonetheless, approaches exist to resolve this conflict between bulk viscosity and apparent microviscosity at the molecular scale. Forster and Hoffmann examined some triphenylamine dyes with TICT characteristics. These dyes are characterized by radiationless relaxation from the TICT state. Forster and Hoffmann found a power-law relationship between quantum yield and solvent viscosity both analytically and experimentally [28]. For a quantitative derivation of the power-law relationship, Forster and Hoffmann define the solvent s microfriction k by applying the Debye-Stokes-Einstein diffusion model (2)... 

The second label also may be a fluorescent compound, but doesn t necessarily have to be. As long as the second label can absorb the emission of the first label and modulate its signal, binding events can be observed. Thus, the two labeled DNA probes interact with each other to produce fluorescence modulation only after both have bound target DNA and are in enough proximity to initiate energy transfer. Common labels utilized in such assay techniques include the chemiluminescent probe, N-(4-aminobutyl)-N-ethylisoluminol, and reactive fluorescent derivatives of fluorescein, rhodamine, and the cyanine dyes (Chapter 9). For a review of these techniques, see Morrison (1992). 

Fortunately, recent advances in molecular techniques have made it possible for scientists and engineers to monitor dye-degrading communities and their interaction with the other microorganisms during the degradation process (see review [150]). Before the advent of such techniques, the key microbial species in wastewater treatment plants were either unknown or sometimes inefficient bacteria were... 

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