Malachite green, fluorescence

Rhodamine differs from malachite green in the same way as fluorescein differs from phenolphthalein. The latter is known to be non-fluorescent. 

Figure 14.2. Chemical structures of some commonly used organic fluorescent probes 1, fluorescein-5-isothiocyanate (FITC) 2, tetramethylrhodamine-5-isothiocyanate (TRITC) 3, 5-carboxyrhodamine B 4, rhodamine X isothiocyanate (XRITC) 5, malachite green isothiocyanate 6, eosin-5-isothiocyanate 7, 1-pyreneisothiocyanate 8, 7-dimethylaminocoumarin-4-acetic acid 9, CY5.180Su.

Rushing and Hansen (504) described a sensitive analytical procedure for screening and confirmation of residues of malachite green, gentian violet, and their leuco analogs in catfish and trout tissues using liquid chromatographic separation and electrochemical, diode array, and fluorescence detection in series. 

When the coulometric detector was turned on, both leuco forms were completely oxidized to their nonfluorescing chromatic forms and thus vanished from the fluorescence channel. This disappearance was balanced by the arrearance of their chromatic forms in the diode array channel. The confirmation of malachite green, gentian violet, and tlieir leuco analogs in catfish and trout tissue could be based, therefore, on the correct retention times, the observation of the natural fluorescence of the leuco forms when the coulometric detector was turned off, the absence of the leuco form peaks in the 588 nm channel when the coulometric detector was off, the disappearance of the fluorescence of the leuco forms when the coulometric detector was on, the appearance of peaks of parent drugs formed by oxidation of the leuco forms in tlie. S88-nm diode array channel, and the correct ultraviolet-visible spectra maxima for all four peaks. 

A comparable approach could be used to rationalize the intramolecular fluorescence quenching in triphenylmethane (TPM) dyes.211 TPM dyes are structurally related to Michler s ketone, discussed in the preceding section, but they are generally charged systems. The most well-known TPM dyes, crystal violet (CV) and malachite green (MG), have been studied extensively using both steady-state and nanosecond-to-femtosecond time-resolved methods.211-223 A complete account would be beyond the scope of this section. The important facts are that only the normal fluorescence band (FB) is observable and that a nonradiative... 

In the vast majority of cases reported where a streak camera has been used to measure fluorescence lifetimes, the measurements have been made from a single laser shot. Since a high fluorescence efficiency is necessary for single shot experiments, most of these studies have been concerned with measuring the lifetimes and quenching of organic dye molecules in solution. For example, Yu etal. [67] have made a study of the fluorescence lifetime of malachite green as a function of solvent viscosity and the lifetime and relative yield of erythrosin as a function of water concentration in a water—acetone mixture. The fluorescence lifetimes of these dyes are... 

Kolpashchikov DM. Binary malachite green aptamer for fluorescent detection of nucleic acids. J. Am. Chem. Soc. 2005 127 12442-12443. 

As with DNA aptamers, there is a trend towards applying RNA aptamers to a particular application. Allosteric ribozyme sensors have been developed which are specific for caffeine and aspartame. " Using a fluorescence-based assay, caffeine or aspartame may be detected in solution over a 0.5 5mM concentration range. Aptamers designed to malachite green (151) or other triphenylmethane dyes have been developed that enhance the fluorescence of the dye up to 2300-fold. " A further fluorescence-based assay has been... 

Absorption and fluorescence spectra of 7-aminocoumarin derivatives have been recorded and the photophysics of coumarin inclusion complexes with 0- and y-cyclodextrins investigated. Solvent effects on the photophysical behaviour of pyrrolocoumarin derivatives are similar to those on the psorolens . Vibronic exciton bands and the absorption spectra of Eosin Y dimers have been analysed theoretically and compared with experimental data. Picosecond spectroscopic studies have been made on the ionic photodissociation dynamics of malachite green leucocyanide . The lowest state produces ions within 0.1 to 0.5 ns whilst for higher states 6-13 ps are sufficient for the development of charge separation. The photophysics of crystal violet in a series of n-... 

That the compact structure associated with ring closure enhances fluorescence is indicated by the non-fluorescent malachite green as against the fluorescence of rosamine. A simpler example would be that of fluorene... 

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