Malachite green, structure

Von Baeyer (Nobel Prize, 1905) should be credited for having recognized in 1902 the saltlike character of the compounds formed. He then suggested a correlation between the appearance of color and salt formation—the so-called halochromy. Gomberg (who had just shortly before discovered the related stable triphenylmethyl radical), as well as Walden, contributed to the evolving understanding of the structure of related cationic dyes such as malachite green. 

A different approach for the modification of the basic Malachite Green lactone structure has been the replacement of one 4-dimethylaminophenyl group by electron-rich heterocycles. The most thoroughly investigated heterocycle has been the 3-indolyl residue, which may be introduced by two different routes as shown in Scheme 7. 

The valence-bond (resonance) description of the triphenylmethine dye Malachite Green (125) is illustrated in Figure 6.5. Comparison with Figure 6.4 reveals their structural similarity compared with cyanine dyes. Formally, the dye contains a carbonium ion centre, as a result of a contribution from resonance form II. The molecule is stabilised by resonance that involves delocalisation of the positive charge on to the p-amino... 

Fig. 3.23. Structures of malachite green (MG), leucomalachite green (LMG) and demethylated derivatives. Reprinted with permission from S. J. Culp et al. [103].

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.

LC-PB-MS has been investigated as a potential confirmatory method for the determination of malachite green in incurred catfish tissue (81) and of cephapirin, furosemide, and methylene blue in milk, kidney, and muscle tissue, respectively (82). Results showed that the mobile-phase composition, nebulization-de-solvation, and source temperature all play an important role in the sensitivity of the method. The sensitivity increases with decreasing heat capacity of the mobile phase in the order methanol acetonitrile isopropanol water and with decreasing flow rate. A comparison of the PB with the thermospray interface showed that less structural information was provided by the latter, whereas the sensitivity was generally lower with the thermospray interface. 

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... 

Figure 1 Molecular structures of the chromophores involved in the current work (A) crystal violet (CV), (B) malachite green (MG), (C) rhodamine B (rhB), and (D) 2,-(or-3 )-0-(2, 4, 6-trinitrophenyl) adenosine S -triphosphatc (TNP-ATP).

The history of the discovery of the dye Malachite Green in the mid-1870s, followed by its structural elucidation as a trityl derivative, was reviewed.51 Cationic triarylmethane dyes containing one, two, or three naphthalenes [e.g. (16)] were prepared, and their... 

The structure of TCPM and TCPMe also closely resembles that of malachite green (Fig. 2), a well known carcinogenic dye which easily forms radicals. The presence of a compound resembling such a carcinogenic substance in fish could have serious consequences. 

One of the oldest known methods of producing wash-fast colors involves the use of metallic hydroxides, which form a link, or mordant (L. mordere, to bite), between the fabric and the dye. Other substances, such as tannic acid, also function as mordants. The color of the final product depends on both the dye used and the mordant. For instance, the dye Turkey Red (alizarin) is red with an aluminum mordant, violet with an iron mordant, and brownish-red with a chromium mordant. Some important mordant dyes possess a structure based on triphenylmethane, as do Crystal Violet and Malachite Green. 

The addition of nucleophiles to a carbenium ion (4-nitromalachite green, Equation 46) provides a useful reference reaction for nucleophilic attack. Parameters for nucleophiles (2V+) are defined by Equation (47) (the Ritchie equation) for reactions of nucleophile with malachite green and 4-nitromalachite green (see structures in Equation 46). N+ values are tabulated in Appendix 3, Table 4. 

The 2.8 A resolution crystal structure of an aptamer that binds to the chromo-phore malachite green shows the binding site as an asymmetric internal loop flanked by a pair of helices. There are several tiers of stacked nucleotides arranged in pairs, triples and a novel quadruple that encapsulates the ligand. 

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... 

From these spectral data it was possible to draw some conclusions concerning the bonding involved in this chemisorption. The similarity of the spectrum of the adsorbate with that of the malachite green cation dictates that the resonance system shown in structure B must remain... 

Fig. 7 Charge-transfer interactions, (a) Crystal structure of stoichiometric hydrogen phthalatelmalachite green complex. Photograph (b) and ideal representation (c) of phthalic acid/malachite green mixed crystal. (View this an in color.at www.dekker.com.)...

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