Chromogens color change

Sodagnitins. Chromogenic (color change with aq. KOH colorless reddish violet) triterpenoids (with modified malabaricane skeleton) from die cap skins of the toadstools Cortinarius sodagnitus. C. fulvoincar-natus and C. arcuatorum, e.g., S. C Cj HjoOio, Mr 642.78, colorless powder, mp. 116-119 C (dec.), la) -15 (CHjOH). 

Chemical indicators for dry-heat steriliza tion are available either in the form of pellets enclosed in glass ampuls, or in the form of paper strips containing a heat-sensitive ink. The former displays its end point by melting, the latter by a color change (see Chromogenic materials). 

This type of chromogenic sensor utilizes the coordination chemistry of transition metal complexes, which have vacant binding sites to bind specific anions or have pendant arms containing anion receptor units. Transition metal complexes already have their own specific colors due to their different electronic structures. Coordinating directly to anions or binding of anions by the pendant arms results in perturbations of their electronic structures and causes color changes. 

Recently, Miyaji and coworkers [52] reported the chromogenic molecular switch 65 as a new ditopic ferrocene receptor for anions in the presence of cations. Upon addition of F to a solution of 65 in CH3CN, a new absorbance appeared at 472 nm (Ka=9,340 M"1). Addition of K+ to the solution of 65-F" caused a reverse behavior and the solution turned colorless. This implied that the color change was controlled by F switches on and K+ switches off . This result was... 

Shao and coworkers [61] have demonstrated that a noncovalent charge-transfer complex of calix[4]pyrrole-chloranil can be used as a chromogenic sensor for F and H2POj. Upon addition of calix[4]pyrrole 75 to the solution of chloranil 76 in chloroform, the color changed from pale yellow to blue. This indicated the formation of a charge-transfer complex between calix[4] pyrrole and chloranil in chloroform. The Job s plot analysis showed a 1 1 complex with... 

Besides the covalent attachment of the chromophore to the receptor units or displacement of a chromogenic guest, one can employ the advantages of the selective reactivity between a particular anion and chromogenic hosts, which will display dramatic color changes. There have been at least nine examples of these chromoreactands published recently. 

Chawla and Srinivas have synthesized new chromogenic calix[8]arenes (Figure 97) which exhibit observable color changes (with Al up to 100 nm) with mono- and diamines, the shift being larger for diamines [125]. Diamines were also detected in the presence of an excess of monoamines. 

Chromogenic assays are colorimetric assays which use a substrate containing a chromophore. The substrate itself is designed such that it is colorless, and during the enzymatic reaction the chromophore is released and the color change is measured by a plate reader. This technique is applied for certain enzyme reactions for which a conversion of assays to fluorescent readout for HTS is Hkely to be problematic or even impossible, e.g., when it would require labehng of a small substrate with a large fluorophore. 

Color reactions of mushrooms. The fruit bodies of macromycetes often show characteristic color changes at injury or bruising sites in addition mycologists have described numerous chemical spot reactions. The responsible chromogens are summarized in the table. Lit. 2 hmeister 51,249 ff. 

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