Rhodamine/ˈroʊdəmiːn/ is a family of related dyes, a subset of thetriarylmethane dyes. They are derivatives ofxanthene. Important members of the rhodamine family arerhodamine 6G,Rhodamin WT,Texas Red (Sulforhodamin 101),rhodamine 123, andrhodamine B. They are mainly used to dye paper and inks, but they lack thelightfastness for fabric dyeing.[1]
Aside from their major applications, they are often used as atracer dye, e.g. to determine the rate and direction of flow and transport of water. Rhodamine dyesfluoresce and can thus be detected usingFluorometers. Rhodamine dyes are used extensively in biotechnology applications such asfluorescence microscopy,flow cytometry,fluorescence correlation spectroscopy andELISA.[2] Rhodamine 123 is used in biochemistry to inhibitmitochondrion function. Rhodamine 123 appears to bind to the mitochondrial membranes and inhibit transport processes, especially theelectron transport chain, thus slowing downcellular respiration. It is a substrate ofP-glycoprotein (Pgp), which is usually overexpressed in cancer cells. Recent reports indicate that rhodamine 123 may also be a substrate of multidrug resistance-associated protein (MRP), or more specifically,MRP1.[3]
In addition to their major applications, rhodamines are used indye laser asgain media.[4][5]
There are many rhodamine derivatives used for imaging purposes, for example Carboxytetramethylrhodamine (TAMRA),[6] tetramethylrhodamine (TMR) and its isothiocyanate derivative (TRITC) andsulforhodamine 101 (and its sulfonyl chloride formTexas Red) and Rhodamine Red. TRITC is the base rhodamine molecule functionalized with anisothiocyanate group (−N=C=S), replacing ahydrogen atom on the bottom ring of the structure. This derivative is reactive towardsamine groups on proteins inside cells. Asuccinimidyl-ester functional group attached to the rhodamine core, creating NHS-rhodamine, forms another common amine-reactive derivative.
Other derivatives of rhodamine include newer fluorophores such asAlexa 546, Alexa 633,DyLight 550 and DyLight 633,HiLyte fluor 555 HiLyte 594,Janelia Dyes JF549 and JF669 have been tailored for various chemical and biological applications where higherphotostability, increased brightness, different spectral characteristics, or different attachment groups are needed.
Substituents of thexanthene core are influencing the properties of thexanthene dyes by both electronic and steric effects. Specifically designedsubstituents also allows xanthenes to bear specific functions activatable upon excitation byvisible light, e.g. they could act asphotoremovable protecting group forcarboxylates andhalides,[7]carbon monoxide (thus being a photoCORM),[8] or added as a secondary functionality of fluorescent dyes, e.g. fluorescentpH indicators.