A pulse radiolysis study of the leucocyanide of malachite green dye in organic solvents

Abstract

Microsecond pulse radiolysis studies have been carried out on the leucocyanide of malachite green dye (MGCN) dissolved in either 1,2-dichloroethane, chloroform, carbon tetrachloride, acetone, cyclohexane, benzene, toluene, dimethyl sulfoxide, AyV-dimethylformamide, methanol, 2-propanol, tetrahydrofuran, dioxane, benzonitrile, or acetonitrile. The transient absorption spectra obtained in argon-saturated solutions, and with various added electron scavengers (N20, 02, or CC14), indicate that there are several intermediate species and radiolytic products. We suggest that one product is the carbonium ion (MG+) of malachite green dye (wavelength of the absorption maximum, = 620 nm) and the other 4,4'-bis(dimethylamino)triphenylmethyl radical (MG•, = 400 nm). There is evidence for the formation of an intermediate primary radical cation (MGCN+) and a triplet excited state of malachite green cyanide. In oxygen-depleted solutions the absorbing species with ™, at 620 nm is formed in a fast process completed within the time of the 5.5-ms pulse. However, only in 1,2-dichloroethane solution is this absorption stable during the observation time, whereas in all the other solvents it is unstable and decays within tenths of microseconds, the decay time depending of the solvent. In polar solvents such as Me2SO, DMF, alcohols, and acetonitrile, in the presence of oxygen, formation of the 620-nm absorption takes place in two kinetically distinct processes. The first is very fast (much shorter than the 5.5-ms pulse) and the second much slower (lasting tens of microseconds after the pulse). Possible mechanisms for the fast and slow components of radiolytic dye formation are postulated. 127 (1973), and references therein.(19) (a) Z.

Radiochromic film dosimetry: Recommendations of AAPM Radiation Therapy Committee Task Group 55

“…III.͒ Two radiochromic systems that have been developed for radiographic imaging and dosimetry at absorbed doses greater than those used for radiation therapy are thin films containing either amino-triphenylmethane leucodyes or tetrazolium salts as the colorless radiation sensitive ingredients which are changed to deep colors upon irradiation. Historical details and the results of radiation chemical kinetics studies of these systems can be found in a series of publications by McLaughlin et al 2,[11][12][13]18,35,[42][43][44][45][46][47]…”

Three dimensional radiochromic detection of therapeutic radiation

“…Then the colored dye cation forms, absorbing at 600 to 640nm depending on the nature of the DTB. [14][15][16] An initial example of the color change of a prototype dosimeter formulated with a DTB and radical initiator in polyurethane is shown (Figure 2).…”

Detection of therapeutic radiation in three-dimensions

“…The initial radiolytic reaction is the dissociation of the radical initiator and subsequent reaction with LMG to create a radical which absorbs at ca 425 nm followed by the formation of the malachite green cation absorbing at 630 nm [ 51 – 52 ] ( Fig. 3 ).…”

“…For the ortho - and para -methoxy derivatives, 7 and 8 , respectively, the interpretation of the steric and electronic contributions is not as straight forward since 8 is more dose sensitive than 7 and almost that of 5 . The addition of polar aprotic solvents such as DMSO also enhances the dose sensitivity [ 52 ].…”