Fluorescence spectra quinones

Another example of intramolecular CT complex formation is provided by trans-4-dimethvlamino-4 -(1-oxobutvl)stilbene Solvent effects on the spectrum give a value of 22D for the excited state dipole moment. The effect of electric field on the fluorescence of 4-(9-anthry1)-N.N.-2.3,5,G-hexamethy1-aniline shows this compound forms an excited state whose dipole moment does not change with solvent . Chiral discrimination in exciplex formation between 1-dipyrenylamine and chiral amines is very weak . In the probe molecule PRODAN (6-propionyl)-2-(dimethylamino)—naphthalene the initially formed excited state converts to a lower CT state as directly evidenced by time-resolved spectra in n-butanol. Rate constants for intramolecular electron transfer have been measured in both singlet and triplet states of covalently porphyrin-amide-quinone molecules . Intramolecular excimer formation occurs during the lifetime of the excited state of bis-(naphthalene)hydrazides which are used as photochemical deactivators of metals in polyethylene . ... 

Information regarding the solution conformation of 13 was derived from the pyropheophorbide ring current induced shifts in the resonance positions of the carotenoid and quinone moieties. These two species were found to be extended away from the tetrapyrrole, rather than folded back across it. The absorption spectrum of 13 was essentially identical to the sum of the spectra of model compounds. The pyropheophorbide fluorescence, however, was strongly quenched by the addition of the quinone. This implies the formation of a C-Phe -Q state via photoinitiated electron transfer from the pyropheophorbide singlet state, as was observed for C-P-Q triads (see Figure 4). Excitation of the molecule in dichloromethane solution at 207 K with a 590 nm laser pulse led to the observation of a carotenoid radical cation transient absorption. Thus, the C-Phe -Q " state can go on via an electron transfer step analogous to step 4 in Figure 4 to yield a final C -Phe-Q state. This state had a lifetime of 120 ns. The quantum yield at 207 K was 0.04. At ambient temperatures, the lifetime of the carotenoid radical cation dropped to about SO ns, and the quantum yield could not be determined accurately because of the convolution of the decay into the instrument response function. 

The phosphorescence spectrum ofthe primary electron donor is illustrated for Rb. sphaeroides in Fig. 15 (B). Phosphorescence from the Rb. sphaeroides reaction center complex with the quinones removed was detected at 20 Kon the long-wavelength side ofthe fluorescence and displayed an emission band with a maximum at 1318 nm (or 7590 cm ) and a half bandwidth of240 cm. The ratio of the integrated intensities of this 1318-nm luminescence to that ofthe fluorescence was, as expected, quite small, only... 

Fig. 15. (A) Absorption, fluorescence and phosphorescence spectra of BChl a in vitro at 77 K spectra scaled for convenient presentation also note break of horizontal scale (B) Phosphorescence spectrum of quinone-depleted (-Q) and quinone-containing (+Q) Rb. sphaeroides reaction centers in polyvinyl-alcohol film at 22 K (C) Energy diagram for the components involved in triplet-triplet energy transfer with carotenoids. (A) and (B) and numerical values for the triplet-state energies of BChls a and b and the primary-donors of Rb. sphaeroides and Rp. viridis, i.e., [BChl a and [BChl bjj, respectively, are taken from Takiff and Boxer (1987) Phosphorescence spectra ofbacteriochlorophylls. J Am Chem Soc 110 4425.

The absorption spectrum of the copper amine oxidases shows a characteristic broad band at around 500 nm (460-510 nm) that confers a typical pink or yellow-pink color to highly purified enzyme preparations [10,12,32]. Absorption in the visible region is caused by the presence of the quinone cofactor and thus is not affected by removal of copper from the enzyme under non-reducing conditions [12,32], The quinone cofactor shows emission of fluorescence when excited at 280 and 365 nm [41,106]. Electron transition of Cu(II) is seen in circular dichroism spectra at 600-800 nm [12,32,107]. Under aerobic conditions, addition of the substrate leads to a temporary bleaching of the pink color of the enzyme, which is restored after complete consumption of the substrate. However, anaerobic conditions lead to the formation of a stable yellow intermediate... 

Tocopherol carries six methyl groups three on the hydroquinone ring and three on the side chain. The three chiral centers are all of R configuration (2-R, 4 -R, 8 -R). The most significant chiral center at C2 is as stable to oxidative cleavage as the remote centers at C4 and C8, but it disappears, of course, upon oxidation to the quinone (see Scheme 7.2.1). The UV spectrum shows a maximum at 284 nm (e = 30,000) in petrol ether and at 292 nm in ethanol. Quantitative determination in food occurs by extraction with ether, HPLC, and reduction of Fe(III) ions to Fe(II). The iron(II) concentration is then determined colorimet-rically with 2,2 -dipyridyl = 520 nm) or 4,7-diphenyl-1,10-phenanthrolin. Solutions of free tocopherol fluoresce in the UV( ), whereas neither tocopherol acetate nor the quinone shows any fluorescence (Lang, 1974 Isler and Bmbacker, 1982). This phenomenon is not understood. 

Cory and McKnight (2005) analyzed fluorescence EEMs data for a large number of DOM samples and, using PARAFAC analyses, concluded that approximately 50% of the EEMs spectrum for a given sample could be accounted for by quinone-like fluorophores. However, the presence of quinones in these samples was not quantified and the nature of their influence on the EEMs spectra was not explored. Subsequently, Miller et al. (2006) proposed that a ratio of PARAFAC regions thought to be related to the presence of quinone moieties could be utilized as a proxy for DOM redox status (redox index). 

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