Fluorescence microwave irradiation

SRN I reactions are generally accelerated by irradiation with tungsten lamps (200-500 W) or fluorescent lamps. They are retarded in the presence of oxygen or other radical inhibitors. Recently, microwave irradiation has been shown to be effective in inducing S l reactions the reaction of Eq. 5.37 proceeds under microwave irradiation (900 W, 5 min) in the presence of trace amounts of water.55... 

Kitayama, Y., Igarashi, H., and Sugimura, H. 2000. Initial intermittent microwave irradiation for fluorescence irradiation for fluorescence in situ hybridization analysis in paraffin-embedded tissue sections of gastrointestinal neoplasia. Lab. Invest. 50 779-781. 

Rosania et al. [19] have shown this straightforward preparation to be advantageous for the transposition to a diversity-oriented, combinatorial approach to an organelle-targeted fluorescent library. Therefore, the condensation of 9 and 10 (Fig. 5.4) with pyrrolidine as a catalyst was performed in 96-well plates and the dehydration reaction was accelerated by microwave irradiation for 5 min to give 10-90% conversion. The resulting library compounds were analyzed using an LC-MS system with diode-array and fluorescence detectors and a fluorescence plate-reader to determine the absorption and emission maxima and the emission colors. 

Recently, Muller and co-workers [145] have reported a series of 3,5-disubstituted and 1,3,5-trisubstituted pyrazoles 104 and 105 by reacting an acyl chloride, a terminal alkyne and a hydrazine via a consecutive one-pot three-component Sonogashira coupling/Michael addition/cyclocondensation sequence under microwave irradiation. The desired products were obtained in good to excellent yields. These obtained pyrazoles are highly fluorescent, both in solution and in the solid state (Scheme 81). 

A, A -dimethylaniline group has been synthesized by a copper-free Sonogashira cross-coupling reaction using microwave irradiation as the source of energy <2006EJO2344>. The electrochemical and photophysical properties of the triad were systematically investigated by techniques such as time-resolved fluorescence and transient absorption spectroscopy. 

Lu et al. have obtained poly(amic acid) side-chain polymers by polycondensation of benzoguanamine and pyromellitic dianhydride under microwave irradiation conditions [65-67]. The reactions were performed in a household microwave oven in which 100 mL DMF solution of 33 mmol benzoguanamine and an equimolar amount of pyromellitic dianhydride were stirred and irradiated for 1 h at 60 °C (Scheme 14.31). The resulting poly(amic acid) was precipitated from the solution and then modified to obtain side-chain polymers with fluorescent and third-order NLO properties. 

Since aU steps of the three-component sequence are conducted under microwave irradiation, the tide compounds can be rapidly obtained (within a total reaction time of 90 min) in mostly moderate yields. As a general trend p-chlorophenyl-substituted N-(prop-2-yn-lyl) acetamide furnishes higher average yields in comparison to the p-tolyl-substituted analogs, which was attributed to the cycloisomerization step of the sequence, where the deprotonarion of the propargyHc position essentially terminates the oxazole formation. Interestingly, the aryl substituted 5-(3-indolyl)oxazoles 43 display intense blue fluorescence and large Stokes shifts upon UV-irradiation both in solution and in the soHd state. 

The correlation function of the fluorescence intensity and the influence of microwave irradiation... 

Clarke and Hofeldt determined the depopulation rates for the individual triplet state spin sublevels of chlorophyll a and chlorophyll b by microwave-modulated fluorescence intensity measurements. The species was dissolved in n-octane at a temperature of 2 K. The solvent n-octane is a low-temperature host matrix which allows high-resolution spectroscopy in the chlorophyll triplet state. Triplet absorption detection of magnetic resonance as well as fluorescence-microwave double resonance techniques were applied. The experimental arrangement was described in Ref. 167. In the case of fluorescence detection, chlorophyll b was irradiated with the 457.9-nm single-mode line of an Ar" laser. Microwave transitions were... 

Li et al. reported the first solid-phase synthesis of a DOFL based on the styryl structure." Styryl compoimds are simple fluorescent molecules that can be prepared by condensation of aldehydes and pyridinium salts. After testing a series of resins and reaction routes, the authors employed a 2-chlorotrityl polystyrene resin to load two amino alcohols with different length chains. The alcohol groups were then mesylated and subsequently treated with four picoline and three quinoline derivatives to render solid-supported pyridinium salts that were then condensed with 64 chemically diverse aldehydes under microwave irradiation (Figure 14.9a). Final cleavage with TFA-DCM (1 99) yielded a collection of 320 styryl dyes with very diverse spectral properties, and they were evaluated as amyloid probes without further purification. 

Bromo-N-alkylnaphthalimides undergo aromatic nucleophilic substitution reaction with amines, alkoxides and thiols under microwave irradiation in the presence of KF/AI2O3 under solvent-free conditions to afford a number of fluorescent 4-sub-stituted-l,8-naphthalimide dyes. This is an efficient method for C-N, C-0 and C-S bond formation by applying suitable nucleophiles. Adducts were produced in good to excellent yields (70-95%) and relatively in short times (Bardajee, 2013). 

Engelhardt et al. (1990) reported that the detection of sensitivity for proteins can be improved significantly by microwave enhanced hydrolysis and snbseqnent postcolumn OPA derivatization. It was observed that the detection limit can be lowered by a factor between 60 and 120 depending on the amino acid composition of the protein in comparison to native fluorescence detection. A hydrolysis time of 45 sec with microwave energy of 750 W was sufficient to reduce the detection limit to 0.04 rg/mL for BSA. It was also shown that protein hydrolysis was not only enhanced by the higher temperatnre achieved but microwave irradiation seems to play a major role in improving the efficiency of the hydrolysis. 

The photochemical reactor used for microwave-assisted experiments is an essential tool for experimental work. Such equipment enables simultaneous irradiation of the sample with both MW and UV-visible radiation. The idea of using an electrodeless lamp, in which the discharge is powered by the MW field, for photochemistry was born half a century ago [53, 62]. The lamp was originally proposed as a source of UV radiation only, without considering the effects of microwaves on photochemical reactions. The first applications of EDL were connected with the construction of a high-intensity source of UV radiation for atomic fluorescence flame spectrometry [88-90]. 

As a second example, Fig. 7.7 shows the optical detection of the zero-field resonance (ODMR) from X-traps (cf Sect. 4.1) in an anthracene crystal at T = 1.2 K [6]. Here, both the variation of the intensity of the phosphorescence. Alp, and also the changes in the intensity AIdf of the delayed fluorescence (cf Sect. 6.9.2) were measured as functions of the microwave frequency. With both methods, aU three zero-field resonances were detected. The optical detection of the resonance at 1850MHz requires simultaneous irradiation at one of the other two resonance frequencies. The method of (optical) detection of this resonance is therefore referred to as electron-electron double resonance (FEDOR). From the three zero-field resonances and their structures, the three fine-structure parameters of two different X-traps in the anthracene crystal were found to be... 

Fig. 7.7 ODMR signals from X-traps in an anthracene crystal at T = 1.2 K. The variations A Ip in the phosphorescence intensity and A Iqp of the intensity of the delayed fluorescence are plotted as functions of the microwave frequency vpp. The signal at 1850 MHz (EEDOR) was detected via simultaneous irradiation with one of the other resonance frequencies.

Moschou et al. used the compact disc microfluidic platform that is spun to allow the centripetal force to achieve pumping of the mobile phase through the channel. They incorporated a poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate-co-[2-(methacryloyloxy) ethyl] trimethylammonium chloride) monolith in the channel of a poly(dimethylsiloxane) (PDMS) chip. The unusual feature of this preparation is the use of irradiation with microwaves in a common domestic microwave oven to initiate the polymerization reaction, which is then completed in only 4.5 min. This is a significantly shorter time compared to 20 h required to obtain monolith using thermally initiated polymerization of the same mixture. This monolith was then used for the purification of enhanced green fluorescent protein in ion-exchange mode. 

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