Fluorescent probes, proposed

From the results obtained, it was found that compound 10a showed very high fluorescence intensity in the presence of the BSA and BSA/SDS mixture ( F 0.27) together with a noticeable emission enhancement. The presence of dimethyl indo-lenyl increased the affinity of the dyes to both native and denatured proteins. The authors proposed compound 10a for further studies as fluorescent probes for protein detection. 

A method has been proposed for evaluation of LIP concentration in living cells based on the fluorescent probe calcein (Breuer etai, 1995 Epsztejn etai, 1997). The authors assumed that calcein bound Fe2+. However, a more recent thermodynamic and kinetic study indicates that the preferred form bound is Fe3+, and that calcein is a good chemosensor of Fe3+ (Thomas, etai., 1999). The iron... 

Fluorescence probing has also been used by us to investigate the mechanism of vesicle to micelle transformation due to interaction of liposome with sodium dodecyl sulfate micelles. An increase in optical density and hydrodynamic diameter was observed at low SDS concentrations (Fig. 24). The increase was attributed to the incorporation of SDS monomers on liposome vesicles. The point where the hydrodynamic diameter and optical density reached a maximum was proposed to correspond to the saturation of bilayers of the first inflection point. Upon further increase in the SDS concentration... 

Initially, this mechanism was proposed on the basis of results obtained for zeta potential and flotation (Fig. 29). The formation of the hydrophobic aggregates at the interface was confirmed after the advent of the fluorescence probing technique. The adsorption isotherm is determined in the presence of pyrene as the fluorescent probe and the emission spectra of pyrene in both supernatant and slurries were analyzed after adsorption. The h/h of pyrene in solutions of SDS containing 0.1 M NaCl and in the slurry are shown in Figs. 30 and 31. In solution, the ratio remains at around 0.6 till the CMC (as determined by surface tension measurement) is attained. Above CMC, the value becomes 1.0 due to the solubilization of pyrene in micelles. In... 

CD) in comparison with the star shaped analog 43. They also showed that 42 is incorporated easily into phospholipid bilayers. On the other hand, the same group reported the preparation of the coiled coil structure 44 with two amphiphilic 14-residue peptides linked to a bipyridyl template [37], The incorporation of a fluorescent probe, pyrenyl-L-alanine, near the supercoiling region helped them to demonstrate by fluorescence the formation of the proposed structure in water. 

Aldini et al. proposed a method for measuring TAC fractions due to hydrophilic and hydrophobic antioxidants (A6). The hydrophilic system used a water-soluble free radical initiator (ABAP) and a hydrophilic fluorogenic probe (2, 7 -dichloro-dihydrofluorescein). The hydrophobic system was based on a hydrophobic initiator, 2,2/-azobis(4-methoxy-2,4-dimethylvaleronitrile) (MeO-AMVN), and a lipophilic fluorescence probe, 4,4-difluoro-5(4-phenyl-l,3-butadienyl)-4-bora-3a, 4a-diaza-s-indacene-3-undecanoic acid (Cl 1-BODIPY581/591). The red fluorescence of the probe decreased and green fluorescence increased upon oxidation (A6). 

The modulation of synaptosomal plasma membranes (SPMs) by adriamycin and the resultant effects on the activity of membrane-bound enzymes have been reported [58]. Again DPH was used as fluorescence probe. Adriamycin increased the lipid fluidity of the membrane labeled with DPH, as indicated by the steady-state fluorescence anisotropy. The lipid-phase separation of the membrane at 23.3 °C was perturbed by adriamycin so that the transition temperature was reduced to 16.2 °C. At the same time it was found that the Na+,K+-stimulated ATPase activity exhibits a break point at 22.8 °C in control SPMs. This was reduced to 15.8 °C in adriamydn-treated SPMs. It was proposed that adriamycin achieves this effect through asymmetric perturbation of the lipid membrane structure and that this change in the membrane fluidity may be an early key event in adriamycin-induced neurotoxicity. 

Also, HPLC methods with electrochemical or fluorescent detection are used (H19, M3). In proteins, dityrosine can be estimated by immunochemical methods employing dityrosine-specific antibodies (K5). Measurements of o,o -dityrosine and o-tyrosine levels in rat urine express dityrosine contents in skeletal muscle proteins, and have been proposed as the noninvasive oxidative stress test in vivo. One should be aware, however, that A-formylkynurenine, also formed in protein oxidation, has similar fluorescence properties as dityrosine (excitation 325 nm, emission at 400-450 nm) (G29). Also, oxidation of mellitin when excited at 325 nm produces an increase in fluorescence at 400—450 nm, despite the fact that mellitin does not contain tyrosine. Oxidation of noncontaining Trp residues ribonuclease A and bovine pancreatic trypsin inhibitor with "OH produces loss of tyrosine residues with no increase in fluorescence at 410 nm (S51). There are also methods measuring the increased hydrophobicity of oxidized proteins. Assays are carried out measuring protein binding of a fluorescent probe, 8-anilino-l-naphthalene-sulfonic acid (ANS). Increase in probe binding reflects increased surface hydrophobicity (C7). 

Solvatochromic fluorescent probe molecules have also been used to establish solvent polarity scales. The solvent-dependent fluorescence maximum of 4-amino-V-methylphthalimide was used by Zelinskii et al. to establish a universal scale for the effect of solvents on the electronic spectra of organic compounds [80, 213], More recently, a comprehensive Py scale of solvent polarity including 95 solvents has been proposed by Winnik et al. [222]. This is based on the relative band intensities of the vibronic bands I and III of the % - n emission spectrum of monomeric pyrene cf. Section 6.2.4. A significant enhancement is observed in the 0 0 vibronic band intensity h relative to the 0 2 vibronic band intensity /m with increasing solvent polarity. The ratio of emission intensities for bands I and III serves as an empirical measure of solvent polarity Py = /i/Zm [222]. However, there seems to be some difficulty in determining precise Py values, as shown by the varying Py values from different laboratories the reasons for these deviations have been investigated [223]. 

Time-resolved fluorescence spectroscopy and fluorescence anisotropy measurements have been applied to study (i) excimer formation and energy transfer in solutions of poly(acenaphthalene) (PACE) and poly(2-naphthyl methacrylate) (P2NMA) and (ii) the conformational dynamics of poly(methacrylic acid) (PMA) and poly (acrylic acid) as a function of solution pH. For PACE and P2NMA, analysis of projections in which the spectral, temporal and intensity information are simultaneously displayed have been used to re-examine kinetic models proposed to account for the complex fluorescence decay behaviour that is observed. Time-resolved fluorescence anisotropy measuranents of fluorescent probes incorporated in PMA have led to the proposal of a "connected cluster" model for the hypercoiled conformation of this polymer existing at low pH. 

It is proposed that in the presence of fluorescent probes, the energy transfer from excited carbonyl (donor molecule) to an originally unexcited acceptor molecule can take place. Because the energy of excitation of the acceptor comes from the excited donor, the donor is radiationlessly deactivated to its ground electronic state. The acceptor molecule, which has become excited at the expense of the donor, may return... 

In other studies of a broader scope, Loutfy and Law (15,16) reported on the spectroscopy of fluorescence probes in polymeric matrices and on their intramolecular charge-transfer (ICT) interactions. Law (17) also proposed application of the viscosity-dependent fluorescence dyes as sensitive probes for measuring polarity, microviscosity, and structural changes in a micro- environment. More recently, Loutfy and Teegarden (18) have exploited the unique properties of julolidinemalononitr ile (a "molecular rotor" probe with viscosity-dependent fluorescence) for determination of polymer chain tacticity. 

As we have seen so far, interesting pathways have been proposed for the S3mthesis of indoles and indolizines. Many of these molecules have subsequently been involved in tests to assess their biological activity. Natural compoimds with these moieties have also attracted interest, not just as extracts, but as targets for total/semisynthesis or as frameworks for compound libraries. Next, we shall review some of the extremely diverse pharmaceutical appHcations of these derivatives, ranging from fluorescence probes, to antiviral, to anticancer molecules currently in clinical trials. 

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