Solvent effects on fluorescence

A wide range of fluorescent derivatization reagents and techniques have been developed to utilize the analytical advantages that fluorescence offers. These derivatization reagents are usually specific to functional groups (e.g., amine, hydroxy, thiol), and their specificity offers yet another opportunity for discriminating against interferents. For excellent reviews, the reader is referred to references [38] and [39]. 

The choice of a fluorescent tag depends on the type of derivatization (e.g., precolumn or postcolunui) because the stability of analyte-tag chemical bonds varies greatly. Therefore, for precolunm derivatization it is important to determine the time delay between derivatization and analysis as well as the stability of the reaction product in the mobile phase prior to HPLC method development. For postcolunm derivatization, compatibility of the reaction solvent with the chromatographic system as well as the rate of reaction are variables that must be considered. 

If a fluorescent derivatizing reagent that is non-fluorescent when unreacted (and therefore detector-transparent) but fluoresces when it becomes the tag (i.e., the part of the derivatizing reagent that is chemically bonded to the analyte) cannot be found. 

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Studies of solvent effects on fluorescence of donor and/or acceptor substituted CPEs demonstrate that in these systems aggregation leads to complete or nearly complete quenching of the fluorescence. For example, in recent work we have shown that the anionic PPE-type CPEs EDOT-PPE-SOa and BDT-PPE-SOa" display relatively strong fluorescence in methanol, DMSO, and DMF however, in water the fluorescence is almost completely quenched. This effect is seen clearly in Figure 14.4 which illustrates the fluorescence of the two polymers in a series of methanol/water mixtures. This effect is believed to... 

Figure 2. Solvent effect on fluorescence of PNA in an aqueous MES buffer (pH 6.0) containing 5%(V/v) ethanol for APC(C2Lys2Cj 4)4 and APC-(CioN+)4 in an aqueous HEPES buffer (pH 8.0) containing 10%(v/v) ethanol for capped-APC in an aqueous CAPS buffer (pH 10.0) containing 5%(v/v) dimethylsulfoxide for APC(CioC02H), APyC(C oC02H)4, and APy+C(CioC02H)4.

A) solvent effects on the fluorescence emission, and (5) the effects of additional reagents and catalysts normally encountered in HPLC assays. 

Samples for studies of CDx effects on fluorescence enhancement in organic solution were prepared using pyrene, because pyrene possesses a long lifetime and is very susceptible to quenching and enhancement in solution (23). An aliquot of pyrene stock solution in cyclohexane was placed under a nitrogen purge to evaporate the cyclohexane. Samples were redissolved in a 1 A mixture of Isopropyl ether and 1-butanol, which was saturated with aqueous CDx solution. Pyrene samples were also prepared in which the organic solvent was not saturated with CDx solution. The mixed solvent was used in order to minimize the effects of ether evaporation and thus allow more accurate quantitation. Fluorescence measurements were made on diluted samples of these solutions. The solvent used to make up the... 

Kamlet MJ, Dickinson C, Taft RW (1981) Linear solvation energy relationship. Solvent effects on some fluorescent probes. Chem Phys Lett 77 69-72... 

Muino PL, Callis PR (2009) Solvent effects on the fluorescence quenching of tryptophan by amides via electron transfer. Experimental and computational studies. J Phys Chem B 113 2572-2577... 

Altoe P, Bemardi F, Garavelli M, Orlandi G, Negri F (2005) Solvent effects on the vibrational activity and photodynamics of the green fluorescent protein chromophore a quantum-chemical study. J Am Chem Soc 127 3952-3963... 

Gorsuch and Hercules 109> stated that certain discrepancies between the fluorescence spectrum of 3-amino-phthalate dianion and the chemiluminescence spectrum of luminol are partly due to reabsorption of the shorter-wavelength chemiluminescence light by the luminol monoanion. These authors confirmed the results of E. H. White and M. M. Bursey 114> concerning the very essential solvent effect on luminol chemiluminescence the relative intensity of the latter in anhydrous DMSO/t-BuOK/ oxygen was found to be about 30,000 times that in DMSO/28 mole % water/potassium hydroxide/oxygen. 

Kamlet M. J., Dickinson C. and Taft R. W. (1981) Linear Solvation Energy Relationships. Solvent Effects on Some Fluorescent Probes, Chem. Phys. Lett. 77, 69-72. 

In this respect, the solvatochromic approach developed by Kamlet, Taft and coworkers38 which defines four parameters n. a, ji and <5 (with the addition of others when the need arose), to evaluate the different solvent effects, was highly successful in describing the solvent effects on the rates of reactions, as well as in NMR chemical shifts, IR, UV and fluorescence spectra, sol vent-water partition coefficients etc.38. In addition to the polarity/polarizability of the solvent, measured by the solvatochromic parameter ir, the aptitude to donate a hydrogen atom to form a hydrogen bond, measured by a, or its tendency to provide a pair of electrons to such a bond, /, and the cavity effect (or Hildebrand solubility parameter), S, are integrated in a multi-parametric equation to rationalize the solvent effects. 

The goal of theory and computer simulation is to predict S i) and relate it to solvent and solute properties. In order to accomplish this, it is necessary to determine how the presence of the solvent affects the So —> Si electronic transition energy. The usual assmnption is that the chromophore undergoes a Franck-Condon transition, i.e., that the transition occurs essentially instantaneously on the time scale of nuclear motions. The time-evolution of the fluorescence Stokes shift is then due the solvent effects on the vertical energy gap between the So and Si solute states. In most models for SD, the time-evolution of the solute electronic stracture in response to the changes in solvent environment is not taken into accoimt and one focuses on the portion AE of the energy gap due to nuclear coordinates. 

Dipole Moments from Solvent Effect on Exciplex Fluorescence Maxima ... 

Transient absorption experiments have shown that all of the major DNA and RNA nucleosides have fluorescence lifetimes of less than one picosecond [2—4], and that covalently modified bases [5], and even individual tautomers [6], differ dramatically in their excited-state dynamics. Femtosecond fluorescence up-conversion studies have also shown that the lowest singlet excited states of monomeric bases, nucleosides, and nucleotides decay by ultrafast internal conversion [7-9]. As discussed elsewhere [2], solvent effects on the fluorescence lifetimes are quite modest, and no evidence has been found to date to support excited-state proton transfer as a decay mechanism. These observations have focused attention on the possibility of internal conversion via one or more conical intersections. Recently, computational studies have succeeded in locating conical intersections on the excited state potential energy surfaces of several isolated nucleobases [10-12]. 

The solvent pH and polarity will affect the absorbance and fluorescence properties of a protein. A notable example of pH effects on absorbance is seen with tyrosine residues, where a change in pH from neutral to alkaline results in a shift of the absorbance maximum to a longer wavelength and an increase in absorptivity due to dissociation of the tyrosine phenolic hydroxyl group (Freifelder, 1982 Fasman, 1989). An example of solvent polarity effects on fluorescence is observed with tryptophan, where a decrease in solvent polarity... 

Several examples have shown that specific interactions such as hydrogen bonding interactions should be considered as one of the intrinsic aspects of solvent effects on absorption or fluorescence spectra. 

As an example of application of the method we have considered the case of the acrolein molecule in aqueous solution. We have shown how ASEP/MD permits a unified treatment of the absorption, fluorescence, phosphorescence, internal conversion and intersystem crossing processes. Although, in principle, electrostatic, polarization, dispersion and exchange components of the solute-solvent interaction energy are taken into account, only the firsts two terms are included into the molecular Hamiltonian and, hence, affect the solute wavefunction. Dispersion and exchange components are represented through a Lennard-Jones potential that depends only on the nuclear coordinates. The inclusion of the effect of these components on the solute wavefunction is important in order to understand the solvent effect on the red shift of the bands of absorption spectra of non-polar molecules or the disappearance of... 

Natural sunlight induced photooxidation of naphthalene in aqueous solution has also been reported by McConkey et al. to produce six major products including 1-naphthol, coumarin, and two hydroxyquinone [9]. The authors proposed that the initially formed 2 + 2 and 2 + 4 photo cyclo addition products undergo subsequent oxidation and/or rearrangement to form the observed products [9]. Grabner et al. have studied solvent effects on the photophysics of naphthalene and report that fluorescence lifetime decreases by a factor of 2.5 in aqueous solution compared to organic solvents (e.g. ethanol, hexane, acetonitrile) [10]. Based on the observed differences in naphthalene excited triplet state properties in aqueous and organic media, the decrease... 

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