Solvatochromic Fluorescent Probes Research Articles

Lipoplexes formed from sugar-based gemini surfactants undergo a lamellar-to-micellar phase transition at acidic pH. Evidence for a non-inverted membrane-destabilizing hexagonal phase of lipoplexes

The present study aims at a better understanding of the mechanism of transfection mediated by two sugar-based gemini surfactants GS1 and GS2. Previously, these gemini surfactants have been shown to be efficient gene vectors for transfection both in vitro and in vivo. Here, using Nile Red, a solvatochromic fluorescent probe, we investigated the phase behavior of these gemini surfactants in complexes with plasmid DNA, so-called lipoplexes. We found that these lipoplexes undergo a lamellar-to-non-inverted micellar phase transition upon decreasing the pH from neutral to mildly acidic. This normal (non-inverted) phase at acidic pH is confirmed by the colloidal stability of the lipoplexes as shown by turbidity measurements. We therefore propose a normal hexagonal phase, H I, for the gemini surfactant lipoplexes at acidic endosomal pH. Thus, we suggest that besides an inverted hexagonal (H II) phase as reported for several transfection-potent cationic lipid systems, another type of non-inverted non-bilayer structure, different from H II, may destabilize the endosomal membrane, necessary for cytosolic DNA delivery and ultimately, cellular transfection.

Phase behavior of laundry surfactants in polar solvents

AbstractLaundry surfactants are usually mixtures of ionic and nonionic detergents that exhibit a complex phase behavior. Here the ternary phase behavior of an isotropic and a liquid crystalline (LC) surfactant mixture has been examined in water/solvent systems. The size of the LC area in the ternary phase diagram was correlated to solvent parameters including the dielectric constant and the Gordon cohesiveness parameter. The Gordon parameter was found to have a linear relationship with the amount of solvent needed to go from an LC to an isotropic state over a wide range of solvents from polar to apolar. For solvents in which no surfactant aggregation (micellar or inverted micellar) is expected, the size of the LC area is linear with the reciprocal of the dielectric constant of the solvent. On diluting practical detergent liquids with water, a large LC area can be avoided by using solvents with a relatively low dielectric constant and with a relatively low molecular weight.The aggregated state of the surfactant mixtures in the isotropic regions of the phase diagram was studied using the solvatochromic fluorescent probe Nile Red. In the water corner of the phase diagram, the surfactants are aggregated into micelles. In strongly polar solvents, such as glycerol, ethylene glycol, formamide, and ethanolamine, the surfactants are also aggregated into micelles. In somewhat less polar solvents, such as methanol, ethanol, and t‐butanol, the surfactant molecules are randomly distributed. In the surfactant‐rich corner of the phase diagram of the isotropic mixture, the surfactant forms inverted micelles. An inverted micelle‐to‐micelle transition could be observed on dilution in ethylene glycol as a discontinuity in the trend of the Nile Red fluorescence maxima.

N-Acylureido Functionality as Acceptor Substituent in Solvatochromic Fluorescence Probes: Detection of Carboxylic Acids, Alcohols, and Fluoride Ions

N,N'-Dicyclohexyl-N-(6'-methoxyanthryl-2-carbonyl)urea (1a) exhibits a strong solvatochromism with respect to its fluorescence properties. The emission maxima of 1a correlate well with the anion-stabilizing properties of the solvent. This feature allows the detection of analytes with high acceptor numbers, such as alcohols and carboxylic acids, and the detection of analytes such as fluoride ions which form strong hydrogen bonds with the amido hydrogen atom.

Reactivity of Benzoyl Chlorides in Nonionic Microemulsions: Potential Application as Indicators of System Properties

The solvolysis reactivity of benzoyl chlorides entails a high sensitivity on medium properties. A systematic study of the reaction of a series of these substrates, varying the electron-withdrawing character of the substituent, has been performed in nonionic microemulsions. The kinetic effects due to variation of microemulsion compositions can be assigned to modifications in system properties, to be precise, to modifications in interface properties. Microemulsion properties that are obtained from kinetic analysis of solvolysis show a good agreement with the characterization of the microemulsion that was made via 1H NMR and solvatochromic fluorescence probes. Benzoyl chlorides with electron-donating groups react through a dissociative mechanism, whereas electron-withdrawing groups favor an associative mechanism. A comparative analysis of reactivity between the different substrates at the interface shows a variation in the contributions of both reaction pathways, associative and dissociative, to the whole reaction mechanism. The confined media shift the point where the mechanism changes from an associative to a dissociative pathway, far away from the turning point in water. Furthermore, the change in mechanism can be modulated by modification of the microemulsion composition.

Phenylene Alkylene Dendrons with Site-Specific Incorporated Fluorescent Pyrene Probes

This report deals with the synthesis and the spectroscopic properties of two second generation (G2) dendrons with site-specific incorporated phenyl pyrene derivatives as solvatochromic fluorescent probes. The generations that do not carry the probe are equipped with volume dummies, pyrene moieties that do not show a solvatochromic effect. Two complementary G2 phenylene alkylene dendrons were synthesized using Suzuki-Miyaura cross coupling. Most of the reactions used in the 10-step sequence generating the target compounds proceeded in good yields. The incorporated probes can be selectively photoexcited and show solvatochromic shifts that are of the same magnitude as for the free probes in a homogeneous solvent environment. In addition to the charge-transfer fluorescence, a broad emission band is observed that is assigned to an intramolecular exciplex formation between the aryl pyrene chromophores.

Nanosecond Dynamics of a Mimicked Membrane-Water Interface Observed by Time-Resolved Stokes Shift of LAURDAN

We studied the dipolar relaxation of the surfactant-water interface in reverse micelles of AOT-water in isooctane in the nanosecond and subnanosecond time ranges by incorporating the amphipathic solvatochromic fluorescent probes LAURDAN and TOE. A negative component was observed in the fluorescence decays in the red edge of the emission spectrum—the signature of an excited state reaction—with LAURDAN but not for TOE. The deconvolution of the transient reconstructed spectra of LAURDAN based on a model constructed by adding together three log-normal Gaussian equations made it possible to separate the specific dynamic solvent response from the intramolecular excited state reactions of the probe. The deconvoluted spectrum of lowest energy displayed the largest Stokes shift. This spectral shift was described by unimodal kinetics on the nanosecond timescale, whereas the relaxation kinetics of water-soluble probes have been reported to be biphasic (on the subnanosecond and nanosecond timescales) due to the heterogeneous distribution of these probes in the water pool. Most of this spectral shift probably resulted from water relaxation as it was highly sensitive to the water to surfactant molar ratio ( w 0) (60–65 nm at w 0 = 20–30). A small part of this spectral shift (9 nm at w 0 = 0) probably resulted from dipolar interaction with the AOT polar headgroup. The measured relaxation time values were in the range of the rotational motion of the AOT polar headgroup region as assessed by LAURDAN and TOE fluorescence anisotropy decays.

Dansylated Aminopropyl Controlled Pore Glass: A Model for Silica−Liquid Solvation

We have prepared a series of aminopropyl controlled pore glass (CPG) particles that have been labeled with a solvatochromic fluorescent probe molecule (dansyl). We report on the behavior of the attached dansyl reporter as a function of dansyl-to-amine molar ratio (i.e., dansyl loading), solvent dipolarity, and surface-residue end capping. In these experiments, we systematically adjust the dansyl loading by 10(5); a range much larger than ever explored. The dansylated CPG particles were also end capped with trimethylchlorosilane to derivatize most of the residual silanol and/or aminopropyl groups. The attached dansyl molecules can be surrounded by other dansyl molecules; they can be distributed within an ensemble of sites with differing physicochemical properties, and/or they can be distributed in sites that are restrictive to dansyl motion and/or solvent inaccessible. At high dansyl loadings, the majority of the dansyl groups are solvated by other dansyl moieties and solvent does not significantly alter the local microenvironment surrounding the average dansyl molecule (i.e., the cybotactic region) to any significant level. At intermediate dansyl loadings, the average distance between the dansyl groups increases and solvent is able to access/solvate/wet the dansyl groups and alter their cybotactic region to a greater extent. At the lowest dansyl loadings studied, the results suggest that these dansyl moieties are localized within solvent inaccessible/restrictive SiO2 sites (e.g., small pores).

Effect of CO2 on the Properties of AOT/Water/Isooctane Reverse Micelles by Fluorescence Study

The effect of compressed CO2 on the properties of sodium bis(2-ethylhexyl) sulfosuccinate/water/isooctane reverse micelles was investigated by steady-state and time-resolved fluorescence spectroscopic techniques. With the solvatochromic fluorescent probe 6-propionyl-2-(dimethylamino)-naphthalene, the steady-state fluorescence spectroscopy indicates a changed environment in multiple microregions of the reverse micelles with increasing CO2 pressure. Quantitative estimates for the micropolarities of micellar cores at different pressures were carried out in terms of the empirical polarity parameter ET(30). The results show that ET(30) is gradually increased with the pressure. The emission of 8-anilino-1-naphthalenesulfonic acid indicates a reduced viscosity inside the micellar cores. Its reduced lifetime characterizes the dynamic property of solvent reorientation within micellar cores increases with the increasing CO2 pressure.

Fluorescent probes for monitoring the pulsed‐laser‐induced photocuring of poly(urethane acrylate)‐based adhesives

AbstractFluorescence spectroscopy was used to study the kinetics of polymerization of acrylic adhesive formulations exposed to a 355‐nm pulsed emission from an Nd‐YAG laser. Nine fluorescent probes were used for monitoring the laser curing, showing different sensitivities. In general, the fluorescence intensity emission increased as crosslinking occurred. In addition, solvatochromic fluorescent probes showed a blueshift in their emission. A relative method was applied for the evaluation of the polymerization rates in three different acrylic systems. Special features of pulsed‐laser‐induced polymerization were treated in detail, such as the influence of the laser pulse frequency and the incident laser beam intensity. The polymerization rate slowed down as the pulse repetition rate decreased. An inhibition period due to oxygen quenching was observed, and it was highly dependent on the laser repetition rate and the nature of the photoinitiator. The effect of the laser beam intensity on the kinetics of such fast reactions was studied. In general, increasing the laser energy improved the rate of polymerization. The degree of cure improved as the polymerization rate increased as a result of faster crosslinking, rather than relaxation volume kinetics. Moreover, a saturation rate effect occurred that depended on the photoinitiator. The different behaviors of the two photoinitiators in the curing of the same acrylic formulation was explained on the basis of primary radical termination. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1227–1238, 2004

Monitoring Ternary Systems of C12E5/Water/Tetradecane via the Fluorescence of Solvatochromic Probes

In this work ternary systems of the nonionic surfactant C12E5 (C12H25(OCH2CH2)5OH), tetradecane, and water were probed by the use of steady state and time-resolved fluorescence. Microemulsions, which were rich in oil, rich in water, and also both continuous in oil and water, were monitored via the application of solvatochromic fluorescent probes. The hydrophobic laser dye Nile Red was used to report from the side of the oil−surfactant interface, while Prodan, which is soluble in each of the constituent solvents, was used to provide a global picture. To complement these, the hydrophilic dye 4-(2-(dimethylamino)phenyl)-1-methylpyridinium iodide was used to report from the side of the water−surfactant interface. The results show the partitioning of the probes into different environments within the ternary systems as evident from the solvatochromic shift in the emission spectra, uncovering similarities between the water-rich and bicontinuous regions in terms of polarity. Estimates for the polarity of the envi...

Solvatochromic fluorescent probes in bicontinuous microemulsions

The fluorescence probes nile red and prodan have been used to study the structure of the bicontinuous phase of C 12E 5/alkane/water microemulsions. For nile red the steady state fluorescence spectrum show contributions from probe located in alkane and surfactant rich regions, together with indications of surfactant hydration. Fluorescence lifetime measurements show multiexponential decay kinetics consistent with this idea. The steady state fluorescence spectrum of prodan in the bicontinuous region also suggests different environments for the probe. Fluorescence anisotropy measurements using rhodamine 6G show that this bicontinuous phase is more ordered than either oil in water or water in oil microemulsions. The fluorescence technique provides a valuable tool with which to elucidate the structure of these complex systems.

Solvatochromic Fluorescent Probes for Monitoring the Photopolymerization of Dimethacrylates

The fluorescent probes 7-(dimethylamino)-4-(trifluoromethyl)coumarin (1), N,N-di-n-butyl-5-(dimethylamino)-1-naphthalenesulfonamide (2), 4-(dimethylamino)-4'-(methylsulfonyl)stilbene (3), 4-(di-methylamino)-4'-(methylsulfonyl)diphenylbutadiene (4), and 4-(dimethylamino)-4'-nitrostilbene (5)(Figure 2) were incorporated in polymeric networks formed by photopolymerization of dimethacrylates of different molecular sizes and polarities (Figure 3). The response of the probe's emission to changes in its environment during photopolymerization was determined and compared with the emissions in solvents of low viscosity of differing polarities (solvatochromism). A comparison between these data reveals that the blue shifts observed during polymerization are roughly proportional to the solvatochromism of each probe.

Synthesis and phase properties of phosphatidylcholine labeled with 8-(2-anthroyl)-octanoic acid, a solvatochromic fluorescent probe

8-(2-Anthroyl)-octanoic acid is a chromophore whose fluorescence properties are strongly dependent on the polarity of the surrounding medium. Synthesis and phase properties of anthroylphosphatidylcholine molecules which were obtained by condensing this anthroyl fatty acid with egg lysophosphatidylcholine are described. In lipid bilayers, fluorescence quenching experiments performed with Cu 2+ ions as quenchers show that the 2-anthroyl group is immersed in the depths of the membrane, at the expected position. In monolayers, anthroyl-PC exhibits a compression curve similar to that of anthryl-PC molecules also obtained by condensing 9-(2-anthryl)-nonanoic acid with egg lysophosphatidylcholine (J. de Bony and J.F. Tocanne (1983) Chem. Phys. Lipids 32, 105–121). These curves were similar to that recorded for dipalmitoylphosphatidylcholine, indicating that in monolayers, anthroyl-PC undergoes a liquid-expended to liquid-condensed phase transition. Molecular area of 0.44, 0.45 and 0.48 nm 2 were measured at π = 30 nM m −1 for anthroyl-PC, DPPC and anthryl-PC, respectively. Fluorescence polarization and differential scanning calorimetry experiments show that in the form of liposomes or when fully hydrated, anthroyl-PC undergoes a gel to liquid phase transition at a temperature of 53°C ( ΔT = 4 K). All these data indicate that in anthroyl-PC, the 2-anthroyl group is no more bulky than a normal acyl chain and that it does not affect the regular phospholipid molecular packing. Anthroyl-PC displays quite distinct fluorescence excitation and emission spectra when dispersed in water, alone, or in the form of a 0.5% (mol/mol) mixture with egg-PC, thus enabling the aggregated and diluted forms of the probe molecules to be identified. On these grounds, it is shown that anthroyl-PC exhibits good miscibility properties with lipids in the liquid phase (egg-PC, or dipalmitoylphosphatidylcholine (DPPC), distearoylphosphatidylcholine (DSPC) and dipalmitoylphosphatidylglycerol (DPPG) above T t) but not with lipids in the gel phase (DPPC, DSPC and DPPG, below T t). Finally, fluorescence polarization experiments show that anthroyl-PC can be used for monitoring lipid phase transition. The potential use of this 2-anthroyl chromophore, when attached to a lipid molecule, for probing microenvironmental polarity and dynamics in membranes is discussed.

Maintaining photographic standards

A novel aminoquinoline derivative (AQ) was synthesized and applied as a solvatochromic fluorescent probe to study proteins and their alterations. AQ is not fluorescent in aqueous solution but has its fluorescence quantum yield significantly increased upon binding to albumin. The generation of an induced circular dichroism signal in AQ confirmed the complexation. The Job's plot method revealed an 1:1 stoichiometry for the host-guest complex. The binding constant was determined by AQ fluorescence increase (2.7 × 105 mol−1 L) and by protein intrinsic fluorescence quenching (5.1 × 105 mol−1 L). The displacement of AQ from albumin by warfarin and ibuprofen showed that Sudlow's drug site-I is the preferential binding site. By applying the Bilot-Kawski solvatochromic model to the spectral shifts of fifteen solvents, the microenvironment dielectric constant at albumin site-I was estimated (ε = 14.8). In agreement, the average fluorescence lifetime of AQ complexed with albumin (6.11 ns) was close to dichloromethane (6.53 ns) and acetone (6.34 ns), which have dielectric constants of 8.9 and 21.0, respectively. Albumin was thermically treated to formation of amyloid fibril aggregates. AQ was able to differentiate the altered and native protein. Sodium dodecyl sulfate-induced aggregation of lysozyme to amyloid fibril was also efficiently detected by the AQ fluorescence increase. AQ was as efficient as the chromogenic bromocresol purple in the quantitative analysis of albumin. In conclusion, AQ can be considered a new solvatochromic fluorescent probe with several potential applications.