Introduction to fluorescence probing of biological membranes.

Fluorescence is one of the most powerful and commonly used tools in biophysical studies of biomembrane structure and dynamics that can be applied on different levels, from lipid monolayers and bilayers to living cells, tissues, and whole animals. Successful application of this method relies on proper design of fluorescence probes with optimized photophysical properties. These probes are efficient for studying the microscopic analogs of viscosity, polarity, and hydration, as well as the molecular order, environment relaxation, and electrostatic potentials at the sites of their location.

Tuning excited-state proton transfer dynamics of a 3-hydroxychromone dye in supramolecular complexes via host-guest steric compatibility.

The photophysics of 2-(2'-benzofuryl)-3-hydroxychromone (BFHC) is remarkably modulated in its complexes with macrocyclic hosts such as β-cyclodextrin (β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD) and methyl-β-cyclodextrin (M-β-CD). BFHC exhibits dual emission bands, attributable to excited normal (N*) and tautomer (T*) forms, where the latter originates from the former through an excited-state intramolecular proton transfer (ESIPT) reaction. Fluorescence lifetimes of the tautomer, along with the intensity ratio (IT*/IN*) of the dual emission bands, and the fluorescence quantum yield (Φ) of the dye, increase significantly in the order β-CD < HP-β-CD < M-β-CD to indicate increasing hydrophobicity of the dye environment in the host CD cavity.

Site-selective probing of cTAR destabilization highlights the necessary plasticity of the HIV-1 nucleocapsid protein to chaperone the first strand transfer.

The HIV-1 nucleocapsid protein (NCp7) is a nucleic acid chaperone required during reverse transcription. During the first strand transfer, NCp7 is thought to destabilize cTAR, the (-)DNA copy of the TAR RNA hairpin, and subsequently direct the TAR/cTAR annealing through the zipping of their destabilized stem ends. To further characterize the destabilizing activity of NCp7, we locally probe the structure and dynamics of cTAR by steady-state and time resolved fluorescence spectroscopy.

Sentinel lymph nodes fluorescence detection and imaging using Patent Blue V bound to human serum albumin.

Patent Blue V (PBV), a dye used clinically for sentinel lymph node detection, was mixed with human serum albumin (HSA). After binding to HSA, the fluorescence quantum yield increased from 5 × 10(-4) to 1.7 × 10(-2), which was enough to allow fluorescence detection and imaging of its distribution.

Ab initio study of the solvent H-bonding effect on ESIPT reaction and electronic transitions of 3-hydroxychromone derivatives.

The electronic transitions occurring in 4-(N,N-dimethylamino)-3-hydroxyflavone (DMAF) and 2-furanyl-3-hydroxychromone (FHC) were investigated using the TDDFT method in aprotic and protic solvents. The solvent effect was incorporated into the calculations via the PCM formalism. The H-bonding between solute and protic solvent was taken into account by considering a molecular complex between these molecules.

Sensing micelle hydration by proton-transfer dynamics of a 3-hydroxychromone dye: role of the surfactant headgroup and chain length.

The dynamics of the excited-state intramolecular proton-transfer (ESIPT) reaction of 2-(2'-furyl)-3-hydroxychromone (FHC) was studied in micelles by time-resolved fluorescence. The proton-transfer dynamics of FHC was found to be sensitive to the hydration and charge of the micelles, demonstrated through a decrease of the ESIPT rate constant (k(PT)) in the sequence cationic → nonionic → anionic micelles. A remarkably slow ESIPT with a time constant (τ(PT)) of ~100 ps was observed in the anionic sodium dodecyl sulfate and sodium tetradecyl sulfate micelles, whereas it was quite fast (τ(PT) ≈ 15 ps) in the cationic cetyltrimethylammonium bromide and tetradecyltrimethylammonium bromide micelles.

Lactose-ornithine bolaamphiphiles for efficient gene delivery in vitro.

The development of new nonviral vectors characterized by high transfection efficiency and low cytotoxicity remains an important challenge in the field of gene delivery. Unsymmetrical bolaamphiphiles (bolas) appear as new emerging candidates for this application. In this work, new unsymmetrical bolas, bearing neutral lactonic acid and cationic ornithine residues at the two ends of a hydrophobic spacer, were synthesized and their properties were compared to analogues bearing a gluconic acid residue.

Specific implications of the HIV-1 nucleocapsid zinc fingers in the annealing of the primer binding site complementary sequences during the obligatory plus strand transfer.

Synthesis of the HIV-1 viral DNA by reverse transcriptase involves two obligatory strand transfer reactions. The second strand transfer corresponds to the annealing of the (-) and (+) DNA copies of the primer binding site (PBS) sequence which is chaperoned by the nucleocapsid protein (NCp7). NCp7 modifies the (+)/(-)PBS annealing mechanism by activating a loop-loop kissing pathway that is negligible without NCp7.

New unsymmetrical bolaamphiphiles: synthesis, assembly with DNA, and application for gene delivery.

The success in gene therapy relies strongly on new efficient gene delivery vectors. Nonviral vectors based on lipids and polymers constitute an important alternative to the viral vectors. However, the key problem with these vectors is the poor structural control of their DNA complexes.

Extracellular haemoglobin, oxidative stress and quality of red blood cells relative to perioperative blood salvage.

Background: The quality of blood-pack units in perioperative blood salvage was studied with respect to the presence of extracellular haemoglobin (Hb) and in terms of oxidative stress and the mechanical properties of red blood cells (RBC).

Methods: The study was performed on blood-pack units and patients' blood after retransfusion. Results were compared to those obtained in patients prior to autotransfusion.

Liquid ordered phase in cell membranes evidenced by a hydration-sensitive probe: effects of cholesterol depletion and apoptosis.

Herein, using a recently developed hydration-sensitive ratiometric biomembrane probe based on 3-hydroxyflavone (F2N12S) that binds selectively to the outer leaflet of plasma membranes, we compared plasma membranes of living cells and lipid vesicles as model membranes. Through the spectroscopic analysis of the probe response, we characterized the membranes in terms of hydration and polarity (electrostatics). The hydration parameter value in cell membranes was in between the values obtained with liquid ordered (Lo) and liquid disordered (Ld) phases in model membranes, suggesting that cell plasma membranes exhibit a significant fraction of Lo phase in their outer leaflet.

Unusually slow proton transfer dynamics of a 3-hydroxychromone dye in protic solvents.

The photophysics of a 3-hydroxychromone dye, 2-(2-furyl)-3-hydroxychromone (FHC) was explored in different types of protic solvents by steady-state and time-resolved fluorescence spectroscopy. FHC exhibits a dual emission, attributable to the excited normal (N*) and tautomer (T*) forms resulting from an excited state intramolecular proton transfer (ESIPT) reaction (N*-->T*). The ESIPT rate decreases with an increase in the hydrogen-bond donating ability of protic solvents.

Monitoring biophysical properties of lipid membranes by environment-sensitive fluorescent probes.

We review the main trends in the development of fluorescence probes to obtain information about the structure, dynamics, and interactions in biomembranes. These probes are efficient for studying the microscopic analogs of viscosity, polarity, and hydration, as well as the molecular order, environment relaxation, and electrostatic potentials at the sites of their location. Progress is being made in increasing the information content and spatial resolution of the probe responses.

Visualization of lipid domains in giant unilamellar vesicles using an environment-sensitive membrane probe based on 3-hydroxyflavone.

We characterized the recently introduced environment-sensitive fluorescent membrane probe based on 3-hydroxyflavone, F2N12S, in model lipid membranes displaying liquid disordered (Ld) phase, liquid ordered (Lo) phase, or their coexistence. Steady-state fluorescence studies in large unilamellar vesicles show that the probe dual emission drastically changes with the lipid bilayer phase, which can be correlated with the difference in their hydration. Using two-photon excitation microscopy on giant unilamellar vesicles, the F2N12S probe was found to bind both Ld and Lo phases, allowing visualization of the individual phases from the fluorescence intensity ratio of its two emission bands.

Dual-fluorescence probe of environment basicity (hydrogen bond accepting ability) displaying no sensitivity to polarity.

3-Hydroxyquinolones (3HQs) are a new class of water soluble dual fluorescence probes that can monitor both polarity and basicity (H-bond accepting ability) parameters. Both parameters play an important role in proteins and lipid membranes. Nevertheless, no method exists actually to measure the basicity parameter separately from the polarity.

Combining fluorescence lifetime and polarization microscopy to discriminate phase separated domains in giant unilamellar vesicles.

Using fluorescence lifetime microscopy we study the structure of lipid domains in giant unilamellar vesicles made from sphingomyelin, 1,2-dioleoyl-sn-glycero-3-phosphocholine, and cholesterol. Lifetimes and orientation of a derivative of the fluorescent probe DPH embedded in the membrane were measured for binary and ternary lipid mixtures incorporating up to 42 mol % of cholesterol. The results show that adding cholesterol always increases the lifetime of the probe studied.

Excited state proton transfer and solvent relaxation of a 3-hydroxyflavone probe in lipid bilayers.

The photophysics of a ratiometric fluorescent probe, N-[[4'- N, N-diethylamino-3-hydroxy-6-flavonyl]methyl]- N-methyl- N-(3-sulfopropyl)-1-dodecanaminium, inner salt (F2N12S), incorporated into phospholipid unilamellar vesicles is presented. The reconstructed time-resolved emission spectra (TRES) unravels a unique feature in the photophysics of this probe. TRES exhibit signatures of both an excited-state intramolecular proton transfer (ESIPT) and a dynamic Stokes shift associated with solvent relaxation in the lipid bilayer.

Liquid ordered and gel phases of lipid bilayers: fluorescent probes reveal close fluidity but different hydration.

Hydration and fluidity of lipid bilayers in different phase states were studied using fluorescent probes selectively located at the interface. The probe of hydration was a recently developed 3-hydroxyflavone derivative, which is highly sensitive to the environment, whereas the probe of fluidity was the diphenylhexatriene derivative, 1-[4-(trimethylamino)phenyl]-6-phenylhexa-1,3,5-triene. By variation of the cholesterol content and temperature in large unilamellar vesicles composed of sphingomyelin or dipalmitoylphosphatidlycholine, we generated different phases: gel, liquid ordered (raft), liquid crystalline, and liquid disordered (considered as liquid crystalline phase with cholesterol).

Hydrophobically modified low molecular weight chitosans as efficient and nontoxic gene delivery vectors.

Background: Chitosan derivatives are potential candidates for gene delivery because they are biocompatible and low toxic. However, their use has been limited by their moderate transfection efficiency and the rather large sizes of DNA complexes with high molecular weight chitosans. To circumvent these limitations, we used low molecular weight (approximately 5 kDa) chitosans grafted at 3 and 18 mol% with N-/2(3)-(dodec-2-enyl)succinoyl groups (HM-LMW-ch) that exhibit surfactant-like properties.

Modulation of excited-state intramolecular proton transfer by viscosity in protic media.

3-Hydroxyquinolones undergo excited-state intramolecular proton transfer (ESIPT), resulting in a dual emission highly sensitive to H-bonding perturbations. Here, we report on the strong effect of viscosity on the dual emission of 2-(2-thienyl)-3-hydroxyquinolone in protic solvents. An increase in viscosity significantly decreases the formation of the ESIPT product, thus changing dramatically the ratio of the two emission bands.

Steric control of the excited-state intramolecular proton transfer in 3-hydroxyquinolones: steady-state and time-resolved fluorescence study.

3-Hydroxyquinolones (3HQs), similarly to their 3-hydroxychromone analogs, undergo excited state intramolecular proton transfer (ESIPT) resulting in dual emission. In the ground state, 2-phenyl-3HQ derivatives are not flat due to a steric hindrance between the 2-phenyl group and the 3-OH group that participates in the ESIPT reaction. To study the effect of this steric hindrance on the ESIPT reaction, a number of 3HQ derivatives have been synthesized and characterized in different organic solvents by steady-state and time-resolved fluorescence techniques.

Cell envelope fluidity modification for an effective glutamate excretion in Corynebacterium glutamicum 2262.

1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) was used to assess the cell envelope fluidity of Corynebacterium glutamicum 2262 during a temperature-triggered glutamate producing process. Because the fluorescence lifetime of TMA-DPH was shown to be constant all over the process, fluorescence anisotropy can be considered as a good index of cell envelope fluidity. When the temperature of the fed-batch culture was increased from 33 to 39 degrees C to induce glutamate excretion, the fluorescence anisotropy values decreased from 0.

Sensing of adenosine-5'-triphosphate anion in aqueous solutions and mitochondria by a fluorescent 3-hydroxyflavone dye.

The current work demonstrates the formation of complexes between the tetraanion adenosine-5'-triphosphate (ATP) and the flavone derivative 3-hydroxy-4'-(dimethylamino)flavone (FME). Two kinds of complexes are evidenced. The higher affinity ATP-FME complex corresponds to a stacking of the two aromatic molecules and leads to a strong hypochromicity of the absorption spectrum of the dye.

Fluorescent biomembrane probe for ratiometric detection of apoptosis.

Herein, we developed the first ratiometric fluorescent probe for apoptosis detection. This probe incorporates selectively into the outer leaflet of the cell plasma membrane and senses the loss of the plasma membrane asymmetry occurring during the early steps of apoptosis. The high specificity to the plasma membranes was achieved by introduction into the probe of a membrane anchor, composed of a zwitterionic group and a long (dodecyl) hydrophobic tail.