3-Hy­droxy-2-(4-hy­droxy­phen­yl)-4H-chromen-4-one

In the title compound, C15H10O4, the benzene ring is twisted at an angle of 20.7 (1)° relative to the 4H-chromene skeleton. In the crystal, adjacent mol­ecules are linked via a network of O—H⋯O and C—H⋯O hydrogen bonds. The mean planes of adjacent 4H-chromene moieties are parallel or oriented at an angle of 20.9 (1)° in the crystal structure

2-(Furan-2-yl)-3-hy­droxy-4H-chromen-4-one

In the crystal structure of the title compound, C13H8O4, the inversely oriented mol­ecules form inversion dimers through pairs of O—H⋯O hydrogen-bonding inter­actions. An intramolecular O—H⋯O hydrogen bond occurs. In the packing of the mol­ecules, the nearly planar 2-(furan-2-yl)-4H-chromene units [dihedral angle between the chromene and furan rings = 3.8 (1)°] are either parallel or inclined at an angle of 80.7 (1)°

Non-coordinating anions assemble cyanine amphiphiles into ultra-small fluorescent nanoparticles

A non-coordinating anion, fluorinated tetraphenylborate, assembles specially designed cationic cyanine amphiphiles into 7–8 nm fluorescent nanoparticles that are >40-fold brighter than a single cyanine dye. This kind of anion, combining hydrophobic and electrostatic forces in aqueous media, constitutes promising building blocks in the self-assembly of functional nanomaterials

In Vivo Behavior of the Antibacterial Peptide Cyclo[RRRWFW], Explored Using a 3-Hydroxychromone-Derived Fluorescent Amino Acid

Labeling biomolecules with fluorescent labels is an established tool for structural, biochemical, and biophysical studies; however, it remains underused for small peptides. In this work, an amino acid bearing a 3-hydroxychromone fluorophore, 2-amino-3-(2-(furan-2-yl)-3-hydroxy-4-oxo-4H-chromen-6-yl)propanoic acid (FHC), was incorporated in a known hexameric antimicrobial peptide, cyclo[RRRWFW] (cWFW), in place of aromatic residues. Circular dichroism spectropolarimetry and antibacterial activity measurements demonstrated that the FHC residue perturbs the peptide structure depending on labeling position but does not modify the activity of cWFW significantly. FHC thus can be considered an adequate label for studies of the parent peptide. Several analytical and imaging techniques were used to establish the activity of the obtained labeled cWFW analogues toward animal cells and to study the behavior of the peptides in a multicellular organism. The 3-hydroxychromone fluorophore can undergo excited-state intramolecular proton transfer (ESIPT), resulting in double-band emission from its two tautomeric forms. This feature allowed us to get insights into conformational equilibria of the labeled peptides, localize the cWFW analogues in human cells (HeLa and HEK293) and zebrafish embryos, and assess the polarity of the local environment around the label by confocal fluorescence microscopy. We found that the labeled peptides efficiently penetrated cancerous cells and localized mainly in lipid-containing and/or other nonpolar subcellular compartments. In the zebrafish embryo, the peptides remained in the bloodstream upon injection into the cardinal vein, presumably adhering to lipoproteins and/or microvesicles. They did not diffuse into any tissue to a significant extent during the first 3 h after administration. This study demonstrated the utility of fluorescent labeling by double-emission labels to evaluate biologically active peptides as potential drug candidates in vivo

Org Biomol Chem

A new fluorescent label N-[4'-(dimethylamino)-3-hydroxyflavone-7-yl]-N-methyl-beta-alanine () was synthesized. Due to two electron donor groups at the opposite ends of the chromophore, an excited state intramolecular proton transfer (ESIPT) resulting in a dual emission was observed even in highly polar media and its fluorescence quantum yield was found to be remarkably high in a broad range of solvents including water. As a consequence, this label exhibits a remarkable sensitivity to the hydration of its environment, which is observed as a color switch between the emission of the ESIPT product (T* form) and that of the normal N* form. The label was coupled to the N-terminus of penetratin, a cell penetrating peptide, in order to study its interactions with lipid membranes and internalization inside the cells. As expected, the binding of penetratin to lipid membranes resulted in a dramatic switch in the relative intensity of its two emission bands as compared to its emission in buffer. Our studies with different lipid compositions confirmed the preference of penetratin to lipid membranes of the liquid disordered phase. After incubation of low concentrations of labeled penetratin with living cells, ratiometric imaging revealed, in addition to membrane-bound species, a significant fraction of free peptide in cytosol showing the characteristic emission from aqueous medium. At higher concentrations of penetratin, mainly peptides bound to cell membrane structures were observed. These observations confirmed the ability of penetratin to enter the cytosol by direct translocation through the cell plasma membrane, in addition to the classical entry by endocytosis. The present probe constitutes thus a powerful tool to study the interaction of peptides with living cells and their internalization mechanisms

Multi-parametric sensing by multi-channel molecular fluorescent probes based on excited state intramolecular proton transfer and charge transfer processes

Considering the applications of fluorescent probes and the information they provide, their brightness of fluorescence and photostability are of paramount importance. However, in the case of steady-state fluorescence spectroscopy and fluorescence microscopy, the amount of information can be increased by the application of multi-channel probes, via a multi-band fluorophore introduced in the probe molecule. In most cases, the use of such a multi-band (or multi-channel) fluorophore can also be combined with the concomitant introduction of one or several analyte receptors. Most often, the design of ratiometric probes with multi-band fluorescence emission are based on phenomena such as photoinduced intramolecular charge transfer (ICT) or excited state intramolecular proton transfer (ESIPT). Although ICT probes were up to recently the most popular, ESIPT probes and among them 3-hydroxyflavone derivatives, were shown to be the most productive. Several general problems were resolved by this family of probes, as for example the measurement of local dielectric constant, local H-bond accepting ability, water local concentration and ATP concentration in small volumes.Incorporation of such multi-channel probes into lipid membranes allowed to measure the different membrane potentials and to detect cell apoptosis. Also, it enabled to recognize and characterize the rafts formation in different lipid bilayers and peculiar features of the charged membrane interface. Such probes are also able to provide a concentration-dependent fluorescence signals upon binding of H+, Mg2+and Ba2+ions, and thus to recognize these different cations.The multi-channel probes are effective tools in the study of interactions of macromolecules such as peptides, proteins and nucleic acids. The most useful feature is that they inform simultaneously about several physical parameters, in this way giving a better insight in the investigated system. Thus, by comparing the reviewed probes with other modern fluorescent approaches, it can be concluded they are more informative and accurate tools