-
[show abstract]
[hide abstract]
ABSTRACT: The fluorescence lifetimes of most red emitting organic probes are under 4 nanoseconds, which is a limiting factor in studying interactions and conformational dynamics of macromolecules. In addition, the nanosecond background autofluorescence is a significant interference during fluorescence measurements in cellular environment. Therefore, red fluorophores with longer lifetimes will be immensely helpful. Azaoxa-triangulenium fluorophores ADOTA and DAOTA are red emitting small organic molecules with high quantum yield, long fluorescence lifetime and high limiting anisotropy. In aqueous environment, ADOTA and DAOTA absorption and emission maxima are respectively 540 nm and 556 nm, and 556 nm and 589 nm. Their emission extends beyond 700 nm. Both probes have the limiting anisotropy between 0.36-0.38 at their absorption peak. In both protic and aprotic solvents, their lifetimes are around 20 ns, making them among the longest-lived red emitting organic fluorophores. Upon labeling of avidin, streptavidin and immunoglobulin their absorption and fluorescence are red-shifted. Unlike in free form, the protein-conjugated probes have heterogeneous fluorescence decays, with the presence of both significantly quenched and unquenched populations. Despite the presence of significant local motions due to a flexible trimethylene linker, we successfully measured both intermediate nanosecond intra-protein motions and slower rotational correlation times approaching 100 ns. Their long lifetimes are unaffected by the cell membrane (hexadecyl-ADOTA) and the intra-cellular (DAOTA-Arginine) localization. Their long lifetimes also enabled successful time-gating of the cellular autofluorescence resulting in background-free fluorescence lifetime based images. ADOTA and DAOTA retain a long fluorescence lifetime when free, as protein conjugate, in membranes and inside the cell. Our successful measurements of intermediate nanosecond internal motions and long correlations times of large proteins suggest that these probes will be highly useful to study slower intra-molecular motions and interactions among macromolecules. The fluorescence lifetime facilitated gating of cellular nanosecond autofluorescence should be of considerable help in in vitro and in vivo applications.
PLoS ONE 01/2013; 8(5):e63043. · 4.09 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Curcumin, a naturally occurring yellow-orange pigment with potent antioxidant and antitumor properties, has been attracting researchers from a wide range of fields including chemistry, spectroscopy, biology, and medicine. Ultrafast excited-state processes such as solvation and excited-state intramolecular hydrogen atom transfer (ESIHT) make curcumin an attractive agent for photodynamic therapy. In this report we present studies of linear dichroism and fluorescence anisotropy in oriented and isotropic media. The results show transition moments (long wavelength absorption and emission) oriented along the long molecular axis. Comparison of linear dichroism and excitation anisotropy in oriented and isotropic media suggests that excited-state intramolecular hydrogen atom transfer is probably associated with intramolecular conformational changes that can be constrained in highly stretched poly(vinyl alcohol) (PVA) film.
The Journal of Physical Chemistry B 10/2010; 114(39):12679-84. · 3.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Several derivatives of two new dye systems, with one or two dialkylamino donor groups attached to resonant positions at the periphery of a trioxatriangulenium ion, were synthesized. The mono- and bis-dialkylamino trioxatriangulenium salts (A(1)-TOTA(+) and A(2)-TOTA(+)) were prepared from methoxy-substituted triphenylmethylium (TPM) compounds by aromatic nucleophilic substitution with secondary amines and subsequent intramolecular ring closure. The optical properties of the new triangulenium dyes and their TPM precursors were investigated and compared to those of known TPM and xanthenium dyes. The optical properties were found to be dependent on symmetry and charge localization in the conjugated framework. The trioxatriangulenium dye with two amino groups (A(2)-TOTA(+)) was found to be a strong fluorophore with properties as a blue-shifted rhodamine B. The mono-substituted compound (A(1)-TOTA(+)) was found to be only weakly fluorescent. We assign the weak fluorescence of A(1)-TOTA(+) to an efficient but reversible formation of a nonfluorescent conformation in the excited state, favored by the large degree of charge localization in this dye with only one donor group.
The Journal of Organic Chemistry 09/2010; 75(18):6182-90. · 4.45 Impact Factor
-
Chemistry 02/2010; 16(10):2992-6. · 5.93 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We report a multi-fold enhancement of the fluorescence of methyl-azadioxatriangulenium chloride (Me-ADOTA*Cl) in PVA deposited on a 50 nm thick gold mirror carrying an evaporation induced self-assembly of colloidal silver nanoparticles (Ag-SACs). The average measured increase in fluorescence emission of about 50-fold is accompanied by hot spots with a local enhancement in brigthness close to 200. The long lifetime of the dye allows for the first direct determination of the correlation between the enhancement of emission intensity and the decrease in fluorescence lifetime. The Ag-SACs surface preparation and observed enhancements are highly reproducible. We believe that these robust plasmonic surfaces will find use in sensing platforms for ultrasensitive detection.
Chemical Physics Letters 07/2009; 476(1):46-50. · 2.34 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The super stabilized tris(dialkylamino)-azadioxatriangulenium carbenium ion (A-ADOTA(+)) 4 has been synthesized and characterized. As a result of extended delocalization of the positive charge in the planar triangulenium system and the presence of several strongly electron-donating groups, the A-ATOTA(+) ion displays extreme cation stability with a pK(R+) value close to 25. Furthermore the A-ATOTA(+) ion shows excellent dye properties with intense absorption at 458 nm and high fluorescence quantum yield.
The Journal of Organic Chemistry 05/2009; 74(8):3183-5. · 4.45 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: By use of specular X-ray reflectivity (XR) the structure of a metal-covered organic thin film device is measured with angstrom resolution. The model system is a Langmuir-Blodgett (LB) film, sandwiched between a silicon substrate and a top electrode consisting of 25 A titanium and 100 A aluminum. By comparison of XR data for the five-layer Pb2+ arachidate LB film before and after vapor deposition of the Ti/Al top electrode, a detailed account of the structural damage to the organic film at the buried metal-molecule interface is obtained. We find that the organized structure of the two topmost LB layers (approximately 5 nm) is completely destroyed due to the metal deposition.
Nano Letters 03/2009; 9(3):1052-7. · 13.20 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Paraquat bis(hexafluorophosphate) undergoes stepwise dissociation in acetone. All three species-the neutral molecule, and the mono- and dications-are represented significantly under the experimental conditions typically used in host-guest binding studies. Paraquat forms at least four host-guest complexes with dibenzo[24]crown-8. They are characterized by both 1:1 and 1:2 stoichiometries, and an overall charge of either zero (neutral molecule) or one (monocation). The monocationic 1:1 host-guest complex is the most abundant species under typical (0.5-20 mM) experimental conditions. The presence of the dicationic 1:1 host-guest complex cannot be excluded on the basis of our experimental data, but neither is it unambiguously confirmed to be present. The two confirmed forms of paraquat that do undergo complexation-the neutral molecule and the monocation-exhibit approximately identical binding affinities toward dibenzo[24]crown-8. Thus, the relative abundance of neutral, singly, and doubly charged pseudorotaxanes is identical to the relative abundance of neutral, singly, and doubly charged paraquat unbound with respect to the crown ether in acetone. In the specific case of paraquat/dibenzo[24]crown-8, ion-pairing does not contribute to host-guest complex formation, as has been suggested previously in the literature.
Chemistry 01/2009; 15(1):106-16. · 5.93 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We report a simple synthetic route to novel symmetrical alkylated and acylated amphiphilic 4,4'-diaminoazobenzene dyes, with their optical axis perpendicular to the amphiphilic direction of the molecule. Three different substitution patterns are reported, two of which are highly amphiphilic. At the air-water interface, the amphiphilic azobenzenes form noncrystalline but stable Langmuir films that display an unusual reversible monolayer collapse close to 35 mN/m. The structures and phase transitions were studied by X-ray reflectivity (XR) and grazing-incidence X-ray diffraction, both utilizing synchrotron radiation. Compression beyond the collapse point does not change the XR data, showing that the film is unchanged at the molecular level, even at areas less than half of that of the collapse. This leads to the conclusion that few macroscopic collapse sites are responsible for reversibly removing large amounts of material from the interface.
Langmuir 05/2008; 24(7):3223-7. · 4.19 Impact Factor
