Fluorescence properties of Ca2+-independent discharged obelin and its application prospects

Discharged obelin, a complex of coelenteramide and polypeptide, is a fluorescent protein produced from the photoprotein obelin, which is responsible for bioluminescence of the marine hydroid Obelia longissima. Discharged obelin is stable and nontoxic and its spectra are variable, and this is why it can be used as a fluorescent biomarker of variable color in vivo and in vitro. Here we examined light-induced fluorescence of Ca²⁺-independent discharged obelin (obtained without addition of Ca²⁺). Its emission and excitation spectra were analyzed under variation of the excitation wavelength (260–390 nm) and the emission wavelength (400–700 nm), as well as the 40 °C exposure time. The emission spectra obtained with excitation at 260–300 nm (tryptophan absorption region) included three peaks with maxima at 355, 498, and 660 nm, corresponding to fluorescence of tryptophan, polypeptide-bound coelenteramide, and a hypothetical indole–coelenteramide exciplex, respectively. The emission spectra obtained with excitation at 310–380 nm (coelenteramide absorption region) did not include the 660-nm maximum. The peak in the red spectral region (λ _max?=?660 nm) has not been previously reported. Exposure to 40 °C under excitation at 310–380 nm shifted the obelin fluorescence spectra to the blue, whereas excitation at 260–300 nm shifted them to the red. Hence, red emission and variation of the excitation wavelength form a basis for development of new medical techniques involving obelin as a colored biomarker. The addition of red color to the battery of known (violet to yellow) colors increases the potential of application of obelin.     

Development of a new fluorescent probe for transition metal cations based upon fluorescence resonance energy transfer

A novel fluorescent probe for metal cations, which has a large Stokes shift, was synthesized from the reaction of N-(3-carboxy-2-naphthyl)-ethylenediamine-N,N′,N′-triacetic acid (CNEDTA) with 4-(N,N-dimethylaminosulfonyl)-7-(2-aminoethylamino)-2,1,3-benzoxadiazole (DBD-ED). The large Stokes shift is due to the FRET phenomenon between a donor (CNEDTA) and an acceptor (DBD-ED) fluorophore. When the fluorescent probe, DBD-ED-CNEDTA, was excited at 240, 340 and 440 nm, an emission maximum was observed only at 560 nm. However, the fluorescence (FL) at 480 nm, based upon the CNEDTA moiety, was not detected with excitation at 340 nm. The FL intensity of DBD-ED-CNEDTA was dependent upon the acidity of the medium and highest at pH 4.1. DBD-ED-CNEDTA reacted with metal cations, i.e., Zn, Cd, Al, Y, and La, in aqueous medium to form chelates. The spectral change of FL excitation and emission was small before and after the addition of the metal ions. However, the FL intensity was dependent upon the concentrations of the metal ions. In the case of Zn²⁺, the molar ratio bound with DBD-ED-CNEDTA was calculated as 1:1. The FL intensities after chelate formation of Zn/DBD-ED-CNEDTA (1:1) were enhanced by 3.8-fold (excitation at 340 nm, emission at 560 nm), 4.2-fold (excitation at 440 nm, emission at 560 nm), and 5.9-fold (excitation at 240 nm, emission at 560 nm), respectively. The FL probe was applied to the determination of Zn in a food supplement.     

Reversible intermolecular energy transfer between saturated amines and benzene in non-polar solution

Excitation of a mixture of dimethylethylamine (DEMA) and benzene in n-hexane at 222 nm primarily produces excited amine, while at 261 nm excited benzene predominantly results. The fluorescence spectra appreciably overlap. With 222 nm excitation, DEMA fluorescence is quenched by benzene at the diffusion-controlled rate; this quenching results with nearly unit efficiency in sensitized benzene fluorescence. With 261 nm excitation, some sensitized DEMA fluorescence is observed: the rate constant for tins process is ≈ 2.6 × 10⁹ M^?1 s^?1.     

The photoexcitation of trapped electrons produced in the photoionization of anthracene in liquid n-hexane

The increase in free ions generated by 347 nm light pulses in an n-hexane solution of anthracene by additional excitation at 694 nm is measured at 180–300 K. Combined photoexcitation gives up to 40 times more ions at 185 K. The effect is attributed to an increased probability of electron-ion separation by excitation of elections trapped near positive ions.     

Doublet-doublet fluorescence of benzyl,p-methylbenzyl and p-chlorobenzyl radicals in solution

The doublet-doublet fluorescence spectra of benzyl, p-methylbenzyl and p-chlorobenzyl radicals were detected in the 450–650 nm region upon the double-pulse (248 nm→308 nm) excitation of corresponding benzyl chlorides in hexane at room temperature. The respective fluorescence lifetimes were determined to be ≈ 1 ns or less (benzyl), 14 ns (p-methylbenzyl) and 81 ns (p-chlorobenzyl). Extensively temperature-dependent non-radiative relaxation was confirmed for these benzyl radicals with close-lying lowest doublet excited states.     

Dependencies of the Raman spectra of p-oligophenyls on the chain length and the excitation wavelength

The 1064 nm excited Raman spectra of p-terphenyl, p-quaterphenyl, p-quinquephenyl and p-sexiphenyl have been observed and compared with the 514.5 nm excited spectra. Dependencies of intensities of some major bands on the chain length and the excitation wavelength are discussed in terms of the preresonant Raman effect. A method for estimating the chain length from relative intensities is proposed.     

Optical Gain in Semiconducting Polymer Nano and Mesoparticles

The presence of excited-states and charge-separated species was identified through UV and visible laser pump and visible/near-infrared probe femtosecond transient absorption spectroscopy in spin coated films of poly[N-9″-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) nanoparticles and mesoparticles. Optical gain in the mesoparticle films is observed after excitation at both 400 and 610 nm. In the mesoparticle film, charge generation after UV excitation appears after around 50 ps, but little is observed after visible pump excitation. In the nanoparticle film, as for a uniform film of the pure polymer, charge formation was efficiently induced by UV excitation pump, while excitation of the low energetic absorption states (at 610 nm) induces in the nanoparticle film a large optical gain region reducing the charge formation efficiency. It is proposed that the different intermolecular interactions and molecular order within the nanoparticles and mesoparticles are responsible for their markedly different photophysical behavior. These results therefore demonstrate the possibility of a hitherto unexplored route to stimulated emission in a conjugated polymer that has relatively undemanding film preparation requirements.     

The Fluorescence of native DNA at room temperature

The fluorescence spectra (300–500nm) quantum yields (φ_f) and excitation spectra (240–285 nm) are reported for neutral aqueous sloutions of purified native DNA from calf thymus, E. coli bacterium, and hen erythrocyte near 20°C. The same properties were also measured for a reference solution of mononucleotides, and direct comparisons were made. Whether purified or not, the DNA spectra all closely resemble that from the monomer mixture between 300 and 360 nm but shows a broad, low level shoulder at λ_max ≈ 450nm which is absent in the monomer spectrum. The φ_f for the purified DNA is (4 = 1) x 10^-5, about half that of the monomer reference solution and unpurified DNA. The excitation spectrum is slightly red-shifted from the absorption for both the DNA and the monomer mixture, but not for the individual monomers. The fluorescence exhibits abrupt changes associated with the denaturation of DNA at ≈ 80°C and pII) <4 or > 11.     

Emission spectrum and formation kinetics of neon fluoride

The emission spectrum and the formation kinetics of NeF* is studied using two different excitation techniques. Bye-beam excitation of a Ne/F₂ mixture the yield was found to be low having a maximum at 0.2 hPa of F₂ and at a low neon pressure of less than 0.2 MPa. An ion exchange reaction between Ne⁺ and RbF leading to NeF* was initiated by irradiation of a mixture of neon and RbF vapor using an argon-ion beam. TheD →X transition of NeF* was observed at 107.0 nm, theB →X transition at 108.8 nm. The kinetics of the reactions are discussed.     

Laser photodissociation of Hg(CH3)2: Infrared emission studies of vibrational and rotational excitation in the CH3 fragments

Single-photon dissociation of Hg(CH₃)₂ at 248 and 193 nm produces CH₃ radicals with substantial excitation in the v₂ out-of-plane bend and the v₃ antisymmetric stretch. At 248 nm the antisymmetric stretch excitation is characterized by a 1200–1500 K rotational temperature and a vibrational distribution v=1:v2:v3 of 1.0:0.2±0.1:0.05±0.05.     

On the applicability of the Kasha—Vavilov rule to C60

Via full correction for the instrumental response function, the fluorescence excitation spectrum of C₆₀ in methylcyclohexane between 240 and 580 nm is shown to match the absorption spectrum. This proves that, in contrast to earlier reports, also after UV excitation into higher S_n states, deactivation proceeds virtually completely via the S₁ state, in accordance with the Kasha—Vavilov rule.     

Expanding excitation wavelengths for azobenzene photoswitching into the near-infrared range via endothermic triplet energy transfer

Developing azobenzene photoswitches capable of selective and efficient photoisomerization by long-wavelength excitation is an enduring challenge. Herein, rapid isomerization from the Z- to E-state of two ortho-functionalized bistable azobenzenes with near-unity photoconversion efficiency was driven by triplet energy transfer upon red and near-infrared (up to 770 nm) excitation of porphyrin photosensitizers in catalytic micromolar concentrations. We show that the process of triplet-sensitized isomerization is efficient even when the sensitizer triplet energy is substantially lower (>200 meV) than that of the azobenzene used. This makes the approach applicable for a wide variety of sensitizer-azobenzene combinations and enables the expansion of excitation wavelengths into the near-infrared spectral range. Therefore, indirect excitation via endothermic triplet energy transfer provides efficient and precise means for photoswitching upon 770 nm near-infared light illumination with no chemical modification of the azobenzene chromophore, a desirable feature in photocontrollable biomaterials.

Triplet energy transfer enables efficient Z-to-E photoswitching of azobenzenes even with near-infrared light. Ultrafast intersystem crossing of azobenzene makes the process entropy-driven and enables the use of endothermic sensitizer-azobenzene pairs.     

γ-Fe2O3 Nanoparticles Covered with Glutathione-Modified Quantum Dots as a Fluorescent Nanotransporter

The present paper describes the synthesis, characterization, and utilization of multi-functional magnetic conjugates that integrate optical and magnetic properties in a single structure for use in many biomedical applications. Spontaneous interaction with eukaryotic cell membrane (HEK-239 cell culture) was determined using fluorescence microscopy, and fluorescence analyses. Both, differences in excitation, and emission wavelength were observed, caused by glutathione intake by cells, resulting in disintegration of core–shell structure of quantum dots, as well as adhesion of conjugate onto cell surface. When compared with quantum dots fluorescent properties, HEK-239 cells with incorporated nanoconjugate exhibited two excitation maxima (λ _ex = 430 and 390 nm). Simultaneously, application of ideal λ _ex for quantum dots (λ _ex = 430 nm), resulted in two emission maxima (λ = 740 and 750 nm). This nanoconjugate fulfills the requirements of term theranostics, because it can be further functionalized with biomolecules as DNA, proteins, peptides or antibodies, and thus serves as a tool for therapy in combination with simultaneous treatment.     

Valence States and Luminescence Properties of Ytterbium Ions in Strontium Haloborates

The luminescence properties of ytterbium ions in strontium haloborates were studied under optical, X-ray and synchrotron excitation. The coexistence of Yb ions in two valence states (divalent and trivalent) was detected in the Sr₂B₅O₉X:Yb (X=Cl, Br) powder materials prepared in a slightly reducing (H₂/N₂) or an oxidizing atmosphere. Under optical excitation, the 5d→4f Yb²⁺ luminescence at 420 nm is observed. Even under X-ray excitation, an emission band with a maximum of about 340nm appears in the spectra. This broadband emission is attributed to charge transfer luminescence of Yb³⁺. The influence of the structural features of Sr₂B₅O₉X and some preparative conditions of the samples on the luminescent behavior of Yb are discussed.     

Rapid detection of hydroxyl groups on solid-phase

A rapid method for the qualitative detection of hydroxyl groups on solid-phase has been developed. The method employs N-methylisatoic anhydride to derivatise resin-bound substrates possessing free hydroxyl functionality. The resultant fluorescent ester can be detected by visualisation under a standard laboratory UV lamp at 365 nm excitation.     

Photo-thermal oxidation of thermoplastic polyurethane elastomers: Part 3—Influence of the excitation wavelengths on the oxidative evolution of polyurethanes in the solid state

The detrimental oxidative reactions which occur in thermoplastic polyurethane elastomers based on aromatic isocyanate monomers during irradiation with polychromatic light (λ > 300 nm) may be accounted for by the interference of two mechanisms. The first mechanism, observed at λ < 330–340 nm, involves a photo-Fries rearrangement. The second mechanism is a photo-induced hydroperoxidation. The photo-Fries products exhibit an anti-ultraviolet effect and partially inhibit the photo-induced oxidation. In contrast to aromatic polyurethane elastomers, aliphatic models exposed to ultraviolet light undergo a photo-induced oxidation which is independent of the excitation wavelength.     

Near-infrared excitation of Raman scattering by chromophoric proteins

Fourier-transformed Raman spectra of bacteriorhodopsin, the photosynthetic reaction center, and myoglobin in aqueous solution excited at 1064 nm are presented. These proteins are representative of three important classes of chromophoric proteins. The observed vibrational modes are assigned and discussed based on the known resonance Raman spectra of these proteins. In each case, chromophore vibrations dominate the Raman scattering, with little or no contribution from other protein vibrations. However, the limitations encountered in resonance Raman studies of chromophoric proteins due to sample fluorescence or sample photolability are circumvented. The relative intensities in the bacteriorhodopsin Raman spectrum excited at 1064 nm are nearly identical to the relative intensities previously observed by resonance excitation. The Raman spectrum of the reaction center of the photosynthetic bacterium Rhodobacter sphaeroides excited at 1064 nm contains contributions from both bacteriochlorophyll and bacteriopheophytin pigments, with possible preresonance enhancement of bacteriochlorophyll modes. The 1064-nm-excited Raman spectrum of myoglobin displays several marker bands that have been characterized previously in resonance Raman investigations with excitation in both the Soret and Q-band regions.     

Heterogeneous photosensitization—III the benzaldehyde photopolymer photosensitization of the 1,3-pentadienes in the gas phase [1]

The i.r. absorption spectrum of benzaldehyde photopolymer, formed by photolysis of benzaldehydc: (λ > 300 nm, T = 50°) in a Pyrex cell, shows the absence of specific benzoin absorption at 10·2 μm. The kinetics of the photopolymer sensitized cis ? trans isomerization of the 1.3-pentadienes have been studied for λ > 300 nm and pentadiene pressures between 1 and 470 torr. The luminescence excitation spectra of the photopolymer, the Stern- Volmer plots, and the photostationary state ratios of the 1.3-pentadienes all indicate the presence of two different types of active chromophores in the photopolymer.     

β-Cyclodextrin derived full-spectrum fluorescent carbon dots: The formation process investigation and biological applications

Carbon dots (CDs), a new building unit, have been revolutionizing the fields of biomedicine, bioimaging, and optoelectronics with their excellent physical, chemical, and biological properties. However, the difficulty of preparing excitation-dependent full-spectrum fluorescent CDs has seriously hindered their further research in fluorescence emission mechanisms and biomedicine. Here, we report full-spectrum fluorescent CDs that exhibit controlled emission changes from purple (380 nm) to red (613 nm) at room temperature by changing the excitation wavelength, and the excitation dependence was closely related to the regulation of sp² and sp³ hybrid carbon structures by β-cyclodextrin-related groups. In addition, by regulating the content of β-cyclodextrin, the optimal quantum yields of full-spectrum fluorescent CDs were 8.97%, 8.35%, 7.90%, 9.69% and 17.4% at the excitation wavelengths of 340, 350, 390, 410 and 540 nm, respectively. Due to their excellent biocompatibility and color tunability, full-spectrum fluorescent CDs emitted bright and steady purple, blue, green, yellow, and red fluorescence in MCF-7 cells. Moreover, we optimized the imaging conditions of CDs and mitochondrial-specific dyes; and realized the mitochondrial-targeted co-localization imaging of purple, blue and green fluorescence. After that, we also explored the effect of full-spectrum fluorescent CDs in vivo fluorescence imaging through the intratumorally, subcutaneously, and caudal vein, and found that full-spectrum fluorescent CDs had good fluorescence imaging ability in vivo.     

Excited-state processes in the carotenoid zeaxanthin after excess energy excitation

Aiming for better understanding of the large complexity of excited-state processes in carotenoids, we have studied the excitation wavelength dependence of the relaxation dynamics in the carotenoid zeaxanthin. Excitation into the lowest vibrational band of the S2 state at 485 nm, into the 0-3 vibrational band of the S2 state at 400 nm, and into the 2B(u)+ state at 266 nm resulted in different relaxation patterns. While excitation at 485 nm produces the known four-state scheme (S2 --> hot S1 --> S1 --> S0), excess energy excitation led to additional dynamics occurring with a time constant of 2.8 ps (400 nm excitation) and 4.9 ps (266 nm excitation), respectively. This process is ascribed to a conformational relaxation of conformers generated by the excess energy excitation. The zeaxanthin S state was observed regardless of the excitation wavelength, but its population increased after 400 and 266 nm excitation, suggesting that conformers generated by the excess energy excitation are important for directing the population toward the S state. The S2-S1 internal conversion time was shortened from 135 to 70 fs when going from 485 to 400 nm excitation, as a result of competition between the S2-S1 internal conversion from the vibrationally hot S2 state and S2 vibrational relaxation. The S1 lifetime of zeaxanthin was within experimental error the same for all excitation wavelengths, yielding approximately 9 ps. No long-lived species have been observed after excitation by femtosecond pulses regardless of the excitation wavelength, but excitation by nanosecond pulses at 266 nm generated both zeaxanthin triplet state and cation radical.