Dependence Of Fluorescence Intensity Research Articles

Developing a method of rapid diagnosis of the photosynthetic apparatus status of sugar beet plants based on chlorophyll fluorescence intensity

Chloropyll fluorescence intensity dependence on biological features of sugar beet hybrids and plant growth stages is described. Accuracy of a method of rapid diagnosis of the photosynthetic apparatus status of sugar beet plants are evaluated.

Three-photon excitation of quantum dots with a telecom-band ultrafast fiber laser

We demonstrate three-photon excitation in quantum dots with a mode-locked fiber laser operating in the telecommunications band. We compare spectra and intensity dependence of fluorescence from one- and three-photon excitation of commercially available 640 nm quantum dots, using a 372 nm diode laser for one-photon excitation and 116 fs pulses from a mode-locked fiber laser with a center wavelength of 1575 nm for three-photon excitation.

Luminescent lanthanide-containing chiral liquid crystalline polymers in the side chain

Luminescent lanthanide-containing chiral liquid crystalline polymers are graft-copolymerised using poly(methylhydrogeno)siloxane (PMHS), crosslinking agent, liquid crystalline monomer and lanthanide complexes. The chemical structures of the monomers are characterised by FTIR, 1 H NMR and elemental analyses. The mesomorphic properties and phase behaviour are investigated by differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy and X-ray diffraction. The polymers containing less than 9 mol% of the crosslinking units reveal reversible mesomorphic phase transition, wide mesophase temperature ranges and high thermal stability. With the introduction of lanthanide complex units, the polymers are enabled with the significant luminescent properties. The temperature dependence of fluorescence intensity was studied in the liquid crystalline phase. The IR imaging shows that the lanthanide complex units evenly distribute in polymers.

Strongly conjugated hydroporphyrin dyads: extensive modification of hydroporphyrins' properties by expanding the conjugated system.

We report the synthesis and basic photophysical characterization of strongly conjugated hydroporphyrin (chlorin and bacteriochlorin) dyads. Hydroporphyrins are connected at their respective 13 (β) or 15 (meso) positions by ethynyl or butadiynyl linkers. Synthesis entails a series of palladium-catalyzed reactions, starting from appropriate bromobacteriochlorin or bromochlorin. Strong conjugation in the dyads results in a significant bathochromic shift of longest-wavelength (Qy-like) band, which in case of the 13-13' ethynyl-linked bacteriochlorin dyad is positioned past 800 nm. The Qy-like band is broad and split for the 13-13' linked chlorin and bacteriochlorin dyads. All dyads exhibit an intense, relatively narrow fluorescence emission band in nonpolar solvents. Bacteriochlorin dyads exhibit a strong dependence of fluorescence intensity on the solvent polarity, which results in more than 10-fold quenching of fluorescence in dimethylformamide. The assembling of hydroporphyrins into strongly conjugated arrays represents an efficient means to tune and expand their optical and photochemical properties, which should greatly broaden the properties attainable for these chromophores.

Fluorescence of dyes in solutions with high absorbance. Inner filter effect correction.

Fluorescence is a proven tool in all fields of knowledge, including biology and medicine. A significant obstacle in its use is the nonlinearity of the dependence of the fluorescence intensity on fluorophore concentration that is caused by the so-called primary inner filter effect. The existing methods for correcting the fluorescence intensity are hard to implement in practice; thus, it is generally considered best to use dilute solutions. We showed that correction must be performed always. Furthermore, high-concentration solutions (high absorbance) are inherent condition in studying of the photophysical properties of fluorescent dyes and the functionally significant interactions of biological macromolecules. We proposed an easy to use method to correct the experimentally recorded total fluorescence intensity and showed that informative component of fluorescence intensity numerically equals to the product of the absorbance and the fluorescence quantum yield of the object. It is shown that if dye molecules do not interact with each other and there is no reabsorption (as for NATA) and spectrofluorimeter provides the proportionality of the detected fluorescence intensity to the part of the absorbed light (that is possible for spectrofluorimeter with horizontal slits) then the dependence of experimentally detected total fluorescence intensity of the dye on its absorbance coincides with the calculated dependence and the correction factor for eliminating the primary inner filter effect can be calculated on the basis of solution absorbance. It was experimentally shown for NATA fluorescence in the wide range of absorbance (at least up to 60). For ATTO-425, which fluorescence and absorption spectra overlap, the elimination of the primary and secondary filter effects and additional spectral analysis allow to conclude that the most probable reason of the deviation of experimentally detected fluorescence intensity dependence on solution absorbance from the calculated dependence is the dye molecules self-quenching, which accompanies resonance radiationless excitation energy transfer.

Production of CH (A2 Δ) by multi-photon dissociation of (CH3)2CO, CH3NO2, CH2Br2, and CHBr3 at 213 nm

In order to realize electrostatic Stark deceleration of CH radicals and study cold chemistry, the fifth harmonic of a YAG laser is used to prepare CH (A2Δ) molecules through using the multi-photon dissociation of (CH3)2CO, CH3NO2, CH2Br2, and CHBr3 at ∼ 213 nm. The CH product intensity is measured by using the emission spectrum of CH (A2 Δ → X2 Π). The dependence of fluorescence intensity on laser power is studied, and the probable dissociation channels are analyzed. The relationship between the fluorescence intensity and some parameters, such as the temperature of the beam source, stagnation pressure, and the time delay between the opening of pulse valve and the photolysis laser, are also studied. The influence of three different carrier gases on CH signal intensity is investigated. The vibrational and rotational temperatures of the CH (A2 Δ) product are obtained by comparing experimental data with the simulated ones from the LIFBASE program.

Spectrofluorimetric determination of melatonin in kernels of four different Pistacia varieties after ultrasound-assisted solid–liquid extraction

Melatonin is normally consumed to regulate the body’s biological cycle. However it also has therapeutic properties, such as anti-tumor, anti-aging and protects the immune system. There are some reports on the presence of melatonin in edible kernels such as walnuts, but the extraction of melatonin from pistachio kernels is reported here for the first time. For this, the methanolic extract of pistachio kernels was exposed to gas chromatography/mass spectrometry analysis which confirmed the presence of melatonin. A fluorescence-based method was applied for the determination of melatonin in different extracts. When excited at λ=275nm, the fluorescence emission intensity of melatonin was measured at λ=366nm. Ultrasound-assisted solid–liquid extraction was used for the extraction of melatonin from pistachio kernels prior to fluorimetric determination. To achieve the highest extraction recovery, the main parameters affecting the extraction efficiency such as extracting solvent type and volume, temperature, sonication time and pH were evaluated. Under the optimized conditions, a linear dependence of fluorescence intensity on melatonin concentration was observed in the range of 0.0040–0.160μgmL−1, with a detection limit of 0.0036μgmL−1. This method was applied successfully for measuring and comparing the melatonin content in the kernels of four different varieties of Pistacia including Ahmad Aghaei, Akbari, Kalle Qouchi and Fandoghi. In addition, the results obtained were compared with those obtained using GC/MS. A good agreement was observed indicating the reliability of the proposed method.

Dissociative recombination in ultraviolet filamentary plasma gratings.

We investigated collisions of nitrogen and argon gas mixture with energetic electrons accelerated by Bragg incident intense infrared femtosecond laser pulses in ultraviolet filamentary plasma gratings. Significant decrease of fluorescence spectra of argon atoms were observed when a small amount of nitrogen gas was mixed with argon gas that facilitated observable argon-nitrogen collisions. We experimentally measured the fluorescence emission from the argon and nitrogen gas mixture under different driving pulse energies, the fluorescence decay dynamics after the impact excitation, as well as the fluorescence intensity dependence on the nitrogen and argon pressures. The experimental measurements were based on the electron acceleration and its subsequent impact with the gas mixture in the filamentary plasma gratings, which was essential for the observation of the dominant dissociative recombination in the gas mixture.

Optical temperature sensing of hexagonal Na0.82Ca0.08Er0.16Y0.853F4 phosphor

The hexagonal Na0.82Ca0.08Er0.16Y0.853F4 phosphor was prepared by the high temperature solid-state reaction. Novel six-photon ultraviolet up-conversion emissions in the range of 260–320 nm are observed under 1.54 μm excitation. Using the ratio of 523 nm and 542 nm fluorescence emissions, low-temperature optical temperature sensing in the resulting phosphor is studied. The temperature sensitivity of the resulting phosphor in the region of 5–300 K is obtained by measuring the temperature dependent fluorescence intensity ratio of the 523 nm and 542 nm emissions originated from two thermally coupled 2H11/2 and 4S3/2 emitting levels. The temperature sensitivity with a maximum sensitivity of 0.0022 K−1 at 338 K is obtained experimentally. The results reveal that the resulting phosphor may be a promising material for the sensing system at low temperature.

Polyacrylate Microspheres for Tunable Fluorimetric Zinc Ions Sensor

A novel concept of optical fluorimetric sensing using polymeric microspheres is explored on example of zinc ions sensors. The novel approach proposed uses the advantage of concomitant presence in a microsphere of two compounds: a receptor, fluorescently silent complexing ligand and an optical transducer, fluorescent compound. Binding of the analyte by the ligand affects its absorption spectrum, leading to decrease of the free ligand absorption and increase of complex absorption band. The decrease of free ligand absorption exposes emission of the transducer, yielding increase in fluorescence intensity on analyte concentration increase. This approach was verified experimentally using Zn(2+) as a model analyte, the fluorimetric sensor obtained uses 1-(2-pyridylazo)-2-naphthol (PAN) as analyte sensitive receptor and pyrene as optical transducer. In the absence of zinc ions in the sample emission of pyrene embedded in the spheres was significantly quenched, whereas increase of Zn(2+) ions concentration in the sample resulted in dependence of fluorescence intensity on logarithm of zinc ions concentration in extraordinary wide range, from 10(-7) to 0.1 M. The response mechanism was explained by surface accumulation of zinc ion-PAN complex on the microsphere/sample solution interface. It was also shown that introduction of cation-exchanging sites to the microspheres significantly alters the responses pattern leading to high sensitivity over relatively limited concentration range (3-4 orders of magnitude). In the latter case the observed responses can be tuned to occur in chosen concentration range, simply by adjusting sample pH.

Effect of N-dodecyl-N,N-dimethylamine N-oxide on unilamellar liposomes

Abstract The effect of N-dodecyl-N,N-dimethylamine N-oxide (C12NO) on the unilamellar liposomes prepared from egg yolk phosphatidylcholine (EYPC) was studied using turbidimetric and fluorescence spectroscopic methods. The concentrations of C12NO causing saturation and total solubilization of membrane were evaluated turbidimetrically. Liposomes filled with hydrophilic fluorescent probe calcein were used for the fluorescence leakage measurements. Dependence of fluorescence intensity on C12NO concentration can be divided into three linear sections. The turning points between individual sections represent two concentrations of C12NO which induce formation of small defects, specifically large pores in liposomal membrane. These pores are wide enough to enable calcein to be washed out from liposomes completely. We compared results obtained by the two methods used. Measurements of fluorescent probe leakage showed that free diffusion of calcein through pores in EYPC bilayer was observed at such C12NO concentrations when the form of liposome is still preserved and the saturation of bilayer is not yet finished. Higher C12NO concentrations are needed for solubilization, a phase transition from bilayers to micelles.

Investigation of binding of nanomarkers of fluorescein family to bovine serum albumin at various values of pH: Spectroscopic study

This work is dedicated to investigation of influence of different values of pH on binding of nanomarkers of fluorescein family (fluorescein, erythrosin, eosin and Bengal rose) to bovine serum albumin (BSA). For this purpose dependences of nanomarkers fluorescence, of nanomarkers molecular association, of types of chemical bonds between BSA and nanomarkers on pH are detected. The red shift of fluorescence spectra and the quenching of fluorescence of nanomarkers of fluorescein family in BSA solutions are observed. The decrease of degree of molecular association of nanomarkers in BSA solutions is found out. The dependences of fluorescence intensity and dependences of degree of molecular association on pH of halogen-derivatives of fluorescein differ dramatically from that of fluorescein.

Simultaneous Determination of Critical Micelle Temperature and Micelle Core Glass Transition Temperature of Block Copolymer–Solvent Systems via Pyrene-Label Fluorescence

The critical micelle temperature (CMT) and micelle core glass transition temperature (Tg) for a poly(methyl methacrylate) (PMMA)-poly(tert-butyl methacrylate) (PtBMA) diblock copolymer system were measured by fluorescence via single temperature (T) ramps. Synthesis yielded identical block lengths in unlabeled and pyrene-labeled diblocks, the latter with dye at the PMMA block terminus. Studies were conducted at 5–18 wt % diblock in 2-ethylhexanol (2EH) with a trace of labeled diblock (0.2 wt % of total copolymer). The T dependence of pyrene-label fluorescence intensity yielded the CMT and micelle core Tg in systems where the PMMA-block and the 2EH within the cores constituted 1.9–7.8% of sample mass. While the CMT can be measured by many methods, this is the first direct measurement of micelle core Tg at low core content (e.g., 1.9 wt %) in a block copolymer/solvent system. Differential scanning calorimetry was done on diblock samples, showing severe limitations for sensing and characterizing core Tg. Fluorescence from trace levels of labeled diblock was used with 5–20 wt % PMMA–poly(n-butyl acrylate)–PMMA triblocks in 2EH. The micelle core Tg is important in triblock systems that form thermoreversible gels because it fundamentally underlies the viscoelastic to elastic gel transition. Fluorescence results demonstrated the dependence of the CMT and the near invariance of the micelle core Tg on core-block molecular weight in these diblock and triblock systems for PMMA blocks with Mn = 15–25 kg/mol and solvent in the micelle core.

Comparative spectroscopic studies on liposomes containing chlorophyll a and chlorophyllide a

Chlorophyll a (Chla) and chlorophyllyde a (Chlida) - a derivative of Chla, have been incorporated in the lipid bilayers of two types of liposomes, small unilamellar vesicles (SUV) and multilamelar vesicles (MLV). The objective of the present work was to compare the spectral behaviour of Chla and Chlida incorporated in the lipid bilayers and their sensing behaviour at molecular level. The VIS absorption and fluorescence emission presented differences depending on the type of liposomes and inserted pigment, reflecting the different localization of porphyrin macrocycle in the lipid moieties. The temperature dependence of emission anisotropy and fluorescence intensity, for both Chla and Chlida incorporated in DPPC SUV, revealed the presence of different lipid phases. The degree of incorporation of quercetin (QCT) in liposome membrane was studied by using Chla and Chlida as molecular sensors. The fluorescence polarisation data and the fluorescence quenching process provided arguments for the insertion of the QCT at the interface lipid/water, in the vicinity of lipid polar heads and porphyrin macrocycle. The phytyl chain of Chla penetrating in the hydrophobic core of the lipid bilayers is responsible for the observed differences among Chla and Chlida in sensing the lipid phase transition and the fluorescence quenching process induced by QCT.

Study of aqueous phase aggregation of FTY720 (fingolimod hydrochloride) and its effect on DMPC liposomes using fluorescent molecular probes

This work focuses on the study of aqueous phase aggregation of the recently FDA approved oral drug molecule FTY720 (fingolimod hydrochloride) and its effect on dimyristoylphosphatidylcholine (DMPC) liposomes using different fluorescent molecular probes and fluorescence parameters. The variation of the steady state fluorescence intensity of 8-anilino-1-naphthalene sulfonic acid (ANS) with FTY720 in water shows an efficient micellar aggregation with the critical micellar concentration (CMC) at ~75 μM. The aggregation number calculation from steady state fluorescence quenching of pyrene shows the formation of small micellar aggregates in aqueous solution having an aggregation number of 42 ± 3 with the free energy of micellization ~-23 kJ mol(-1). Fluorescence intensity and lifetime decay analysis of the molecular probe 1-naphthol indicate that the interaction of FTY720 with the DMPC lipid bilayer membrane prevents partitioning of small molecules such as 1-naphthol to the membrane in both solid gel (SG) and liquid crystalline (LC) phases. Temperature dependent fluorescence intensity studies of 1-naphthol and fluorescence anisotropy measurements of 1,6-diphenyl-1,3,5-hexatriene (DPH) have shown that above the CMC of FTY720, the SG to LC main phase transition temperature (T(M)) of the lipid bilayer membrane decreases from 23 °C to 21 °C in the aqueous medium.

Interruption of hydration state of thermoresponsive polymer, poly(N-isopropylacrylamide) in guanidinium hydrochloride

In this article, we investigate the effect of guanidinium hydrochloride (GdnHCl) on the phase transition temperature of poly (N-isopropylacrylamide) (PNIPAM) in aqueous solution with the aid of fluorescence spectroscopy, viscosity (η), and dynamic light scattering (DLS) measurements. Temperature dependent fluorescence intensity measurements have been employed successfully to determine the conformational change of PNIPAM through evaluating the Gibbs free energy changes. Additionally, direct hydrogen bonding formation between GdnHCl and PNIPAM has been confirmed by Fourier transform infrared (FTIR) spectroscopy measurements at various concentrations of GdnHCl. The intermolecular interactions were also studied in terms of amide I band analysis, which reveals the interruption of hydrated coil conformation of PNIPAM. The degree of destabilization of PNIPAM progressively increases with increasing concentration of the denaturant.

Neutralizing Aspartate 83 Modifies Substrate Translocation of Excitatory Amino Acid Transporter 3 (EAAT3) Glutamate Transporters

Excitatory amino acid transporters (EAATs) terminate glutamatergic synaptic transmission by removing glutamate from the synaptic cleft into neuronal and glial cells. EAATs are not only secondary active glutamate transporters but also function as anion channels. Gating of EAAT anion channels is tightly coupled to transitions within the glutamate uptake cycle, resulting in Na(+)- and glutamate-dependent anion currents. A point mutation neutralizing a conserved aspartic acid within the intracellular loop close to the end of transmembrane domain 2 was recently shown to modify the substrate dependence of EAAT anion currents. To distinguish whether this mutation affects transitions within the uptake cycle or directly modifies the opening/closing of the anion channel, we used voltage clamp fluorometry. Using three different sites for fluorophore attachment, V120C, M205C, and A430C, we observed time-, voltage-, and substrate-dependent alterations of EAAT3 fluorescence intensities. The voltage and substrate dependence of fluorescence intensities can be described by a 15-state model of the transport cycle in which several states are connected to branching anion channel states. D83A-mediated changes of fluorescence intensities, anion currents, and secondary active transport can be explained by exclusive modifications of substrate translocation rates. In contrast, sole modification of anion channel opening and closing is insufficient to account for all experimental data. We conclude that D83A has direct effects on the glutamate transport cycle and that these effects result in changed anion channel function.

Photoinduced Reactivity of Doxorubicin: Catalysis and Degradation

Doxorubicin exhibits unusual photoreactivity in aqueous solutions. Our data show that there are two distinct photoreactive pathways for doxorubicin. One is a two-step process that leads to the formation of 3-methoxysalicylic acid, a stable degradation product. The other pathway is a photoreduction of doxorubicin to form the corresponding dihydroquinone, which undergoes spontaneous oxidation mediated by dissolved oxygen to recover doxorubicin with the formation of hydrogen peroxide. Our data account for the known nonlinear dependence of doxorubicin fluorescence intensity on concentration.

Site of non-photochemical quenching of the phycobilisome by orange carotenoid protein in the cyanobacterium Synechocystis sp. PCC 6803

In cyanobacteria, the thermal dissipation of excess absorbed energy at the level of the phycobilisome (PBS)-antenna is triggered by absorption of strong blue-green light by the photoactive orange carotenoid protein (OCP). This process known as non-photochemical quenching, whose molecular mechanism remains in many respects unclear, is revealed in vivo as a decrease in phycobilisome fluorescence. In vitro reconstituted system on the interaction of the OCP and the PBS isolated from the cyanobacterium Synechocystis sp. PCC 6803 presents evidence that the OCP is not only a photosensor, but also an effecter that makes direct contacts with the PBS and causes dissipation of absorbed energy. To localize the site(s) of quenching, we have analyzed the role of chromophorylated polypeptides of the PBS using PBS-deficient mutants in conjunction with in vitro systems of assembled PBS and of isolated components of the PBS core. The results demonstrated that LCM, the core-membrane linker protein and terminal emitter of the PBS, could act as the docking site for OCP in vitro. The ApcD and ApcF terminal emitters of the PBS core are not directly subjected to quenching. The data suggests that there could be close contact between the phycocyanobilin chromophore of LCM and the 3′-hydroxyechinenone chromophore present in OCP and that LCM could be involved in OCP-induced quenching. According to the reduced average life-time of the PBS-fluorescence and linear dependence of fluorescence intensity of the PBS on OCP concentration, the quenching has mostly dynamic character. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

Doppler-free two-photon resonances for atom detection and sum frequency stabilization

We investigate the excitation of the 5D5/2 level in Rb atoms using counter-propagating laser beams, which are nearly resonant to the one-photon 5S1/2 → 5P3/2 and 5P3/2 → 5D5/2 transitions, ensuring that a sum of the optical frequencies corresponds to the 5S1/2 → 5D5/2 transition. The excitation produced by two-photon and stepwise processes is detected via spontaneously emitted fluorescence at 420 nm arising from the 6P3/2 → 5S1/2 transition. The dependences of blue fluorescence intensity on atomic density and laser detuning from the intermediate 5P3/2 level have been investigated. The sensitivity of the frequency-detuned bi-chromatic scheme for atom detection has been estimated. A novel method for sum-frequency stabilization of two free-running lasers has been suggested and implemented using two-photon Doppler-free fluorescence and polarization resonances.