Blue Shift Of Emission Peak Research Articles

2,5-di-[2-(3,5-bis(2-pyridylmethyl)amine -4-hydroxy-phenyl) ethylene] pyrazine zinc complex as fluorescent probe for labeling proteins

The binding characteristics between 2,5-di-[2-(3,5-bis(2-pyridylmethyl)amine -4-hydroxy-phenyl) ethylene] pyrazine ( 1) or its complex ( 1-Zn) and serum albumins were studied by fluorescence spectroscopy in pH 7.4 aqueous solution. 1-Zn emitted weak fluorescence at 580 nm in a pH 7.4 Tris–HCl buffer solution when excited at 435 nm, however, the fluorescence intensity increased upon addition of serum albumins with the blue shift of emission peak to 524 nm. The binding constants were estimated as 8.40 × 10 7 and 3.03 × 10 6 mol −1 L for bovine serum albumin (BSA) and human serum albumin (HSA) respectively, and the number of binding sites was 1 for each. The quenching mechanism of fluorescence of serum albumins by 1-Zn was considered as a static quenching process. The binding distance between 1-Zn and serum albumins and the energy transfer efficiency were obtained based on the theory of Förester spectroscopy energy transfer. The effect of 1-Zn on the conformation of serum albumins was further analyzed using synchronous fluorescence spectrometry. The experiment results clearly showed that 1-Zn is a highly sensitive protein sensor.

Synthesis and temperature dependent photoluminescence of Zn1−x Mg x O films grown by ultrasonic spray pyrolysis

Zn1−xMgxO films were deposited on single crystal Si (100) substrates using ultrasonic spray pyrolysis under ambient atmosphere. A strong ultraviolet near-band-edge (NBE) emission was observed in the room temperature photoluminescence (PL) measurement for all the as-grown Zn1−xMgxO films, while the deep-level emission was almost undetectable, suggesting that the obtained Zn1−xMgxO-based films are well close to stoichiometry and of optically high quality. A distinct blue-shift of NBE emission peak from 386 nm to 358 nm was observed as the Mg concentration increases from 0% to 25 %. The photoluminescence spectra as a function of temperature were also investigated to examine the emission mechanism of Zn1−xMgxO films.

Fabrication and Characterization of In-Doped Zinc Oxide Nanodisks

In-doped ZnO nanodisks were successfully fabricated by thermal evaporation Zn, In2O3 and graphite powder mixture without catalyst. Morphology, structures and components of ZnO nanodisks were investigated by SEM, HRTEM, EDS and X-Ray diffraction. ZnO nanodisks have perfect hexagonal shape, with 1~3μm size and 40~100 nm in thickness. The nanodisks are single-crystalline ZnO with wurtzite structure and In content of nanodisks reaches 2.2%. The growth along [0001] is suppressed leading to the formation of ZnO nanodisks. Room temperature photoluminescence spectra of the nanodisks shows that the UV emission peak blueshifts and becomes broader after doping.

Enhanced electroluminescence of ZnO nanocrystalline annealing from mesoporous precursors

An improved sol–gel method was used to prepare ZnO nanoparticles. EL results showed that slowing the addition of LiOH solution and heating in vacuum to obtain gel precipitation made the final ZnO samples’ emission peak blue shift to 520 nm. Simultaneously, the peak value of the sample processed with no templates was enhanced 4.68 times and that of the sample processed with ODA was enhanced 0.71 times. Two copolymers Pluronic P123 (P123) and Pluronic F-127 (F-127) were adopted respectively as template reagents. The obtained mesoporous ZnO precursors exhibited a surface area of 69.21 m 2/g and 103.57 m 2/g and an average pore size of 6.61 nm and 5.70 nm, respectively. After calcining in a muffle furnace in air, the obtained ZnO nanocrystalline samples from these precursors revealed stronger green emission than the samples dealt with ODA. Compared to the magnification multiple of 0.89 times of the sample processed with ODA, the peak intensity of the sample processed with P123 was 2.03 times higher than that of the sample processed with no template reagents, and the intensity of the sample processed with F-127 was 3.3 times higher. This may be due to the larger surface area of samples from the longer molecule chains of the two template reagents.

In-doped zinc oxide dodecagonal nanometer thick disks

In-doped ZnO nanometer thick disks were successfully fabricated by thermal evaporation of a powder mixture of Zn, In 2O 3 and graphite without catalyst. SEM images show that some ZnO disks have perfect dodecagon shape. These disks are about 1∼3 μm in size and 40∼100 nm in thickness. XRD, TEM and EDS observations show that the disks are single-crystalline ZnO with wurtzite structure. The disks grow mainly along the twelve symmetric directions of <21¯1¯0> and <101¯0>, while the growth along [0001] is suppressed. The In content of the disks reaches 27.4 at.%. Room temperature photoluminescence spectra show that the UV emission peak blueshifts and become broader after doping.

Study of carrier localization in InGaN/GaN quantum well blue-light-emitting diode structures

The effect of temperature and excitation power on the characteristics of InGaN/GaN single quantum well (SQW) and multiple quantum well (MQW) light-emitting diodes (LED) has been investigated in-depth over a broad range of temperatures from 9 to 300 K. It was found that the device with a stair-shaped SQW structure exhibited stronger localization effect, as well as had higher internal quantum efficiency than that of the conventional MQW and SQW LEDs. This is interpreted as due to the stair-shaped SQW configuration, which offered a large contribution to the exciton capturing. The adoption of an appropriate heterostructure in active region allows the achievement of improved LED performance. With increasing the excitation power intensity, QW photoluminescence (PL) line broadening and emission peak blue shifts were observed, which are assumed to be caused by the disordering formed in the In-rich heterostructures of QW ensembles. We expect that distinct degree of carrier localization occurs in these samples.

Purification and Characterization of a Recombinant G-Protein-Coupled Receptor, Saccharomyces cerevisiae Ste2p, Transiently Expressed in HEK293 EBNA1 Cells

The production of milligram quantities of purified, active, folded membrane protein from heterologous expression systems remains a general challenge due to intrinsically low expression levels, misfolding, and instability. Here we report the overexpression and purification of milligram quantities of functional Saccharomyces cerevisiae G-protein-coupled receptor, Ste2p, from transiently transfected human embryonic kidney 293 EBNA1 cells. Fluorescent microscopy indicates localization of Ste2p-GFP and Fc-Ste2p-GFP fusion receptors to the cell membrane. Up to 2 mg (approximately 10 pmol/million cells) of the Fc-Ste2p-GFP fusion and 1 mg of a Ste2p-Strep-TagII/(His)8-tagged version were purified per liter of culture following protein A-Sepharose and Talon metal affinity chromatography, respectively. Two distinct fluorescent labels, the hydrophobic 7-(diethylamino)-3-(4'-maleimidylphenyl)-4-methylcoumarin (CPM) and the more hydrophilic fluorescein-5-maleimide (FM), were individually attached to the C-terminus of the alpha-mating factor ligand by addition of a reactive cysteine residue to produce active fluorescent pheromones. In vitro fluorescent ligand binding assays demonstrated that a high percentage of the recombinant purified receptor is correctly folded and able to bind ligand. KD values of 34 +/- 3 and 300 +/- 20 nM were observed respectively for the CPM- and FM-labeled ligands. These results combined with blue-shifted emission peaks and loss of fluorescent quenching observed for both fluorescent-labeled Cys alpha-factors when bound to receptor support a model in which the C-terminus of the ligand is packed in a hydrophobic pocket at the interface between the transmembrane and extracellular loop domains. Overall, we present an efficient system for recombinant production of milligram quantities of purified Ste2p in a biologically active form with applications to future structure and functional studies.

Growth of Semiconducting GaN Hollow Spheres and Nanotubes with Very Thin Shells via a Controllable Liquid Gallium–Gas Interface Chemical Reaction

An in situ liquid gallium-gas interface chemical reaction route has been developed to synthesize semiconducting hollow GaN nanospheres with very small shell size by carefully controlling the synthesis temperature and the ammonia reaction gas partial pressure. In this process the gallium droplet does not act as a catalyst but rather as a reactant and a template for the formation of hollow GaN structures. The diameter of the synthesized hollow GaN spheres is typically 20-25 nm and the shell thickness is 3.5-4.5 nm. The GaN nanotubes obtained at higher synthesis temperatures have a length of several hundreds of nanometers and a wall thickness of 3.5-5.0 nm. Both the hollow GaN spheres and nanotubes are polycrystalline and are composed of very fine GaN nanocrystalline particles with a diameter of 3.0-3.5 nm. The room-temperature photoluminescence (PL) spectra for the synthesized hollow GaN spheres and nanotubes, which have a narrow size distribution, display a sharp, blue-shifted band-edge emission peak at 3.52 eV (352 nm) due to quantum size effects.

Substitution of a Chlorophyll into the Inactive Branch Pheophytin-Binding Site Impairs Charge Separation in Photosystem II

All photosynthetic reaction centers (RCs) have two parallel sets of electron transfer cofactors that cross the membrane. In quinone-type RCs (including photosystem II (PSII)), however, only one pathway (the active branch) is used for electron transfer. Since the electron transfer cofactors of each pathway have nearly identical distance and orientation relationships, it is assumed that local differences in protein environment determine the directionality of electron transfer. To understand further the factors that affect energy distribution among the PSII RC cofactors, we altered the PSII RC cofactor symmetry by replacing the inactive-branch pheophytin (Pheo) with a chlorophyll (Chl). We mutated the D1-L210 residue to a histidine (D1-L210H) to provide a Mg ligand for Chl. Analyses of the pigment composition of D1-L210H RCs indicated that the inactive-branch Pheo had been replaced by a Chl. Comparisons of wild-type and D1-L210 transient absorption spectra confirmed that the red-shifted Pheo Qx absorption band (543.5 nm) belonged to the active-branch Pheo. Surprisingly, intact D1-L210H PSII complexes were unable to evolve oxygen, lacked Chl variable fluorescence, (following a flash), and were unable to photoaccumulate reduced Qa, indicating that electron transfer in D1-L210H PSII complexes was severely perturbed. The kinetics of primary charge separation, however, were not substantially altered in D1-L210H RCs, indicating that the Chl substitution had not perturbed the energetics of the primary electron donor/acceptor pair. Significantly, intact D1-L210H PSII core complexes had a substantially increased and red-shifted Chl fluorescence emission band attributed to fluorescence from Chl's of the distal antenna complex as well as a blue-shifted fluorescence emission peak attributed to Chl's of the proximal antenna complex (77 K). These results are interpreted in terms of a redistribution of the excited-state energy among the pigments of the RC multimer, leading to loss of the excited state via fluorescence in the D1-L210H mutant.

Radical Terpolymerization of Organoarsenic Homocycle, Phenylacetylene, and Vinyl or Butadienyl Monomers

The free radical terpolymerization of pentamethylcyclopentaarsine (cyclo-(MA)5), phenylacetylene (PA), and various vinyl monomers in toluene is described. The terpolymerization of cyclo-(MA)5, PA, and styrene (St) in the molar ratio 1:5:5 with a catalytic amount of AIBN at 60 °C for 8 h provided a polymer in 38% yield after reprecipitation. The terpolymer was soluble in common organic solvents such as tetrahydrofuran, chloroform, benzene, and toluene. In the GPC analysis (chloroform, PSt standards), the terpolymer showed a single peak, and the number-average molecular weight was estimated to be 10 200. The structure of the terpolymer obtained was compared with those of poly(vinylene−arsine) and polystyrene by use of 1H NMR and 13C NMR and found to have two block units, [poly(MA-alt-PA)−poly(St)]. The integral ratio of the peak area in the 1H NMR spectrum revealed the terpolymer composition, MA:PA:St = 1:0.99:0.56. The terpolymer showed fluorescence properties attributable to the n−π* transition in the poly(MA-alt-PA) block. The terpolymerization of cyclo-(MA)5, PA, and St in various feed ratios was carried out in the presence of AIBN to yield the terpolymers which possessed poly(MA-alt-PA) and poly(St) blocks with various compositions. The terpolymer with the higher content of St unit exhibited a more blue-shifted emission peak. The radical terpolymerization of methyl methacrylate (MMA) with cyclo-(MA)5 and PA also yielded the corresponding terpolymer with a poly(MA-alt-PA) unit and a poly(MMA) unit, while the terpolymerization employing vinyl acetate (VA) as a vinyl monomer produced poly(vinylene−arsine) with no VA segment. The radical reaction of 2,3-dimethyl-1,3-butadiene (DB) with cyclo-(AsMe)5 and PA formed a different type of terpolymer which had alternating sequences of AsMe and PA or DB, e.g., [(MA-PA)−(MA-DB)]n.

Optical properties of single-crystalline ZnO nanowires on m-sapphire

ZnO nanowires have been synthesized using a catalyst-assisted heteroepitaxial carbothermal reduction approach on a m-sapphire substrate. Intricate and uniform arrays have been obtained with each nanowire forming an angle ∼30° with the substrate normal. Photoluminescence studies at room temperature for wavelengths between 335 and 620 nm reveal a strong single exciton peak at ∼380 nm (3.26 eV) with accompanying deep-level blueshifted emission peaks at ∼486, 490, and 510 nm. UV resonant Raman spectroscopy has been used to characterize the nanowires at room temperature with multiphonon scattering exhibiting phonon quantum confinement.

Evolution of the Fu Orionis Object BBW 76

We have carried out a long-term photometric and spectroscopic monitoring program of the southern FU Orionis–type object BBW 76 spanning the period from 1982 to 1997. BBW 76 has the same radial velocity as the small cloud toward which it is projected, and for which a kinematic distance of about 1.8 kpc has been derived. We have determined a large reddening of E(B-V) ~ 0.7 for BBW 76. Optical and infrared spectra show the change toward later spectral type with increasing wavelength characteristic of FU Orionis stars and indicative of a hot luminous disk. High-resolution echelle spectra of BBW 76 show P Cygni profiles with extended blueshifted absorption troughs at the Hα and sodium lines from a neutral, supersonic wind. Comparison of such spectra obtained at six different epochs between 1985 and 1997 reveals major changes in these Hα and sodium line profiles. For a period of 10 years from 1985, the massive absorption troughs diminished in extent and depth, until by 1994 they had all but disappeared, while at the same time the blueshifted emission peak in the Hα line increased markedly in strength. However, when observed in 1997, the absorption had increased again and the emission had diminished. We interpret this in terms of an extended period during which accretion through a circumstellar disk decreased, with a resulting decrease in wind production. But the increased activity by 1997 shows that this is not a constant decay and that the star was not about to revert to its presumably original T Tauri stage. We monitored the star with optical photometry from 1983 to 1994, during which period it decreased almost monotonically in brightness by 0.2 mag in V. Infrared J, H, and K photometry from 1983 to 1991 shows a period of monotonic fading between 1984 and 1988, followed by more irregular behavior. In a search of the Harvard plate archives we have found a plate from the year 1900 on which BBW 76 is seen at approximately its present brightness, certainly not 2 mag brighter as expected if the optical decline between 1983 and 1994 had persisted during the whole century. Also, a plate taken for the Franklin-Adams charts in 1927 again shows BBW 76 at approximately the same brightness. This historical light curve makes BBW 76 the FU Orionis star with the longest-documented period in a high state. Overall, the observations suggest that BBW 76 is virtually identical to the prototype of its class, FU Orionis itself, in all respects except that BBW 76 has not shown the regular fading that FU Orionis has displayed after its eruption in 1936. This may be due to continued replenishment of the circumstellar accretion disk.

Calculation of spontaneous emission and gain spectra for quantum cascade lasers

In this paper, a quantum cascade laser has been treated as a three-level system, and the calculation of the spontaneous emission and gain spectra has been given. In the calculation, the conduction band nonparabolicity and the injection and exit of electrons have been considered. Results have shown that with increasing injection current, the spontaneous emission peak blue shifts, and the peak intensity increases near linearly with current. With increasing temperatures, the broadening of the spontaneous emission spectra has been attributed to the electron-optical phonon interactions. The peak gain of the stimulated emission has been shown to be determined mainly by the subband lifespans. We have pointed out that it is essential to obtain a long lifespan for the second excited state and short lifespan for the first excited state in order to obtain efficient population inversion and high peak gain for quantum cascade lasers.

DNA binding studies of a solvatochromic fluorescence probe 3-methoxybenzanthrone

A fluorescence probe of 3-methoxybenzanthrone (MBA) exhibits significant solvatochromic characteristics correlated with the polarity of solvents. The interaction of the solvatochromic fluorescence probe with calf thymus DNA (ct-DNA) has been investigated. In the presence of ct-DNA the fluorescence of MBA is strongly quenched with a blue-shift of emission peak and a hypochromism in absorption spectra. The absorption spectra, fluorescence quenching and fluorescence polarization experiments show that the MBA molecule as an intercalator is inserted into the base-stacking domain of the ct-DNA double helix, and the interaction of the nucleobases with the MBA molecule causes quenching of fluorescence and hypochromism in the absorption spectra. The intrinsic binding constant and the binding site number were determined to be 1.70×10 5 mol l −1 in base pairs and six, respectively. The I 0/ I versus [ct-DNA] plot shows linear relationship in the range covering 4.3×10 −7–1.02×10 −4 mol l −1 in base pairs which can be used for ct-DNA determination. The limit of detection was found to be 4.3×10 −7 mol l −1 in base pairs (0.5 μg ml −1).

Fabrication of nanoscale structures of InGaN by MOCVD lateral overgrowth

Nanoscale InGaN quantum wires and quantum dots (QDs) have been realized on the top of micron size of GaN dots and wires by lateral overgrowth with Si mask using metal-organic chemical vapor deposition (MOCVD). Patterning of the mask was carried out by focused ions beam method to form the stripe and square windows in Si covered MOCVD-GaN substrate. The density, sizes and positions of InGaN nano-structures have been artificially designed and controlled. The characteristics of InGaN nano-structures have been studied by scanning electron microscopy, transmission electron microscopy and cathodoluminescence (CL). A lot of dislocations were found in the interface between underlying and regrown GaN due to damage of ion sputtering. However, the propagation of dislocations was changed the direction parallel to the c plane in the region of laterally overgrown GaN, and no dislocations in the top of GaN dots and wires were observed. Compared to band-gap emission from InGaN/GaN multi-quantum well, the blue-shift of emission peak in InGaN QDs is observed by CL, which suggest that the carriers in InGaN QDs are three-dimensionally confined. It also demonstrates that InGaN structures grown on the top of GaN dots and wires with micron sizes are nanometric scale.

The bipolar molecular outflow of V645 Cygni

A map is presented of the CO J = 3-2 line emission from the cloud associated with V645 Cygni. Line wings extending to 15 km/s on either side of the central velocity can be attributed to a bipolar outflow over a region 1 arcmin in angular extent. The redshifted and blueshifted emission peaks are separated by 20 arcsecs along an axis that is approximately perpendicular to the polarization vector of the visible light. The outflow is of relatively low velocity, low mass, and low mechanical luminosity.