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1.
n-Dodecyl-β-d-maltoside solubilized glucuronide transporter (GusB), the product of gusB gene from Escherichia coli, was treated with Bio-Beads as an agent for removing the detergent from a micellar solution under suitable combination with dimyristoylphosphatidylcholine. Optimizing conditions led to a two-dimensional crystalline array formation of GusB. The crystalline arrays appear to have a hexagonal lattice with layer group P6, the unit cell dimensions of a = b = 13.8 nm and γ = 120°. Each stain-protruding periodic unit showed approximately 11.8 ± 0.3 nm in a diameter in the inverse Fourier-filtered image to have formed with pentameric GusB (5 × 49.7 kDa).  相似文献   

2.
We have investigated the potential of new methods of analysis of sedimentation velocity (SV) analytical ultracentrifugation (AUC) for the characterization of detergent-solubilized membrane proteins. We analyze the membrane proteins Ca++-ATPase and ExbB solubilized with DDM (dodecyl-β-d-maltoside). SV is extremely well suited for characterizing sample heterogeneity. DDM micelles (s 20w?=?3.1 S) and complexes (Ca++-ATPase: s 20w?=?7.3 S; ExbB: s 20w?=?4 S) are easily distinguished. Using different detergent and protein concentrations, SV does not detect any evidence of self-association for the two proteins. An estimate of bound detergent of 0.9 g/g for Ca++-ATPase and 1.5 g/g for ExbB is obtained from the combined analysis of SV profiles obtained using absorbance and interference optics. Combining s 20w with values of the hydrodynamic radius, R s?=?5.5 nm for Ca++-ATPase or R s?=?3.4 nm for ExbB, allows the determination of buoyant molar masses, M b. In view of their M b and composition, Ca++-ATPase and ExbB are monomers in our experimental conditions. We conclude that one of the main advantages of SV versus other techniques is the possibility to ascertain the homogeneity of the samples and to focus on a given complex even in the presence of other impurities or aggregates. The relative rapidity of SV measurements also allows experiments on unstable samples.  相似文献   

3.
Intrinsic properties of surface plasmons (SPs) excited with Kretschmann configuration were analyzed as a function of wavelength, including the propagation length, the penetration depth, the Goos–Hänchen (GH) shift, and the field enhancement. The calculated results indicate that there exists a critical thickness (t cr) of the gold layer and that the maximum GH shift occurring exactly at the SP resonance wavelength (λ R) rapidly varies from positive to negative with changing of the gold layer thickness from t?<?t cr to t?>?t cr. The maximum field enhancement happens not at λ R but at a wavelength smaller than λ R due to the phase retardation between the transmitted and reflected light. Simulations also reveal that a broadband collimated near-infrared beam can simultaneously excite two SPs with different responses to a refractive index (RI) change: the shorter-wavelength SP able to make a small redshift and the longer-wavelength SP capable of yielding a large blueshift. Only the shorter-wavelength SP was experimentally observed and its RI sensitivity was measured to increase from 3,539 nm/RIU at λ R?=?707.6 nm to 57,143 nm/RIU at λ R?=?1,398 nm. The SP at λ R?=?1,013 nm moved to λ R?=?1,029 nm in response to the saturation adsorption of bovine serum albumin, and the corresponding surface coverage was determined to be Γ?=?1.565 ng/mm2 based on a quasilinear dependence of Γ on the resonance wavelength shift (?λ R) deduced theoretically. Butyrylcholinesterase adsorption from a dilute solution of 10 nM protein in phosphate buffer solution leads to a redshift of ?λ R?=?10 nm, corresponding to Γ?≈?0.97 ng/mm2.  相似文献   

4.
We investigated pollen dispersal and breeding structure in the tropical tree species Caryocar brasiliense Camb. (Caryocaraceae), using genetic data from ten microsatellite loci. All adult trees (101) within a patch of 8.3 ha were sampled, and from these adults 18 open-pollinated maternal progeny arrays were analyzed (280 seeds from 265 fruits). Most fruits presented only one seed (median equal to 1.000) and mean number of ripened seeds per fruit was 1.053 (SD?=?0.828). Our results showed that C. brasiliense presents a mixed-mating system, with 11.4% of self-pollination, multilocus outcrossing rate of t m?=?0.891?±?0.025, and high probability of full-sibship within progeny arrays (r p?=?0.135?±?0.032). Outcrossing rate and self-pollination varied significantly among mother trees. We could detect a maximum pollen dispersal distance of ~500 m and a mean pollen dispersal distance of ~132 m. However, most pollination events (80%) occurred at distances less than 200 m. Our results also indicated that pollen dispersal is restricted to a neighborhood of 5.4 ha with rare events of immigration (~1% N e m?=?0.35). C. brasiliense also presents a significant but weak spatial genetic structure (Sp?=?0.0116), and extension of pollen dispersal distance was greater than seed dispersal (N b?=?86.20 m). These results are most likely due to the foraging behavior of pollinators that may have limited flight range. The highly within-population synchronous flowering, high population density, and clumped distribution reinforce pollinator behavior and affect residence time leading to a short-distance pollen dispersal.  相似文献   

5.
The mutant lacking enzymes BciA and BchU, that catalyzed reduction of the C8-vinyl group and methylation at the C20 position of bacteriochlorophyll (BChl) c, respectively, in the green sulfur bacterium Chlorobaculum tepidum, were constructed. This mutant accumulated C8-vinyl-BChl d derivatives, and a molecular structure of the major pigment was fully characterized by its NMR, mass, and circular dichroism spectra, as well as by chemical modification: (31 R)-8-vinyl-12-ethyl-(R[V,E])BChl d was confirmed as a new BChl d species in the cells. In vitro chlorosome-like self-aggregates of this pigment were prepared in an aqueous micellar solution, and formed more rapidly than those of (31 R)-8,12-diethyl-(R[E,E])BChl d isolated from the green sulfur bacterium Chlorobaculum parvum NCIB8327d synthesizing BChl d homologs. Their red-shifted Q y absorption bands were almost the same at 761 nm, and the value was larger than those of in vitro self-aggregates of R[E,E]BChl c (737 nm) and R[V,E]BChl c (726 nm), while the monomeric states of the former gave Q y bands at shorter wavelengths than those of the latter. Red shifts by self-aggregation of the two BChl d species were estimated to be 110 nm and much larger than those by BChls c (75 nm for [E,E] and 64 nm for [V,E]).  相似文献   

6.
The enhancement of the internal quantum efficiency (IQE) of deep-ultraviolet Al x Ga1-x N/Al y Ga1-y N (x < y) quantum wells (QWs) by fabricating one-dimensional Al nanogratings on a QW structure for inducing surface plasmon (SP) coupling is demonstrated. Through temperature-dependent photoluminescence (PL) measurement, the enhancements of IQE in different emission polarizations are illustrated. Due to the small difference in energy band level between the heavy/light hole and split-off valence bands, the IQEs of the transverse electric- (TE-) and transverse magnetic- (TM-) polarized emissions are about the same. When emission polarization is perpendicular to Al-grating ridges, the SP resonance mode for coupling with the QWs is dominated by localized surface plasmon (LSP). When emission polarization is parallel with Al-grating ridges, the coupled SP resonance mode may mix LSP and SP polariton. In this polarization, LSP can be excited because of the width fluctuation of a grating ridge. When the excitation laser polarization is perpendicular to Al-grating ridges, the strong LSP resonance at the excitation laser wavelength leads to stronger excitation and hence higher IQE levels.  相似文献   

7.
Eu2+ single-doped SiO2 (SiO2/Eu2+) and Eu2+, Ag nanowires co-doped SiO2 (SiO2/Eu2+–Ag) luminescent nanomaterials were prepared by an efficient one-step sol–gel method. Their microstructure and optical properties were characterized, and the fluorescence enhancement of Eu2+ by Ag nanowires was investigated. The experimental results indicate that the average diameter of Ag nanowires doped is 12.5 nm, and the length–diameter ratio is 30. The Ag nanowires cannot only enhance the light absorption of SiO2/Eu2+ in the range of 230–350 nm, but also reduce the fluorescence lifetime of Eu2+. More importantly, the emission intensity is enhanced after doping Ag nanowires, and the red shift phenomenon of the emission spectrum is observed, red shift occurs between 10 and 56 nm. The highest fluorescence intensity is accessed under the Ag doping concentration of 0.10 %. Additionally, the emission of SiO2/Eu2+ with 0.10 % of Ag doping at 456 nm is 16 times stronger than that of pure SiO2/Eu2+. The present results indicate that the fluorescence enhancement is attributed to the local field enhancement and the increased radiative decay rates induced by Ag nanowires.  相似文献   

8.
We report microbially facilitated synthesis of cadmium sulfide (CdS) nanostructured particles (NP) using anaerobic, metal-reducing Thermoanaerobacter sp. The extracellular CdS crystallites were <10 nm in size with yields of ~3 g/L of growth medium/month with demonstrated reproducibility and scalability up to 24 L. During synthesis, Thermoanaerobacter cultures reduced thiosulfate and sulfite salts to H2S, which reacted with Cd2+ cations to produce thermodynamically favored NP in a single step at 65 °C with catalytic nucleation on the cell surfaces. Photoluminescence (PL) analysis of dry CdS NP revealed an exciton-dominated PL peak at 440 nm, having a narrow full width at half maximum of 10 nm. A PL spectrum of CdS NP produced by dissimilatory sulfur reducing bacteria was dominated by features associated with radiative exciton relaxation at the surface. High reproducibility of CdS NP PL features important for scale-up conditions was confirmed from test tubes to 24 L batches at a small fraction of the manufacturing cost associated with conventional inorganic NP production processes.  相似文献   

9.
The collective electronic excitations in thin Ag films deposited onto the Ni(111) surface were studied by high-resolution electron energy loss spectroscopy. A broad loss peak at 7.7 eV was assigned to the Ag multipole plasmon, in excellent agreement with calculations based on s-d polarization model. Ag multipole plasmon was excited only at grazing incidence. Furthermore, a strong dependence on the impinging energy exists. Multipole plasmon could be measured only for a very strict range of primary electron beam energies and it was excited by electrons scattered at a reflection plane located just underneath the jellium edge. Such mode was found to be dramatically more sensible to the state of the surface with respect to ordinary surface plasmon. Moreover, we report experimental evidence of interference effects in surface plasmon excitation.  相似文献   

10.
Heparinases are widely used for production of clinically and therapeutically important bioactive oligosaccharides and in analyzing the polydisperse, heterogeneous, and complex structures of heparin/heparan sulfate. In the present study, the gene (1911 bp) encoding heparinase II/III of family 12 polysaccharide lyase (PsPL12a) from Pseudopedobacter saltans was cloned, expressed, and biochemically and functionally characterized. The purified enzyme PsPL12a of molecular size approximately 76 kDa exhibited maximum activity in the temperature range 45–50 °C and at pH 6.0. PsPL12a gave maximum activity at 1% (w/v) heparin under optimum conditions. The kinetic parameters, K m and Vmax, for PsPL12a were 4.6?±?0.5 mg/ml and 70?±?2 U/mg, respectively. Ten millimolars of each Mg2+ and Mn2+ ions enhanced PsPL12a activity by 80%, whereas Ni2+ inhibited by 75% and Co2+ by 10%, and EDTA completely inactivated the enzyme. Protein melting curve of PsPL12a gave a single peak at 55 °C and 10 mM Mg2+ ions and shifted the peak to 60 °C. The secondary structure analysis of PsPL12a by CD showed 65.12% α-helix, 11.84% β-strand, and 23.04% random coil. The degradation products of heparin by PsPL12a analyzed by ESI-MS spectra displayed peaks corresponding to heparin di-, tetra-, penta-, and hexa-saccharides revealing the endolytic mode of enzyme action. Heparinase II/III (PsPL12a) from P. saltans can be used for production of low molecular weight heparin oligosaccharides for their utilization as anticoagulants. This is the first report on heparinase cloned from P. saltans.  相似文献   

11.
We have previously investigated the response mechanisms of photosystem II complexes from spinach to strong UV and visible irradiations (Wei et al J Photochem Photobiol B 104:118–125, 2011). In this work, we extend our study to the effects of strong light on the unusual cyanobacterium Acaryochloris marina, which is able to use chlorophyll d (Chl d) to harvest solar energy at a longer wavelength (740 nm). We found that ultraviolet (UV) or high level of visible and near-far red light is harmful to A. marina. Treatment with strong white light (1,200 μmol quanta m?2 s?1) caused a parallel decrease in PSII oxygen evolution of intact cells and in extracted pigments Chl d, zeaxanthin, and α-carotene analyzed by high-performance liquid chromatography, with severe loss after 6 h. When cells were irradiated with 700 nm of light (100 μmol quanta m?2 s?1) there was also bleaching of Chl d and loss of photosynthetic activity. Interestingly, UVB radiation (138 μmol quanta m?2 s?1) caused a loss of photosynthetic activity without reduction in Chl d. Excess absorption of light by Chl d (visible or 700 nm) causes a reduction in photosynthesis and loss of pigments in light harvesting and photoprotection, likely by photoinhibition and inactivation of photosystem II, while inhibition of photosynthesis by UVB radiation may occur by release of Mn ion(s) in Mn4CaO5 center in photosystem II.  相似文献   

12.
In the last years, there has been a growing interest in the study of transition metal nanoparticles (Nps) due to their potential applications in several fields of science and technology. In particular, their optical properties are governed by the characteristics of the dielectric function of the metal, its size and environment. This work analyses the separated contribution of free and bound electrons on the optical properties of copper Nps. Usually, the contribution of free electrons to the dielectric function is corrected for particle size through the modification of the damping constant, which is changed as usual introducing a term inversely proportional to the particle’s radius to account for the extra collisions with the boundary when the size approaches the electronic mean free path limit (about 10 nm). For bound electron contribution, the interband transitions from the d-band to the conduction band are considered together with the fact that the electronic density of states in the conduction band must be made size-dependent to account for the larger spacing between electronic energy levels as the particle decreases in size below 2 nm. Taking into account these specific modifications of free and bound electron contributions to the dielectric function, it was possible to fit the bulk complex dielectric function, and consequently, determine optical parameters and band energy values such as the coefficient for bound electron contribution Q bulk?=?2?×?1024, gap energy E g?=?1.95 eV, Fermi energy E F?=?2.15 eV, and damping constant for bound electrons γ b?=?1.15?×?1014 Hz. With both size-dependent contributions to the dielectric function, extinction spectra of copper Nps in the subnanometer radius range can be calculated using Mie’s theory and its behaviour with size can be analysed. These studies are applied to fit experimental extinction spectra of very small spherical core–shell Cu–Cu2O Nps generated by ultrafast laser ablation of a solid target in water. Theoretical calculations for subnanometric core radius are in excellent agreement with experimental results obtained from core–shell colloidal Nps. From the fitting, it is possible determining core radius and shell thickness of the Nps, showing that optical extinction spectroscopy is a good complementary technique to standard high-resolution electron microscopy for sizing spherical nanometric-subnanometric Nps.  相似文献   

13.
To reduce CO2 emissions from alcoholic fermentation, Arthrospira platensis was cultivated in tubular photobioreactor using either urea or nitrate as nitrogen sources at different light intensities (60 μmol m?2 s?1?≤?I?≤?240 μmol m?2 s?1). The type of carbon source (pure CO2 or CO2 from fermentation) did not show any appreciable influence on the main cultivation parameters, whereas substitution of nitrate for urea increased the nitrogen-to-cell conversion factor (Y X/N ), and the maximum cell concentration (X m ) and productivity (P X ) increased with I. As a result, the best performance using gaseous emissions from alcoholic fermentation (X m ?=?2,960?±?35 g m?3, P X ?=?425?±?5.9 g m?3 day?1 and Y X/N ?=?15?±?0.2 g g?1) was obtained at I?=?120 μmol m?2 s?1 using urea as nitrogen source. The results obtained in this work demonstrate that the combined use of effluents rich in urea and carbon dioxide could be exploited in large-scale cyanobacteria cultivations to reduce not only the production costs of these photosynthetic microorganisms but also the environmental impact associated to the release of greenhouse emissions.  相似文献   

14.
Graphene, new generation advance material of two dimensional hexagonal lattice having extraordinary optical signatures, is used as coating material to enhance the surface plasmon resonance (SPR) effect of core@shell metal nanospheres. In a core@shell nanosphere, we have chosen metal as a core and graphene monolayer (GML) as a shell. We have analysed optical signature of coated and non-coated nanospheres in terms of extinction efficiency (Q ext) and tunabilty of surface plasmon resonances using electrostatic model, where particle size is much smaller than the wavelength of incident light. We analysed this model over different metals (silver, gold and aluminium) core, coated with different thickness of GML (d?=?0.1 to 0.5 nm). These core@shell nanospheres are embedded in refractive index media of air (n em?=?1), SiO2 (n em?=?1.47) and TiO2 (n em?=?2.79). The Q ext has been calculated by varying both the core radii as well as the GML shell thickness. Graphene-coated metal nanosphere exhibits SPRs that have wide range tunability from 300 to 1500 nm. In the presenting work, we also analysed that extinction efficiency for metal@GML is higher in TiO2 than others. The optimum value of GML shell thickness is 0.4 nm for TiO2, the magnitude of extinction efficiency is maximum for the optimum thickness. The tunability of these plasmonic resonances is highly dependent on the core@shell material, thickness of Graphene shell and surrounding environment while non-coated metal nano-spheres do not show appropriate SPR tunability.  相似文献   

15.
The gene coding for d-psicose 3-epimerase (DPEase) from Clostridium sp. BNL1100 was cloned and expressed in Escherichia coli. The recombinant enzyme was purified by Ni-affinity chromatography. It was a metal-dependent enzyme and required Co2+ as optimum cofactor. It displayed catalytic activity maximally at pH 8.0 and 65 °C (as measured over 5 min). The optimum substrate was d-psicose, and the K m, turnover number (k cat), and catalytic efficiency (k cat/K m) for d-psicose were 227 mM, 32,185 min?1, and 141 min?1 mM?1, respectively. At pH 8.0 and 55 °C, 120 g d-psicose l?1 was produced from 500 g d-fructose l?1 after 5 h.  相似文献   

16.
We study an active modulation of surface plasmon resonance (SPR) of Au nanoparticles based on highly doped graphene in visible and near-infrared regions. We find that compared to the traditional metal SPR, the SPR of Au nanoparticles based on graphene causes a remarkable blue shift. The field intensity in the gap is redistributed to standing wave. The field intensity of standing wave is about one order of magnitude higher than the traditional model. Moreover, the SPR of Au nanoparticles can be actively modulated by varying the graphene Fermi energy. We find the maximum modulation of field intensity of absorption spectra is more than 21.6 % at λ?=?822?nm and the amount of blue shift is 17.4 nm, which is about 2.14 % of the initial wavelength λ 0?=?813.4?nm, with increasing monolayer graphene Fermi energy from 1.0 to 1.5 ev. We find that the SPR sensitivity to the refractive index n of the environment is about 642 nm per refractive index unit (RIU). The SPR wavelengths have a big blue shift, which is about 33 nm, with increasing number of graphene layers from 1 to 3, and some shoulders on the absorption spectra are observed in the models with multilayer graphene. Finally, we study the Au nanorod array based on monolayer graphene. We find that the blue shift caused by the graphene increases from 14 to 24 nm, with increasing gap g y from 10 to 20 nm. Then, it decreases from 24 to 14 nm, with increasing gap g y from 20 to 50 nm. This study provides a new way for actively modulating the optical and optoelectronic devices.  相似文献   

17.
In pH 8.4 Tris–HCl buffer solutions, alcohol dehydrogenase catalyzed the reaction between ethanol and nicotinamide adenine dinucleotide to produce acetaldehyde. In the medium of HCl, acetaldehyde reduced HAuCl4 to form gold particles that exhibited a strong resonance scattering (RS) peak at 600 nm. The RS peak increased with ethanol concentration. The increased RS intensity at 600 nm (ΔI 600 nm) was proportional to the ethanol concentration (C) from 0.068 to 10.2 mmol/L, with a regression equation of ΔI 600 nm?=?35.59?C?+?16.1, and a detection limit (3σ) of 3.2 μmol/L. This proposed method was applied to detect ethanol in saliva and plant cell culture medium samples, with satisfactory results.  相似文献   

18.
The sensitivity of the wavelength position of localized surface plasmon resonance (LSPR) in metal nanostructures to local changes in the refractive index has been widely used for label-free detection strategies. Tuning the optical properties of the nanostructures from the visible to the infrared region is expected to have a drastic effect on the refractive index sensitivity. Here, we theoretically investigate the optical response of a newly designed plasmonic interface to changes in the bulk refractive index by the finite difference time domain method. It consists of a structured interface, where the planar interface is superposed with dielectric pillars 30 nm in height and 125 nm in length with a separation distance of 15 nm. The pillars are covered with U-shaped gold nanostructures of 50 nm in height, 125 nm in length, and 5 nm of gold base thickness. The whole structure is finally covered with a 5-nm thick dielectric layer of n 2?=?2.63. This plasmonic structure shows bulk refractive index sensitivities up to 1750 nm/RIU (RIU : refractive index unit) in the near infrared (λ?=?2621 nm). The enhanced sensitivity is a consequence of the extremely enhanced electrical field between the gold nanopillars of the plasmonic interface.  相似文献   

19.
We investigated the effect of SiO2 spacer layer thickness between the textured silicon surface and silver nanoparticles (Ag NPs) on solar cell performance using quantum efficiency analysis. Separation of Ag NPs from high index silicon with SiO2 layer led to modified absorption and scattering cross-sections due to graded refractive index medium. The forward scattering from Ag NPs is very sensitive to SiO2 layer thickness in plasmonic silicon cell performance due to the evanescent character of generated near-fields around the NPs. With the optimized ~30–40 nm SiO2 spacer layer, we observed an enhancement of solar cell efficiency from ~8.7 to ~10 %, which is due to the photocurrent enhancement in the off-resonance surface plasmon region. We also estimated minority carrier diffusion lengths (L eff) from internal quantum efficiency data, which are also sensitive to SiO2 spacer layer thickness. We observed that the L eff values are enhanced from ~356 to ~420 μm after placing Ag NPs on ~40 nm spacer layer due to improved forward (angular) scattering of light from the Ag NPs into silicon.  相似文献   

20.
Titanium dioxide is a promising photoanode material for water oxidation, but it is substantially limited by its poor efficiency in the visible light range. Herein, an innovative carbon/nitrogen coimplantation method is utilized to realize the “Midas touch” transformation of TiO2 nanowire (NW) arrays for photoelectrochemical (PEC) water splitting in visible light. These modified golden–yellow rutile TiO2 NW arrays (C/N‐TiO2) exhibit remarkably enhanced absorption in visible light regions and more efficient charge separation and transfer. As a result, the photocurrent density of carbon/nitrogen co‐implanted TiO2 under visible light (>420 nm) can reach 0.76 mA cm?2, which far exceeds the value of 3 µA cm?2 seen for pristine TiO2 nanowire arrays at 0.8 V versus Ag/AgCl. An incident photon to electron conversion efficiency of ≈14.8% is achieved at 450 nm on C/N‐TiO2 without any other cocatalysts. The ion implantation doping approach, combined with codoping strategies, is proved to be an effective strategy for enhancing the photoelectrochemical conversion and can enable further improvement of the PEC water‐splitting performance of many other semiconductor photoelectrodes.  相似文献   

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