The Tunable and Well-Controlled Surface Plasmon Resonances of Au Hollow Nanostructures by a Chemical Route

Au plasmonic hollow spherical nanostructures were synthesized by electrochemical reduction (GRR, the Galvanic Replacement Reaction) using Ag nanoparticles as templates. From UV-visible absorption spectroscopy, it was found that the surface plasmon resonance (SPR) of gold hollow spherical nanostructures first showed red shift and then blue shift. However, further addition of gold precursor (HAuCl₄) resulted into a red shift of SPR peak. The morphological changes from Ag nanoparticles to Au hollow nanostructures were assessed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX)analysis. The Mie Scattering theory based simulations of SPR of Au hollow nanostructures were performed which are in good agreement with the experimental observations. Based on the experimental observations and theoretical calculations, a complete growth mechanism for Au hollow nanostructures is proposed.     

Comparative Theoretical Study of the Optical Properties of Silicon/Gold,Silica/Gold Core/Shell and Gold Spherical Nanoparticles

The scattering and absorption efficiencies of light by individual silicon/gold core/shell spherical nanoparticles in air are analysed theoretically in the framework of Lorenz-Mie formalism. We have addressed the influence of particle-diameter and gold-shell thickness on the scattering and absorption efficiencies of such nano-heterostructures. For comparison, we also considered the famous silica/gold core/shell nanoparticle and pure gold nanoparticle. Our simulation clearly shows that the optical response of the illuminated Si/Au core/shell nanoparticle differs markedly from that of the famous SiO₂/Au heterostructure which in turn does not show a significant difference with that of the pure gold nanoparticle. This difference is clearly evident for shell thickness to outer particle radius ratio of less than 0.5. It manifests itself essentially by the occurrence of a strong and sharp absorption resonance beyond the wavelength of 600 nm where the silica/gold and the pure gold nanoparticles never absorb. The characteristics of this resonance are found to be sensitive to the particle diameter and the shell thickness. In particular, its spectral position can be adjusted over a wide spectral range from the visible to the mid-IR by varying the particle diameter and/or the shell thickness.     

Obtain Quadruple Intense Plasmonic Resonances from Multilayered Gold Nanoshells by Silver Coating: Application in Multiplex Sensing

Four intense and separate localized surface plasmon resonance (LSPR) absorption peaks have been obtained in the gold-dielectric–gold–silver multilayer nanoshells. The silver coating on the gold shell results in a new LSPR peak at about 400 nm corresponding to the $ {{\left| {\omega_{+}^{-}} \right\rangle}_{Ag }} $ mode. The intense local electric field concentrated in the silver shell at the wavelength of 400 nm indicates that this new plasmonic band is coming from the symmetric coupling between the antibonding silver shell plasmon mode and the inner sphere plasmon. Increasing the silver shell thickness also leads to the intensity increasing of the $ {{\left| {\omega_{+}^{-}} \right\rangle}_{Au }} $ mode and blue shift of $ \left| {\omega_{-}^{+}} \right\rangle $ and $ \left| {\omega_{-}^{-}} \right\rangle $ modes. Therefore, quadruple intense plasmonic resonances in the visible region could be achieved in gold-dielectric–gold–silver multilayer nanoshells by tuning the geometrical parameters. And the quadruple intense plasmonic resonances in the visible region provide well potential for multiplex biosensing based on LSPR.     

Theoretical Studies of Tunable Localized Surface Plasmon Resonance of Gold-Dielectric Multilayered Nanoshells

Tunable properties of localized surface plasmon resonances (LSPR) of gold-dielectric multilayered nanoshells are studied by quasi-static theory and plasmon hybridization theory. Multilayered nanoshells with the gold core and nanoshell separated by a spacer layer exhibit strong coupling between the core and nanoshell plasmon resonance modes. It is found that the absorption spectra characteristics of LSPR are sensitive to multiple parameters including the surrounding medium refractive index, the dielectric constant of spacer layer, the radius of inner core gold sphere, outer shell layer thickness, and their coupling strength. The results show that LSPR is mainly influenced by the ratio of spacer layer dielectric constant ε ₂ to surrounding medium dielectric constant ε ₄. Absorption spectrum of \(\left |\omega _{-}^{+}\right \rangle \) mode is red-shifted with increasing core radius when ε ₂ > ε ₄. It is surprising to find that LSPR is blue-shifted with increasing core radius when ε ₂ < ε ₄, and no shift when ε ₂ = ε ₄. These interesting contrary shifts of \(\left |\omega _{-}^{+}\right \rangle \) mode with different ratios ε ₂/ε ₄ are well analysed with plasmon hybridization theory and the distributions of induced charges interaction between the inner core and outer shell. In addition, for the sake of clarity, the distributions of electric filed intensity at their plasmon resonance wavelengths are also calculated. This work may provide an alternative approach to analyse property of the core-shell nanoshell particles based on plasmon hybridization theory and the induced charge interaction.     

Tailoring LSPR-Based Absorption and Scattering Efficiencies of Semiconductor-Coated Au nanoshells

Absorption and scattering efficiencies of semiconductor-coated Au nanoshell have been studied by the extended Mie theory for their possible solar cell, optical imaging, and photothermal applications, etc. The effect of Au shell layer thickness, core size, and surrounding medium on the absorption and scattering efficiencies at the localized surface plasmon resonance (LSPR) wavelengths has been reported. It has been found that both the absorption and scattering efficiencies get blue-shifted with an increase in Au shell layer thickness from 2 to 10 nm and with an increase in surrounding refractive index whereas the corresponding LSPR peaks shift towards red. It has also been found that the spectra are red-shifted with an increase in the core radius from 20 to 40 nm while keeping the shell thickness same. The effect of shell thickness on the absorption peak position and absorption linewidth has also been studied. Hence, the optical response of both CdSe- and CdTe-coated Au nanoshells can be tuned and controlled from the visible to the near-infrared (NIR) region of the electromagnetic (EM) spectrum. Finally, the CdSe-coated Au nanoshell exhibits high scattering and absorption efficiencies in comparison to the CdTe-coated nanoshell.     

Theoretical Study of Sensitivity and Localized Surface Plasmon Resonance of Ag-Dielectric Core-Shell Multi-layered Nanosphere

Localized surface plasmon resonances (LSPRs) of Ag-dielectric-Ag multi-layered nanoshell are studied by quasi-static approximation and plasmon hybridization theory. Absorption properties of multi-layered nanoshell with the silver core and nanoshell separated by a dielectric layer exhibit strong coupling between the core and nanoshell. The result shows absorption spectrum of LSPRS is influenced by the refractive index of surrounding medium, the dielectric constant of middle dielectric layer, the thickness of inner core radius and outer shell layer. LSPR shift of the longest wavelength \(\left |\omega _{-}^{-}\right >\) is red-shifted with increasing the inner core radius. It is interesting to find that longer wavelength \(\left |\omega _{-}^{+}\right >\) mode is mainly effected by the ratio constant of the surrounding medium refractive index ε ₄ to the middle layer dielectric constant ε ₂. \(\left |\omega _{-}^{+}\right >\) mode takes place a blue-shift with increasing inner core radius when ε ₂ > ε ₄, a red-shift when ε ₂ < ε ₄, and no-shifting when ε ₂ = ε ₄. However, the influence of dielectric layer radius to \(\left |\omega _{-}^{+}\right >\) mode shows the different property as that of increasing the inner core radius. The underlying mechanisms are analyzed with the plasmon hybridization theory and the distribution of induced charge interaction between the inner core and outer shell. In addition, the influence of core radius, middle dielectric layer radius and outer shell radius to sensitivity of Ag-dielectric-Ag multi-layered nanoshell are also reported, a higher sensitivity could be gotten by adjusting geometrical parameters. Our theoretical study could give an easy way to analyze properties of the core-shell nanosphere based on plasmon hybridization theory and the induced charge interaction, and usefully broaden the applications in nano-optics.     

Modulation of Visible and Near-Infrared Surface Plasmon Resonance of Au Nanoparticles Based on Highly Doped Graphene

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.     

Optical Absorption Modeling of Plasmonic Organic Solar Cells Embedding Silica-Coated Silver Nanospheres

We numerically study plasmonic solar cells in which a square periodic array of core–shell Ag@SiO₂ nanospheres (NSs) are placed on top of the indium tin oxide (ITO) layer using a 3D finite-difference time-domain (FDTD) method. We investigate the influence of various parameters such as the periodicity of the array, the Ag core diameter, the active layer thickness, the shell thickness, and the refractive index of the shell materials on the optical performance of the organic solar cells (OSC). Our results show that the optimal periodicity of the array of NSs is dependent on the size of Ag core NSs in order to maximize optical absorption in the active layer. A very thin active layer (<70 nm) and an ultrathin (<5 nm) SiO₂ shell are needed in order to obtain the highest optical absorption enhancement. Strong electric field localization is observed around the plasmonic core–shell nanoparticles as a result of localized surface plasmon resonance (LSPR) excited by Ag NSs with and without silica shell. Embedding 50 nm Ag NSs with 1-nm-thick SiO₂ shell thickness on top of ITO leads to an enhanced intrinsic optical absorption in a 40-nm-thick poly(3-hexylthiophene):phenyl-C₆₁-butyric acid methyl ester (P3HT:PCBM) active layer by 24.7% relative to that without the NSs. The use of 1-nm-thick ZnO shell instead of SiO₂ leads to an enhanced intrinsic absorption in a 40-nm-thick P3HT:PCBM active layer by 27%.

     

Light-induced red shift of the Qx absorption band of light-harvesting bacteriochlorophyll in Rhodopseudomonas capsulata and Rhodopseudomonas sphaeroides

In chromatophores from Rhodopseudomonas sphaeroides and Rhodopseudomonas capsulata, the Q_x band(s) of the light-harvesting bacteriochlorophyll (BChl) (λ_max ~590 nm) shifts to the red in response to a light-induced membrane potential, as indicated by the characteristics of the light-minus-dark difference spectrum. In green strains, containing light-harvesting complexes I and II, and one or more of neurosporene, methoxyneurosporene, and hydroxyneurosporene as carotenoids, the absorption changes due to the BChl and carotenoid responses to membrane potential in the spectral region 540–610 nm are comparable in magnitude and overlap with cytochrome and reaction center absorption changes in coupled chromatophores. In strains lacking carotenoid and light-harvesting complex II, the BChl shift absorption change is relatively smaller, due in part to the lower BChl/reaction center ratio.In the carotenoid-containing strains, the peak-to-trough absorption change in the BChl difference spectrum is 5–8% of the peak-to-trough change due to the shift of the longest-wavelength carotenoid band, although the absorption of the BChl band is 25–40% of that of the carotenoid band. The responding BChl band(s) does not appear to be significantly red-shifted in the dark in comparison to the total BChl Q_x band absorption.     

Effect of solvent environment on the CO band position in the infrared spectrum of trans-[Fe(CN)4(CO)2]

Density functional theory (DFT) is used to understand the effect of hydrogen bonding solvents on the CO band position in the infrared (IR) spectrum of a mono-iron complex, trans-[Fe^II(CN)₄(CO)₂]²⁻. This mono-iron complex has received much attention recently due its potential relation to the biosynthesis of Fe-only hydrogenase enzymes. Our calculations show that the polar solvent molecules preferentially hydrogen bond to the cyano ligands in this complex. The effect of such hydrogen bonding on the electron density distribution is analyzed in terms of the population in natural bond orbitals (NBO). Our results show that the presence of hydrogen bonding to the cyano ligands decreases the extent of back bonding from the metal to the carbonyl ligand. This results in decreased electron density in the π^∗ orbitals of the carbonyl bond leading to a strengthening of the CO bond and a consequent blue shift in the IR band position of the carbonyl group. We also show that the extent of blue shift correlates with the number of nearest neighbor solvent molecules.     

Study of Surface Plasmon Resonances of Core-Shell Nanosphere: A Comparison between Numerical and Analytical Approach

An investigation of the wavelength dependent extinction spectra of coated sphere with different core@shell compositions based on discrete dipole approximation technique has been presented in this paper. We have used combinations of A g, A u, and S i O ₂ for this analysis. Specifically, we study the impact of spherical core-shell thickness on its surface plasmon resonance (SPR) peak positions and corresponding spectral widening in distinct regimes of the spectrum. We observe that SPR peak of core-shell nanoparticle(CSNP) can be tuned over the visible to near-infrared spectrum region by manipulating the core/shell ratio and composition of core and shell. Specifically, for dielectric@metal (core@shell) nanoparticle, SPR peak position shifted towards lower wavelength as we increase the shell thickness, which is opposite to the SPR behavior of metal@dielectric. The extinction spectrum shows linear relation between SPR position and thickness of the shell. Further, we observed two resonant peaks for the case of metal@metal CSNP. The SPR peak of Au@Ag (a _eff 100 nm with shell thickness 8 nm) reveals two resonant peak corresponding to Au (594 nm) in red domain, while the peak in blue domain corresponds to Ag (402 nm). We also observe that optical resonance of CSNP can be tuned across the near-infrared region by changing the surrounding medium of higher refractive index. Further, near field pattern of core@shell geometry at resonance wavelength is also shown in the present study. We have also compared the numerical and analyticalmethod for smaller size CSNP with varying thickness and the results show good agreement.     

Investigating the Effect of Ag and Au Nanostructures with Spherical and Rod Shapes on the Emission Wavelength of OLED

Noble metals, especially Ag and Au nanostructures, have unique and adjustable optical attributes in terms of surface plasmon resonance. In this research, the effect of Ag and Au nanoparticles with spherical and rod shapes on the light extraction efficiency and the FWHM of OLED structures was investigated using the finite difference time domain (FDTD) method. The simulation results displayed that by changing the shape and size of Ag and Au nanostructures, the emission wavelength can be adjusted, and the FWHM can be reduced. The presence of Ag and Au nanoparticles in the OLEDs showed a blue and red shift of the emission wavelength, respectively. Also, the Ag and Au nanorods caused a significant reduction in the FWHM and a shift to the longer wavelengths in the structures. The structures containing Ag nanorods showed the narrowest FWHM and longer emission wavelength than the other structures.

     

A Computational Study of the Giant Local Electric Field Enhancement in Al-Au-Ag Trimetallic Three-Layered Nanoshells

The surface plasmon resonance (SPR)-induced local field effect in Al-Au-Ag trimetallic three-layered nanoshells has been studied theoretically. Because of having three kinds of metal, three plasmonic bands have been observed in the absorption spectra and the local electric field factor spectra. The local electric field enhancement and the corresponding resonance wavelength for different plasmon coupling modes and spatial positions of the Al-Au-Ag nanoshells with various geometry dimensions are investigated to find the maximum local electric field enhancement. The calculation results indicate that the giant local electric field enhancement could be stimulated by the plasmon coupling in the middle Au shell or the outer Ag shell and could be optimized by increasing the Ag shell thickness and decreasing the Au shell thickness. What is more, the local electric field enhancement also nonmonotonously depends on the dielectric constant of the environment; the local electric field intensity will be weakened when the surrounding dielectric constant is too small or too large.

     

Redshift of the purple membrane absorption band and the deprotonation of tyrosine residues at high pH: Origin of the parallel photocycles of trans-bacteriorhodopsin

At high pH (> 8) the 570 nm absorption band of all-trans bacteriorhodopsin (bR) in purple membrane undergoes a small (1.5 nm) shift to longer wavelengths, which causes a maximal increase in absorption at 615 nm. The pK of the shift is 9.0 in the presence of 167 mM KCl, and its intrinsic pK is ~8.3. The red shift of the trans-bR absorption spectrum correlates with the appearance of the fast component in the light-induced L to M transition, and absorption increases at 238 and 297 nm which are apparently caused by the deprotonation of a tyrosine residue and red shift of the absorption of tryptophan residues. This suggests that the deprotonation of a tyrosine residue with an exceptionally low pK (pK_a ≈ 8.3) is responsible for the absorption shift of the chromophore band and fast M formation. The pH and salt dependent equilibrium between the two forms of bR, “neutral” and “alkaline,” bR ↔ bR_a, results in two parallel photocycles of trans-bR at high pH, differing in the rate of the L to M transition. In the pH range 10-11.8 deprotonation of two more tyrosine residues is observed with pK's ~ 10.3 and 11.3 (in 167 mM KCL). Two simple models discussing the role of the pH induced tyrosine deprotonation in the photocycle and proton pumping are presented.

It is suggested that the shifts of the absorption bands at high pH are due to the appearance of a negatively charged group inside the protein (tyrosinate) which causes electrochromic shifts of the chromophore and protein absorption bands due to the interaction with the dipole moments in the ground and excited states of bR (Stark effect). This effect gives evidence for a significant change in the dipole moment of the chromophore of bR upon excitation.

Under illumination alkaline bR forms, besides the usual photocycle intermediates, a long-lived species with absorption maximum at 500 nm (P500). P500 slowly converts into bR_a in the dark. Upon illumination P500 is transformed into an intermediate having an absorption maximum at 380 nm (P380). P380 can be reconverted to P500 by blue light illumination or by incubation in the dark.

     

Preparation and optical properties of alloyed ZnxCd1‐xS/alginate core/shell nanoparticles

Zn_xCd_1‐xS/alginate core/shell nanoparticles were synthesized via a colloidal route by reacting zinc and cadmium ions with sulfide ions, followed by coating with alginate. The crystal structure, morphology, size and optical properties of the core/shell nanoparticles were characterized by X‐ray diffraction, transmission electron microscopy, UV/vis and photoluminescent spectra, respectively. The Zn_xCd_1‐xS nanoparticles are spherical and have a cubic structure with a mean crystalline size of 2–4 nm. The band gap of Zn_xCd_1‐xS/alginate core/shell nanoparticles increases with increasing Zn/Cd molar ratio, and the UV/vis absorption blue‐shifts correspondingly. Two emissions related to zinc and sulfide ion vacancies were observed for the Zn_xCd_1‐xS/alginate core/shell nanoparticles due to the surface changes from the alginate coating. A cadmium‐related emission was observed for both the uncovered Zn_xCd_1‐xS and Zn_xCd_1‐xS/alginate core/shell nanoparticles, which has a significant blue‐shift with increasing Zn/Cd molar ratio. Copyright © 2014 John Wiley & Sons, Ltd.     

Solubilization and purification of cytochrome a1 from Nitrosomonas

Cytochrome a₁ was solubilized with Triton X-100 from a membrane-envelope preparation of Nitrosomonas and partially purified by repeated fractionation with (NH₄)₂SO₄. The purified fraction of cytochrome a₁ was enriched over the crude extract by a factor of 16 and 300 with respect to protein and c-type cytochrome, respectively. The cytochrome was characterized as cytochrome a₁ on the basis of (a) reduced absorption maxima at 444 nm and 595 nm, (b) acid acetone extractibility and ether solubility of the heme and (c) absorption maximum of 587 nm of the ferro-hemochrome in alkaline pyridine. The α absorption band shifted from 600 nm to 595 nm upon solubilization of the cytochrome with Triton X-100. Spectral shifts were observed in the presence of cyanide and azide and the cytochrome changed with aging to a form with a reduced absorption band at 422 nm. Cytochrome a₁ was reduced anaerobically in the presence of reduced mammalian cytochrome c and was rapidly reoxidized in the presence of O₂. CO caused a shift in the soret peak of the reduced form but did not prevent reoxidation of cytochrome a₁ in the presence of CO-O₂ (95:5, v/v).     

Scattering Efficiency and LSPR Tunability of Bimetallic Ag,Au, and Cu Nanoparticles

Scattering efficiencies of Ag–Cu, Ag–Au, and Au–Cu alloy nanoparticles are studied based on Mie theory for their possible applications in solar cells. The effect of size (radius), surrounding medium, and alloy composition on the scattering efficiency at the localized surface plasmon resonance (LSPR) wavelengths has been reported. In the alloy nanoparticles of Ag_1?x Cu _x , Au_1?x Cu _x and Ag_1?x Au _x ; the scattering efficiency gets red-shifted with increase in x. Moreover, the scattering efficiency enhancement can be tuned and controlled with both the alloy composition and the surrounding medium refractive index. A linear relationship which is in good agreement to the experimental observations between the scattering efficiency and metal composition in the alloys are found. The effect of nanoparticle size and LSPR wavelength (scattering peak position) on the full width half maxima and scattering efficiency has also been studied. Comparison of Au–Ag, Au–Cu, and Ag–Cu alloy nanoparticles with 50-nm radii shows the optical response of Ag–Cu alloy nanoparticle with wide bandwidth in the visible region of the electromagnetic spectrum making them suitable for plasmonic solar cells. Further, the comparison of Ag–Cu alloy and core@shell nanoparticles of similar size and surrounding medium shows that Cu@Ag nanoparticle exhibits high scattering efficiency with nearly the same bandwidth.     

Quantifying the Usefulness of Oxide-Encapsulated Silver Nanoparticles in Semiconducting Films

Incorporating plasmonic nanoparticles (NPs) in an organic solar cell (OSC) can improve device performance. In our simulation studies, at NP resonance, absorption in poly(3-hexythiophene)/phenyl-C61-butyric acid methyl ester (P3HT/PCBM) can be increased by encapsulating 50 nm Ag NPs with Al₂O₃, HfO₂, MoO₃, and SiO₂. At Ag NP resonance, when the oxide thickness is significant enough, oxides with high relative permittivity induces a higher electric field enhancement at the metal/dielectric interface. This is translated to improved absorption in the polymer layer. By integrating against AM1.5G, overall absorption in P3HT/PCBM is improved when incorporating Ag NPs encapsulated with a thin oxide shell into the polymer film. However, polymeric absorption loss is induced for oxide-encapsulated Ag NPs if MoO₃ and SiO₂ shells are more than 5 nm. For Al₂O₃ and HfO₂, Ag NPs should not be encapsulated with shells thicker than 10 nm. Modeling studies are also extended to absorption in a CH₃NH₃PbI₃ perovskite layer. It is revealed that both Al₂O₃ and HfO₂ have an optimal shell thickness of about 20 nm to ensure maximum absorption in CH₃NH₃PbI₃. The results can be utilized as a useful guideline when designing photovoltaics from an optical point of view.     

Fluorescent (Au@SiO2)SiC Nanohybrids: Influence of Gold Nanoparticle Diameter and SiC Nanoparticle Surface Density

Gold@silica core–shell nanoparticles were prepared with various gold core diameters (ranging from 20 to 150 nm) and silica thicknesses (ranging from 10 to 30 nm). When the gold diameter is increased, the size dispersion became larger, leading to a broader plasmon band. Then, silicon carbide (SiC) nanoparticles were covalently immobilized onto silica to obtain hybrid (Au@SiO₂) SiC nanoparticles. The absorption properties of these hybrid nanoparticles showed that an excess of SiC nanoparticles in the dispersion can be identified by a strong absorption in the UV region. Compared to SiC reference samples, a blue shift of the fluorescence emission, from 582 to 523 nm, was observed, which was previously attributed to the strong surface modification of SiC when immobilized onto silica. Finally, the influence of several elaboration parameters (gold diameter, silica thickness, SiC concentration) on fluorescence enhancement was investigated. It showed that the highest enhancements were obtained with 10 nm silica thickness, low concentration of SiC nanoparticles, and surprisingly, with a 20-nm gold core diameter. This last result could be attributed to the broad plasmon band of big gold colloids. In this case, SiC emission strongly overlapped gold absorption, leading to possible quenching of SiC fluorescence by energy transfer.     

Identification of the carotenoid present in the B-800–850 antenna complex from Rhodopseudomonas capsulata as that which responds electrochromically to transmembrane electric fields

Mild proteolysis of Rhodopseudomonas capsulata chromatophores results in a parallel loss of the 800 nm bacteriochlorophyll absorption band and a blue shift in the carotenoid absorption bands associated with the B-800–850 light-harvesting complex. Both the light-induced and the salt-induced electrochromic carotenoid band shift disappear in parallel to the loss of the 800 nm bacteriochlorophyll absorption upon pronase treatment of chromatophores. During the time required for the loss of the 800 nm bacteriochlorophyll absorption and the loss of the electrochromic carotenoid band shift photochemistry is not inhibited and the ionic conductance of the membrane remains very low. We conclude that the carotenoid associated with the B-800–850 light-harvesting complex is the one that responds electrochromically to the transmembrane electric field. Analysis of the pigment content of Rps. capsulata chromatophores indicates that all of the carotenoid may be accounted for in the well defined pigment-protein complexes.