Measured Action Spectra Research Articles

Selective Excitation of Carotenoids of the Allochromatium vinosum Light-Harvesting LH2 Complexes Leads to Oxidation of Bacteriochlorophyll.

The mechanism of bacteriochlorophyll photooxidation in light-harvesting complexes of a number of purple photosynthetic bacteria when the complexes are excited into the carotenoid absorption bands remains unclear for many years. Here, using narrow-band laser illumination we measured action spectrum of this process for the spectral ranges of carotenoid and bacteriochlorophyll. It is shown that bacteriochlorophyll excitation results in almost no photooxidation of these molecules, while carotenoid excitation leads to oxidation with quantum yield of about 0,0003. Low value of the yield enabled an assumption that the studied process is initiated by the triplet states of the main carotenoids of the complexes with the number of conjugated double-bond chain length of N = 11. Interaction of these states with oxygen facilitates formation, though with low efficiency, of the excited singlet oxygen, which oxidizes bacteriochlorophylls. The carotenoid triplet states are formed in the process of the earlier studied singlet-triplet fission. The obtained results point at the necessity of reconsidering the functions of carotenoids in the light-harvesting complexes of purple bacteria.

Action Plots in Action: In-Depth Insights into Photochemical Reactivity.

Predicting wavelength-dependent photochemical reactivity is challenging. Herein, we revive the well-established tool of measuring action spectra and adapt the technique to map wavelength-resolved covalent bond formation and cleavage in what we term "photochemical action plots". Underpinned by tunable lasers, which allow excitation of molecules with near-perfect wavelength precision, the photoinduced reactivity of several reaction classes have been mapped in detail. These include photoinduced cycloadditions and bond formation based on photochemically generated o-quinodimethanes and 1,3-dipoles such as nitrile imines as well as radical photoinitiator cleavage. Organized by reaction class, these data demonstrate that UV/vis spectra fail to act as a predictor for photochemical reactivity at a given wavelength in most of the examined reactions, with the photochemical reactivity being strongly red shifted in comparison to the absorption spectrum. We provide an encompassing perspective of the power of photochemical action plots for bond-forming reactions and their emerging applications in the design of wavelength-selective photoresists and photoresponsive soft-matter materials.

Photoinactivation Sensitivity of Staphylococcus carnosus to Visible-light Irradiation as a Function of Wavelength.

Inactivation properties of visible light are of increasing interest due to multiple possible fields of application concerning antibacterial treatment. For violet wavelengths, the generation of reactive oxygen species by porphyrins is accepted as underlying mechanism. However, there is still little knowledge about photosensitizers at blue wavelengths. While flavins were named as possible candidates, there is still no experimental evidence. This study investigates the photoinactivation sensitivity of Staphylococcus carnosus to selected wavelengths between 390 and 500nm in 10- to 25-nm intervals. Absorption and fluorescence measurements in bacterial lysates confirmed inactivation findings. By means of a mathematical calculation in MATLAB® , a fit of different photosensitizer absorption spectra to the measured action spectrum was determined to gain knowledge about the extent to which specific photosensitizers are involved. The most effective wavelength for S.carnosus at 415nm could be explained by the involvement of zinc protoporphyrin IX. Between 450 and 470nm, inactivation results indicated a broad plateau, statistically distinguishable from 440 and 480nm. This observation points to flavins as responsible photosensitizers, which furthermore seem to be involved at violet wavelengths. A spectral scan of sensitivities might generally be an advantageous approach for examining irradiation impact.

(Invited) Inorganic Solid-State Solar Cells Using Plasmon-Induced Charge Separation

[Introduction] Metallic nanostructures which show localized surface plasmon resonances have received considerable attention as a light harvesting optical antenna for light-energy conversion systems such as solar cells as well as artificial photosynthesis [1-5]. Recently, we have successfully fabricated a plasmonic photoelectric conversion device using a gold nanostructured titanium dioxide photoelectrode with a nickel oxide (NiO) thin film as a hole transport layer [6]. However, the conversion efficiency was still low. To overcome this problem, we investigated the modulation of the diffusion potential of the junction to control the cell voltage and rectification characteristics. Yajima et al. reported that an interface dipole in an atomic scale strongly affects the rectification characteristics [7]. In this study, we fabricated plasmonic solar cells composed of n-strontium titanate (SrTiO3), gold nanoparticles (Au-NPs) and p-NiO. Also, we inserted a unit cell (uc) of lanthanum aluminate (LaAlO3) as an interface dipole between SrTiO3 and NiO to modulate the diffusion potential. [Experimental] We prepared the plasmonic solar cells as the following procedure. At first, a 0.05wt% niobium-doped SrTiO3 single crystal (100) was treated with HF and NH4F to expose the TiO2 surface of SrTiO3 (t-SrTiO3). Au-NPs were fabricated on the t-SrTiO3 by the deposition of the gold thin film by a pulsed laser deposition (PLD) and subsequent annealing of the substrate at 800°C. After that, the following different cells were prepared. (i) NiO was deposited on Au-NPs/t-SrTiO3 with a thickness of 100 nm by PLD (NiO/Au-NPs/t-SrTiO3); (ii) 100 nm thick NiO was deposited after the deposition of 1uc of LaAlO3 (NiO/LaAlO3/Au-NPs/t-SrTiO3); (iii) 100 nm thick NiO was deposited after the deposition of 1uc of SrO and 1uc of LaAlO3 (NiO/LaAlO3/SrO/Au-NPs/t-SrTiO3). A gold thin film with a thickness of 4 nm was deposited by the helicon sputtering as an electrode. Photoelectric properties of the plasmonic solar cell were measured by the solar simulator (AM 1.5G). [Results and Discussion] First of all, we evaluated current-voltage characteristics of cells under the irradiation of AM 1.5G. The open circuit voltages were dramatically changed by the insert of the LaAlO3 layer and showed large values in the order of (ii)>(i)>(iii). Additionally, the cell (ii) showed most clear rectification characteristics. Furthermore, the cell (ii) showed the largest solar energy conversion efficiency. These results indicate that the diffusion potential was increased in the case of cell (ii) and decreased in the case of (iii). It is considered that the difference is derived from the deposition order of LaAlO3 layer. It was reported that LaAlO3 was deposited in the order of LaO+ and AlO2 - on the TiO2 surface of SrTiO3 [7]. In contrast, LaAlO3 was deposited in the order of AlO2 - and LaO+ on the SrO surface of SrTiO3. As a result, the opposite dipole direction had an opposite effect on the diffusion potential. We also measured action spectra of incident photon-to-current efficiency to evaluate the contribution of the plasmon to photoelectric conversion. As a result, all cells showed a visible light responsivity in the region of plasmon resonance, indicating plasmon-induced charge separation works well even in the presence of the interface dipole.

Computational Evidence for the Role of Arabidopsis thaliana UVR8 as UV–B Photoreceptor and Identification of Its Chromophore Amino Acids

A homology model of the Arabidopsis thaliana UV resistance locus 8 (UVR8) protein is presented herein, showing a seven-bladed β-propeller conformation similar to the globular structure of RCC1. The UVR8 amino acid sequence contains a very high amount of conserved tryptophans, and the homology model shows that seven of these tryptophans cluster at the 'top surface' of the UVR8 protein where they are intermixed with positive residues (mainly arginines) and a couple of tyrosines. Quantum chemical calculations of excitation spectra of both a large cluster model involving all twelve above-mentioned residues and smaller fragments thereof reveal that absorption maxima appearing in the 280-300 nm range for the full cluster result from interactions between the central tryptophans and surrounding arginines. This observation coincides with the published experimentally measured action spectrum for the UVR8-dependent UV-B stimulation of HY5 transcription in mature A. thaliana leaf tissue. In total these findings suggest that UVR8 has in fact in itself the ability to be an ultraviolet-B photoreceptor in plants.

LIGHT USE EFFICIENCY AT DIFFERENT WAVELENGTHS IN ROSE PLANTS

Current knowledge about the spectral dependence of leaf light use efficiency of leaf photosynthesis (LUE; rate of leaf photosynthesis per unit incident light energy) is based on investigations of mostly arable crops. The leaf LUE depends on the optical properties of the leaf (light absorption), on the fraction of light energy absorbed by photosynthetically active pigments and on the excitation balance of the two photosystems. These properties have hardly been investigated on modern vegetable and especially ornamental greenhouse crops. In this research we investigated the action spectrum of leaf photosynthesis and related leaf optical properties of reddish young leaves and green middle aged leaves of rose ‘Akito’. The crop was grown in a heated greenhouse in Wageningen (The Netherlands, latitude 52°N). The green and reddish leaves had similar total absorptance of 87% on average in the PAR range (400 to 700 nm). In the green leaves, however, leaf absorptance around 550 nm was lower than in the reddish leaves, but slightly higher at longer wavelengths. Red light of 680 nm was found to be the most effective for leaf photosynthesis in the short term. Leaf LUEs were calculated for supplemental light by HPS and 645 and 680 nm LEDs based on their emission spectra and the measured action spectra of leaf photosynthesis. These calculations showed that a 645 nm LED light yielded more improvement in LUE compared to HPS light than 680 nm LED light. This is because the 680 nm LED also emits light >700 nm at which the LUE is much lower. If these calculated improvements in leaf LUE for red LED-light compared to HPS-light are sustained at the crop level during prolonged illumination, substantial energy savings may be realized in rose by supplemental lighting with red LED light

Role of OH-stretch/torsion coupling and quantum yield effects in the first OH overtone spectrum of cis-cis HOONO

A joint theoretical and experimental investigation is undertaken to study the effects of OH-stretch/HOON torsion coupling and of quantum yield on the previously reported first overtone action spectrum of cis-cis HOONO (peroxynitrous acid). The minimum energy path along the HOON dihedral angle is computed at the coupled cluster singles and doubles with perturbative triples level with correlation consistent polarized quadruple zeta basis set, at the structure optimized using the triple zeta basis set (CCSD(T)/cc-pVQZ//CCSD(T)/cc-pVTZ). The two-dimensional ab initio potential energy and dipole moment surfaces for cis-cis HOONO are calculated as functions of the HOON torsion and OH bond length about the minimum energy path at the CCSD(T)/cc-pVTZ and QCISD/AUG-cc-pVTZ (QCISD-quadratic configuration interaction with single and double excitation and AUG-augmented with diffuse functions) level of theory/basis, respectively. The OH-stretch vibration depends strongly on the torsional angle, and the torsional potential possesses a broad shelf at approximately 90 degrees , the cis-perp conformation. The calculated electronic energies and dipoles are fit to simple functional forms and absorption spectra in the region of the OH fundamental and first overtone are calculated from these surfaces. While the experimental and calculated spectra of the OH fundamental band are in good agreement, significant differences in the intensity patterns are observed between the calculated absorption spectrum and the measured action spectrum in the 2nu(OH) region. These differences are attributed to the fact that several of the experimentally accessible states do not have sufficient energy to dissociate to OH+NO(2) and therefore are not detectable in an action spectrum. Scaling of the intensities of transitions to these states, assuming D(0)=82.0 kJ/mol, is shown to produce a spectrum that is in good agreement with the measured action spectrum. Based on this agreement, we assign two of the features in the spectrum to Deltan=0 transitions (where n is the HOON torsion quantum number) that are blue shifted relative to the origin band, while the large peak near 7000 cm(-1) is assigned to a series of Deltan=+1 transitions, with predominant contributions from torsionally excited states with substantial cis-perp character. The direct absorption spectrum of cis-cis HOONO (6300-6850 cm(-1)) is recorded by cavity ringdown spectroscopy in a discharge flow cell. A single band of HOONO is observed at 6370 cm(-1) and is assigned as the origin of the first OH overtone of cis-cis HOONO. These results imply that the origin band is suppressed by over an order of magnitude in the action spectrum, due to a reduced quantum yield. The striking differences between absorption and action spectra are correctly predicted by the calculations.

Age-related changes in the photoreactivity of retinal lipofuscin granules: role of chloroform-insoluble components.

Lipofuscin accumulates in human retinal pigment epithelium (RPE) cells with age and may be the main factor responsible for the increasing susceptibility of RPE to photo-oxidation with age. As the composition, absorption, and fluorescence of lipofuscin undergo age-related changes, the purpose of this study was to determine whether photoreactivity of lipofuscin granules also changes with the donor age. To determine whether the photoreactivity of lipofuscin itself is age related, lipofuscin granules were isolated from human RPE and pooled into age groups. Photoreactivity was assessed by measuring action spectra of photo-induced oxygen uptake and photogeneration of reactive oxygen species. Separation of chloroform-soluble (ChS) and -insoluble (ChNS) components by Folch's extraction was used to determine the factors responsible for the age-related increase in lipofuscin photoreactivity. The observed rates of photo-induced oxygen uptake and photo-induced accumulation of superoxide-derived spin adducts indicated that when normalized to equal numbers of lipofuscin granules, aerobic photoreactivity of lipofuscin increased with age. Both ChS and ChNS mediated photogeneration of singlet oxygen, superoxide radical anion, and photo-oxidation of added lipids and proteins. Although both ChS and ChNS exhibited substantial photoreactivities, neither exhibited significant age-related changes when normalized to equal dry mass. In contrast, ChNS contents in lipofuscin granules significantly increased with aging. Aerobic photoreactivity of RPE lipofuscin substantially increases with aging. This effect may be ascribed to the increased content of insoluble components.

Action spectra of apoptosis induction and reproductive cell death in L5178Y cells in the UV-B region.

We investigated the action spectra for the induction of apoptosis and reproductive cell death in mouse lymphoma L5178Y cells using a high-performance spectroirradiator, the Okazaki Large Spectrograph at the National Institute for Basic Biology, Okazaki. L5178Y cells were exposed to monochromatic light at different wavelengths in the UV-B and UV-A regions. The frequencies of apoptosis induction and reproductive cell death were determined by counting cells with chromatin condensation and by a semi-solidified agarose colony formation assay, respectively. The measured action spectra for the two end-points were similar. The sensitivity decreased steeply with an increase of wavelength in the UV-B region, but showed no further decrement in the UV-A region. The action spectra were slightly steeper than that for the minimum erythematic dose (MED), and were similar to the light-absorption spectrum of DNA in the UV-B region. On the other hand, in the UV-A region, the spectra for both endpoints were close to the MED, but not to DNA absorption spectra. The difference between the measured spectra and that for MED may have been caused by the absorption of the light by the skin. Differences in the time course and morphological difference of apoptosis were found between the UV-B and UV-A region. These results suggest that although DNA damage induced by UV-B light can trigger apoptosis, or lead to reproductive cell death, other damage (membrane, protein and so on) may trigger those effects in the UV-A region.

Photogeneration of charge carriers in titanium oxides

We have measured action spectra of the photoconductivity of rutile crystal at ∼4 K. The photoconductivity spectrum shows a keen rise at 3.0 eV and shows a peak at 3.2 eV and a shoulder around 3.7 eV. The threshold energy of the photoconductivity excitation well agrees with the onset of the fundamental optical absorption. This result indicates that the carriers contributing to the photoconductivity are generated by the fundamental excitation of the crystal. We have found that the photoconductivity shows remarkable field dependence. Below 5 V/mm, the photoconductivity was almost field independent. On the other hand, increasing the field strength in the range from 5 to 25 V/mm strongly enhanced the photoconductivity and varied the shape of the action spectrum. The origin of the field dependence is discussed.

Light pulses induce "singular" behavior and shorten the period of the circadian phototaxis rhythm in the CW15 strain of Chlamydomonas.

While measuring action spectra for phase-shifting the circadian clock of Chlamydomonas, we observed that light pulses started near the phase response curve (PRC) "breakpoint" caused a reduction of the amplitude of the phototactic rhythm and two unexpected effects: (1) nonmonotonic fluence response curves (FRCs), and (2) shortening of the period of the subsequent free-running rhythm. The reduction of the rhythm's amplitude is dependent upon both the fluence and wavelength of the light pulse. The results are consistent with the amplitude being dependent upon the perceived "strength" of the stimulus, and with the nonmonotonic FRCs and reduced amplitude reflecting a light-induced change of the pacemaker's state variables to a region of the phase plane close to the "singularity." The period change that is evoked by single stimuli exhibits novel characteristics: large changes in period and a phase specificity that correlates with "singular" behavior. These period changes also appear to be a function of the stimulus strength, but indirectly; the magnitude of the period change is most strongly correlated with the magnitude of the light-induced phase shift. These results are interpreted in the context of limit cycle models of circadian clocks, and are used to suggest new tactics for measuring action spectra of light-induced clock resetting.

INVARIANT PROPERTIES OF ABSORPTION PROFILES IN SPORANGIOPHORES OF Phycomyces blakesleeanus UNDER BALANCING BILATERAL ILLUMINATION

Abstract— Absorption spectra and spectra of the refractive indices were separately measured for cytoplasm and vacuole of Phycomyces blakesleeanus in the wavelengths domains 300 to 750 nm and 250 to 750 nm respectively. These data were then used to simulate absorption profiles for different orientations of the photoreceptor for measured action spectra for phototropic balance. The photoreceptor was assumed to be a flavin. Using the reference wavelengths 394, 450 and 507 nm as an example it is shown that the absorption profiles have, independent of the photoreceptor orientation, invariant properties. Under bilateral balancing illumination the symmetry of the absorption profiles is conserved and the total amount of energy absorbed at proximal and distal sides is an invariant under a symmetry transformation front to the rear side.

Photoelectrochemical solar energy conversion by polycrystalline films of phthalocyanine

A novel photoelectrochemical cell based on an organic paint has been developed. The principal element of the cell is a thin organic film of microcrystalline particles of x-metal free phthalocyanine (x-H 2Pc) dispersed in a polymer binder painted onto a conductive substrate. These films functioned as photocathodes (in electrochemical cells) in contact with an aqueous electrolyte containing redox couples such as p-benzoquinone. Under solar illumination the cells develop photocurrents in the order of a few milliamperes/cm 2 and a photovoltage of 250 mV. The mechanism of the photocurrent and -voltage generation was investigated by measuring action spectra, capacitance-voltage dependence and current-voltage characteristics. The action spectrum indicates that the cathodic photocurrent arises from excitons generated near the semiconductor (x-H 2Pc) electrolyte interface. p-benzoquinone act as electron acceptor, enhancing the photocurrent significantly. The most striking features of these devices are the linear dependence of the photocurrent on light intensity, stability and simplicity of fabrication.

ACTION SPECTRA OF PHOTOPHOSPHORYLATION–II. ATP FORMATION CATALYZED BY PHENAZINEMETHOSULPHATE SUGGESTING THE INVOLVEMENT OF LONG WAVELENGTH PIGMENT FORMS IN THE LIGHT‐HARVESTING PROCESS FOR PS II AND PS I

Abstract— Action spectra of phenazinemethosulfate (PMS)‐catalyzed photophosphorylation, measured under aerobic conditions without added reductants, show the involvement of both photosystem 2 (PS II) and photosystem 1 (PS I). Addition of low concentrations 3‐(3,4)dichlorophenly‐l, 1‐dimethylurea (DCMU) changes the shape of the curves and causes formation of typical PS II action spectra. This can be understood by the partial inhibition of PS II electron flow by DCMU, which therefore becomes rate‐limiting. The presence of DCMU causes a strong decrease of photochemical activity in these spectra at 638, 660 and 690 nm, which we attribute to decreasing activity of PS I pigments.Curve analysis of the action spectra suggests the presence of different Chi forms at room temperature peaking at: 641.6; 650.3; 661.2; 669.8; 677.1; 684.0 and 690.6 nm. Comparison of our data with published data from low temperature absorption spectra indicates that lowering the temperature causes a decrease in halfwidth of the absorption bands but no significant change in peak position. Our data support the hypothesis of French and co‐workers that there are four universal forms of Chi a also at 25â°C.Careful investigation of data in literature does not give evidence that the pigment peaking at 641 nm is a second form of Chi b, as is sometimes assumed.Because our action spectra show two small but distinct maxima at703–705 and718–720 nm when PS II is rate‐limiting, we also measured action spectra of PS I (reduced PMS + DCMU) and PS II (ferricyanide‐ions + 2,5‐dibromo‐3‐methyl‐6‐isopropylbenzoquinone) separately.They show, in agreement with published data, that PS I is operating more efficiently in the spectral region690–725 nm than PS II. The Chi form peaking at 690 nm is absent in the PS II action spectrum, whereas this curve has two small but distinct maxima around703–705 and718–720 nm, respectively, which are also present in the PS I action spectrum.We, therefore, suggest that light absorbed by these pigments can be transferred to either of the two photosystems, and not to PS I exclusively as is sometimes assumed.ATP,adenosine–5′‐triphosphate; BSA, bovine serum albumin; Chi, chlorophyll; DBMIB, 2,5‐dibromo‐3‐methyl‐6‐isopropylbenzoquinone; DCMU, 3‐(3,4)‐dichlorophenyl‐1,1‐dimethyl urea; NADP, nicotinamide adenine dinucleotide phosphate; Pi orthophosphate‐ion; PMS, JV‐methylphenazonium sulphate or phenazinemethosulphate; PS I, photosystem 1; PS II, photosystem 2.

Elevated blood histamine levels and mast cell degranulation in solar urticaria.

1 Ultraviolet radiation (UVR)-induced wealing was studied in four patients with solar urticaria, whose measured action spectra were within the range 300 to 700 nm. 2 Elevated histamine levels were found in blood draining wealed skin in all four patients. 3 Histological and electron microscopial studies of the irradiated skin showed evidence of mast cell degranulation. 4 These findings demonstrate an association between histamine release from mast cells and wealing in solar urticaria, and should encourage evaluation of drugs which suppress histamine release in this disorder.

Initial-image and afterimage discrimination in the human rod and cone systems.

1. The rod-isolation technique of Aguilar & Stiles (1954) was used to obtain scotopic increment-threshold functions in the dark-adapted eye. Increment-threshold functions were obtained for background durations of 50 to 500 msec, but the onset of the background and increment fields was always simultaneous. In all conditions the duration of the increment field was 50 msec. 2. The pattern of results obtained is the same as that reported earlier for the cone system (Geisler, 1978). For background durations greater than that of the increment field, the increment-threshold functions have two distinct branches. It was shown, by measuring action spectra, that both branches reflect the sensitivity of the rod system. 3. When the increment thresholds are plotted as a function of background retinal illuminance, all the lower branches superimpose. This implies that those thresholds are dependent only on the number of background quanta absorbed during presentation of the increment field. On the other hand, when the increment thresholds are plotted as a function of background energy, all the upper branches superimpose, implying that those thresholds are determined by the total number of background quanta absorbed. 4. For the thresholds falling on the lower branches observes reported that the increment field was detected in the initital image of the background and increment fields when they were flashed. For the upper branches, the increment field was detected in a short-term afterimage that appeared after the background was extinguished. The higher the background intensity the longer was the latency until the increment appeared in the afterimage. 5. All of the above findings appear to be consistent with the known properties of the electrical responses of vertebrate photoreceptors. A model based on Penn & Hagins' (1972) model for the photocurrent in rat rods predicts, fairly accurately, the rod and cone increment-threshold results. The parameters estimated by fitting the model support the hypothesis that the short-term rod and cone afterimages are due to the relatively slow decay of internal transmitter, but they suggest that post-receptor mechanisms are responsible for the threshold saturation observed with flashed backgrounds.