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- 2017
- photosynthesis
- dry matter
- gas exchange
- chlorophyll content
- ozone layer.
- Agronomy
- University of Basilicata
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Theoretical Model of Exciton States and Ultra-fast Energy Transfer in Heliobacterial Type-I Homodimeric Reaction Center
摘要： A simple theoretical model of exciton dynamics was proposed to interpret the fast excitation energy transfer process in the Type-I homodimeric reaction center of Heliobacterium modesticaldum (hRC); this structure was recently identified and shown to resemble that of the plant/cyanobacterial photosystem I (PSI) reaction center. The exciton state model, which mainly relies on the geometries of 54 bacteriochlorophyll (BChl) g, 4 BChl-g′ and 2 chlorophyll (Chl) a on hRC and assumes constant site energy values for the pigments, reproduced the absorption spectrum of hRC rather well. The model also enabled numerical analysis of the exciton dynamics on hRC, which can be compared with the decay-associated spectra obtained by the laser spectroscopy experiments. The model indicates that the stronger transition-dipole moment on BChl-g contributes to the faster energy transfer due to the higher coherency of the delocalized exciton states on hRC compared to that on PSI that arranges Chl-a at almost homologous locations.
关键词： chlorophyll,photosystem I,bacteriochlorophyll,exciton dynamics,energy transfer,reaction center
更新于2025-09-23 15:21:21
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Photoelectricity and thermoelectricity in organic chlorophyll phototransistors
摘要： As one kind of organic semiconductor materials, Chlorophyll has been attracted great attention with remarkable optical properties. Here, we demonstrate photoresponse and thermoelectric current in the biological Chlorophyll A field effect phototransistors (FEpTs). Meanwhile, it exhibits excellent performances including high responsivity (5×1013 A/W) and relatively fast response time (rise time ~ 20.3 s, fall time ~ 28.2 s) under illumination by 405 nm. Utilizing thermionic emission theory and typical Arrehenius plot, Schottky barrier B is found to be 76.6 meV. The biological phototransistor via low-cost, simple, and scalable fabrication processes opens up new opportunities to realize flexible, transparent organic electronic, and biologically optoelectronic devices.
关键词： Schottky junction,photoelectricity and thermoelectricity,Chlorophyll,Organic phototransistor
更新于2025-09-23 15:21:21
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Physico-chemical chlorophyll-a species in aqueous alcohol solutions determine the rate of its discoloration under UV light
摘要： Chlorophyll-a (Chl-a) discolors when it is exposed to light, and such discoloration decreases food quality. To elucidate the discoloration mechanism of Chl-a, we determined discoloration rate in di?erent Chl-a chemical species and assessed the size of Chl-a aggregates in mixed aqueous solutions of methanol and ethanol. Chl-a existed as monomer, J-aggregate, and random aggregate in solutions with di?erent alcohol concentrations. The predominant species depended on the alcohol concentration. Monomeric Chl-a and J-aggregates discolored quickly, whereas random aggregates discolored slowly. Particle sizes of J-aggregates were 319 and 2305 nm in diameter in aqueous solutions of methanol and ethanol, respectively. The sizes of random aggregates were 51 and 79 nm in 10% (v/v) aqueous solutions of methanol and ethanol, respectively. The size of Chl-a aggregates positively correlated with the rate of Chl-a discoloration under UV light. Based on the results obtained, we propose a mechanism of Chl-a discoloration.
关键词： Chlorophyll-a,Discoloration,Random aggregates,Particle size,J-aggregates
更新于2025-09-23 15:21:21
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Syntheses of Chalcone-Type Chlorophyll Derivatives Possessing a Bacteriochlorin, Chlorin, or Porphyrin <i>π</i> -System and Their Optical Properties
摘要： C3-(Trans-arylethenyl)carbonylated chlorophyll derivatives possessing a bacteriochlorin or chlorin π-system were synthesized by cross-aldol (Claisen-Schmidt) condensation of methyl pyrobacteriopheophorbide-a or 3-acetyl-3-devinyl-pyropheophorbide-a bearing the C3-acetyl group with p-(un)substituted benzaldehydes under basic conditions. The corresponding porphyrin-type chlorophyll derivatives were prepared by the oxidation (17,18-didehydrogenation) of the chlorin-type. Their Qy absorption and fluorescence emission maxima in dichloromethane correlated well with Hammett substituent constants of the p-substituents. Several electron-withdrawing p-substituents suppressed the emission due to photoinduced electron transfer quenching in a molecule. The substitution sensitivities for their maxima and fluorescence quantum yields decreased in the order of bacteriochlorin-, chlorin-, and porphyrin-type derivatives.
关键词： Chlorophyll derivatives,Optical properties,Bacteriochlorin,Cross-aldol condensation,Hammett substituent constants,Porphyrin,Chlorin
更新于2025-09-23 15:21:01
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Correlation of bio-optical properties with photosynthetic pigment and microorganism distribution in microbial mats from Hamelin Pool, Australia
摘要： Microbial mats and stromatolites are widespread in Hamelin Pool, Shark Bay, however the phototrophic capacity of these systems is unknown. This study has determined the optical properties and light-harvesting potential of these mats with light microsensors. These characteristics were linked via a combination of 16S rDNA sequencing, pigment analyses, and hyperspectral imaging. Local scalar irradiance was elevated over the incident down-welling irradiance by 1.5-fold, suggesting light trapping and strong scattering by the mats. Visible light (400-700 nm) penetrated to a depth of 2 mm, whereas near infrared light (700-800 nm) penetrated to at least 6 mm. Chlorophyll a and bacteriochlorophyll a (Bchl a) were found to be the dominant photosynthetic pigments present, with BChl a peaking at the subsurface (2-4 mm). Detailed 16S rDNA analyses revealed the presence of putative Chl f-containing Halomicronema sp. and photosynthetic members primarily decreased from the mat surface down to a depth of 6 mm. Data indicated high abundances of some pigments and phototrophic organisms in deeper layers of the mats (6-16 mm). It is proposed that the photosynthetic bacteria present in this system undergo unique adaptations to lower light conditions below the mat surface, and that phototrophic metabolisms are major contributors to ecosystem function.
关键词： chlorophyll,phototrophy,microbial mats,Hamelin Pool,pigments,stromatolite
更新于2025-09-23 15:21:01
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - A Simple Fusion Approach of Chlorophyll Images and Sea Surface Temperature Images for Improving the Detection of Moroccan Coastal Upwelling
摘要： In order to improve the decision-making on the Moroccan upwelling region detection, we present in this paper a simple and reliable fusion approach. In this context, we started by applying Fuzzy C-means algorithm on each 46 Sea Surface Chlorophyll images and on each 46 Sea Surface Temperature images during the year of 2014. After that, we implement post classification fusion by using logical AND operator set to combine FCM result of the both types and consequently having single image more informative and suitable for visual perception. The oceanographer validation indicate that the proposed methodology detect automatically and effectively the different Moroccan coastal upwelling scenarios of our database.
关键词： Moroccan Coastal Upwelling,Fuzzy C-means,Sea Surface Temperature Image,Sea Surface Chlorophyll Image,Post Classification Fusion
更新于2025-09-23 15:21:01
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Long-Term Agroecosystem Research in the Central Mississippi River Basin: Hyperspectral Remote Sensing of Reservoir Water Quality
摘要： In situ methods for estimating water quality parameters would facilitate efforts in spatial and temporal monitoring, and optical reflectance sensing has shown potential in this regard, particularly for chlorophyll, suspended sediment, and turbidity. The objective of this research was to develop and evaluate relationships between hyperspectral remote sensing and lake water quality parameters—chlorophyll, turbidity, and N and P species. Proximal hyperspectral water reflectance data were obtained on seven sampling dates for multiple arms of Mark Twain Lake, a large man-made reservoir in northeastern Missouri. Aerial hyperspectral data were also obtained on two dates. Water samples were collected and analyzed in the laboratory for chlorophyll, nutrients, and turbidity. Previously reported reflectance indices and full-spectrum (i.e., partial least squares regression) methods were used to develop relationships between spectral and water quality data. With the exception of dissolved NH3, all measured water quality parameters were strongly related (R2 ≥ 0.7) to proximal reflectance across all measurement dates. Aerial hyperspectral sensing was somewhat less accurate than proximal sensing for the two measurement dates where both were obtained. Although full-spectrum calibrations were more accurate for chlorophyll and turbidity than results from previously reported models, those previous models performed better for an independent test set. Because extrapolation of estimation models to dates other than those used to calibrate the model greatly increased estimation error for some parameters, collection of calibration samples at each sensing date would be required for the most accurate remote sensing estimates of water quality.
关键词： water quality,Mark Twain Lake,partial least squares regression,chlorophyll,hyperspectral remote sensing,nutrients,turbidity
更新于2025-09-23 15:21:01
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Retrieval of Chlorophyll-a and Total Suspended Solids Using Iterative Stepwise Elimination Partial Least Squares (ISE-PLS) Regression Based on Field Hyperspectral Measurements in Irrigation Ponds in Higashihiroshima, Japan
摘要： Concentrations of chlorophyll-a (Chl-a) and total suspended solids (TSS) are significant parameters used to assess water quality. The objective of this study is to establish a quantitative model for estimating the Chl-a and the TSS concentrations in irrigation ponds in Higashihiroshima, Japan, using field hyperspectral measurements and statistical analysis. Field experiments were conducted in six ponds and spectral readings for Chl-a and TSS were obtained from six field observations in 2014. For statistical approaches, we used two spectral indices, the ratio spectral index (RSI) and the normalized difference spectral index (NDSI), and a partial least squares (PLS) regression. The predictive abilities were compared using the coefficient of determination (R2), the root mean squared error of cross validation (RMSECV) and the residual predictive deviation (RPD). Overall, iterative stepwise elimination based on PLS (ISE–PLS), using the first derivative reflectance (FDR), showed the best predictive accuracy, for both Chl-a (R2 = 0.98, RMSECV = 6.15, RPD = 7.44) and TSS (R2 = 0.97, RMSECV = 1.91, RPD = 6.64). The important wavebands for estimating Chl-a (16.97% of all wavebands) and TSS (8.38% of all wavebands) were selected by ISE–PLS from all 501 wavebands over the 400–900 nm range. These findings suggest that ISE–PLS based on field hyperspectral measurements can be used to estimate water Chl-a and TSS concentrations in irrigation ponds.
关键词： total suspended solids,partial least squares regression,irrigation ponds,hyperspectral,chlorophyll-a
更新于2025-09-23 15:21:01
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Remote sensing bio-control damage on aquatic invasive alien plant species
摘要： Aquatic Invasive Alien Plant (AIAP) species are a major threat to freshwater ecosystems, placing great strain on South Africa’s limited water resources. Bio-control programmes have been initiated in an effort to mitigate the negative environmental impacts associated with their presence in non-native areas. Remote sensing can be used as an effective tool to detect, map and monitor bio-control damage on AIAP species. This paper reconciles previous and current research concerning the application of remote sensing to detect and map bio-control damage on AIAP species. Initially, the spectral characteristics of bio-control damage are described. Thereafter, the potential of remote sensing chlorophyll content and chlorophyll fluorescence as pre-visual indicators of bio-control damage are reviewed and synthesised. The utility of multispectral and hyperspectral sensors for mapping different severities of bio-control damage are also discussed. Popular machine learning algorithms that offer operational potential to classify bio-control damage are proposed. This paper concludes with the challenges of remote sensing bio-control damage as well as proposes recommendations to guide future research to successfully detect and map bio-control damage on AIAP species.
关键词： machine learning algorithms,multispectral sensors,chlorophyll content,Aquatic Invasive Alien Plant (AIAP) species,chlorophyll fluorescence,hyperspectral sensors,Remote sensing,bio-control damage
更新于2025-09-23 15:19:57
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A Biomimetic-Computational Approach to Optimizing the Quantum Efficiency of Photovoltaics
摘要： The most advanced low-cost organic photovoltaic cells have a quantum efficiency of ~10%. This is in stark contrast to plant/bacterial light-harvesting systems which offer quantum efficiencies close to unity. Of particular interest is the highly effective quantum coherence-enabled energy transfer. Noting that quantum coherence is promoted by charged residues and local dielectrics, classical atomistic simulations and Time-Dependent Density Functional Theory (TD-DFT) can be used to identify charge/dielectric patterns and electronic coupling at exactly defined energy transfer interfaces incorporating structural information obtained on photosynthetic protein-pigment complexes. To this end, the project focuses on the first protein-pigment-redox carrier complex of the linear electron transport phosphorylation chain termed photosystem II [PSII]. PSII contains more than 10 major polypeptides in addition to hundreds of pigment molecules amounting to a molecular mass in excess of 1 Mio Dalton. Owing to the complexity and fragility of PSII, this project bases the overall architecture of PSII on in situ EM data providing structural clues about the entire, unperturbed PSII complex. Albeit not to high resolution when compared to X-ray crystallography and NMR spectroscopy, the EM tomographic results and projection maps provide an accurate delineation of the native complex suitable for fitting high-resolution X-ray data of PSII subcomplexes towards an atomistic model of the entire PSII complex. This must also include the light-harvesting antennae, i.e. the light-harvesting chlorophyll (Chl) a/b protein complex [LHCII]. With respect to LHCII one should take into account positioning LHCII next to PSII as well as in a separate, complementary membrane thus permitting to test for both, horizontal (intramembrane) and vertical (intermembrane) energy transfer, respectively. The presence of LHCII in a membrane different from PSII is supported by strong biochemical evidence and tomographic data, and it has also been noted that the organization of LHCII may change in response to environmental conditions.
关键词： photosystem II,biomimetic,computational approach,quantum efficiency,light-harvesting chlorophyll,photovoltaics
更新于2025-09-23 15:19:57