Electrochemical Studies on the Biopigment Eumelanin

Pour répondre à la demande énergétique mondiale croissante, nous devons fabriquer des dispositifs de stockage d'énergie pour de multiples besoins futurs. La durabilité motive la recherche de matériaux / produits chimiques abondants, non toxiques et bon marché pour des dispositifs de stockage d'énergie à faible consommation d'énergie et dont l’utilisation n’a pas d’impact négatif sur l'environnement. Les matières organiques actives redox extraites de sources naturelles (bio-sourcées) sont intrigantes pour de tels dispositifs de stockage d'énergie. L'eumélanine qui est un bio-pigment brun-noir à base de quinone est un candidat prometteur pour les électrodes organiques conçus à partir de matériaux provenant des bio-sources. L'eumélanine présente des propriétés fonctionnelles intéressantes, notamment l'absorption optique à large bande, l'activité redox (propriétés de transfert d'électrons) et des propriétés antioxydantes (par chélation des ions métalliques et piégeage des radicaux). Parmi ces propriétés fonctionnelles, le transfert d'électrons est essentiel pour le stockage d'énergie ainsi que pour exploiter les propriétés anti-oxydantes du biopigment. L'eumélanine naturelle est composée de deux éléments de base, le 5,6-dihydroxyindole (DHI) et l'acide 5,6-dihydroxyindole-2-carboxylique (DHICA). Cependant, son hétérogénéité chimique est reconnue comme le principal défi pour l'étude de ses propriétés redox. Dans cette thèse de doctorat, nous avons fabriqué des eumélanines contrôlées chimiquement à partir leurs éléments constitutifs, à savoir DHI-mélanine, DHICA-mélanine et DHI-DHICA-mélanine dans des rapports contrôlés. L'objectif principal de ce travail est de faire la lumière sur les propriétés redox de l'eumélanine à l'aide de méthodes électrochimiques. Dans l'article 1 et l'article 3, nous avons caractérisé l’eumélanine par les techniques de voltampérométrie et une microscopie électronique à balayage (SEM) dans le but de comprendre et de contrôler davantage ses propriétés électrochimiques basées sur l'effet des ions métalliques, les valeurs de pH des électrolytes, etc. À l'article 2, nous avons étudié l'effet de l'irradiation lumineuse sur les propriétés de stockage d'énergie de l'eumélanine, dans le but d'améliorer lesdites propriétés par la lumière solaire qui est considérée comme source d’énergie durable. En effet, une augmentation de la capacité / capacité d'environ 50% de l'eumélanine est observée sous irradiation lumineuse.----------Abstract To meet the growing global energy demand, we need to fabricate energy storage devices for multiple future needs. Sustainability motivates the search for abundant, non-toxic, low-cost materials/chemicals for low-embedded energy and eco-friendly energy storage devices. Redox active organic materials extracted from natural sources (bio-sourced) are intriguing for such energy storage devices. The quinone-based brown-black biopigment eumelanin is a promising candidate for bio-sourced organic electrode materials. Eumelanin features interesting functional properties including broadband optical absorption, redox activity (electron transfer properties), and antioxidant properties (through metal ion chelation and radical scavenging). Among these functional properties, electron transfer is essential for energy storage as well as to exploit the antioxidant properties of the biopigment. Natural eumelanin is composed of two building blocks, 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA). Natural eumelanin features chemical heterogeneity, which is recognized as the main challenge for studying its redox properties. In this work, we fabricated chemically controlled eumelanins from the building blocks, i.e. DHI-melanin, DHICA-melanin, and DHI-DHICA-melanin in controlled ratios. The main goal of this work is to shed light on the redox properties of eumelanin using electrochemical methods. In Article 1 and Article 3, we conducted cyclic voltammetry and scanning electron microscopy (SEM) on eumelanin, aiming at understanding and further controlling its electrochemical properties based on the effect of metal ions, pH values of the electrolytes, etc. In Article 2, we studied the effect of light irradiation on the energy storage properties of eumelanin, aiming at enhancing its energy storage properties by the sustainable source solar light. Indeed, ca 50% enhanced capacity/capacitance of eumelanin is observed under light irradiation. In Article 3, the antioxidant/prooxidant dual properties of eumelanin are studied by exposing the samples to reactive oxygen species (ROS) and transition metal ions. Cyclic voltammetry, X-ray photoelectron spectroscopy (XPS) and SEM are used to characterize such effects. Article 3 aims at understanding the dual properties of eumelanin and proposing possible methods to suppress the prooxidant properties of eumelanin, which is reported to be the main cause of neurondegeneration-related diseases

Multilevel Nitrogen Additions Alter Chemical Composition and Turnover of the Labile Fraction Soil Organic Matter via Effects on Vegetation and Microorganisms

Global nitrogen (N) deposition greatly impacts soil carbon sequestration. A 2- yr multiple N addition (0, 10, 20, 40, 80, and 160 kg N·ha- 1·yr- 1) experiment was conducted in alpine grassland to illustrate the mechanisms underlying the observed soil organic matter (SOM) dynamics on the Qinghai- Tibet Plateau (QTP). Labile fraction SOM (LF- SOM) fingerprints were characterized by pyrolysis- gas chromatography/tandem- mass spectrometry, and microbial functional genes (GeoChip 4.6) were analyzed in conjunction with LF- SOM fingerprints to decipher the responses of LF- SOM transformation to N additions. The significant correlations between LF- SOM and microbial biomass, between organic compounds in LF- SOM and compound degradation- related genes, and between LF- SOM and net ecosystem exchange implied LF- SOM were the main fraction utilized by microorganisms and the most sensitive fraction to N additions. The LF- SOM increased at the lowest N addition levels (10 and 20 kg N·ha- 1·yr- 1) and decreased at higher N addition levels (40 to 160 kg N·ha- 1·yr- 1), but the decrease of LF- SOM was weakened at 160 kg N·ha- 1·yr- 1 addition. The nonlinear response of LF- SOM to N additions was due to the mass balance between plant inputs and microbial degradation. Plant- derived compounds in LF- SOM were more sensitive to N addition than microbial- derived and aromatic compounds. It is predicted that when the N deposition rate increased by 10 kg N·ha- 1·yr- 1 on the QTP, carbon sequestration in the labile fraction may increase by nearly 170% compared with that under the current N deposition rate. These findings provide insight into future N deposition impacts on LF- SOM preservation on the QTP.Key PointsThe LF- SOM quantity increased at the lowest N additions (N10 and N20) and decreased from N40 to N160, but the decrease was weakened at the highest N addition (N160)Plant- derived compounds in LF- SOM were more sensitive to N addition than microbial- derived and aromatic compoundsThe organic compounds in LF- SOM were significantly correlated with compound degradation- related genesPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154963/1/jgrg21637_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154963/2/jgrg21637.pd

Isolation and antibacterial activity of anabaena phycocyanin

The isolation and antibacterial activity of anabaena phycocyanin were investigated. The result indicates that three kinds of protein ingredients: PC-A, PC-B and PC-C were obtained using high performance liquid chromatography. The estimated molecular masses of PC-A and PC-B were 14 to 18 kD. PC-B and PC-C had certain antibacterial activity on Bibrio parahemolyticus, Bacillus mucilaginosus and Sarcina lutea. In addition, PC-C had certain antibacterial activity on Vibrio harveyi. PC-A did not possess antibacterial activity in the study.Keywords: Anabaena, phycocyanin, liquid chromatogram, antibacterialAfrican Journal of Biotechnology Vol. 12(15), pp. 1869-187

An electrochemical study on the effect of metal chelation and reactive oxygen species on a synthetic neuromelanin model

Neuromelanin is present in the cathecolaminergic neuron cells of the substantia nigra and locus coeruleus of the midbrain of primates. Neuromelanin plays a role in Parkinson's disease (PD). Literature reports that neuromelanin features, among others, antioxidant properties by metal ion chelation and free radical scavenging. The pigment has been reported to have prooxidant properties too, in certain experimental conditions. We propose an explorative electrochemical study of the effect of the presence of metal ions and reactive oxygen species (ROS) on the cyclic voltammograms of a synthetic model of neuromelanin. Our work improves the current understanding on experimental conditions where neuromelanin plays an antioxidant or prooxidant behavior, thus possibly contributing to shed light on factors promoting the appearance of PD

Emergence of the periodic oscillatory modulation in time-like nucleon form factors

We have studied the oscillatory behavior exhibited in the timelike electromagnetic form factors of nucleons by considering the final-state interaction effect. This mechanism introduces the Jost function of $N\bar N$ pair into the time-like form factors with the help of the distorted-wave Born approximation. Using a simple square-well potential, the contribution from the final-state interaction in our approach is naturally damped oscillatory, which can explain the experimental data very nicely. This scenario seems to be universal considering that it also reproduces well the threshold enhancements on the cross sections for $e^+e^-\to n\bar n$, $\Lambda\bar\Lambda$, and $\Lambda_c\bar\Lambda_c$.Comment: 6 pages, 2 figure

Data based reconstruction of complex geospatial networks, nodal positioning, and detection of hidden node

Funding This work was supported by ARO under grant no. W911NF-14-1-0504.Peer reviewedPublisher PD

Single-pixel imaging of a translational object

Image-free tracking methods based on single-pixel detectors (SPDs) can track a moving object at a very high frame rate, but they rarely can achieve simultaneous imaging of such an object. In this study, we propose a method for simultaneously obtaining the relative displacements and images of a translational object. Four binary Fourier patterns and two differential Hadamard patterns are used to modulate one frame of the object and then modulated light signals are obtained by SPD. The relative displacements and image of the moving object can be gradually obtained along with the detection. The proposed method does not require any prior knowledge of the object and its motion. The method has been verified by simulations and experiments, achieving a frame rate of 3332 Hz to acquire relative displacements of a translational object at a spatial resolution of $128 \times 128$ pixels using a 20000-Hz digital micro-mirror device. This proposed method can broaden the application of image-free tracking methods and obtain spatial information about moving objects.Comment: 15 pages, 9 figures, 1 tabl

Tracking and fast imaging of a translational object via Fourier modulation

The tracking and imaging of high-speed moving objects hold significant promise for application in various fields. Single-pixel imaging enables the progressive capture of a fast-moving translational object through motion compensation. However, achieving a balance between a short reconstruction time and a good image quality is challenging. In this study, we present a approach that simultaneously incorporates position encoding and spatial information encoding through the Fourier patterns. The utilization of Fourier patterns with specific spatial frequencies ensures robust and accurate object localization. By exploiting the properties of the Fourier transform, our method achieves a remarkable reduction in time complexity and memory consumption while significantly enhancing image quality. Furthermore, we introduce an optimized sampling strategy specifically tailored for small moving objects, significantly reducing the required dwell time for imaging. The proposed method provides a practical solution for the real-time tracking, imaging and edge detection of translational objects, underscoring its considerable potential for diverse applications.Comment: 6 figure