Ion-exchange and adsorption of Fe(III) by Sepia melanin

Adaptation in the Alleyways: Candidate Genes Under Potential Selection in Urban Coyotes

In the context of evolutionary time, cities are an extremely recent development. Although our understanding of how urbanization alters ecosystems is well developed, empirical work examining the consequences of urbanization on adaptive evolution remains limited. To facilitate future work, we offer candidate genes for one of the most prominent urban carnivores across North America. The coyote (Canis latrans) is a highly adaptable carnivore distributed throughout urban and nonurban regions in North America. As such, the coyote can serve as a blueprint for understanding the various pathways by which urbanization can influence the genomes of wildlife via comparisons along urban-rural gradients, as well as between metropolitan areas. Given the close evolutionary relationship between coyotes and domestic dogs, we leverage the well-annotated dog genome and highly conserved mammalian genes from model species to outline how urbanization may alter coyote genotypes and shape coyote phenotypes. We identify variables that may alter selection pressure for urban coyotes and offer suggestions of candidate genes to explore. Specifically, we focus on pathways related to diet, health, behavior, cognition, and reproduction. In a rapidly urbanizing world, understanding how species cope and adapt to anthropogenic change can facilitate the persistence of, and coexistence with, these species.

Multifunctional Natural and Synthetic Melanin for Bioelectronic Applications: A Review

Emerging material interest in bioelectronic applications has highlighted natural melanin and its derivatives as promising alternatives to conventional synthetic conductors. These materials, traditionally noted for their adhesive, antioxidant, biocompatible, and biodegradable properties, have barely been used as conductors due to their extremely low electrical activities. However, recent studies have demonstrated good conductive properties in melanin materials that promote electronic-ionic hybrid charge transfer, attributed to the formation of an extended conjugated backbone. This review examines the multifunctional properties of melanin materials, focusing on their chemical and electrochemical synthesis and their resulting structure-property-function relationship. The wide range of bioelectronic applications will also be presented to highlight their importance and potential to expand into new design concepts for high-performance electronic functional materials. The review concludes by addressing the current challenges in utilizing melanin for biodegradable bioelectronics, providing a perspective on future developments.

A new non-destructive method to decipher the origin of organic matter in fossils using Raman spectroscopy

Ancient biomolecules provide a unique perspective on the past but are underutilized in paleontology because of challenges in interpreting the chemistry of fossils. Most organically preserved soft tissues in fossils have been altered by thermal maturation during the fossilization process, obscuring original chemistry. Here, we use a comprehensive program of thermal maturation experiments on soft tissues from diverse extant organisms to systematically test whether thermally altered biosignatures can be discriminated using Raman spectroscopy. All experimentally matured samples show chemical signatures that are superficially similar. Comparative analysis of Raman spectra following peak deconvolution, however, reveals strong tissue-specific signals. Application of this approach to fossils from the Bolca (49 Ma) and Libros (10 Ma) Konservat-Lagerstätten successfully discriminates fossil vertebrate soft tissue from that of fossil plants. Critically, our data confirm that a robust interrogation of Raman spectra coupled with multivariate analysis is a powerful tool to shed light on the taxonomic origins of thermally matured fossil soft tissues.

Characterization of melanin from Exophiala mesophila with the prospect of potential biotechnological applications

Introducion

Fungal melanin is an underexplored natural biomaterial of great biotechnological interest in different areas. This study investigated the physical, chemical, electrochemical, and metal-binding properties of melanin extracted from the metallotolerant black fungus Exophiala mesophila strain IRTA-M2-F10.

Materials and methods

Specific inhibitory studies with tricyclazole and biochemical profiling of whole cells by synchrotron radiation-based Fourier-transform infrared spectral microscopy (SR-FTIRM) were performed. An optimized extraction protocol was implemented, and purified fungal melanin was characterized using an array of spectrophotometric techniques (UV-Vis, FTIR, and EPR) and by cyclic voltammetry (CV) experiments. The metal-binding capacity of melanin extracts was also assessed by using Cr(VI) as a model heavy metal.

Results

Inhibitory studies indicated that 1,8-dihydroxynaphthalene may be the main precursor molecule of E. mesophila melanin (DHN-melanin). The biochemical characterization of fungal melanin extracts were benchmarked against those from two melanins comprising the precursor molecule L-3,4-dihydroxiphenylalanine (DOPA-melanin): extracts from the ink of the cephalopod Sepia officinalis and DOPA-melanin synthesized in the laboratory. The CV results of melanin extracts incubated with and without cell suspensions of the electroconductive bacterium Geobacter sulfurreducens were indicative of novel semiquinone/hydroquinone redox transformations specific for each melanin type. These interactions may play an important role in cation exchange for the adsorption of metals and in microbial interspecies electron transfer processes.

Discussion

The obtained results provided further evidence for the DHN-nature of E. mesophila melanin. The FTIR profiling of melanin extracts exposed to Cr(VI), compared to unexposed melanin, resulted in useful information on the distinct surface-binding properties of fungal melanin. The parameters of the Langmuir and Freundlicht isotherms for the adsorption of Cr(VI) were determined and compared to bibliographic data. Altogether, the inherent properties of fungal melanin suggest its promising potential as a biomaterial for environmental applications.

Exploring the optical properties of metal-modified melanin following ultraviolet irradiation: An experimental and theoretical study using density functional theory

Melanin has an important function to protect humans from sunlight because of its broad spectrum of light absorption. This characteristic varies according to the nature of absorption and the amount of melanin manufactured. This study focused on UV-Vis absorption of melanin doped with (Fe, Co, Zn) ions. According to the result, eumelanin exhibits substantial absorption in a broad range between (200-500 nm) corresponding to the extension of the violet to the visible region. In the theoretical section of the results, using density functional theory (DFT) revealed an improvement in the optical reactivity properties of transition metals eumelanin. The presence of transition metals led to semiconductor-like behavior and optical reactivity regions in the energy range of 4.4-4.6 electron volts, clearly indicating enhanced structural properties in the presence of metals. In this study, we aspire to investigate the ability to modify the absorption properties of eumelanin can effectively contribute to the treatment of some skin diseases caused by excessive eumelanin secretion.

Riddles in the dark: Decoding the relationship between neuromelanin and neurodegeneration in locus coeruleus neurons

The noradrenergic locus coeruleus (LC) is among the first regions of the brain affected by pathology in both Alzheimer's disease (AD) and Parkinson's disease (PD), but the reasons for this selective vulnerability are not completely understood. Several features of LC neurons have been proposed as contributing factors to this dysfunction and degeneration, and this review will focus on the presence of neuromelanin (NM). NM is a dark pigment unique to catecholaminergic cells that is formed of norepinephrine (NE) and dopamine (DA) metabolites, heavy metals, protein aggregates, and oxidated lipids. We cover what is currently known about NM and the limitations of historical approaches, then discuss the new human tyrosinase (hTyr) model of NM production in rodent catecholamine cells in vivo that offers unique opportunities for studying its neurobiology, neurotoxicity, and potential of NM-based therapeutics for treating neurodegenerative disease.

Bioinorganic Chemistry of Micronutrients Related to Alzheimer's and Parkinson's Diseases

Metal ions are fundamental to guarantee the regular physiological activity of the human organism. Similarly, vitamins play a key role in many biological functions of the metabolism, among which are coenzymes, redox mediators, and antioxidants. Due to their importance in the human organism, both metals and vitamins have been extensively studied for their involvement in neurodegenerative diseases (NDs). However, the full potential of the interaction between vitamins and metal ions has not been fully explored by researchers yet, and further investigation on this topic is needed. The aim of this review is to provide an overview of the scientific literature on the implications of vitamins and selected metal ions in two of the most common neurodegenerative diseases, Alzheimer's and Parkinson's disease. Furthermore, vitamin-metal ion interactions are discussed in detail focusing on their bioinorganic chemistry, with the perspective of arousing more interest in this fascinating bioinorganic field.

Autophagy: Guardian of Skin Barrier

Autophagy is a major degradation pathway that removes harmful intracellular substances to maintain homeostasis. Various stressors, such as starvation and oxidative stress, upregulate autophagy, and the dysregulation of autophagy is associated with various human diseases, including cancer and skin diseases. The skin is the first defense barrier against external environmental hazards such as invading pathogens, ultraviolet rays, chemical toxins, and heat. Although the skin is exposed to various stressors that can activate autophagy, the roles of autophagy in the skin have not yet been fully elucidated. Accumulating evidence suggests that autophagy is closely associated with pathogenesis and the treatment of immune-related skin diseases. In this study, we review how autophagy interacts with skin cells, including keratinocytes and immune cells, enabling them to successfully perform their protective functions by eliminating pathogens and maintaining skin homeostasis. Furthermore, we discuss the implications of autophagy in immune-related skin diseases, such as alopecia areata, psoriasis, and atopic dermatitis, and suggest that a combination of autophagy modulators with conventional therapies may be a better strategy for the treatment of these diseases.

The importance of water content on the conductivity of biomaterials and bioelectronic devices

Conductive biocompatible-, bioinspired- and biomaterials are increasing in importance, especially in bioelectronic applications where these materials are used in a variety of devices. Given the intended purpose of many of these devices is to interface with the human body, a pertinent issue is the effect of water from the environment on the electrical properties of the materials and devices. A researcher on biomaterials may currently not be aware, but the conductivity of these materials and device performances can be significantly altered with the presence of hydration in the environment. Examples will be given to highlight the problem that the conductivity of biomaterials can change by orders of magnitude depending on water content. Furthermore, case studies will be discussed in which control of the water content was key to understanding the underlying charge transport mechanism of conductive biomaterials. Examples of various devices and their response to hydration content will also be covered. Finally, this perspective will also mention the various methods of hydration control (including contrast studies) that can be used to perform careful work on conductive biomaterials and devices. Overall, water content should be considered an environmental variable as important as temperature to control for sound scientific investigation and to yield understanding of conductive biomaterials and bioelectronic devices.

Identification of black sturgeon caviar pigment as eumelanin

Reported herein is the purification of the pigment of black sturgeon caviar and its unambiguous identification as a typical eumelanin by means of chemical degradation coupled with electron paramagnetic resonance (EPR) evidence. HPLC and LC-MS analysis of oxidative degradation mixtures revealed the formation of pyrrole-2,3,5-tricarboxylic acid (PTCA), a specific marker of eumelanin pigments, in yields compatible with a 6.5% w/w pigment content. EPR spectral features and parameters were in close agreement with those reported for a typical natural eumelanin such as Sepia melanin from squid ink. The identification for the first time of eumelanin in a fish roe is expected to provide a novel molecular basis for the valorization of black caviar and production wastes thereof in food chemistry and diet.

Characterization of an Insoluble and Soluble Form of Melanin Produced by Streptomyces cavourensis SV 21, a Sea Cucumber Associated Bacterium

Melanin is a widely distributed and striking dark-colored pigment produced by countless living organisms. Although a wide range of bioactivities have been recognized, there are still major constraints in using melanin for biotechnological applications such as its fragmentary known chemical structure and its insolubility in inorganic and organic solvents. In this study, a bacterial culture of Streptomyces cavourensis SV 21 produced two distinct forms of melanin: (1) a particulate, insoluble form as well as (2) a rarely observed water-soluble form. The here presented novel, acid-free purification protocol of purified particulate melanin (PPM) and purified dissolved melanin (PDM) represents the basis for an in-depth comparison of their physicochemical and biological properties, which were compared to the traditional acid-based precipitation of melanin (AM) and to a synthetic melanin standard (SM). Our data show that the differences in solubility between PDM and PPM in aqueous solutions may be a result of different adjoining cation species, since the soluble PDM polymer is largely composed of Mg²⁺ ions and the insoluble PPM is dominated by Ca²⁺ ions. Furthermore, AM shared most properties with SM, which is likely attributed to a similar, acid-based production protocol. The here presented gentler approach of purifying melanin facilitates a new perspective of an intact form of soluble and insoluble melanin that is less chemical altered and thus closer to its original biological form.

Polydopamine Shell as a Ga3+ Reservoir for Triggering Gallium-Indium Phase Separation in Eutectic Gallium-Indium Nanoalloys

Low melting point eutectic systems, such as the eutectic gallium-indium (EGaIn) alloy, offer great potential in the domain of nanometallurgy; however, many of their interfacial behaviors remain to be explored. Here, a compositional change of EGaIn nanoalloys triggered by polydopamine (PDA) coating is demonstrated. Incorporating PDA on the surface of EGaIn nanoalloys renders core-shell nanostructures that accompany Ga-In phase separation within the nanoalloys. The PDA shell keeps depleting the Ga³⁺ from the EGaIn nanoalloys when the synthesis proceeds, leading to a Ga³⁺-coordinated PDA coating and a smaller nanoalloy. During this process, the eutectic nanoalloys turn into non-eutectic systems that ultimately result in the solidification of In when Ga is fully depleted. The reaction of Ga³⁺-coordinated PDA-coated nanoalloys with nitrogen dioxide gas is presented as an example for demonstrating the functionality of such hybrid composites. The concept of phase-separating systems, with polymeric reservoirs, may lead to tailored materials and can be explored on a variety of post-transition metals.

Anisotropic Synthetic Allomelanin Materials via Solid-State Polymerization of Self-Assembled 1,8-Dihydroxynaphthalene Dimers

Melanosomes in nature have diverse morphologies, including spheres, rods, and platelets. By contrast, shapes of synthetic melanins have been almost entirely limited to spherical nanoparticles with few exceptions produced by complex templated synthetic methods. Here, we report a non-templated method to access synthetic melanins with a variety of architectures including spheres, sheets, and platelets. Three 1,8-dihydroxynaphthalene dimers (4-4', 2-4' and 2-2') were used as self-assembling synthons. These dimers pack to form well-defined structures of varying morphologies depending on the isomer. Specifically, distinctive ellipsoidal platelets can be obtained using 4-4' dimers. Solid-state polymerization of the preorganized dimers generates polymeric synthetic melanins while maintaining the initial particle morphologies. This work provides a new route to anisotropic synthetic melanins, where the building blocks are preorganized into specific shapes, followed by solid-state polymerization.

Relationships between soil pollution by heavy metals and melanin-dependent coloration of a fossorial amphisbaenian reptile

Melanin is the basis of coloration in many animals, and although it is often used in communication, thermoregulation, or camouflage, melanin has many other physiological functions. For example, in polluted habitats, melanin can have a detoxifying function. Melanic coloration would help to sequester in the skin the heavy metal contaminants from inside the body, which will be expelled to the exterior when the skin is sloughed. Moreover, animals should have evolved more melanic colorations in more polluted habitats ("industrial melanism" hypothesis). We examined whether the fossorial amphisbaenian reptile, Trogonophis wiegmanni, is able to eliminate heavy metals, derived from soil pollution by seagull depositions, through sloughing its skin. Our results suggest a covariation between levels of soil pollution by heavy metals and the concentration of heavy metals in the sloughed skins of amphisbaenians. This suggests that amphisbaenians may expel heavy metals from their bodies when they slough the skins. We also tested whether amphisbaenians inhabiting soils with higher levels of heavy metal pollution had darker (melanin-dependent) body colorations. However, contrary to predictions from the "industrial melanization" hypothesis, we found a negative relationship between soil pollution and proportions of melanic coloration. This contradictory result could, however, be explained because heavy metals have endocrine disruption effects that increase physiological stress, and higher stress levels could result in decreased melanogenesis. We suggest that although amphisbaenians might have some detoxifying mechanism linked to melanin in the skin, this process might be negatively affected by stress and result ineffective under conditions of high soil pollution.

Melanin, the What, the Why and the How: An Introductory Review for Materials Scientists Interested in Flexible and Versatile Polymers

Today, western society is facing challenges to create new medical technologies to service an aging population as well as the ever-increasing e-waste of electronic devices and sensors. A key solution to these challenges will be the use of biomaterials and biomimetic systems. One material that has been receiving serious attention for its biomedical and device applications is eumelanin. Eumelanin, or commonly known as melanin, is nature's brown-black pigment and is a poly-indolequinone biopolymer, which possess unique physical and chemical properties for material applications. Presented here is a review, aimed at polymer and other materials scientists, to introduce eumelanin as a potential material for research. Covered here are the chemical and physical structures of melanin, an overview of its unique physical and chemical properties, as well as a wide array of applications, but with an emphasis on device and sensing applications. The review is then finished by introducing interested readers to novel synthetic protocols and post synthesis fabrication techniques to enable a starting point for polymer research in this intriguing and complex material.

Synthetic Porous Melanin

Commonly known as a skin pigment, melanin has a vital role in UV radiation protection, primarily acting as a radical scavenger. However, a lesser known natural property of melanin, observed in some melanized organisms, is its capacity to adsorb toxins, including metals and organic molecules. Inspired by this, we set out to generate a synthetic porous melanin that would pave the way to enhancing the natural adsorbent properties of melanin and melanin-like materials. Here, we developed a method for the synthesis of porous polydopamine-based melanin utilizing a mesoporous silica (MS) nanoparticle template and characterized its physical properties. Through the oxidative polymerization of dopamine, followed by the etching of silica, we generated synthetic porous melanin (SPM) with the highest measured surface area of any known polydopamine-based material. The prepared SPM was effective for the uptake of various gases and organophosphate toxins, with the material exhibiting high selectivity for CO₂ over CH₄ and high potential for ammonia capture. Given the demonstrated advantages provided by synthetic porous melanin and melanin's role as an adsorbent in nature, we anticipate the discovery of porous analogues in biological systems.

Melanins as Sustainable Resources for Advanced Biotechnological Applications

Melanins are a class of biopolymers that are widespread in nature and have diverse origins, chemical compositions, and functions. Their chemical, electrical, optical, and paramagnetic properties offer opportunities for applications in materials science, particularly for medical and technical uses. This review focuses on the application of analytical techniques to study melanins in multidisciplinary contexts with a view to their use as sustainable resources for advanced biotechnological applications, and how these may facilitate the achievement of the United Nations Sustainable Development Goals.

COVID-19 and the ethnicity link - is there a photochemical link?

A hypothesis is proposed to explain the increased detrimental effect of COVID-19 for Black, Asian and Minority Ethnic (BAME) men and women compared to Caucasian individuals. This is based on the differing photochemistry of phaeomelanin in fair skin and eumelanin in dark/black skin. It is suggested that a range of reactive oxygen species, including, singlet oxygen and the superoxide radical anion, derived via direct photolysis of phaeomelanin, may escape the melanocyte and cause subsequent damage to the SARS-CoV-2 virus. It is further suggested that (large) carbon and sulphur peroxy radicals, from oxygen addition to radicals formed by carbon–sulphur bond cleavage, may assist via damage to the cell membranes. It is also speculated that light absorption by phaeomelanin and the subsequent C-S bond cleavage, leads to release of pre-absorbed reactive oxygen species, such as singlet oxygen and free radicals, which may also contribute to an enhanced protective effect for fair-skinned people.

64Cu-labeled melanin nanoparticles for PET/CT and radionuclide therapy of tumor

Melanin is a group of natural pigments found in living organism. It can be used for positron emission tomography (PET) imaging due to its inherent chelating ability to radioactive cupric ion. This study was to prepare ⁶⁴Cu-labeled PEGylated melanin nanoparticles (⁶⁴Cu-PEG-MNPs), and to further take advantage of the enhanced permeability and retention (EPR) effect of radiolabeled nanoparticles to realize the integration of tumor diagnosis and treatment. We successfully synthesized PEG-MNPs. Saline and serum stability experiments demonstrated good stability. PET/CT showed high tumor aggregation. Moreover, ⁶⁴Cu-PEG-MNPs resulted in a therapeutic effect on the A431 tumor-bearing mice in the treatment group. The pathological results further confirmed that the therapeutic doses of ⁶⁴Cu-PEG-MNPs cause pathological changes of tumor tissues while showing minimal toxicity to normal tissues. Our data successfully demonstrate the good imaging performance of ⁶⁴Cu-PEG-MNPs on A431 tumors and further proved its therapeutic effect, highlighting a great potential in targeted radionuclide therapy.

Hierarchical biota-level and taxonomic controls on the chemistry of fossil melanosomes revealed using synchrotron X-ray fluorescence

Fossil melanosomes, micron-sized granules rich in melanin in vivo, provide key information for investigations of the original coloration, taxonomy and internal anatomy of fossil vertebrates. Such studies rely, in part, on analysis of the inorganic chemistry of preserved melanosomes and an understanding of melanosome chemical taphonomy. The extent to which the preserved chemistry of fossil melanosomes is biased by biotic and abiotic factors is, however, unknown. Here we report the discovery of hierarchical controls on the inorganic chemistry of melanosomes from fossil vertebrates from nine biotas. The chemical data are dominated by a strong biota-level signal, indicating that the primary taphonomic control is the diagenetic history of the host sediment. This extrinsic control is superimposed by a biological, tissue-level control; tissue-specific chemical variation is most likely to survive in fossils where the inorganic chemistry of preserved melanosomes is distinct from that of the host sediment. Comparative analysis of our data for fossil and modern amphibians reveals that most fossil specimens show tissue-specific melanosome chemistries that differ from those of extant analogues, strongly suggesting alteration of original melanosome chemistry. Collectively, these findings form a predictive tool for the identification of fossil deposits with well-preserved melanosomes amenable to studies of fossil colour and anatomy.

Synthetic melanin nanoparticles as peroxynitrite scavengers, photothermal anticancer and heavy metals removal platforms

Melanin is a ubiquitous natural polyphenolic pigment with versatile applications including physiological functions. This polymeric material is found in a diversity of living organisms from bacteria to mammals. The biocompatibility and thermal stability of melanin nanoparticles make them good candidates to work as free radical scavengers and photothermal anticancer substrates. Research studies have identified melanin as an antioxidative therapeutic agent and/or reactive oxygen species (ROS) scavenger that includes neutralization of peroxynitrite. In addition, melanin nanoparticles have emerged as an anticancer photothermal platform that has the capability to kill cancer cells. Recently, melanin nanoparticles have been successfully used as chelating agents to purify water from heavy metals, such as hexavalent chromium. This review article highlights some selected aspects of cutting-edge melanin applications. Herein, we will refer to the recent literature that addresses melanin nanoparticles and its useful physicochemical properties as a hot topic in biomaterial science. It is expected that the techniques of Dynamic Light Scattering (DLS), Scanning Electron Microscopy (SEM), and time-resolved Electron Paramagnetic Resonance (EPR) will have a strong impact on the full characterization of melanin nanoparticles and the subsequent exploration of their physiological and chemical mechanisms.

Melanin nanoparticles as a promising tool for biomedical applications - a review

Melanin is a biopolymer of easy and cheap availability that can be found among the living organisms and excels for its biocompatibility and biodegradability properties, along with scavenging abilities, metal chelation and electronic conductance. This biomaterial can act as a nanocarrier or agent itself to be used in diverse biomedical applications, such as imaging, controlled drug release, bioengineering and bioelectronics, antioxidant applications and theranostics. In this review, the melanin source and structure, its physicochemical properties, melanin-like polymers as well as the differences among those will be elucidated. The focus will be the discussion of the current approaches that apply melanin nanoparticles (MNPs) and melanin-like nanoparticles (MLNPs) in the biomedical field, to which promising capabilities have been attributed, regarding optoelectronic, photoconductivity and photoacoustic. The use of these nanoparticles, in the last 10 years, in topics as drug delivery or theranostics will be detailed and the major achievements will be discussed. Overall, we anticipate that melanin can drive us toward a new paradigm in medical diagnostics and treatments, since applying melanin features possibly its use as a theranostics nanocarrier agent, not only for diagnostics, but also for photothermal therapy and controlled drug release through chemotherapy. STATEMENT OF SIGNIFICANCE: We present here a timely and opportune review article focusing the significant potential of melanin nanoparticles in biomedical applications, which will be discussed thoroughly. This biomaterial presents multiple capabilities that may be taken into consideration towards cancer theranostics, expecting a high future impact in the nanosized-platforms design and performance.

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.

Artificial Allomelanin Nanoparticles

Allomelanin is a type of nitrogen-free melanin most commonly found in fungi. Its existence enhances resistance of the organisms to environmental damage and helps fungi survive harsh radiation conditions such as those found on spacecraft and inside contaminated nuclear power plants. We report the preparation and characterization of artificial allomelanin nanoparticles (AMNPs) via oxidative oligomerization of 1,8-dihydroxynaphthalene (1,8-DHN). We describe the resulting morphological and size control of AMNPs and demonstrate that they are radical scavengers. Finally, we show that AMNPs are taken up by neonatal human epidermal keratinocytes and packaged into perinuclear caps where they quench reactive oxygen species generated following UV exposure.

Melanosomes: Biogenesis, Properties, and Evolution of an Ancient Organelle

Melanosomes are organelles that produce and store melanin, a widespread biological pigment with a unique suite of properties including high refractive index, semiconducting capabilities, material stiffness, and high fossilization potential. They are involved in numerous critical biological functions in organisms across the tree of life. Individual components such as melanin chemistry and melanosome development have recently been addressed, but a broad synthesis is needed. Here, we review the hierarchical structure, development, functions, and evolution of melanosomes. We highlight variation in melanin chemistry and melanosome morphology and how these may relate to function. For example, we review what is known of the chemical differences between different melanin types (eumelanin, pheomelanin, allomelanin) and whether/how melanosome morphology relates to chemistry and color. We integrate the distribution of melanin across living organisms with what is known from the fossil record and produce hypotheses on its evolution. We suggest that melanin was present in life forms early in evolutionary history and that melanosomes evolved at the origin of organelles. Throughout, we discuss the (sometimes gaping) holes in our knowledge and suggest areas that need particular attention as we move forward in our understanding of these still-mysterious organelles and the materials that they contain.

Functional Effects of a Neuromelanin Analogue on Dopaminergic Neurons in 3D Cell Culture

The substantia nigra pars compacta (SNpc) is a discrete region of the brain that exhibits a dark pigment, neuromelanin (NM), a biomaterial with unique properties and the subject of ongoing research pertaining to neurodegenerative conditions like Parkinson's disease (PD). Obtaining human tissue to isolate this pigment is costly and labor intensive, making it necessary to find alternatives to model the biochemical interaction of NM and its implications on PD. To address this limitation, we modified our established silk 3D brain tissue model to emulate key characteristics of the SNpc by using a structural analogue of NM to examine the effects of the material on dopaminergic neurons using Lund's human mesencephalon (LUHMES) cells. We utilized a sepia-melanin, squid ink, derived NM analogue (NM-sim) to chelate ferric iron, and this iron-neuromelanin precipitate (Fe-NM) was purified and characterized. We then exposed LUHMES dopaminergic cells to the NM-sim, Fe-NM-sim, and control vehicle within 3D silk protein scaffolds. The presence of both NM-sim and Fe-NM-sim in the scaffolds negatively impacted spontaneous electrical activity from the LUMES networks, as evidenced by changes in local field potential (LFP) electrophysiological recordings. Furthermore, the Fe-NM-sim precipitate generated peroxides, depleted nutrients/antioxidants, and increased protein oxidation by carbonylation in sustained (>2 weeks) 3D cultures, thereby contributing to cell dysfunction. The results suggest that this 3D tissue engineered brain-like model may provide useful readouts related to PD neuro-toxicology research.

Marine and Freshwater Feedstocks as a Precursor for Nitrogen-Containing Carbons: A Review

Marine-derived as well as freshwater feedstock offers important benefits, such as abundance, morphological and structural variety, and the presence of multiple elements, including nitrogen and carbon. Therefore, these renewal resources may be useful for obtaining N- and C-containing materials that can be manufactured by various methods, such as pyrolysis and hydrothermal processes supported by means of chemical and physical activators. However, every synthesis concept relies on an efficient transfer of nitrogen and carbon from marine/freshwater feedstock to the final product. This paper reviews the advantages of marine feedstock over synthetic and natural but non-marine resources as precursors for the manufacturing of N-doped activated carbons. The manufacturing procedure influences some crucial properties of nitrogen-doped carbon materials, such as pore structure and the chemical composition of the surface. An extensive review is given on the relationship between carbon materials manufacturing from marine feedstock and the elemental content of nitrogen, together with a description of the chemical bonding of nitrogen atoms at the surface. N-doped carbons may serve as effective adsorbents for the removal of pollutants from the gas or liquid phase. Non-recognized areas of adsorption-based applications for nitrogen-doped carbons are presented, too. The paper proves that nitrogen-doped carbon materials belong to most of the prospective electrode materials for electrochemical energy conversion and storage technologies such as fuel cells, air⁻metal batteries, and supercapacitors, as well as for bioimaging. The reviewed material belongs to the widely understood field of marine biotechnology in relation to marine natural products.

Cytotoxicity of paramagnetic cations-Loaded polydopamine nanoparticles

Polydopamine (PD) is a synthetic melanin pigment of great importance in biomedicine, where its affinity for metallic cations, especially paramagnetic ions, has sparked interest in its use in the development of magnetic resonance imaging (MRI) contrast agents. In this work, we report the cytotoxicity of metal-enriched PD nanoparticles on NIH3T3, a healthy cell line and BT474, a breast cancer cell line. Remarkably, it was found that the metal- enriched PD particles (Mⁿ⁺ = Fe³⁺, Fe²⁺ and Cu²⁺) were highly cytotoxic to the breast cancer cells, even after 24 h of treatment. Although, this effect was not selective systems, since an acute cytotoxic effect was also observed on the healthy cell line, this system can be considered as starting point for designing advanced antineoplastic agents.

Neuromelanin in Parkinson's Disease: from Fenton Reaction to Calcium Signaling

Neuromelanin is supposed to play a key role in the pathogenesis of Parkinson's disease. A common theory is the formation of reactive oxygen species through the Fenton reaction catalyzed by neuromelanin-bound iron ions and subsequent death of the dopaminergic cells in the substantia nigra. From a physicochemical point of view, this pathway is rather implausible: a highly reactive radical built within a powerful radical scavenger would more promptly be inactivated before it might diffuse within the cell to reach a target to exert its deleterious potential. This review of the literature provides evidence for an interaction of neuromelanin with the calcium signaling pathway in Parkinson's disease and expands the view of the pathophysiological contribution of neuromelanin towards a cytoprotective involvement of this macromolecule in the calcium signaling system. More probably than being directly involved in the production of reactive oxygen species, neuromelanin may act as a calcium reservoir and thus protect dopaminergic cells from cell death. A loss of neuromelanin, as observed in the substantia nigra of Parkinson patients, would lead to enhanced calcium messaging through the loss of an important calcium reservoir and thus finally via the formation of reactive oxygen species to cell death within the substantia nigra.

Interactions of iron, dopamine and neuromelanin pathways in brain aging and Parkinson's disease

There are several interrelated mechanisms involving iron, dopamine, and neuromelanin in neurons. Neuromelanin accumulates during aging and is the catecholamine-derived pigment of the dopamine neurons of the substantia nigra and norepinephrine neurons of the locus coeruleus, the two neuronal populations most targeted in Parkinson's disease. Many cellular redox reactions rely on iron, however an altered distribution of reactive iron is cytotoxic. In fact, increased levels of iron in the brain of Parkinson's disease patients are present. Dopamine accumulation can induce neuronal death; however, excess dopamine can be removed by converting it into a stable compound like neuromelanin, and this process rescues the cell. Interestingly, the main iron compound in dopamine and norepinephrine neurons is the neuromelanin-iron complex, since neuromelanin is an effective metal chelator. Neuromelanin serves to trap iron and provide neuronal protection from oxidative stress. This equilibrium between iron, dopamine, and neuromelanin is crucial for cell homeostasis and in some cellular circumstances can be disrupted. Indeed, when neuromelanin-containing organelles accumulate high load of toxins and iron during aging a neurodegenerative process can be triggered. In addition, neuromelanin released by degenerating neurons activates microglia and the latter cause neurons death with further release of neuromelanin, then starting a self-propelling mechanism of neuroinflammation and neurodegeneration. Considering the above issues, age-related accumulation of neuromelanin in dopamine neurons shows an interesting link between aging and neurodegeneration.

Mechanistic insights into the bleaching of melanin by alkaline hydrogen peroxide

This work aims to determine the roles of reactive oxygen species HO∙ and HO₂^- in the bleaching of melanins by alkaline hydrogen peroxide. Experiments using melanosomes isolated from human hair indicated that the HO∙ radical generated in the outside solution does not contribute significantly to bleaching. However, studies using soluble Sepia melanin demonstrated that both HO₂^- and HO∙ will individually bleach melanin. Additionally, when both oxidants are present, bleaching is increased dramatically in both rate and extent. Careful experimental design enabled the separation of the roles and effects of these key reactive species, HO∙ and HO₂^-. Rationalisation of the results presented, and review of previous literature, allowed the postulation of a simplified general scheme whereby the strong oxidant HO∙ is able to pre-oxidise melanin units to o-quinones enabling more facile ring opening by the more nucleophilic HO₂^-. In this manner the efficiency of the roles of both species is maximised.

Surface-rough Fe-N/C composite wrapped on carbon nanotubes as efficient electrocatalyst for oxygen reduction reaction

Fe-N/C composites are considered one of the most promising non-precious-metal electrocatalysts for oxygen reduction reaction (ORR). In this paper, we fabricate a novel and efficient carbon nanotube (CNT)-supported Fe-N/C composite catalyst, via the surface-self-polymerization of polydopamine and then the incorporation with Fe species on CNTs, followed by the pyrolysis process. The obtained catalyst demonstrates excellent electrocatalytic performance towards ORR in alkaline media. The modification of Fe-incorporated nitrogen-rich-carbons (Fe-CN_x) on CNTs lowers the ORR half-wave-potential by ∼190 mV, giving this catalyst with an onset ORR potential of 0.95 V (versus reversible hydrogen electrode (RHE)), a half-wave potential of 0.82 V (versus RHE), and the limiting current density of 5.39 mA cm^-2 in 0.1 M KOH. The performance of the as-prepared catalyst is comparatively better than the commercially available Pt/C in terms of positive half-wave potential and larger limiting current, superior durability, and higher tolerance to the methanol.

Zebrafish phosvitin-derived peptide Pt5 inhibits melanogenesis via cAMP pathway

Zebrafish phosvitin-derived peptide Pt5, consisting of the C-terminal 55 residues of phosvitin, has been shown to have an antimicrobial-immunomodulatory activity comparable to phosvitin. Here, we showed clearly that Pt5 had the capacity to inhibit tyrosinase (TYR) activity and melanin biosynthesis, and this inhibition was independent of cell proliferation and cytotoxic effects. Incubation of fluorescein isothiocyanate (FITC)-labeled Pt5 with B16F10 melanoma cells revealed that Pt5 was localized in the cytoplasm of the cells. In addition, Pt5 inhibited the expression of TYR, tyrosinase-related protein-1 (TRP-1), tyrosinase-related protein-2 (TRP-2), and microphthalmia-associated transcription factor (MITF) in B16F10 melanoma cells and reduced the intracellular cyclic adenosine monophosphate (cAMP) concentration in the cells, but it did not affect the cellular contents of pERK1/2 and β-catenin, suggesting that Pt5 regulates melanin biosynthesis via cAMP signaling pathway rather than Wnt and MAPK pathways. Collectively, these data indicate that Pt5 has the potential to be used as a melanogenesis inhibitor in medical and cosmetic industry, a novel role ever reported.

Analysis of major elements in pigmented melanocytic chicken skin using laser-induced breakdown spectroscopy

The concentration difference of major elements in melanocytic skin with respect to pigmentation level is analysed by laser-induced breakdown spectroscopy (LIBS) to investigate the applicability of LIBS as an in situ feedback tool for selective and complete laser removal of melanocytic skin tissue like nevus. The skin of black silkie chicken which had a characteristic darkly pigmented perifollicular skin surrounded by lightly pigmented extrafollicular skin was used as the sample. The results showed higher LIBS signal intensities of Ca²⁺ and Mg²⁺ but lower intensities of Na⁺ , Cl^- and K⁺ in the perifollicular skin than in the extrafollicular skin, which demonstrated the feasibility to use LIBS as a reliable method to distinguish skin tissues with difference in pigmentation level. Plasma emission of biochemical elements generated with a laser irradiation on melanocytic skin lesion.

Functions of fungal melanin beyond virulence

Melanins are ancient biological pigments found in all kingdoms of life. In fungi, their role in microbial pathogenesis is well established; however, these complex biomolecules also confer upon fungal microorganisms the faculty to tolerate extreme environments such as the Earth's poles, the International Space Station and places contaminated by toxic metals and ionizing radiation. A remarkable property of melanin is its capacity to interact with a wide range of electromagnetic radiation frequencies, functioning as a protecting and energy harvesting pigment. Other roles of fungal melanin include scavenging of free radical, thermo-tolerance, metal ion sequestration, cell development, and mechanical-chemical cellular strength. In this review, we explore the various functions ascribed to this biological pigment in fungi and its remarkable physicochemical properties.

Molecular imaging probes for multi-spectral optoacoustic tomography

In this review, we discuss recent progress in emerging optoacoustic probes, their mechanisms, applications and challenges for biological imaging using MSOT.

Calcium-Mediated Control of Polydopamine Film Oxidation and Iron Chelation

The facile preparation of conformal polydopamine (PDA) films on broad classes of materials has prompted extensive research into a wide variety of potential applications for PDA. The constituent molecular species in PDA exhibit diverse chemical moieties, and therefore highly variable properties of PDA-based devices may evolve with post-processing conditions. Here we report the use of redox-inactive cations for oxidative post-processing of deposited PDA films. PDA films incubated in alkaline CaCl₂ solutions exhibit accelerated oxidative evolution in a dose-dependent manner. PDA films incubated in CaCl₂ solutions exhibit 53% of the oxidative charge transfer compared to pristine PDA films. Carboxylic acid groups generated from the oxidation process lower the isoelectric point of PDA films from pH = 4.0 ± 0.2 to pH = 3.1 ± 0.3. PDA films exposed to CaCl₂ solutions during post-processing also enhance Fe2+/Fe3+ chelation compared to pristine PDA films. These data illustrate that the molecular heterogeneity and non-equilibrium character of as-deposited PDA films afford control over the final composition by choosing post-processing conditions, but also demands forethought into how the performance of PDA-incorporated devices may change over time in salt solutions.

Elemental characterisation of melanin in feathers via synchrotron X-ray imaging and absorption spectroscopy

Melanin is a critical component of biological systems, but the exact chemistry of melanin is still imprecisely known. This is partly due to melanin’s complex heterogeneous nature and partly because many studies use synthetic analogues and/or pigments extracted from their natural biological setting, which may display important differences from endogenous pigments. Here we demonstrate how synchrotron X-ray analyses can non-destructively characterise the elements associated with melanin pigment in situ within extant feathers. Elemental imaging shows that the distributions of Ca, Cu and Zn are almost exclusively controlled by melanin pigment distribution. X-ray absorption spectroscopy demonstrates that the atomic coordination of zinc and sulfur is different within eumelanised regions compared to pheomelanised regions. This not only impacts our fundamental understanding of pigmentation in extant organisms but also provides a significant contribution to the evidence-based colour palette available for reconstructing the appearance of fossil organisms.

Paraquat-Melanin Redox-Cycling: Evidence from Electrochemical Reverse Engineering

Parkinson's disease is a neurodegenerative disorder associated with oxidative stress and the death of melanin-containing neurons of the substantia nigra. Epidemiological evidence links exposure to the pesticide paraquat (PQ) to Parkinson's disease, and this link has been explained by a redox cycling mechanism that induces oxidative stress. Here, we used a novel electrochemistry-based reverse engineering methodology to test the hypothesis that PQ can undergo reductive redox cycling with melanin. In this method, (i) an insoluble natural melanin (from Sepia melanin) and a synthetic model melanin (having a cysteinyldopamine-melanin core and dopamine-melanin shell) were entrapped in a nonconducting hydrogel film adjacent to an electrode, (ii) the film-coated electrode was immersed in solutions containing PQ (putative redox cycling reductant) and a redox cycling oxidant (ferrocene dimethanol), (iii) sequences of input potentials (i.e., voltages) were imposed to the underlying electrode to systematically engage reductive and oxidative redox cycling, and (iv) output response currents were analyzed for signatures of redox cycling. The response characteristics of the PQ-melanin systems to various input potential sequences support the hypothesis that PQ can directly donate electrons to melanin. This observation of PQ-melanin redox interactions demonstrates an association between two components that have been individually linked to oxidative stress and Parkinson's disease. Potentially, melanin's redox activity could be an important component in understanding the etiology of neurological disorders such as Parkinson's disease.