Protocellular Heme and Iron-Sulfur Clusters

ConspectusCentral to the quest of understanding the emergence of life is to uncover the role of metals, particularly iron, in shaping prebiotic chemistry. Iron, as the most abundant of the accessible transition metals on the prebiotic Earth, played a pivotal role in early biochemical processes and continues to be indispensable to modern biology. Here, we discuss our recent contributions to probing the plausibility of prebiotic complexes with iron, including heme and iron-sulfur clusters, in mediating chemistry beneficial to a protocell. Laboratory experiments and spectroscopic findings suggest plausible pathways, often facilitated by UV light, for the synthesis of heme and iron-sulfur clusters. Once formed, heme displays catalytic, peroxidase-like activity when complexed with amphiphiles. This activity could have been beneficial in two ways. First, heme could have catalytically removed a molecule (H2O2) that could have had degradative effects on a protocell. Second, heme could have helped in the synthesis of the building blocks of life by coupling the reduction of H2O2 with the oxidation of organic substrates. The necessity of amphiphiles to avoid the formation of inactive complexes of heme is telling, as the modern-day electron transport chain possesses heme embedded within a lipid membrane. Conversely, prebiotic iron-sulfur peptides have yet to be reported to partition into lipid membranes, nor have simple iron-sulfur peptides been found to be capable of participating in the synthesis of organic molecules. Instead, iron-sulfur peptides span a wide range of reduction potentials complementary to the reduction potentials of hemes. The reduction potential of iron-sulfur peptides can be tuned by the type of iron-sulfur cluster formed, e.g., [2Fe-2S] versus [4Fe-4S], or by the substitution of ligands to the metal center. Since iron-sulfur clusters easily form upon stochastic encounters between iron ions, hydrosulfide, and small organic molecules possessing a thiolate, including peptides, the likelihood of soluble iron-sulfur clusters seems to be high. What remains challenging to determine is if iron-sulfur peptides participated in early prebiotic chemistry or were recruited later when protocellular membranes evolved that were compatible with the exploitation of electron transfer for the storage of energy as a proton gradient. This problem mirrors in some ways the difficulty in deciphering the origins of metabolism as a whole. Chemistry that resembles some facets of extant metabolism must have transpired on the prebiotic Earth, but there are few clues as to how and when such chemistry was harnessed to support a (proto)cell. Ultimately, unraveling the roles of hemes and iron-sulfur clusters in prebiotic chemistry promises to deepen our understanding of the origins of life on Earth and aids the search for life elsewhere in the universe.

Structural Characterization of Pyruvic Acid Dimers Formed inside Helium Nanodroplets by Infrared Spectroscopy and Ab Initio Study

The structural arrangements of α-keto acid complexes hold significant interest across various fields of chemistry such as enzyme modeling, drug design, or polymer blending. Herein, we report mass-selective infrared (IR) spectra of pyruvic acid monomers and dimers in the range 1720-1820 cm-1 recorded in helium nanodroplets at 0.37 K. The monomer features IR bands at 1807.1 and 1734.5 cm-1, which are assigned to the carboxylic and ketonic C═O stretching vibrations, respectively. Furthermore, the pyruvic acid dimers generated inside the helium nanodroplets are characterized by carboxylic and ketonic C═O stretch vibrations appearing at 1799.2 and 1737.0 cm-1, respectively. This frequency shift of ±7 cm-1 for both C═O stretching bands from the monomer to the dimer demonstrates that the structural motif of the monomer is maintained upon dimer aggregation in helium nanodroplets. The structural assignments were supported by a comparison of the MP2/aug-cc-pVDZ-predicted harmonic vibrational spectra at the C═O stretching region with the experiments. The global minimum monomer structure with an intramolecular hydrogen bond and its dimer stabilized by both inter- and intramolecular hydrogen bonding interactions reproduce the experimental spectra from the monomer and dimer. This assigned dimer structure lies ca.11 kJ/mol above the corresponding global minimum and is favored in helium nanodroplets due to the long-range realignment of molecules via dipole-dipole interaction, followed by short-range stabilization upon intermolecular hydrogen bond formation. The barrier for reconfiguration of the precooled monomer conformer leading to the formation of the most stable dimer structure is around 58 kJ/mol, which is infeasible at 0.37 K.

Aqueous pyruvate partly dissociates under deep ultraviolet irradiation but is resilient to near ultraviolet excitation

The deep ultraviolet photochemistry of aqueous pyruvate is believed to have been essential to the origin of life, and near ultraviolet excitation of pyruvate in aqueous aerosols is assumed to contribute significantly to the photochemistry of the Earth's atmosphere. However, the primary photochemistry of aqueous pyruvate is unknown. Here we study the susceptibility of aqueous pyruvate to photodissociation by deep ultraviolet and near ultraviolet irradiation with femtosecond spectroscopy supported by density functional theory calculations. The primary photo-dynamics of the aqueous pyruvate show that upon deep-UV excitation at 200 nm, about one in five excited pyruvate anions have dissociated by decarboxylation 100 ps after the excitation, while the rest of the pyruvate anions return to the ground state. Upon near-UV photoexcitation at a wavelength of 340 nm, the dissociation yield of aqueous pyruvate 200 ps after the excitation is insignificant and no products are observed. The experimental results are explained by our calculations, which show that aqueous pyruvate anions excited at 200 nm have sufficient excess energy for decarboxylation, whereas excitation at 340 nm provides the aqueous pyruvate anions with insufficient energy to overcome the decarboxylation barrier.

First-Row Transition Metals for Catalyzing Oxygen Redox

Rechargeable zinc-air batteries are widely recognized as a highly promising technology for energy conversion and storage, offering a cost-effective and viable alternative to commercial lithium-ion batteries due to their unique advantages. However, the practical application and commercialization of zinc-air batteries are hindered by the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Recently, extensive research has focused on the potential of first-row transition metals (Mn, Fe, Co, Ni, and Cu) as promising alternatives to noble metals in bifunctional ORR/OER electrocatalysts, leveraging their high-efficiency electrocatalytic activity and excellent durability. This review provides a comprehensive summary of the recent advancements in the mechanisms of ORR/OER, the performance of bifunctional electrocatalysts, and the preparation strategies employed for electrocatalysts based on first-row transition metals in alkaline media for zinc-air batteries. The paper concludes by proposing several challenges and highlighting emerging research trends for the future development of bifunctional electrocatalysts based on first-row transition metals.

Metabolomic profiling between vitiligo patients and healthy subjects in plateau exhibited significant differences with those in plain

Vitiligo is the most common disorder of depigmentation, which is caused by multiple factors like metabolic abnormality, oxidative stress and the disorders of immune. In recent years, several studies have used untargeted metabolomics to analyze differential metabolites in patients with vitiligo, however, the subjects in these studies were all in plain area. In our study, multivariate analysis indicated a distinct separation between the healthy subjects from plateau and plain areas in electrospray positive and negative ions modes, respectively. Similarly, a distinct separation between vitiligo patients and healthy controls from plateau and plain areas was detected in the two ions modes. Among the identified metabolites, the serum levels of sphingosine 1-phosphate (S1P) were markedly higher in vitiligo patients compare to healthy subjects in plain and markedly higher in healthy subjects in plateau compare to those in plain. There are significant differences in serum metabolome between vitiligo patients and healthy subjects in both plateau and plain areas, as well as in healthy subjects from plateau and plain areas. S1P metabolism alteration may be involved in the pathogenesis of vitiligo.

Characterizing Interfaces by Voronoi Tessellation

The chemistry of interfaces differs markedly from that of the bulk. Calculation of interfacial properties depends strongly on the definition of the interface, which can lead to ambiguous results that vary between studies. There is a need for a method that can explicitly define the interfaces and boundaries in molecular systems. Voronoi tessellation offers an attractive solution to this problem through its ability to determine neighbors among specified groups of atoms. Here we discuss three cases where Voronoi tessellation combined with modeling of vibrational sum frequency generation (SFG) spectroscopy yields relevant insights: the breakdown of the air-water interface into clear and intuitive molecular layers, the study of the hydration shell in biological systems, and the acceleration of difficult spectral calculations where intermolecular vibrational couplings dominate. The utility of Voronoi tessellation has broad applications that extend beyond any single type of spectroscopy or system.

Impact of M Dwarfs Ultraviolet Radiation on Prebiotic Chemistry: The Case of Adenine

To date, several exoplanets have been found to orbit within the habitable zone of main sequence M stars (M dwarfs). These stars exhibit different levels of chromospheric activity that produces ultraviolet (UV) radiation. UV may be harmful to life, but it can also trigger reactions of prebiotic importance on the surface of a potentially habitable planet (PHP). We created a code to obtain the adenine yield for a known adenine synthesis route from diaminomaleonitrile (DAMN). We used computational methods to calculate the reaction coefficient rates (photolysis rate J and rate constant K) for the intermediate molecules DAMN, diaminofumaronitrile (DAFN), and 4-aminoimidazole-5-carbonitrile (AICN) of the adenine synthesis route. We used stellar UV sources and a mercury lamp to compare the theoretical results with experiments performed with lamps. The surface UV flux of planets in the habitable zone of two active M dwarfs (Proxima Centauri and AD Leonis) and the prebiotic Earth was calculated using the photochemical model ATMOS, considering a CO₂-N₂-H₂O atmosphere. We obtained UV absorption coefficients for DAMN and DAFN and thermodynamic parameters that are useful for prebiotic chemistry studies. According to our results, experiments using UV lamps may underestimate the photolysis production of molecules of prebiotic importance. Our results indicate that photolysis reactions are fast with a yield of 50% of AICN in 10 s for the young Sun and ∼1 h for Proxima Centauri b. Planets around active M dwarfs may provide the most favorable environment for UV-mediated production of compounds relevant to the origins of life. The kinetic reaction AICN + HCN  adenine is the bottleneck of the pathway with reaction rates <10^-22 L/(mol·s).

Photochemical Synthesis of Porous Triazine-/Heptazine-Based Carbon Nitride Homojunction for Efficient Overall Water Splitting

Porous triazine-/heptazine-based carbon nitride (THCN) homojunction with chloride (Cl) doping was synthesized by a simple, one-step photochemical synthesis route for efficient visible-light-driven overall water splitting. The phase ratio of triazine-based carbon nitride (TCN) and heptazine-based carbon nitride (HCN), texture and morphology of the THCN isotype junction were finely tuned by varying ultraviolet irradiation time and washing solvents. After washing with acetonitrile, the resulting porous THCN nanosheets with 48 h irradiation contain 21 wt % TCN and 79 wt % HCN units and reveal a significantly improved photocatalytic performance with H₂ and O₂ production rates up to 7.9 and 4.2 μmol h^-1 , respectively, about 3.8 times higher than that of THCN prepared by 36 h illumination. The dual-phase interaction, holey structure, and Cl dopants favor the exposure of active sites, extended visible-light harvesting, accelerated charge transfer, and enhanced photoreduction ability, thereby improving photocatalytic activity.

Natural Selection and Scale Invariance

This review points out that three of the essential features of natural selection—competition for a finite resource, variation, and transmission of memory—occur in an extremely simple, thermalized molecular population, one of colliding “billiard balls” subject to an anisotropy, a directional flux of energetic molecules. The emergence of scaling behavior, scale invariance, in such systems is considered in the context of the emergence of complexity driven by Gibbs free energy, the origins of life, and known chemistries in planetary and astrophysical conditions. It is suggested that the thermodynamic formalism of statistical multifractality offers a parallel between the microscopic and macroscopic views of non-equilibrium systems and their evolution, different from, empirically determinable, and therefore complementing traditional definitions of entropy and its production in living systems. Further, the approach supports the existence of a bridge between microscopic and macroscopic scales, the missing mesoscopic scale. It is argued that natural selection consequently operates on all scales—whether or not life results will depend on both the initial and the evolving boundary conditions. That life alters the boundary conditions ensures nonlinearity and scale invariance. Evolution by natural selection will have taken place in Earth’s fluid envelope; both air and water display scale invariance and are far from chemical equilibrium, a complex condition driven by the Gibbs free energy arising from the entropy difference between the incoming solar beam and the outgoing infrared radiation to the cold sink of space acting on the initial conditions within evolving boundary conditions. Symmetry breaking’s role in the atmospheric state is discussed, particularly in regard to aerosol fission in the context of airborne bacteria and viruses in both current and prebiotic times. Over 4.4 billion years, the factors operating to support natural selection will have evolved along with the entire system from relative simplicity to the current complexity.

Semiclassical Dynamics on Machine-Learned Coupled Multireference Potential Energy Surfaces: Application to the Photodissociation of the Simplest Criegee Intermediate

Determination of high-dimensional potential energy surfaces (PESs) and nonadiabatic couplings have always been quite challenging. To this end, machine learning (ML) models, trained with a finite set of ab initio data, allow accurate prediction of such properties. To express the PESs in terms of atomic contributions is the cornerstone of any ML based technique because it can be easily scaled to large systems. In this work, we have constructed high fidelity PESs and nonadiabatic coupling terms at the CASSCF level of ab initio data using a machine learning technique, namely, kernel-ridge regression. Additional MRCI-level calculations were carried out to assess the quality of the PESs. We use these machine-learned PESs and nonadiabatic couplings to simulate excited-state molecular dynamics based on Tully's fewest-switches surface hopping method (FSSH). FSSH is a semiclassical method in which nuclei move on the PESs due to the electrons according to the laws of classical mechanics. Nonadiabatic effects are taken into account in terms of transitions between PESs. We apply this scheme to study the O-O photodissociation of the simplest Criegee intermediate (CH₂OO). The FSSH trajectories were initiated on the lowest optically bright singlet excited state (S₂) and propagated along the three most important internal coordinates, namely, O-O and C-O bond distances and the COO bond angle. Some of the trajectories end up on energetically lower PESs as a result of radiationless transfer through conical intersections. All of the trajectories lead to the dissociation of the O-O bond due to the dissociative nature of the excited PESs through one of the two dissociative channels. The simulation reveals that there is about 88.4% probability of dissociation through the lower channel leading to the H₂CO (X¹A₁) and O (¹D) products, whereas there is only 11.6% probability of dissociation through the upper channel leading to H₂CO (a³A″) and O (³P) products.

Model Atmospheric Aerosols Convert to Vesicles upon Entry into Aqueous Solution

Aerosols are abundant on the Earth and likely played a role in prebiotic chemistry. Aerosol particles coagulate, divide, and sample a wide variety of conditions conducive to synthesis. While much work has centered on the generation of aerosols and their chemistry, little effort has been expended on their fate after settling. Here, using a laboratory model, we show that aqueous aerosols transform into cell-sized protocellular structures upon entry into aqueous solution containing lipid. Such processes provide for a heretofore unexplored pathway for the assembly of the building blocks of life from disparate geochemical regions within cell-like vesicles with a lipid bilayer in a manner that does not lead to dilution. The efficiency of aerosol to vesicle transformation is high with prebiotically plausible lipids, such as decanoic acid and decanol, that were previously shown to be capable of forming growing and dividing vesicles. The high transformation efficiency with 10-carbon lipids in landing solutions is consistent with the surface properties and dynamics of short-chain lipids. Similar processes may be operative today as fatty acids are common constituents of both contemporary aerosols and the sea. Our work highlights a new pathway that may have facilitated the emergence of the Earth's first cells.

Detecting the First Hydration Shell Structure around Biomolecules at Interfaces

Understanding the role of water in biological processes remains a central challenge in the life sciences. Water structures in hydration shells of biomolecules are difficult to study in situ due to overwhelming background from aqueous environments. Biological interfaces introduce additional complexity because biomolecular hydration differs at interfaces compared to bulk solution. Here, we perform experimental and computational studies of chiral sum frequency generation (chiral SFG) spectroscopy to probe chirality transfer from a protein to the surrounding water molecules. This work reveals that chiral SFG probes the first hydration shell around the protein almost exclusively. We explain the selectivity to the first hydration shell in terms of the asymmetry induced by the protein structure and specific protein-water hydrogen-bonding interactions. This work establishes chiral SFG as a powerful technique for studying hydration shell structures around biomolecules at interfaces, presenting new possibilities to address grand research challenges in biology, including the molecular origins of life.

Protection of the DNA from Selected Species of Five Kingdoms in Nature by Ba(II), Sr(II), and Ca(II) Silica-Carbonates: Implications about Biogenicity and Evolving from Prebiotic Chemistry to Biological Chemistry

The origin of life on Earth is associated with the Precambrian era, in which the existence of a large diversity of microbial fossils has been demonstrated. Notwithstanding, despite existing evidence of the emergence of life many unsolved questions remain. The first question could be as follows: Which was the inorganic structure that allowed isolation and conservation of the first biomolecules in the existing reduced conditions of the primigenial era? Minerals have been postulated as the ones in charge of protecting theses biomolecules against the external environment. There are calcium, barium, or strontium silica-carbonates, called biomorphs, which we propose as being one of the first inorganic structures in which biomolecules were protected from the external medium. Biomorphs are structures with different biological morphologies that are not formed by cells, but by nanocrystals; some of their morphologies resemble the microfossils found in Precambrian cherts. Even though biomorphs are unknown structures in the geological registry, their similarity with some biological forms, including some Apex fossils, could suggest them as the first "inorganic scaffold" where the first biomolecules became concentrated, conserved, aligned, and duplicated to give rise to the pioneering cell. However, it has not been documented whether biomorphs could have been the primary structures that conserved biomolecules in the Precambrian era. To attain a better understanding on whether biomorphs could have been the inorganic scaffold that existed in the primigenial Earth, the aim of this contribution is to synthesize calcium, barium, and strontium biomorphs in the presence of genomic DNA from organisms of the five kingdoms in conditions emulating the atmosphere of the Precambrian era and that CO₂ concentration in conditions emulating current atmospheric conditions. Our results showed, for the first time, the formation of the kerogen signal, which is a marker of biogenicity in fossils, in the biomorphs grown in the presence of DNA. We also found the DNA to be internalized into the structure of biomorphs.

Photochemistry of 2-thiooxazole: a plausible prebiotic precursor to RNA nucleotides

Potentially prebiotic chemical reactions leading to RNA nucleotides involve periods of UV irradiation, which are necessary to promote selectivity and destroy biologially irrelevant side products. Nevertheless, UV light has only been applied to promote specific stages of prebiotic reactions and its effect on complete prebiotic reaction sequences has not been extensively studied. Here, we report on an experimental and computational investigation of the photostability of 2-thiooxazole (2-TO), a potential precursor of pyrimidine and 8-oxopurine nucleotides on early Earth. Our UV-irradiation experiments resulted in rapid decomposition of 2-TO into unidentified small molecule photoproducts. We further clarify the underlying photochemistry by means of accurate ab initio calculations and surface hopping molecular dynamics simulations. Overall, the computational results show efficient rupture of the aromatic ring upon the photoexcitation of 2-TO via breaking of the C-O bond. Consequently, the initial stage of the divergent prebiotic synthesis of pyrimidine and 8-oxopurine nucleotides would require periodic shielding from UV light either with sun screening chromophores or through a planetary scenario that would protect 2-TO until it is transformed into a more stable intermediate compound, e.g. oxazolidinone thione.

Understanding How a New Hachimoji Nucleobase Alters Photodynamics of Genetic Building Blocks

This article is a highlight of the paper by Krul et al. in this issue of Photochemistry and Photobiology. It describes the excited state dynamics of 5-aza-7-deazaguanine (^5N7C G), which has recently been proposed as an alternative nucleobase. Upon UV absorption to the lowest energy ¹ ππ* state, ^5N7C G returns to the electronic ground state an order of magnitude more slowly than guanine with a corresponding greater fluorescence quantum yield. These findings are significant because they suggest that ^5N7C G is less UV photostable that its canonical nucleobase equivalent, which would have been a selective disadvantage in prebiotic conditions.

Light-Induced Synthesis of Oxygen-Vacancy-Functionalized Ni(OH)2 Nanosheets for Highly Selective CO2 Reduction

Solar-driven CO₂ reduction into fuels and chemicals has gained increasing attention in recent years. In this study, oxygen-vacancies-functionalized Ni(OH)₂ (OVs-Ni(OH)₂ ) nanosheets are synthesized by a photochemical method to serve as a catalyst for CO₂ reduction. Characterization reveals that COOH* is the key intermediate for CO₂ -to-CO photoreduction. Experimental results and theoretical calculations confirm that OVs modification can greatly modulate the interaction strength between the OVs-Ni(OH)₂ and CO₂ , while lowering the energy barrier for COOH* formation, thereby preferentially facilitating CO₂ reduction. As a result, the OVs-Ni(OH)₂ catalyst exhibits outstanding activity and selectivity for CO₂ -to-CO photoreduction with visible light. A CO evolution rate of 31.58 μmol h^-1 (0.35 mg catalyst, 90228 μmol h^-1  g^-1 ) with a selectivity of 98 % over OVs-Ni(OH)₂ was achieved, outperforming most analogous reported catalysts. Moreover, even under a low CO₂ concentration of 0.04 % (representative of the CO₂ concentration in air) and low reaction temperature (273 K, 0 °C), this catalyst can still trigger CO₂ reduction. This work provides a new method to synthesize OVs-Ni(OH)₂ catalysts for efficient CO₂ reduction and establishes a relationship between the OVs and the catalytic activity, which may guide the design of highly selective CO₂ reduction catalysts.

The essence of life revisited: how theories can shed light on it

Disagreement over whether life is inevitable when the conditions can support life remains unresolved, but calculations show that self-organization can arise naturally from purely random effects. Closure to efficient causation, or the need for all specific catalysts used by an organism to be produced internally, implies that a true model of an organism cannot exist, though this does not exclude the possibility that some characteristics can be simulated. Such simulations indicate that there is a limit to how small a self-organizing system can be: much smaller than a bacterial cell, but around the size of a typical virus particle. All current theories of life incorporate, at least implicitly, the idea of catalysis, but they largely ignore the need for metabolic regulation.

Photosensitization mechanisms at the air-water interface of aqueous aerosols

Photosensitization reactions are believed to provide a key contribution to the overall oxidation chemistry of the Earth's atmosphere. Generally, these processes take place on the surface of aqueous aerosols, where organic surfactants accumulate and react, either directly or indirectly, with the activated photosensitizer. However, the mechanisms involved in these important interfacial phenomena are still poorly known. This work sheds light on the reaction mechanisms of the photosensitizer imidazole-2-carboxaldehyde through ab initio (QM/MM) molecular dynamics simulations and high-level ab initio calculations. The nature of the lowest excited states of the system (singlets and triplets) is described in detail for the first time in the gas phase, in bulk water, and at the air-water interface, and possible intersystem crossing mechanisms leading to the reactive triplet state are analyzed. Moreover, the reactive triplet state is shown to be unstable at the air-water surface in a pure water aerosol. The combination of this finding with the results obtained for simple surfactant-photosensitizer models, together with experimental data from the literature, suggests that photosensitization reactions assisted by imidazole-2-carboxaldehyde at the surface of aqueous droplets can only occur in the presence of surfactant species, such as fatty acids, that stabilize the photoactivated triplet at the interface. These findings should help the interpretation of field measurements and the design of new laboratory experiments to better understand atmospheric photosensitization processes.

The primary photo-dissociation dynamics of lactic acid: decarboxylation as CO2, CO2•-

We study the primary photolysis dynamics of lactic acid induced by excitation at λ = 200 nm with the aim of elucidating how simple aqueous carboxyl acids react to the...

The Impact of the Spectral Radiation Environment on the Maximum Absorption Wavelengths of Human Vision and Other Species

Since the earliest development of the eye (and vision) around 530 million years ago (Mya), it has evolved, adapting to different habitats, species, and changing environmental conditions on Earth. We argue that a radiation environment determined by the atmosphere played a determining role in the evolution of vision, specifically on the human eye, which has three vision regimes (photopic-, scotopic-, and mesopic vision) for different illumination conditions. An analysis of the irradiance spectra, reaching the shallow ocean depths, revealed that the available radiation could have determined the bandwidth of the precursor to vision systems, including human vision. We used the radiative transfer model to test the existing hypotheses on human vision. We argue that, once on the surface, the human photopic (daytime) and scotopic (night-time) vision followed different evolutionary directions, maximum total energy, and optimum information, respectively. Our analysis also suggests that solar radiation reflected from the moon had little or no influence on the evolution of scotopic vision. Our results indicate that, apart from human vision, the vision of only a few birds, rodents, and deep-sea fish are strongly correlated to the available radiation within their respective habitats.

Bio-inspired strategies for next-generation perovskite solar mobile power sources

Smart electronic devices are becoming ubiquitous due to many appealing attributes including portability, long operational time, rechargeability and compatibility with the user-desired form factor. Integration of mobile power sources (MPS) based on photovoltaic technologies with smart electronics will continue to drive improved sustainability and independence. With high efficiency, low cost, flexibility and lightweight features, halide perovskite photovoltaics have become promising candidates for MPS. Realization of these photovoltaic MPS (PV-MPS) with unconventionally extraordinary attributes requires new 'out-of-box' designs. Natural materials have provided promising designing solutions to engineer properties under a broad range of boundary conditions, ranging from molecules, proteins, cells, tissues, apparatus to systems in animals, plants, and humans optimized through billions of years of evolution. Applying bio-inspired strategies in PV-MPS could be biomolecular modification on crystallization at the atomic/meso-scale, bio-structural duplication at the device/system level and bio-mimicking at the functional level to render efficient charge delivery, energy transport/utilization, as well as stronger resistance against environmental stimuli (e.g., self-healing and self-cleaning). In this review, we discuss the bio-inspired/-mimetic structures, experimental models, and working principles, with the goal of revealing physics and bio-microstructures relevant for PV-MPS. Here the emphasis is on identifying the strategies and material designs towards improvement of the performance of emerging halide perovskite PVs and strategizing their bridge to future MPS.

The Prebiotic Kitchen: A Guide to Composing Prebiotic Soup Recipes to Test Origins of Life Hypotheses

“Prebiotic soup” often features in discussions of origins of life research, both as a theoretical concept when discussing abiological pathways to modern biochemical building blocks and, more recently, as a feedstock in prebiotic chemistry experiments focused on discovering emergent, systems-level processes such as polymerization, encapsulation, and evolution. However, until now, little systematic analysis has gone into the design of well-justified prebiotic mixtures, which are needed to facilitate experimental replicability and comparison among researchers. This paper explores principles that should be considered in choosing chemical mixtures for prebiotic chemistry experiments by reviewing the natural environmental conditions that might have created such mixtures and then suggests reasonable guidelines for designing recipes. We discuss both “assembled” mixtures, which are made by mixing reagent grade chemicals, and “synthesized” mixtures, which are generated directly from diversity-generating primary prebiotic syntheses. We discuss different practical concerns including how to navigate the tremendous uncertainty in the chemistry of the early Earth and how to balance the desire for using prebiotically realistic mixtures with experimental tractability and replicability. Examples of two assembled mixtures, one based on materials likely delivered by carbonaceous meteorites and one based on spark discharge synthesis, are presented to illustrate these challenges. We explore alternative procedures for making synthesized mixtures using recursive chemical reaction systems whose outputs attempt to mimic atmospheric and geochemical synthesis. Other experimental conditions such as pH and ionic strength are also considered. We argue that developing a handful of standardized prebiotic recipes may facilitate coordination among researchers and enable the identification of the most promising mechanisms by which complex prebiotic mixtures were “tamed” during the origin of life to give rise to key living processes such as self-propagation, information processing, and adaptive evolution. We end by advocating for the development of a public prebiotic chemistry database containing experimental methods (including soup recipes), results, and analytical pipelines for analyzing complex prebiotic mixtures.

Water-Air Interfaces as Environments to Address the Water Paradox in Prebiotic Chemistry: A Physical Chemistry Perspective

The asymmetric water-air interface provides a dynamic aqueous environment with properties that are often very different than bulk aqueous or gaseous phases and promotes reactions that are thermodynamically, kinetically, or otherwise unfavorable in bulk water. Prebiotic chemistry faces a key challenge: water is necessary for life yet reduces the efficiency of many biomolecular synthesis reactions. This perspective considers water-air interfaces as auspicious reaction environments for abiotic synthesis. We discuss recent evidence that (1) water-air interfaces promote condensation reactions including peptide synthesis, phosphorylation, and oligomerization; (2) photochemistry at water-air interfaces may have been a significant source of prebiotic molecular complexity, given the lack of oxygen and increased availability of near-ultraviolet radiation on early Earth; and (3) water-air interfaces can promote spontaneous reduction and oxidation reactions, potentially providing protometabolic pathways. Life likely began within a relatively short time frame, and water-air interfaces offer promising environments for simultaneous and efficient biomolecule production.

Kinetic Study of Gas-Phase Reactions of Pyruvic Acid with HO2

Gas-phase reactions between pyruvic acid (PA) and HO₂ radicals were examined using ab initio quantum chemistry and transition state theory. The rate coefficients were determined over a temperature range of 200-400 K including tunneling contributions. Six potential reaction pathways were identified. The two hydrogen abstraction reactions yielding the H₂O₂ product were found to have high barriers. The HO₂ radical was also found to have a catalytic effect on the intramolecular hydrogen transfer reactions occurring by three distinct routes. These hydrogen-shift reactions are very interesting mechanistically although they are highly endothermic. The only reaction that contributes significantly to the consumption of PA is a multistep pathway involving a peroxy-radical intermediate, PA + HO₂ → CH₃COOH + OH + CO₂. This exothermic process has potential atmospheric relevance because it produces an OH radical as a product. Atmospheric models currently have difficulty predicting accurate OH concentrations for certain atmospheric conditions, such as environments free of NOx and the nocturnal boundary layer. Reactions of this sort, although not necessary with PA, may account for a portion of this deficit. The present study helps settle the issue of the relative roles of reaction and photolysis in consumption of PA in the troposphere.

The primary photo-dissociation dynamics of lactate in aqueous solution: decarboxylation prevents dehydroxylation

We study the primary photolysis dynamics of aqueous lactate induced by photo-excitation at λ = 200 nm. Our calculations indicate that both decarboxylation and dehydroxylation are energetically possible, but decarboxylation is favoured dynamically. UV pump - IR probe transient absorption spectroscopy shows that the photolysis is dominated by decarboxylation, whereas dehydroxylation is not observed. Analysis of the transient IR spectrum suggests that photo-dissociation of lactate primarily produces CO₂ and CH₃CHOH^- through the lowest singlet excited state of lactate, which has a lifetime of τ = 11 ps. UV pump - VIS probe transient absorption spectroscopy of electrons from the dissociating lactate anion indicates that the anionic electron from the CO₂˙^- fragment is transferred to the CH₃CHOH˙ counter radical during the decarboxylation process, and CO₂˙^- is consequently only observed as a minor photo-product. The photo-dissociation quantum yield after the full decay of the excited state is Φ(100ps) = 38 ± 5%.

The primary photolysis dynamics of oxalate in aqueous solution: decarboxylation

We study the primary reaction dynamics of aqueous oxalate following photo-excitation of the nO → πCO* transition at λ = 200 nm. After the excitation, some of the oxalate molecules return to the electronic ground state on two very different time scales: a fast component of τ = 1.1 ± 0.5 ps comprising 40% of the excited molecules and a much slower component of τ = 0.28 ± 0.05 ns accounting for 15% of the excited molecules. The remaining 45% of the excited molecules do not return to the ground state during the first 500 ps, because they either detach an electron, dissociate or stay excited for hundreds of picoseconds. Dissociation and electron detachment of oxalate predominantly produces CO2 molecules with only minor yields of CO2˙- radical anions. The CO2 formation is accompanied by the ejection of electrons.

Photoinduced Oxidation Reactions at the Air-Water Interface

Chemistry on water is a fascinating area of research. The surface of water and the interfaces between water and air or hydrophobic media represent asymmetric environments with unique properties that lead to unexpected solvation effects on chemical and photochemical processes. Indeed, the features of interfacial reactions differ, often drastically, from those of bulk-phase reactions. In this Perspective, we focus on photoinduced oxidation reactions, which have attracted enormous interest in recent years because of their implications in many areas of chemistry, including atmospheric and environmental chemistry, biology, electrochemistry, and solar energy conversion. We have chosen a few representative examples of photoinduced oxidation reactions to focus on in this Perspective. Although most of these examples are taken from the field of atmospheric chemistry, they were selected because of their broad relevance to other areas. First, we outline a series of processes whose photochemistry generates hydroxyl radicals. These OH precursors include reactive oxygen species, reactive nitrogen species, and sulfur dioxide. Second, we discuss processes involving the photooxidation of organic species, either directly or via photosensitization. The photochemistry of pyruvic acid and fatty acid, two examples that demonstrate the complexity and versatility of this kind of chemistry, is described. Finally, we discuss the physicochemical factors that can be invoked to explain the kinetics and thermodynamics of photoinduced oxidation reactions at aqueous interfaces and analyze a number of challenges that need to be addressed in future studies.

Emerging Strategies to Protect the Skin from Ultraviolet Rays Using Plant-Derived Materials

Sunlight contains a significant amount of ultraviolet (UV) ray, which leads to various effects on homeostasis in the body. Defense strategies to protect from UV rays have been extensively studied, as sunburn, photoaging, and photocarcinogenesis are caused by excessive UV exposure. The primary lines of defense against UV damage are melanin and trans-urocanic acid, which are distributed in the stratum corneum. UV rays that pass beyond these lines of defense can lead to oxidative damage. However, cells detect changes due to UV rays as early as possible and initiate cell signaling processes to prevent the occurrence of damage and repair the already occurred damage. Cosmetic and dermatology experts recommend using a sunscreen product to prevent UV-induced damage. A variety of strategies using antioxidants and anti-inflammatory agents have also been developed to complement the skin's defenses against UV rays. Researchers have examined the use of plant-derived materials to alleviate the occurrence of skin aging, diseases, and cancer caused by UV rays. Furthermore, studies are also underway to determine how to promote melanin production to protect from UV-induced skin damage. This review provides discussion of the damage that occurs in the skin due to UV light and describes potential defense strategies using plant-derived materials. This review aims to assist researchers in understanding the current research in this area and to potentially plan future studies.

Factoring Origin of Life Hypotheses into the Search for Life in the Solar System and Beyond

Two widely-cited alternative hypotheses propose geological localities and biochemical mechanisms for life's origins. The first states that chemical energy available in submarine hydrothermal vents supported the formation of organic compounds and initiated primitive metabolic pathways which became incorporated in the earliest cells; the second proposes that protocells self-assembled from exogenous and geothermally-delivered monomers in freshwater hot springs. These alternative hypotheses are relevant to the fossil record of early life on Earth, and can be factored into the search for life elsewhere in the Solar System. This review summarizes the evidence supporting and challenging these hypotheses, and considers their implications for the search for life on various habitable worlds. It will discuss the relative probability that life could have emerged in environments on early Mars, on the icy moons of Jupiter and Saturn, and also the degree to which prebiotic chemistry could have advanced on Titan. These environments will be compared to ancient and modern terrestrial analogs to assess their habitability and biopreservation potential. Origins of life approaches can guide the biosignature detection strategies of the next generation of planetary science missions, which could in turn advance one or both of the leading alternative abiogenesis hypotheses.

Gibbs Free Energy and Reaction Rate Acceleration in and on Microdroplets

Recent observations show that many reactions are accelerated in microdroplets compared to bulk liquid and gas media. This acceleration has been shown to feature Gibbs free energy changes, ΔG, that are negative and so reaction enabling, compared to the reaction in bulk fluid when it is positive and so reaction blocking. Here, we argue how these ΔG changes are relatable to the crowding enforced by microdroplets and to scale invariance. It is argued that turbulent flow is present in microdroplets, which span meso and macroscales. That enables scale invariant methods to arrive at chemical potentials for the substances involved. G and ΔG can be computed from the difference between the whole microdroplet and the bulk medium, and also for individual chemical species in both cases, including separately the microdroplet’s surface film and interior, provided sufficiently fine resolution is available in the observations. Such results can be compared with results computed by quantum statistical mechanics using molecular spectroscopic data. This proposed research strategy therefore offers a path to test its validity in comparing traditional equilibrium quantum statistical thermodynamic tests of microdroplets with those based on scale invariant analysis of both their 2D surface and 3D interior fluid flows.

Chronic exposure to green light aggravates high-fat diet-induced obesity and metabolic disorders in male mice

Light is involved in many critical physiological or biochemical processes of human beings, such as visual sensing and the production of vitamin D. Recent studies have showed that the lights of different wavelengths have a profound influence in life activities. For example, blue light promotes alertness, whereas green light (GL) induces sleep in mice. On the other hand, metabolic homeostasis is regulated by a variety of factors, including dietary habits and light exposure. Our study aims to study whether certain wavelength of light would affect metabolic status of mice. Mice were divided into normal diet-fed group and high-fat diet (HFD)-fed group, and then exposed to various colors of the light. Physiological parameters, such as body weight, food intake and water drinking were regularly measured. Glucose tolerance test and pyruvate tolerance test were simultaneously performed. After mice were humanely sacrificed, liver histology and serologic analysis were performed for detecting lipid levels. We found that GL group showed obvious glucose intolerance and increased levels of serum and liver lipid contents compared to white light group. Meanwhile, the expression levels of lipid metabolism-related genes were almost down-regulated in liver. Furthermore, melatonin receptor-1b and thyroid hormone receptor-β expression levels were significantly lowered in liver of GL-treated obese mice, suggesting that these hormone pathways may mediate the changes of lipid metabolism. Our data indicate that GL has a detrimental effect on the energy metabolism and aggravates HFD-induced obesity in mice. In addition to malnutrition, the colors of the lights also have a profound influence in the metabolic homeostasis and should be taken into consideration in the therapy of metabolic disorders.

Progress in synthesizing protocells

IMPACT STATEMENT

Advances in the understanding of the biophysics of membranes, the nonenzymatic and enzymatic polymerization of RNA, and in the design of complex chemical reaction networks have led to a new, integrated way of viewing the shared chemistry needed to sustain life. Although a protocell capable of Darwinian evolution has yet to be built, the seemingly disparate pieces are beginning to fit together. At the very least, better cellular mimics are on the horizon that will likely teach us much about the physicochemical underpinnings of cellular life.

The primary photo-dissociation dynamics of carboxylate anions in aqueous solution: decarboxylation

Photo-excitation of aqueous carboxylates results in decarboxylation.

Photodynamics of alternative DNA base isoguanine

Pump–probe experiments and quantum-chemical simulations of UV-excited isoguanine elucidate its tautomer dependent photochemical properties.

Modeling Repeated M Dwarf Flaring at an Earth-like Planet in the Habitable Zone: Atmospheric Effects for an Unmagnetized Planet

Understanding the impact of active M dwarf stars on the atmospheric equilibrium and surface conditions of a habitable zone Earth-like planet is key to assessing M dwarf planet habitability. Previous modeling of the impact of electromagnetic (EM) radiation and protons from a single large flare on an Earth-like atmosphere indicated that significant and long-term reductions in ozone were possible, but the atmosphere recovered. However, these stars more realistically exhibit frequent flaring with a distribution of different total energies and cadences. Here, we use a coupled 1D photochemical and radiative-convective model to investigate the effects of repeated flaring on the photochemistry and surface UV of an Earth-like planet unprotected by an intrinsic magnetic field. As input, we use time-resolved flare spectra obtained for the dM3 star AD Leonis, combined with flare occurrence frequencies and total energies (typically 10^30.5 to 10³⁴ erg) from the 4-year Kepler light curve for the dM4 flare star GJ1243, with varied proton event impact frequency. Our model results show that repeated EM-only flares have little effect on the ozone column depth but that multiple proton events can rapidly destroy the ozone column. Combining the realistic flare and proton event frequencies with nominal CME/SEP geometries, we find the ozone column for an Earth-like planet can be depleted by 94% in 10 years, with a downward trend that makes recovery unlikely and suggests further destruction. For more extreme stellar inputs, O₃ depletion allows a constant ∼0.1-1 W m^-2 of UVC at the planet's surface, which is likely detrimental to organic complexity. Our results suggest that active M dwarf hosts may comprehensively destroy ozone shields and subject the surface of magnetically unprotected Earth-like planets to long-term radiation that can damage complex organic structures. However, this does not preclude habitability, as a safe haven for life could still exist below an ocean surface.

Photostability of oxazoline RNA-precursors in UV-rich prebiotic environments

Pentose aminooxazolines and oxazolidinone thiones are considered as the key precursors which could have enabled the formation of RNA nucleotides under the conditions of early Earth. UV-irradiation experiments and quantum-chemical calculations demonstrate that these compounds are remarkably photostable and could accumulate over long periods of time in UV-rich prebiotic environments to undergo stereoisomeric purification.

Enhanced Acidity of Acetic and Pyruvic Acids on the Surface of Water

Understanding the acid-base behavior of carboxylic acids on aqueous interfaces is a fundamental issue in nature. Surface processes involving carboxylic acids such as acetic and pyruvic acids play roles in (1) the transport of nutrients through cell membranes, (2) the cycling of metabolites relevant to the origin of life, and (3) the photooxidative processing of biogenic and anthropogenic emissions in aerosols and atmospheric waters. Here, we report that 50% of gaseous acetic acid and pyruvic acid molecules transfer a proton to the surface of water at pH 2.8 and 1.8 units lower than their respective acidity constants p K_a = 4.6 and 2.4 in bulk water. These findings provide key insights into the relative Bronsted acidities of common carboxylic acids versus interfacial water. In addition, the work estimates the reactive uptake coefficient of gaseous pyruvic acid by water to be γ_PA = 0.06. This work is useful to interpret the interfacial behavior of pyruvic acid under low water activity conditions, typically found in haze aerosols, clouds, and fog waters.

Sulfidic Anion Concentrations on Early Earth for Surficial Origins-of-Life Chemistry

A key challenge in origin-of-life studies is understanding the environmental conditions on early Earth under which abiogenesis occurred. While some constraints do exist (e.g., zircon evidence for surface liquid water), relatively few constraints exist on the abundances of trace chemical species, which are relevant to assessing the plausibility and guiding the development of postulated prebiotic chemical pathways which depend on these species. In this work, we combine literature photochemistry models with simple equilibrium chemistry calculations to place constraints on the plausible range of concentrations of sulfidic anions (HS-, HSO3-, SO32-) available in surficial aquatic reservoirs on early Earth due to outgassing of SO2 and H2S and their dissolution into small shallow surface water reservoirs like lakes. We find that this mechanism could have supplied prebiotically relevant levels of SO2-derived anions, but not H2S-derived anions. Radiative transfer modeling suggests UV light would have remained abundant on the planet surface for all but the largest volcanic explosions. We apply our results to the case study of the proposed prebiotic reaction network of Patel et al. ( 2015 ) and discuss the implications for improving its prebiotic plausibility. In general, epochs of moderately high volcanism could have been especially conducive to cyanosulfidic prebiotic chemistry. Our work can be similarly applied to assess and improve the prebiotic plausibility of other postulated surficial prebiotic chemistries that are sensitive to sulfidic anions, and our methods adapted to study other atmospherically derived trace species.

Primitive Photosynthetic Architectures Based on Self-Organization and Chemical Evolution of Amino Acids and Metal Ions

The emergence of light-energy-utilizing metabolism is likely to be a critical milestone in prebiotic chemistry and the origin of life. However, how the primitive pigment is spontaneously generated still remains unknown. Herein, a primitive pigment model based on adaptive self-organization of amino acids (Cystine, Cys) and metal ions (zinc ion, Zn2+) followed by chemical evolution under hydrothermal conditions is developed. The resulting hybrid microspheres are composed of radially aligned cystine/zinc (Cys/Zn) assembly decorated with carbonate-doped zinc sulfide (C-ZnS) nanocrystals. The part of C-ZnS can work as a light-harvesting antenna to capture ultraviolet and visible light, and use it in various photochemical reactions, including hydrogen (H2) evolution, carbon dioxide (CO2) photoreduction, and reduction of nicotinamide adenine dinucleotide (NAD+) to nicotinamide adenine dinucleotide hydride (NADH). Additionally, guest molecules (e.g., glutamate dehydrogenase, GDH) can be encapsulated within the hierarchical Cys/Zn framework, which facilitates sustainable photoenzymatic synthesis of glutamate. This study helps deepen insight into the emergent functionality (conversion of light energy) and complexity (hierarchical architecture) from interaction and reaction of prebiotic molecules. The primitive pigment model is also promising to work as an artificial photosynthetic microreactor.

Selective aqueous acetylation controls the photoanomerization of α-cytidine-5'-phosphate

Nucleic acids are central to information transfer and replication in living systems, providing the molecular foundations of Darwinian evolution. Here we report that prebiotic acetylation of the non-natural, but prebiotically plausible, ribonucleotide α-cytidine-5'-phosphate, selectively protects the vicinal diol moiety. Vicinal diol acetylation blocks oxazolidinone formation and prevents C2'-epimerization upon irradiation with UV-light. Consequently, acetylation enhances (4-fold) the photoanomerization of α-cytidine-5'-phosphate to produce the natural β-pyrimidine ribonucleotide-5'-phosphates required for RNA synthesis.

How UV Light Touches the Brain and Endocrine System Through Skin, and Why

The skin, a self-regulating protective barrier organ, is empowered with sensory and computing capabilities to counteract the environmental stressors to maintain and restore disrupted cutaneous homeostasis. These complex functions are coordinated by a cutaneous neuro-endocrine system that also communicates in a bidirectional fashion with the central nervous, endocrine, and immune systems, all acting in concert to control body homeostasis. Although UV energy has played an important role in the origin and evolution of life, UV absorption by the skin not only triggers mechanisms that defend skin integrity and regulate global homeostasis but also induces skin pathology (e.g., cancer, aging, autoimmune responses). These effects are secondary to the transduction of UV electromagnetic energy into chemical, hormonal, and neural signals, defined by the nature of the chromophores and tissue compartments receiving specific UV wavelength. UV radiation can upregulate local neuroendocrine axes, with UVB being markedly more efficient than UVA. The locally induced cytokines, corticotropin-releasing hormone, urocortins, proopiomelanocortin-peptides, enkephalins, or others can be released into circulation to exert systemic effects, including activation of the central hypothalamic-pituitary-adrenal axis, opioidogenic effects, and immunosuppression, independent of vitamin D synthesis. Similar effects are seen after exposure of the eyes and skin to UV, through which UVB activates hypothalamic paraventricular and arcuate nuclei and exerts very rapid stimulatory effects on the brain. Thus, UV touches the brain and central neuroendocrine system to reset body homeostasis. This invites multiple therapeutic applications of UV radiation, for example, in the management of autoimmune and mood disorders, addiction, and obesity.