Terminal Electron Donor Research Articles

Root-Driven Soil Reduction in Wadden Sea Salt Marshes

The soil redox potential in wetlands such as peatlands or salt marshes exerts a strong control over microbial decomposition processes and consequently soil carbon cycling. Wetland plants can influence redox by supplying both terminal electron acceptors (i.e. oxygen) and electron donors (i.e. organic matter) to the soil system. However, quantitative insight into the importance of plant effects on wetland soil redox and associated plant traits are scarce. In a combined mesocosm and field study we investigated the impact of plants on soil reduction using IRIS (Indicator of Reduction in Soils) sticks. Vegetated plots were compared to non-vegetated plots along an elevational gradient in a salt marsh of the Wadden Sea and along an artificially created gradient in a tidal tank mesocosm experiment. Our findings from the mesocosm experiment demonstrated that vegetation both enhanced and suppressed soil reduction relative to non-vegetated control pots. The direction of the plant effect (i.e., net oxidizing or net reducing) was inversely correlated with background redox conditions. Insights from high-resolution oxygen profiling via planar optode imaging corroborated these findings. In the field study, vegetation consistently reduced the comparatively well-aerated Wadden Sea salt marsh soil. Reduction correlated positively with soil organic matter content and belowground biomass, indicating that greater availability of plant-derived electron donors, in the form of organic matter, increased soil reduction. Challenging the dominant paradigm that wetland plants primarily act as soil oxidizers, our study reveals their potential to exert a net reducing effect. The documented impact of these plant-induced changes in soil redox conditions suggests a previously overlooked role in shaping the stability of soil organic carbon stocks in wetland ecosystems with variable water tables.

In-situ modification of nickel electrode by coupling the microbial corrosion and microbial reduction using Shewanella oneidensis for enhanced electrocatalysis

Shewanella oneidensis is a facultative anaerobe with the ability to use different terminal electron donors and acceptors. Therefore, S. oneidensis can be used either as an oxidizing agent for microbial corrosion of metals or as a reducing agent for microbial synthesis of metal nanoparticles depending on the metal type. Herein, we have shown that S. oneidensis MR-1 can be used for both microbial corrosion of nickel foam (NF) and microbial synthesis of Ni nanoparticles under environmentally benign conditions. It is found that S. oneidensis MR-1 can accelerate the corrosion process to form metal hydroxides on the surface of NF in the presence of Fe3+, and the obtained electrode shows improved electrocatalytic activity toward oxygen evolution reaction with an overpotential of 0.265 V to achieve a current density of 10 mA cm−2. However, the corrosion process of NF by S. oneidensis MR-1 is severely inhibited in the presence of Fe2+. In addition, aside from the corrosion process of NF, we have for the first time shown that Ni nanoparticles can be synthesized by the reduction of Ni2+ ions using S. oneidensis MR-1. The results show that the microbial energy metabolism of S. oneidensis MR-1 facilitates the electron transfer from electron-donating NF to the electron-accepting metal ions (Fe3+, Ni2+) across the microbes, coupling the corrosion process (Ni → Ni2+) and metal ions reductions (Fe3+ → Fe2+, Ni2+ → Ni), which demonstrates great potential for in-situ modification of electrode with microorganism and provides new avenue for electrode fabrication.

Theoretical and conceptual framework to design D-π-A type organic dyes for application dye-sensitized solar cells

The optimized structures and absorption spectra of five D-A-type organic dyes (M1, M2, M3, M4, and M5) were investigated using Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT). These dyes contain the same electron acceptors and -spacers but distinct 3,6- and 2,7-carbazole electron-donating groups. The results showed coplanar geometries for the dyes, which implied strong conjugation. When intramolecular charge transfer was investigated, it was discovered that 3,6-carbazole had a better capacity to give electrons than 2,7-carbazole. These dyes' projected orbital energy levels indicate that excited dyes might successfully decrease by electrolyte while oxidized dyes could successfully inject electrons into semiconductor conduction bands. The study investigated the suitability of different dyes for use in dye-sensitized solar cells (DSSCs) and found that the M2 dye, which contains a thio group as the terminal electron donor, exhibited the most promising optoelectronic properties. In particular, M2 had a narrow energy gap, superior optical qualities, optimal FMO energy levels, the lowest total value, and greater GInject and GReg values compared to the other dyes tested. These factors contributed to M2's superior photosensitizing performance, suggesting that using M2 in DSSCs may lead to higher optoelectronic characteristics and total energy conversion efficiency compared to using other dyes.

Dioxaborin Compounds with Terminal Carbazole Groups: Enhancing Electron Acceptor in Organic Photovoltaics

AbstractThree donor−acceptor−donor dioxaborin compounds containing carbazoles as the terminal electron donor groups were synthesized. Their electronic and photovoltaic properties were compared with those of an analog with terminal triphenylamine groups. The HOMO and LUMO levels of the N‐phenylcarbazole derivative were 0.3 and 0.1 eV lower, respectively, than those of the triphenylamine analog. During the evaluation of organic photovoltaic characteristics, the N‐phenylcarbazole derivative exhibited a power conversion efficiency (PCE) of 2.06 % when combined with a conducting polymer (PTB7‐Th). Contrarily, the triphenylamine analog exhibited a PCE of 2.85 % when combined with a fullerene acceptor (PC61BM). The results showed that the N‐phenylcarbazole and triphenylamine derivatives functioned as electron acceptor and donor materials, respectively. The conversion from the electron donor to the acceptor was achieved via a slight change in the structure of the terminal donor groups of the dioxaborin compounds. This study will prove valuable for the development of nonfullerene acceptors.

Photophysical properties of several multi-branched oligomers: An ultrafast excited state dynamics and quantum chemical calculation study

Multi-branched oligomers F1, F2 and F3 were investigated by spectroscopic experiments as well as quantum chemical calculations to elucidate the structure–property relationships and intramolecular charge transfer (ICT) characteristics of typical nonlinear optical materials. A better ICT property of F2 is obtained by replacing terminal electron donors with stronger electron-donating ability. The degree of ICT is effectively increased, which can be clearly seen from the frontier molecular orbitals contribution of central anthracene between HOMO and LUMO. The central group plays a major role in the direction as well as effective path of ICT process. In the X-shaped oligomers with anthracene as central group, ICT process takes place from terminal groups of [Formula: see text] position branches, to the central anthracene group. However, the electron distribution as well as the ICT of tri-branched oligomer F3 with triazine as central group is not symmetric. ICT process of F3 takes place from terminal triphenylamine groups to the central triazine and two fluorene groups at [Formula: see text] position branches. Y-shaped oligomer F3 has a longer lifetime of ICT state as well as a higher fluorescence quantum yield, which is consistent with the results of time-resolved fluorescence spectroscopy. Z-scan results show that the TPA cross-section value of F3 is 10.6 and 2.9 times higher than that of X-shaped F1 and F2. The dynamics curves of transient absorption spectroscopy also indicate that oligomer F3 structure has relatively stronger ICT properties. To verify the substituent effect, two linear molecules F4 and F5 were also calculated. The quantum chemical calculations result shows that the branches at positions 4 and 11 of the central anthracene group have little effect on the electron cloud distribution, and there are indeed significant differences in the contributions of branches at different positions. Our results may provide some reference for molecular design.

Chlorophyll triplet states in thylakoid membranes of Acaryochloris marina. Evidence for a triplet state sitting on the photosystem I primary donor populated by intersystem crossing.

Photo-induced triplet states in the thylakoid membranes isolated from the cyanobacterium Acaryocholoris marina, that harbours Chlorophyll (Chl) d as its main chromophore, have been investigated by Optically Detected Magnetic Resonance (ODMR) and time-resolved Electron Paramagnetic Resonance (TR-EPR). Thylakoids were subjected to treatments aimed at poising the redox state of the terminal electron transfer acceptors and donors of Photosystem II (PSII) and Photosystem I (PSI), respectively. Under ambient redox conditions, four Chl d triplet populations were detectable, identifiable by their characteristic zero field splitting parameters, after deconvolution of the Fluorescence Detected Magnetic Resonance (FDMR) spectra. Illumination in the presence of the redox mediator N,N,N',N'-Tetramethyl-p-phenylenediamine (TMPD) and sodium ascorbate at room temperature led to a redistribution of the triplet populations, with T3 (|D|= 0.0245cm-1, |E|= 0.0042cm-1) becoming dominant and increasing in intensity with respect to untreated samples. A second triplet population (T4, |D|= 0.0248cm-1, |E|= 0.0040cm-1) having an intensity ratio of about 1:4 with respect to T3 was also detectable after illumination in the presence of TMPD and ascorbate. The microwave-induced Triplet-minus-Singlet spectrum acquired at the maximum of the |D|-|E| transition (610MHz) displays a broad minimum at 740nm, accompanied by a set of complex spectral features that overall resemble, despite showing further fine spectral structure, the previously reported Triplet-minus-Singlet spectrum attributed to the recombination triplet of PSI reaction centre, [Schenderlein M, Çetin M, Barber J, et al. Spectroscopic studies of the chlorophyll d containing photosystem I from the cyanobacterium Acaryochloris marina. Biochim Biophys Acta 1777:1400-1408]. However, TR-EPR experiments indicate that this triplet displays an eaeaea electron spin polarisation pattern which is characteristic of triplet sublevels populated by intersystem crossing rather than recombination, for which an aeeaae polarisation pattern is expected instead. It is proposed that the observed triplet, which leads to the bleaching of the P740 singlet state, sits on the PSI reaction centre.

DFT and TD-DFT studies of phenothiazine based derivatives as fluorescent materials for semiconductor applications

A series of nine phenothiazine-based derivatives (PTZ1-PTZ9) have been computationally designed and investigated as organic fluorophores by employing two different topologies i.e., D-π-D-π-D and D-π-D-π-A in our scheme of study. All these designed derivatives consist of a phenothiazine core as central donor fragment (DF), thiophene/furan/pyrrole as π-spacers (P1/P2/P3), triphenylamine as terminal electron donor unit (DF1), and terminal acceptor unit (A1/A2). The effect of these substituents was studied on their optoelectronic and stability characteristics. TD-DFT calculations explores that bathochromically-shifted absorption (423–994 nm) and emission (524–1103 nm) bands of the designed derivatives cover the visible region and are also extended to the infrared regions of the spectrum. Among all designed fluorescent emitters, PTZ7-PTZ9 derivatives exhibit the lowest energy levels, energy gaps (1.44–1.57 eV), exclusive broad absorption, and emission peaks owing to their strong electron-withdrawing fragments. The computational analysis of frontier molecular orbitals, population analysis, and natural transition orbital analysis has revealed that PTZ1-PTZ3 derivatives exhibited π-π* excitations while the remaining six molecules (PTZ4-PTZ9) displayed ICT in addition to π-π* electronic transitions. The dipole moments of all investigated molecules (3.30–18.78 D) are higher than the reference molecule (2.20 D), indicating their greater solubility in dichloromethane solvent. The nine newly designed fluorescent materials are also studied for their charge transport/injection properties like radiative lifetime and light harvesting efficiency. This theoretical study has disclosed PTZ-derivatives as potential fluorescent emitters with intense and pure color emission for semiconductor devices.

Enhanced electronic communication through a conjugated bridge in a porphyrin–fullerene donor–acceptor couple

The electronic communication between the terminal electron-donor ZnP and electron-acceptor C60 units is enhanced by the conjugated EDOTV-based spacer leading to photoinduced electron transfer over the distance >2 nm in the picosecond time domain.

Probing extracellular reduction mechanisms of Bacillus subtilis and Escherichia coli with nitroaromatic compounds

Redox transformations of organic contaminants by bacterial extracellular polymeric substances (EPS) and the associated electron transfer mechanisms are rarely reported. Here we show that a nitroaromatic compound (1,3-dinitrobenzene) can be readily reduced to 3-hydroxylaminonitrobenzene and 3-nitroaniline in aqueous suspension of common bacteria (E. coli or B. subtilis) or in aqueous dissolved EPS extracted from the bacteria. The loss ratio of 1,3-dinitrobenzene by E. coli was unaffected after knocking out the nfsA gene encoding nitroreductase, but was suppressed by removing EPS attached to cells. In contrast, the loss ratio was enhanced by adding aqueous dissolved EPS to E. coli or B. subtilis suspension. The residual 1,3-dinitrobenzene and products formed after reduction were only presented outside the bacterial cells. Thus, bacterial reduction of 1,3-dinitrobenzene was mediated by nonenzymatic extracellular reduction. This was further corroborated by the observation that the stoichiometric demand of electrons in 1,3-dinitrobenzene reduction was nearly equal to the quantity of electrons donated by bacterial cells in the electrochemical cell experiment. Inhibition on the reduction of 1,3-dinitrobenzene by chemical probes combined with fluorescence detection demonstrated that reducing sugars in EPS might act as electron donors, while cytochromes and some low-molecular weight molecules (flavins and quinones) were involved as electron transfer mediators. Linear relationships were observed between the reduction kinetics and the one-electron reduction potentials for a series of substituted dinitrobenzenes in the presence of bacterial cells or dissolved EPS. Their close linear regression slope values suggest that the extracellular matrix and the exfoliated EPS utilized the same reducing agents (likely hydroquinones and reduced flavins) as terminal electron donors to reduce NACs. These results reveal a previously unrecognized mechanism for nonenzymatic extracellular reduction of NACs by common bacteria. CapsuleThe extracellular matrix of E. coli or B. subtilis supplies both electron donors and electron transfer mediators to efficiently reduce nitroaromatic compounds.

Ultrafast excited-state dynamics in land plants Photosystem I core and whole supercomplex under oxidised electron donor conditions.

The kinetics of excited-state energy migration were investigated by femtosecond transient absorption in the isolated Photosystem I-Light-Harvesting Complex I (PSI-LHCI) supercomplex and in the isolated PSI core complex of spinach under conditions in which the terminal electron donor P700 is chemically pre-oxidised. It is shown that, under these conditions, the relaxation of the excited state is characterised by lifetimes of about 0.4ps, 4.5ps, 15ps, 35ps and 65ps in PSI-LHCI and 0.15ps, 0.3ps, 6ps and 16ps in the PSI core complex. Compartmental spectral-kinetic modelling indicates that the most likely mechanism to explain the absence of long-lived (ns) excited states is the photochemical population of a radical pair state, which cannot be further stabilised and decays non-radiatively to the ground state with time constants in the order of 6-8ps.

Electron transfer and spin dynamics of the radical-pair in the cryptochrome from Chlamydomonas reinhardtii by computational analysis

In an effort to elucidate the origin of avian magnetoreception, it was postulated that a radical-pair formed in a cryptochrome upon light activation provided the basis for the mechanism that enables an inclination compass sensitive to the geomagnetic field. Photoreduction in this case involves formation of a flavin adenine dinucleotide (FAD)-tryptophan (TRP) radical-pair, following electron transfer within a conserved TRP triad in the cryptochrome. Recently, an animal-like cryptochrome from Chlamydomonas reinhardtii (CraCRY) was analyzed, demonstrating the role of a fourth aromatic residue, which serves as a terminal electron donor in the photoreduction pathway, resulting in the creation of a more distal radical-pair and exhibiting fast electron transfer. In this work, we investigated the electron transfer in CraCRY with a combination of free energy molecular dynamics (MD) simulations, frozen density functional theory, and QM/MM MD simulations, supporting the suggestion of a proton coupled electron transfer mechanism. Spin dynamics simulations discerned details on the dependence of the singlet yield on the direction of the external magnetic field for the [FAD•- TYRH•+] and [FAD•- TYR•] radical-pairs in CraCRY, in comparison with the previously modeled [FAD•- TRPH•+] radical-pair.

Symbiosis extended: exchange of photosynthetic O2 and fungal-respired CO2 mutually power metabolism of lichen symbionts

Lichens are a symbiosis between a fungus and one or more photosynthetic microorganisms that enables the symbionts to thrive in places and conditions they could not compete independently. Exchanges of water and sugars between the symbionts are the established mechanisms that support lichen symbiosis. Herein, we present a new linkage between algal photosynthesis and fungal respiration in lichen Flavoparmelia caperata that extends the physiological nature of symbiotic co-dependent metabolisms, mutually boosting energy conversion rates in both symbionts. Measurements of electron transport by oximetry show that photosynthetic O2 is consumed internally by fungal respiration. At low light intensity, very low levels of O2 are released, while photosynthetic electron transport from water oxidation is normal as shown by intrinsic chlorophyll variable fluorescence yield (period-4 oscillations in flash-induced Fv/Fm). The rate of algal O2 production increases following consecutive series of illumination periods, at low and with limited saturation at high light intensities, in contrast to light saturation in free-living algae. We attribute this effect to arise from the availability of more CO2 produced by fungal respiration of photosynthetically generated sugars. We conclude that the lichen symbionts are metabolically coupled by energy conversion through exchange of terminal electron donors and acceptors used in both photosynthesis and fungal respiration. Algal sugars and O2 are consumed by the fungal symbiont, while fungal delivered CO2 is consumed by the alga.

Mutations in a conserved loop in the PSST subunit of respiratory complex I affect ubiquinone binding and dynamics

Respiratory complex I catalyses the reduction of ubiquinone (Q) from NADH coupled to proton pumping across the inner membrane of mitochondria. The electrical charging of the inner mitochondrial membrane drives the synthesis of ATP, which is used to power biochemical reactions of the cell. The recent surge in structural data on complex I from bacteria and mitochondria have contributed to significant understanding of its molecular architecture. However, despite these accomplishments, the role of various subdomains in redox-coupled proton pumping remains entirely unclear. In this work, we have mutated conserved residues in the loop of the PSST subunit that faces the ~30 Å long unique Q-binding tunnel of respiratory complex I. The data show a drastic decrease in Q reductase activity upon mutating several residues despite full assembly of the complex. In-silico modeling and multiple microsecond long molecular dynamics simulations of wild-type and enzyme variants with exchanges of conserved arginine residues revealed remarkable ejection of the bound Q from the site near terminal electron donor N2. Based on experiments and long-time scale molecular simulations, we identify microscopic elements that dynamically control the diffusion of Q and are central to redox-coupled proton pumping in respiratory complex I.

A theoretical investigation of the optoelectronic performance of some new carbazole dyes

Density functional theory and time-dependent approaches are applied for theoretical investigation of a new class of novel carbazole-based d–D–π–A-type dyes, where the carbazole moiety is the main electron donor, bithiophene behaves as a π-bridge, and cyanoacetic acid as an electron acceptor for all the studied dyes, whereas the terminal electron donor unit is varied to thiophene, thienothiophene, carbazole, dimethoxyphenyl, and indole. The influence of the terminal electron donor on the optoelectronics properties is investigated for the dyes in isolated state and in chloroform solvent. Their absorption spectra and electronic and structural properties are evaluated and discussed. The theoretical results show that all the dyes exhibit excellent optoelectronic properties. In particular, D5 with indole as the terminal electron donor moiety has potential for use as a sensitizer for nanocrystalline TiO2 solar cells based on its red-shifted absorption spectrum, reduced energy gap, lowest λtotal value, and higher $$\Delta G^{\text{Inject}}$$ and $$\Delta G^{\text{Reg}}$$ values.

Anaerobic Cancer Cell Metabolism and Viability

IntroductionNormal internal human physiologic oxygen levels are hypoxic, ranging from about 0.5 to 14%. However, in solid tumors, there are intra‐tumor niches, which like stem cell niches, are anaerobic. A historical roadblock to studying anaerobic cancer cell metabolism is the inability to maintain cell viability in an oxygen‐free environment for longer than 36 hrs. We previously showed that anaerobic cancerous and non‐cancerous cells, which survive at least 14d of anaerobic culture, exhibit an altered cell phenotype, i.e. diminished attachment capacity, slowed growth rate, and inverse hypoxia inducible factor‐1α mRNA and protein expression relative to anaerobic endogenous reactive oxygen species production. Since bacteria (mitochondrial precursors) use Nitric Oxide (NO) and Hydrogen Sulfide (H2S) as terminal electron acceptors, we focused on determining the role NO and H2S generating pathways play in sustaining anaerobic cancer cell viability.MethodsHeLa 229 cells were grown to 80% confluence in 24 well plates (normoxic conditions, 5% CO2 in air; 10% FBS; DMEM medium) then transferred to degassed PS‐74656 medium (Whitley A35, anaerobic gas mixture: H2, CO2, N2; 37°C). Viability was determined by trypan blue dye exclusion. Anoxic nitric oxide production was determined by fluorescent microscopy (DAF‐2; excitation 491 nm; emission 513 nm), with NO positive cells counted (10 random fields; Mean ± SEM; p < 0.05). Controls consisted of cells from the same lot processed in parallel but anaerobically incubated in control PS‐74656 medium without additional NO and H2S pathway precursors or inhibitors.ResultsUpon anaerobic incubation, NO was detected at days 3 and 10 of culture. NO is a by‐product of the Xanthine Oxidase (XO) and Nitric Oxide Synthase (NOS) pathways. Addition of pathway precursors xanthine (4 × 10−5 M) or arginine (50 mM), respectively, significantly (p < 0.05) increased HeLa cell viability by 3 and 20.9 fold, respectively, at day 10 of anaerobic incubation. Allopurinol (200 μM), an XO pathway inhibitor, inhibited the xanthine induced increase in viability while L‐NAME had a similar effect on arginine‐mediated viability, which was also reduced to control level.To determine if H2S supports HeLa cell anaerobic viability, the effects of H2S pathway precursor cysteine (0.4 mM), and H2S donors JK‐2 (300 μM) and GYY4137 (400 μM) were tested. Overall, any treatment that should increase cellular H2S levels caused significantly (p < 0.05) enhanced viability, as compared to medium alone (cysteine, 3.6; JK‐2, 6.3; and GYY4137, 7.6 fold increases).These results confirm our hypothesis that similar to bacteria, terminal electron donors other than oxygen can function to support tumor cell anaerobic respiration.Support or Funding InformationThis project was supported by research funds from Office of Research and Sponsored Programs (ORSP), Midwestern University, IL, College of Osteopathic Medicine (CCOM) at Midwestern University and College of Graduate Studies (CGS) at Midwestern University with assistance from the MWU Core Facility.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Tracing the Pathways of Waters and Protons in Photosystem II and Cytochrome c Oxidase

Photosystem II (PSII) uses water as the terminal electron donor, producing oxygen in the Mn4CaO5 oxygen evolving complex (OEC), while cytochrome c oxidase (CcO) reduces O2 to water in its heme–Cu binuclear center (BNC). Each protein is oriented in the membrane to add to the proton gradient. The OEC, which releases protons, is located near the P-side (positive, at low-pH) of the membrane. In contrast, the BNC is in the middle of CcO, so the protons needed for O2 reduction must be transferred from the N-side (negative, at high pH). In addition, CcO pumps protons from N- to P-side, coupled to the O2 reduction chemistry, to store additional energy. Thus, proton transfers are directly coupled to the OEC and BNC redox chemistry, as well as needed for CcO proton pumping. The simulations that study the changes in proton affinity of the redox active sites and the surrounding protein at different states of the reaction cycle, as well as the changes in hydration that modulate proton transfer paths, are described.

Molecular Cobalt Catalysts for H2 Generation with Redox Activity and Proton Relays in the Second Coordination Sphere.

Two new Co(II) complexes have been synthesized and investigated as catalysts for H2 generation. These catalysts were designed to incorporate redox-active bipyridine components and nitrogen groups, which can participate in electron and proton transfer steps in the catalytic cycle. The two catalysts differ by only one amino group, yielding a completely closed macrocycle and an open "macrocycle" complex. Removing just one nitrogen linker between the Co(II)-binding bipyridine groups has a profound impact on the molecular geometry observed by single crystal analysis. Photocatalysis experiments show that both catalysts are highly active for aqueous proton reduction at moderate pH levels, with the closed macrocycle reaching almost 2 × 104 turnovers of H2 when photodriven by [Ru(2,2'-bipyridine)3]2+ using ascorbate as an electron relay and a phosphine compound as the terminal electron donor. Measurements of the electrocatalytic activity were used to investigate key steps in the mechanism of proton reduction by the molecular catalysts. The formation of a new reversible peak on addition of moderately strong acids in organic solvents suggests that protonation of the macrocycle plays an important role in H2 generation. Onset of the catalytic current occurs near the reduction potential of the bipyridine components, suggesting that catalysis is mediated by electron transfer from the macrocycle to the cobalt center. From these observations, we propose a mechanism for catalytic proton reduction to H2, which involves both intramolecular proton and electron transfer steps from the macrocycle ligand to the cobalt center. The vital role of the second coordination sphere in the catalytic cycle places these relatively simple complexes on the pathway toward molecular catalysts that mimic the valuable features of enzymatic catalysis.

Ultrafast responses of multi-branched compounds based on 1,3,5-triazine: investigation of the reason for enhanced two-photon absorption property

The fluorescence and ultrafast response of several modified tri-branched compounds based on 1,3,5-triazine (T03-1, T03-2, and T03-3) were investigated to study the effects of stronger electron donor substitution or extended conjugated length on two-photon absorption/two-photon fluorescence and excited-state decay properties. After substitution with a stronger terminal electron donor, N,N-dimethylbenzenamine, the two-photon absorption cross section and fluorescence quantum yield of T03-2 were enhanced by 1.9-fold and 1.4-fold, respectively, compared with T03-1. After extending the conjugated length with thiophene groups connected to π-bridge styryl groups, a similar fluorescence quantum yield and larger two-photon absorption (2.3-fold) of T03-3 were obtained. The ultrafast response processes revealed the effects on the intramolecular charge-transfer properties. These results can also assist in the design of new molecular probes with improved two-photon absorption and two-photon fluorescence properties. Moreover, our study also indicates that these 1,3,5-triazine-based tri-branched derivatives can be employed as molecular probes for biological two-photon fluorescence imaging.

Temporal dynamics of CO2 and CH4 loss potentials in response to rapid hydrological shifts in tidal freshwater wetland soils

Earth System Models predict climate extremes that will impact regional and global hydrology. Aquatic-terrestrial transition zones like wetlands are subjected to the immediate consequence of climate change with shifts in the magnitude and dynamics of hydrologic flow. Such fluctuating hydrology can alter the nature and rate of biogeochemical transformations and significantly impact the carbon balance of the ecosystem. We tested the impacts of fluctuating hydrology and, specifically, the role of antecedent moisture conditions in determining the dominant carbon loss mechanisms in soils sampled from a tidal freshwater wetland system in the lower Columbia River, WA, USA. Our objective was to understand shifts in biogeochemical processes in response to changing soil moisture, based on soil respiration and methane production rates, and to elucidate such responses based on the observed electron acceptor and metabolite profiles under laboratory conditions. Metabolomics and biogeochemical process rates provided evidence that soil redox was the principal factor driving metabolic function. Fluctuating redox conditions altered terminal electron acceptor and donor availability and recovery strengths of their concentrations in soil such that a disproportionate release of carbon dioxide stemmed from alternative anaerobic degradation processes like sulfate and iron reduction compared to carbon loss due to methanogenesis. Our results show that extended and short-term saturation created conditions conducive to increasing metabolite availability for anaerobic decomposition processes, with a significant lag in methanogenesis. In contrast, extended drying caused a cellular-level stress response and rapid recycling of alternate electron acceptors.

Submarine Basaltic Glass Colonization by the Heterotrophic Fe(II)-Oxidizing and Siderophore-Producing Deep-Sea Bacterium Pseudomonas stutzeri VS-10: The Potential Role of Basalt in Enhancing Growth.

Phylogenetically and metabolically diverse bacterial communities have been found in association with submarine basaltic glass surfaces. The driving forces behind basalt colonization are for the most part unknown. It remains ambiguous if basalt provides ecological advantages beyond representing a substrate for surface colonization, such as supplying nutrients and/or energy. Pseudomonas stutzeri VS-10, a metabolically versatile bacterium isolated from Vailulu’u Seamount, was used as a model organism to investigate the physiological responses observed when biofilms are established on basaltic glasses. In Fe-limited heterotrophic media, P. stutzeri VS-10 exhibited elevated growth in the presence of basaltic glass. Diffusion chamber experiments demonstrated that physical attachment or contact of soluble metabolites such as siderophores with the basaltic glass plays a pivotal role in this process. Electrochemical data indicated that P. stutzeri VS-10 is able to use solid substrates (electrodes) as terminal electron donors and acceptors. Siderophore production and heterotrophic Fe(II) oxidation are discussed as potential mechanisms enhancing growth of P. stutzeri VS-10 on glass surfaces. In correlation with that we discuss the possibility that metabolic versatility could represent a common and beneficial physiological trait in marine microbial communities being subject to oligotrophic and rapidly changing deep-sea conditions.