Spontaneous Exciton Dissociation at Organic Semiconductor Interfaces Facilitated by the Orientation of the Delocalized Electron–Hole Wavefunction

In organic semiconductors, optical excitation does not necessarily produce free carriers. Very often, electron and hole are bound together to form an exciton. Releasing free carriers from the exciton is essential for the functioning of photovoltaics and optoelectronic devices, but it is a bottleneck process because of the high exciton binding energy. Inefficient exciton dissociation can limit the efficiency of organic photovoltaics. Here, nanoscale features that can allow the free carrier generation to occur spontaneously despite being an energy uphill process are determined. Specifically, by comparing the dissociation dynamics of the charge transfer (CT) exciton at two donor–acceptor interfaces, it is found that the relative orientation of the electron and hole wavefunction within a CT exciton plays an important role in determining whether the CT exciton will decompose into the higher energy free electron–hole pair or relax to the lower energy tightly‐bound CT exciton. The concept of the entropic driving force is combined with the structural anisotropy of typical organic crystals to devise a framework that can describe how the orientation of the delocalized electronic wavefunction can be manipulated to favor the energy‐uphill spontaneous dissociation of CT excitons over the energy‐downhill CT exciton cooling.     

Luciferase-based reporter system for in vitro evaluation of elongation rate and processivity of ribosomes

The elongation step of translation is a key contributor to the abundance, folding and quality of proteins and to the stability of mRNA. However, control over translation elongation has not been thoroughly investigated. In this study, a Renilla–firefly luciferase fusion reporter system was further developed to investigate the in vitro elongation rate and processivity of ribosomes independent of the initiation and termination steps. The reporter mRNA was constructed to contain a single ORF encoding in-frame Renilla luciferase, a specific domain moiety and firefly luciferase. Such a reporter structure enables the quantitative and individual evaluation of the synthesis of a specific domain. As a proof of principle, the synthesis of three protein domains of different lengths and structures was analyzed. Using a cell-free translation assay, both the elongation rate and processivity of ribosomes were shown to vary depending on the domain synthesized. Additionally, a stalling sequence consisting of ten rare arginine codons notably reduced the elongation rate and the processivity of the ribosomes. All these results are consistent with the previously known dynamics of elongation in vivo. Overall, the methodology presented in this report provides a framework for studying aspects that contribute to the elongation step of translation.     

RAN-Binding Protein 9 is Involved in Alternative Splicing and is Critical for Male Germ Cell Development and Male Fertility

As a member of the large Ran-binding protein family, Ran-binding protein 9 (RANBP9) has been suggested to play a critical role in diverse cellular functions in somatic cell lineages in vitro, and this is further supported by the neonatal lethality phenotype in Ranbp9 global knockout mice. However, the exact molecular actions of RANBP9 remain largely unknown. By inactivation of Ranbp9 specifically in testicular somatic and spermatogenic cells, we discovered that Ranbp9 was dispensable for Sertoli cell development and functions, but critical for male germ cell development and male fertility. RIP-Seq and proteomic analyses revealed that RANBP9 was associated with multiple key splicing factors and directly targeted >2,300 mRNAs in spermatocytes and round spermatids. Many of the RANBP9 target and non-target mRNAs either displayed aberrant splicing patterns or were dysregulated in the absence of Ranbp9. Our data uncovered a novel role of Ranbp9 in regulating alternative splicing in spermatogenic cells, which is critical for normal spermatogenesis and male fertility.     

Tracking a century of change in trophic structure and dynamics in a floodplain wetland: integrating palaeoecological and palaeoisotopic evidence

相似文献   

Recent ecological change in a remote Scottish mountain loch: An evaluation of a Cladocera-based temperature transfer-function

Recent ecological changes in a small Scottish mountain loch, Loch Coire Fionnaraich (LCFR), were inferred using Cladocera analysis and an application of a Cladocera-based temperature transfer-function approach. Modern assemblages of Cladocera from 68 mountain lakes in Scotland and Norway were used to derive the transfer function. Among 21 measured environmental variables, mean summer lake surface-water temperature (LSWT) accounted for the highest (8%) variation in a redundancy analysis of the modern data. A quantitative inference model (r² = 0.72, RMSEP = 1.81 °C) for summer LSWT was developed using linear partial least squares regression and calibration. The resulting reconstructed summer LSWT at LCFR was compared with local instrumental air-temperature records over the last 20 yr and the Central England Temperature (CET) series over the last 110 yr. The reconstruction showed a broadly similar pattern to the local instrumental temperature records. However, the relationship between the longer CET series and reconstructed summer LSWT was poor suggesting that the site was relatively insensitive to temperature changes prior to the recent warming of the last few decades. Clear changes in Cladoceran species diversity and relative abundance of littoral taxa coincident with the most recent period of climate warming recorded both locally and in the CET suggest that Cladocera do respond to climate change. However, their response to temperature is complex and indirect. The underlying mechanism leading to change in Cladocera assemblages may involve changes in trophic status and habitat availability of the system. It is concluded that understanding other factors such as atmospheric pollution, controls of community dynamics of Cladocera and the overall ecological complexity of mountain lakes is required before any reliance can be placed on a Cladocera-temperature transfer-function for reconstructing climatic change.     

Palaeocladocerans as indicators of environmental, cultural and archaeological developments in Eifel maar lakes region (West Germany) during the Lateglacial and Holocene periods

The use of subfossil cladocerans is rare for understanding environmental, cultural and archaeological developments of lakes in Europe. In 2007, we collected a 12-m long sediment core from Lake Schalkenmehrener Maar (SMM), Germany for the analyses of subfossil cladocerans. Dating of core was based on tephrochronology, radiocarbon and pollen stratigraphy. Pollen-based chronostratigraphy indicated a decline of species richness and abundance of chydorids during the Lateglacial (ca.14500?cal?yr?bp) with dominant cold preferring taxa Acroperus harpae Baird and Alona affinis Leydig. During the early B?lling, the abundance of cladocerans increased commensurate with growth of birch (Betula L.) and pine (Pinus L.) trees. Except a spike of Bosmina coregoni Baird during the Younger Dryas, cladoceran assemblages remained stable from the B?lling to the mid-Atlantic period. During the Neolithic (ca. 4300?bc), the abundance of B. coregoni increased sharply with reciprocal decrease in Daphnia. However, as soon as Daphnia was dominant (ca. 4250?bc), a reciprocal decline in abundance of B. coregoni occurred. The mid-Holocene change in cladoceran abundance coincided with the use of hardwood forest. This situation ended at ca. 4000?bc and remained unchanged throughout the Neolithic and Bronze Age (ca. 3000?C1200?bc). Low Daphnia abundance indicated reduced water quality in the Hunsr??ck-Eifel culture (ca. 800?bc). A spike of B. coregoni at ca. ad 150 indicates construction of the Roman Villa Rustica and extensive farming. However, reoccurrence of Daphnia at ca. ad 470 indicates the retreat of the Romans from the Eifel region. From the early Frankish rule (ca. ad 500) to the Medieval period (ca. ad 1500), species richness reduced but abundance of B. coregoni increased indicating a switch in lake ecosystem. The loss of species richness and the lack of precise evidence of the human activity in the region in the past have impeded the restoration of the ecosystem of the Lake SMM.     

Shape‐Controlled CO2 Electrochemical Reduction on Nanosized Pd Hydride Cubes and Octahedra

Electrochemical CO₂ reduction reaction (CO₂RR) provides a potential pathway to mitigate challenges related to CO₂ emissions. Pd nanoparticles have shown interesting properties as CO₂RR electrocatalysts, while how different facets of Pd affect its performance in CO₂ reduction to synthesis gas with controlled H₂ to CO ratios has not been understood. Herein, nanosized Pd cubes and octahedra particles dominated by Pd(100) and Pd(111) facets are, respectively, synthesized. The Pd octahedra particles show higher CO selectivity (up to 95%) and better activity than Pd cubes and commercial particles. For both Pd octahedra and cubes, the ratio of H₂/CO products is tunable between 1 and 2, a desirable ratio for methanol synthesis and the Fischer–Tropsch processes. Further studies of Pd octahedra in a 25 cm² flow cell show that a total CO current of 5.47 A is achieved at a potential of 3.4 V, corresponding to a CO partial current density of 220 mA cm^?2. In situ X‐ray absorption spectroscopy studies show that regardless of facet Pd is transformed into Pd hydride (PdH) under reaction conditions. Density functional theory calculations show that the reduced binding energies of CO and HOCO intermediates on PdH(111) are key parameters to the high current density and Faradaic efficiency in CO₂ to CO conversion.     

The Multicenter Aerobic Iron Respiratory Chain of Acidithiobacillus ferrooxidans Functions as an Ensemble with a Single Macroscopic Rate Constant

Electron transfer reactions among three prominent colored proteins in intact cells of Acidithiobacillus ferrooxidans were monitored using an integrating cavity absorption meter that permitted the acquisition of accurate absorbance data in suspensions of cells that scattered light. The concentrations of proteins in the periplasmic space were estimated to be 350 and 25 mg/ml for rusticyanin and cytochrome c, respectively; cytochrome a was present as one molecule for every 91 nm² in the cytoplasmic membrane. All three proteins were rapidly reduced to the same relative extent when suspensions of live bacteria were mixed with different concentrations of ferrous ions at pH 1.5. The subsequent molecular oxygen-dependent oxidation of the multicenter respiratory chain occurred with a single macroscopic rate constant, regardless of the proteins'' in vitro redox potentials or their putative positions in the aerobic iron respiratory chain. The crowded electron transport proteins in the periplasm of the organism constituted an electron conductive medium where the network of protein interactions functioned in a concerted fashion as a single ensemble with a standard reduction potential of 650 mV. The appearance of product ferric ions was correlated with the reduction levels of the periplasmic electron transfer proteins; the limiting first-order catalytic rate constant for aerobic respiration on iron was 7,400 s⁻¹. The ability to conduct direct spectrophotometric studies under noninvasive physiological conditions represents a new and powerful approach to examine the extent and rates of biological events in situ without disrupting the complexity of the live cellular environment.     

Role of Telokin in Regulating Murine Gastric Fundus Smooth Muscle Tension

Telokin phosphorylation by cyclic GMP-dependent protein kinase facilitates smooth muscle relaxation. In this study we examined the relaxation of gastric fundus smooth muscles from basal tone, or pre-contracted with KCl or carbachol (CCh), and the phosphorylation of telokin S13, myosin light chain (MLC) S19, MYPT1 T853, T696, and CPI-17 T38 in response to 8-Bromo-cGMP, the NO donor sodium nitroprusside (SNP), or nitrergic neurotransmission. We compared MLC phosphorylation and the contraction and relaxation responses of gastric fundus smooth muscles from telokin^-/- mice and their wild-type littermates to KCl or CCh, and 8-Bromo-cGMP, SNP, or nitrergic neurotransmission, respectively. We compared the relaxation responses and telokin phosphorylation of gastric fundus smooth muscles from wild-type mice and W/W ^V mice which lack ICC-IM, to 8-Bromo-cGMP, SNP, or nitrergic neurotransmission. We found that telokin S13 is basally phosphorylated and that 8-Bromo-cGMP and SNP increased basal telokin phosphorylation. In muscles pre-contracted with KCl or CCh, 8-Bromo-cGMP and SNP had no effect on CPI-17 or MYPT1 phosphorylation, but increased telokin phosphorylation and reduced MLC phosphorylation. In telokin^-/- gastric fundus smooth muscles, basal tone and constitutive MLC S19 phosphorylation were increased. Pre-contracted telokin^-/- gastric fundus smooth muscles have increased contractile responses to KCl, CCh, or cholinergic neurotransmission and reduced relaxation to 8-Bromo-cGMP, SNP, and nitrergic neurotransmission. However, basal telokin phosphorylation was not increased when muscles were stimulated with lower concentrations of SNP or when the muscles were stimulated by nitrergic neurotransmission. SNP, but not nitrergic neurotransmission, increased telokin Ser13 phosphorylation in both wild-type and W/W ^V gastric fundus smooth muscles. Our findings indicate that telokin may play a role in attenuating constitutive MLC phosphorylation and provide an additional mechanism to augment gastric fundus mechanical responses to inhibitory neurotransmission.