Impact of Triplet Excited States on the Open‐Circuit Voltage of Organic Solar Cells

The best organic solar cells (OSCs) achieve comparable peak external quantum efficiencies and fill factors as conventional photovoltaic devices. However, their voltage losses are much higher, in particular those due to nonradiative recombination. To investigate the possible role of triplet states on the donor or acceptor materials in this process, model systems comprising Zn‐ and Cu‐phthalocyanine (Pc), as well as fluorinated versions of these donors, combined with C₆₀ as acceptor are studied. Fluorination allows tuning the energy level alignment between the lowest energy triplet state (T₁) and the charge‐transfer (CT) state, while the replacement of Zn by Cu as the central metal in the Pcs leads to a largely enhanced spin–orbit coupling. Only in the latter case, a substantial influence of the triplet state on the nonradiative voltage losses is observed. In contrast, it is found that for a large series of typical OSC materials, the relative energy level alignment between T₁ and the CT state does not substantially affect nonradiative voltage losses.     

Modifying Rap1-signalling by targeting Pde6δ is neuroprotective in models of Alzheimer’s disease

Background

Neuronal Ca²⁺ dyshomeostasis and hyperactivity play a central role in Alzheimer’s disease pathology and progression. Amyloid-beta together with non-genetic risk-factors of Alzheimer’s disease contributes to increased Ca²⁺ influx and aberrant neuronal activity, which accelerates neurodegeneration in a feed-forward fashion. As such, identifying new targets and drugs to modulate excessive Ca²⁺ signalling and neuronal hyperactivity, without overly suppressing them, has promising therapeutic potential.

Methods

Here we show, using biochemical, electrophysiological, imaging, and behavioural tools, that pharmacological modulation of Rap1 signalling by inhibiting its interaction with Pde6δ normalises disease associated Ca²⁺ aberrations and neuronal activity, conferring neuroprotection in models of Alzheimer’s disease.

Results

The newly identified inhibitors of the Rap1-Pde6δ interaction counteract AD phenotypes, by reconfiguring Rap1 signalling underlying synaptic efficacy, Ca²⁺ influx, and neuronal repolarisation, without adverse effects in-cellulo or in-vivo. Thus, modulation of Rap1 by Pde6δ accommodates key mechanisms underlying neuronal activity, and therefore represents a promising new drug target for early or late intervention in neurodegenerative disorders.

Conclusion

Targeting the Pde6δ-Rap1 interaction has promising therapeutic potential for disorders characterised by neuronal hyperactivity, such as Alzheimer’s disease.

     

Costs and benefits of admixture between foreign genotypes and local populations in the field

Admixture is the hybridization between populations within one species. It can increase plant fitness and population viability by alleviating inbreeding depression and increasing genetic diversity. However, populations are often adapted to their local environments and admixture with distant populations could break down local adaptation by diluting the locally adapted genomes. Thus, admixed genotypes might be selected against and be outcompeted by locally adapted genotypes in the local environments. To investigate the costs and benefits of admixture, we compared the performance of admixed and within‐population F1 and F2 generations of the European plant Lythrum salicaria in a reciprocal transplant experiment at three European field sites over a 2‐year period. Despite strong differences between site and plant populations for most of the measured traits, including herbivory, we found limited evidence for local adaptation. The effects of admixture depended on experimental site and plant population, and were positive for some traits. Plant growth and fruit production of some populations increased in admixed offspring and this was strongest with larger parental distances. These effects were only detected in two of our three sites. Our results show that, in the absence of local adaptation, admixture may boost plant performance, and that this is particularly apparent in stressful environments. We suggest that admixture between foreign and local genotypes can potentially be considered in nature conservation to restore populations and/or increase population viability, especially in small inbred or maladapted populations.     

Specific Labeling of Stem Cell Activity in Human Colorectal Organoids Using an ASCL2-Responsive Minigene

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Isolation and characterization of lectins and lectin-alliinase complexes from bulbs of garlic (Allium sativum) and ramsons (Allium ursinum)

A procedure developed to separate the homodimeric and heterodimeric mannose-binding lectins from bulbs of garlic (Allium sativum L.) and ramsons (Allium ursinum L.) also enabled the isolation of stable lectin-alliinase complexes. Characterization of the individual lectins indicated that, in spite of their different molecular structure, the homomeric and heteromeric lectins resemble each other reasonably well with respect to their agglutination properties and carbohydrate-binding specificity. However, a detailed analysis of the lectin-alliinase complexes from garlic and ramsons bulbs demonstrated that only the heterodimeric lectins are capable of binding to the glycan chains of the alliinase molecules (EC 4.4.1.4). Moreover, it appears that only a subpopulation of the alliinase molecules is involved in the formation of lectin-alliinase complexes and that the complexed alliinase contains more glycan chains than the free enzyme. Finally, some arguments are given that the lectin-alliinase complexes do not occur in vivo but are formed in vitro after homogenization of the tissue. This revised version was published online in November 2006 with corrections to the Cover Date.     

Isolation,characterization and molecular cloning of the mannose-binding lectins from leaves and roots of garlic (Allium sativum L.)

Two novel lectins were isolated from roots and leaves of garlic. Characterization of the purified proteins indicated that the leaf lectin ASAL is a dimer of two identical subunits of 12 kDa, which closely resembles the leaf lectins from onion, leek and shallot with respect to its molecular structure and agglutination activity. In contrast, the root lectin ASARI, which is a dimer of subunits of 15 kDa, strongly differs from the leaf lectin with respect to its agglutination activity. cDNA cloning of the leaf and root lectins revealed that the deduced amino acid sequences of ASAL and ASARI are virtually identical. Since both lectins have identical N-terminal sequences the larger Mr of the ASARI subunits implies that the root lectin has an extra sequence at its C-terminus. These results not only demonstrate that virtually identical precursor polypeptides are differently processed at their C-terminus in roots and leaves but also indicate that differential processing yields mature lectins with strongly different biological activities. Further screening of the cDNA library for garlic roots also yielded a cDNA clone encoding a protein composed of two tandemly arrayed lectin domains. Since the presumed two-domain root lectin has not been isolated yet, its possible relationship to the previously described two-domain bulb lectin could not be studied at the protein level.     

Isolation,characterization and molecular cloning of a leaf-specific lectin from ramsons (Allium ursinum L.).

Lectins were isolated from roots and leaves of ramsons and compared to the previously described bulb lectins. Biochemical analyses indicated that the root lectins AUAIr and AUAIIr are identical to the bulb lectins AUAI and AUAII, whereas the leaf lectin AUAL has no counterpart in the bulbs. cDNA cloning confirmed that the leaf lectin differs from the bulb lectins. Northern blot analysis further indicated that the leaf lectin is tissue-specifically expressed. Sequence comparisons revealed that the ramsons leaf lectin differs considerably from the leaf lectins of garlic, leek, onion and shallot.     

Two 1 : 1 binding modes for distamycin in the minor groove of d(GGCCAATTGG).

Single-crystal X-ray structure determinations of the complex between the minor-groove binder distamycin and d(GGCCAATTGG) reveal two 1 : 1 binding modes which differ in the orientation of the drug molecule in the minor groove. The two crystals were grown from different crystallization conditions and found to diffract to 2.38 and 1.85 A, respectively. The structures were refined to completion using SHELXL-93, resulting in a residual R factor of 20.30% for the 2.38-A resolution structure (including 46 water molecules) and 19.74% for the 1.85-A resolution structure (including 74 water molecules). In both orientations, bifurcated hydrogen bonds are formed between the amide nitrogen atoms of the drug and AT base pairs. With a binding site of at least five base pairs, close contacts between the terminal distamycin atoms and guanine amino groups are inevitable. The detailed nature of several of these interactions was further investigated by ab initio quantum chemical methods.     

RESURRECTION OF MESOPLODON TRAVERSII (GRAY, 1874), SENIOR SYNONYM OF M. BAHAMONDI REYES, VAN WAEREBEEK, CÁRDENAS AND YÁÑEZ, 1995 (CETACEA: ZIPHIIDAE)

Mesoplodon traversii (Gray, 1874) is shown to be a senior synonym of the recently described beaked whale Mesoplodon hahamondi Reyes et al. , 1995 on the basis of a phylogenetic analysis of mitochondrial DNA control region sequences. The mandible and teeth of M. traversii , first reported in 1873 by Hector as Dolichodon layardii . are redescribed. The species can be distinguished by features of the calvaria; including the large jugal, broad rostrum, and small distance between premaxillary foramina. The male teeth, which are large and spade-shaped with a strong terminal denticle, are also diagnostic. M. traversii is known only from Pitt Island and White Island, New Zealand and Robinson Crusoe Island, Juan Fernandez Archipelago, Chile.