Acceptor Junction Research Articles

Optimization of quinolinium-carbazole theranostics for the improved photooxidation of β-amyloid aggregates with the variation of conjugation site

Alzheimer’s disease (AD), the most prevalent neurodegenerative condition, is characterized by a gradual decline in cognitive function and memory loss. Presently, it ranks as the fifth leading cause of death worldwide. Photodynamic therapy, with its operational flexibility, noninvasive approach, and high spatial and temporal resolution, has emerged as an innovative therapeutic method, enhancing therapeutic efficacy and minimizing systemic toxicity. In this work, we have designed two donor-π-acceptor (D-π-A) type photosensitizers targeting amyloid, differing in the donor and acceptor junction sites. Surprisingly we found that by altering the junction site of the donor and acceptor from the 2-position to the 3-position of carbazole, the binding affinity and singlet oxygen efficiency of compound 3-QM16 improved compared to compound 2-QM16. This modification facilitated β-amyloid imaging and photooxidative therapy. Our study might shed light on the further optimization of the photooxidation performance of photosensitizers on misfolded proteins.

Molecular engineering of benzothiadiazole core based non-fullerene acceptors to tune the optoelectronic properties of perovskite solar cells

Non-fullerene acceptors exhibit durable absorption capacity, and exceptional power conversion efficiency that make them appealing photovoltaic material for use as hole transport materials in perovskite solar cells (PSCs). To interpret the benzothiadiazole as the central-core unit, five novel acceptors (U1-U5) have been successfully fabricated by end-capped engineering. Their electrical and optical performance have been investigated theoretically. Utilizing density functional theory (DFT) and time-dependent DFT computations, we have examined the photo-physical and optoelectronic characteristics. U4 exhibits 3.80 eV optical band gap with an absorption (λmax) of 670.58 nm. Lowest excitation energy (1.85 eV), greater LHE (0.98) and improved PCE (18.31 eV) validate the U4 designed molecule as a brilliant photovoltaic material for PSCs. Outstanding charge transfer at the donor–acceptor junction has also been revealed by thorough analysis of U4/PTB7-Th. Therefore, substitution of alternate functional groups in terminal moieties is efficient for effective PSCs that can be used as photon harvesting materials.

Using the Chou’s 5-steps rule to predict splice junctions with interpretable bidirectional long short-term memory networks

Neural models have been able to obtain state-of-the-art performances on several genome sequence-based prediction tasks. Such models take only nucleotide sequences as input and learn relevant features on their own. However, extracting the interpretable motifs from the model remains a challenge. This work explores various existing visualization techniques in their ability to infer relevant sequence information learnt by a recurrent neural network (RNN) on the task of splice junction identification. The visualization techniques have been modulated to suit the genome sequences as input. The visualizations inspect genomic regions at the level of a single nucleotide as well as a span of consecutive nucleotides. This inspection is performed based on the modification of input sequences (perturbation based) or the embedding space (back-propagation based). We infer features pertaining to both canonical and non-canonical splicing from a single neural model. Results indicate that the visualization techniques produce comparable performances for branchpoint detection. However, in the case of canonical donor and acceptor junction motifs, perturbation based visualizations perform better than back-propagation based visualizations, and vice-versa for non-canonical motifs. The source code of our stand-alone SpliceVisuL tool is available at https://github.com/aaiitggrp/SpliceVisuL.

The crucial role of a spacer material on the efficiency of charge transfer processes in organic donor-acceptor junction solar cells.

Organic photovoltaic donor-acceptor junction devices composed of π-conjugated polymer electron donors (D) and fullerene electron acceptors (A) show greatly increased performance when a spacer material is inserted between the two layers (W. Y. Nie, G. Gupta, B. K. Crone, F. L. Liu, D. L. Smith, P. P. Ruden, C. Y. Kuo, H. Tsai, H. L. Wang, H. Li, S. Tretiak and A. D. Mohite, Adv. Sci., 2015, 2, 1500024.). For instance, experimental results reveal significant improvement of photocurrent when a terthiophene oligomer derivative is inserted in between π-conjugated poly(3-hexylthiophene-2,5-diyl) (P3HT) donor and C60 acceptor. These results indicate favorable charge separation dynamics, which is addressed by our present joint theoretical/experimental study establishing the beneficial alignment of electronic levels due to the specific morphology of the material. Namely, based on the experimental data we have constructed extended structural interface models containing C60 fullerenes and P3HT separated by aligned oligomer chains. Our time-dependent density functional theory (TD-DFT) calculations based on a long-range corrected functional, allowed us to address the energetics of essential electronic states and analyze them in terms of charge transfer (CT) character. Specifically, the simulations reveal the electronic spectra composed of a ladder of excited states evolving excitation toward spatial charge separation: an initial excitonic excitation at P3HT decomposes into charges by sequentially relaxing through bands of C60-centric, oligomer → C60 and P3HT → C60 CT states. Our modeling exposes a critical role of dielectric environment effects and electronic couplings in the self-assembled spacer oligomer layer on the energetics of critical CT states leading to a reduced back-electron transfer, preventing recombination losses, and thus rationalizes physical processes underpinning experimental observations.

Investigation of Current Gain in Superconducting-Ferromagnetic Transistors With High-j ${}_{\rm c}$ Acceptor

We report the results of a study of the current gain in high Josephson critical current density ( j ${}_{\rm c}$ ) superconducting-ferromagnetic transistors with the SISFIFS structure [where S, I, and F denote a superconductor (Nb), an insulator (AlO ${}_{x}$ ), and a ferromagnetic material (permalloy, Py), respectively]. The Nb/AlO ${}_{x}$ /Nb trilayer, which serves as the acceptor (SIS) junction, is estimated to have Josephson critical current density j ${}_{\rm c}$ of 19 kA/cm2. The Al/Py/Al/AlO ${}_{x}$ /Py/Al/Nb multilayer is deposited in a separate vacuum run after in situ ion milling of about 8 nm of the top Nb layer. The devices are patterned using optical lithography and tested at 4.2 K. We have observed a small-signal current gain in the range of 5–9. We demonstrate that proper device engineering allows one to efficiently control the maximum Josephson current in the SISF acceptor junction using the quasiparticle injection.

Comparison of the solution and vacuum-processed quinacridones in homojunction photovoltaics

In this work, we explored industrially relevant pigments quinacridones as organic semiconductors with respect to their applicability in air-stable homojunction (single material-single layer) organic photovoltaic cells. We studied quinacridone and two linear transquinacridones, i.e., Pigment Red 122 (2,9′-dimethylquinacridone) and Pigment Red 202 (2,9′-dichloroquinacridone) in vacuum-processible OPV films and compared their performance to OPV films made from their solution-processed counterparts. We show that this class of materials generates photocurrent without the need of creating a donor–acceptor junction. Stable homojunctions were created both via vacuum-processible and solution-processible routes, with the latter method based on the chemical functionalization of the respective molecules with the thermolabile group, t-BOC, that affords solubility in various organic solvents and conversion back to the parent molecule via exposure to temperatures around 170 °C for periods not exceeding 30 min. We show that power conversion efficiencies around 0.15% are reachable without scrupulous optimization of the homojunction cells in terms of electrode surface functionalization or film deposition conditions. This class of materials holds promise for the further development of a new generation of air-stable organic photovoltaic cells based on simple fabrication technologies.

Critical Current Gain in High-jc Superconducting-Ferromagnetic Transistors

We report experimental and theoretical results on the current gain in superconductor-ferromagnetic transistors (SFTs) with the SISFIFS structure [where S, I, and F denote a superconductor (Nb), an insulator ( ${\rm{AlO}}_{x}$ ), and a ferromagnetic material (Ni), respectively]. The Josephson critical current density $j_{{\rm{ca}}}$ of the acceptor (SISF) junction in the devices is above 9 kA/cm2, which is higher than that in our previous devices. The critical current gain is defined as $ \vert \delta I_{{\rm{ca}}}\vert / \vert \delta I_{i}\vert $ , where a change $\vert \delta I_{i}\vert $ in the injector (SFIFS junction) current produces a change $\vert \delta I_{{\rm{ca}}}\vert $ in the acceptor maximum Josephson current. We observed a small-signal gain as high as 7.8 and a large-signal current gain of about 2.2. In addition, we found that the Josephson current of the acceptor junction is sensitive to the state of the ferromagnetic layers. A theoretical model is proposed to describe the nonequilibrium processes in the SFT devices, which agrees with the experimental observations. The calculation shows that, in the present device configuration, the dominant contribution to the gap suppression in the middle Nb electrode is due to the quasiparticle injection; spin injection plays a secondary role. We demonstrate that proper device engineering allows one to efficiently control the maximum Josephson current in the SISF acceptor junction using the quasiparticle injection. We conclude that SFT devices can be used as input/output isolators and amplifiers for memory, digital, and RF applications.

Solution-processed organic trilayer solar cells incorporating conjugated polyelectrolytes

We report solution-processed organic trilayer solar cells consisting of a bottom poly(3-hexylthiophene) (P3HT) layer, a conjugated polyelectrolyte (CPE) interlayer and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) top layer, wherein the CPE exists as an interlayer within the donor–acceptor junction. The influence of interlayer thickness on device properties was investigated, as well as the behavior of molecular dipoles in the trilayer solar cells when influenced by external electrical stimuli. We found that incorporation of an interlayer which is too thick results in decreased performance due to reduced short-circuit current (JSC), open-circuit voltage (VOC), and fill factor (FF). However the VOC is found to increase significantly when a thin CPE layer is used in conjunction with an external electric field. These results provide an experimental approach to probe the influence of interfacial dipoles on the solar cell parameters and behavior of charge separating organic donor/acceptor junctions, yielding fundamental information about the influence of electrical dipoles on the donor/acceptor interface in organic solar cells.

Superconducting-Ferromagnetic Transistor

We report experimental results on the dc and ac characterization of multiterminal SFIFSIS devices (where S, I, and F denote a superconductor (Nb), an insulator (AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ), and a ferromagnetic material (Ni), respectively), which display transistor-like properties. We investigated two types of such superconducting-ferromagnetic transistors (SFTs): ordinary devices with a single acceptor (SIS) junction, and devices with a double acceptor. The devices with the single SIS acceptor were investigated and demonstrated a modulation of the maximum Josephson current as a function of the SFIFS current injection level. For devices of the second type, by applying an ac signal (in the kilohertz range) with a constant dc bias current to the injector (SFIFS) junction, we observed a voltage gain of about 25 on the double acceptor with the operating point chosen in the subgap region of the acceptor current-voltage characteristic. We also observed an excellent input-output isolation in our SFIFSIS devices. The experiments indicate that, after optimization of the device parameters, they can be used as input/output isolators and amplifiers for memory, digital, and RF applications.

Long-term clinical outcome and carrier phenotype in autosomal recessive hypophosphatemia caused by a novel DMP1 mutation

Homozygous inactivating mutations in DMP1 (dentin matrix protein 1), the gene encoding a noncollagenous bone matrix protein expressed in osteoblasts and osteocytes, cause autosomal recessive hypophosphatemia (ARHP). Herein we describe a family with ARHP owing to a novel homozygous DMP1 mutation and provide a detailed description of the associated skeletal dysplasia and carrier phenotype. The two adult patients with ARHP, a 78-year-old man and his 66-year-old sister, have suffered from bone pain and lower extremity varus deformities since early childhood. With increasing age, both patients developed severe joint pain, contractures, and complete immobilization of the spine. Radiographs showed short and deformed long bones, significant cranial hyperostosis, enthesopathies, and calcifications of the paraspinal ligaments. Biochemistries were consistent with hypophosphatemia owing to renal phosphate wasting; markers of bone turnover and serum fibroblast growth factor 23 (FGF-23) levels were increased significantly. Nucleotide sequence analysis of DMP1 revealed a novel homozygous mutation at the splice acceptor junction of exon 6 (IVS5-1G > A). Two heterozygous carriers of the mutation also showed mild hypophosphatemia, and bone biopsy in one of these individuals showed focal areas of osteomalacia. In bone, DMP1 expression was absent in the homozygote but normal in the heterozygote, whereas FGF-23 expression was increased in both subjects but higher in the ARHP patient. The clinical and laboratory observations in this family confirm that DMP1 has an important role in normal skeletal development and mineral homeostasis. The skeletal phenotype in ARHP may be significantly more severe than in other forms of hypophosphatemic rickets. © 2010 American Society for Bone and Mineral Research.

The magneto conductance responses in polymer photovoltaic devices

This article studies the magneto conductance (MC) responses of regioregular poly(3-hexylthiophene) (P3HT)-based polymer photovoltaic devices. The net MC results of devices are the sum of the positive and negative MC effects. The positive MC effect is due to the increased population of the singlet polaron-pair (PP) states (of the high dissociation rate to charge carriers) under the magnetic field. The negative MC effect results from the decline on the triplet exciton–charge reactions to charge carriers (the mobility and concentration of triplet excitons are decreased by the magnetic field). The MC responses of P3HT-based photovoltaic devices can be manipulated by the applied magnetic field, the electrical bias, the built-in potential, and the interfacial dipole layer. An inversion in the MC response is observed at the electrical bias near the open-circuit voltage. In addition, blending of an electron acceptor material, [6,6]-phenyl C61-butyric acid methyl ester, in P3HT active layer quenches the photo-excited states at the donor–acceptor interface and results in distinct MC responses of photovoltaic cells, which probably are related to the features indicating the formation of inter-molecular charge–transfer complexes at donor–acceptor junction.

A superconducting transistor with improved isolation between the input and outputterminals

A new design for a multi-terminal superconducting transistor-like device exploiting tunnellinginjection of quasiparticles is proposed, in which parasitic back-action of the acceptor junction (S1IS2) bias current on theinjector junction (S2FIS3) current–voltage characteristic (CVC) is dramatically reduced as compared with that forthe formerly reported quiteron (here S, I, and F denote a superconductor, aninsulator and a ferromagnetic material). Improvement of the isolation is achievedowing to the short electron mean free path and short coherence length ina thin F layer that screens the superconducting energy gap in the perturbedS2 layer preventing its manifestation in the CVC of the injector.

A superconducting transistorlike device having good input-output isolation.

A multiterminal superconducting device with the S1IS2FIS3 structure (where S, I, and F denote a superconductor, an insulator, and a ferromagnetic material) is fabricated and characterized. Introducing a thin ferromagnetic layer into the middle electrode dramatically reduces parasitic back action of the acceptor junction (S1IS2) bias current on the injector junction (S2FIS3) current-voltage characteristic as compared with that for the formerly reported quiteron, a device exploiting similar operation principle.

Analysis of the excited states of regioregular polythiophene P3HT

Poly(3-hexylthiophene) (P3HT) [90–93% regioregular, Mw ∼55 kDa, PDI <2] is studied by transient absorption spectroscopy and the properties of excited state P3HT in solution and thin film contrasted. In solution, excitation of P3HT yields the first singlet state which has a characteristic lifetime of ∼600 ps, and a measured high quantum yield of fluorescence in chlorobenzene solution of 0.33 ± 0.07. The long lived (∼μs) species in solution is ascribed to the P3HT triplet state, formed by intersystem crossing from the singlet state with a lifetime of around 300 ns in aerated chlorobenzene solution. By contrast the properties of P3HT in the solid state are very different to that in solution. The quantum yield of fluorescence is found to be reduced to only 0.02 ± 0.001 and transient absorption data show the presence of two species in P3HT on a ∼500 ps timescale, one with a lifetime of less than 500 ps and the other a longer lived nanosecond time region decay which follows a bimolecular recombination pattern. Alongside the different kinetics, both short and long lived species also show contrasting transient absorption spectra and therefore are assigned to two different species in P3HT thought to be the singlet emissive state of P3HT and charged species/polaron state respectively. Analysis of the decay kinetics suggest that P3HT singlet emissive states in the film do not decay into polaron states and therefore polaron formation must originate on earlier timescales. The competitive formation of polarons compared to emissive states in P3HT film could be exploited to generate power in organic solar cell devices more efficiently than is currently possible with donor–acceptor junction organic solar cells.

A point mutation within CD45 exon A is the cause of variant CD45RA splicing in humans.

The leukocyte common antigen (CD45) is alternatively spliced, generating various isoforms expressed on hemopoietic cells. The splicing pattern of CD45 in T cells is altered in some individuals who show abnormal expression of high molecular weight isoforms containing exon A. The variant splicing pattern was shown to be associated with heterozygosity for a silent point mutation within CD45 exon A. This C to G transition is located 77 nucleotides downstream of the splice acceptor junction of exon A (198 bp total length). Here we report that this mutation is the cause of abnormal splicing. To isolate the mutant gene, somatic cell hybrids of lymphocytes with a CD45 splicing defect and a mouse lymphoid line were produced and clones expressing different isoforms of CD45 were isolated. Expression of the high molecular weight isoform containing exon A was associated with the mutation within exon A. All hybrids expressing the low molecular weight isoforms lacking exon A contained the normal allele of CD45 only. In addition, minigenes including this mutation were constructed and transfected into various cell lines (COS-7, HeLa, CHO). Semi-quantitative reverse transcription polymerase chain reaction showed an increase of more than tenfold in splicing to CD45RA (concomitant with a decrease in splicing to CD45RO) when compared with the normal minigene. Taken together, these results demonstrate a causal relationship between the mutation in CD45 exon A and the variant splicing pattern observed. The involvement of trans-acting splicing factors that interact with this region of CD45 pre-mRNA is currently under investigation.

Structure and conformation of the duplex consensus acceptor exon:intron junction d[(CpTpApCpApGpGpT). (ApCpCpTpGpTpApG)] deduced from high-field 1H-NMR of non-exchangeable and imino protons.

The complementary consensus acceptor exon:intron junction d(ApCpCpTpGpTpApG) has been synthesized by a modified phosphotriester method. The non self-complementary octamer exists in the random coil form in aqueous buffer at 20 degrees C as evidenced by temperature variable 1H-NMR and NOE measurements. The non-exchangeable proton assignments were secured using a combination of techniques including two-dimensional COSY, NOESY and 1H-1H-INADEQUATE. The octamer was annealed with the primary consensus sequence d(CpTpApCpApGpGpT). Confirmation of complete duplex formation was confirmed by detection and assignment of imino protons in D2O:H2O mixtures. Assignment of the non-exchangeable proton signals in the duplex consensus junction was then secured by a combination of two-dimensional COSY correlations, NOESY and NOE experiments. Determination of individual vicinal coupling constants in the component deoxyribose moieties permitted deduction of the population of S conformations in this sequence. It is concluded that the consensus acceptor junction exists in solution in a conformation belonging to the B family, and that the bases are oriented anti. In addition the deoxyribose moieties in the 5' regions exist predominantly in the S form (2'endo-3'exo) whereas those residues on or adjacent to the junction on the primary strand show more N character (2'exo-3'endo). The contiguous bases A5-G6 (adjacent to the junction) and A15-G16 are stacked more closely than the other neighbor bases in this duplex sequence. These subtle structural and conformational differences in the exon:intron junction may serve as recognition signals for these critical sites in the genome.