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991.
《Current Applied Physics》2015,15(11):1318-1323
The electroreflectance (ER) and current–voltage (J–V) of InAs/InGaAs dots in a well (DWELL) solar cell (SC) were measured to examine the optical and electrical properties. To investigate the carrier capturing and escaping effects in the quantum dot (QD) states the above and below optical biases of the GaAs band gap were used. In the reverse bias region of the J–V curve, the tunneling effect in the QD states was observed at low temperature. The ideality factors (n) were calculated from the J–V curves taken from various optical bias intensities (Iex). The changes in the ideality factor (n) and short circuit current (JSC) were attributed mainly to carrier capture at low temperature, whereas the carrier escaping effect was dominant at room temperature. ER measurements revealed a decrease in the junction electric field (FJ) due to the photovoltaic effect, which was independent of the optical bias source at the same temperature. At low temperature, the reduction of photovoltaic effect could be explained by the enhancement carrier capturing effect due to the strong carrier confinement in QDs. 相似文献
992.
Investigation of laterally single-diffused metal oxide semiconductor (LSMOS) field effect transistor
《Current Applied Physics》2015,15(10):1130-1133
We propose a distinct approach to implement a laterally single diffused metal-oxide-semiconductor (LSMOS) FET with only one impurity doped p-n junction. In the LSMOS, a single p-n junction is first created using lateral dopant diffusion. The channel is formed in the p region of the p-n junction and the n region acts as the drift region. Two distinct metals of different work function are used to form the “n+” source/drain regions and “p+” body contact using the charge plasma concept. We demonstrate that the LSMOS is similar in performance to a laterally double diffused metal-oxide-semiconductor (LDMOS) although it has only one impurity doped p-n junction. The LSMOS exhibits a breakdown voltage of ∼50.0 V, an average ON-resistance of 48.7 mΩ-mm2 and a peak transconductance of 53.6 μS/μm similar to that of a comparable LDMOS. 相似文献
993.
In this study, alleviation of ion suppression effect in sonic spray ionization mass spectrometry (SSI‐MS) was investigated. Ion suppression effect was firstly compared between electrospray ionization (ESI) and conventional SSI, and more severe ion suppression effect was observed with SSI. Ion suppression effect of SSI was also found difficult to be alleviated by simply optimizing major parameters. Alternatively, we found that with the assistance of an alternating current (AC) voltage with low amplitude, the ion suppression effect was greatly alleviated (comparable with conventional ESI). That AC voltage was applied outside the SSI spray tip, and no direct contact between the electrode and spray solution was necessary. Besides the alleviation of the ion suppression effect, this newly‐developed method, termed as induced electrosonic spray ionization (IESSI), appeared to preserve similar charge state distribution with SSI for protonated cytochrome c, hemoglobin, and bradykinin. IESSI could also obtain significantly improved ion intensities (~1000‐fold over conventional SSI). In addition, tolerance of concentrated salts for IESSI‐MS was investigated through the analysis of cytochrome c in the presence of concentrated sodium chloride (NaCl) or ammonium acetate (NH4OAc). Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
994.
Min Cheng Daoyuan Kang Xiaoli Zhang Huawei Yin Yuhong Wang 《Crystal Research and Technology》2015,50(4):331-337
Comparing with the traditional concentric rotation method (rotation radius is 0 cm), the effects of different rotation radii on the growth rate of KDP crystals were studied by experimental methods. It was found that with the increase of rotation radius from 0 cm, the growth rate of each direction of crystals first increased and then decreased in a size‐unchanged vessel. The smaller the distance between the crystal and vessel wall, the less the growth rate. This phenomenon was named the “wall collision effect”. Also, the value of growth rate reached a maximum when the rotation radius was about half of its allowable largest value in the size‐unchanged vessel. In addition, an increase of the rotation radius could improve the crystal growth rate under the same linear velocity of crystal movement. Finally, the uniformity of crystal growth has also been analyzed compared with the concentric rotation radius. It was found that the uniformity of crystal growth was best when the rotation radius was half of its allowable maximum value, and it was more conducive to the actual application of KDP crystals. 相似文献
995.
Cucurbit[7]uril: A High‐Affinity Host for Encapsulation of Amino Saccharides and Supramolecular Stabilization of Their α‐Anomers in Water
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Yoonjung Jang Dr. Ramalingam Natarajan Dr. Young Ho Ko Prof. Dr. Kimoon Kim 《Angewandte Chemie (International ed. in English)》2014,53(4):1003-1007
Cucurbit[7]uril (CB[7]), an uncharged and water‐soluble macrocyclic host, binds protonated amino saccharides (D ‐glucosamine, D ‐galactosamine, D ‐mannosamine and 6‐amino‐6‐deoxy‐D ‐glucose) with excellent affinity (Ka=103 to 104 M ?1). The host–guest complexation was confirmed by NMR spectroscopy, isothermal titration calorimetry (ITC), and MALDI‐TOF mass spectral analyses. NMR analyses revealed that the amino saccharides, except D ‐mannosamine, are bound as α‐anomers within the CB[7] cavity. ITC analyses reveal that CB[7] has excellent affinity for binding amino saccharides in water. The maximum affinity was observed for D ‐galactosamine hydrochloride (Ka=1.6×104 M ?1). Such a strong affinity for any saccharide in water using a synthetic receptor is unprecedented, as is the supramolecular stabilization of an α‐anomer by the host. 相似文献
996.
Organozinc Pivalate Reagents: Segregation,Solubility, Stabilization,and Structural Insights
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Dr. Alberto Hernán‐Gómez Emma Herd Prof. Eva Hevia Dr. Alan R. Kennedy Prof. Dr. Paul Knochel Prof. Dr. Konrad Koszinowski Sophia M. Manolikakes Prof. Robert E. Mulvey Christoph Schnegelsberg 《Angewandte Chemie (International ed. in English)》2014,53(10):2706-2710
The pivalates RZnOPiv?Mg(OPiv)X?n LiCl (OPiv=pivalate; R=aryl; X=Cl, Br, I) stand out amongst salt‐supported organometallic reagents, because apart from their effectiveness in Negishi cross‐coupling reactions, they show more resistance to attack by moist air than conventional organometallic compounds. Herein a combination of synthesis, coupling applications, X‐ray crystallographic studies, NMR (including DOSY) studies, and ESI mass spectrometric studies provide details of these pivalate reagents in their own right. A p‐tolyl case system shows that in [D8]THF solution these reagents exist as separated Me(p‐C6H4)ZnCl and Mg(OPiv)2 species. Air exposure tests and X‐ray crystallographic studies indicate that Mg(OPiv)2 enhances the air stability of aryl zinc species by sequestering H2O contaminants. Coupling reactions of Me(p‐C6H4)ZnX (where X=different salts) with 4‐bromoanisole highlight the importance of the presence of Mg(OPiv)2. Insight into the role of LiCl in these multicomponent mixtures is provided by the molecular structure of [(THF)2Li2(Cl)2(OPiv)2Zn]. 相似文献
997.
Interaction with the Surrounding Water Plays a Key Role in Determining the Aggregation Propensity of Proteins
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Dr. Song‐Ho Chong Prof. Sihyun Ham 《Angewandte Chemie (International ed. in English)》2014,53(15):3961-3964
Understanding the molecular determinants of the relative propensities of proteins to aggregate in a cellular environment is a central issue for treating protein‐aggregation diseases and developing peptide‐based therapeutics. Despite the expectation that protein aggregation can largely be attributed to direct protein–protein interactions, a crucial role the surrounding water in determining the aggregation propensity of proteins both in vitro and in vivo was identified. The overall protein hydrophobicity, defined solely by the hydration free energy of a protein in its monomeric state sampling its equilibrium structures, was shown to be the predominant determinant of protein aggregation propensity in aqueous solution. Striking discrimination of positively and negatively charged residues by the surrounding water was also found. This effect depends on the protein net charge and plays a crucial role in regulating the solubility of the protein. These results pave the way for the design of aggregation‐resistant proteins as biotherapeutics. 相似文献
998.
Synthesis and Properties of Semiconducting Bispyrrolothiophenes for Organic Field‐Effect Transistors
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Crystalann Jones Dr. Damien Boudinet Dr. Yu Xia Mitch Denti Adita Das Dr. Antonio Facchetti Prof. Dr. Tom G. Driver 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(20):5938-5945
A series of new highly soluble bispyrrolothiophenes were synthesized from vinyl azides by using transition‐metal‐catalyzed C?H‐bond functionalization. In addition to modifying the substituents present on the end‐pyrrolothiophene moieties, the arene linker in between the two units was also varied. The solution‐state properties and field‐effect‐transistor (FET) electrical behavior of these bispyrrolothiophenes was compared. Our investigations identified that the optical properties and oxidation potential of our compounds were dominated by the pyrrolothiophene unit with a λmax value of approximately 400 nm and oxidation at approximately 1 V. FET devices constructed with thin films of these bispyrrolothiophenes were also fabricated by means of thin‐film solution processing. One of these compounds, a bispyrrolothiophene linked with benzothiodiazole, exhibits a mobility of approximately 0.3 cm2 V?1 s?1 and the Ion/Ioff value is greater than 106. 相似文献
999.
Phenothiazine–BODIPY–Fullerene Triads as Photosynthetic Reaction Center Models: Substitution and Solvent Polarity Effects on Photoinduced Charge Separation and Recombination
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Chandra B. KC Gary N. Lim Dr. Vladimir N. Nesterov Prof. Dr. Paul A. Karr Prof. Dr. Francis D'Souza 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(51):17100-17112
Novel photosynthetic reaction center model compounds of the type donor2–donor1–acceptor, composed of phenothiazine, BF2‐chelated dipyrromethene (BODIPY), and fullerene, respectively, have been newly synthesized using multistep synthetic methods. X‐ray structures of three of the phenothiazine‐BODIPY intermediate compounds have been solved to visualize the substitution effect caused by the phenothiazine on the BODIPY macrocycle. Optical absorption and emission, computational, and differential pulse voltammetry studies were systematically performed to establish the molecular integrity of the triads. The N‐substituted phenothiazine was found to be easier to oxidize by 60 mV compared to the C‐substituted analogue. The geometry and electronic structures were obtained by B3LYP/6‐31G(dp) calculations (for H, B, N, and O) and B3LYP/6‐31G(df) calculations (for S) in vacuum, followed by a single‐point calculation in benzonitrile utilizing the polarizable continuum model (PCM). The HOMO?1, HOMO, and LUMO were, respectively, on the BODIPY, phenothiazine and fullerene entities, which agreed well with the site of electron transfer determined from electrochemical studies. The energy‐level diagram deduced from these data helped in elucidating the mechanistic details of the photochemical events. Excitation of BODIPY resulted in ultrafast electron transfer to produce PTZ–BODIPY.+–C60.?; subsequent hole shift resulted in PTZ.+–BODIPY–C60.? charge‐separated species. The return of the charge‐separated species was found to be solvent dependent. In nonpolar solvents the PTZ.+–BODIPY–C60.? species populated the 3C60* prior to returning to the ground state, while in polar solvent no such process was observed due to relative positioning of the energy levels. The 1BODIPY* generated radical ion‐pair in these triads persisted for few nanoseconds due to electron transfer/hole‐shift mechanism. 相似文献
1000.
Mechanistic Insights into RNA Transphosphorylation from Kinetic Isotope Effects and Linear Free Energy Relationships of Model Reactions
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Haoyuan Chen Dr. Timothy J. Giese Dr. Ming Huang Prof. Dr. Kin‐Yiu Wong Prof. Dr. Michael E. Harris Prof. Dr. Darrin M. York 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(44):14336-14343
Phosphoryl transfer reactions are ubiquitous in biology and the understanding of the mechanisms whereby these reactions are catalyzed by protein and RNA enzymes is central to reveal design principles for new therapeutics. Two of the most powerful experimental probes of chemical mechanism involve the analysis of linear free energy relations (LFERs) and the measurement of kinetic isotope effects (KIEs). These experimental data report directly on differences in bonding between the ground state and the rate‐controlling transition state, which is the most critical point along the reaction free energy pathway. However, interpretation of LFER and KIE data in terms of transition‐state structure and bonding optimally requires the use of theoretical models. In this work, we apply density‐functional calculations to determine KIEs for a series of phosphoryl transfer reactions of direct relevance to the 2′‐O‐transphosphorylation that leads to cleavage of the phosphodiester backbone of RNA. We first examine a well‐studied series of phosphate and phosphorothioate mono‐, di‐ and triesters that are useful as mechanistic probes and for which KIEs have been measured. Close agreement is demonstrated between the calculated and measured KIEs, establishing the reliability of our quantum model calculations. Next, we examine a series of RNA transesterification model reactions with a wide range of leaving groups in order to provide a direct connection between observed Brønsted coefficients and KIEs with the structure and bonding in the transition state. These relations can be used for prediction or to aid in the interpretation of experimental data for similar non‐enzymatic and enzymatic reactions. Finally, we apply these relations to RNA phosphoryl transfer catalyzed by ribonuclease A, and demonstrate the reaction coordinate–KIE correlation is reasonably preserved. A prediction of the secondary deuterium KIE in this reaction is also provided. These results demonstrate the utility of building up knowledge of mechanism through the systematic study of model systems to provide insight into more complex biological systems such as phosphoryl transfer enzymes and ribozymes. 相似文献