Enhancing the performance of poly(3-hexylthiophene)/ZnO nanorod arrays based hybrid solar cells through incorporation of a third component

Sparse ZnO nanorod arrays(NRAs)are fabricated on transparent conducting oxide coated glass substrates by using a modified liquid phase epitaxial growth method.By adjusting the polymer concentrations and the spin-coating parameters,full infiltration of poly(3-hexylthiophene)(P3HT)into the as-prepared ZnO NRAs is achieved at 130°C in vacuum.A third component is incorporated into the P3HT/ZnO NRAs ordered bulk heterojunctions(BHJs)either through ZnO surface modification with N719dye or CdS shell layer or by inclusion of a fullerene derivative into the P3HT matrix.Experimental results indicate that performances of the hybrid solar cells are improved greatly with the incorporation of a third component.However,the working principles of these third components differ from one another,according to morphology,structure,optical property,charge transfer and interfacial properties of the composite structures.An ideal device architecture for hybrid solar cells based on P3HT/ZnO NRAs ordered BHJs is proposed,which can be used as a guidance to further increase the power conversion efficiency of such solar cells.     

Characterization of an O2 adduct of an active cobalt-substituted extradiol-cleaving catechol dioxygenase

The first example of an O(2) adduct of an active Co-substituted oxygenase has been observed in the extradiol ring cleavage of the electron-poor substrate 4-nitrocatechol (4NC) by Co(II)-homoprotocatechuate 2,3-dioxygenase (Co-HPCD). Upon O(2) binding to the high-spin Co(II) (S = (3)/(2)) enzyme-substrate complex, an S = (1)/(2) EPR signal exhibiting (59)Co hyperfine splitting (A = 24 G) typical of a low-spin Co(III)-superoxide complex was observed. Both the formation and decay of the new intermediate are very slow in comparison to the analogous steps for turnover of 4NC by native high-spin Fe(II)-HPCD, which is likely to remain high-spin upon O(2) binding. A similar but effectively stable S = (1)/(2) intermediate was formed by the inactive [H200N-Co-HPCD(4NC)] variant. The observations presented shed light on the key roles played by the substrate, the second-sphere His200 residue, and the spin state of the metal center in facilitating O(2) binding and activation.     

Evaluating the identity and diiron core transformations of a (μ-oxo)diiron(III) complex supported by electron-rich tris(pyridyl-2-methyl)amine ligands

The composition of a (μ-oxo)diiron(III) complex coordinated by tris[(3,5-dimethyl-4-methoxy)pyridyl-2-methyl]amine (R(3)TPA) ligands was investigated. Characterization using a variety of spectroscopic methods and X-ray crystallography indicated that the reaction of iron(III) perchlorate, sodium hydroxide, and R(3)TPA affords [Fe(2)(μ-O)(μ-OH)(R(3)TPA)(2)](ClO(4))(3) (2) rather than the previously reported species [Fe(2)(μ-O)(OH)(H(2)O)(R(3)TPA)(2)](ClO(4))(3) (1). Facile conversion of the (μ-oxo)(μ-hydroxo)diiron(III) core of 2 to the (μ-oxo)(hydroxo)(aqua)diiron(III) core of 1 occurs in the presence of water and at low temperature. When 2 is exposed to wet acetonitrile at room temperature, the CH(3)CN adduct is hydrolyzed to CH(3)COO(-), which forms the compound [Fe(2)(μ-O)(μ-CH(3)COO)(R(3)TPA)(2)](ClO(4))(3) (10). The identity of 10 was confirmed by comparison of its spectroscopic properties with those of an independently prepared sample. To evaluate whether or not 1 and 2 are capable of generating the diiron(IV) species [Fe(2)(μ-O)(OH)(O)(R(3)TPA)(2)](3+) (4), which has previously been generated as a synthetic model for high-valent diiron protein oxygenated intermediates, studies were performed to investigate their reactivity with hydrogen peroxide. Because 2 reacts rapidly with hydrogen peroxide in CH(3)CN but not in CH(3)CN/H(2)O, conditions that favor conversion to 1, complex 1 is not a likely precursor to 4. Compound 4 also forms in the reaction of 2 with H(2)O(2) in solvents lacking a nitrile, suggesting that hydrolysis of CH(3)CN is not involved in the H(2)O(2) activation reaction. These findings shed light on the formation of several diiron complexes of electron-rich R(3)TPA ligands and elaborate on conditions required to generate synthetic models of diiron(IV) protein intermediates with this ligand framework.     

Fluxes in "free" and total zinc are essential for progression of intraerythrocytic stages of Plasmodium falciparum

Dynamic fluxes in the concentration of ions and small molecules are fundamental features of cell signaling, differentiation, and development. Similar roles for fluxes in transition metal concentrations are less well established. Here, we show that massive zinc fluxes are essential in the infection cycle of an intracellular eukaryotic parasite. Using single-cell quantitative imaging, we show that growth of the blood-stage Plasmodium falciparum parasite requires acquisition of 30 million zinc atoms per erythrocyte before host cell rupture, corresponding to a 400% increase in total zinc concentration. Zinc accumulates in a freely available form in parasitophorous compartments outside the food vacuole, including mitochondria. Restriction of zinc availability via small molecule treatment causes a drop in mitochondrial membrane potential and severely inhibits parasite growth. Thus, extraordinary zinc acquisition and trafficking are essential for parasite development.     

一种针对软错误的流水线电路加固方案

针对纳米级工艺下瞬态故障引发的软错误可能造成电路失效这一问题,提出一种容软错误的流水线电路加固方案.该方案面向软错误的主要诱因——单事件翻转(single event upset,SEU),利用新型的容错结构锁存器(radiation hardened by design latch,RHBDL),构造高可靠性的触发器RHBD-DFF,对电路中原始时序单元进行加固,同时对流水线电路进行了软错率理论分析.考虑到加固所带来的附加开销,采取选择性加固的策略,对电路中的关键时序单元进行加固.实验结果表明,基于开销限制前提的选择性加固,能够达到以低开销代价换取高容错性能的目的.     

Resonance Raman studies of the iron(II)--alpha-keto acid chromophore in model and enzyme complexes.

The bidentate coordination of an alpha-keto acid to an iron(II) center via the keto group and the carboxylate gives rise to metal-to-ligand charge-transfer transitions between 400 and 600 nm in model complexes and in alpha-ketoglutarate-dependent dioxygenases. Excitation into these absorption bands of the Fe(II)TauD(alpha-KG) complex (TauD = taurine/alpha-ketoglutarate dioxygenase, alpha-KG = alpha-ketoglutarate) elicits two resonance Raman features at 460 and 1686 cm(-1), both of which are sensitive to (18)O labeling. Corresponding studies of model complexes, the six-coordinate [Fe(II)(6-Me(3)-TPA)(alpha-keto acid)](+) and the five-coordinate [Fe(II)(Tp(Ph2))(alpha-keto acid)] (6-Me(3)-TPA = tris[(6-methyl-2-pyridyl)methyl]amine, Tp(Ph2) = hydrotris(3,5-diphenylpyrazol-1-yl)borate), lead to the assignment of these two features to the Fe(II)(alpha-keto acid) chelate mode and the nu(C==O) of the keto carbonyl group, respectively. Furthermore, the chelate mode is sensitive to the coordination number of the metal center; binding of a sixth ligand to the five-coordinate [Fe(II)(Tp(Ph2))(benzoylformate)] elicits a 9--20 cm(-1) downshift. Thus, the 10 cm(-1) upshift of the chelate mode observed for Fe(II)TauD(alpha-KG) upon the addition of the substrate, taurine, is associated with the conversion of the six-coordinate metal center to a five-coordinate center, as observed for the iron center of clavaminate synthase from X-ray crystallography (Zhang, Z.; et al. Nat. Struct. Biol. 2000, 7, 127-133) and MCD studies (Zhou, J.; et al. J. Am. Chem. Soc. 1998, 120, 13539--13540). These studies provide useful insights into the initial steps of the oxygen activation mechanism of alpha-ketoglutarate-dependent dioxygenases.     

Axial ligand substituted nonheme FeIV=O complexes: observation of near-UV LMCT bands and Fe=O Raman vibrations

Axial ligand substitution of a mononuclear nonheme oxoiron(IV) complex, [FeIV(O)(TMC)(NCCH3)]2+ (1) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), leads to the formation of new FeIV=O species with relatively intense electronic absorption features in the near-UV region. The presence of these near-UV features allowed us to make the first observation of Fe=O vibrations of S = 1 mononuclear nonheme oxoiron(IV) complexes by resonance Raman spectroscopy. We have also demonstrated that the reactivity of nonheme oxoiron(IV) intermediates is markedly influenced by the axial ligands.     

Bis(mu-oxo)dimetal "diamond" cores in copper and iron complexes relevant to biocatalysis

Although quite a familiar feature in high-valent manganese chemistry, the M(2)(mu-O)(2) diamond core motif has only recently been found in synthetic complexes for M=Cu or Fe. Structural and spectroscopic characterization of these more reactive Cu(2)(mu-O)(2) and Fe(2)(mu-O)(2) compounds has been possible through use of appropriately designed supporting ligands, low-temperature handling methods, and techniques such as electrospray ionization mass spectrometry and X-ray crystallography with area detector instrumentation for rapid data collection. Despite differences in electronic structures that have been revealed through experimental and theoretical studies, Cu(2)(mu-O)(2) and Fe(2)(mu-O)(2) cores exhibit analogously covalent metal-oxo bonding, remarkably congruent Raman and extended X-ray absorption fine structure (EXAFS) signatures, and similar tendencies to abstract hydrogen atoms from substrates. Core isomerization is another common reaction attribute, although different pathways are traversed; for Fe, bridge-to-terminal oxo migration has been discovered, while for Cu, reversible formation of an O-O bond to yield a peroxo isomer has been identified. Our understanding of biocatalysis has been enhanced significantly through the isolation and comprehensive characterization of the Cu(2)(mu-O)(2) and Fe(2)(mu-O)(2) complexes. In particular, it has led to the development of new mechanistic notions about how non-heme multimetal enzymes, such as methane monooxygenases, fatty acid desaturase, and tyrosinase, may function in the activation of dioxygen to catalyze a diverse array of organic transformations.