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排序方式: 共有491条查询结果,搜索用时 31 毫秒
101.
Abstract— Anabaena doliolum , when exposed to either ultraviolet-B (UVB) radiation or Pb, showed reduced growth rate, carbon fixation, O2 -evolution, photosynthetic electron transport activity and ATP pool size. The rate of respiration was found to increase in UVB-treated cells; this increase was more pronounced in the cells exposed to UVB and Pb simultaneously. The UVB-induced inhibition of 2,6-dichlorophenol indophenol (DCPIP) photoreduction and lowering of chlorophyll a fluorescence could not be reversed by artificial electron donors (diphenyl carbazide, NH2 OH and MnCl2 ). These electron donors, however, substantially reversed the inhibition caused by Pb, thereby suggesting that UVB primarily inhibits the photosys-tem II (PS II) reaction center and Pb arrests the electron flow at the water splitting site. Nevertheless, the suppressed fluorescence intensity and the reduced emission and excitation peaks of phycobilisomes indicate the involvement of Pb in inhibition of PS II. All combinations of UVB and Pb inhibited the different metabolic processes in a synergistic manner. 相似文献
102.
Summary The kinetic behaviour of cis-[Ru(bipy)2(H2O)2]2+ towards the anating ligand pyridine-2-aldoxime as a function of temperature, ligand concentration, substrate complex concentration and pH is reported and the rate expression Rate = k
1
k
2[Ru(bipy)2(H2O)2]2+ [LL]/(k
-1 + k
2[LL]) is established where k
1 is the water dissociation rate constant for the slow step, k
-1 is the rate constant for the aquation, k
2 is the ligand-capturing rate constant of the five-coordinate intermediate [Ru(bipy)2(H2O)]2+ and LL is pyridine-2-aldoxime. The reaction is pH-dependent in the pH range 3.65–5.50. The enthalpy and entropy of activation were obtained using Eyring plots. The results are in conformity with a dissociative mechanism. 相似文献
103.
Summary Paramagnetic [OsIIIDQ2]+ and diamagnetic [OsIIAQ2] (Q = deprotonated 8-quinolinols, D = diimines and A = azoimines) complexes were prepared and characterised by physicochemical, magnetic and spectroscopic methods. The complexes exhibit several spin-allowed and spinforbidden charge-transfer transitions in the visible region. In MeCN solution the OsN4O2 unit displays nearly reversible OsIV-OsIII and OsIII-OsII couples in the ca. -0.4 to +1.1 V range versus SCE. An anodic shift of these responses is seen in going from diimines to azoimines. The stability of metal oxidation levels is correlated on the basis of -acceptor properties of these ligands. 相似文献
104.
We prove that first-passage percolation times across thin cylinders of the form [0, n] × [?h n , h n ] d-1 obey Gaussian central limit theorems as long as h n grows slower than n 1/(d+1). It is an open question as to what is the fastest that h n can grow so that a Gaussian CLT still holds. Under the natural but unproven assumption about existence of fluctuation and transversal exponents, and strict convexity of the limiting shape in the direction of (1, 0, . . . , 0), we prove that in dimensions 2 and 3 the CLT holds all the way up to the height of the unrestricted geodesic. We also provide some numerical evidence in support of the conjecture in dimension 2. 相似文献
105.
Lukas Mai Nils Boysen David Zanders Dr. Teresa de los Arcos Dr. Felix Mitschker Dr. Bert Mallick Prof. Dr. Guido Grundmeier Prof. Dr. Peter Awakowicz Prof. Dr. Anjana Devi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(31):7489-7500
New precursor chemistries for the atomic layer deposition (ALD) of aluminium oxide are reported as potential alternatives to the pyrophoric trimethylaluminium (TMA) which is to date a widely used Al precursor. Combining the high reactivity of aluminium alkyls employing the 3-(dimethylamino)propyl (DMP) ligand with thermally stable amide ligands yielded three new heteroleptic, non-pyrophoric compounds [Al(NMe2)2(DMP)] ( 2 ), [Al(NEt2)2(DMP)] ( 3 , BDEADA) and [Al(NiPr2)2(DMP)] ( 4 ), which combine the properties of both ligand systems. The compounds were synthesized and thoroughly chemically characterized, showing the intramolecular stabilization of the DMP ligand as well as only reactive Al−C and Al−N bonds, which are the key factors for the thermal stability accompanied by a sufficient reactivity, both being crucial for ALD precursors. Upon rational variation of the amide alkyl chains, tunable and high evaporation rates accompanied by thermal stability were found, as revealed by thermal evaluation. In addition, a new and promising plasma enhanced (PE)ALD process using BDEADA and oxygen plasma in a wide temperature range from 60 to 220 °C is reported and compared to that of a modified variation of the TMA, namely [AlMe2(DMP)] (DMAD). The resulting Al2O3 layers are of high density, smooth, uniform, and of high purity. The applicability of the Al2O3 films as effective gas barrier layers (GBLs) was successfully demonstrated, considering that coating on polyethylene terephthalate (PET) substrates yielded very good oxygen transmission rates (OTR) with an improvement factor of 86 for a 15 nm film by using DMAD and a factor of 25 for a film thickness of just 5 nm by using BDEDA compared to bare PET substrates. All these film attributes are of the same quality as those obtained for the industrial precursor TMA, rendering the new precursors safe and potential alternatives to TMA. 相似文献
106.
107.
Dr. Sourav Khan Dr. Rayappan Pavul Raj Dr. Laurel George Dr. G. S. Kamali Kannangara Dr. Adriyan Milev Prof. Dr. Upadhyayula V. Varadaraju Prof. Dr. Parasuraman Selvam 《ChemistryOpen》2020,9(1):23-31
The synthesis of morphology-controlled carbon-coated nanostructured LiFePO4 (LFP/Carbon) cathode materials by surfactant-assisted hydrothermal method using block copolymers is reported. The resulting nanocrystalline high surface area materials were coated with carbon and designated as LFP/C123 and LFP/C311. All the materials were systematically characterized by various analytical, spectroscopic and imaging techniques. The reverse structure of the surfactant Pluronic® 31R1 (PPO-PEO-PPO) in comparison to Pluronic® P123 (PEO-PPO-PEO) played a vital role in controlling the particle size and morphology which in turn ameliorate the electrochemical performance in terms of reversible specific capacity (163 mAh g−1 and 140 mAh g−1 at 0.1 C for LFP/C311 and LFP/C123, respectively). In addition, LFP/C311 demonstrated excellent electrochemical performance including lower charge transfer resistance (146.3 Ω) and excellent cycling stability (95 % capacity retention at 1 C after 100 cycles) and high rate capability (163.2 mAh g−1 at 0.1 C; 147.1 mAh g−1 at 1 C). The better performance of the former is attributed to LFP nanoparticles (<50 nm) with a specific spindle-shaped morphology. Further, we have also evaluated the electrode performance with the use of both PVDF and CMC binders employed for the electrode fabrication. 相似文献
108.
Sourav Kar Subhash Bairagi Gaurav Joshi Prof. Dr. Eluvathingal D. Jemmis Prof. Dr. Sundargopal Ghosh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(63):15634-15637
Despite the synthesis and structural characterization of closo-hydroborate dianions, [BnHn]2− (n=6–12) more than 50 years ago, some ambiguity remains about the structure of [B8H8]2−. Although the solid-state structure of [B8H8]2− was established by single-crystal X-ray studies in 1969, fast rearrangements in solution at accessible temperatures prevented its detailed characterization. We therefore stabilized a derivative of [B8H8]2− by using Cp2MBH3 and structurally characterized two new octaborane analogues, [(Cp2MBH3)2B8H6] (Cp=η5-C5H5; M=Zr ( 1-Zr ) and Hf ( 1-Hf )), so that the dynamics of the B8 skeleton were arrested. The solid-state structures of both 1-Zr and 1-Hf comprise a dodecahedron core protected by {Cp2MBH3} moieties on both sides of the cluster. Spectroscopic characterization (11B NMR) validates the intactness of the B8 dodecahedron core in solution as well. Theoretical calculations establish that the two exo-{Cp2MBH3} fragments provide structural and electronic structural stability to the B8 core and its intact dodecahedral dianionic nature. Furthermore, we propose isodesmic equations for the formation of higher analogues of the Bn core (n>8) guarded by different group 4 transition metals. Our analysis suggests that, as we move to higher polyhedra (n>10), the formation becomes unfavourable irrespective of metal. 相似文献
109.
110.
Taichi Ikeda Dr. Sourav Saha Dr. Ivan Aprahamian Dr. Ken C.‐F. Leung Dr. Adides Williams Wei‐Qiao Deng Dr. Amar H. Flood Dr. William A. Goddard III Prof. J. Fraser Stoddart Prof. 《化学:亚洲杂志》2007,2(1):76-93
Encouraged by the prospect of producing an electrochemical, color‐switchable red–green–blue (RGB) dye compound, we have designed, synthesized, and characterized two three‐station [2]catenanes. Both are composed of macrocyclic polyethers containing three π‐electron‐rich stations, which act as recognition sites for a π‐electron‐deficient tetracationic cyclophane. The molecular structures of the two three‐station [2]catenanes were characterized fully by mass spectrometry and 1H NMR spectroscopy. To anticipate the relative occupancies of the three stations in each [2]catenane by the cyclophane, model compounds with the same constitutions in the vicinity of the stations were synthesized. The relative ground‐state populations of the three stations occupied in both [2]catenanes were estimated from the thermodynamic parameters for 1:1 complexes between all these model compounds and the cyclophane, obtained from isothermal titration calorimetry (ITC). The electrochemical and electromechanical properties of the three‐station [2]catenanes were analyzed by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and spectroelectrochemistry (SEC). The first three‐station [2]catenane was found to behave like a bistable system, whereas the second can be described as a quasi‐tristable system. 相似文献