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931.
Tenderholt AL Szilagyi RK Holm RH Hodgson KO Hedman B Solomon EI 《Inorganic chemistry》2008,47(14):6382-6392
Sulfur K-edge X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations have been used to determine the electronic structures of a series of Mo tris(dithiolene) complexes, [Mo(mdt)3](z) (where mdt = 1,2-dimethylethene-1,2-dithiolate(2-) and z = 2-, 1-, 0), with near trigonal-prismatic geometries (D3h symmetry). These results show that the formally Mo(IV), Mo(V), and Mo(VI) complexes actually have a (dz(2))(2) configuration, that is, remain effectively Mo(IV) despite oxidation. Comparisons with the XAS data of another set of Mo tris(dithiolene) complexes, [Mo(tbbdt)3](z) (where tbbdt = 3,5-ditert-butylbenzene-1,2-dithiolate(2-) and z = 1-, 0), show that both neutral complexes, [Mo(mdt)3] and [Mo(tbbdt)3], have similar electronic structures while the monoanions do not. Calculations reveal that the "Bailar twist" present in the crystal structure of [Mo(tbbdt)3](1-) (D3 symmetry) but not [Mo(mdt)3](1-) (D3h symmetry) is controlled by electronic factors which arise from bonding differences between the mdt and tbbdt ligands. In the former, configuration interaction between the Mo d(z(2)) and a deeper energy, occupied ligand orbital, which occurs in D3 symmetry, destabilizes the Mo d(z(2)) to above another ligand orbital which is half-occupied in the D3h [Mo(mdt)3](1-) complex. This leads to a metal d(1) configuration with no ligand holes (i.e., d(1)[L3](0h)) for [Mo(tbbdt)3](1-) rather than the metal d(2) configuration with one ligand hole (i.e., d(2)[L3](1h)) for [Mo(mdt)3](1-). Thus, the Bailar twist observed in some metal tris(dithiolene) complexes is the result of configuration interaction between metal and ligand orbitals and can be probed experimentally by S K-edge XAS. 相似文献
932.
A simple non-aqueous reversed-phase separation HPLC-MS method has been developed to allow for the rapid screening and separation of fullerenes and substituted fullerenes. This procedure provides confirmation that the proposed substitution methodology for the fullerene is not only successful but that multiple substitution products are obtained. The methodology is being expanded to analyze other substituted fullerene product mixtures. 相似文献
933.
Intramolecular Pd(II)-catalyzed oxidative biaryl synthesis under air: reaction development and scope
Liégault B Lee D Huestis MP Stuart DR Fagnou K 《The Journal of organic chemistry》2008,73(13):5022-5028
New reaction conditions for intramolecular palladium(II)-catalyzed oxidative carbon-carbon bond formation under air are described. The use of pivalic acid as the reaction solvent, instead of acetic acid, results in greater reproducibility, higher yields, and broader scope. This includes the use of electron-rich diarylamines as illustrated in the synthesis of three naturally occurring carbazole products: Murrayafoline A, Mukonine, and Clausenine. A variety of side products have also been isolated, casting light on competing reaction pathways and revealing new reactivity with palladium(II) catalysis. 相似文献
934.
Natasha M. Kreitals Keith A. Hobson Brittney M. Hoemsen Adam L. Crane Van Wishingrad Janelle Sloychuk 《Isotopes in environmental and health studies》2016,52(6):592-602
Naturally occurring deuterium (2H) in biota can be used to trace movement, migration and geographic origin of a range of organisms. However, to evaluate movements of animals using δ2H measurements of tissues, it is necessary to establish the turnover time of 2H in the tissues and the extent of isotopic discrimination from different environmental 2H sources to those tissues. We investigated the turnover of 2H in lake sturgeon (Acipenser fulvescens) blood by manipulating both environmental water δ2H and diet δ2H over a four-month period. The half-life of deuterium in lake sturgeon blood was 37.9 days after an increase in the environmental water δ2H of +714?‰. However, no clear turnover in blood 2H occurred over the same period in a separate trial following a change of ?63.8?‰ or +94.2?‰ in diet. These findings suggest that environmental water 2H exchanges much faster with blood than diets and that blood δ2H values can be used to trace movements of sturgeon and other fish moving among isotopically distinct waters. 相似文献
935.
936.
937.
A blocking semioval is a set of points in a projective plane that is both a blocking set (i.e., every line meets the set, but the set contains no line) and a semioval (i.e., there is a unique tangent line at each point). The minimum size of a blocking semioval is currently known in all projective planes of order < 11, with the exception of PG(2, 9). In this note we show by demonstration of an example that the smallest blocking semioval in PG(2, 9) has size 21 and investigate some properties of this set. 相似文献
938.
William J. Keith 《The Ramanujan Journal》2016,40(1):71-92
We generalize overpartitions to (k, j)-colored partitions: k-colored partitions in which each part size may have at most j colors. We find numerous congruences and other symmetries. We use a wide array of tools to prove our theorems: generating function dissections, modular forms, bijections, and other combinatorial maps. In the process of proving certain congruences, we find results of independent interest on the number of partitions with exactly 2 sizes of part in several arithmetic progressions. We find connections to divisor sums, the Han/Nekrasov–Okounkov hook length formula and a possible approach to finitization, and other topics, suggesting that a rich mine of results is available. We pose several immediate questions and conjectures. 相似文献
939.
Nucleophilic Aromatic Substitution on Pentafluorophenyl‐Substituted Dipyrranes and Tetrapyrroles as a Route to Multifunctionalized Chromophores for Potential Application in Photodynamic Therapy 下载免费PDF全文
Claudia S. Gutsche Marlene Ortwerth Dr. Susanna Gräfe Keith J. Flanagan Prof. Mathias O. Senge Prof. Hans‐Ulrich Reissig Prof. Nora Kulak Dr. Arno Wiehe 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(39):13953-13964
The application of porphyrinoids in biomedical fields, such as photodynamic therapy (PDT), requires the introduction of functional groups to tune their solubility for the biological environment and to allow a coupling to other active moieties or carrier systems. A valuable motif in this regard is the pentafluorophenyl (PFP) substituent, which can easily undergo a regiospecific nucleophilic replacement (SNAr) of its para‐fluorine atom by a number of nucleophiles. Here, it is shown that, instead of amino‐substitution on the final porphyrinoid or BODIPY (boron dipyrromethene), the precursor 5‐(PFP)‐dipyrrane can be modified with amines (or alcohols). These dipyrranes were transformed into amino‐substituted BODIPYs. Condensation of these dipyrranes with aldehydes gave access to trans‐A2B2‐porphyrins and trans‐A2B‐corroles. By using pentafluorobenzaldehyde, it was possible to introduce another para‐fluorine atom, which enabled the synthesis of multifunctionalized tetrapyrroles. Furthermore, alkoxy‐ and amino‐substituted dipyrranes were applied to the synthesis of A3B3‐hexaphyrins. The polar porphyrins that were prepared by using this method exhibited in vitro PDT activity against several tumor cell lines. 相似文献
940.
We prove that if A is a finite algebra with a parallelogram term that satisfies the split centralizer condition, then A is dualizable. This yields yet another proof of the dualizability of any finite algebra with a near unanimity term, but more importantly proves that every finite module, group or ring in a residually small variety is dualizable. 相似文献