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941.
Two types of manganese complexes with [Mn4] cores featuring the unusual distorted cube topology are presented, the first of which comprises new modifications of the reported complex [MnIII4(sao)4(saoH)4]·3CHCl3: [Mn4(sao)4(saoH)4]·1.32(C4H10O)·0.43(CH4O) ( 1a ) and [Mn(sao)4(saoH)4]·0.5(CH4O)·0.5(C2H3N) ( 1b ) sao = salicylaldoxime. The second, 0.55[Mn4Cl4(C12H9N2O)4(CH3OH)2(H2O)2]·0.45[Mn4Cl4(C12H9N2O)4(CH3OH)4] ( 2 ), is the first reported case of a {MnII4} core of this topology besides known {MnIII4} compounds. Differences between the {MnII4} and {MnIII4} situation are discussed, and so far overlooked differences in magnetic properties between different {MnIII4} compounds are pointed out. 相似文献
942.
Detecting short RNA strands with high fidelity at any of the bases of their sequence, including the termini, can be challenging, since fraying, wobbling, and refolding all compete with canonical base pairing. We performed a search for 5'-substituents of oligodeoxynucleotides that increase base pairing fidelity at the terminus of duplexes with RNA target strands. From a total of over 70 caps, differing in stacking moiety and linker, a phosphodiester-linked sequence of the residues of L-prolinol, glycine, and oxolinic acid, dubbed ogOA, was identified as a 5'-cap that stabilizes any of the four canonical base pairs, with ΔT(m) values of up to +13.1 °C for an octamer. At the same time, the cap increases discrimination against any of the 12 possible terminal mismatches, including mismatches that are more stable than their perfectly matched counterparts in the control duplex, such as A:A. A probe with the cap also showed increased selectivity in the detection of two closely related microRNAs, let7c and let7a, with a ΔT(m) value of 9.2 °C. Melting curves also yielded thermodynamic data that shed light on the uniformity of molecular recognition in the sequence space of DNA:DNA and DNA:RNA duplexes. Hybridization probes with fidelity-enhancing caps should find applications in the individual and parallel detection of biologically active RNA species. 相似文献
943.
The migration of particles induced by the forces of light is known as photophoresis. The photophoretic velocity of particles under the influence of a strong light source, e.g. a laser beam, is recorded and measured by means of digital image processing which is called photophoretic velocimetry (PPV). The photophoretic velocity depends on the particle size as well as on its refractive index. By applying PPV, we show the determination of the intrinsic properties of polystyrene (PS), melamine resin (MF) and SiO(2) particles, deduced from velocity distributions of both monodisperse as well as polydisperse suspensions. Especially the continuous determination of the refractive index of single hydrocolloids is of great interest for quality assurance and the discrimination of polydisperse biological or inorganic samples. Also, PPV is not restricted to in water dispersed samples only. 相似文献
944.
One of the key points of interest in pyrochlore materials containing bismuth derives from the dielectric properties of some such materials that are linked to the displacements of the bismuth atoms from the ideal site. This study uses high pressure to probe the variations in, and causes of, these displacements. Under compression Bi(2)Ti(2)O(7) does not undergo any phase changes, but Bi(2)Sn(2)O(7) undergoes a similar series of changes to those observed during heating. The trigonal β-Bi(2)Sn(2)O(7) structure is solved from high temperature powder neutron diffraction data and hence the sequence of phases observed in Bi(2)Sn(2)O(7) is discussed for the first time. The variation in Bi displacements can be considered in terms of the frustration of the tetrahedral lattice that accommodates them. It can also be inferred that the main driver for Bi displacement is a deficiency in the bond valence sum of bismuth. 相似文献
945.
Tobias Danczul Clemens Hofreither Joachim Schöberl 《Numerical Linear Algebra with Applications》2023,30(5):e2488
We present a unified framework to efficiently approximate solutions to fractional diffusion problems of stationary and parabolic type. After discretization, we can take the point of view that the solution is obtained by a matrix-vector product of the form , where is the discretization matrix of the spatial operator, a prescribed vector, and a parametric function, such as a fractional power or the Mittag-Leffler function. In the abstract framework of Stieltjes and complete Bernstein functions, to which the functions we are interested in belong to, we apply a rational Krylov method and prove uniform convergence when using poles based on Zolotarëv's minimal deviation problem. The latter are particularly suited for fractional diffusion as they allow for an efficient query of the map and do not degenerate as the fractional parameters approach zero. We also present a variety of both novel and existing pole selection strategies for which we develop a computable error certificate. Our numerical experiments comprise a detailed parameter study of space-time fractional diffusion problems and compare the performance of the poles with the ones predicted by our certificate. 相似文献
946.
Beier René Röglin Heiko Rösner Clemens Vöcking Berthold 《Mathematical Programming》2023,200(1):319-355
Mathematical Programming - A well-established heuristic approach for solving bicriteria optimization problems is to enumerate the set of Pareto-optimal solutions. The heuristics following this... 相似文献
947.
948.
949.
Jianyang Han Jakob Arnold Christophe Pannecouque Graciela Andrei Robert Snoeck Clemens Richert 《Helvetica chimica acta》2023,106(1):e202200157
Strongly pairing ethynylpyridone C-nucleosides are attractive surrogates for thymidine in oligonucleotides. Exploratory work on the antiviral activity of 3′-azidothymidine (AZT) derivatives with ethynylpyridone as base had identified strong lipophilicity as a limiting factor. Two strategies are being pursued to overcome this issue. In order to make the base more polar, the ethynyl group has been replaced with a cyano group, leading to a cyanopyridone C-nucleoside, whose eleven-step synthesis is reported here, together with the synthesis of a 3′-azido-2′,3′-dideoxynucleoside derivative. The base pairing with adenine in a DNA duplex was studied by UV melting analysis of a self-complementary hexamer containing the 6-cyano-2′-deoxynucleoside instead of thymidine. A melting point increase of 2 °C compared to the unmodified control was found. The other strategy employs a phosphoramidate prodrug design with less lipophilic amino acid esters. Here, anti-HIV test of the alaninyl and prolinyl methyl esters of AZT gave promising results in cell culture experiments, increasing the selectivity index up to 5.8-fold for the IIIB strain and up to 5-fold for the ROD strain of the virus, as compared to the parent nucleoside. These findings help to design the next generation of pyridone C-nucleosides with potential applications as antivirals. 相似文献
950.