排序方式: 共有10条查询结果,搜索用时 15 毫秒
1
1.
Recent experiments suggest that the Ising pyrochlore magnets Ho2Ti2O7 and Dy2Ti2O7 display qualitative properties of the nearest-neighbor "spin ice" model. We discuss the dipolar energy scale present in both these materials and discuss how spin-ice behavior can occur despite the presence of long-range dipolar interactions. We present results of numerical simulations and a mean field analysis of Ising pyrochlore systems. Based on our quantitative theory, we suggest that the spin-ice behavior in these systems is due to long-range dipolar interactions, and that the nearest-neighbor exchange in Dy2Ti2O7 is antiferromagnetic. 相似文献
2.
3.
BC Makhubela AM Jardine G Westman GS Smith 《Dalton transactions (Cambridge, England : 2003)》2012,41(35):10715-10723
The synthesis and characterization of low-generation pyridylimine Rh(i) metallodendrimers is described. These metallodendrimers were obtained via a Schiff base condensation of tris-2-(aminoethyl)amine with 2-pyridinecarboxaldehyde to afford the tris-2-(2-pyridylimine ethyl) amine ligand (1). Subsequent complexation reactions with [RhCl(CO)(2)](2) and [RhCl(COD)](2) yielded the corresponding metal-containing dendrimers containing -RhCl(CO) and -Rh(COD) moieties on the periphery. These new rhodium metallodendrimers (2 and 3) and their precursor ligand (1) are thermally stable and have been characterized using (1)H NMR, (13)C NMR, (31)P NMR, FT-IR spectroscopy, elemental analysis as well as mass spectrometry. The Rh(i) metallodendrimers are highly active and chemo- and regioselective in the hydroformylation of 1-octene. Aldehydes were favoured at moderate to high temperatures (95 °C and 75 °C) and pressure (30 bars), while more iso-octenes were formed at low temperature (55 °C) and pressures (5 and 10 bars). The mononuclear analogues (5 and 6) also produced more aldehydes (albeit showing catalyst decomposition at 95 °C and 75 °C, 30 bars) and these aldehydes were mostly branched. 相似文献
4.
John R. Moss Siyabonga Ngubane Banothile C.E. Makhubela Jay A. Labinger Lawrence M. Henling 《Journal of organometallic chemistry》2008,693(16):2700-2702
Irradiation of Cp∗Ru(CO)2CH3 (1) in C6D6 at room temperature yields Cp∗Ru(CO)2C6D5 and CH3D (where Cp∗ = n5-C5Me5). Cp∗Ru(CO)2CD3 (2) has also been prepared and similar irradiation in C6H6 yields Cp∗Ru(CO)2C6H5 (3) and CD3H. This latter reaction confirms that it is the methyl group bonded to ruthenium that is involved in the C-H activation process and not the methyl groups on the Cp∗ ligand system. The compound Cp∗Ru(CO)2C6H5 (3) has been prepared for the first time in good yield by the reaction of Cp∗Ru(CO)2Br with NaBPh4. X-ray crystal structures of both Cp∗Ru(CO)2CH3 (1) and Cp∗Ru(CO)2C6H5 (3) have been determined and the results are reported and discussed. 相似文献
5.
We obtain exact cosmological solutions of a higher derivative theory described by the Lagrangian L=R+2αR
2 in the presence of interacting scalar field. The interacting scalar field potential required for a known evolution of the
FRW universe in the framework of the theory is obtained using a technique different from the usual approach to solve the Einstein
field equations. We follow here a technique to determine potential similar to that used by Ellis and Madsen in Einstein gravity.
Some new and interesting potentials are noted in the presence of R
2 term in the Einstein action for the known behaviours of the universe. These potentials in general do not obey the slow rollover
approximation. 相似文献
6.
Cisplatin and other metallodrugs have realised great success in clinical chemotherapeutic applications as anticancer drugs. However, severe toxicity to healthy cells and non-selectivity to cancer cells remains a challenge, warranting the further search for alternative agents. Herein, we report the anticancer potential of a series of complexes of the general formula [MCl(p-cym)(k2-N^N-L)]+ X− and [MCl(Cp*)(k2-N^N-L)]+ X−, where M is the metal centre (Ru(II), Os(II), Rh(III) or Ir(III)), L = 1-benzyl-4-pyridinyl-1-H-1,2,3-triazole for L1 and 1-picolyl-4-pyridinyl-1-H-1,2,3-triazole for L2 and X− = Cl−, BF4−, BPh4−. When evaluated for activity against some cancerous and non-cancerous cell lines (namely, HeLa, HEK293, A549 and MT4 cancer cells and the normal healthy kidney cells (BHK21)), most of the compounds displayed poor cytotoxicities against cancer cells except for complexes C2 ([RuCl(p-cym)(k2-N^N-L1)]+ BPh4−, EC50 = 9–16 µM and SI = 14), C7 ([RuCl(p-cym)(k2-N^N-L2)]+ BPh4−, EC50 = 17–53 µM and SI = 4) and C11 ([IrCl(Cp*)(k2-N^N-L2)]+ BF4−, EC50 < 5 µM and SI > 10). Selected complexes C1 ([RuCl(p-cym)(k2-N^N-L1)]+ BF4−), C5 ([IrCl(Cp*)(k2-N^N-L1)]+ BF4−) and C11 showed significant interactions with model biomolecules such as guanosine-5′-monophosphate (5′-GMP), bovine serum albumin (BSA) and amino acids under physiological conditions, possibly through carbenylation and N-coordination with 5′-GMP, N-coordination with L-Histidine and L-proline. While the compounds showed good activities in reducing pyruvate to lactate, there was no direct correlation between catalytic transfer hydrogenation of pyruvate and the observed cytotoxic activities. As observed in this work, the marked influence of single atom replacement in ligand may provide a pivotal approach to improving the cytotoxicity and fine-tuning the selectivity to cancer cells. 相似文献
7.
We compare the orbital angular momentum of the ‘quark’ in the scalar diquark model as well as that of the electron in QED (to order α) obtained from the Jaffe–Manohar decomposition to that obtained from the Ji relation. We estimate the importance of the vector potential in the definition of orbital angular momentum. 相似文献
8.
Malose J. Mphahlele Omankutty Gheevarghese Nkosinathi F. H. Makhubela 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):303-314
Abstract O-Mesyloximes derived from 2-aryl-1,2,3,4-tetrahydro-1-methylsulfonyl-4-quinolones react with sodium ethoxide in ethanol to afford the 4-amino-2-arylquinolines in high yield. No traces of the 3-amino-2-aryl-4-quinolones expected from the Neber rearrangement of the substrates were detected or isolated from the reaction mixture. The structures of the products were determined using a combination of 1H NMR, 13C NMR, IR and mass spectroscopic techniques. 相似文献
9.
AbstractA series of seven coumarinyl-amino acid ester conjugates have been synthesized and characterized by NMR (1H and 13C) and mass spectra. Further, the compounds were investigated for their therapeutic applications such as anti-inflammatory and antioxidant activities. Among the synthesized compounds most of the analogs showed good efficiency compared with the standard. 相似文献
10.
Gamede Noluthando V. Kapfunde Tsitsi A. Ocansey Edward Ngumbu Denis M. Darkwa James Makhubela Banothile C. E. 《Transition Metal Chemistry》2020,45(1):1-8
Transition Metal Chemistry - The industrial process of hydroformylation or the oxo process has been used for many years in the production of aldehydes from alkenes. Different metals have been used... 相似文献
1