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E Virtanen M Nissinen R Suontamo J Tamminen E Kolehmainen 《Journal of Molecular Structure》2003,649(3):207-218
13C NMR chemical shifts have been measured and assigned for epimeric methyl 3α/β-hydroxy-5β-cholan-24-oates (methyl lithocholate [3α-OH epimer] and methyl iso-lithocholate [3β-OH epimer]). Their molecular dynamics simulations suggest that for both epimers there exists two predominant gas phase conformations, which have been further forwarded for ab initio/HF optimizations and DFT/GIAO based 13C NMR chemical shift calculations. Excellent linear relationships have been observed between experimental and calculated 13C NMR chemical shifts for both epimers. For methyl lithocholate (MeLC), the other minimum energy conformation equates very well with the single crystal X-ray structure (orthorhombic, space group P212121, unit cell ). The crystalline packing of MeLC consists of continuous parallel intermolecular hydrogen bonded [3α-OH?OC24] head-to-tail polymeric chains, which are further cross-linked by many simultaneous weak C(sp3)H?O-type of interactions. 相似文献
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Maija Nissinen Terhi Alaviuhkola Kari Rissanen Jouni Pursiainen 《Journal of chemical crystallography》2006,36(12):863-868
The crystal structure of the potassium tris[3-(2-pyridyl)pyrazolyl]hydroborate has been determined. Potassium tris[3-(2-pyridyl)pyrazolyl]hydroborate crystallizes in the orthorhombic space group Pca21 with the parameters a=30.7323(5) ?, b=8.3083(1) ? and c=9.2173(2) ?, V=2353.48(7) ?3 with Z=4. The crystal structure reveals the formation of continuous chains where two bidentate arms of the hydroborate ligand are coordinated to one potassium and the third to another cation. The structures of numerous transition metal and actinide salts have been reported during the last decades but no alkali metal complexes were available. 相似文献
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Koivunen JT Nissinen L Käpylä J Jokinen J Pihlavisto M Marjamäki A Heino J Huuskonen J Pentikäinen OT 《Journal of the American Chemical Society》2011,133(37):14558-14561
Collagen binding integrins are an important family of cell surface receptors that mediate bidirectionally signals between the interior of the cell and the extracellular matrix. The protein-protein interactions between cells and collagen are necessary for many physiological functions, but also promote diseases. For example, the interaction of α2β1 integrin and collagen has been shown to have an important role in thrombus formation and cancer spread. The fact that the discovery of small molecules that can block such protein-protein interactions is highly challenging has significantly hindered the discovery of pharmaceutical agents to treat these diseases. Here, we present a rationally designed novel fluorescent molecule that can be synthesized in just a few minutes from commercially available starting materials. This molecule blocks the protein-protein interaction between α2β1 integrin and collagen, and due to its fluorescent properties, it can be employed in wide variety of biological applications. 相似文献
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Characterization of silane layers on modified stainless steel surfaces and related stainless steel-plastic hybrids 总被引:1,自引:0,他引:1
Mari Honkanen Maija HoikkanenMinnamari Vippola Jyrki VuorinenToivo Lepistö Petri JussilaHarri Ali-Löytty Markus LampimäkiMika Valden 《Applied Surface Science》2011,257(22):9335-9346
The aim of this work was to characterize silane layers on the modified stainless steel surfaces and relate it to the adhesion in the injection-molded thermoplastic urethane-stainless steel hybrids. The silane layers were characterized with scanning electron microscope and transmission electron microscope, allowing the direct quantization of silane layer thickness and its variation. The surface topographies were characterized with atomic force microscope and chemical analyses were performed with X-ray photoelectron spectroscopy. The mechanical strength of the respective stainless steel-thermoplastic urethane hybrids was determined by peel test. Polishing and oxidation treatment of the steel surface improved the silane layer uniformity compared to the industrially pickled surface and increased the adhesion strength of the hybrids, resulting mainly cohesive failure in TPU. XPS analysis indicated that the improved silane bonding to the modified steel surface was due to clean Fe2O3-type surface oxide and stronger interaction with TPU was due to more amino species on the silane layer surface compared to the cleaned, industrially pickled surface. Silane layer thickness affected failure type of the hybrids, with a thick silane layer the hybrids failed mainly in the silane layer and with a thinner layer cohesively in plastic. 相似文献
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Dynamic systems view of learning a three‐tiered theory in physics: robust learning outcomes as attractors 下载免费PDF全文
The process of learning scientific knowledge from the dynamic systems viewpoint is studied in terms probabilistic learning model (PLM), where learning accrues from foraging in the epistemic landscape. The PLM leads to the formation of attractor‐type regions of preferred models in an epistemic landscape. The attractor‐type states correspond to robust learning outcomes which are more probable than others. These can be assigned either to the high confidence in model selection or to the dynamic evolution of a learner's proficiency, which depends on the learning history. The results suggest that robust learning states are essentially context dependent, and that learning is a continuous development between these context dependent states. © 2016 Wiley Periodicals, Inc. Complexity 21: 259–267, 2016 相似文献
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We have studied the mechanical compressibility and band structure of solid nitromethane both in equilibrium and compressed states using Hartree-Fock and density functional theory (DFT) with atom-centered all-electron linear combination of atomic orbitals basis sets. Hartree-Fock calculations with a 6-21G basis set, uncorrected for basis set superposition error, gave the best agreement with experimental compression studies. These results may be due to the cancellation of basis set superposition error with dispersion force errors. The equilibrium DFT band gap is comparable to the lowest-energy feature in electron-impact spectroscopy of nitromethane but underpredicts the optical absorption gap; we interpret these features in terms of the presence of tightly bound excitons. Only minor changes in the gap are observed under hydrostatic compression. 相似文献