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11.
Pulkkinen M Palmgrén JJ Auriola S Malin M Seppälä J Järvinen K 《Rapid communications in mass spectrometry : RCM》2008,22(2):121-129
This paper describes a straightforward and rapid on-line characterization using high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC/ESI-MS(n)) of the enzymatic degradation products of 2,2'-bis(2-oxazoline)-linked poly-epsilon-caprolactone (PCL-O). These new PCL-O polymers are expected to be used in a variety of pharmaceutical and biomedical applications since they are degraded enzymatically by surface erosion. PCL-O was polymerized in a three-step reaction and characterized by (1)H-NMR and size-exclusion chromatography (SEC). Solvent cast polymer films were exposed to enzymatic degradation in phosphate buffer (pH 7.5, 1% pancreatin). The enzymatic degradation of the polymer produced a wide variety of water-soluble oligomers which were separated and identified by HPLC/ESI-MS(n). Optimization of the gradient HPLC method resulted in effective separation of the oligomers. Furthermore, specific structures of the oligomers were clearly identified by tandem mass spectrometry. According to these results, ester bonds seem to be most sensitive to enzymatic degradation and, correspondingly, pancreatic lipase seems to be mainly responsible for the enzymatic erosion of the PCL-O films. This novel mass spectrometric method provides important knowledge about the enzymatic degradation process and structure of the polymer which is difficult to ascertain by other conventional methods. 相似文献
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At the beginning of 1975 the Federation of the Finnish Chemical Industry and the University of Helsinki, Department of Computer Science, set up a project to develop a mathematical model to be used as a planning tool during accidental raw material shortages in the Finnish chemical industry. The model has been designed, programmed, and tested. The main part of the system consists of a linear programming model, which is used to answer “what-if” questions.This paper describes the model, the programs and the main problems encountered in the design process. The present version of the system can solve problems involving at most 100 firms, 400 products, 400 types of raw materials and 200 technical or policy constraints. 相似文献
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Abstract The geometry of dimethylmercury was studied in several mixtures of the liquid crystals ZLI 1167 and phase 4. The variation of the geometry is not very large but systematic changes can be detected as a function of the liquid crystal composition. The anisotropics, δ[sgrave], of the 1H, 13C and 199Hg shielding tensors were investigated by applying two methods based on mixing liquid crystals with opposite diamagnetic anisotropies and by applying various referencing methods. Apart from these, the anisotropy, δJ HgC, of the 199Hg–13C spin–spin coupling tensor was studied in four mixtures of these liquid crystals, and was found to vary with the solvent. 相似文献
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Satu Strandman Petri Pulkkinen Heikki Tenhu 《Journal of polymer science. Part A, Polymer chemistry》2005,43(15):3349-3358
The effect of the steric hindrance on the initiating properties of two multifunctional resorcinarene‐based initiators in atom transfer radical polymerization (ATRP) was studied by using Cu(I)‐complexes of three multidentate amine ligands in the polymerization of tert‐butyl acrylate and methyl methacrylate. These ligands are less sterically hindered and have higher activities in the catalysis of ATRP of (meth)acrylates than 2,2′‐bipyridine. The polymerizations were faster and more controlled than with the 2,2′‐bipyridyl catalyst, but the tendency for bimolecular coupling increased. Even though the initiator was octafunctional, the resulting star polymers had only four arms. This indicates that the steric hindrance arising from the conformations of the initiators determines the structure of the polymer, but the ligand noticeably affects the controllability of the polymerization © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3349–3358, 2005 相似文献
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P. Surya Mohan Tanja Tarvainen Martin Schweiger Aki Pulkkinen Simon R. Arridge 《Journal of computational physics》2011,230(19):7364-7383
We propose the PN approximation based on a finite element framework for solving the radiative transport equation with optical tomography as the primary application area. The key idea is to employ a variable order spherical harmonic expansion for angular discretization based on the proximity to the source and the local scattering coefficient. The proposed scheme is shown to be computationally efficient compared to employing homogeneously high orders of expansion everywhere in the domain. In addition the numerical method is shown to accurately describe the void regions encountered in the forward modeling of real-life specimens such as infant brains. The accuracy of the method is demonstrated over three model problems where the PN approximation is compared against Monte Carlo simulations and other state-of-the-art methods. 相似文献
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Hiltunen Y Kaartinen J Pulkkinen J Häkkinen AM Lundbom N Kauppinen RA 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,154(1):1-5
Long echo time (TE=270 ms) in vivo proton NMR spectra resembling human brain metabolite patterns were simulated for lineshape fitting (LF) and quantitative artificial neural network (ANN) analyses. A set of experimental in vivo 1H NMR spectra were first analyzed by the LF method to match the signal-to-noise ratios and linewidths of simulated spectra to those in the experimental data. The performance of constructed ANNs was compared for the peak area determinations of choline-containing compounds (Cho), total creatine (Cr), and N-acetyl aspartate (NAA) signals using both manually phase-corrected and magnitude spectra as inputs. The peak area data from ANN and LF analyses for simulated spectra yielded high correlation coefficients demonstrating that the peak areas quantified with ANN gave similar results as LF analysis. Thus, a fully automated ANN method based on magnitude spectra has demonstrated potential for quantification of in vivo metabolites from long echo time spectroscopic imaging. 相似文献
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Aki Pulkkinen Katariina Pussi 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(10):184
We study atomic oxygen adsorption on a Pb(1 0 0) surface using density functional theory. The structures, binding energies, work function, and charge transfer of on-surface and subsurface adsorption are investigated at a range of coverages from 0.06 to 1.00 ML. The energetically favored adsorption site for on-surface adsorption is found to be a distorted hollow site for the whole coverage range studied. The distorted structures are stabilized by mixing of 6s and 6p states of lead mediated by the 2p states of oxygen. For subsurface adsorption, the sub-bridge site is found to be preferred to the sub-hollow site at low coverages, the two being nearly equal in energy at monolayer coverage. At 0.11 ML coverage, diffusion from an on-surface hollow site to a sub-bridge site is found to be barrierless, suggesting facile subsurface oxidation at low coverages. Combined on-surface and subsurface adsorption leads to the formation of a two-layer oxide structure resembling β-PbO. 相似文献
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Yrjö Hiltunen Jukka Jokisaari Anja Pulkkinen Taito Väänänen 《Chemical physics letters》1984,109(5):509-513
The structure of benzene dissolved in various thermotropic nematic liquid crystals has been studied. 13C-methane was used as an internal “deformation reference”. The results indicate that the HH distance ratios obtained front the direct dipole-dipole coupling constants correspond to the hexagon values in cases where benzene is dissolved in mixtures of nematic liquid crystals which produce negligible dipolar CH splittings for methane. The ratio rCH/r CC for benzene is in good accord with the value obtained by other spectroscopic means. The proton structure of benzene in the smectic and nematic phases of p,p′-di-n-heptylazoxybenzene (HAB), however, does not follow the general trend observed in the purely nematic phases. But the dipolar CH splitting of methane also behaves inconsistently. 相似文献