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21.
Processes such as chromatographic separation and nanofiltration can remove low molecular weight sugars from liquid mixtures of oligosaccharides. As an alternative for the separation of such liquid mixtures, we studied mass diffusion separation of such sugars in a microfluidic device with incorporated nanofiltration membranes. This separation method is based on differences between diffusivities of components and does not require high transmembrane pressures. The effects of channel depth and flow rate were studied in experiments. The key parameters selectivity and rejection increased with increasing channel depth due to increased external mass transfer limitations. Among the studied membranes, the obtained selectivities and rejections correlated to the specified retention values by the manufacturers. Compared to more conventional nanofiltration where high pressure forces solutes through membranes, we obtained corresponding selectivities and fluxes of only an order of magnitude smaller. Simulated results indicated that with optimized microchannel and membrane dimensions, the presented separation process can compete with currently available separation technologies. 相似文献
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23.
This paper presents a new microreactor dedicated for pulsed electric field treatment (PEF), which is a pasteurization method that inactivates microorganisms with short electric pulses. The PEF microreactor consists of a flow-through channel with a constriction where the electric field is focussed. Compared to a laboratory-scale setup 25 times lower voltages were needed to obtain the same electric field strength due to the close electrode spacing. A finite element model showed that the electric field intensity is very homogeneous throughout the channel, which is crucial for the pasteurization processes. Experiments where artificial vesicles, loaded with carboxyfluorescein, were electroporated showed that the maximum transmembrane potential adequately described the processes both in the microreactor and the laboratory-scale setup, although the length scales are different. Electroporation started at a transmembrane potential of 0.5 V, reaching a maximum fraction of electroporated vesicles of 51% at a transmembrane potential of 1.5 V. The partial electroporation is not a result of the heterogenity of the vesicles or the electric field. With this new PEF microreactor it is possible to study the PEF process in more detail. 相似文献
24.
M. Remko 《Chemical Papers》2007,61(2):133-141
Computational chemical methods have been used to correlate the molecular properties of the 10 ACE inhibitors (captopril, enalapril,
perindopril, lisinopril, ramipril, trandolapril, quinapril, fosinopril, benazepril, and cilazapril) and some of their active
metabolites (enalaprilat, perindoprilat, ramiprilat, trandolaprilat, quinaprilat, fosinoprilat, benazeprilat, and cilazaprilat).
The computed pK
a values correlate well with the available experimental values. In the dicarboxylic ACE inhibitors, the carboxyalkyl carboxylate
group of the ACE inhibitors studied is more acidic than the C-terminal carboxylate. However, at physiological pH = 7.4 both
carboxyl groups of ACE inhibitors are completely ionized and the dicarboxyl-containing ACE inhibitors behave as strong acids.
The available experimental partition coefficients of these ACE inhibitors investigated are well reproduced by the neural network-based
ALOGPs and the fragment-based KoWWiN methods. All parent drugs (and prodrugs), with the exception of fosinopril, are compounds
with low lipophilicity. Calculated pK
a, lipophilicity, solubility, absorption, and polar surface area of the most effective ACE inhibitors for the prevention of
myocardial infarction, perindopril and ramipril, were found similar. Therefore, it is probable that the experimentally observed
differences in the survival benefits in the first year after acute myocardial infarction in patients 65 years of age or older
correlate closely to the physicochemical and pharmacokinetic characteristics of the specific ACE inhibitor that is used. 相似文献
25.
The formation of 2-aminoacetamide from ammonia and glycine and N-glycylglycine from two glycine molecules with and without Mg2+, Cu2+, and Zn2+ cations as catalysts have been studied as model reactions for peptide bond formation using the B3LYP functional with 6–311+G(d,p) and 6–31G(d) basis sets. The B3LYP method was also used to characterize the nine gas–phase complexes of neutral glycine, its amide (2-aminoacetamide), and N-glycylglycine with Lewis acids Mg2+, Cu2+, and Zn2+, respectively. Further, the gas-phase hydration of metal-coordinated complexes of glycine, 2-aminoacetamide, and N-glycylglycine was also investigated. Finally, the effect of water on the structure and reactivity of the metal coordinated complexes was determined. Enthalpies and Gibbs energies for the stationary points of each reaction have been calculated to determine the thermodynamics of the reactions investigated. A substantial decrease in reaction enthalpies and Gibbs energies was found for glycine–ammonia and glycine–glycine reactions coordinated by Mg2+, Cu2+, and Zn2+ ions compared to those of the uncoordinated 2-aminoacetamide bond formation. The formation of a dipeptide is a more exothermic process than the creation of simple 2-aminoacetamide from glycine. The energetic effect of the transition metal ions Cu2+ and Zn2+ is of similar strength and more pronounced than that of the Mg2+ cation. The basicity order of the amides investigated shows the order: NH2CH2CO2H < NH2CH2CONH2 < NH2CH2CONHCH2CO2H. Interaction enthalpies and Gibbs energies of metal ion–amide complexes increase as Mg2+2+2+. In both reactant (glycine) and reaction products (2-aminoacetamide, N-glycylglycine) dihydration caused considerable reduction (about 200–500 kJ-mol–1) of the strength of the bifurcated metal–amide bonds. Solvent effects also reduce the reaction enthalpy and Gibbs energy of reactions under study. 相似文献
26.
Norbert Hubin Robin Arsenault Ralf Conzelmann Bernard Delabre Miska Le Louarn Stefan Stroebele Remko Stuik 《Comptes Rendus Physique》2005,6(10):1099-1109
We will introduce the present knowledge of the turbulence profile and in particular we will emphasise the existence of a turbulence layer close to the ground. Then we will present the concept of Ground Layer Adaptive Optics and will provide estimates of performance expected from such systems and their potential for astronomical applications. Finally we will provide practical implementation concepts for two instruments at the VLT, MUSE and HAWK-I using multi-Laser Guide Stars and a large Deformable Secondary Mirror. The latter will also be described as its use is optimum for GLAO systems. To cite this article: N. Hubin et al., C. R. Physique 6 (2005). 相似文献
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This study reports in detail the results of systematic large-scale theoretical investigations of the acidic dimeric structural
units (D–E, E–F, F–G, and G–H) and pentamer D–E–F–G–H (fondaparinux) of the glycosaminoglycan heparin, and their anionic forms.
The geometries and energies of these oligomers have been computed using HF/6–31G(d), Becke3LYP/6–31G(d), and Becke3LYP/6–311+G(d,p)
methods. The optimized geometries indicate that the most stable structure of these units in the neutral state is stabilized
via a system of intramolecular hydrogen bonds. The equilibrium structure of these species changed appreciably upon dissociation.
Water has a remarkable effect on the geometry of the anions studied. Because of high negative charge, the solvent effect also
resulted in an appreciable energetic stabilization of biologically active anionic forms of these glycosaminoglycans. The stable
energy conformations around glycosidic bonds found for dimers and pentamer investigated are compared and discussed with the
available experimental X-ray structural data for the structurally related heparin-derived pentasaccharides in cocrystals with
proteins. 相似文献
29.
Interactions between metal ions and amino acids are common both in solution and in the gas phase. Here, the effect of metal ions and water on the structure of glycine is examined. The effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) and water on structures of Gly.Mn+(H2O)m and GlyZwitt.Mn+(H2O)m (m = 0, 2, 5) complexes have been determined theoretically by employing the hybrid B3LYP exchange-correlation functional and using extended basis sets. Selected calculations were carried out also by means of CBS-QB3 model chemistry. The interaction enthalpies, entropies, and Gibbs energies of eight complexes Gly.Mn+ (Mn+ = Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) were determined at the B3LYP density functional level of theory. The computed Gibbs energies DeltaG degrees are negative and span a rather broad energy interval (from -90 to -1100 kJ mol(-1)), meaning that the ions studied form strong complexes. The largest interaction Gibbs energy (-1076 kJ mol(-1)) was computed for the NiGly2+ complex. Calculations of the molecular structure and relative stability of the Gly.Mn+(H2O)m and GlyZwitt.Mn+(H2O)m (Mn+ = Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+; m = 0, 2, and 5) systems indicate that in the complexes with monovalent metal cations the most stable species are the NO coordinated metal cations in non-zwitterionic glycine. Divalent cations Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+ prefer coordination via the OO bifurcated bonds of the zwitterionic glycine. Stepwise addition of two and five water molecules leads to considerable changes in the relative stability of the hydrated species. Addition of two water molecules at the metal ion in both Gly.Mn+ and GlyZwitt.Mn+ complexes reduces the relative stability of metallic complexes of glycine. For Mn+ = Li+ or Na+, the addition of five water molecules does not change the relative order of stability. In the Gly.K+ complex, the solvation shell of water molecules around K+ ion has, because of the larger size of the potassium cation, a different structure with a reduced number of hydrogen-bonded contacts. This results in a net preference (by 10.3 kJ mol(-1)) of the GlyZwitt.K+H2O5 system. Addition of five water molecules to the glycine complexes containing divalent cations Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+ results in a net preference for non-zwitterionic glycine species. The computed relative Gibbs energies are quite high (-10 to -38 kJ mol(-1)), and the NO coordination is preferred in the Gly.Mn+(H2O)5 (Mn+ = Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) complexes over the OO coordination. 相似文献
30.
Detz RJ Heras SA de Gelder R van Leeuwen PW Hiemstra H Reek JN van Maarseveen JH 《Organic letters》2006,8(15):3227-3230
[Structure: see text] A novel P,N-type ligand family (ClickPhine) is disclosed that is easily accessible using the Cu(I)-catalyzed azide-alkyne "click" cycloaddition. A diverse set of ligands was made in just three steps from readily available starting materials to give several homogeneous and a heterogeneous catalyst. Preliminary experiments show the efficacy of these ligands in the Pd-catalyzed allylic alkylation reaction. 相似文献