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61.
The attachment of single ions to putative adsorption sites in the tails of collagen fibers is investigated by means of molecular dynamics simulations and discussed with respect to the very early steps of apatite/collagen biomineral formation. Our studies clearly demonstrate an increased flexibility of the tails of the triple‐helical collagen protein. Apart from the termini of the backbone, several side chains were also observed to be freely accessible to ion attachment from aqueous solution. The teleopeptide was systematically scanned for suitable adsorption sites for calcium, phosphate and fluoride ions. Association of these ions was then explored from potential of mean force calculations. The resulting energy profiles reveal a variety of favorable protein‐ion bonds and hint at the suitability of the collagen tails to promote apatite aggregation. 相似文献
62.
Joachim Angelkort Sander van Smaalen Prof. Dr. Sven Oliver Hauber Mark Niemeyer 《无机化学与普通化学杂志》2007,633(7):1031-1035
Single crystal X‐ray diffraction of Eu(SC36H49)2 has revealed a first order phase transition at a temperature of 119 K, that involves a reduction of the specific volume by 1 %. The transition corresponds to a doubling of the unit cell, as it is the result from reorientations of isopropyl groups that appear at peripheral sites of the organic ligands. It is argued that a denser packing is achieved at the expense of a less favourable conformation of one of the two crystallographically‐independent complexes in the low‐temperature phase. The Bond‐Valence method is used to show that interactions of equal strengths are present between europium and both sulphur atoms and both coordinating phenyl rings. 相似文献
63.
Maurer HH Tenberken O Kratzsch C Weber AA Peters FT 《Journal of chromatography. A》2004,1058(1-2):169-181
A liquid chromatographic-mass spectrometric assay with atmospheric pressure chemical ionization (LC-APCI-MS) is presented for screening for, library-assisted identification (both in scan mode) and quantification (selected-ion mode) of the beta-blockers acebutolol, diacetolol, alprenolol, atenolol, betaxolol, bisoprolol, bupranolol, carazolol, carteolol, carvedilol, celiprolol, esmolol, labetalol, metoprolol, nadolol, nebivolol, oxprenolol, penbutolol, propranolol, sotalol, talinolol and timolol in blood plasma after mixed-mode (HCX) solid-phase extraction (SPE) and separation by reverse-phase liquid chromatography with gradient elution. The validation data were within the required limits. The assay was successfully applied to authentic plasma samples allowing confirmation of diagnosis of overdose situations as well as monitoring of patients' compliance. 相似文献
64.
Molt O Rübeling D Schäfer G Schrader T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(17):4225-4232
Host molecule 1 displays a high affinity in water towards catecholamines and especially related structures such as beta-blockers with extended aromatic pi-faces (up to 7x10(3) M(-1) for each single complexation step or 5x10(7) M(-2) for both steps). The amphiphilic structural design leads to an extensive self-association of host molecules through their aromatic flanks. Above a cmc (critical micelle concentration) of 3x10(-4) M, host 1 forms micelles that produce a favorable microenvironment for hydrophobic interactions with the included guest molecules. Electrostatic attraction of the ammonium alcohol by the phosphonate anions is thus combined with hydrophobic contributions between the aromatic moieties. Ionic hydrogen bonds with polar OH or NH groups of the guest enforce the non-covalent interactions, and finally lead to increased specificity. Both its affinity and its selectivity towards adrenergic receptor substrates are greatly enhanced if the receptor molecule 1 is transferred from water into a lipid monolayer. Catecholamines and beta-blockers lead to drastically different effects at concentrations approaching the micromolar regime. Especially beta-blockers with minute structural changes can be easily distinguished from each other. In both cases, extensive hydrophobic interactions with a self-associated and/or self-organized microenvironment are largely responsible for the observed high efficiency and specificity. 相似文献
65.
66.
The creation and use of unnatural molecules to control cellular function is a long standing goal of the chemical community, but in general, these efforts have been directed at finding molecules to inhibit or activate a particular molecular target or function, or to elicit a particular phenotype. Here we show that multiple unnatural molecules (orthogonal ribosomes) can be used combinatorially, in a single cell, to program Boolean logic functions. These experiments show how attention to the molecular specificity of noncovalent interactions between unnatural macromolecules allows the synthesis of complex function from the "bottom-up" in living matter. 相似文献
67.
Summary In this work, an optimization procedure for gradient RPLC separation, using ternary mobile phases, is described. This procedure requires eight preliminary experiments in gradient elution mode to predict the retention surface for each solute over the whole triangular space. This is followed by computerized calculations to determine the best ternary gradient elution profile with respect to both selectivity and analysis time. The efficiency of this procedure from the point of view of rapidity and of accuracy, is illustrated for the specific separation of twelve phenyl urea herbicides. 相似文献
68.
Rapid prototyping of polymer microsystems via excimer laser ablation of polymeric moulds 总被引:1,自引:0,他引:1
Jensen MF McCormack JE Helbo B Christensen LH Christensen TR Geschke O 《Lab on a chip》2004,4(4):391-395
This study presents a novel method for rapid prototyping of polymer microsystems. The method is based on excimer laser ablation of a thermally and mechanically stable polymer, such as PEEK (poly-ether-ether-ketone). A negative of the desired microsystem is laser machined in PEEK, which can then be used directly for hot embossing or injection moulding of a series of prototypes. This approach is very rapid and considerably cheaper than more traditional approaches to toolmaking, while still performing well in terms of reproduction of tool dimensions. The reduction in time and cost for a master tool using this method opens up new possibilities for testing small series in the R&D phase of a microsystem. Finally, two particular applications of the technique are presented. 相似文献
69.
Kaval N Ermolat'ev D Appukkuttan P Dehaen W Kappe CO Van der Eycken E 《Journal of combinatorial chemistry》2005,7(3):490-502
The "click chemistry" approach has been explored on the 2-(1H)-pyrazinone scaffold for the generation of pharmacologically interesting heterocyclic moieties. Huisgen 1,3-dipolar cycloaddition has been evaluated as the key step for the construction of the 1,2,3-triazole ring at the C-3 position of 2-(1H)-pyrazinones. Two different pathways have been successfully evaluated: (1) via C-C or C-O linkage of the acetylenic part to the C-3 position of the 2-(1H)-pyrazinone scaffold or (2) via azide introduction in the C-3 position. The subsequent application of "click chemistry" resulted in the formation of hitherto unknown skeletons. Microwave irradiation has successfully been applied in different steps of the sequence. 相似文献
70.
Extraction of capsaicins in aerosol defense sprays from fabrics 总被引:2,自引:0,他引:2
The use of aerosol defense sprays has increased as a means of self-defense and as a weapon in the commission of a crime. The residue of these sprays is often left behind as physical evidence on a victim's clothing or personal belongings. As the popularity of self-defense weaponry increases, so does the likelihood that it will be encountered in forensic casework. The extraction, recovery from fabrics, and identification of residue from defense sprays is described. The commonly used extraction method of liquid-liquid extraction is compared to solid phase microextraction (SPME) to recover capsaicin and dihydrocapsaicin from cotton swabs. The use of SPME resulted in lower limits of detection and greater recovery efficiency when compared to solvent extraction. SPME also provided more consistent recovery and less variability when compared to solvent extraction. The effect of use of various types of evidence packages on the preservation of this type of evidence is also reported. The collection and analysis of hand swabs after normal discharge of pepper spray canisters was studied indicating the low persistence of these compounds on the hands of the person conducting the spraying. Finally, the results of a real case whereby solvent-solvent extraction did not provide the necessary sensitivity for extracting the capsaicin compounds on the garments of a victim of an alleged spraying and the SPME extraction provided the recovery and identification of the compounds is also presented. 相似文献