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861.
862.
Ferstl M Strasser A Wittmann HJ Drechsler M Rischer M Engel J Goepferich A 《Langmuir : the ACS journal of surfaces and colloids》2011,27(23):14450-14459
We investigated whether cationic peptides that contain hydrophobic side chains were able to stabilize themselves via hydrophobic interactions between neighboring peptide molecules upon electrostatic binding to oppositely charged polyelectrolytes. The interaction mechanism was examined through a model system consisting of the anionic polyelectrolyte alginate and the cationic decapeptide ozarelix. The interaction resulted in the formation of highly ordered complexes that were noticeable upon visual inspection. These complexes were then investigated by microscopic techniques and shown to exhibit a branched network structure. Cryogenic-temperature transmission electron microscopy (cryo-TEM) and negative staining TEM revealed that the molecular interactions between alginate and ozarelix led to the formation of nanofibers. The rodlike nanofibers had a diameter distribution of 4-8 nm. Isothermal titration calorimetry was used to determine the thermodynamic parameters of the alginate-ozarelix interaction. The binding constant was found to be on the order of 10(6) M(-1), indicating a high binding affinity. The interaction of the peptide with the polyelectrolyte triggered profound changes in the conformation of ozarelix, which was confirmed by UV spectroscopy and circular dichroism. On the basis of these experimental results, a theoretical modeling study of the alginate-ozarelix interaction was conducted to gain a better molecular-level understanding of the complex structure. It revealed that, upon binding of ozarelix to alginate, new intermolecular and intramolecular aromatic interactions between the ozarelix molecules occurred. These interactions changed the conformation of the peptide, a modification in which the aromatic side chains played a major role. Our results indicate that the cationic peptides interact with the polyanions via electrostatic interactions, but are additionally stabilized via hydrophobic interactions. This binding mode may serve as a powerful tool to extend the duration of drug release in hydrogel drug delivery systems. 相似文献
863.
Burghart J Sorg A Brückner R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(23):6469-6483
Stereoselective syntheses of 1,6‐bis(tributylstannyl)hexa‐1,3,5‐trienes, 1,8‐bis(tributylstannyl)octa‐1,3,5,7‐tetraenes, and 1,10‐bis(tributylstannyl)deca‐1,3,5,7,9‐pentaenes with various methylation patterns were achieved based on stereocomplementary C?C bond‐forming reactions. All‐E isomers resulted from Ramberg–Bäcklund rearrangements of distannylated diallyl‐, allylpentadienyl‐, or bis‐ (pentadienyl)sulfones. Mono‐Z‐configured 1,ω‐bis(tributylstannyl)‐1,3,5‐polyenes emerged from (Sylvestre–)Julia olefinations of Bu3Sn‐substituted enals or dienals with Bu3Sn‐substituted allyl or pentadienyl benzothiazolylsulfones. Related Ramberg–Bäcklund approaches provided all‐E‐1‐bromo‐6‐(tributylstannyl)hexa‐1,3,5‐triene but not all‐E‐1‐(tetramethyldioxaborolanyl)‐6‐(tributylstannyl)hexa‐1,3,5‐triene. 相似文献
864.
Markus Ostermann Achim Berger Christian Mans Christoph Simons Stephanie Hanning Anton Janßen Martin Kreyenschmidt 《Accreditation and quality assurance》2011,16(10):515-522
The Federal Institute for materials research and testing (BAM) in cooperation with the Fachhochschule Münster has developed
a new certified polymeric reference material, BAM-H010. The reference material consists of acrylonitrile–butadiene–styrene
terpolymer (ABS) and has been doped with different contents of the elements Br, Cd, Cr, Hg and Pb. The monitoring of these
elements is demanded in the EU directive 2002/95/EG, commonly referred to as RoHS. We have shown that the uncertainty contribution
of the thermal long-term stability (u
stability) is negligible compared to the contribution to the uncertainty caused by the method used for the characterization of the
elemental content and the batch inhomogeneity (u
homogeneity). The stability of the ABS material during exposure of the samples with hard X-radiation leads to a degradation of the ABS
matrix with either long- or short-chain products. 相似文献
865.
Najbjerg H Afseth NK Young JF Bertram HC Pedersen ME Grimmer S Vogt G Kohler A 《The Analyst》2011,136(8):1649-1658
We investigated the applicability of FTIR-spectroscopy as a high throughput screening method for detection of biochemical changes in intact liver cells in bulk upon fatty acid exposure. HepG2 cells adapted to serum free (HepG2-SF) growth were exposed to four different fatty acids, three octadecenoic acids, differing in cis/trans-configuration or double bond position (oleic acid, elaidic acid and vaccenic acid) as well as palmitic acid in three days. High throughput FTIR spectroscopic measurements on dried films of intact cells showed spectra with high signal-to-noise ratio and great reproducibility. When applying principal component analysis (PCA) a clear discrimination between fatty acid exposures was observed. Higher levels of triacylglycerides were accumulated in cells exposed to elaidic acid than when exposed to the other fatty acids; the least accumulation appeared to be in cells exposed to palmitic acid. An increased absorption at ~966 cm(-1) corresponding to trans-double bond was detected upon elaidic acid exposure but not upon vaccenic acid exposure. Instead, upon vaccenic acid exposure two new absorption bands were observed at 981 and 946 cm(-1) due to the presence of double bond conjugation. Raman spectroscopy on single cells, with and without treatment by vaccenic acid, confirmed the presence of conjugation. By fatty acid composition analysis, the conjugation was further specified to be conjugated linoleic acid (CLA) isomers. Thus, instead of being preserved as a monounsaturated fatty acid, vaccenic acid was converted into CLA in HepG2 cells. The results demonstrate the applicability of high-throughput FTIR spectroscopy as an explorative method in in vitro systems from which biologically relevant hypotheses can be generated and further investigated. 相似文献
866.
Excited state dynamics of Eu3+ in the partially disordered crystals La3Ga5SiO14 and La3Ga5.5Ta0.5O14
S. Georgescu O. Toma A.M. Chinie L. Gheorghe A. Achim A.S. Stefan 《Journal of luminescence》2008,128(5-6):741-743
The spectroscopic properties of two partially disordered crystals, langasite (LGS) and langatate (LGT), doped with Eu3+ were investigated. The fluorescence lifetimes of the 5D0 and 5D1 excited levels are measured. The spectral overlapping between the luminescence from the 5D0 and 5D1 levels was eliminated using pulsed excitation at 532 nm and suitable delays in order to improve the precision of the calculation of the spectroscopic figures of merit R0, R2 (the areas of the electric-dipole transitions 5D0→7F0 and 5D0→7F2, respectively, divided by the area of the magnetic-dipole one—5D0→7F1). The maximum splitting of the 7F1 level (ΔE) is calculated from the luminescence spectra and the B20 crystal field parameter is determined. We obtain R0(LGS)>R0(LGT), R2(LGS)<R2(LGT), and ΔE(LGS)>ΔE(LGT), and we discuss these results taking into account structural data, covalency and J-mixing effects. 相似文献
867.
For unifying the chemical nomenclature the International Union of Pure and Applied Chemistry (IUPAC) has given actual recommendations which already influence our daily use in the naming of the elements. As a typical example taken the naming of element 74 – wolfram or tungsten – the historical delevopment of this more than two hundred years lasting controversy is highlighted. 相似文献
868.
Beil FW Wixforth A Wegscheider W Schuh D Bichler M Blick RH 《Physical review letters》2008,100(2):026801
We study the formation of shock waves in a nanomechanical resonator with an embedded two-dimensional electron gas using surface acoustic waves. The mechanical displacement of the nanoresonator is read out via the induced acoustoelectric current. Applying acoustical standing waves, we are able to determine the so-called anomalous acoustocurrent. This current is found only in the regime of shock wave formation. 相似文献
869.
Hans‐Achim Wagenknecht 《Chemie in Unserer Zeit》2002,36(5):318-330
DNA charge transfer chemistry has been subject of considerable interest with consequences in the formation of oxidative damage to the DNA which can result in mutagenesis or carcinogenesis. In this article, important examples of spectroscopical and biochemical assays are compared and discussed in terms of the effiencies, rates, and mechanisms. Coupled with the demonstration that such charge transfer can be modulated both negatively and positively by DNA‐binding proteins, these observations therefore suggest the intriguing possibility that DNA‐mediated charge transfer chemistry is biological relevant and may play a role in cellular processes. Additionally, charge transfer chemistry plays a growing role in the recent development of DNA chips detecting mutations or lesions of nucleic acids. 相似文献
870.
This paper discusses the suitability of hydrogel actuators as drives of automatic pumps for long-term drug release. We demonstrate that such actuators can execute a defined task if several functional units are connected serially. Investigated functions of this pump are the adjustability of the time-delay from the initial operation up to the beginning of the drug release, opening the sterile drug ampoule, and the drug release at a specified timeframe. The described parameters to influence the pump behaviour are satisfying only for realization of continuous working devices. An outlook of the development of programmable pulsate pumps is given. 相似文献