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21.
A highly modular approach to fused 1,2,3-triazoles has been developed featuring a one-pot procedure combining copper(I) catalyzed azide-alkyne cycloaddition and palladium-catalyzed C-H bond functionalization. A class of structurally unique heterocycles was synthesized in good yields. 相似文献
22.
In continuing our studies of temporal slicings of spacetimes, we consider the collapse from rest of an initially homogeneous dust sphere, known as Oppenheimer-Snyder collapse. It is shown that in the case of harmonic slicing the whole spacetime becomes covered by slices extending to spatial infinity in contrast to maximal slicing. The behavior of the lapse function is discussed, especially for various data on the initial slice, and it is demonstrated that not every choice of the initial lapse leads to meaningful slicings. 相似文献
23.
Regioselective Ring‐Opening Polymerization of a Polyhydroxycarboxylic Acid for the Synthesis of a Nanoscale Carrier Material with pH‐Dependent Stability and Sustained Drug Release 下载免费PDF全文
Dipl.‐Chem. Alexander Ewe Dr. Anita Jansen de Salazar Dipl.‐Phys. Katharina Lemmnitzer Michael Marsch Prof. Dr. Achim Aigner Prof. Dr. Armin Geyer 《Angewandte Chemie (International ed. in English)》2015,54(21):6364-6369
Synthetic polyesters are usually composed of monohydroxycarboxylic acids to avoid the problem of regioselectivity during ring‐opening polymerization. In contrast, the linear polyester BICpoly contains four secondary OH groups and is nevertheless esterified regioselectively at only one of these positions. Neither the synthesis of the tricyclic monomers nor the ring‐opening polymerization requires protecting groups, making BICpoly an attractive novel and biocompatible polymer. BICpoly nanoparticles can be loaded with low‐molecular weight drugs or coated onto surfaces as thin films. The release of loaded compounds makes BICpoly an attractive depot for drug release, as shown herein by loading BICpoly with dyes or the cytostatic drug doxorubicin. BICpoly is distinguishable from other polymers by its characteristic pH‐dependent degradation. 相似文献
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Thomas A Höppner S Geyer H Schänzer W Petrou M Kwiatkowska D Pokrywka A Thevis M 《Analytical and bioanalytical chemistry》2011,401(2):507-516
A family of small peptides has reached the focus of doping controls representing a comparably new strategy for cheating sportsmen.
These growth hormone releasing peptides (GHRP) are orally active and induce an increased production of endogenous growth hormone
(GH). While the established test for exogenous GH fails, the misuse of these prohibited substances remains unrecognized. The
present study provides data for the efficient extraction of a variety of known drug candidates (GHRP-1, GHRP-2, GHRP-4, GHRP-5,
GHRP-6, alexamorelin, ipamorelin, and hexarelin) from human urine with subsequent mass spectrometric detection after liquid
chromatographic separation. The used method potentially enables the retrospective evaluation of the acquired data for unknown
metabolites by means of a non-targeted approach with high-resolution/high-accuracy full-scan mass spectrometry with additional
higher collision energy dissociation experiments. This is of great importance due to the currently unknown metabolism of most
of the targets and, thus, the method is focused on the intact peptidic drugs. Only the already characterised major metabolite
of GHRP-2 (d-Ala-d-2-naphthylAla-l-Ala, as well as its stable isotope-labelled analogue) was synthesised and implemented in the detection assay. Method validation
for qualitative purpose was performed with respect to specificity, precision (<20%), intermediate precision (<20%), recovery
(47–95%), limit of detection (0.2–1 ng/mL), linearity, ion suppression and stability. Two stable isotope-labelled internal
standards were used (deuterium-labelled GHRP-4 and GHRP-2 metabolite). The proof-of-principle was obtained by the analysis
of excretion study urine samples obtained from a single oral administration of 10 mg of GHRP-2. Here, the known metabolite
was detectable over 20 h after administration while the intact drug was not observed. 相似文献
27.
Geyer FL Ueda E Liebel U Grau N Levkin PA 《Angewandte Chemie (International ed. in English)》2011,50(36):8424-8427
High-density cell microarrays based on superhydrophilic microspots separated by superhydrophobic barriers have been realized. The microspots absorb water solutions, while the barriers prevent cross-contamination, thus allowing the spots to be used as reservoirs for transfection mixtures and preventing cell proliferation and cell migration between the microspots. The picture shows four cell types after two days of culturing on the microarray. 相似文献
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We prove the existence of a hyperbolic surface spread over the sphere for which the projection map has all its singular values
on the extended real line and such that the preimage of the extended real line under the projection map is homeomorphic to
the square grid in the plane. This answers a question raised by è. B. Vinberg.
Supported by the Alexander von Humboldt Foundation.
Supported by NSF grants DMS-0400636, DMS-0244421, and DMS-0244547. 相似文献
30.
D. Sieger H. Tietze-Jaensch R. Geick W. Zulehner A. F. Wright A. de Geyer 《Applied Physics A: Materials Science & Processing》1991,53(5):422-425
Czochralski grown silicon crystals contain interstitially dissolved oxygen which diffuses on heating to form precipitates of silica. We have examined these precipitates by small angle neutron scattering (SANS) in the Q-range 0.05 Å–1<Q<0.4 Å–1. The obtained SANS patterns reveal pronounced anisotropic intensity distributions which resemble the symmetry of the host crystal. The SANS spectra show an anisotropic central peak at Q<0.1 Å–1 due to the single particle shape and a number of weak intensities for larger Q-values. These weak side maxima are considered correlation peaks or quasi-elastic interference peaks. They show, however, an unexpected and distinct temperature dependence: with decreasing temperature below values of 220 K their intensity is lost slowly, but reversibly. At T = 50 K only the central peak from the single-particle scattering remains unchanged. Upon heating, the correlation peaks regain their former value of intensity and Q-position without any evidence of thermal hysteresis. 相似文献