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31.
Peter Brenneisen Jinsook Oh Meinhard Wlaschek Jutta Wenk Karlis Briviba Christina Hommel Gemot Herrmann Helmut Sies Karin Scharffetter-Kochanek 《Photochemistry and photobiology》1996,64(5):877-885
Abstract— The wavelength dependence for the regulation of two major matrix-metalloproteinases, interstitial collagenase (MMP-1) and stromelysin-1 (MMP-3), and their major inhibitor, tissue inhibitor of metalloproteinases (TIMP-1), was studied in human dermal fibroblasts in vitro. Monochromatic irradiation at 302, 307, 312 and 317 nm with intensities ranging from 20 to 300 J/m2 increased MMP-1 and MMP-3 mRNA steady-state levels and the secretion of the corresponding proteins up to 4.4-fold, whereas almost no increase was observed at wavelengths <290 nm. In contrast, the synthesis of TIMP-1 increased only marginally. This unbalance may contribute to the severe connective tissue damage related to photoaging of the skin. The wavelengths responsible for MMP-1 and MMP-3 induction reported here are distinct from the absorption spectrum of DNA and are different from results previously reported in the literature. Importantly, they overlap with wavelengths whose intensity is predicted to increase on the earth's surface upon ozone depletion. Intensities and particular wavelengths used in our studies in vitro can be absorbed readily by fibroblasts within the skin in vivo and, thus, are relevant for risk assessment and development of protective agents. 相似文献
32.
Background
One of the signatures of Alzheimer's disease is the accumulation of aggregated amyloid protein, Aβ, in the brain. Aβ arises from cleavage of the Amyloid Precursor protein by β and γ secretases, which present attractive candidates for therapeutic targeting. Two β-secretase candidates, ASP-1 and ASP-2, were identified as aspartic proteases, both of which cleave the amyloid precursor at the β-site. These are produced as immature transmembrane proteins containing a pro-segment.Results
ASP-2 expressed in HEK293-cells cleaved the Swedish mutant amyloid precursor at different β-sites at different pHs in vitro. Recent reports show that furin cleaves the pro-peptide of ASP-2, whereas ASP-1 undergoes auto-catalysis. We show that purified recombinant ASP-2 cleaves its own pro-peptide at ph 5 but not pH 8.5 as seen by mass spectrometry, electrophoresis and N-terminal sequencing.Conclusion
We suggest that ASP-2 processing as well as activity are influenced by pH, and hence the cellular localisation of the protein may have profound effects on the production of Aβ. These factors should be taken into consideration in the design of potential inhibitors for these enzymes. 相似文献33.
Christina Prveva Pawel Ganev Venetta Ninova und Antoanetta Delijska 《Fresenius' Journal of Analytical Chemistry》1971,255(2):113-115
Zusammenfassung Ein zweites spektrochemisches Verfahren zur Bestimmung von Silber, Blei, Zinn, Wismut, Tellur, Arsen und Antimon in Eisen und Stahl wurde entwickelt. Auch hier wird die spektrographische Analyse nach Auflösen der Probe in Salpetersäure und Eindampfen der Lösung zur Trockne durchgeführt. Die leichtflüchtigen Elemente werden ohne Puffer durch Anwendung eines inhomogenen Magnetfeldes und einer zweckmäßigen Elektrodenform störungsfrei und mit guter Reproduzierbarkeit bestimmt. Dabei sind die unteren Bestünmungsgrenzen gleich oder niedriger als die anderer spektrochemischer Methoden, die bisher beschrieben wurden. Das Verfahren zeichnet sich durch Schnelligkeit und Einfachheit aus.
Teil I: diese Z. 254, 16 (1971). 相似文献
Spectrochemical determination of trace elements in iron and steelPart II. determination of Ag, Pb, Sn, Bi, Te, As and Sb by using an inhomogeneous magnetic field
A second spectrochemical method for the determination of silver, lead, tin, bismuth, tellurium, arsenic and antimony in iron and steel has been developed. Here also the spectrographic analysis is to be carried out after dissolution of the sample in nitric acid and evaporation of the solution to dryness. Without buffer, the easily volatile elements are determined free of interferences and with good reproducibility by using an inhomogeneous magnetic field and electrodes of an appropriate form. The lower limits of determination are the same or lower than those obtained by any other spectrochemical method described. The method is characterised by rapidity and simplicity of procedure.
Teil I: diese Z. 254, 16 (1971). 相似文献
34.
Gray TG Rudzinski CM Meyer EE Holm RH Nocera DG 《Journal of the American Chemical Society》2003,125(16):4755-4770
The electronic, vibrational, and excited-state properties of hexanuclear rhenium(III) chalcogenide clusters based on the [Re(6)(mu(3)-Q)(8)](2+) (Q = S, Se) core have been investigated by spectroscopic and theoretical methods. Ultraviolet or visible excitation of [Re(6)Q(8)](2+) clusters produces luminescence with ranges in maxima of 12 500-15 100 cm(-)(1), emission quantum yields of 1-24%, and emission lifetimes of 2.6-22.4 microseconds. Nonradiative decay rate constants and the luminescence maxima follow the trend predicted by the energy gap law (EGL). Examination of 24 clusters in solution and 14 in the solid phase establish that exocluster ligands engender the observed EGL behavior; clusters with oxygen- or nitrogen-based apical ligands achieve maximal quantum yields and the longest lifetimes. The excited-state decay mechanism was investigated by applying nonradiative decay models to temperature-dependent emission experiments. Solid-state Raman spectra were recorded to identify vibrational contributions to excited-state deactivation; spectral assignments were enabled by normal coordinate analysis afforded from Hartree-Fock and DFT calculations. Excited-state decay is interpreted with a model where normal modes largely centered on the [Re(6)Q(8)](2+) core induce nonradiative relaxation. Hartree-Fock and DFT calculations of the electronic structure of the hexarhenium family of compounds support such a model. These experimental and theoretical studies of [Re(6)Q(8)](2+) luminescence provide a framework for elaborating a variety of luminescence-based applications of the largest series of isoelectronic clusters yet discovered. 相似文献
35.
Reducing the use of solvents is an important aim of green chemistry. Using micelles self-assembled from amphiphilic molecules dispersed in water (considered a green solvent) has facilitated reactions of organic compounds. When performing reactions in micelles, the hydrophobic effect can considerably accelerate apparent reaction rates, as well as enhance selectivity. Here, we review micellar reaction media and their potential role in sustainable chemical production. The focus of this review is applications of engineered amphiphilic systems for reactions (surface-active ionic liquids, designer surfactants, and block copolymers) as reaction media. Micelles are a versatile platform for performing a large array of organic chemistries using water as the bulk solvent. Building on this foundation, synthetic sequences combining several reaction steps in one pot have been developed. Telescoping multiple reactions can reduce solvent waste by limiting the volume of solvents, as well as eliminating purification processes. Thus, in particular, we review recent advances in “one-pot” multistep reactions achieved using micellar reaction media with potential applications in medicinal chemistry and agrochemistry. Photocatalyzed reactions in micellar reaction media are also discussed. In addition to the use of micelles, we emphasize the process (steps to isolate the product and reuse the catalyst). 相似文献
36.
Johan Hygum Dam Niels Langkjr Christina Baun Birgitte Brinkmann Olsen Aaraby Yoheswaran Nielsen Helge Thisgaard 《Molecules (Basel, Switzerland)》2022,27(20)
Background: The somatostatin receptors 1–5 are overexpressed on neuroendocrine neoplasms and, as such, represent a favorable target for molecular imaging. This study investigates the potential of [18F]AlF-NOTA-[1-Nal3]-Octreotide and compares it in vivo to DOTA- and NOTA-[1-Nal3]-Octreotide radiolabeled with gallium-68. Methods: DOTA- and NOTA-NOC were radiolabeled with gallium-68 and NOTA-NOC with [18F]AlF. Biodistributions of the three radioligands were evaluated in AR42J xenografted mice at 1 h p.i and for [18F]AlF at 3 h p.i. Preclinical PET/CT was applied to confirm the general uptake pattern. Results: Gallium-68 was incorporated into DOTA- and NOTA-NOC in yields and radiochemical purities greater than 96.5%. NOTA-NOC was radiolabeled with [18F]AlF in yields of 38 ± 8% and radiochemical purity above 99% after purification. The biodistribution in tumor-bearing mice showed a high uptake in tumors of 26.4 ± 10.8 %ID/g for [68Ga]Ga-DOTA-NOC and 25.7 ± 5.8 %ID/g for [68Ga]Ga-NOTA-NOC. Additionally, [18F]AlF-NOTA-NOC exhibited a tumor uptake of 37.3 ± 10.5 %ID/g for [18F]AlF-NOTA-NOC, which further increased to 42.1 ± 5.3 %ID/g at 3 h p.i. Conclusions: The high tumor uptake of all radioligands was observed. However, [18F]AlF-NOTA-NOC surpassed the other clinically well-established radiotracers in vivo, especially at 3 h p.i. The tumor-to-blood and -liver ratios increased significantly over three hours for [18F]AlF-NOTA-NOC, making it possible to detect liver metastases. Therefore, [18F]AlF demonstrates promise as a surrogate pseudo-radiometal to gallium-68. 相似文献
37.
Sreekar Wunnava Christina F. Dirscherl Jakub Výravský Dr. Aleš Kovařík Dr. Roman Matyášek Prof. Jiří Šponer Prof. Dieter Braun Dr. Judit E. Šponer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(70):17581-17585
The assembly of ancient informational polymers from nucleotide precursors is the central challenge of life's origin on our planet. Among the possible solutions, dry polymerization of 3’,5’-cyclic guanosine monophosphate (3’,5’-cGMP) has been proposed as a candidate to create oligonucleotides of 15–20 units in length. However, the reported sensitivity of the reaction to the presence of cations raised questions of whether this chemistry could be relevant in a geological context. The experiments in this study show that the presence of cations is not restrictive as long as the reaction is conducted in an acidic environment, in contrast to previous reports that suggested optimal conditions at pH 9. 相似文献
38.
Dr. Mohd Nazish Dr. Mujahuddin M. Siddiqui Dr. Samir Kumar Sarkar Dr. Annika Münch Christina M. Legendre Dr. Regine Herbst-Irmer Prof. Dietmar Stalke Prof. Dr. Herbert W. Roesky 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(5):1744-1752
This work describes the synthesis and coordination behavior of a new mixed-donor ligand PhC(NtBu)2SiC6H4PPh2 ( 1 ) containing both silylene and phosphine donor sites. Ligand 1 was synthesized from a reaction of ortho-lithiated diphenylphosphinobenzene (LiC6H4PPh2) with chlorosilylene (PhC(NtBu)2SiCl). Treatment of 1 with Se and GeCl2 resulted in SiIV compounds 2 and 3 by selective oxidation of the silylene donor. This strong σ-donor ligand induces dissociation of CuCl and PhBCl2 leading to formation of ionic complexes 4 and 5 respectively. The reaction of 1 with ZnCl2 and AlCl3 resulted in the formation of chelate complexes 5 and 7 , respectively, while treatment with EtAlCl2 and GaCl3 forms monodentate complexes 8 and 9 . X-ray analysis of 4 showed that the copper is in the spiro center of the two five-membered rings. Moreover, the copper(I)chloride has not been oxidized but dissociates to Cu+ and [CuCl2]−. All the compounds are well characterized by mass spectrometry, elemental analysis, NMR spectroscopy, and single-crystal X-ray diffraction studies. 相似文献
39.