An efficient protocol for the preparative purification of the major tea catechins (−)-epicatechin gallate (3) and epigallocatechin gallate (5) has been developed, employing liquid−liquid ...partitioning, high-speed countercurrent chromatography, and gel chromatography for final purification. The method is suitable for scale-up to significantly larger quantities.
The detection limits in two bioautographic assays have been determined for a series of antifungal compounds, including clinically used antimycotics, fungicidal agrochemicals, and various classes of ...secondary plant metabolites. Target organisms were the filamentous fungus Cladosporium cucumerinum and the yeast Candida albicans. For clinical agents and agrochemicals, the detection limits in the two assays reflected to a certain extent their known spectrum of activity. Most of the plant-derived compounds tested showed a positive response in both assays, but with detection limits varying by a factor up to tenfold. For screening purposes, it is thus advisable to use both tests, as some activities would otherwise go undetected. The MIC values of these substances were determined in order to verify a possible correlation with the detection limit in the bioautographic assays.
Global Positioning System (GPS) measurements (1991–1994) traversing the Greater and Lesser Caucasus mountains indicate a minimum N‐S shortening of 10±2 mm/yr. This represents approximately 30–50% of ...the NUVEL‐1A convergence rate between the Arabian and Eurasian plates. The remainder of the convergence appears to be accommodated in the areas south of the Lesser Caucasus, by a combination of right‐lateral strike‐slip faulting on planes oriented N 120°E, and shortening on thrust faults with similar orientations. More dense GPS observations conducted in the epicentral area of the April 29, 1991, Ms=7.0 Racha, Georgia earthquake, which occurred along the southern boundary fault of the Greater Caucasus mountains, indicate N‐S shortening following the earthquake which we interpret as due to post‐seismic slip. This mechanism may contribute to the substantially lower shortening rates derived from seismic moment tensors compared with tectonic estimates of shortening rates in the Caucasus.
Four alkaloids, previously identified in Isatis species, were tested for their inhibitory effect on histamine release. Whereas tryptanthrin, indirubin and deoxyvasicinone did not inhibit histamine ...release, the effect of indolin-2-one exceeded that of the mast cell stabilizing
drug disodium chromoglycate.
Data from a dual-frequency GPS network operated continuously from May 1998–October 1999 on Taal volcano, Philippines, were processed on a daily basis to monitor processes of crustal deformation ...associated with volcanic activity. During the 16-month period of observations, displacements totaled nearly 30
mm in the horizontal and 50
mm in the vertical over 2.7 and 5.8
km baselines. Relative site velocities, estimated from daily site coordinates using 60-day tapered windows, vary significantly and can exceed 150
mm
yr
−1 in the horizontal. Velocity estimates were used to invert for parameters of a point-source model of elastic strain. During periods in which velocities are significant, the motions have a localized source at very high confidence, and the source magnitude term fluctuates between inflationary and deflationary behavior on time scales of weeks to months. The largest site velocities (and corresponding deformation model parameters) are time-correlative with anomalous bursts of hydrothermal activity and high-frequency local seismicity. In each instance the onset of deformation precedes both seismicity and hydrothermal activity, and the hydrothermal event coincides with a rapid shift in the velocity behavior. The relative timing of these phenomena suggests that deformation and seismicity both are responding to punctuated migration of hydrothermal fluids.
A novel Self‐assembled Monolayer (SAM) forming molecule bisjulolidyldisulfide (9,9'‐disulfanediylbis(2,3,6,7‐tetrahydro‐1H,5H‐pyrido3,2,1‐ijquinoline)) is demonstrated which lowers the work function ...of metal surfaces by ≈1.2 eV and can be deposited in a 1 min process. Bisjulolidyldisulfide exists in a stable disulfide configuration prior to surface exposure and can therefore be stored, handled, and processed in ambient conditions. SAM from bisjulolidyldisulfide are deposited on metal surfaces (Au and Ag), including inkjet printed Ag on polyethylene terephthalate substrates, investigated by photoelectron and infrared spectroscopy, and used as electrodes in n‐type organic field effect transistor (OFET). Treatment of electrodes in OFET devices with with bisjulolidyldisulfide‐SAMs reduces the contact resistance by two orders of magnitude and improves shelf life with respect to pristine metal electrodes. The presented treatment also increases the surfaces wettability and thereby facilitates solution processing of a subsequent layer. These beneficial properties for device performance, processing, and stability, combined with ease of preparation and handling, render this SAM‐forming molecule an excellent candidate for the high‐throughput production of flexible electronic devices.
An ambient stable disulfide Self‐Assembled Monolayer‐forming molecule reduces the work function of metal electrodes by ≈1.2 eV and can be deposited from solution in 1 min. These monolayers have a strong effect on electron injection, improve surface wettability, device life time, and can be processed on printed silver electrodes.
Over the past decade, a number of new technologies and tools have become available in the biosciences and in analytical chemistry. They enable new approaches in the discovery of bioactive natural ...products which can be summarized with a few keywords such as miniaturization, on-line analysis of complex samples, study of molecular modes of action, and systems oriented approaches towards the characterization of drug effects in vitro and in vivo. Some of the technologies which are useful in the context of natural products discovery will be discussed and illustrated with examples from our lab. The efficient tracking of bioactivity in an extract remains a major challenge. We have replaced preparative activity-directed isolation by HPLC-based activity profiling at analytical scale. In the search for natural products leads, we prefer assays with high information content and complex endpoints, such as phenotypical screens, over biochemical assays. The molecular targets for these leads are subsequently studied with the tools of molecular and cell biology. HPLC-based activity and metabolite profiling will be illustrated with the example of the anti-inflammatory plant Isatis tinctoria, while phenotypical screening and subsequent characterization of signaling pathways will be discussed with the example of fungal pyridone alkaloids from Paecilomyces militaris.
The postgenomic era offers a range of new tools and approaches for an essentially unbiased and global investigation which does not need to be hypothesis-driven. The application of genome-wide expression profiling in the characterization of extracts will be described with our ongoing studies on Cimicifuga racemosa (L.) Nutt. and Leuzea carthamoides DC. Findings from array experiments are confirmed by quantitative PCR and functional assays, followed by HPLC-based activity profiling, eg. for AhR-agonistic activity, and by structure determination with LC-PDA-MS and microprobe NMR in HPLC fractions.
Reference
: 1. Potterat, O., Hamburger, M. (2006), Curr. Org. Chem., in press.
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