Recent developments in the rapid analysis of plants and tracking their bioactive constituents

Natural products chemistry has witnessed many new developments in the last 5 years like extractions with subcritical water and ionic liquids, LC/HRMS and LC/SPE/cryo-NMR, UHPLC, TLC/MS, MS-based preparative HPLC, comprehensive chromatography (GC × GC, LC × LC), high-throughput screening, introduction of monolithic columns, miniaturisation, and automated structure identification. Nevertheless identifying bioactive constituents in complex plant extracts remains a tedious process. The classical approach of bioassay guided fractionation is time-consuming while off-line screening of extracts does not provide information on individual compounds and sometimes suffers from false positives or negatives. One way out of this is by coupling chromatography with chemical or biochemical assays, so called high resolution screening. An example is the development of HPLC on-line assays for antioxidants. By the post-column addition of a relatively stable coloured radical like DPPH¿ or ABTS¿+, radical scavengers are detected as negative peaks because in a reaction coil they reduce the model radical to its reduced, non-coloured form. When combined with LC/DAD/MS and LC/SPE/NMR, reliable identification of active constituents becomes possible without the necessity of ever isolating them in a classical sense. Also for finding leads for new drugs, combining HPLC with biochemical assays is interesting but technically more difficult. Most enzymes do not work at the organic modifier concentrations commonly encountered in RP-HPLC and the reaction time is often longer requiring dilution and lengthy coils respectively. Therefore, new techniques have to be implemented to gain the required sensitivity for on-line enzyme assays. For stable analytes, high temperature LC offers a solution to the organic modifier problem. When enzymes are highly expensive, like those used in the screening for Cytochrome P450 inhibitors, miniaturisation to chip format may offer a way out. Microreactors (chips) are not only useful for miniaturising larger assays but also offer completely new prospects in phytochemical analysis. One such application is in the sample clean-up of acids and bases like alkaloids. In a lay-out of three parallel channels of 100 ¿m width with the middle one containing organic phase and the two outer ones water of high pH (feed phase) and low pH (trapping phase) such a chip replaces two classical LLE steps but is much faster and requires less solvents and less manpower input

Backward Erosion Piping Model Verification Using Cases in China and The Netherlands

Backward erosion piping, the process of shallow pipe development in the sandy foundation of levees, is a threat to the safety of levees in countries like China and the Netherlands. Several models are available to predict the required critical head for this phenomenon, i.e. Bligh’s model and Sellmeijer’s model. Well-documented breach cases, which unfortunately are rare, give the opportunity to verify the applicability of prediction models. In this paper two piping cases in China and one piping case in the Netherlands have been described and analyzed in order to compare the outcome of prediction models with this actual data. It is concluded that Bligh’s model is easy to apply due to a small number of input parameters. The use of this model as a first step in safety assessment is limited due to the fact that it can give lower critical head predictions than the more accurate Sellmeijer model. On the other hand, the Sellmeijer model is more difficult to apply due to its sensitivity to permeability and grain size parameters. This sensitively results in a wide range for the critical head due to large uncertainties in the parameters. A probabilistic approach for parameter estimation combined with a more detailed soil investigation where necessary is recommended for a more accurate piping prediction

How to assist probationers with debt problems during supervision?:A qualitative study into the experiences of both probation officers and clients

Little research exists on what works in the supervision of offenders with debt problems. This qualitative study aims to provide insight into the barriers probation officers and clients experience during supervision regarding debt and the support that clients need. Interviews were conducted with 33 Dutch probation officers and 16 clients. The results show that debt often negatively influences clients’ lives and hinders their resocialization. Probation officers lack effective methods to support clients with debt problems. To adequately help clients with debt problems, probation officers should obtain more knowledge about effective interventions and collaborate more closely with debt specialists from the probation supervision outset

Modelling survival and connectivity of Mnemiopsis leidyi in the south-western North Sea and Scheldt estuaries

Three different models were applied to study the reproduction, survival and dispersal of Mnemiopsis leidyi in the Scheldt estuaries and the southern North Sea: a high-resolution particle tracking model with passive particles, a low-resolution particle tracking model with a reproduction model coupled to a biogeochemical model, and a dynamic energy budget (DEB) model. The results of the models, each with its strengths and weaknesses, suggest the following conceptual situation: (i) the estuaries possess enough retention capability to keep an overwintering population, and enough exchange with coastal waters of the North Sea to seed offshore populations; (ii) M. leidyi can survive in the North Sea, and be transported over considerable distances, thus facilitating connectivity between coastal embayments; (iii) under current climatic conditions, M. leidyi may not be able to reproduce in large numbers in coastal and offshore waters of the North Sea, but this may change with global warming; however, this result is subject to substantial uncertainty. Further quantitative observational work is needed on the effects of temperature, salinity and food availability on reproduction and on mortality at different life stages to improve models such as used here

Defect-unbinding and the Bose-glass transition in layered superconductors

The low-field Bose-glass transition temperature in heavy-ion irradiated Bi_2Sr_2CaCu_2O_8+d increases progressively with increasing density of irradiation-induced columnar defects, but saturates for densities in excess of 1.5 x10^9 cm^-2. The maximum Bose-glass temperature corresponds to that above which diffusion of two-dimensional pancake vortices between different vortex lines becomes possible, and above which the ``line-like'' character of vortices is lost. We develop a description of the Bose-glass line that is in excellent quantitative agreement with the experimental line obtained for widely different values of track density and material parameters.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let