An analysis of an induced-fit type inclusion phenomenon of a paracyclophane with benzene by means of van der waals potential calculations

The binding process of the paracyclophane 1 with benzene is classified into two types; namely simple fit and induced fit. In the former case, it is assumed that the geometry of the host is fixed to that in the free state during complexation. On the basis of the MMP2 calculations, the induced fit type process, allowing all motional freedoms of the host and the guest, is essential in forming the stable inclusion complex with benzene. By the use of van der Waals potential maps, it is confirmed that the force-field inside the cavity of the host is effective for the inclusion of benzene.     

Fast HPLC for quality control of Harpagophytum procumbens by using a monolithic silica column: method transfer from conventional particle-based silica column

The applicability of a monolithic C18-bonded silica column for the rapid HPLC separation of ingredients in medicinal plants and their phytopharmaceutical preparations has been evaluated in the author's laboratory. In this presentation, an existing method for the determination of the iridoid glycoside harpagoside in Harpagophytum procumbens (Devil's Claw) was successfully transferred from a conventional particle-based C18 silica column to a monolithic silica column. The very high porosity of the stationary phase allows chromatography with a much lower backpressure than on conventional columns. Therefore, the flow rate could be easily increased from 0.8 mL/min (particle-based column) to 5 mL/min (monolithic column) and the run-time reduced from 30 to 5 min (that is a reduction about 85% !), without losing any chromatographic resolution of the compound of interest. The amount of harpagoside was measured with the original method on a conventional particle-based silica column and on the adapted method on a monolithic silica column. The statistical mean t-test showed no significant differences of the variances and the means indicating that the fast HPLC method is an acceptable alternative. The shorter analysis time makes the method very valuable for commercial quality control of Harpagophytum extracts and its pharmaceutical preparations.     

A method for the mg scale separation of curium(III) from americium(III) by HPLC using a SCX column

Radon, thoron and their progeny are responsible for more than 50% of the total ionizing radiation dose received by human population. In the present work, radon, thoron and their progeny concentration measurements have been carried out in 150 dwellings in different villages of Faridabad district of Haryana, India. Pin-holes based twin cup dosimeter containing LR-115 type-II film (solid state nuclear track detectors) has been used for the time-integrated passive measurement of radon and thoron concentrations. The dosimeters were deployed for three seasons each having 4 months of exposure period. For measurement of radon and thoron progeny concentration (EERC/EETC), deposition based direct radon/thoron progeny sensors (DRPS/DTPS) were deployed with dosimeters. Based on the gamma exposure rate in different villages during preliminary survey and type of houses available in the regions, numbers of dwellings of different categories have been selected. Radon, thoron and their progeny concentration and total annual effective inhalation dose were calculated and compared with the recommended limits by UNSCEAR, ICRP and WHO.

     

Development of an automatic solid phase extraction and liquid chromatography mass spectrometry method by using a monolithic column for the analysis of Cyclosporin A in human plasma

A sensitive and specific and automated liquid chromatography-electrospray mass spectrometric (LC-ESI-MS) assay for the quantification of Cyclosporin A in human plasma was developed. Following a simple protein precipitation step, the supernatant was extracted on-line and directly injected into the system LC-ESI-MS. A relatively new type of monolithic column consisting of a silica rod with bimodal pore structure was used to achieve a retention time of 2.4 min with a very low backpressure at a flow rate of 1 ml/min. The assay was linear from 0.050 to 1.000 μg/ml. The mean recovery was 91%. The mean inter-day and intra-day precisions were 1.85% and 2.83%, respectively. The combination of the automated solid phase extraction and the low retention time achieved with this columns increase the throughput and decrease the time of analysis of each sample. This technology is useful in order to improve the efficiency of the bioanalytical studies.