NMR determination of pKa values of indoloquinoline alkaloids

Malaria is one of the most serious global health problems. Isolating new therapeutic agents with potential antimalarial activity from natural sources or preparing such agents either semisynthetically or synthetically is one strategy for solving the problem of resistance constantly evolving to the drugs currently in use. For alkaloids, the acid–base dissociation constant, pK_a, is an important characteristic, thought to be associated with biological activity. In this contribution, pK_a values for several indoloquinoline alkaloids were determined by using ¹H NMR spectroscopy in a mixture of solvents. The data were recalculated for water solutions using the correction factors reported previously. The structural dependence of the pK_a values for cryptolepine and its isomers neocryptolepine, isocryptolepine and isoneocryptolepine as well as some substituted neocryptolepine derivatives is discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Changes in 13C/12C of oil palm leaves to understand carbon use during their passage from heterotrophy to autotrophy

The carbon isotope composition of leaf bulk organic matter was determined on the tropical tree Elaeis guineensis Jacq. (oil palm) in North Sumatra (Indonesia) to get a better understanding of the changes in carbon metabolism during the passage from heterotrophy to autotrophy of the leaves. Leaf soluble sugar (sucrose, glucose and fructose) contents, stomatal conductance and dark respiration, as well as leaf chlorophyll and nitrogen contents, were also investigated. Different growing stages were sampled from leaf rank ?6 to rank 57. The mean values for the δ¹³C of bulk organic matter were ?29.01 ± 0.9‰ for the leaflets during the autotrophic stage, ?27.87 ± 1.08‰ for the petioles and ?28.17 ± 1.09‰ for the rachises, which are in the range of expected values for a C₃ plant. The differences in δ¹³C among leaf ranks clearly revealed the changes in the origin of the carbon source used for leaf growth. Leaves were ¹³C‐enriched at ranks below zero (around ?27‰). During this period, the ‘spear’ leaves were completely heterotrophic and reserves from storage organs were mobilised for the growth of these young emerging leaves. ¹³C‐depletion was then observed when the leaf was expanding at rank 1, and there was a continuous decrease during the progressive passage from heterotrophy until reaching full autotrophy. Thereafter, the δ¹³C remained more or less constant at around ?29.5‰. Changes in sugar content and in δ¹³C related to leaf ranks showed an interesting similarity of the passage from heterotrophy to autotrophy of oil palm leaves to the budburst of some temperate trees or seed germination reported in the literature. Copyright © 2009 John Wiley & Sons, Ltd.     

Fixed-bed study for adsorptive removal of furfural by activated carbon

In our previous study [A.K. Sahu, V.C. Srivastava, I.D. Mall, D.H. Latye, Sep. Sci. Technol. 43 (5) (2008) 1239], commercial grade activated carbon (ACC) was used for adsorptive removal of furfural from aqueous solution using batch studies. In the present study, continuous fixed-bed adsorption was carried out in ACC packed bed for the removal of furfural from aqueous solution. The effects of important factors namely bed height (Z = 15–60 cm), influent concentration of furfural (C_o = 50–200 mg/l), the flow rate (Q = 0.02–0.04 l/min) and column diameter (D = 2–4 cm) were studied. Capacity of the bed to adsorb furfural was found to increase with an increase in the value of Z, C_o and D; and with decrease in the value of Q. Adams–Bohart, Bed-Depth Service-Time, Thomas, Yoon–Nelson, Clark and Wolborska models were applied to the experimental data for the prediction of the breakthrough point, and to determine the characteristic parameters of the column. Error analysis showed that the Yoon–Nelson model best described the experimental breakthrough curve, while Wolborska model showed good prediction of breakthrough curve for the relative concentration region up to 0.5.     

Collagen-grafted ultra-high molecular weight polyethylene for biomedical applications

A novel material for hard tissue implants has been prepared. The ultra-high molecular weight polyethylene (UHMWPE) was grafted with collagen I, to improve its biocompatibility with soft tissue in case of its usage in bone engineering. Before collagen immobilization, commercial grade UHMWPE was treated with air plasma to introduce hydroperoxides onto the surface and subsequently grafted with carboxylic acid to functionalize the surface. Acrylic acid and itaconic acid were used for surface functionalization. After graft polymerization of carboxylic acids, collagen was immobilized covalently through the amide bonds between residual amino and carboxyl groups in the presence of water-soluble carbodiimide/hydroxysuccinimide cross-linking system. Each step of modification was characterized using spectroscopic (EPR, ATR-FTIR, and XPS), microscopic (SEM and CLSM), and contact angle measurement methods. The experimental results showed that plasma treatment led to a generation of free radicals on the UHMWPE surface resulting in the formation of unstable hydroperoxides. These reactive species were used to graft unsaturated carboxylic acids onto UHMWPE. Consequently, collagen was grafted via the-NH₂ and-COOH reaction. The obtained experimental data along with microscopic observations confirmed the success of graft poly-merization of itaconic as well as of acrylic acid and collagen immobilization onto the UHMWPE surface. Presented at the 1st Bratislava Young Polymer Scientists Workshop, Bratislava, 20–23 August, 2007.     

Fast isolation of hydrophobic organic environmental contaminants from exposed semipermeable membrane devices (SPMDs) prior to GC analysis

Semipermeable membrane devices (SPMD) represent a passive sampling technology that is becoming widely used for monitoring of surface waters pollution. While "classic" procedures employ dialysis to recover target compounds from exposed SPMDs, in the present study analytes were isolated from cut membrane together with sequestering medium (triolein) using hexane as an extraction solvent. This approach allowed us to reduce the time needed for accomplishment of isolation step from 48 h to only 1 h. Automated gel permeation chromatography (GPC) clean-up is employed in the following step to separate triolein from analytes fraction. Musk compounds (MCs), polychlorinated biphenyls (PCBs), brominated flame retardants (BFRs) and several other persistent organochlorine compounds (OCs) were determined in the respective fraction by GC method employing selective detectors (MSD, ECD). As shown in a series of analyses of SPMDs deployed in various aquatic ecosystems, high recoveries and good repeatability of results together with a possibility to obtain the information on the pollution of sampling site at the day of sample arrival to laboratory make this newly implemented procedure an interesting alternative to time consuming dialysis.     

Detection system for electro-separation analytical methods

The paper provides information about the on-line monitoring of components analysed by capillary electrophoresis. For this purposes we developed a whole-capillary transverse scanning detection system, which helps to improve and control the separation processes. A picture from a colour line scanner was used as a source of basic information for autonomous control of the separation process by regulation of the high voltage source. The application and algorithms for machine vision were designed in the progressive graphic development system LabVIEW. Real-time control of the separation process was implemented in a compact control process logic controller. The performance of the detection system was evaluated and the function of the overall system was tested by performing isotachophoretic analysis of a model mixture.     

First principles study and database analyses of structural preferences for sodium ion (Na+) solvation and coordination

Extensive computations were performed on aqueous clusters of monovalent sodium cation [Na⁺(H₂O) _n ; (n = 1–20)] using MP2/cc-pVTZ and density functional theory. The structure, energy, and coordination number (CN) preference of a large number of competing conformations of different complexes have been explored. For complexes up to n = 12, the CN 4 is most preferred while 5, 6 CNs are favored in case of larger complexes containing up to 20 water molecules. These results are in very good agreement with experimental observations. The strength of hydrogen bonding among the waters coordinated to the Na⁺ ion is found to play a major role in the stability of the complexes. The varying preferences for CN of Na⁺ ion were explored by screening two important databases: Protein Databank and Cambridge Structural Database. A linear correlation is observed between the M (Metal)–O distance and the charge on metal ion in complex with the increase in CN of metal ion.