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The mystery surrounding high concentrations of Cr(III) in plants has been uncovered. It is attributed to the presence of low molecular weight organic acids (LMWOA) in soil in which the plants are growing. Apart from that, the factors influencing solubility of Cr(VI) in soil have also been investigated. It was found that the solubility of Cr(VI) species is governed by the presence of CO3 2− ions in a soil solution that resulted when atmospheric CO2 dissolves in soil–water. Concentrations of Cr(VI) and Cr(III) were determined in plants, collected on unpolluted soils in different geographical areas. It was found that the concentration of Cr(VI) in plants correlated with the soluble fraction of Cr(VI) in soil, while Cr(III) concentration in plants is limited by concentration LMWOA in soil. It can therefore be concluded that the high level of Cr(III) in plants is also due to the direct absorptions of the species from soil rich in organic acids.

Diss. (sammanfattning) Stockholm : Karol. inst. / Härtill 6 uppsatser.

A research report submitted to the Faculty of Health Sciences, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Pharmacy Johannesburg 2001. i / The use of a low molecular weight heparin, enoxaparin was evaluated in the prevention and treatment of deep vein thrombosis. Patterns of use were analysed and measured against pre-determined criteria with a view to promoting optimal use and identifying those factors, which may contribute to safer use of the drug. / IT2018

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The operation and optimisation of a distillation train directly effects the total energy consumption of a typical processing plant. With this in mind, the efficient separation of low molecular weight alcohol azeotropes, using heterogeneous azeotropic distillation, is of great economic and environmental importance. Heterogeneous azeotropic distillation involves the addition of an extraneous component, known as an entrainer, to the mixture to facilitate separation. Benzene has long been replaced as the entrainer of choice, due to its carcinogenic nature, and research into finding a more suitable entrainer has commenced. To determine if an entrainer is suitable for a particular separation, detailed phase behaviour information of the ternary alcohol/entrainer/water system is required; vapour-liquid (VLE), vapour-liquid-liquid (VLLE) equilibria data and the composition of all azeotropes present. This is complicated by the fact that thermodynamic models (like the nonrandom two-liquid (NRTL), universal functional (UNIFAC) and universal quasichemical (UNIQUAC) activity coefficient models) often fail to predict the phase equilibria of ternary systems. The lack of available experimental phase equilibria data, and the inability of thermodynamic models to predict phase equilibria data, has fueled the need for the experimental determination of accurate, repeatable isobaric VLE, VLLE and azeotropic data. With this in mind, this research is focused on the experimental determination of VLE, VLLE and azeotropic data for three low molecular weight alcohol/entrainer/water systems at 101.3 kPa. Following an extensive literature study on azeotropes, applicable separation techniques and available VLE and VLLE data in literature, the ethanol/2-butanone/water, n-propanol/2-butanone/water and iso-propanol/2-butanone/water systems were chosen for experimental investigation. The experimental determination was carried out in a Gillespie type still, equipped with an ultrasonic homogenizer. The temperature and pressure accuracies of the equipment were found to be 0.03°C and 2mbar respectively. The chosen experimental methodology was verified, and its repeatability tested, through the measurement of isobaric VLE and VLLE data of ethanol/isooctane, ethanol/n-butanol/water and n-propanol/isooctane/water systems at 101.3 kPa and subsequent comparison of the measured data with literature data. The compositional error reported, taking into account experimental and analysis effects, is ±0.014 mole fraction. All experimentally determined data sets, verification and new data, were tested for thermodynamic consistency by using the Wisniak modification of the Herrington test, the L/W consistency test, as well as the McDermott-Ellis consistency test, and found to be consistent. The Othmer-Tobias correlation was used to ensure the measured LLE data followed a steady trend, with all R-values larger than 0.910. For all three of the new systems chosen, the absence of ternary heterogeneous azeotropes was noted. The presence of a ternary homogeneous azeotrope was found for both the ethanol/2-butanone/water and iso-propanol/2-butanone/water systems. No ternary azeotropes are present for the n-propanol/2-butanone/water system. Suitable entrainers were compared to 2-butanone (MEK) by plotting measured data and literature information of five similar alcohol/entrainer/water systems on a ternary phase diagram. It was found that MEK could not be considered as a suitable entrainer for heterogeneous azeotropic distillation of ethanol, n-propanol and IPA. This is due to the absence of a ternary heterogeneous azeotrope for the aforementioned alcohol/MEK/water systems. Finally, the ability of thermodynamic models (NRTL, UNIFAC and UNIQUAC) to predict experimental data was determined both visually and through descriptive statistics. This entailed the inspection of ternary phase diagrams and the calculation and evaluation of average absolute deviation (AAD) and and average absolute relative deviation (AARD%) values. The measured data were modelled in Aspen Plus®. It was found that none of the models could predict the ternary systems with acceptable accuracy and the data were regressed. In general, the regressed parameters for the NRTL, UNIFAC and UNIQAC models improved the model predictions when compared to the built-in Aspen parameters. The UNIFAC model predicted the ethanol/MEK/water and n-propanol/MEK/water systems most accurately while none of the models could predict the IPA/MEK/water systems with acceptable accuracy. / AFRIKAANSE OPSOMMING: Die ontwerp en optimering van 'n distillasietrein het ‘n duidelike effek op die totale energieverbruik van ‘n tipiese prosesaanleg. Met dit in gedagte, is ‘n meer doeltreffende skeiding van lae molekulêre massa alkohol aseotrope, met behulp van heterogene aseotropiese distillasie, voordelig vir die ekonomie en die omgewing. Heterogene aseotropiese distillasie behels die toevoeging van 'n eksterne komponent, wat bekend staan as 'n skeidingsagent, om uiteindelik die skeiding te fasiliteer deur die komponente se dampdrukke te verander. Benseen was in die verlede ‘n gewilde skeidingsagent, maar dit is a.g.v. sy karsenogeniese eienskappe nie meer aanvaarbaar om te gebruik nie. Nuwe navorsing in hierdie veld fokus dus onder andere op die identifisering van meer geskikte skeidingsagente. Om te bepaal of 'n skeidingsagent geskik is, word indiepte fasegedrag inligting benodig, i.e. damp-vloeistof en damp-vloeistof-vloeistof ewewigsdata en die samestelling van alle aseotrope teenwoordig. Ongelukkig kan termodinamiese modelle dikwels nie die fasegedrag van ternêre stelsels voorspel nie. Dit, sowel as die beperkte beskikbaarheid van eksperimentele ewewigsdata in die literatuur, het dus hierdie navorsing aangevuur. Die projek het gefokus op die experimentele bepaling van damp-vloeistof en damp-vloeistof-vloeistof ewewigsdata en aseotropiese data vir drie alkohol/skeidingsagent/water-stelsels by 101.3 kPa. Na ‘n indiepte literatuurstudie van aseotrope, gepaste skeidingstegnieke en beskikbare damp-vloeistof en damp-vloeistof-vloeistof ewewigsdata, is 2-butanone (MEK) gekies as ‘n moontlike skeidingsagent en die etanol/MEK/water-, n-propanol/MEK/water- en iso-propanol/MEK/water-stelsels gekies vir eksperimentele ondersoek. Die data is met ‘n dinamiese Gillespie eenheid gemeet, toegerus met ‘n ultrasoniese homogeniseerder om vloeistof-vloeistof skeiding te voorkom. Die akkuraatheidsbande van temperatuur- en druk meetinstrumente was 0,03°C en 2 mbar, onderskeidelik. Die eksperimentele metode en die herhaalbaarheid van metings is bevesting, deur die isobariese damp-vloeistof en damp-vloeistof-vloeistof ewewigsdata van etanol/iso-oktaan, etanol/n-butanol/water en n-propanol/iso-oktaan/water te vergelyk met onafhanklike stelle ooreenstemmende data uit die literatuur. Die gesamentlike eksperimentele en analitiese fout wat gemaak kon word tydens bepaling van molfraksie samestellings was ±0.014 molfraksie. Alle gemete eksperimentele data is getoets vir termodinamiese samehang deur middel van beide die L/W en McDermott-Ellis konsekwentheidstoetse. Die Othmer-Tobias korrelasie is gebruik om seker te maak dat die gemete LLE data ‘n konstante tendens volg, met alle R-waardes groter as 0.910. Vir al drie van die nuwe stelsels wat gekies is, was ‘n drieledige heterogene aseotroop afwesig. Die teenwoordigheid van drieledige homogene aseotrope is egter waargeneem vir die etanol/MEK/water- en IPA/MEK/water-stelsels. Geen drieledige aseotrope is vir die n-propanol/MEK/water-sisteem gevind nie. Alle gemete data, asook literatuur inligting van vyf soortgelyke alkohol/skeidingsagent/water sisteme, is op ‘n drieledige fase diagram voorgestel om die skeidingsagente met mekaar te vergelyk. Hiervolgens word dit getoon dat MEK nie as ‘n gepaste skeidingsagent vir heterogene aseotropiese distillase beskou kan word nie a.g.v. die afwesigheid van ‘n drieledige heterogene aseotroop in die voorgenoemde alkohol/MEK/waterstelsels. Die vermoë van die termodinamiese modelle (NRTL, UNIFAC en UNIQUAC) om die eksperimentele data te voorspel is visueel (per grafiek) sowel as deur beskrywende statistiek bepaal. Dit behels die inspeksie van drieledige fasediagrame en die berekening en evaluasie van die gemiddelde absolute afwyking en gemiddelde absolute relatiewe afwykingswaardes. Hierdie teoretiese data is met Aspen Plus® bepaal. Nie een van die modelle kon die drieledige stelsels se fasegedrag met aanvaarbare akkuraatheid voorspel nie. Die parameters vir die NRTL-,UNIFAC- en UNIQUAC-modelle kan verbeter word deur middel van regressie, in vergelyking met die ingeboude Aspen parameters. Dit is bevind dat die UNIFAC model die etanol/MEK/water- en n-propanol/MEK/water-stelsel die beste kan voorspel. Nie een van die bogenoemde modelle kon egter die fasegedrag van die IPA/MEK/water-stelsel voorspel nie.

Statement of the problem The primary objective of this thesis was to determine the best study design to evaluate the safety and effectiveness of an intermediate dose of low molecular weight heparin for secondary prevention of pregnancy associated VTE (PAVTE). An RCT was deemed unfeasible,so the use of a single arm study with prior evaluation of feasibility with a pilot study is proposed. // Methods - A systematic review was conducted to evaluate the efficacy of current strategies used for secondary prevention of PAVTE.A survey was used to elicit the non-inferiority margin. // Results - The pooled proportion of recurrent VTE in patients treated with full dose LMWH was 0.012(95% CI 0.006 to 0.02) and the rate of major bleeding was 0.025(95% CI=0.01 to 0.041). The non-inferiority margin was elicited at 2.5%. // Conclusions - Although a randomized controlled trial should be conducted whenever possible, in certain scenarios they are unfeasible. Therefore, an alternative study design should perhaps be used to evaluate the safety and efficacy of therapeutic strategies.

Low molecular weight gelators (LMWGs) are interesting materials whose applications are as diverse and wide ranging as their molecular structures. These materials self-assemble through the formation of non-covelent intermolecular forces and interactions to form supramolecular assemblies that trap solvent within their matrices. Because of the non-covalent nature of the forces of self-assembly, the gelation process is typically thermally reversible. In addition, low molecular weight gelators can also be modified to respond to various stimuli, such as change in pH, presence of enzymes or metal cations, or exposure to light. The design of low molecular weight gelators is often difficult, and most new classes of low molecular weight gelators are discovered by serendipity. As such, it is often useful to use structural templates in the design of LMWGs. Biomolecules, such as steroids, amino acids and peptides, and carbohydrates make excellent templates due to their inherent propensity to self assemble. A review of the current literature regarding the use of biomolecules as templates for the design and synthesis of LMWGs will be presented in chapter 1. Our research group has been active in the research of carbohydrate-based LMWGs for several years, and these results are also briefly reviewed in the related chapters. The synthesis and characterization of ester derivatives of D-galactose, D-glucose, and amide derivatives of D-glucosamine will be discussed in chapters 2-4, along with their evaluation for gelation in aqueous and organic solvents, such as hexane, ethanol, water, and aqueous DMSO or ethanol mixtures.

Systems formed by the supramolecular assemblages of organic molecules known as organogelators and hydrogelators are currently, and only recently, a subject of great attention and promise. In this context, low molecular weight gelators (LMWGs) are of particular interest because they provide a bottom-up approach to the formation of supramolecular architectures through self-assembly. Gelator molecules do so via the initial formation of a one-dimensional array of individual molecules bound non-covalently through forces such as: hydrogen bonds, electrostatic forces, Van der Waals interactions, and other weak forces such as π-π interactions. These interactions then lead to secondary structure formation through a similar assembly mechanism. Understanding the gelation process through characterization techniques is critical to the development of a design rationale for gelator molecules. Past and current research performed by the Wang group indicates that analogues of various 4,6-benzylidene acetals form stable gels in organic, aqueous, and organic/aqueous solvents at varying concentrations. The basis of varying the 4,6-protecting groups on glucose and glucosamine derivatives is to discern the relative structure activity relationships of these systems, and as well to fabricate functional systems which respond to external stimulus. Stimuli responsive or trigger release gel systems formed by sugar based low molecular weight gelators (LMWGs) have applications as smart biocompatible materials, and such responsiveness in various media was explored and developed to determine the feasibility of such applications using monosaccharide derivatives.

Low molecular weight gelators (LMWGs) have gained great attention over the past two decades. These compounds form self-assembled fibrous networks like micelles, cylindrical, sheets, fibers, layers and so on. The fibrous network entraps the solvent and form gel. LMWGs are interesting compounds with many potential applications in material and biomedical sciences. Many different structures have been found to be good LMWGs. Our interests focus on the carbohydrate based LMWGs. Previously, we have found that several ester derivatives of methyl 4, 6-O-benzylidene-α-D-glucopyranoside are good gelators for organic solvents and aqueous solutions. In this study, in order to understand the structure requirement, we systematically investigated the influence of sugar head groups and the attached hydrophobic tails towards gelation. The design, synthesis and gel properties of esters, amides, ureas, carbamates which derived from sugar head groups show above will be discussed in chapter II, III, IV.

Statement of the problem The primary objective of this thesis was to determine the best study design to evaluate the safety and effectiveness of an intermediate dose of low molecular weight heparin for secondary prevention of pregnancy associated VTE (PAVTE). An RCT was deemed unfeasible,so the use of a single arm study with prior evaluation of feasibility with a pilot study is proposed. // Methods - A systematic review was conducted to evaluate the efficacy of current strategies used for secondary prevention of PAVTE.A survey was used to elicit the non-inferiority margin. // Results - The pooled proportion of recurrent VTE in patients treated with full dose LMWH was 0.012(95% CI 0.006 to 0.02) and the rate of major bleeding was 0.025(95% CI=0.01 to 0.041). The non-inferiority margin was elicited at 2.5%. // Conclusions - Although a randomized controlled trial should be conducted whenever possible, in certain scenarios they are unfeasible. Therefore, an alternative study design should perhaps be used to evaluate the safety and efficacy of therapeutic strategies.