ON THE DISSOLVED SOLIDS OF THE PONGOLO FLOOD PLAIN PANS

SUMMARY

The water retained in the Pongolo flood plain pans differs from that of the Pongolo River not only in having a higher TDS, but also in the composition of the solutes, which approximate to seawater in their equivalent ionic proportions at high concentrations. These solutes are shown to originate from very highly mineralised seepage water characteristic of soils overlying Cretaceous sediments of marine origin found elsewhere in South Africa. This feature of the soils of the flood plain precludes the use of irrigation seepage water to maintain the water levels in the pans, and stresses the need for the release of simulated floods from the Pongolo-poort Dam to flush the system if the present biological characteristics of the pans are to be maintained.     

NOTES ON THE AVAILABILITY AND CHEMICAL COMPOSITION OF WATER FROM THE GRAVEL PLAINS OF THE NAMIB-NAUKLUFT PARK

SUMMARY

Data are presented on the occurrence of a surprising number of permanent water sources on the gravel plains of the Namib-Naukluft Park, South West Africa. As a consequence, no game animal is further than ca 25 km away from the nearest watering-place. Within a broad range of ionic contents, the surface waters of the desert display a marked similarity in their chemical composition, being mainly dominated by Na⁺>Ca⁺⁺>Mg⁺⁺: Cl^?>SO₄ ^?>HCO₃ ^??CO_3- ^?. Evaporation, precipitation and rock dominance seem to be the main controlling mechanisms involved in determining the chemical composition of the waters.     

Complexation of trace metals with humic acids from soil,sediment and sewage

ABSTRACT

Metal—humate interactions in aqueous and terrestrial ecosystems control the speciation of trace metals and hence, their bioavailability and toxicity. The present study investigated the complexation interactions of copper, cadmium and lead, in their divalent states, with humic acids extracted from three different sources: the treated sewage from a treatment plant, Yamuna river bed sediment, and Yamuna river flood plain soil, all at Okhla, Delhi, employing ion selective electrode potentiometry. The conditional stability constants of the complexes were computed from Scatchard plots. The influences of the two important metal speciation factors, viz., pH and ionic strength of the reaction medium on the conditional stability constants were ascertained by investigating the reactions under three different pH: 5.0, 6.0 and 7.0 and three different ionic strengths: 0.01, 0.03 and 0.1. Stabilities of metal—humic acid (HA) complexes follow the order: Cu-HA > Pb-HA > Cd-HA for humic acids from any single source and are found to increase with a rise in pH and fall in a ionic strength of the medium. The humic acids extracted from the soil and the sediment emerged as stronger complexing agents, as compared to that extracted from sewage.     

Synthesis,molecular docking and ADMET study of ionic liquid as anticancer inhibitors of DNA and COX-2, TOPII enzymes

Abstract

A new ionic liquid was synthesized by the reaction of caprolactam with salicylic acid (CL-SA) and characterized by analysis of spectroscopic and DSC data. The optimized geometry and the electrostatic potential map of CL-SA were calculated with DFT method using the wb97xd/6-31++G(d,p) level of theory. Molecular docking study of the CL-SA was carried out to clarify the probable binding modes between the title compound and DNA and COX-2 and TOPII enzymes. In silico ADMET study was also performed for predicting pharmacokinetic and toxicity profile of the synthesized ionic liquid which expressed good oral drug-like behavior and non-toxic nature. It was revealed that the compound has a potential to become a lead molecule in drug discovery process.

Communicated by Ramaswamy H. Sarma     

Synthesis,Biophysical Properties,and Stability Studies of Mixed Backbone Oligonucleotides Containing Novel Non-Ionic Linkages

Abstract

Mixed backbone oligonucleotides (MBOs) (containing ionic and non-ionic internucleotidic linkages) in which the non-ionic segments are either methylphosphotriester (PO-OMe) or primary phosphoramidate (PO-NH₂) linkages have been prepared using the recently described N-pent-4-enoyl (PNT) nucleoside phosphoramidates and H-phosphonates. Biophysical properties and stability studies suggest that these MBOs are novel antisense molecules.     

Index to Subjects,Volume 5

Abstract

The interaction of histone H5 labelled with fluorescein isothiocyanate (FITC) with DNA has been studied by fluorescence titration, and diffusion-enhanced fluorescence energy transfer (DEFET) measurements with Tb(III) lanthanide chelates as donors.

Analysis of the binding data by the model of Schwarz and Watanabe (J. Mol. Biol. 163, 467-484 (1983)) yielded a mean stoichiometry of 60 nucleotides per H5 molecule, independently of ionic strength, in the range of 3 to 300 mM NaCl, at very low DNA concentration (6 μM in mononucleotide). It ensues an approximate electroneutrality of the saturated complexes. Histone H5 molecules appeared to be clustered along the DNA lattice in clusters containing on average 3 to 4 H5 molecules separated by about 79 base pairs, at mid-saturation of the binding sites. The interaction process was found highly cooperative but the cooperativity parameter was also insensitive to ionic strength in the above range.

DEFET experiments indicated an important decrease of accessibility of the FITC label to the TbHED3A° and TbEDTA^? chelates with ionic strength in the 0 to 100 mM NaCl range. In the presence of DNA, H5 appears already folded at low ionic strength so that the FITC probe is also not accessible to the donor chelate. The present study constitutes an indispensable preliminary step to further studies on the localization of histone H5 in condensed chromatin structures.     

A preliminary survey of Beanrig Moss,a fen in South Scotland

Summary

A preliminary survey by the Mires Research Group was carried out at Beanrig Moss, near Selkirk. The distribution of plant communities, showing a zonation from the margins of the site to its centre, appeared to be related mainly to variations in water table depth in relation to surface contours, with differences in the ionic composition of the water itself playing a secondary role. Stratigraphical investigation revealed the presence of a deep basin beneath the thin peat deposit, and within the clays lining this, an Allerød deposit.     

STEREOSELECTIVE SYNTHESIS OF 3-HYDROXYMETHYL-D-CYCLOPENTENONE,THE VERSATILE INTERMEDIATE FOR THE SYNTHESIS OF CARBOCYCLIC NUCLEOSIDES

The preparative and stereoselective synthesis (45–50% overall yields, >50 g scale) of the key carbasugars 7a–d was achieved from D-ribose via stereoselective Grignard reaction and oxidative rearrangement as key reactions.     

Sequestration of organometallic compounds by synthetic and naturally occurring polycarboxylate ligands. Binding of monomethylmercury(II) by polyacrylic and alginic acids

Abstract

The sequestering capacity of synthetic and naturally occurring polycarboxylate ligands towards mono-methylmercury(II) was evaluated by stability quantitative data on the interaction of CH₃Hg⁺ with different molecular weight synthetic polyacrylates (2 and 20kDa average M.wt) and alginate (70–100 kDa) extracted from brown algae Macrocystis pyrifera. The influence of ionic medium was evaluated by measurements on the CH₃Hg⁺-polyacrylate systems in NaNO₃ medium at different ionic strengths (0.10, 0.25, 0.50 and 0.75 mol L^?1), and a Debye-HiJckel type equation was used for the dependence of complex formation constants on ionic strength. Measurements on the CH3Hg⁺ - alginate system were carried out at l = 0.10 mol L^?1 in NaNO₃ medium. By using the stability data, the sequestering capacity of both ligands towards monomethylmercury(II) was determined at different pH values. Results obtained show that the binding ability of polyacrylic ligands (PAA) is stronger than the alginate (AA), following the trend PAA (20 kDa)> PAA (2kDa)>AA.     

FIRST RECORD OF THE SNAKE CATFISH CLARIAS THEODORAE (WEBER, 1897) (CLARIIDAE: PISCES) FROM THE TRANSVAAL,SOUTH AFRICA

SUMMARY

Two new distributional records of the snake catfish Clarias theodorae (Clariidae: Pisces) from Transvaal tributaries of the Limpopo River are documented. This is also the first record of the snake catfish from the Transvaal. The habitat preference of this species is briefly discussed and brief comment is made on probable migration routes.     

The solvent at antigen-binding site regulated C3d–CR2 interactions through the C-terminal tail of C3d at different ion strengths: insights from molecular dynamics simulation

BackgroundThe interactions of complement receptor 2 (CR2) and the degradation fragment C3d of complement component C3 play important links between the innate and adaptive immune systems. Due to the importance of C3d–CR2 interaction in the design of vaccines and inhibitors, a number of studies have been performed to investigate C3d–CR2 interaction. Many studies have indicated C3d–CR2 interactions are ionic strength-dependent.MethodsTo investigate the molecular mechanism of C3d–CR2 interaction and the origin of effects of ionic strength, molecular dynamics simulations for C3d–CR2 complex together with the energetic and structural analysis were performed.ResultsOur results revealed the increased interactions between charged protein and ions weaken C3d–CR2 association, as ionic strengths increase. Moreover, ion strengths have similar effects on antigen-binding site and CR2 binding site. Meanwhile, Ala17 and Gln20 will transform between the activated and non-activated states mediated by His133 and Glu135 at different ion strengths.ConclusionsOur results reveal the origins of the effects of ionic strengths on C3d–CR2 interactions are due to the changes of water, ion occupancies and distributions.General significanceThis study uncovers the origin of the effect of ionic strength on C3d–CR2 interaction and deepens the understanding of the molecular mechanism of their interaction, which is valuable for the design of vaccines and small molecule inhibitors.     

Glycerol-Furcated Oligonucleotides: Synthesis and Aggregation

Abstract

The synthesis of the bi-furcated complementary oligonucleotides 2 and 3 is described and their complex formation is studied as a function of their molar ratio and ionic strength by means of temperature-dependent UV- and CD spectroscopy as well as by dynamic light scattering. Structural proposals for the different aggregates are given.     

Synthesis, characterization, and in vitro antitumor properties of gold(III) compounds with the traditional Chinese medicine (TCM) active ingredient liriodenine

Abstract  

Liriodenine, an oxoaporphine alkaloid with anticancer activity isolated from Zanthoxylum nitidum (rutaceous anticancer traditional Chinese medicine), was selected as a bioactive ligand to react with HAuCl₄ and NaAuCl₄ to afford [LH][AuCl₄] (1) and [AuCl₃L] (2), respectively (where L is liriodenine). The structures of 1 and 2 were characterized by IR spectroscopy, electrospray ionization mass spectrometry, ¹H-NMR spectroscopy, and elemental analysis. The single-crystal X-ray diffraction analysis of 1 revealed that it is an ionic compound consisting of protonated liriodenine cation [LH]⁺ and [AuCl₄]⁻ anion. The spectroscopic analysis showed that 2 is a coordination compound, in which one liriodenine coordinates to gold via its 7-N donor. In aqueous solution, 1 is relatively stable, but 2 undergoes rapid hydrolysis. The in vitro cytotoxicity towards five human tumor cell lines shows that 1 and 2 manifest roughly similar biological behavior and appreciable antiproliferative properties, with IC₅₀ values falling in the 2–16 μM range. The flow-cytometric analysis of 1 and 2 suggests that both compounds induced an S-phase arrest. Compounds 1 and 2 significantly poison topoisomerase I in vitro at low concentration (25 μM or less). DNA binding studies indicate that both 1 and 2 interact with DNA mainly via intercalation between the neighboring base pairs of the DNA double helix. Electrostatic interactions of 1 and 2 with the polyanionic DNA phosphate backbone may reinforce the intercalation because both 1 and 2 are composed of planar cationic species.     

Differential Estrogenic Responsiveness of MCF-7 Cells Relationship to the Presence of two Different Estrogen Receptors

Abstract

Estradiol stimulation of thymidine incorporation and progesterone receptor synthesis is at a maximum in exponentially growing cells. These activities are found to disappear in confluent MCF-7 cells. Since no significant differences in the binding of estradiol to its receptor site (Kd = 10^?10 M, Bmax = 150 fm/mg protein) are observed in these two conditions, receptor structure was analyzed in both cell populations. Various methods demonstrated that receptor size is related to the state of confluence. The hydrodynamic properties of estradiol receptors complexed with ³H-estradiol from cells in the two different growth phases are similar in low ionic strength but different in high ionic strength media. Moreover, when the cell extracts are analyzed in denaturing     

Ewald Summation in the Molecular Dynamics Simulation of Large Ionic Systems

Abstract

The accuracy and efficiency of the direct Ewald summation are discussed in terms of the size of a Molecular Dynamics (MD) ionic system and the ranges of the r-space and q-space summations. The dependence of the convergence parameter α on the size of the system and on the choice of cut-off radius for the short-range potential is given. The possibility of neglecting the q-space term for large ionic systems is discussed in terms of the accuracy and efficiency of the simulation.     

CLEANING BEHAVIOUR BETWEEN THE CICHLID FISH TILAPIA RENDALLI FENDALLI BOULENGER 1896 AND THE CYPRINID,LABEO CYLINDRICUS PETERS, 1852

SUMMARY

A case of interspecific cleaning behaviour is described between a cichlid host Tilapia rendalli rendalli and a Juvenile cyprinid Labeo cylindricus, in captivity. The host fish initiated the cleaning behaviour with a ‘head down’ display.     

THE CONDUCTIVITIES OF AQUEOUS SOLUTIONS OF GLYCINE,d,l-VALINE,AND l-ASPARAGINE

1. The conductivities of aqueous solutions of glycine, d,l-valine, and l-asparagine have been determined, and comparisons have been made with similar data reported in the literature. 2. On the basis of certain theoretical considerations, calculations of the expected conductivities of aqueous solutions of glycine, asparagine, aspartic acid, and glutamic acid have been made and these data have been compared with similar data obtained experimentally. 3. The dissociation constants of the carboxyl groups of aspartic acid and glutamic acid have been calculated from conductivity data. 4. It is shown that alanine has no effect on the ionic atmosphere of solutions of potassium chloride.     

THE JOURNAL OF THE LIMNOLOGICAL SOCIETY OF SOUTHERN AFRICA: APPRAISAL,ANALYSIS, APPROACH AND APPLICATION

SUMMARY

In accordance with the Silver Jubilee theme of ‘reminisce and assess’, the editorial takes a critical look at the Journal of the Limnological Society of Southern Africa with the objective of examining its raison d'etre. After briefly examining the need for a journal in the context of southern African limnology and oceanography, an analysis of the strengths, weaknesses, opportunities and threats facing the Journal is conducted. As a result of this analysis, a mission statement and action plan for the continued development of a useful and relevant publication, reflecting the needs and concerns of the total membership of the Limnological Society of Southern Africa, are presented. This approach places the Journal on a sound strategic footing and gives substance to the extended scope of the Journal which, since 1986, has included contributions from freshwater, estuarine and coastal marine scientists. A change in title to the Southern African Journal of Aquatic Sciences is announced - the change will take effect in 1989 with volume 15.