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Magnesium Ions (magnesium + ion)
Selected AbstractsCONSTRAINTS ON DIAGENESIS AND RESERVOIR QUALITY IN THE FRACTURED HASDRUBAL FIELD, OFFSHORE TUNISIAJOURNAL OF PETROLEUM GEOLOGY, Issue 1 2001C. I. Macaulay The hydrocarbon reservoir of the Hasdrubal field (offshore Tunisia) lies within the Eocene El Garia Formation. This formation was deposited on a shallow north- to NE-facing ramp in the Early Eocene and is composed of a belt of nummulitic wackestones-grainstones. The nummulitic fades occupies a range of depositional environments from outer to mid ramp. In addition to Hasdrubal, several other producing oil- and gasfields have been discovered in the variably dolomitised El Garia Formation offshore Tunisia. Cores from three Hasdrubal wells were examined. Reservoir quality shows a limited relationship to primary depositional fabric and has been influenced significantly by compaction and later diagenesis. The highest permeabilities are typically developed within a dolomitised zone which occurs near the middle of the reservoir interval across the entire field, and which may follow a primary wackestone lithofabric (typically 20,30% bulk volume dolomite, with porosities of 15,22% and permeabilities of l-30mD). Fractures, particularly in zones surrounding faults, have resulted in enhanced permeabilities. Combined results of isotope (,18 O -5.0 to -7.3%oPDB) and fluid inclusion (Th 80,90d,C) analyses of dolomites from this dolomitised zone indicate that matrix dolomites are burial diagenesis cements. Dolomitisation of the reservoir was a "closed system " event and was not the result of major fluid flow or mixing. Magnesium ions for dolomitisation were derived from the transformation of high-Mg to low-Mg calcite in nummulite tests within the reservoir fades. Our analyses indicate that calcite cements were precipitated at temperatures of up to almost 150d,C in primary and secondary pores and in variably-sealed fractures Fracture lining and filling cements show a range of ,18 O values, which suggests that the fractures acted as fluid conduits over a range of temperatures during burial diagenesis Fracture densities measured in core increase rapidly close to seismically-resolvable faults in the reservoir facies Fracturing probably resulted in the leakage of hydrocarbons through the Compact Micrite Member seal which overlies the accumulation, as well as facilitating the ingress of hot fluids from stratigraphically deeper levels in the basin [source] Synthesis and Hybridization Properties of Modified Oligodeoxynucleotides Carrying Non-Natural BasesCHEMISTRY & BIODIVERSITY, Issue 2 2009Anna Aviñó Abstract The impact of the presence of nonnatural bases on the properties of oligodeoxynucleotides has been studied. First, oligodeoxynucleotides carrying 2,-deoxyzebularine were prepared, and the stability of duplexes carrying this analogue was determined by DNA melting experiments. Melting temperatures and thermodynamic data indicated the preference of 2,-deoxyzebularine for 2,-deoxyguanosine, which behaves as a 2,-deoxycytidine analogue, forming a less stable base pair due to the absence of the amino group at position 4. Moreover, the duplex,hairpin equilibrium of a self-complementary oligodeoxynucleotide carrying several natural and nonnatural bases including 2,-deoxyzebularine as a central mispair, was studied. Depending on the base present in the middle of the sequence, it is possible to affect the stability of the bimolecular duplex modulating the duplex,hairpin equilibrium. Magnesium ions were shown to stabilize preferentially the bimolecular duplex form. The results indicate the importance of the modifications and the role of cations in shifting the structural equilibrium. [source] Crystal structure of human Rad GTPase of the RGK-familyGENES TO CELLS, Issue 8 2006Arry Yanuar Rad (Ras associated with diabetes) is an RGK-family small GTPase that is over-expressed in the skeletal muscle of humans with type II diabetes. Unlike other small GTPases, RGK family members including Rad lack several conserved residues in the GTPase domain. Here, we report the crystal structure of the GTPase domain of human Rad in the GDP-bound form at 1.8 Å resolution. The structure revealed unexpected disordered structures of both switches I and II. We showed that the conformational flexibility of both switches is caused by non-conservative substitutions in the G2 and G3 motifs forming the switch cores together with other substitutions in the structural elements interacting with the switches. Glycine-rich sequences of the switches would also contribute to the flexibility. Switch I lacks the conserved phenylalanine that makes non-polar interactions with the guanine base in H-Ras. Instead, water-mediated hydrogen bonding interactions were observed in Rad. The GDP molecule is located at the same position as in H-Ras and adopts a similar conformation as that bound in H-Ras. This similarity seems to be endowed by the conserved hydrogen bonding interactions with the guanine base-recognition loops and the magnesium ion that has a typical octahedral coordination shell identical to that in H-Ras. [source] Intramolecular proton transfer induced by divalent alkali earth metal cation in the gas stateINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2003Hongqi Ai Abstract Interactions between divalent alkali earth metal (DAEM) ions M (MBe, Mg, Ca, Sr, Ba) and the second stable glycine conformer in the gas phase, which can transfer into the ground-state glycine-M2+ (except the glycine,Be2+) among each corresponding isomers when these divalent metal ions are bound, are studied at the hybrid three-parameter B3LYP level with three different basis sets. Proton transfers from the hydroxyl to the amino nitrogen of the glycine without energy barriers have been first observed in the gas phase in these glycine,M2+ systems. The interaction between the glycine and these DAEM ions except beryllium and magnesium ion only create an amino hydrogen pointing to the original hydroxyl due to their weaker interaction relative to those divalent transition metal (DTM) ion-bound glycine derivatives, being obviously different from that between the glycine and DTM ions, in which two amino hydrogens point to the original hydroxyl oxygen when these metal-chelated glycine derivatives are produced. The interaction energy between the glycine and divalent magnesium would be the boundary of one or two amino hydrogens pointing to the hydrogyl oxygen, i.e., the ,170.3 kcal/mol of binding energy is a critical point. Similar intramolecular proton transfer has also been predicted for those DTM ion-chelated glycine systems; however, that in the gas state has not been observed in the monovalent metal ion-coordinated glycine systems. The binding energy between some monovalent TM ion and the glycine is similar to that of the glycine,Ba2+, which has the lowest binding strength among these DAEM,ion chelated glycine complexes. The difference among them only lies in the larger electrostatic and polarized effects in the latter, which favor the stability of the zwitterionic glycine form in the gas phase. According to these observations, we predict that the zwitterionic glycine would exist in the field of two positive charges in the gas phase. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 205,214, 2003 [source] Structural studies of the catalytic core of the primate foamy virus (PFV-1) integraseACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 8 2010Stéphane Réty Retroviral integrases are vital enzymes in the viral life cycle and thus are important targets for antiretroviral drugs. The structure of the catalytic core domain of the integrase from human foamy virus, which is related to HIV-1, has been solved. The structure of the protein is presented in two different crystal forms, each containing several molecules in the asymmetric unit, with and without the essential manganese or magnesium ion, and the structures are compared in detail. This allows regions of high structural variability to be pinpointed, as well as the effect of divalent cations on the conformation of the catalytic site. [source] Effects of Antiepileptic Drugs on Refractory Seizures in the Intact Immature Corticohippocampal Formation In VitroEPILEPSIA, Issue 11 2003Pascale Paule Quilichini Summary:,Purpose: We developed a new in vitro preparation of immature rats, in which intact corticohippocampal formations (CHFs) depleted in magnesium ions become progressively epileptic. The better to characterize this model, we examined the effects of 14 antiepileptic drugs (AEDs) currently used in clinical practice. Methods: Recurrent ictal-like seizures (ILEs, four per hour) were generated in intact CHFs of P7,8 rats, and extracellular recordings were performed in the hippocampus and neocortex. AEDs were applied at clinically relevant concentrations (at least two), during 30 min after the third ILE. Their ability to prevent or to delay the next ILE was examined. Results: Valproic acid and benzodiazepines (clobazam and midazolam) but also phenobarbital and levetiracetam prevent the occurrence of seizures. In contrast, usual concentrations of carbamazepine (CBZ), phenytoin, vigabatrin, tiagabine, gabapentin, lamotrigine (LTG), topiramate, felbamate, and ethosuximide did not suppress ILEs. In addition, LTG and CBZ aggravate seizures in one third of the cases. Conclusions: This intact in vitro preparation in immature animals appears to be quite resistant to most AEDs. Blockade of seizures was achieved with drugs acting mainly at the ,-aminobutyric acid (GABA)A -receptor site but not with those that increase the amount of GABA. Drugs with a broad spectrum of activity are efficient but not those preferentially used in partial seizures or absences. We suggest that this preparation may correspond to a model of epilepsy with generalized convulsive seizures and could be helpful to develop new AEDs for refractory infantile epilepsies. [source] Controlling the biodegradation rate of magnesium using biomimetic apatite coatingJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2009Yajing Zhang Abstract Magnesium is light, biocompatible and has similar mechanical properties to natural bone, so it has the potential to be used as a biodegradable material for orthopedic applications. However, pure magnesium severely corrodes in a physiological environment, which may result in fracture prior to substantial tissue healing. Hydroxyapatite (HA) is the main composition of natural bone. It has excellent bioactivity and osteoconductivity. In this study, HA coating with two different thicknesses was applied onto the surface of pure magnesium substrates using a biomimetic technique. The corrosion rate of the surface-treated substrates was tested. It was found that both types of coatings substantially slowed down the corrosion of the substrate, and the dual coating was more effective than the single coating in hindering the degradation of the substrate. Thus, the corrosion rate of magnesium implants can be closely tailored by adjusting apatite coating thickness and thereby monitoring the release of magnesium ions into the body. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009 [source] Magnesium and biological activity of oxytocin analogues modified on aromatic ring of amino acid in position 2JOURNAL OF PEPTIDE SCIENCE, Issue 8 2001ina Slaninová Abstract For the purpose of evaluating substitution effects in the ortho, meta or para positions of the aromatic ring of tyrosine or phenylalanine in position 2 of oxytocin on uterotonic activity in vitro in the presence and absence of magnesium ions, six new analogues of oxytocin ([,,- and ,,- m -methylphenylalanine2]oxytocin, [,,- and ,,- m -methoxyphenylalanine2]oxytocin and [,,- and ,,- o -methyltyrosine2]oxytocin) were synthesized and several previously described analogues resynthesized. For the phenylalanine series, it is found that, in the absence of magnesium ions, substitution of the ortho and meta positions leads to loss of intrinsic activity (the analogues are antagonists) in contrast to the para position. In the tyrosine series, only methyl substitution in the meta position has this effect (substitution of ortho position only attenuates the agonistic biological activity). Addition of Mg ions restores to a certain degree the agonistic activity in the case of the o -methylphenylalanine analogue and enhances the agonistic activity of o -methyltyrosine oxytocin. All other analogues keep the original qualities as in the absence of Mg. Molecular modelling calculations of the structure of the above analogues was carried out to help explain these findings of the molecular level. Copyright © 2001 European Peptide Society and John Wiley & Sons, Ltd. [source] Raman microspectroscopic study on low-pH-induced DNA structural transitions in the presence of magnesium ionsJOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2002C. M. Muntean Low-pH-induced DNA structural changes were investigated in the pH range 6.8,2.10 by Raman microspectroscopy. Measurements were carried out on calf thymus DNA in the presence of low concentrations of Mg2+ ions. Vibrational spectra are presented in the wavenumber region 500,1650 cm,1. Large changes in the Raman spectra of calf-thymus DNA were observed on lowering the pH value. These are due to protonation and unstacking of the DNA bases during DNA melting and also to changes in the DNA backbone conformation. The intensities of the Raman bands of guanine (681 cm,1), adenine (728 cm,1), thymine (752 cm,1) and cytosine (785 cm,1), typical of the C2,- endo - anti conformation of B-DNA, are discussed. The B-form marker near 835 cm,1 and the base vibrations in the higher wavenumber region (1200,1680 cm,1) are analysed. Effects of low pH value upon the protonation mechanism of opening AT and changing the protonation of GC base pairs in DNA are discussed. Copyright © 2002 John Wiley & Sons, Ltd. [source] Diet and arterial hypertension: Is the sodium ion alone important?MEDICINAL RESEARCH REVIEWS, Issue 4 2002Michele Buemi Abstract Hypertension is a widespread phenomenon whose ultimate cause is still unknown. Many factors contribute to this disease, and partially for this reason, hypertension responds to different treatments in different individuals. It is difficult to generalize about therapies for general populations. In particular, the role of electrolytes in hypertension varies widely across individuals. This review focuses its attention on sodium, potassium, calcium, and magnesium ions in order to investigate whether these electrolytes play a role in the pathogenesis of arterial hypertension and its treatment. Some individuals are especially sensitive to sodium, and changing their intake of dietary sodium may lead to variations in the levels of the other electrolytes. These changes in electrolyte levels can complicate treatments for arterial hypertension in some patients. © 2002 Wiley Periodicals, Inc. Med Res Rev, 22, No. 4, 419,428, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/med.10013 [source] Effect of Illite Clay and Divalent Cations on Bitumen RecoveryTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2006Xinlin Ding Abstract The adverse effect of illite clay on bitumen recovery was found to be related to its acidity. The addition of calcium or magnesium ions to the flotation deionized water had a marginal effect on bitumen recovery when measured using a Denver flotation cell. However, the co-addition of illite clay and divalent cations caused a significant reduction in bitumen recovery. The effect was found to be compounded at a lower process temperature and low pH values. Zeta potential distributions of illite suspensions and bitumen emulsions were measured individually and as a mixture to investigate the effect of divalent cations on the interaction between bitumen and illite clay. The presence of 1 mM calcium or magnesium ions in deionized water had a significant effect on the interactions between bitumen and illite clay. Slime coating of illite onto bitumen was not observed in zeta potential distribution measurements performed in alkaline tailings water. On a trouvé que l'effet adverse de l'argile d'illite sur la récupération de bitume était relié à son acidité. L'ajout d'ions de calcium ou de magnésium à l'eau déionisée de flottation a un effet marginal sur la récupération de bitume lorsqu'on la mesure avec une cellule de flottation de Denver. Toutefois, l'ajout combiné d'argile d'illite et de cations divalents entraîne une réduction significative de la récupération de bitume. On a trouvé que les effets étaient combinés à une faible température de procédé et de faibles valeurs de pH. Les distributions de potentiel zéta des suspensions d'illite et des émulsions de bitume ont été mesurées individuellement et dans le mélange afin d'étudier les effets des cations divalents sur l'interaction entre le bitume et l'argile d'illite. La présence de 1 mM d'ions de calcium ou de magnésium dans l'eau déionisée a un effet significatif sur les interactions entre le bitume et l'argile d'illite. On n'a pas observé de couche de boues d'illite sur le bitume dans les mesures de distributions de potentiel zéta obtenues dans de l'eau de rejets alcaline. [source] The RNA-Cleaving Bipartite DNAzyme Is a Distinctive MetalloenzymeCHEMBIOCHEM, Issue 1 2006Anat R. Feldman Dr. Abstract Much interest has focused on the mechanisms of the five naturally occurring self-cleaving ribozymes, which, in spite of catalyzing the same reaction, adopt divergent strategies. These ribozymes, with the exception of the recently described glmS ribozyme, do not absolutely require divalent metal ions for their catalytic chemistries in vitro. A mechanistic investigation of an in vitro-selected, RNA-cleaving DNA enzyme, the bipartite, which catalyzes the same chemistry as the five natural self-cleaving ribozymes, found a mechanism of significant complexity. The DNAzyme showed a bell-shaped pH profile. A dissection of metal usage indicated the involvement of two catalytically relevant magnesium ions for optimal activity. The DNAzyme was able to utilize manganese(II) as well as magnesium; however, with manganese it appeared to function complexed to either one or two of those cations. Titration with hexaamminecobalt(III) chloride inhibited the activity of the bipartite; this suggests that it is a metalloenzyme that utilizes metal hydroxide as a general base for activation of its nucleophile. Overall, the bipartite DNAzyme appeared to be kinetically distinct not only from the self-cleaving ribozymes but also from other in vitro-selected, RNA-cleaving deoxyribozymes, such as the 8,17, 10,23, and 614. [source] | ||||||||||