Simple Cation Research Articles

Elucidation of specific ion association in nonaqueous solution environments

Abstract The paper reviews ion aggregation in ionic solution in solvents of low and high permittivity. Although higher ion aggregates from 1:1 type electrolytes in low-pemittivity media (εr < 10) are widely accepted, only a few chemists have recognized the higher ion aggregation in the higher-permittivity media. However, we have clarified that the chemical interaction, such as coordination, can operate between simple anions and cations in nonaqueous solvents (20 < εr < 65) of low solvation ability. Acids (HA) and their conjugate base anions (A-) may react with each other to form homoconjugated species, such as A-(HA)2, in acetonitrile or benzonitrile (i.e., solvents possessing poor hydrogen-bonding donor and acceptor abilities). An analytical method of conductivity data for 1:1 electrolytes has been developed and successfully applied to very complicated systems, in which the ion pair (1:1), triple ions (2:1 and 1:2), and the quadrupole (2:2 association) are involved in a solution at the same time. After observing the direct reaction of some anions (e.g., Cl-) and cations (e.g., Li+) toward a certain species, we interpreted comprehensively the salt effects in chemical equilibria, based on distinct chemical interactions and not merely a vague term, "medium effect". The mechanism of salt effects on solvolysis reactions of the SN1 type in organic-aqueous mixed solvents has been elucidated. We discussed that a reaction manner similar to that in nonaqueous solution can take place even in some "aqueous" solution if the huge network of hydrogen-bonding of bulk water (the number of water, n w > ~108) is destroyed due to any spatial barriers (such as ions, molecules, surface) or elevated temperature.

Oxoanion Binding by Flexible Guanidiniocarbonyl Pyrrole−Ammonium Bis-Cations in Water

The syntheses of several bis-cations 1-5 with a simple primary ammonium cation attached via flexible linkers of varying length to a guanidiniocarbonyl pyrrole oxo anion binding site are reported. In UV-binding studies in aqueous buffer solution these bis-cations showed efficient binding of various N-acetyl amino acid carboxylates. However, complex affinity is significantly depending on both the anion and the length of the linker in the bis-cation. With increasing linker length, complex stability first increases until an optimum is reached for bis-cation 3 with a C4-linker. Then the complex stability decreases again. The best binding substrate in this series is N-acetyl phenyl alanine, most likely due to additional cation-pi-interactions between the aromatic ring and the guanidiniocarbonyl pyrrole cation. The formation of the complex between bis-cation 3 and N-acetyl phenyl alanine carboxylate was investigated further by fluorescence titrations and NOE studies, as well as molecular mechanics calculations.

Preparation of inorganic–organic pillared montmorillonite using ultrasonic treatment

Montmorillonite (Mt) is a clay mineral with expandable layer structure. Mesoporous pillared montmorillonite can be prepared by introducing gallery templates, such as simple metal cations, quaternary ammonium cations, long chain amines, and hydroxyed inorganic metal ions. In this paper, inorganic–organic pillared montmorillonite intercalated by aluminium and alkyl ammonium chloridize (HDTMA–Cl) was successfully prepared by ultrasonic treatment, and the physicochemical properties of the materials were systematically characterized by XRD, FT-IR, SEM and TEM techniques. The d001 basal spacings and microstructures of Mt–Al–HDTMA were characterized by XRD. The function group, crystal surface morphology, structural and chemical analysis of Mt–Al–HDTMA were measured by FT-IR, SEM, TEM and EDX. The results indicated that ultrasonic method might accelerate the diffusion of the intercalating species, which enhanced the textural properties and the morphologies. The results also suggested that aluminium and HDTMA–Cl reagent entered the interlayer of Mt, and that the crystal structure of the final Mt was preserved.

Penta- and Hexaruthenium Carbonyl ‘Raft' Complexes Supported by Monocarborane Cage Ligands

Reaction between [PPh4][closo-4-CB8H9] and [Ru3(CO)12] in refluxing toluene affords the unprecedented hexaruthenium metallacarborane salt [PPh4][2,3,7-{Ru(CO)3}-2,6,11-{Ru(CO)3}-7,11,12-{Ru(CO)3}-3,6,12-(micro-H)3-2,2,7,7,11,11-(CO)6-closo-2,7,11,1-Ru3CB8H6] (1a), which contains a planar Ru6 'raft' supported by a {CB8} monocarborane cluster. Addition of [CuCl(PPh3)]4 and Tl[PF6] to a CH2Cl2 solution of 1a results in simple cation replacement, forming the analogous [Cu(PPh3)3]+ salt (1b). The phenyl-substituted monocarborane [NEt4][6-Ph-nido-6-CB9H11] reacts with [Ru3(CO)12] in refluxing 1,2-dimethoxyethane to afford the pentaruthenium cluster species [N(PPh3)2][2,3,7-{Ru(CO)3}-3,4,8-{Ru(CO)3}-7,8-(micro-H)2-1-Ph-2,2,3,3,4,4-(CO)6-hypercloso-2,3,4,1-Ru3CB8H6] (2), after addition of [N(PPh3)2]Cl. Treatment of 2 with [CuCl(PPh3)]4 and Tl[PF6] in CH2Cl2 forms the zwitterionic complex [10,12-{exo-Cu(PPh3)2}-2,3,7-{Ru(CO)3}-3,4,8-{Ru(CO)3}-7,8,10,12-(micro-H)4-1-Ph-2,2,3,3,4,4-(CO)6-hypercloso-2,3,4,1-Ru3CB8H4] (3). Substitution of CO by PPh3 with concomitant cation replacement occurs on introduction of [AuCl(PPh3)], Tl[PF6], and PPh3 to a CH2Cl2 solution of 2, forming [Au(PPh3)2][2,3,7-{Ru(CO)2PPh3}-3,4,8-{Ru(CO)2PPh3}-7,8-(micro-H)2-1-Ph-2,2,3,3,4,4-(CO)6-hypercloso-2,3,4,1-Ru3CB8H6] (4). Crystallographic studies confirmed the cluster architectures in 1b, 2, and 3.

In Search of the Holy Grail for the Treatment of Neurodegenerative Disorders: Has a Simple Cation Been Overlooked?

In recent years, there has been considerable excitement about the possibility that the “molecular medicine revolution” would lead to identification of numerous putative targets designed to slow the atrophic/degenerative process in various neuropsychiatric disorders. Indeed, tremendous progress was made in the identification of cellular processes and pathways involved in numerous degenerative diseases; however, to date, proliferation of candidate drugs has not resulted in viable novel clinical treatments for these devastating disorders (Heemskerk et al., 2002). Ironically, the paper by Bearden and associates in this issue of the journal suggests that an old medication present in our therapeutic armamentarium for half a century, exerts neurotrophic effects not only in animal models, but also in humans. Bearden et al. used high-resolution magnetic resonance imaging and cortical pattern matching methods to map gray matter differences in 28 bipolar patients; 20 lithium-treated, and 28 healthy controls. Their results showed gray matter density was significantly greater in bipolar patients, compared with healthy subjects, in diffuse cortical regions, notably bilateral cingulated and paralimbic cortices, areas utilized in attention, motivation and emotion. Additionally, their data revealed greater gray matter density in the right anterior cingulate in lithium-treated patients relative to the bipolar subjects not taking lithium. Their lithium-treated sample included subjects who were on lithium for varying time durations, at different individual doses. The lack of difference in gray mater density between the untreated patients and healthy controls, as well as growing evidence that lithium exerts major effects on a number of cellular proteins and pathways (vide infra) known to regulate cell atrophy/death lends support to the view that gray matter enlargement is mediated through the trophic actions of lithium in the brain.

Including Students with Severe, Multiple Disabilities in General Physical Education

T he least restrictive environment (LRE) doctrine in the Individual with Disabilities Education Act (IDEA) mandates that students with disabilities be educated together with students without disabilities. Placing students with disabilities into a separate adapted physical education program should occur only when the students are clearly not successful in general physical education (GPE) or when they pose a clear safety risk to others or to themselves (Wright & Wright, 2005). This LRE doctrine has been interpreted to suggest that most students with disabilities should start out in GPE with supplemental aids and supports as needed to ensure success. If the student is not successful even with these supports, then the student can be placed in an alternative setting (Block, 1996, 2007). Unfortunately, in practice, students with more severe disabilities never have the opportunity to try GPE. These students are directly placed in an alternative setting because the student’s IEP team (including the GPE teacher) believes that the student will not be safe or successful in GPE, will not benefi t from GPE activities, or may require so many accommodations that his or her participation will detract from the experience of peers without disabilities. While these are all valid concerns, many students with severe disabilities can safely, successfully, and meaningfully participate in GPE programs at all age levels with careful planning and proper support (Block, Zeman, & Henning, 1997; Obrusnikova, Block, & Valkova, 2003; Vogler, Koranda, & Romance, 2000). The purpose of this article is to detail specifi c strategies that allow a student with severe, multiple disabilities (SMD) to be included in GPE. These strategies revolve around three major themes: (1) identifying and selecting appropriate goals and objectives for the student with disabilities and then fi nding ways to help the student achieve these goals and objectives while in GPE, (2) making the GPE setting safe for the student with SMD, and (3) facilitating social interaction between students with and without SMD. Specifi c examples of simple modifi cations that allow the student with SMD to be safely and meaningfully involved in GPE will be presented throughout. With careful planning and support, you can successfully include students with severe, multiple disabilities in general physical education.

Experimental and theoretical studies of solvent effects on the hydrogen bonds in homoconjugated cations of substituted 4-halo (Cl, Br) pyridine N-oxide derivatives

Hydrogen bond OHO-type bridges formed between six substituted 4-halo (Cl, Br) pyridine N-oxide systems and their simple cations have been investigated by using the potentiometric titration method. The formation constants of these complexes (expressed as lg K BHB + ) have been determined in two non-aqueous aprotic solvents with different polarity, i.e., acetone (AC) and acetonitrile (AN). It has been observed that tri- and tetra-substituted pyridine N-oxides [B] and their cationic acids [BH +] form stable homocomplexed cations [BHB +] stabilized by O⋯H⋯O bridges in both solvents used. It has been found that the most stable homocomplexed system is formed by 3,5-dimethyl-4-chloropyridine N-oxide (3,5Me 24ClPyO). The lg K BHB + values for this compound in acetone and acetonitrile are 3.15 and 2.82, respectively. Furthermore, by using ab initio methods at the RHF and MP2 levels utilizing the Gaussian 6-31++G ∗∗ basis set, the energies of formation of the homocomplexed cations and Gibbs free energies have been determined in vacuo. The calculated energy parameters in vacuo have been compared with the cationic homoconjugation constants determined potentiometrically in acetone and acetonitrile to establish a correlation between these magnitudes. Additionally, the results of potentiometric measurements have been used to determine the acidity constants of the conjugate acids of N-oxides.

Factors affecting the relative stability of a series of iminium cation stereoisomers

The role of three structural variables on the stability of simple iminium cations has been examined via molecular orbital calculations. In general, the more stable conformation for the hydroxyl substituent is axial, and the more stable geometry for each of the two double bonds is E. These conclusions apply also to more complex iminium cations derived from acyl pyrrolidines that could be precursors for the aza-Cope rearrangement – Mannich cyclization reaction. For these systems, molecular orbital calculations are also used to determine the effect of pyrrolidine substituent steric bulk on the relative stability of the cations. Results indicate that larger groups favor the E geometry of the iminium cation. This holds true for either geometry ( E or Z) of the second double bond. For all substituent groups except hydrogen, the E geometry of both double bonds leads to the most stable isomers. When both double bonds are in the E geometry, the axial position for the OR substituent is preferred for all substituents but R = phenyl.

A study of fluid properties and microfiltration characteristics of room temperature ionic liquids [C 10-min][NTf 2] and N 8881[NTf 2] and their polar solvent mixtures

Room temperature ionic liquids (RTILs) are non-volatile and exhibit distinctive fluid properties with high viscosity typically 2–3 orders of magnitude higher than water, rendering their separation, recovery and reuse from some reaction mixtures a difficult and highly challenging task for conventional separation processes. This work investigates the potential application of microfiltration process in ionic liquid separation based on experimental studies of fluid properties and filtration characteristics of two ionic liquids C 10-min[NTf 2] and N 8881[NTf 2]. It was found that direct filtration of the pure ionic liquids through Nuclepore microfiltration membranes yielded very low permeation rate, a direct consequence of exceedingly high viscosity. The ionic liquid viscosity can be drastically reduced by mixing with a small volumetric proportion of simple diluting agents of methanol or ethanol, and the mixed solution permeated through the microfiltration membranes with ease. Methanol and ethanol were easily separated by additional post processing of evaporation, taking advantage of the non-volatile properties of the ionic liquids. The decrease of viscosity with increasing methanol to ionic liquids ratio follows an exponential fashion, and the viscosity–temperature relationship was found following Arrhenius equation for the pure ionic liquids with simple asymmetric cations without functional groups. The mixing ratio of the simple diluting agents to ionic liquids had significant impact on permeation rate, but effective filtration can be carried out at 20% (v/v) diluting agents to ionic liquid ratio. The difference in molecular structure of the asymmetric ionic species was further analysed for their effect on the microfiltration permeation rate.

Boroarsenates: A Framework Motif and Family Templated on Cations and Anions.

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Editorial:Dependability and Security - Looking Foward to 2006

DURING its fi rst two years, TDSC mapped out the challenges and new directions the journal would pursue. With this issue, the fi rst of its third year, I see the journal as continuing to evolve and beginning to gain a high profi le in the dependability and security arenas. A brief overview of this issue’s offerings shows the range and quality of this up-and-coming journal. “From Set Membership to Group Membership: A Separation of Concerns,” by Andre Schiper and Sam Toueg, presents a new way of looking at group membership, giving a simple and succinct specifi cation of the problem and outlining a simple implementation approach based on the state machine paradigm. In “Achieving Privacy in Trust Negotiations with an Ontology-Based Approach,” Anna Squicciarini et al. introduce the notion of privacy-preserving disclosure, that is, a set that does not include attributes, credentials, or combinations of these that may compromise privacy; they propose two techniques based on the notions of substitution and generalization to obtain privacy-preserving disclosure. “An Active Splitter Architecture for Intrusion Detection and Prevention,” by Kostas Xinidis et al., argues that rather than just passively providing generic load distribution, traffi c splitters should implement active operations on the traffi c stream with the goal of reducing the load on the sensors. Gal Badishi et al.’s “Exposing and Eliminating Vulnerabilities to Denial of Service Attacks in Secure Gossip-Based Multicast” proposes a framework and methodology for quantifying the effect of denial-of-service attacks on a distributed system. “A Key Predistribution Scheme for Sensor Networks Using Deployment Knowledge,” by Wenliang Du et al., shows that the performance of sensor networks can be substantially improved using a scheme that recognizes the importance of node-deployment knowledge. “Install-Time Vaccination of Windows Executables to Defend against Stack Smashing Attacks,” by Danny Nebenzahl et al., demonstrates a scheme to detect and vaccinate against smashing attacks, with promising performance results. In Shyh-Yih Wang and Chi-Sung Laih’s “Merging: An Effi cient Solution for a Time-Bound Hierarchical Key Assignment Scheme,” we see that some problems usually addressed by conventional key assignment schemes can be solved directly via merging, with better performance. The past year saw the fi rst special issue of TDSC. The April-June issue featured a special section containing three selected papers from the 2005 IEEE Symposium on Security and Privacy, which took place in Oakland, California. So that the dissemination of these papers would not be held up by publishing schedules, preprints were made available at the conference, where they were well received. We expect to build on this success by publishing another special issue containing papers from the 2006 conference. We are also working on a special issue based on the 2005 International Conference on Dependable Systems and Networks, for which the conference program chairs, in conjunction with TDSC Associate Editors Drs. Arlat and Verissimo, are currently selecting the best papers. The journal plans to continue publishing special issues based on these two premier conferences and to start looking into emerging areas to address via special issues. A statistic of interest is that during the past year TDSC received a total of 179 manuscripts. Six have been received so far in 2006. Last year, we published 39 papers, with an average time from submission to decision of 110 days, a decrease of 28 days from last year. We continue to strive to keep the decision-making time as short as possible, while attempting to attract high-quality submissions. On this second anniversary, I wish to thank all of our 2005 associate editors, submitters, authors, and reviewers, each of whom make the growing success of TDSC possible. I also wish to thank the wonderful publications staff at the IEEE Computer Society Publications offi ce, in particular Suzanne Werner, Selina Flynn, and Joyce Arnold, whose support and dedication have helped us through our second year. Here, at the University of Illinois, special thanks go to Tammi O’Neill, Gerssimoula Kokkosis, and Heidi Leerkamp for providing exceptional support during this past year. Most importantly, my thanks go to the peer community at large—with your support TDSC goes forth into its third year with confi dence and enthusiasm.

Desorption electrospray ionization mass spectrometry for the analysis of pharmaceuticals and metabolites

The performance of desorption electrospray ionization (DESI) in the analysis of a group of pharmaceuticals and their glucuronic acid conjugates is reported. The suitability of different sprayer solvents and different surfaces was examined. In the positive ion mode, water/methanol/trifluoroacetic acid performed best, whereas, in the negative ion mode, water/methanol/ammonium hydroxide was found to be the most suitable spray solvent. Of the surfaces investigated, polymethylmethacrylate (PMMA) was found to give the best performance in terms of sensitivity. Spray solution flow rate and the distance of the sprayer tip from the surface were also found to have significant effects on the signal intensity. Analytes with basic groups efficiently formed the corresponding protonated molecules in the positive ion mode, whereas acidic analytes, such as the glucuronic acid conjugates, formed intense signals due to the deprotonated molecules in the negative ion mode. Ionization of neutral compounds was less efficient and in many cases it was achieved through adduct formation with simple anions or cations.

Diferenciación y delimitación municipal de los modelos turísticos en la provincia de Alicante

El artículo trata de exponer una nueva metodología para la diferenciación y la delimitación territorial de los espacios turísticos litorales e interiores en la provincia de Alicante. Por la imposibilidad de establecer una clasificación simple basada únicamente en municipios de vocación turística litoral e interior. Se propone por la heterogeneidad del espacio de trabajo crear un tercer grupo formado por los municipios inmediatos al litoral, el cual a su vez, queda subdividido en municipios accesorios del litoral y municipios de ocupación ocasional surgidos como respuesta a la movilidad de los flujos turísticos litorales. La metodología empleada se basa en la creación de capas de información para la posterior superposición mediante la utilización de SIG. En este sentido, se ha tenido en cuenta la presencia de fachada marítima dentro de los términos municipales, el análisis de la promoción turística del interior en el espacio litoral, la estructura provincial de la oferta de alojamiento y la presencia y consolidación de los programas europeos para el desarrollo rural (PRODER 2 y LEADER +).

ZnSe∕GaAs(001)heterostructures with defected interfaces: Structural, thermodynamic, and electronic properties

We have performed accurate \emph{ab--initio} pseudopotential calculations for the structural and electronic properties of ZnSe/GaAs(001) heterostructures with interface configurations accounting for charge neutrality prescriptions. Beside the simplest configurations with atomic interdiffusion we consider also some configurations characterized by As depletion and cation vacancies, motivated by the recent successfull growth of ZnSe/GaAs pseudomorphic structures with minimum stacking fault density characterized by the presence of a defected (Zn,Ga)Se alloy in the interface region. We find that--under particular thermodynamic conditions--some defected configurations are favoured with respect to undefected ones with simple anion or cation mixing, and that the calculated band offsets for some defected structures are compatible with those measured. Although it is not possible to extract indications about the precise interface composition and vacancy concentration, our results support the experimental indication of (Zn,Ga)Se defected compounds in high-quality ZnSe/GaAs(001) heterojunctions with low native stacking fault density. The range of measured band offset suggests that different atoms at interfaces rearrange, with possible presence of vacancies, in such a way that not only local charges but also ionic dipoles are vanishing.

Boroarsenates: A Framework Motif and Family Templated on Cations and Anions

Molten salt reactions of NH4H2AsO4, H3BO3, and MX (M = Li, Na, K, Rb Cs, NH4 and X = F, Cl, Br) yield numerous new alkali metal and alkali metal salt templated three-dimensional boroarsenate and fluoroboroarsenate frameworks. The structures of these materials are formed from BO4 (BO3F) and As(O,OH)4 tetrahedra defining channels and interlayer regions containing either simple alkali metal cations or both cations and halide anions. These boroarsenate-based frameworks are unusual in comparison with other oxotetrahedral-based materials in that terminal OH, on As, may be present, decorating the inner surfaces of the channels, as in the 12-membered rings of K2[B(AsO3O)2H]. This unit also permits coordination to nonframework anions as well as cations, so that (Cs2[BAsO3OH]8[AsO4]2[CsCl4]Cl)2 (and its Br analogue) contains layers of [CsCl4]3- and Cl- ions separated and coordinated by the protonated boroarsenate framework.

Direct Observation of Cations and Polynucleotides Explains Polyion Adsorption to Like-Charged Surfaces

We show an experimental approach for directly observing the condensation of polynucleotides and their electrolyte counterions at a liquid/solid interface. X-ray standing waves (XSW) generated by Bragg diffraction from a d = 20 nm Si/Mo multilayer substrate are used to measure the distinct distribution profiles of the polyanions and simple cations along the surface normal direction with subnanometer resolution. The 1D spatial sensitivity of this approach is enhanced by observing the XSW induced fluorescence modulations over multiple orders of Bragg peaks. We study the interesting divalent cation driven adsorption of anionic polynucleotides to anionic surfaces by exposing a hydroxyl-terminated silica surface to an aqueous solution with ZnCl2 and mercurated poly-uridylic acid (a synthetic RNA molecule). The in situ long-period XSW measurements are used to follow the evolution of both the Zn and Hg distribution profiles during the adsorption process. The conditions and physical mechanisms that govern the observed divalent cation adsorption and subsequent polynucleotide adsorption to an anionic surface are explained by a thermodynamic model that incorporates nonlinear electrostatic effects.

Disproportionation of hydrogen peroxide into singlet oxygen catalyzed by lanthanum-exchanged zeolites

Lanthanum(III) was immobilized on various zeolite supports by simple cation exchange. The resulting materials were tested in the disproportionation of H 2O 2 into singlet molecular oxygen ( 1O 2). The rate of H 2O 2 disproportionation and the reaction of the formed 1O 2 with citronellol as a typical olefinic substrate were strongly dependent on the zeolite topology and composition. Zeolites with a large crystal size, small pores, or a one-dimensional pore system showed low activity in the disproportionation of H 2O 2. In contrast, zeolites with a small crystal size or zeolites possessing large intersecting pores were active 1O 2 generators. La supported on ultrastable Y zeolite (USY) and zeolite Beta were identified as the most active and efficient catalysts. Typically, within 24 h at 40 °C, 100 mol of citronellol hydroperoxides is produced per mol of La supported on USY zeolite. Within this time, 800 mol of H 2O 2 is disproportionated into 1O 2. In comparison with unsupported La-hydroxide, La-USY shows a significantly higher activity and a slightly more efficient use of H 2O 2. The heterogeneous nature of the catalysis by La-USY was verified by filtration tests, and its stability was proved by X-ray diffraction and recycle experiments. Finally, the catalyst was used in the peroxidation of various olefinic compounds. Compared with conventional molybdate catalysts, La-USY is particularly useful for the selective peroxidation of allylic alcohol derivatives, with very little competitive epoxidation and no alcohol oxidation being observed.

Modelling of geochemical reactions and experimental cation exchange in MX80 bentonite

Bentonites are widely used for waste repository systems because of their hydrodynamic, surface and chemical-retention properties. MX80 bentonite (bentonite of Wyoming) contains approximately 85% Na/Ca-montmorillonite and 15% accessory minerals. The dominant presence of Na/Ca-montmorillonite in this clay mineral could cause it to perform exceptionally well as an engineered barrier for a radioactive waste repository because this buffer material is expected to fill up by swelling the void between canisters containing waste and the surrounding ground. However, the Na/Ca-montmorillonite could be transformed to other clay minerals as a function of time under repository conditions. Previous modelling studies based on the hydrolysis reactions have shown that the Na/Ca-montmorillonite-to-Ca-montmorillonite conversion is the most significant chemical transformation. In fact, this chemical process appears to be a simple cation exchange into the engineered barrier. The purpose of the present study was two-fold. Firstly, it was hoped to predict the newly formed products of bentonite-fluid reactions under repository conditions by applying a thermokinetic hydrochemical code (KIRMAT: Kinetic Reactions and Mass Transport). The system modelled herein was considered to consist of a 1-m thick zone of water-saturated engineered barrier. This non-equilibrated system was placed in contact with a geological fluid on one side, which was then allowed to diffuse into the barrier, while the other side was kept in contact with iron-charged water. Reducing initial conditions ( P O 2 ≅ 0 ; Eh=−200 mV) and a constant reaction temperature (100 °C) were considered. Secondly, it was hoped to estimate the influence of interlayer cations (Ca and Na) on the swelling behaviour of the MX80 bentonite by using an isothermal system of water vapour adsorption and an environmental scanning electron microscope (ESEM) coupled with a digital image analysis (DIA) program. Here, the MX80 bentonite was previously treated with concentrated solutions (1 N) of calcium and sodium chlorides. The results confirmed that the Na/Ca-montmorillonite-to-Ca-montmorillonite conversion was the main chemical transformation in the bentonite barrier under repository conditions. A simplified method (based on volume balance) has shown that the swelling capacity of the engineered barrier would be slightly affected after 1000 years of diffusion-reaction because the volume of neo-formed swelling clays is almost directly proportional to the volume of transformed initial-montmorillonite. Minimal neo-formation of saponites, vermiculites and chlorites was also observed. In addition, an isothermal system of water adsorption and ESEM-DIA methods showed that in the raw-bentonite-to-Ca-bentonite exchange there is a small decrease in the amount of adsorbed water and the swelling potential.

High-resolution structure ofmyo-inositol monophosphatase, the putative target of lithium therapy

Inositol monophosphatase is a key enzyme of the phosphatidylinositol signalling pathway and the putative target of the mood-stabilizing drug lithium. The crystal structure of bovine inositol monophosphatase has been determined at 1.4 A resolution in complex with the physiological magnesium ion ligands. Three magnesium ions are octahedrally coordinated at the active site of each of the two subunits of the inositol monophosphatase dimer and a detailed three-metal mechanism is proposed. Ligands to the three metals include the side chains of Glu70, Asp90, Asp93 and Asp220, the backbone carbonyl group of Ile92 and several solvent molecules, including the proposed nucleophilic water molecule (W1) ligated by both Mg-1 and Mg-3. Modelling of the phosphate moiety of inositol monophosphate to superpose the axial phosphate O atoms onto three active-site water molecules orientates the phosphoester bond for in-line attack by the nucleophilic water which is activated by Thr95. Modelling of the pentacoordinate transition state suggests that the 6-OH group of the inositol moiety stabilizes the developing negative charge by hydrogen bonding to a phosphate O atom. Modelling of the post-reaction complex suggests a role for a second water molecule (W2) ligated by Mg-2 and Asp220 in protonating the departing inositolate. This second water molecule is absent in related structures in which lithium is bound at site 2, providing a rationale for enzyme inhibition by this simple monovalent cation. The higher resolution structural information on the active site of inositol monophosphatase will facilitate the design of substrate-based inhibitors and aid in the development of better therapeutic agents for bipolar disorder (manic depression).

DIASTEREOSELECTIVE DIELS-ALDER REACTIONS OF POLYETHER BASED CHIRAL 9-SUBSTITUTED ANTHRACENES

Polyether derivatives of 9-anthryl ethanol undergo highly diastereoselective Diels-Alder additions with maleic anhydride and N-methyl maleimide. Addition of simple cations did not increase reaction rates or change the sense of selectivity through coordinative control induced by binding of the cation to the pendant polyether side-chain.