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Brevetoxins, the toxic components of 'red tide' algae, all share one of two robust polycyclic ether backbone structures, but they are distinguished by differing side-chain substituents. Electrospray ionization mass spectrometry analyses of brevetoxins have shown that the polyether structure invariably has a very high affinity for sodium cations that results in the production of abundant (M + Na)(super +) ions even when sodium cations are only present as impurities. Because the ionic charge tends to remain localized on the sodium atom and because at least two bonds must be broken in order to produce polycyclic backbone fragmentation, it is extremely difficult to obtain abundant product ions (other than Na(super +)) from (M + Na)(super +) brevetoxin precursor ions in low-energy collision-induced dissociation (CID) MS/MS experiments. This report establishes that acid additives (oxalic acid, trifluoroacetic acid, and particularly hydrochloric acid) in aqueous methanol solutions can promote high yields of protonated brevetoxin molecules (MH(super +) ions) for Btx-1, -2, and -9 brevetoxins. Most importantly, unlike their (M + Na)(super +) counterparts, MH(super +) precursor ions offer readily detectable product ions in CID MS/MS experiments, even under low-energy collisions. This direct structural characterization approach has provided decomposition information from brevetoxins that was previously inaccessible, including the identification of diagnostic product ions for 'type A' brevetoxins (m/z 611) and 'type B' brevetoxins (m/z 779, 473, 179) and characteristic ions for Btx-1 (m/z 221, 139), Btx-2 (m/z 153), and Btx-9 (m/z 157, 85). Precursor ion scans and constant neutral loss scans are proposed to enable screening of individual type A or type B brevetoxins present in naturally occurring mixtures.

The side arm effects on cyclen-alkali metal cation binding are investigated by preparing various armed cyclens in which ester, amide, nitrile and pyridine moieties are appended as cation-ligating side arms to a 12-membered ring. Ester, amide and pyridine-armed 12-membered cyclens are found to easily accomodate a Na+ ion in a 3D manner and highly discriminate the cation from Li+ and K+ ions. It was also observed that these cyclens are more efficient and selective in binding Na+ ion than common Na+ ion-selective ligands.

The function of acidic amino acid residues in cation recognition and selectivity by the Na+/dicarboxylate cotransporter NaDC-1 was studied by site-directed mutagenesis and expression in Xenopus oocytes. Four of the residues tested, Asp-52, Glu-74, Glu-101 and Glu-332, were observed to be unessential for transport activity. However, substitutions of Asp-373 and Glu-475, conserved residues found in transmembrane domains M8 and M9, respectively, modified transport kinetics.

Research was conducted to examine the differential inhibition of Na+/Ca2+ exchanger isoforms by divalent cations and isothiourea derivative. The properties of three mammalian Na+/Ca2+ exchanger isoforms, NCX1, NCX2 and NCX3, were compared through an analysis of the effects of Ni2+ and other cations and the inhibitor isothiourea derivatives on intracellular Na+-dependent 45Ca2+ uptake into CCL-39 fibroblasts stably expressing each isoform. It was observed that there were distinct differences in the kinetic and pharmacological characteristics between the three isoforms.

A study was conducted to analyze the solvent exchange mechanism around alkali cations in dilute aqueous solutions, specifically mechanisms associated with lithium ions and sodium ions. Molecular dynamics simulations were carried out at constant temperature and constant pressure for three systems. Experimental results indicated that most of the exchange process could be categorized. Findings also showed that water changes occurred more frequently around the sodium ion than around the lithium ion.

A study was conducted on sodium binding effects on conformational exchange in a diquinone calix[4]arene. The findings indicate that the presence of sodium ion favors a syn-cone-Na+ complex and the absence of a cation effect on the rate of interconversion between the conformers. Moreover, it was observed that the initially dominant anti-aryl conformer seems to be a kinetic product of the oxidation step of the synthesis with Tl(CF3CO2)3.

The interaction of the Pi-cloud of C6F6 with cations (Y(super +) = Li(super +), Na(super +), and K(super +)) is characterized by using ab initio MP2(full)/6-31++G** and MP2(full)/6-311++G * * levels. Complexes where the Pi-cloud of the aromatic ring interacts with a cation or a cation and an anion is found to be mimima structures.

The ethynyl-expanded cubane 2 is studied at the B3LYP/6-31G* level for its structure, and ring-strain energy, deprotonation energy, and affinity toward lithium and sodium cation. The estimate of the ring-strain energy of 2 is found to be 48.3 kcal mol super (-1).

A combined solid-state (super 23)Na nuclear magnetic resonance (NMR) and quantum mechanical study of four hydrated disodium salts of nucleoside 5'-phosphates is discussed. The first reliable solid-state (super 23)Na NMR characterization for the pentacoordinate Na(super +1) ions in nucleoside 5'-phosphates is provided.

Static and [sup.23]Na MAS and [sup.1]H MAS NMR experiments at temperatures down to 100 K as well as high temperature static and [sup.23]Na MAS NMR experiments up to 873 K were carried out to study the dynamics of the sodium cation in nitrate cancrinite. In addition, X-ray powder data were recorded at 296 K and 673 K to obtain information about long-range order changes in the structure. Low temperature [sup.23]Na NMR experiments show almost no change in signal, whereas the [sup.1]H MAS NMR spectra show the freezing of cage water motion. The two different crystallographic sodium sites cannot be distinguished in the [sup.23]Na MAS NMR spectra at low and room temperature. In contrast, two [sup.23]Na NMR signals exist at high temperatures above 673 K, a quadrupolar pattern and a Lorentzian signal. Rietveld structure refinements of powders show no change in the local environment of sodium. The strong quadrupolar coupling results from the loss of cage water and the near planar O atom coordination of Na in the [Epsilon]-cage, while the interaction of [Na.sup.+] in the channel remains similar. Thus the change in quadrupolar interaction is mainly caused by the absence of electrostatic shielding of cage water after dehydration.

Sciortino, Christopher M., and Michael F. Romero. Cation and voltage dependence of rat kidney electrogenic [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] cotransporter, rkNBC, expressed in oocytes. Am. J. Physiol. 277 (Renal Physiol. 46): F611-F623, 1999.--Recently, we reported the cloning and expression of the rat renal electrogenic [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] cotransporter (rkNBC) in Xenopus oocytes [M. F. Romero, P. Fong, U. V. Berger, M. A. Hediger, and W. F. Boron. Am. J. Physiol. 274 (Renal Physiol. 43): F425-F432, 1998]. Thus far, all NBC cDNAs are at least 95% homologous. Additionally, when expressed in oocytes the NBCs are 1) electrogenic, 2) [Na.sup.+] dependent, 3) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] dependent, and 4) inhibited by stilbenes such as DIDS. The apparent [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] coupling ratio ranges from 3:1 in kidney to 2:1 in pancreas and brain to 1:1 in the heart. This study investigates the cation and voltage dependence of rkNBC expressed in Xenopus oocytes to better understand NBC's apparent tissue-specific physiology. Using two-electrode voltage clamp, we studied the cation specificity, [Na.sup.+] dependence, and the current-voltage (I-V) profile of rkNBC. These experiments indicate that [K.sup.+] and choline do not stimulate [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] -sensitive currents via rkNBC, and [Li.sup.+] elicits only 3 [+ or -] 2% of the total [Na.sup.+] current. The [Na.sup.+] dose response studies show that the apparent affinity of rkNBC for extracellular [Na.sup.+] (~30 mM [[[Na.sup.+]].sub.o]) is voltage and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] independent, whereas the rkNBC I-V relationship is [Na.sup.+] dependent. At [[[Na.sup.+]].sub.o] [V.sub.max] (96 mM), the I-V response is approximately linear; both inward and outward [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] cotransport are observed. In contrast, only outward cotransport occurs at low [[[Na.sup.+]].sub.o] ([is less than] 1 mM [[[Na.sup.+]].sub.o]). All rkNBC currents are inhibited by extracellular application of DIDS, independent of voltage and [[[Na.sup.+]].sub.o]. Using ion-selective microelectrodes, we monitored intracellular pH and [Na.sup.+] activity. We then calculated intracellular [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and, with the observed reversal potentials, calculated the stoichiometry of rkNBC over a range of [[[Na.sup.+]].sub.o] values from 10 to 96 mM at 10 and 33 mM [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. rkNBC stoichiometry is 2 [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] over this entire [Na.sup.+] range at both [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] concentrations. Our results indicate that rkNBC is highly selective for [Na.sup.+], with transport direction and magnitude sensitive to [[[Na.sup.+]].sub.o] as well as membrane potential. Since the rkNBC protein alone in oocytes exhibits a stoichiometry of less than the 3 [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] thought necessary for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] reabsorption by the renal proximal tubule, a control mechanism or signal that alters its in vivo function is hypothesized. sodium/bicarbonate cotransport; NBC; Xenopus oocyte expression; intracellular pH; sodium transport; bicarbonate transport; kinetics; voltage clamp

Research is presented concerning the use of pH control to facilitate the exchange of positive ions of K and Na across a bulk liquid membrane. The use of 16-crown-5 carboxylic acid ionophores is discussed.

A study was conducted to analyze the features of p-xylene and my-xylene adsorbed in sodium Y faujasite using grand canonical Monte Carlo simulation. The adsorption isotherms of complex molecules were calculated based on the biased particle insertions and deletions. A unit cell of zeolite was utilized to establish the simulation box and periodic boundary conditions. Results indicated a novel adsorption site in the supercage of the zeolite found in front of the sodium cations.