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TRPM4 has recently been described as a calcium-activated nonselective (CAN) cation channel that mediates membrane depolarization. However, the functional importance of TRPM4 in the context of calcium ([Ca.sup.2+]) signaling and its effect on cellular responses are not known. Here, the molecular inhibition of endogenous TRPM4 in T cells was shown to suppress TRPM4 currents, with a profound influence on receptor-mediated [Ca.sup.2+] mobilization. Agonist-mediated oscillations in intracellular [Ca.sup.2+] concentration ([[[Ca.sup.2+]].sub.i]), which are driven by store-operated [Ca.sup.2+] influx, were transformed into a sustained elevation in [[[Ca.sup.2+]].sub.i]. This increase in [Ca.sup.2+] influx enhanced interleukin-2 production. Thus, TRPM4-mediated depolarization modulates [Ca.sup.2+] oscillations, with downstream effects on cytokine production in T lymphocytes., The intensity and shape of [Ca.sup.2+] signals (e.g., oscillations versus sustained [Ca.sup.2+] influx) have been recognized to be essential in setting the threshold for different transcription programs (1). This has [...]

The orientation dependence of the cation-pi interaction between a phenyl ring and a pyridinium ring in the context of a flexible model system in water is investigated. The observed stability is attributed to the maximization of the electrostatic interaction, minimization of rotamers, and possible differences in hydration phenomena arising from alkylationEs.

The validity of the two-phase folding model and the reaction pathway is examined by performing stoichiometric analyses of the hammerhead ribozyme's activity as a function of the concentration of different monovalent ions in the presence and in the absence of Mg2+ ions. The results strongly support the existence of the novel cooperative pathway in the hammerhead ribozyme reaction and it is also found that the hammerhead ribozyme has a unique characteristic with respect to the dependence of its reaction on Mg2+ ions, even in the presence of approximately 1 M Mg2+ ions.

Hydroxyl radical activation of a [Ca.sup.2+]-sensitive nonselective cation channel involved in epithelial cell necrosis. Am J Physiol Cell Physiol 287: C963-C970, 2004. First published May 26, 2004; 10.1152/ajpcell.00041.2004.--In a previous work the involvement of a fenamate-sensitive [Ca.sup.2+]-activated nonselective cation channel (NSCC) in free radical-induced rat liver cell necrosis was demonstrated (5). Therefore, we studied the effect of radical oxygen species and oxidizing agents on the gating behavior of a NSCC in a liver-derived epithelial cell line (HTC). Single-channel currents were recorded in HTC cells by the excised inside-out configuration of the patch-clamp technique. In this cell line, we characterize a 19-pS [Ca.sup.2+]-activated, ATP- and fenamate-sensitive NSCC nearly equally permeable to monovalent cations. In the presence of [Fe.sup.2+], exposure of the intracellular side of NSCC to [H.sub.2][O.sub.2] increased their open probability ([P.sub.o]) by ~40% without affecting the unitary conductance. Desferrioxamine as well as the hydroxyl radical (.OH) scavenger MCI-186 inhibited the effect of [H.sub.2][O.sub.2], indicating that the increase in [P.sub.o] was mediated by .OH. Exposure of the patch membrane to the oxidizing agent 5,5'-dithio-bis-2-nitrobenzoic acid (DTNB) had a similar effect to -OH. The increase in Po induced by .OH or DTNB was not reverted by preventing formation or by DTNB washout, respectively. However, the reducing agent dithiothreitol completely reversed the effects on [P.sub.o] of both .OH and DTNB. A similar increase in [P.sub.o] was observed by applying the physiological oxidizing molecule GSSG. Moreover, GSSG-oxidized channels showed enhanced sensitivity to [Ca.sup.2+]. The effect of GSSG was fully reversed by GSH. These results suggest an intracellular site(s) of action of oxidizing agents on cysteine targets on the fenamate-sensitive NSCC protein implicated in epithelial cell necrosis. [Ca.sup.2+]-activated channels: radical oxygen species; oxidative stress

Cation transport by the neuronal [K.sup.+]-[Cl.sup.-] cotransporter KCC2: thermodynamics and kinetics of alternate transport modes. Am J Physiol Cell Physiol 287: C919-C931, 2004. First published June 2, 2004; 10.1152/ajpcell.00005. 2004.--Both [Cs.sup.+] and N[H.sup.+.sub.4] alter neuronal [Cl.sup.-] homeostasis, yet the mechanisms have not been clearly elucidated. We hypothesized that these two cations altered the operation of the neuronal [K.sup.+]-[Cl.sup.-] cotransporter (KCC2). Using exogenously expressed KCC2 protein, we first examined the interaction of cations at the transport site of KCC2 by monitoring furosemide-sensitive [sup.86][Rb.sup.+] influx as a function of external [Rb.sup.+] concentration at different fixed external cation concentrations ([Na.sup.+], [Li.sup.+], [K.sup.+], [Cs.sup.+], and N[H.sup.+.sub.4]). Neither [Na.sup.+] nor [Li.sup.+] affected furosemide-sensitive [sup.86][Rb.sup.+] influx, indicating their inability to interact at the cation translocation site of KCC2. As expected for an enzyme that accepts [Rb.sup.+] and [K.sup.+] as alternate substrates, [K.sup.+] was a competitive inhibitor of [Rb.sup.+] transport by KCC2. Like [K.sup.+], both [Cs.sup.+] and N[H.sup.+.sub.4] behaved as competitive inhibitors of [Rb.sup.+] transport by KCC2, indicating their potential as transport substrates. Using ion chromatography to measure unidirectional [Rb.sup.+] and [Cs.sup.+] influxes, we determined that although KCC2 was capable of transporting [Cs.sup.+], it did so with a lower apparent affinity and maximal velocity compared with [Rb.sup.+]. To assess N[H.sup.+.sub.4] transport by KCC2, we monitored intracellular pH ([pH.sup.i] with a pH-sensitive fluorescent dye after an N[H.sup.+.sub.4]-induced alkaline load. Cells expressing KCC2 protein recovered [pH.sup.i] much more rapidly than untransfected cells, indicating that KCC2 can mediate net N[H.sup.+.sub.4] uptake. Consistent with KCC2-mediated N[H.sup.+.sub.4] transport, [pH.sup.i] recovery in KCC2-expressing cells could be inhibited by furosemide (200 [micro]M) or removal of external [Cl.sup.-]. Thermodynamic and kinetic considerations of KCC2 operating in alternate transport modes can explain altered neuronal [Cl.sup.-] homeostasis in the presence of [Cs.sup.+] and N[H.sup.+.sub.4] cesium; ammonium; [Cl.sup.-] homeostasis; competitive inhibition

The metal-cation-mediated hydrolysis of phosphonoformate diesters is described. Chemoselectivity is observed in these reactions. The origins of P-OR/C-OR selectivity are discussed.

The differences between the Gibbs free energies of association of the p-sulfonatocalix[4]arene with the tetramethylammonium cations in acidic aqueous solution are reported. The relative importance of the potential of mean force (pmf) bond correction and of the van der Waals and electrostatic contributions to the total change in the Gibbs free energy of complexation is presented.

The aggregation properties of single-chain cationic surfactants bearing one, two and three pyridinium headgroups are studied by using detailed small-angle neutron scattering (SANS). The critical micellar concentration (cmc) of these surfactants is estimated by measuring the specific conductance of the aqueous solution of the surfactants.

The synthesis and structural characterization, determined by H1 and C13 NMR, for a new tetraester calix[4] arene derivative containing mixed pendant arm in its lower rim are reported. The medium effect on the binding process of tetraester calix[4]arene for metal cations are examined to establish the sites of interaction of the ligand with the metal cation, the composition of complex formed and the strength of ligand-cation interaction in different media.

The controlled chemical grafting of distinct polymer chains onto individual montomorillonite-type clay nanoplatelets is described. The presented approach is based on the use of a surfactant mixture consisting of different proportions of substituted and unsubstituted alkylammonium cations.

The general approach for structure explanation by NMR of several cationic components in a mixture is defined. The established charged dispersion was used as models for the composition of charged solitons.

The relaxation of the O - H stretch vibration of water in aqueous salt solvent using femtosecond bi-color pump-probe spectroscopy is examined. A model explaining all the effects of ions on the vibrational relaxation of liquid water is presented.

The radical cations and dictions of a series of oligothiophenes fully surrounded by bicyclo[2.2.2]octene frameworks are prepared and their properties are determined. The first systematic X-ray structural analysis of the radical cation salts of bi-ad terthiophenes, and dication salts of quarter- and sexithiophenes, obtained as single crystals that are stable at room temperature under air is possible by virtue of the structural modifications.

The relative affinity of monovalent cations for stacking G-quartet structure formed by guanosine 5'monophospahe (5'-GMP) self-association at pH8 is examined by conducting a solid-state multinuclear ((super 23)Na, (super 15)N, (super 13)C and (super 31)P) NMR study. Results show the direct determination of the thermodynamic parameters for competitive binding between Na(super +) and M(super +) ions to two different sites of the 5'-GMP structure.

Bicyclopropylidene and its octamethyl derivative, octamethylbicyclopropylidene, are exposed to ionization by X-irradiation in solid argon, in order to spontaneously open the cyclopropylidene rings and study the resulting tetramethyleneethane radical cation. It is found that two interconvertible species with very similar yet distinct spectra are present in the case of a radical cation of tetramethyleneethane called 2,2'-biallyl.

Hyperpolarization-activated cation (HCN) channels regulate pacemaking activity in cardiac cells and neurons. Like the related depolarization-activated [K.sup.+] channels (Kv channels), HCN channels use an intracellular activation gate to regulate access to an inner cavity, lined by the S6 transmembrane regions, which leads to the selectivity filter near the extracellular surface. Here we describe two types of metal interactions with substituted cysteines in the S6, which alter the voltage-controlled movements of the gate. At one position (L466), substitution of cysteine in all four subunits allows [Cd.sup.2+] ions at nanomolar concentration to stabilize the open state (a 'lock-open' effect). This effect depends on native histidines at a nearby position (H462); the lock-open effect can be abolished by changing the histidines to tyrosines, or enhanced by changing them to cysteines. Unlike a similar effect in Kv channels, this effect depends on a [Cd.sup.2+] bridge between 462 and 466 in the same subunit. Cysteine substitution at another position (Q468) produces two effects of [Cd.sup.2+]: both a lock-open effect and a dramatic slowing of channel activation--a 'lock-closed' effect. The two effects can be separated, because the lock-open effect depends on the histidine at position 462. The novel lock-closed effect results from stabilization of the closed state by the binding of up to four [Cd.sup.2+] ions. During the opening conformational change, the S6 apparently moves from one position in which the 468C cysteines can bind four [Cd.sup.2+] ions, possibly as a cluster of cysteines and cadmium ions near the central axis of the pore, to another position (or flexible range of positions) where either 466C or 468C can bind [Cd.sup.2+] in association with the histidine at 462. KEY WORDS: SPIH * gating * [Cd.sup.2+] * cysteine mutagenesis

The structural and compositional evolution of four members of the AnbWO6 (A=NH4(super +), Rb(super +), H(super +), K(super +)) defect pyrochlore family is studied. The study is made as a function of pressure up to 7 GPa, using a diamond anvil cell and monochromatic synchroton X-ray powder diffraction.

Electrical signaling in neurons is based on the operation of plasmalemmal ion pumps and carriers that establish transmembrane ion gradients, and on the operation of ion channels that generate current and voltage responses by dissipating these gradients. Although both voltage- and ligand-gated channels are being extensively studied, the central role of ion pumps and carriers is largely ignored in current neuroscience. Such an information gap is particularly evident with regard to neuronal [Cl.sup.-] regulation, despite its immense importance in the generation of inhibitory synaptic responses by GABA- and glycine-gated anion channels. The cation-chloride co-transporters (CCCs) have been identified as important regulators of neuronal [Cl.sup.-] concentration, and recent work indicates that CCCs play a key role in shaping GABA- and glycine-mediated signaling, influencing not only fast cell-to-cell communication but also various aspects of neuronal development, plasticity and trauma.

We investigated which transient receptor potential (TRP) channel is responsible for the nonselective cation channel (NSCC) activated by carbachol (CCh) in murine stomach with RT-PCR and the electrophysiological method. All seven types of TRP mRNA were detected in murine stomach with RT-PCR. When each TRP channel was expressed, the current-voltage relationship of mTRP5 was most similar to that recorded in murine gastric myocytes, mTRP5 showed a conductance order of [Cs.sup.+] > [K.sup.+] > [Na.sup.+], similar to that in the murine stomach. With 0.2 mM GTP[gamma]S in the pipette solution, the current was activated transiently in both NSCC in the murine stomach and the expressed mTRP5. Both NSCC activated by CCh in murine stomach and mTRP5 were inhibited by intracellularly applied anti-[G.sub.q/11] antibody, PLC inhibitor U-73122, IICR inhibitor 2-aminoethoxydiphenylborate, and nonspecific cation channel blockers [La.sup.3+] and flufenamate. There were two other unique properties. Both the native NSCC and mTRP5 were activated by 1-oleoyl-2-acetyl-sn-glycerol. Without the activation of NSCC by CCh, the NSCC in murine stomach was constitutively active like mTRP5. From the above results, we suggest that mTRP5 might be a candidate for the NSCC activated by ACh or CCh in murine stomach. transient receptor potential protein

The pace of creation of the pyrene dimer radical cation along with the charge resonance feature absorption group forming a part of the infrared area is displayed to have great utility in getting the structural and dynamical knowledge of transiently created DNA in the time span of 1mu s to 1 ms. Moreover, the rate at which the pyrene dimer radical cation is created depending on the DNA dynamics, which permits the communication between the pyrene radical cation and pyrene.

The ability of the effective fragment potential (EFP) method is assessed to describe the hydration of simple cations, calculations are carried out on alkali metal/alkaline earth cation water clusters containing up to six water molecules. Model chemistry is suggested that is based upon EFP/6-31+G optimizations and Hessians and single-point energies at the MP2/aug-cc-p VDZ level of theory.

Selected-area electron diffraction (SAED) and energy-dispersive analysis were used to study the structure of synthetic heavy-metal sorbed birnessites (MeBi). Samples were prepared by equilibrating a suspension of Na-rich buserite (NaBu) at pH 4 in the presence of various heavy metal cations (Me), including Pb, Cd, Zn, and Cu. Five main types of SAED patterns were observed. Types I and II were observed only for ZnBi micro-crystals, and they both consist of two super-cell reflection networks related by a mirror plane parallel to the a*-c* plane. In direct space, these twinned networks correspond to hexagonal supercells with [A.sub.H] = [B.sub.H] = [square root of (7b)]/[square root of (3), and [A.sub.H] = [B.sub.H] = [square root of (7b)], for ZnBi type I and II, respectively. The supercells in the two varieties result from an ordered distribution of vacant layer octahedra capped by interlayer Zn in ZnBi layers. This distribution is described by a hexagonal cell with [A.sub.H] = [square root of (7b)]. In ZnBi micro-crystals of type I, interstratified twinned right- and left-handed fragments are similar to chalcophanite (Zn[Mn.sub.3][O.sub.7] * 3[H.sub.2]O; Wadsley 1955; Post and Appleman 1988), and distributions of vacant layer octahedra from adjacent layers are regularly shifted with respect to each other by 1/3 of the long diagonal of the hexagonal layer unit cell. In ZnBi micro-crystals of type II, distributions of vacant layer octahedra are not regularly shifted from one layer to the adjacent one. SAED patterns of types III and IV occur for PbBi, ZnBi, and CdBi micro-crystals and contain super-cell reflections distributed parallel to [100]* with a periodicity that is not commensurate with that of the MeBi sub-structure (a*/2.15 and a*/5.25, respectively). The super-cell reflections result from the ordered distribution within MeBi layers of vacant layer sites capped by Me as pairs along the a axis. Within each pair, vacant sites are separated by 2a for type III, and by 5a for type IV. In one-layer monoclinic structures, the apparent incommensurability arises from the +a/3 shift between adjacent layers having a similar one-dimensional periodic distribution of interlayer Me located above and below vacant octahedra sharing three corners with [Mn.sub.layer] octahedra (TC sites). Tetrahedral coordination of these Me cations in TC sites, as in ZnBi, leads to the formation of strong H-bonds between adjacent layers. A similar incommensurate effect occurs in one-layer hexagonal MeBi if octahedrally coordinated Me cations periodically distributed along the a axis are located above and/or below empty tridentate cavities sharing three edges with [Mn.sub.layer] octahedra ([sup.VI]TE sites, PbBi). SAED patterns of type V contain only sub-cell reflections and were observed mostly for PbBi and CuBi micro-crystals. Three different conditions can lead to the absence of super-cell reflections: (1) a low amount of sorbed Me (PbBi); (2) the presence of Me having a scattering power similar to that of Mn on a single side of vacant layer sites (CuBi); or (3) a random distribution of interlayer species.

Excited-state twisting and relaxation of triarylpyrylium cations is studied with various substituents attached to different parts of the molecule by means of femtosecond pump-probe absorption spectroscopy. The modeling shows that a broad population distribution along the twisting angle in the ground state is transferred to the excited state, causing strong fluorescene broadening, while competition between the excited-state twisting and solvation determines a subsequent reaction path.

Hyperpolarization-activated nonselective cation channels (Ih channels) play an important role in the control of membrane excitability and rhythmic neuronal activity. The functional relevance of presynaptic Ih channels in regulating synaptic function, however, is not well established. Recently, it has been proposed [Mellor, J., Nicoll, R. A. & Schmitz, D. (2002) Science 295, 143-147] that presynaptic Ih channels are necessary for hippocampal mossy fiber long-term potentiation (LTP). This observation challenges an alternative model that suggests presynaptic forms of LTP are caused by a direct modification of the transmitter release machinery. Here, we assess the role of Ih in hippocampal mossy fiber LTP as well as cerebellar parallel fiber LTP, forms of potentiation that share common mechanisms. Our results show that after Ih blockade neither mossy fiber LTP nor parallel fiber LTP are affected. Furthermore, Ih does not significantly modify basal excitatory synaptic transmission in the hippocampus, whereas the organic Ih blockers ZD7288 and DK-AH 269 induce a large Ih-independent depression of synaptic transmission. In summary, our results indicate that Ih-mediated persistent changes in presynaptic excitability do not underlie presynaptic forms of LTP.

The structure of dioctahedral 2:1 phyllosilicates with different interlayer charge was studied theoretically using ab initio calculations. The standard Kohn-Sham self-consistent density functional method was used in the generalized gradient approximation (GGA), with numerical atomic orbitals as the basis set, by means of the SIESTA program. Once the method had been checked satisfactorily, the theoretical study was extended beyond the systems for which there are experimental information, and structural characteristics were predicted. The SIESTA program was shown to be a useful tool in studying the crystallographic properties of 2:1-dioctahedral phyllosilicates. The crystal structures of pyrophyllite, beidellite, and other smectites and illites were simulated. The experimental crystallographic properties of phyllosilicates with high, medium, and low interlayer charge were reproduced. The calculated structures agree with the main experimental structural features of the crystal lattice of these minerals. The effect of cation substitutions in the octahedral and tetrahedral sheets was also studied. The calculated effects are consistent with experimental results. The [Mg.sup.2+] cations were found to have a tendency to be distributed in the octahedral sheet, in contrast to [Fe.sup.3+] ions that tend to be clustered.

Density functional theory and ab initio method is used to study the effect of a bridgehead methyl group on the hydride ion affinity in the gas phase of bicyclo-[1.1.1]pentyl-1-yl, 1-norbornyl, cubyl, 1-adamantyl, bicyclo[2.2.2]oct-1-yl and bicyclo[3.1.1]hept-1-y cations. Results revealed that the methyl group always increases the stability of the substituted cations.

Guided ion beam mass spectrometry is used to examine threshold collision-induced dissociation of M(super +)(C6H5CH3)(sub x) with XE, where M(super +) includes alkali metal ions, both with mono- and bis-complexes, (x=1 and 2). The bond dissociation energies of metal cation-toluene complexes are determined theoretically and experimentally to identify the influence of the methyl substituents on the binding energies, and the factors that control the strength of cation-pi interactions.

We examined bovine aortic endothelial cells (BAECs) for the functional expression of P2X receptors, the ATP-gated cation channels. We identified the P2X subtypes present in BAECs using RT-PCR. mRNA was present for only three of seven family members: P2X4, P2X5, and P2X7. We then characterized agonist-activated currents in whole cell and outside-out patch recordings using 2-methyl-thio-ATP (MeSATP) as a P2X4 and P2X5 receptor agonist and 2',3'-O-(4-benzoylbenzoyl)ATP (BzATP) as a P2X7 receptor agonist. MeSATP (10-20 [micro]M) produced current with characteristics of P2X4 receptors. The current was an inwardly rectifying current, reversed near 0 mV, slowly desensitized, was not blocked by suramin (300 [micro]M) or reactive blue (60 [micro]M), and had a single channel conductance of 36 pS. BzATP (10-100 [micro]M), on the other hand, activated a 9-pS channel with sustained activity in the continued presence of the agonist. BzATP-activated current was blocked by reactive blue (60 [micro]M) and by suramin (~50% block at 300 [micro]M). We confirmed, by immunocytochemistry, the presence of P2X4 and P2X7 protein. The agonists failed, however, to induce significant uptake of the large molecule YO-PRO, indicating, the lack of pore development that has been demonstrated for P2X7 and P2X4 in response to agonist in some cell types. P2X4; P2X7; P2X5; endothelial cells; cation channels

Treatment of gold(I) halide complexes of the type L-Au-X [where L = P[Ph.sub.3], P[Et.sub.3] with X = Cl, Br, I, or L = 2,6-[(MeO).sub.2][C.sub.6][H.sub.3]P[Ph.sub.2] with X = CI] with AgSb[F.sub.6] in the molar ratio 2:1 in dichloromethane/tetrahydrofuran at -78 [degrees] C affords high yields of di[gold(I)]halonium salts of the formula {X[[Au(P[R.sub.3])].sub.2]]+ Sb[F.sup.-.sub.6] (2-8). A determination of the crystal structures of the four triarylphosphine complexes (2-4, 8) revealed the presence of novel tetranuclear dications with a highly symmetrical structure (point group [S.sub.4]) that arises from self-assembly of the dinuclear monocations through a set of four equivalent aurophilic Au-Au interactions. A comparison with two reference structures of corresponding chloronium perchlorate and bromonium tetrafluoroborate salts with monomeric, dinuclear cations shows that the geometry of the latter is greatly altered on dimerization to optimize the interactions between the closed-shell metal centers (Au: [5d.sup.10]). Weak metallophilic bonding clearly becomes significant only in crystal lattices where anions with a larger ionic radius (Sb[F.sup.-.sub.6] vs. B[F.sup.-.sub.4], Cl[O.sub.4]) reduce the otherwise dominant role of strong interionic Coulomb forces. The results indicate that aurophilic bonding is indeed an ubiquitous, quite dependable mode of intermetallic interactions provided that the right environment is chosen to allow the weak forces to become operative.

The self-assembly of supramolecular structures depends on a subtle interplay of a series of different control mechanisms. The geometric as well as electronic complementarity of the molecular building blocks is crucial for the specific formation of defined supramolecular species. In addition, secondary effects, like templating, also have an important function. The templating ability of different cations in the formation of triple-stranded helicate-type complexes from alkyl-bridged di(8-hydroxyquinoline) ligands is investigated by introduction of alkyl chains of different length as ligand spacers. Hereby a 'size-selectivity' between the cations and the dinuclear helicate-type complexes {[(ligand).sub.3][M.sub.2]} is observed. Large cations support the formation of big dinuclear complexes, whereas small cations are able to template the formation of small complexes.

The cation-pi interaction is investigated by determining its effect on the helicity of model peptides using a combination of CD and NMR spectroscopy. The results are in qualitative agreement with theoretical calculations emphasizing that cation-pi interactions can contribute significantly to protein stability with the order Trp > Phe.

The analysis and the intervalent electron transfer in organic mixed-valence crystals with bridged aromatic cation radicals using X-ray is described. The X-ray crystallography identifies the aromatic donor group D=2,5-dimethoxy-4-methylphenyl as a suitable redox center for the construction of organic mixed-valence crystals owing to its large structural charge attendant upon 1e oxidation to the cation radical.

Reported here is an efficient recognition of [K.sup.+] by 15-crown-5 functionalized gold nanoparticles in aqueous matrix containing physiologically important cations, such as [Li.sup.+], [Cs.sup.+], N[H.sub.4.sup.+], [Mg.sup.2+], [Ca.sup.2+], and excess amount of [Na.sup.+]. Upon exposure to [K.sup.+], the colloidal solution changes from red to blue, in response to surface plasmon absorption of dispersed and aggregated nanoparticles. The concentration ranges of [K.sup.+] detected in this study are 0.099-0.48 mM and 7.6 [micro]M-0.14 mM, when concentrations of colloidal gold are 54.9 and 7.1 nM, respectively. Recognition of [K.sup.+] and formation of the aggregates are proposed via a sandwich complex of 2:1 between 15-crown-5 moiety and [K.sup.+]. Also discussed is the possibility of a preorganized structure of 15-crown-5 at the water-organic interface for the efficient complexation with [K.sup.+].

Research into the C-F...M+ interaction is presented. It was found that the cation-dipole interaction is predominant in the C-F...M+ interaction, with the coordination bond operating supplementally.

Research describing the characteristics of the chemical reactions of the Na+/phenylalanine complex is presented. Particular attention is given to interactions of the cation-p type and to thermo-chemical processes specific of the gas-phase.

Theoretically the general formula for cations H(sub 3)(super +)Ar(sub n)(H2)m (n=0,m=0,6; and, n+m=6) is used to study the structures and consecutive energies and enthalpies of dissociation reactions. The vibrational frequencies for the H(sub 3)(super +) modes are examined.

The beta-carotene radical cation is studied using the hybrid density functional theory method B3LYP. The way in which the rotation of the headgroups can affect the properties of the radical are discussed.

It has been possible to photochemically produce exo- and endo-2-norbornyloxychlorocarbenes from the corresponding diazirines. It was found that the kinetic disparity between the exo- and endo-2-norbornyl substrates is eliminated when the leaving group is made so reactive that Ea for the C-X heterolysis is close to zero.

Diastereofacial selectivity in tertiary 2-adamantyl cations was investigated in the gas phase.

Research has been conducted on the cationic 4-tert-butylpyridine clusters. The synthesis and characterization of these clusters has been carried out via the reaction of the neutral 4-tert-butylpyridine cluster with [Cp (sub)2 Fe]PF (sub)6 as the oxidant.

Research has been conducted on the tetraoxacalix[3]arenes. The synthesis of the new skeleton of these arenes, their X-ray crystal structure and binding studies toward alkali metal cations are discussed.

Research has been conducted on the stable state molecular species of high multiplicity in a para arrangement pi-system. Results of experiments on isomeric species of different topology are presented.

Research has been conducted on the enol carbonate, carbamate and ester radical cations. The characterization of these cations has been carried out via voltammetry and EPR spectroscopy and the results are presented.

Research describing the study of the reaction between dimethyl ether and protonated dimethyl ether is presented. The paper demonstrates how temperature affects transfer of methyl cations producing methanol and trimethyloxonium cation.

Research is presented concerning the use of mass spectrometry to study the positive ions formed within a low-pressure radio frequency helicon plasma reactor when argon/tetraethoxysilane is mixed with oxygen/tetraethoxysilane.

Research has been conducted on the methyl cations. The synthesis and properties of these cations, their redox behavior and their thermodynamic stability have been examined.

Research has been conducted on the methyl groups substituted onto acridinium skeleton. The unusual acidity of the protons in this group has been investigated.

The multinuclear NMR and IR spectroscopy are used to study the interaction of a number of metal cations with monovacant heteropolyanion [P2W20O70(H2O)(sub 2)](super 10-) (P2W20) in aqueous solutions starting from its K salt. The differences observed in the NMR spectra of NaP2W20 and KP2W20 solutions and the importance of K+ and Na+ for the formation of P2W20 suggest that this polyanion exist only as a complex with the alkaline cations.

It has been possibly to make the first infrared spectroscopic measurement on a dianion sufficiently isolated from cations that no cation perturbation is seen in the dianion spectrum.