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Three kinds of nano-baskets including 1,2-alternate and cone conformers of di-ionizable p-tert-butylcalix[4]arene1, 2-crown-3 and the cone conformer of p-tert-butylcalix[4]arene-1,2-thiacrown-3 were synthesized and the competitive solvent extractions of alkali and alkaline earth metal cations were studied. The novelty of this study is including three binding units of the calixarene's bowl, the crown ether's ring, and electron-donor ionizable moieties in a unique scaffold, in which their sizes were selected based upon their complexation ability to show equal binding tendency towards the cations. The objective of this work is to assess the extraction efficiency, selectivity, and p[H.sub.1/2] of such complexes. The results of solvent extraction experiments indicated that these compounds were effective extractants of alkali and alkaline earth metal cations. Their selectivities were greatly influenced by the acidity of the solution and the conformations of the calixcrown. One conformer was highly selective to [Na.sup.+] and the other to [Ba.sup.2+] in acidic and basic solutions, respectively. Key words: nano-baskets, competitive extraction, calix[4]crown-3, s-block metals. On a realise la synthese de trois nouveaux types de nano-paniers, dont les conformeres 1,2-alternes et a cone du p-tert-butylcalix[4]arene-1,2-couronne-3 et de son conformere en cone, le p-tert-butylcalix[4]arene-1,2-thiacouronne-3 et on en a etudie les capacites d'extraction competitive par solvants de cations alcalins et alcalinoterreux. La nouveaute de cette etude reside dans le fait qu'elle inclut trois unites de fixation, soit le bol du calixarene, le noyau de l'ether couronne et les portions ionisables d' un electrodonneur dans un echafaudage unique dans lequel leurs grandeurs ont ete choisies en raison de leur habilite a former a tous former des complexes avec les cations avec autant de facilite. L'objectif de ce travail etait d'evaluer l'efficacite d'extraction, la selectivite et le p[H.sub.1/2] de tels complexes. Les resultats des experiences d'extraction par les solvants indiquent que ces composes permettent d'extraire d'une facon efficace les cations metalliques alcalins et alcalino-terreux. Leurs selectivites sont fortement influencees par l'acidite de la solution et de la conformation du calixarene couronne. Un conformere est tres selectif pour la [Na.sup.+] et l'autre pour la [Ba.sup.2+] dans des solutions respectivement acides et basiques. Mots-cles: nano-paniers, extraction competitive, calix[4]couronne-3, metaux du bloc s., Introduction Nano-baskets of calixarenes and calixcrowns are a versatile class of macrocycles that have been subject to extensive research in the development of many extractants, transporters, and stationary phases (using [...]

The twin-screw configuration problem (TSCP) involves defining the location of a set of predefined screw elements of a corotating twin-screw extruder configuration to optimize different, often conflicting, objectives. A multiobjective optimization methodology based on Evolutionary Algorithms was developed and applied to solve the TSCP. This methodology is used in starch cationization case studies, involving different screw elements and screw lengths. The results obtained, taking into consideration various conflicting objectives, such as minimizing the specific mechanical energy and maximizing output and reaction efficiency, have physical meaning and thus validate the methodology. POLYM. ENG. SCI., 51:330-340, 2011. [C]2010 Society of Plastics Engineers, INTRODUCTION In a series of previous articles, methods were developed to calculate and optimize starch cationization in a twin-screw extruder (1), (2). Starch cationization consists in replacing the hydroxyl groups [...]

A strategy for naked-eye detection and quantification of heparin in biological media, such as fetal bovine serum (FBS) is demonstrated by monitoring the absorbance change of a water-soluble cationic polythiophene. The negatively charged heparin interacts with positively charged polythiophene through electrostatic interaction, which leads to polymer conformation and color change from yellow to orange in solution. Under optimized conditions, addition of heparin derivatives, such as hyaluronic acid or chondroitin 4-sulfate to the same polymer solution leads to less change in polymer conformation and solution color due to their lower charge density as compared to that of heparin. Increasing the detection temperature or simply adding some organic solvent to the aqueous media reduces the polymer-polymer interchain [pi] stacking, and the polymer color change can be used to clearly differentiate heparin from its analogues in homogeneous solutions. Quantification of heparin is also demonstrated by correlating the changes in polymer absorbance to the heparin concentration. A linear calibration curve is observed in the 0-6.7 U/mL and 0-2.2 U/mL ranges for heparin quantification in pure water and in FBS, respectively. 10.1021/ac902354k

Nucleic acid electrophoresis separation heavily depends upon gel or nongel sieving matrix. Here we propose a metal ion mediated-capillary electrophoresis (MCE-CE) by utilizing the nonspeeific interactions of [Mg.sup.2+] and [Ca.sup.2+] and demonstrate the size, conformation, or sequence based separation and characterization of versatile nucleic acid molecules in free solution. [Mg.sup.2+] and [Ca.sup.2+] can induce DNA separation at the concentrations as low as 100 and 50 [micro]M, respectively. Noteworthy, the two naturally occurring polymorphisms of one base substitution that may change the secondary folding structure or base stacking can be discriminated by MCM-CE, showing its unique capability of resolving length-identical but conformation-different ssDNA. Benefiting from the achieved separation, we further demonstrate that the folding conformation of oligomers and its change caused by single base substitution can be promptly sensed by online coupled fluorescence polarization. We anticipate that this method will be applicable in length polymorphism analysis, singlestrand polymorphism analysis, hybridization analysis, microRNA analysis, and study of protein-nucleic acid interactions and the conformation function relationship. 10.1021/ac9025708

A unique phenomenon of mitochondria-targeted protonophores is described. It consistsin a transmembrane [H.sup.+]-conducting fatty acid cycling mediated by penetrating cations such as 10-(6'-plastoquinonyl) decyltriphenylphosphonium (SkQ1) or dodecyltriphenylphosphonium ([C.sub.12]TPP). The phenomenon has been modeled by molecular dynamics and directly proved by experiments on bilayer planar phospholipid membrane, liposomes, isolated mitochondria, and yeast cells. In bilayer planar phospholipid membrane, the concerted action of penetrating cations and fatty acids is found to result in conversion of a pH gradient ([DELTA]pH) to a membrane potential ([DELTA]/[psi]) of the Nernstian value (about 60 mV [DELTA][psi]/at [DELTA]pH = 1). A hydrophobic cation with localized charge (cetyltrimethylammonium) failed to substitute for hydrophobic cations with delocalized charge. In isolated mitochondria, SkQ1 and [C.sub.12]TPP, but not cetyltrimethylammonium, potentiated fattyacid-induced (i) uncoupling of respiration and phosphorylation, and (ii) inhibition of [H.sub.2][O.sub.2] formation. In intactyeast cells, [C.sub.12]TPP stimulated respiration regardless of the extracellular pH value, whereas a nontargeted protonophorous uncoupler (trifluoromethoxycarbonylcyanide phenylhydrazone)stimulated respiration at pH 5 but not at pH 3. Hydrophobic penetrating cations might be promising to treat obesity, senescence, and some kinds of cancer that require mitochondrial hyperpolarization. mild uncoupling | membrane | Mitochondria-targeted uncoupler | penetrating ion | antioxidant www.pnas.org/cgi/doi/10.1073/pnas.0910216107

An environmental sensor, TRPV4 is a novel regulator of intracellular [Ca.sup.2+] in human synoviocytes. Am J Physiol Cell Physiol 297: C1082-Cl090, 2009. First published September 16, 2009; doi:10.1152/ajpcell.00204.2009.--The activation of a vanilloid type 4 transient receptor potential channel (TRPV4) has an obligatory role in regulation of intracellular [Ca.sup.2+] ([Ca.sup.2+.sub.i]) in several types of cells including vascular and sensory organs. In this study, we provide evidence that TRPV4 is a functional regulator of [Ca.sup.2+.sub.i] in human synoviocytes. Although significant expression of TRPV4 in synoviocytes from patients with (RA) and without (CTR) rheumatoid arthritis was detected at mRNA and protein level, those in the human fibroblast-like synoviocyte line MH7A were rather lower. Consistently, the selective TRPV4 agonist 4[alpha]-phorbol 12,13-didecanoate (4[alpha]PDD) effectively elevated [Ca.sup.2+.sub.i] in the RA and CTR cells, which was abolished by the removal of external [Ca.sup.2+]. Moreover, the elevation was inhibited by ruthenium red, a blocker of TRPVs. In MH7A cells transfected with human TRPV4 (MH7A-V4), 4[alpha]PDD elevated the [Ca.sup.2+.sub.i] in a similar manner to those in the RA and CTR cells. Electrophysiological analysis also revealed that 4[alpha]PDD activated nonselective cationic currents in RA cells. Application of 227 mosM solution to the RA and MH7A-V4 cells elevated their [Ca.sup.2+.sub.i], but this does not occur when it was applied to MHTA cells. Treatment of RA but not MH7A cells with 4[alpha]PDD for 24 h reduced their production of IL-8. These results suggest that an environmental sensor, TRPV4, is a novel regulator of intracellular [Ca.sup.2+] in human synoviocytes. MH7A; rheumatoid arthritis; vanilloid type 4 transient receptor potential channel; 4[alpha]-phorbol 12,13-didecanoate; [Ca.sup.2+] concentration; hypotonic stimulation; interleukin-8 doi: 10.1152/ajpcell.00204.2009.

The design, synthesis and characterization of cationic conjugated polyelectrolytes are described for determining the double-stranded DNA concentration [dsDNA]. The combination of the response from two different initial concentrations of conjugated polyelectrolytes has shown that it is possible to generate calibration curves that respond with a difference in [dsDNA] of over 7 orders of magnitude.

The cation-[pi] interaction is a general, strong, noncovalent binding force that is used throughout nature. The side chains of the aromatic amino acids [phenylalanine (Phe), tyrosine (Tyr), and tryptophan (Trp)] provide a surface of negative electrostatic potential than can bind to a wide range of cations through a predominantly electrostatic interaction. In this brief overview, the fundamental nature of the cation-[pi] interaction will be described, relying on fundamental, gas phase studies of the effect. Then, several examples of cation-[pi] interactions involving aromatic amino acids will be described. These include contributions to protein secondary structure, in which Phe/Tyr/Trp ... lysine (Lys)/arginine interactions are common. We will also describe several examples of protein-ligand interactions that make use of cation-[pi] interactions. We will place special emphasis on the binding of quaternary ammonium ions, such as trimethylated Lys and the neurotransmitter acetylcholine.

The affinity of guanidinium and Cu(II) containing hosts for polycarboxylate guests is studied in water by using UV-visible spectroscopy and isothermal titration calorimetry. By combining a Cu(II) coordination site and a diguanidinium moiety around a single scaffold it is found that the Gibbs free-energy release upon binding is greater than could be expected based on the sum of the free energy released by the binding functional groups when operating in isolation. This effect is known as positive cooperativity and has rarely been observed with synthetic hosts in water. The isothermal titration calorimetry data suggest that the source of this positive cooperativity is enthalpic in origin. We propose that covalently positioning the cationic binding moieties in close proximity destabilizes the unbound host, and thereby the stabilizing effect of binding the anionic carboxylates is exothermic and also, the source of positive cooperativity observed herein. enthalpy | entropy | molecular recognition

Monovalent cation proton antiporter-3 (Mrp) family antiporters are widely distributed and physiologically important in prokaryotes. Unlike other antiporters, they require six or seven hydrophobic gene products for full activity. Standard fluorescence-based assays of Mrp antiport in membrane vesicles from Escherichia coli transformants have not yielded strong enough signals for characterization of antiport kinetics. Here, an optimized assay protocol for vesicles of antiporter-deficient E. coli EP432 transformants produced higher levels of secondary [Na.sup.+] ([Li.sup.+])/[H.sup.+] antiport than previously reported. Assays were conducted on Mrps from alkaliphilic Bacillus pseudofirmus OF4 and Bacillus subtilis and the homologous antiporter of Staphylococcus aureus (Mnh), all of which exhibited [Na.sup.+]([Li.sup.+])/[H.sup.+] antiport. A second paralogue of S. aureus (Mnh2) did not. [K.sup.+], [Ca.sup.2+], and [Mg.sup.2+] did not support significant antiport by any of the test antiporters. All three [Na.sup.+] ([Li.sup.+])/[H.sup.+] Mrp antiporters had alkaline pH optima and apparent [K.sub.m] values for [Na.sup.+] that are among the lowest reported for bacterial [Na.sup.+]/[H.sup.+] antiporters. Using a fluorescent probe of the transmembrane electrical potential ([DELTA][PSI]), Mrp [Na.sup.+]/[H.sup.+] antiport was shown to be [DELTA][PSI] consuming, from which it is inferred to be electrogenic. These assays also showed that membranes from E. coli EP432 expressing Mrp antiporters generated higher [DELTA][PSI] levels than control membranes, as did membranes from E. coli EP432 expressing plasmid-borne NhaA, the well-characterized electrogenic E. coli antiporter. Assays of respiratory chain components in membranes from Mrp and control E. coli transformants led to a hypothesis explaining how activity of secondary, [DELTA][PSI]-consuming antiporters can elicit increased capacity for [DELTA][PSI] generation in a bacterial host.

The folding equilibrium of the Tetrahymena ribozyme is measured by nondenaturing gel electrophoresis in the presence of divalent group IIA metal cations. The results have shown that RNA stability is determined by a combination of counterion charge and the packing efficiency of condensed cations that depends on the excluded volume of the cations.

The mechanisms behind the faceting of vesicles in polymer-catanionic vesicles are investigated where the polymer is oppositely charged to the vesicle and bears a grafted chain. The results show that the faceting involves different mechanisms depending on polymer architecture.

Transient receptor potential vanilloid 1 (TRPV1), a ligand-gated cation channel highly expressed in small-diameter sensory neurons, is activated by heat, protons, and capsaicin. The phosphorylation of TRPV1 provides a versatile regulation of intracellular calcium levels and is critical for TRPV1 function in responding to a pain stimulus. We have previously reported that cyclin-dependent kinase 5 (Cdk5) activity regulates nociceptive signaling. In this article we report that the Cdk5-mediated phosphorylation of TRPV1 at threonine-407 can modulate agonist-induced calcium influx. Inhibition of Cdk5 activity in cultured dorsal root ganglia neurons resulted in a significant reduction of TRPV1-mediated calcium influx, and this effect could be reversed by restoring Cdk5 activity. Primary nociceptor-specific Cdk5 conditional-knockout mice showed reduced TRPV1 phosphorylation, resulting in significant hypoalgesia. Thus, the present study indicates that Cdk5-mediated TRPV1 phosphorylation is important in the regulation of pain signaling. p35 | pain

We present here a first principle computational study of the effect of cation disorder on the elasticity of spinel. Our calculated elastic moduli and structural parameters are comparable with reported experimental and theoretical results. We find that bulk modulus for Mg[Al.sub.2][O.sub.4] spinel does not soften at pressure as high as 27 GPa, while shear modulus [C.sub.s] [1/2([C.sub.11] - [C.sub.11])] decreases with pressure. Disorder increases both the bulk modulus and shear modulus in aluminate spinel, but decreases both for the silicate spinel. The elastic properties of ringwoodite are significantly affected by Si-Mg disorder; a 10% disorder decreases the seismic velocities by 3-5%. Thus, a small amount of disorder will significantly affect seismic observations. Keywords: Spinel, first principle model, elastic anisotropy, cation disorder

TRP channels play an important role as multifunctional cellular sensors. They are involved in so many fundamental cell functions that the investigation of their role in human pathophysiology and disease [...]

The degenerate electron exchange (DEE) reaction involving radical cations (RCs) of n-nonane, n-dodecane, and n-hexadecane in n-hexane solution is analyzed by using the method of time-resolved magnetic field effect in recombination fluorescence of spin-correlated radical ion pairs. The influence of the interaction between RC and a neutral molecule in an encounter complex on DEE rate constant is examined.

Thiazide and loop diuretics induce renal [K.sup.+] secretion, often leading to renal [K.sup.+] wasting and hypokalemia. This phenomenon has been proposed to reflect an increase in delivery to and reabsorption of [Na.sup.+] by the distal nephron, with a resultant increase in the driving force for passive [K.sup.+] efflux across the apical membrane. Recent studies suggest that cellular mechanisms that lead to enhanced rates of [Na.sup.+] reabsorption as well as [K.sup.+] secretion in response to increases tubular flow rates are more complex. Increases in tubular flow rates directly enhance the activity of apical membrane [Na.sup.+] channels and indirectly activate a class of [K.sup.+] channels, referred to as maxi-K, that are functionally inactive under low flow states. This review addresses the role of biomechanical forces, generated by variations in urinary flow rate and tubular fluid volume, in the regulation of transepithelial [Na.sup.+] and [K.sup.+] transport in the distal nephron. The question of why the distal nephron has evolved to include a component of flow-dependent [K.sup.+] secretion is also addressed. epithelial [Na.sup.+] channel; ROMK; cortical collecting duct; shear stress; SK channel

Heteropodal complexes, which include a terephthalamide (TAM) moiety and maintain the high relaxivity characteristics of the Hydroxypyridinone family, are functionalized with water-solubilizing moieties of different charge, which demonstrate high selectivity over physiological anions and cations. Results show that the charge of the substituent significantly affects the stability of the Gd(III) complex, with the most stable complex presenting a neutral charge.

Replacement of halide from N-(haloboryl)formamidines for the weakly coordinating anion [B[([C.sub.6]-[F.sub.5]).sub.4]]-, using [[[Et.sub.3]Si(toluene)].sup.+][B[([C.sub.6][F.sub.5]).sub.4]]-, induces a ring closure leading to the cationic four-[pi]-electron four-membered heterocycles [[HC[(N-2,6-diisopropylphenyl).sub.2][BR].sup.+] [R = N[(i-Pr).sub.2], Phi. Subsequent deprotonation of the B-amino derivative affords the corresponding N-heterocyclic carbene, which has been isolated as yellow crystals. According to single-crystal x-ray diffraction studies, both the carbene and its conjugate acid precursor have a planar structure, with no pyramidalization of the ring atoms. The structural parameters indicate that the four [pi] electrons are mostly distributed over the N-C-N fragment with little involvement of the boron center, and therefore both types of heterocycles escape from antiaromaticity. However, considering the ring strain and the presence of the Lewis acid center, the thermal stability of the carbene (mp 98[degrees]C without decomposition) is rather surprising. These results clearly suggest that the backbone of N-heterocyclic carbenes can be modified at will, without preventing their isolation. aromaticity | boron

Transient receptor potential melastatin- (TRPM) and vanilloid-related (TRPV) channels are nonselective cation channels pertinent to diverse physiological functions. Multiple TRPM and TRPV channel subtypes have been identified and cloned in different tissues. However, their information in vascular tissue is scant. In this study, we sought to identify TRPM and TRPV channel subtypes expressed in rat deendothelialized intralobar pulmonary arteries (PAs) and aorta. With RT-PCR, mRNA of TRPM2, TRPM3, TRPM4, TRPM7, and TRPM8 of TRPM family and TRPV1, TRPV2, TRPV3, and TRPV4 of TRPV family were detected in both PAs and aorta. Quantitative real-time RT-PCR showed that TRPM8 and TRPV4 were the most abundantly expressed TRPM and TRPV subtypes, respectively. Moreover, Western blot analysis verified expression of TRPM2, TRPM8, TRPV1, and TRPV4 proteins in both types of vascular tissue. To examine the functional activities of these channels, we monitored intracellular [Ca.sup.2+] transients ([[[Ca.sup.2+]].sub.i]) in pulmonary arterial smooth muscle cells (PASMCs) and aortic smooth muscle cells (ASMCs). The TRPM8 agonist menthol (300 [micro]M) and the TRPV4 agonist 4[alpha]-phorbol 12,13-didecanoate (1 [micro]M) evoked significant increases in [[[Ca.sup.2+]].sub.i] in PASMCs and ASMCs. These [Ca.sup.2+] responses were abolished in the absence of extracellular [Ca.sup.2+] or the presence of 300 [micro]M [Ni.sup.2+] but were unaffected by 1 [micro]M nifedipine, suggesting [Ca.sup.2+] influx via nonselective cation channels. Hence, for the first time, our results indicate that multiple functional TRPM and TRPV channels are coexpressed in rat intralobar PAs and aorta. These novel [Ca.sup.2+] entry pathways may play important roles in the regulation of pulmonary and systemic circulation. transient receptor potential channels; calcium signaling; nonselective cation channels

An unusual reaction manifold for cyclopropylcarbinyl cations, uncovered using B3LYP and MP2 calculations, is described. The potential energies of these surfaces are often complicated, in some cases flat plateaus and bifurcations with turquoselectivity occurring in some cases due to favorable orbital interactions between the breaking C-C and C-H bonds.

A systematic investigation of the Cu(I) and Cu(II) cation interactions with biologically important types of ligands at the density functional theory level was performed. The results provide in-depth insight into the Cu-binding properties and could be used for calibration of bioinorganic force fields.

Birnessite is an important scavenger of trace metals in soils and aqueous environments. The basic birnessite-type structure consists of sheets of Mn octahedra separated by ~7 or ~10 [Angstrom] ('buserite') interlayer regions filled with cations and water. Synthetic birnessite-like structures were produced through cation exchange reactions with synthetic Na-birnessite. The unheated, synthetic [Mg.sup.2+], [Ca.sup.2+], and [Ni.sup.2+] layer structures have an ~10 [Angstrom] interlayer spacing, whereas the other cation-exchanged synthetic birnessites and the related mineral chalcophanite have an interlayer spacing of ~7 [Angastrom]. The [Li.sup.+], [Na.sup.+], [K.sup.+], [Cs.sup.+], and [Pb.sup.2+] synthetic birnessites each contain two to three structurally different water sites, as evidenced by multiple [H.sub.2]O bending and stretching modes in the infrared spectra. The complexity of the water bands in these spectra is likely related to disordering of cations on the interlayer sites. H-birnessite contains structural water and either hydroxyl, hydronium ([H.sub.3][O.sup.+]), or both. The small difference in the width of the water stretching modes between room temperature and -180 [degrees]C indicates that the water molecules in birnessite-like structures are predominantly structurally, rather than dynamically, disordered. Most of the synthetic birnessites, including Na- and K-birnessite, undergo significant water loss at temperatures below 100 [degrees]C. There is a linear relationship between the temperature at which most of the water is lost from a given cation-exchanged birnessite and the heat of hydration of the interlayer cation. This finding implies that the interlayer water is strongly bound to the interlayer cations, and plays an important role in the thermal stability of birnessite-like structures. Keywords: Birnessite, electron microscopy, IR spectroscopy, order-disorder, thermodynamics, XRD data

The fundamental photophysics and photochemistry of a cationic dye rhodamine 800 (R800) in water studied using steady-state and ultrafast time-resolved spectroscopies shows that the pure dimer spectrum obtained indicates a nonparallel H-dimer and the steady-state fluorescence spectra do not show concentration dependence. The S1 dimer dissociates to produce the S1 monomer or relaxes to the S0 dimer with a short time constant, resulting in the absence of dimer fluorescence.

Dermaseptins S are closely related peptides that are polycationic (Lys-rich), alpha-helical, with their polar and apolar amino acids on opposing faces along the long axis of the helix cylinder. Dermaseptin S9, one of these peptides, has a tripartite structure that includes a hydrophobic core sequence flanked at both termini by cationic and polar residues.

The studies about the TRP (transient receptor potential) superfamily of cation channel reveal that it plays a critical role in sensory physiology which include contributions to vision, taste, olfaction, hearing, touch, and thermo- and osmosensation and also sense changes in their local environment.

In mammals, toxic electrolytes of endogenous and exogenous origin are excreted through the urine and bile. Before excretion, these compounds cross numerous cellular membranes in a transporter-mediated manner. However, the protein transporters involved in the final excretion step are poorly understood. Here, we show that MATE1, a human and mouse orthologue of the multidrug and toxin extrusion family conferring multidrug resistance on bacteria, is primarily expressed in the kidney and liver, where it is localized to the luminal membranes of the urinary tubules and bile canaliculi. When expressed in HEK293 cells, MATE1 mediates [H.sup.+] coupled electroneutral exchange of tetraethylammonium and 1-methyl-4-phenylpyridinium. Its substrate specificity is similar to those of renal and hepatic H+-coupled organic cations (OCs) export. Thus, MATE1 appears to be the long searched for polyspecific OC exporter that directly transports toxic OCs into urine and bile. multidrug and toxin extrusion | multidrug export | urinary tubule | bile canaliculi

A sensor for metal cations is demonstrated using single and binary mixtures of different thiolated ligands as self-assembled monolayers (SAMs) functionalized on silicon microcantilevers (MCs) with gold nanostructured surfaces. Binding of charged metal ions to the active surface of a cantilever induces an apparent surface stress, thereby causing static bending of the MC that is detected in this work by a beam-bending technique. A MC response mechanism based on changes in surface charge is discussed. The monodentated ligands arranged as SAMs on the MC surface are not expected to fully satisfy the coordination sphere of the detected metals. This leads to lower binding constants than would be expected for chelating ligands, but reversible responses. The modest binding constants are compensated in terms of the magnitudes of responses by the inherent higher sensitivity of the nanostructured approach as opposed to more traditional smooth surface MCs. Response characteristics are optimized in terms of SAM formation time, concentration of ligand solution, and pH of working buffer solution. Limits of detection for the tested mono-, di-, and trivalent metal ions are in low to submicromolar range. The results indicated that shapes and magnitudes of response profiles are characteristics of the metal ions and type of SAM. The response factors for a given SAM with the tested metal ions, or for a given metal with the tested SAMs, varied by roughly 1 order of magnitude. While the observed selectivity is not large, it is anticipated that sufficient ionic recognition contrast is available for selective metal ion identification when differentially functionalized arrays of MCs (different ligands on different cantilevers in the array) are used in conjunction with pattern recognition techniques.

Long-distance radical cation transport was studied in DNA condensates. Linearized pUC19 plasmid was ligated to an oligomer containing a covalently linked anthraquinone group and six regularly spaced GG steps, which serve as traps for the migrating radical cation. Treatment of the linear, ligated plasmid with spermidine results in formation of condensates that were detected by light scattering and observed by transmission electron microscopy. Irradiation of the anthraquinone group in the condensate causes long-distance charge migration, which is detected by reaction at the remote guanines. The efficiency of charge migration in the condensate is significantly less than it is for the corresponding oligomer in solution. This result is attributed to a lower mobility for the migrating radical cation in the condensate, which is caused by inhibited formation of charge-transfer-effective states. charge transfer | oxidative damage

We present a structural model for (K,Na)Mg[F.sub.3] perovskite using results from high-resolution synchrotron X-ray powder diffraction and nuclear magnetic resonance (NMR) spectroscopy. (K,Na)Mg[F.sub.3] perovskite is found to transition from orthorhombic (Pbnm) to tetragonal (P4/mbm) to cubic (Pm3m) as potassium concentration is increased. These phase transitions are not accompanied by a discontinuity in pseudo-cubic unit-cell volume and occur close to compositions ([K.sub.0.37]N[a.sub.0.63])Mg[F.sub.3] and ([K.sub.0.47]N[a.sub.0.53])Mg[F.sub.3], respectively. [sup.19F] NMR spectra indicate that the N[a.sup.+] and [K.sup.+] cations do not occupy the A cation site at random and end-member local environments are favored for all compositions. Based on results from both X-ray diffraction and NMR, we propose that diffuse diffraction is the result of strain between coexisting regions of different octahedra (Mg[F.sub.6]) tilts brought about by the ionic radius mismatch of N[a.sup.+] and [K.sup.+] cations. We suggest A-site cations group with like cations as neighbors to reduce excess volume and total strain.

The sodium pump, or Na,K-ATPase, exports three intracellular sodium ions in exchange for two extracellular potassium ions. In the high resolution structure of the related calcium pump, two cation-binding sites have been identified. The two corresponding sites in the sodium pump are expected to be alternatively occupied by sodium and potassium. The position of a third sodium-specific site is still hypothetical. Here, we report the large effects of single residue substitutions on the voltage-dependent kinetics of the release of sodium to the extracellular side of the membrane. These mutations also alter the apparent affinity for intracellular sodium while one of them does not affect the intrinsic affinity for potassium. These results enable us to locate the third sodium-specific site of the sodium pump in a space between the fifth, sixth, and ninth transmembrane helices of the [alpha]-subunit and provide an experimental validation of the model proposed by Ogawa and Toyoshima [Ogawa, H. & Toyoshima, C. (2002) Proc. Natl. Acad. Sci. USA 99, 15977-15982]. cation-binding site | Na, K-ATPase | sodium affinity

Mono-, di-, and trinuclear copper-azido moieties are synthesized by varying the size of the countercations and all the complexes are structurally characterized by single-crystal X-ray analysis. The results not only confirm the prevailing role of the Cu(super II)-mu(sub 1,1)-N(sub azido)-Cu(super II) systems but also validates the lower value predicted for the critical angle.

The classic type of transient receptor potential channel (TRPC) is a molecular candidate for [Ca.sup.2+]-permeable cation channel in mammalian cells. TRPC5 is desensitized rapidly after activation by G protein-coupled receptor. Herein we report our investigation into the desensitization of mTRPC5 and localization of the molecular determinants of this desensitization using mutagenesis. TRPC5 was initially activated by muscarinic stimulation using 100 [micro]M carbachol (CCh) and then decayed rapidly even in the presence of CCh (desensitization). Increased EGTA or omission of MgATP in the pipette solution slowed the rate of this desensitization. The protein kinase C (PKC) inhibitors, 1 [micro]M chelerythrine, 100 nM GF109203X, or PKC peptide inhibitor (19-36), inhibited this desensitization of TRPC5 activated by 100 [micro]M CCh. When TRPC5 current was activated by intracellular GTP[gamma]S, PKC inhibitors prevented TRPC5 desensitization and the mutation of TRPC5 T972 to alanine slowed the desensitization process dramatically. We conclude that the desensitization of TRPC5 occurs via PKC phosphorylation and suggest that threonine at residue 972 of mouse TRPC5 might be required for its phosphorylation by PKC. nonselective cation channels; [Ca.sup.2+]-permeable cation channels

In this study, the electron-transfer dissociation (ETD) behavior of cations derived from 27 different peptides (22 of which are tryptic peptides) has been studied in a 3D quadrupole ion trap mass spectrometer. Ion/ion reactions between peptide cations and nitrobenzene anions have been examined at both room temperature and in an elevated temperature bath gas environment to form ETD product ions. From the peptides studied, the ETD sequence coverage tends to be inversely related to peptide size. At room temperature, very high sequence coverage (~100%) was observed for small peptides ([greater than or equal to] 7 amino acids). For medium-sized peptides composed of 8-11 amino acids, the average sequence coverage was 46%. Larger peptides with 14 or more amino acids yielded an average sequence coverage of 23%. Elevated-temperature ETD provided increased sequence coverage over room-temperature experiments for the peptides of greater than 7 residues, giving an average of 67% for medium-sized peptides and 63% for larger peptides. Percent ETD, a measure of the extent of electron transfer, has also been calculated for the peptides and also shows an inverse relation with peptide size. Bath gas temperature does not have a consistent effect on percent ETD, however. For the tryptic peptides, fragmentation is localized at the ends of the peptides suggesting that the distribution of charge within the peptide may play an important role in determining fragmentation sites. A triply protonated peptide has also been studied and shows behavior similar to the doubly charged peptides. These preliminary results suggest that for a given charge state there is a maximum size for which high sequence coverage is obtained and that increasing the bath gas temperature can increase this maximum.

The [sup.226][Ra.sup.2+] selectivity of the ionizable (thia)calix[4]-crowns 1-4 was determined in the presence of a large excess of the most common alkali and alkaline earth cations. Selective [sup.226][Ra.sup.2+] (2.9 x [10.sup.-8] M) extraction occurs even at extremely high [M.sup.n+]/[sup.226][Ra.sup.2+] ratios of 3.5 x [10.sup.7] [[M.sup.n+] = [Na.sup.+], [K.sup.+], [Rb.sup.+], [Cs.sup.+], [Mg.sup.2+], [Ca.sup.2+], and [Sr.sup.2+] (1 M)] and an ionophore concentration of [10.sup.-4] M. The selectivity coefficients log([K.sup.Ra.sub.ex]/[K.sup.M.sub.ex]) are ~3.5 for [Mg.sup.2+], [Ca.sup.2+], and [Sr.sup.2+]. In the presence of [Ba.sup.2+], which has very similar chemical properties, only the thiacalix[4]crown-6 derivative 4 showed a selectivity for [sup.226][Ra.sup.2+]. In addition to the remarkable [sup.226][Ra.sup.2+] selectivities, the effective pH range (pH 8-13) of the thiacalix[4]crown dicarboxylic acids (3 and 4) allows for full regeneration of the ionophores at lower pH values (pH

This paper presents several new diagrams that document previously unappreciated patterns and predictability in systematic mineralogy. They illustrate, for example, that sulfide minerals of single cations contain only intermediate to soft cations (cations with at least some outer-shell electrons). On the other hand, hard cations (those with no outer-shell electrons) only enter into a few sulfide minerals, all of which also contain intermediate cations. Among the simple chloride, fluoride, oxide, and carbide minerals of hard cations, ionic potential (charge/radius) of cations is proportional to that of anions (e.g., from KCl to SiC). Among the simple nitrate, sulfate, carbonate, phosphate, and silicate minerals of hard cations, ionic potential of inter-radical cations is inversely proportional to the ionic potential of the cations in the oxysalt radical (e.g., from KN[O.sub.3] to ZrSi[O.sub.4]). Across both of these sets of minerals, non-simple minerals ([H.sub.2]O- and O[H.sup.-]-bearing minerals or minerals with extra [O.sup.2-]) in each group typically involve cations of higher ionic potential than those of the simple minerals. The result is predictability and pattern in the compositions of minerals.

Since the discovery a decade ago of rapid photoinduced electron transfer in DNA over a distance >4 nm, a large number of experiments and theories have been advanced in the attempt to characterize the transfer, mainly of a radical cation or hole. Particularly influential experiments were carried out by Giese [Giese, B. (2000) Acc. Chem. Res. 33, 631-636] on the sequence G(A)nGGG, where G is guanine and A is adenine. These experiments were interpreted as showing that for n > 3, after the holes tunnel through the first three As, they hop onto the bridge of As, where they are localized on a single A and travel further by hopping between neighboring As. Recent experiments of Barton and coworkers [Shao, F., O'Neill, M. A. & Barton, J. K. (2004) Proc. Natl. Acad. Sci. USA 101, 17914-17919] have, however, established that the hole wavefunctions are delocalized. One of the mechanisms based on delocalized hole wavefunctions that had been investigated, both experimentally and theoretically, is transport by polarons. For one type of polaron, the properties are determined by polarization of the surrounding medium (water and ions, in this case). Theory predicts that this type of polaron is delocalized over approximately four bases in DNA. Transport by these polarons could explain the results of Giese et al. [Giese, B., Amaudrut, J., Kohler, A.-K., Spormann, M. & Wessely, S. (2001) Nature 412, 318-320], recent experimental results of O'Neill and Barton [O'Neill, M. A. & Barton, J. K. (2004) J. Am. Chem. Soc. 126, 11471-11483] concerning the size of the region over which the hole is delocalized, and other experimental observations. delocalization | polarization | radical cation

The rearrangement of a series of housane-derived cation radicals is investigated. The results indicate that it is possible to influence the direction of migration in housane-derived cation radical rearrangements even when the regiochemical control unit is not directly appended to the migration terminus.

The excess proton in water, [H.sup.+](aq), plays a fundamental role in aqueous solution chemistry. Its solution thermodynamic properties are essential to molecular descriptions of that chemistry and for validation of dynamical calculations. Within the quasichemical theory of solutions those thermodynamic properties are conditional on recognizing underlying solution structures. The quasichemical treatment identifies [H.sub.3][O.sub.+] and [H.sub.2][O.sub.[5].sup.+] as natural inner-shell complexes, corresponding to the cases of n = 1, 2 water molecule ligands, respectively, of a distinguished [H.sup.+] ion. A quantum-mechanical treatment of the inner-shell complex with both a dielectric continuum and a classical molecular dynamics treatment of the outer-shell contribution identifies the latter case (the Zundel complex) as the more numerous species. Ab initio molecular dynamics simulations, with two different electron density functionals, suggest a preponderance of Zundel-like structures, but a symmetrical ideal Zundel cation is not observed. Eigen cation | Zundel cation

The guanosine hydrazide 1 yields a stable supramolecular hydrogel based on the formation of a guanine quartet (G-quartet) in presence of metal cations. The effect of various parameters (concentration, nature of metal ion, and temperature) on the properties of this gel has been studied. Proton NMR spectroscopy is shown to allow a molecular characterization of the gelation process. Hydrazide 1 and its assemblies can be reversibly decorated by acylhydrazone formation with various aldehydes, resulting in formation of highly viscous dynamic hydrogels. When a mixture of aldehydes is used, the dynamic system selects the aldehyde that leads to the most stable gel. Mixing hydrazides 1, 9 and aldehydes 6, 8 in 1:1:1:1 ratio generated a constitutional dynamic library containing the four acylhydrazone derivatives A, B, C, and D. The library constitution displayed preferential formation of the acylhydrazone B that yields the strongest gel. Thus, gelation redirects the acylhydrazone distribution in the dynamic library as guanosine hydrazide 1 scavenges preferentially aldehyde 8, under the pressure of gelation because of the collective interactions in the assemblies of G-quartets B, despite the strong preference of the competing hydrazide 9 for 8. Gel formation and component selection are thermoreversible. The process amounts to gelation-driven self-organization with component selection and amplification in constitutional dynamic hydrogels based on G-quartet formation and reversible covalent connections. The observed self-organization and component selection occur by means of a multilevel self-assembly involving three dynamic processes, two of supramolecular and one of reversible covalent nature. They extend constitutional dynamic chemistry to phase-organization and phase-transition events. dynamic combinatorial chemistry | component selection | supramolecular chemistry

IRK1 (Kir2.1) inward-rectifier K+ channels exhibit exceedingly steep rectification, which reflects strong voltage dependence of channel block by intracellular cations such as the polyamine spermine. On the basis of studies of IRK1 block by various amine blockers, it was proposed that the observed voltage dependence (valence ~5) of IRK1 block by spermine results primarily from K+ ions, not spermine itself, traversing the transmembrane electrical field that drops mostly across the narrow ion selectivity filter, as spermine and K+ ions displace one another during channel block and unblock. If indeed spermine itself only rarely penetrates deep into the ion selectivity filter, then a long blocker with head groups much wider than the selectivity filter should exhibit comparably strong voltage dependence. We confirm here that channel block by two molecules of comparable length, decane-bis-trimethylammonium (bis-[QA.sub.c10]) and spermine, exhibit practically identical overall voltage dependence even though the head groups of the former are much wider (~6 [Angstrom]) than the ion selectivity filter (~3[Angstrom]). For both blockers, the overall equilibrium dissociation constant differs from the ratio of apparent rate constants of channel unblock and block. Also, although steady-state IRK1 block by both cations is strongly voltage dependent, their apparent channel-blocking rate constant exhibits minimal voltage dependence, which suggests that the pore becomes blocked as soon as the blocker encounters the innermost K+ ion. These findings strongly suggest the existence of at least two (potentially identifiable) sequentially related blocked states with increasing numbers of K+ ions displaced. Consequently, the steady-state voltage dependence of IRK1 block by spermine or [bis-QA.sub.cl0] should increase with membrane depolarization, a prediction indeed observed. Further kinetic analysis identifies two blocked states, and shows that most of the observed steady-state voltage dependence is associated with the transition between blocked states, consistent with the view that the mutual displacement of blocker and K+ ions must occur mainly as the blocker travels along the long inner pore. KEY WORDS: Kir * energetics * kinetics * valence * quaternary ammonium

Tests were conducted in [Fe.sup.0]-packed columns to investigate the effects of adding selected cations on nitrate removal by [Fe.sup.0]. Due to a rapid passivation of [Fe.sup.0], only negligible nitrate was reduced in the columns without adding the selected cation. However, adding certain selected cations ([Fe.sup.2+], [Fe.sup.3+], or [Al.sup.3+]) in feed solution can significantly enhance nitrate reduction. Extending hydraulic retention time (HRT) increased nitrate removal by the columns, but the increase was not linearly proportional to HRT. Decreases in columns' hydraulic conductivity (K) were monitored in an 8 month operating period. A modest decrease in K was recorded in the upper and the middle section of the media bed, whereas a significant decrease in K occurred in the inlet section. X-ray diffraction analyses indicate that magnetite (Fe304) was the dominant species of the iron corrosion products in the entire height of the column media under anoxic and other test conditions. In the inlet section, however, lepidocrocite and goethite were also identified. Cementation was found to occur only in the inlet section, suggesting that lepidocrocite and goethite, rather than magnetite, might be responsible for the cementation and thereby cause the hydraulic clogging. The magnetite coating would not necessarily cause clogging of the media. CE Database subject headings: Nitrates; Abatement and removal; Cations; Clogging.

Ion-ion reactions between a variety of peptide cations (doubly and triply charged) and S[O.sub.2] anions have been studied in a 3-D quadrupole ion trap, resulting in proton and electron transfer. Electron transfer dissociation (ETD) gives many c- and z-type fragments, resulting in extensive sequence coverage in the case of triply protonated peptides with S[O.sup.-.sub.2]. For triply charged neurotensin, in which a direct comparison can be made between 3-D and linear ion trap results, abundances of ETD fragments relative to one another appear to be similar. Reactions of doubly protonated peptides with S[O.sup.-.sub.2] give much less structural information from ETD than triply protonated peptides. Collision-induced dissociation (CID) of singly charged ions formed in reactions with S[O.sup.-.sub.2] shows a combination of proton and electron transfer products. CID of the singly charged species gives more structural information than ETD of the doubly protonated peptide, but not as much information as ETD of the triply protonated peptide.

Mass transfer of an alkyl sulfate anion with a (ferrocenylmethyl)trimethylammonium cation from water into single oil microdroplets was kinetically studied by microcapillary injection, fluorescence microspectroscopy, and microelectrochemistry. The partitioning ratio and the extraction rate significantly depended on the alkyl chain length of the alkyl sulfate anion. The extraction rate for the n-dodecyl sulfate or n-tridecyl sulfate ion was proportional to both the alkyl sulfate ion and ferrocene derivative concentrations while that for the n-undecyl sulfate ion was proportional to the anion concentration alone. The results are discussed in terms of transfer of the individual ions across the microdroplet/water interface and adsorption/ ion pair formation of the alkyl sulfate ion at the microdroplet/water interface.

Mutational analyses have suggested that BK channels are regulated by three distinct divalent cation-dependent regulatory mechanisms arising from the cytosolic COOH terminus of the pore-forming [alpha] subunit. Two mechanisms account for physiological regulation of BK channels by [micro]M [Ca.sup.2+]. The third may mediate physiological regulation by mM [Mg.sup.2+]. Mutation of five aspartate residues (5D5N) within the so-called [Ca.sup.2+] bowl removes a portion of a higher affinity [Ca.sup.2+] dependence, while mutation of D362A/D367A in the first RCK domain also removes some higher affinity [Ca.sup.2+] dependence. Together, 5D5N and D362A/D367A remove all effects of [Ca.sup.2+] up through 1 mM while E399A removes a portion of low affinity regulation by [Ca.sup.2+]/[Mg.sup.2+]. If each proposed regulatory effect involves a distinct divalent cation binding site, the divalent cation selectivity of the actual site that defines each mechanism might differ. By examination of the ability of various divalent cations to activate currents in constructs with mutationally altered regulatory mechanisms, here we show that each putative regulatory mechanism exhibits a unique sensitivity to divalent cations. Regulation mediated by the [Ca.sup.2+] bowl can be activated by [Ca.sup.2+] and [Sr.sup.2+], while regulation defined by D362/D367 can be activated by [Ca.sup.2+], [Sr.sup.2+], and [Cd.sup.2+] . [Mn.sup.2+], [Co.sup.2+], and [Ni.sup.2+] produce little observable effect through the high affinity regulatory mechanisms, while all six divalent cations enhance activation through the low affinity mechanism defined by residue E399. Furthermore, each type of mutation affects kinetic properties of BK channels in distinct ways. The [Ca.sup.2+] bowl mainly accelerates activation of BK channels at low [Ca.sup.2+], while the D362/D367-related high affinity site influences both activation and deactivation over the range of 10-300 [micro]M [Ca.sup.2+]. The major kinetic effect of the E399-related low affinity mechanism is to slow deactivation at mM [Mg.sup.2+] or [Ca.sup.2+]. The results support the view that three distinct divalent-cation binding sites mediate regulation of BK channels. KEY WORDS: BK channels * [Ca.sup.2+] regulatory sites * divalent cations * Slo * activation

Abstract -- It was demonstrated that the reduction potentials, dimerization potentials, and half-equivalence point potentials in the titration of aryldiazonium cations X[C.sub.6][H.sub.4][N.sup.+][equivalent to]N are linearly related to the quantum-chemically calculated [...]