Ion In Question Research Articles

Machine Learning Models to Predict Cognitive Impairment of Rodents Subjected to Space Radiation.

This research uses machine-learned computational analyses to predict the cognitive performance impairment of rats induced by irradiation. The experimental data in the analyses is from a rodent model exposed to ≤15 cGy of individual galactic cosmic radiation (GCR) ions: 4He, 16O, 28Si, 48Ti, or 56Fe, expected for a Lunar or Mars mission. This work investigates rats at a subject-based level and uses performance scores taken before irradiation to predict impairment in attentional set-shifting (ATSET) data post-irradiation. Here, the worst performing rats of the control group define the impairment thresholds based on population analyses via cumulative distribution functions, leading to the labeling of impairment for each subject. A significant finding is the exhibition of a dose-dependent increasing probability of impairment for 1 to 10 cGy of 28Si or 56Fe in the simple discrimination (SD) stage of the ATSET, and for 1 to 10 cGy of 56Fe in the compound discrimination (CD) stage. On a subject-based level, implementing machine learning (ML) classifiers such as the Gaussian naïve Bayes, support vector machine, and artificial neural networks identifies rats that have a higher tendency for impairment after GCR exposure. The algorithms employ the experimental prescreen performance scores as multidimensional input features to predict each rodent’s susceptibility to cognitive impairment due to space radiation exposure. The receiver operating characteristic and the precision-recall curves of the ML models show a better prediction of impairment when 56Fe is the ion in question in both SD and CD stages. They, however, do not depict impairment due to 4He in SD and 28Si in CD, suggesting no dose-dependent impairment response in these cases. One key finding of our study is that prescreen performance scores can be used to predict the ATSET performance impairments. This result is significant to crewed space missions as it supports the potential of predicting an astronaut’s impairment in a specific task before spaceflight through the implementation of appropriately trained ML tools. Future research can focus on constructing ML ensemble methods to integrate the findings from the methodologies implemented in this study for more robust predictions of cognitive decrements due to space radiation exposure.

Estimating the Wavenumber of Terminal Metal-Hydride Stretching Vibrations of Octahedral d6 Transition Metal Complexes.

The wavenumbers of 774 terminal hydride infrared active stretching modes of 478 distinct classes of structures of d6 octahedral complexes of Mn(I), Re(I), Fe(II), Ru(II), Os(II), Co(III), Rh(III), Ir(III), and Pt(IV) were collected from the literature. A fair correlation ( R2 0.95 with standard deviation 31 cm-1) is found for the data with the equation νMHcalc = ν0 + Δν t + Δν n, where ν0 is the base wavenumber for the metal ion in question, Δν t is the parameter of influence of the ligand trans to the hydride, and Δν n is a correction for the charge of the complex [MHL5] n+. The introduction of a cis influence parameter has little effect on the correlation, showing that the trans influence dominates in this case. The equation is useful in identifying anomalous data reported in the literature, validating future assignments of νMH, understanding better metal-hydride bonding, and possibly assisting in identifying superior hydride-based catalysts.

The permselectivity and water transference number of ion exchange membranes in reverse electrodialysis

Reverse electrodialysis of saline solutions (RED) is a renewable energy technology with large potential. Key components in the system are the ion exchange membranes. This work evaluates the efficiency of commercially available anion and cation selective membranes for RED. Their efficiency is often described with the apparent transport number for the ion in question, and this number depends on the salt concentration. It is known since long that the water transference coefficient contributes to the apparent transport number, but much of the recent literature on RED takes the permselectivity as defined by the apparent transport number as a direct measure of the membrane selectivity. The purpose of this paper is to clarify that situation with new data on Fumasep membranes. Concentration cell potentials were measured for anion- and cation exchange membranes from Fumasep (FAD and FKS, respectively, Fumatech, Germany) in the temperature range 12−45°C in salt solutions relevant for reverse electrodialysis. The results show that the anion exchange membrane is a perfectly selective ion exchange membrane, and has a water transference coefficient of −6±1. The cation selective membrane has a cation transport number of 0.93 and a water transference coefficient of 8± 7. We suggest that the developers of membranes should pay more attention to the water transference coefficient. To enhance the performance of ion selective membranes and RED, it is beneficial to have water transference coefficients as close to zero as possible.

Limitation of energetic ring current ion spectra

AbstractWe address the problem of determining the limiting energetic ring current ion spectrum resulting from electromagnetic ion cyclotron (EMIC)‐wave‐ion interactions. We solve the problem in a relativistic regime, incorporating a cold background multi‐ion plasma component and without assuming a predetermined form for the ion energy distribution. The limiting (Kennel‐Petschek) spectrum is determined by the condition that the EMIC waves acquire a specified gain over a given convective length scale for all frequencies over which wave growth occurs. We find that the limiting ion spectrum satisfies an integral equation that must be solved numerically. However, at large particle energy E, the limiting spectrum takes the simple form J ∝ 1/E, E → ∞. Moreover, this 1/E spectral shape does not depend on the energetic ion in question nor on the background multi‐ion plasma composition. We provide numerical solutions for the limiting spectra for Earth‐like parameters. In addition, at four planets, Jupiter, Saturn, Uranus, and Neptune, we compare measured ion spectra with corresponding numerical limiting spectra. This paper parallels an earlier analogous study on the limitation of radiation belt electron spectra by whistler mode wave‐electron interactions.

Survival probability of slow ions colliding with room-temperature and heated surfaces of beryllium

Survival probabilities of slow ions colliding with room-temperature and heated (600°C) surfaces of beryllium have been determined. Earlier data on the survival probabilities of ions interacting with surfaces of carbon and tungsten are complemented by measurements of the survival probability of selected C1, C2, and C3 hydrocarbon ions and some non-hydrocarbon ions (, ) on the surfaces of beryllium. For the incident angle of 30° (with respect to the surface) and incident energy of 31 eV, the absolute survival probability (S a) and the ionization energy of the ion in question (IE) can be correlated with the use of the emprirical relation log S a = (2.9 ± 0.6)–(0.31 ± 0.06)IE for both room-temperature (hydrocarbon-covered) and heated (600°C) surfaces. The similar dependence for both non-heated and heated surfaces may presumably be due to a similar work function of the heated samples, containing substantial amounts of beryllium oxide and carbides on the surface, and of hydrocarbon-covered non-heated beryllium surfaces.

Interaction of Ionic Liquids Ions with Natural Cyclodextrins

The interaction of natural α-, β-, and γ-cyclodextrins (CDs) with 14 hydrophobic ionic moieties of ionic liquids (ILs) was systematically examined in dilute aqueous solutions using isothermal titration microcalorimetry (ITC) and NMR spectroscopy. The studied cationic and anionic moieties involved some recently developed heavily fluorinated structures, as well as some others of common use. To isolate the effect of a given ion, the measurements were performed on salts containing the hydrophobic IL ion in question and a complexation-inactive counterion. Additional ITC experiments on ILs whose both cation and anion can interact appreciably with the CD cavity demonstrated that to resolve the effect of individual ions from such data is generally a tricky task and confirmed the superiority of the isolation strategy adopted for the purpose throughout this work. The binding constant, enthalpy and entropy determined at 298.15 K for the 1:1 (ion:CD) inclusion complex formation range in broad limits, being 0 < K < 2 × 10(5), 0 < -Δ(r)H°/(kJ·mol(-1)) < 44, and -28 < TΔ(r)S°/(kJ·mol(-1)) < 14, respectively. The stabilities of complexes of perfluorohexyl bearing ions with β-CD belong to the highest ever observed with natural CDs in water. The established binding affinity scales were discussed in both thermodynamic and molecular terms. The concepts of hydrophobic interaction and guest-host size matching supported by simple molecular modeling proved useful to rationalize the observed widely different binding affinities and suggest possible binding modes. Enthalpy and entropy contributions to the stability of the ion-CD complexes were found to compensate each other considerably obeying more or less the linear compensation relationship marked by existing literature data on binding other guests to natural CDs. As outliers to this pattern, the most stable complexes of -C(6)F(13) bearing ions with β-CD were found to receive an enhanced inherent entropy stabilization due to extraordinarily high extent of desolvation occurring in the course of binding.

Force fields including charge transfer and local polarization effects: Application to proteins containing multi/heavy metal ions

The question whether molecular dynamics (MD) simulations can yield reliable structural and dynamical properties of metalloproteins depend on the accuracy of the force field, i.e., the potential energy function (PEF) and associated parameters modeling the interactions of the metal ion of interest with water and protein ligands. Previously, we had developed a CTPOL PEF for protein simulations of Zn(2+) bound to Cys(-) and/or His(0) that includes charge transfer and local polarization effects as well as metal van der Waals parameters that reproduce the structural and thermodynamical properties of 22 dications. Here, we evaluate if the CTPOL PEF and the new metal parameters (referred to as the CTPOLa force field) can be applied to proteins containing polynuclear metal-binding sites and heavy toxic metal ions, using the CdZn(2)-Cys(9) beta-domain of rat liver metallothionein-2 and the Hg(2+)-bound 18-residue peptide from MerP as test systems. Using the CTPOLa force field, simulations of the beta-domain of rat liver metallothionein-2 totaling 19 ns could preserve the experimentally observed CdZn(2)-Cys(9) complex geometry and overall protein structure, whereas simulations neglecting charge transfer and local polarization effects could not. However, the CTPOLa force field cannot reproduce the experimentally observed linear bicoordination of Hg(2+) in the MerP peptide without adding an angular restraint to the CTPOL PEF to correct the angle distribution about Hg(2+). Thus, the force fields presented herein for the group IIB metal ions can be applied to simulation studies of proteins containing polynuclear metal-binding sites and heavy metal ions in aqueous solution. PEF neglecting charge transfer and local polarization effects in conjunction with vdW parameters adjusted to reproduce the structural and thermodynamical properties of only the metal ion in question could not yield an accurate representation of the metal-binding site and overall protein structure.

Interbasin groundwater flow and groundwater interaction with surface water in a lowland rainforest, Costa Rica: A review

This paper reviews work related to interbasin groundwater flow (naturally occurring groundwater flow beneath watershed topographic divides) into lowland rainforest watersheds at La Selva Biological Station in Costa Rica. Chemical mixing calculations (based on dissolved chloride) have shown that up to half the water in some streams and up to 84% of the water in some riparian seeps and wells is due to high-solute interbasin groundwater flow (IGF). The contribution is even greater for major ions; IGF accounts for well over 90% of the major ions at these sites. Proportions are highly variable both among watersheds and with elevation within the same watershed (there is greater influence of IGF at lower elevations). The large proportion of IGF found in water in some riparian wetlands suggests that IGF is largely responsible for maintaining these wetlands. δ 18O data support the conclusions from the major ion data. Annual water and major ion budgets for two adjacent watersheds, one affected by IGF and the other not, showed that IGF accounted for two-thirds of the water input and 92–99% of the major ion input (depending on the major ion in question) to the former watershed. The large (in some cases, dominating) influence of IGF on watershed surface water quantity and quality has important implications for stream ecology and watershed management in this lowland rainforest. Because of its high phosphorus content, IGF increases a variety of ecological variables (algal growth rates, leaf decay rate, fungal biomass, invertebrate biomass, microbial respiration rates on leaves) in streams at La Selva. The significant rates of IGF at La Selva also suggest the importance of regional (as opposed to small-scale local) water resource planning that links lowland watersheds with regional groundwater. IGF is a relatively unexplored and potentially critical factor in the conservation of lowland rainforest.

Mechanistic aspects of iontophoresis in human epidermal membrane

A large number of factors are involved in the movement of ions and molecules across human epidermal membrane (HEM) under the influence of an electric field. These factors and their interplay need to be understood if our knowledge of iontophoretic transport of drugs across HEM is to reach a point where physical models and strategies may be employed for useful quantitative predictions. In a typical in vitro experiment, the fully hydrated HEM is positioned between aqueous compartments of a two-chamber diffusion cell. When a low electric field is applied across the HEM under these conditions, the transport enhancement of ions in the pre-existing pores of the stratum corneum is the result of, (a) the direct interaction of the electric field with the charge of the ion in question, and (b) convective solvent flow (electroosmosis); in the case where the permeant is non-ionic under these circumstances, transport enhancement is by convective solvent flow only. At moderate-to-high voltage iontophoresis (⩾around 1.0 V applied across a single HEM), in addition to the direct field effect and convective solvent flow in the pre-existing pores, there can generally be a significant (e.g. 10- to 100-fold enhancement) contribution to transport enhancement arising from new pore induction (electroporation). Much of the recent work in our laboratory has been devoted to defining and quantifying HEM electroporation, and an especially difficult aspect has been that of dealing with the large HEM membrane-to-membrane variabilities with regard to, (a) the extent of new pore induction, and (b) the characteristics of the newly induced pores. Recently we discovered that the extent of relevant (i.e. permeant accessible) pore induction may be correlated to the change in HEM electrical conductance (and quantifiable) if an appropriate matching background electrolyte can be selected having ion sizes comparable to that of the permeant. For example, employing tetraethylammonium (TEA) pivalate (PIV) for which the ion sizes are ≈3.5 Å, but not KCl (ion sizes ≈1.9 Å), as the background electrolyte for TEA (as the permeant) gave very good results; in this example, the sizable contribution of pore induction to iontophoresis was quantitatively factored out from the total iontophoretic enhancement. Experiments with a large number of HEM samples gave good agreement with the Nernst–Planck (N–P) predictions of the direct field effect when TEA-PIV was used as the background electrolyte for TEA transport, but large variations (up to 300%) between N–P predictions and experimental results were observed with KCl as the background electrolyte. Another area of recent effort has been HEM pore size determinations, both at low voltages (i.e. for pre-existing pores) and at voltages where the newly induced pores dominate HEM permeability. The sizes of pre-existing pores of HEM have been determined with the hindered diffusion theory (using experimental fluxes of several probe permeants of different known molecular sizes) to be generally in the range, 10–20 Å, by a number of investigators in our laboratory for a large number HEM samples. Deducing pore sizes of electric field induced pores under steady electroporation conditions has been a more challenging task. We succeeded recently in developing a novel method for ‘passively’ determining pore sizes (i.e. by passive diffusion with hindered diffusion theory) under steady electroporation conditions: by using low frequency (12.5 Hz) a.c. at 2–5 V. We have been able to sustain electroporation at a nearly constant state of electroporation long enough to carry out a set of ‘passive’ diffusion experiments with relatively good precision to obtain the sizes of the newly induced pores. Studies to date have revealed that the sizes of pores induced with 2–5 V are of the same order of magnitude as those of the pre-existing pores (i.e. 10–20 Å). Finally, another research question of interest has been that of pore charge (both the sign of the charge and the charge density) distribution of HEM. By conducting both anodal and cathodal electroosmosis experiments with a nonionic permeant, one can evaluate the predictivity of a model based on pores of a single size and single charge. Studies were conducted with HEM at low voltage (little or no electroporation) and at higher voltages (2–4 V). The results to date at neutral pH have shown that, at low voltage, while negative pore charges dominate, there are effectively some positive or positive and neutral pores. At high voltage where new pores dominate, there seem to be only negatively charged pores.

A selected-ion-flow-drift-tube study of charge transfer processes between atomic, molecular, and dimer ion projectiles and polyatomic molecules ethane, propane, and n-butane

Charge transfer processes of Ar+, Kr+, Xe+, N2+, CO+, Ar2+, Kr2+, and N4+ with the alkanes ethane, propane, and n-butane were investigated using the selected-ion-flow-drift-tube (SIFDT) technique. The relative abundances of molecular and fragment hydrocarbon product ions can be explained using the breakdown pattern of the hydrocarbon molecular ion in question and assuming that the recombination energy of the projectile ions is deposited in the quasi continuum of the energy levels of the polyatomic molecular ions in a resonant way. The observed increase of the fragment ion yields with increasing collision energy is due to collision induced excitation up to the dissociation limit of the hydrocarbon ions in collisions with the helium buffer gas atoms rather than to inelastic charge transfer from hyperthermal projectile ions.

Role of calcium and other ions in directing root hair tip growth in Limnobium stoloniferum

The magnitude and spatial localization of Ca2+, K+ and H+ fluxes in growing and non-growing Limnobium stoloniferum root hairs was determined using non-invasive, ion-selective vibrating microelectrodes. Both the spatial pattern and magnitude of the ionic flux was dependent on the particular ion in question. Both H+ and Ca2+ influx was localized almost exclusively to the tips of growing root hairs, suggesting that these fluxes may be involved in directing growth. Influx of K+ showed no distinct localization and uptake appeared uniform along the length of the root hair. Competitive inhibition of Ca2+ influx using a range of Mg+ concentrations indicated that the magnitude of the Ca2+ flux entering the root hair tip did not determine growth rate; however, the presence of Ca2+ on the external face of the membrane was implicit for root hair integrity. Aluminum proved to be a potent inhibitor of root hair growth. At an exogenous Al concentration of 20 μM a complete blockage of Ca2+ influx into root hair tips was observed, suggesting that Al blockage of Ca2+ influx could be involved in Al toxicity. However, at a lower Al concentration (2 μM), Ca2+ fluxes were unaffected while inhibition of growth was still observed along with a distinct swelling of the root hair tip. The swelling at the root hair tips was identical in appearance to that seen in the presence of microtubule inhibitors, suggesting that Al could influence a number of different sites at the plasma-membrane surface and within the cell. The possible role(s) of Ca2+ and H+ fluxes in directing tip growth are discussed.

An examination of a density functional/molecular mechanical coupled potential

AbstractIn this article we describe the coupling of a density functional (DF) Hamiltonian with the molecular mechanics (MM) potential function AMBER. We examine a series of test cases in which we compare the binding energies and geometries of the complexes predicted by this coupled potential with those predicted by other theoretical methods and experiment to establish the relative accuracy of the DF/MM coupled potential. We find that the DF/MM coupled potential performs well in most cases studied and, in general, outperforms the semiempirical/MM approach. The interaction energies and structures obtained using this method appear to be insensitive to the use of nonlocal (NL) corrections to the DF method. The is fortuitous because the NL treatment is significantly more computationally expensive than the local treatment. However, NL corrections may be required to predict accurately the shape of potential energy surfaces that involve bond breaking and formation. The DF/MM method has also been applied to the determination of the solvation free energy for a series of ions using free‐energy perturbation methods. The results obtained are good and can be improved by a simple scaling of the Lennard‐Jones parameters for the ion in question. © 1995 by John Wiley &amp; Sons, Inc.

Estimation of the Ratio of Hidden Multivalent Ions in Nematic Lyomesophases by Using Heteronuclear NMR

Abstract An estimation of the peak areas of the 59Co NMR spectra for cobalt(III) complex ions and of the 25Mg spectra for magnesium aqua ions gave population ratios of their hidden ions, which are defined as too strongly interacting with nematic lyomesophases (composed of cationic or anionic surfactants) to contribute to the NMR spectra. The cobalt(III) complex ions used were [Co(NH3)6]3+, [Co(en)3]3+ (en = ethylenediamine), [Co(phen)3]3+ (phen = 1,10-phenanthroline), and [Co(CN)6]3−. It was revealed that appreciable amounts of multivalent ions are present as hidden ions on the lyomesophase, whose sign of charge is opposite to that of the ion in question. For such hydrophilic ions as [Co(NH3)6]3+, [Co(en)3]3+, [Co(CN)6]3−, and magnesium ions, the ions binding to the mesophases are classified into two states based on the NMR spectra: One is an outer-sphere complex (ion pair); the other is a hidden ion. In these systems the hidden ion/total ion population ratios depending on the composition of the surfactant are roughly proportional to the ion pair/total ion population ratios, which are monitored by the magnitude of the quadrupole splitting. For the phen complex, the presence of a hidden ion was observed in the range where the fraction of the anionic surfactant is high; the quadrupole splittings were also observed only in limited composition ranges.

Transport pathways for Na+ and Br‐ (CI‐) in noradrenaline‐stimulated frog skin (Rana temporaria)

(1) Transport pathways for Na+ and Br- across noradrenaline-stimulated frog skin, in which the sodium channels in the apical membrane had been blocked with amiloride, were examined by pre-steady-state flux ratio experiments. (2) To analyse the experiments, equations are derived from which the fluxes through two parallel pathways can be determined if these differ with respect to the flux ratio as well as the mean passage time for the ion in question. (3) The fluxes of Na+ and Cl- were followed over a period of 3 h and it was found that about 1 h after addition of noradrenaline time-invariant fluxes could be achieved. In that period inward and outward tracer fluxes of Na+ and Br- (used as a substitute for Cl-) were followed during the build-up of isotope in the tissue until steady-state fluxes were attained. (4) The experiments showed that when the Na channels of the capital cells are blocked the glands provide the major pathway for sodium transport across the skin. The efflux of Br- can be separated into two components. A fast one through the mitochondria-rich cells, which is the pathway for passive anion fluxes, and a slower one through the glands. No influx through the slow transport pathway could be detected. In some skins exchange of Br- through the mitochondria-rich cells is revealed. An anion exchange mechanism also appears to be present in the basolateral membrane of the gland cells.

Spectroscopy of diazines soluted in aqueous and protic solvents

The electronic and vibrational spectra of some diazines were investigated in a wide acidity region from strong alkaline solution to strong acidic one. Electronic spectra were applied to the determination of the acidic ionization constants. Besides, ionization constants were calculated quantumchemically, too. Measured and calculated ones are correlated. A theory was developed for the application of ionization constants to multicomponent analysis of ampholytes. Vibrational spectra were measured at pH (Ho) values where the ion in question is the bulk. A special IR cell was elaborated for these measurements. Force constants and fundamental frequencies were calculated at CNDO level by the extension of the force method to soluted molecules (FORSOL programme). Geometric parameters of some ions were optimized byab initio calculations.

Calcium and Potassium Cyclotron Resonance Curves and Harmonics in Diatoms (A.Coeffeaformis)

Our previous findings provide strong evidence that transport of a given ionic species through a cell membrane can be precisely controlled by tuning externally applied magnetic fields to the ion cyclotron resonance (CR) gyrofrequency for the ion in question. Experiment and theory have shown that certain odd harmonics of the fundamental resonance frequency are also effective. In the present experiment we again used the model of Ca-dependent motility of benthic diatoms, extending our harmonic studies through N = 17, for both Ca2+ and K+ fundamentals. Eight separate Ca2+ fundamental frequencies: 8, 12, 16, 23, 31, 32, 46, 64 Hz were attempted and each was found to obey the CR condition. We also report two observations: (1) tuning to K+ results in inhibition of motility, directly opposite to the enhancement that occurs when tuning for Ca2+; (2) both the K+ inhibition and Ca2+ enhancement are independently observed at exactly the same harmonics: N = 1, 3, 5, 15. This strongly suggests that despite differences in ionic selectivity, K+ and Ca2+ channels may share fundamentally similar protein configurations.

ESR Spectra of Benzene Anion

Abstract Based on the spin density calculated in our previous paper, the ESR spectra of the benzene anion (exactly the dihydrophenylide ion) are analyzed by the Bloch equation. A hyperfine spectrum broader than those of usual aromatic radicals attributes to the chemical exchange process that the ion in question surrounded by solvent molecules undergoes a rotational motion characterized by the time τ which is the life time of chemical exchange. The line shape for each hyperfine spectrum is given in terms of 1⁄T2 and τ under the condition of τ⁄T2&amp;lt;&amp;lt;1.

Precipitation, chelation, and the availability of metals as nutrients in anaerobic digestion. II. Applications

The relative importance of the individual effects of precipitation and chelation of metal ions in anaerobic digestion is assessed. Experimentally determined soluble metal ion levels are compared with predicted levels obtained by using a previously described methodology.(1) It is found that soluble metal complexes may increase the level of soluble metals in the presence of CO(3) (2-) and S(2-) by a factor of up to 10(4). The formation of a soluble complex may increase or decrease the availability of the metal ion in question for microbial uptake. Two case studies are presented, one using a defined medium and one a complex medium. It is possible, in the case of the defined medium, to accurately predict the free metal ion concentration using the methodology previously developed.(1) While the identification of the presence of natural chelating compounds in a complex medium is not routinely possible, the significant discrepancy between the measured level of the soluble metal ion Fe(2+) and the calculated level in the case studies presented indicates that natural chelating compounds may play a vital role in providing available metal ions to the microorganisms of an anaerobic digester.

Ionic requirements for H+ secretion and membrane elaboration in frog oxyntic cells

We have tested whether the ions K+, Na+, or Cl- are required for either initiation or maintenance of secretory parameters of amphibian oxyntic cells. In vitro mucosal preparations were washed repeatedly in Ringer solution lacking the ion in question either before (i.e., resting tissues) or after addition of stimulants. Electrophysiology, H+ secretion, and morphology (morphometric analysis of oxyntic cells) were monitored. Na+ or K+. Stimulation of resting tissues in Na+ or K+-free solutions elicited no H+ secretion; there was only a small increase (approximately twofold) in secretory surface density (Sv) (during control Sv increased sixfold). The Na+-free effects were partially reversed by high [K+]. In secreting tissues, Na+ or K+-free solutions caused H+ secretion to decrease to zero. Gastric glands from these mucosae appeared "occluded": the gland lumen was filled with apposed apical projections of oxyntic cells. Cl-. Stimulation after Cl- removal initiated low levels of H+ secretion. Morphologically the cells either appeared normally stimulated (Sv increased eightfold) or, more rarely, took on the occluded appearance. Cl- removal from stimulated mucosae decreased H+ secretion approximately 50%, but the cells were normally elaborate. We conclude that K+ is required for the initiation of H+ secretion and the stimulated morphology change; the effects of Na+ removal are due to effects on internal [K+]; Cl- is not required. The occurrence of occluded morphology under conditions of inhibited H+ and H2O secretion indicates a role for water flow in the maintenance of stimulated morphology.

High-energy fragmentation of chlorophyll a and its fully deuterated analog by californium-252 plasma desorption mass spectrometry

Comparison of the /sup 252/Cf=plasma distortion mass spectrometry (/sup 252/Cf-POMS) spectra of chlorophyll of ordinary isotopic composition((/sup 1/H)Chl a) with those of essentially fully deuterated Chl a ((/sup 2/H)Chl a) led to the establishment of the elemental compositions in the fragmentation pattern and to deduction of plausible structures for the fragment ions produced. The difference in mass between corresponding ions in the spectra gives the number of hydrogens in the molecule. It is necessary to assure that all ions contain 4 nitrogens in order to determine the elemental composition of any ion in question. The /sup 252/Cf-POMS spectra showed an intense molecular ion at 893.6+0.1..mu.., which corresponds to the isotopically averaged molecular weight of (/sup 1/H)Chl a, and 963.3+0.1..mu.., which corresponds to that of (/sup 2/H)Chl a. The mass difference confirms the expected extent of deuteration, 70 of the 72 H atoms in the (/sup 2/H)Chl a molecular ion are D. An intense partially resolved fragmentation pattern was observed from 300 to 700 ..mu... The pattern is mass shifted in the deuterated analog. Some explanation is offered for the fragmentation pattern. (BLM)