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PubMed1951

On the effect of ammonium and lithium ions upon frog nerve deprived of sodium.

An analysis has been made of the effect of ammonium and of lithium ions upon frog nerve deprived of sodium. Ammonium ions cannot substitute for sodium ions and restore the excitability of the nerve fibers; nor can they increase the L fraction of the membrane potential and the efficiency of the nerve reaction. Certain observations, however, indicate that the presence of ammonium ions outside the nerve fibers may delay the development of inexcitability in a sodium-free medium of nerve fibers restored by a moderate amount of sodium ions. Lithium ions can substitute for sodium and restore to nerve fibers of the A and C groups the ability to conduct impulses; the effect upon B fibers has not been investigated. Lithium cannot substitute for sodium in the role that sodium plays in the creation of the L fraction and in the establishment of the nerve reaction. In this respect lithium and sodium have opposite effects. This fact establishes an important difference between the two physiological responses that the nerve fibers can produce, the nerve impulse and the nerve reaction. With untreated nerve the depolarization of nerve by lithium ions at high concentrations is preceded by a phase of hyperpolarization; with nerve deprived of sodium the depolarization begins without delay.

Action Potentials↗
PubMed2001

Mesityllithium as a reagent for chemoselective halogen-lithium exchange reaction.

[figure: see text] Mesityllithium was found to be an excellent selective lithiating agent to prepare aryllithium compounds having alkoxycarbonyl groups. To extend our studies on chemoselective lithiation, an important precursor for the synthesis of camptothecin was prepared using a halogen-lithium exchange reaction followed by an intramolecular 1,2-addition.

Camptothecin↗
PubMed2004

Influence of cyclic loading and luting agents on the fracture load of two all-ceramic crown systems.

STATEMENT OF PROBLEM: Inherent mechanical properties, fabrication techniques, luting agents, and intraoral conditions are primary factors attributing to longevity of all-ceramic crowns. Before doing time-consuming and costly clinical studies, preclinical in vitro studies should be conducted to evaluate the durability of these crowns. Purpose This study investigated the influence of different luting agents and cyclic loading under wet conditions on the fracture load of CAD-CAM and pressable all-ceramic crowns. MATERIAL AND METHODS: Ninety-six human premolars were prepared for all-ceramic crowns with the following preparation criteria: 6-degree axial taper, 1.5-mm shoulder finish line placed 0.5 mm occlusal to the CEJ, 2-mm occlusal reduction, and occluso-gingival height of 5 mm. Sixteen unprepared premolars served as controls. Forty-eight crowns were laboratory fabricated from a lithium disilicate glass-ceramic (IPS-Empress 2), while 48 CAD-CAM crowns were directly fabricated using a leucite-reinforced glass-ceramic (ProCAD) and the Cerec 3 CAD-CAM system. Three luting agents (Panavia F, Superbond C&B and ProTec CEM) were used for cementation (n = 16). After 1 week storage in water, half of the specimens of each subgroup (n = 8) were cyclically loaded and thermal cycled under wet conditions for 600,000 masticatory cycles and 3500 thermal cycles (58 degrees C/4 degrees C; dwell time 60 seconds) in a masticatory simulator. All specimens were loaded in a universal testing machine with the compressive load (N) applied along the long axis of the specimen at a crosshead speed of 1 mm/min until fracture. Fracture load was recorded for each specimen. The Kruskal-Wallis test was used first to detect overall significance, followed by Mann-Whitney U tests to identify which pairs of groups had significant differences (P =.05). RESULTS: Cyclic loading significantly decreased the median fracture load of ProCAD crowns luted using Superbond from 987.2 to 786.0 N (P =.014) and those luted using ProTec CEM from 914.4 to 630.7 N (P =.007). Also, the median fracture load of Empress 2 crowns luted using ProTec CEM decreased significantly from 977.3 to 622.9 N (P =.013). However, cyclic loading did not decrease the median fracture load of crowns luted using Panavia F, Empress 2 (P =.431) and ProCAD (P =.128). With the same loading conditions and luting agents, there were no significant differences in the fracture loads of ProCAD and Empress 2 crowns (P >.05). CONCLUSIONS: Cyclic loading reduced the fracture load of ProCAD crowns luted with Superbond C&B and ProTec CEM and of Empress 2 crowns luted with ProTec CEM.

Bicuspid↗
PubMed1970

Synaptic potentials recorded by the sucrose-gap method from the rabbit superior cervical ganglion.

1. Compound ganglionic potentials evoked by stimulation of the preganglionic nerves to the superior cervical ganglion of the rabbit were recorded by the sucrose-gap method.2. When the distal part of the ganglion was bathed in flowing isotonic sucrose solution or sodium-deficient solutions, ganglionic action potentials were no longer evoked, only large synaptic potentials.3. The compound synaptic potential, which remained unaltered for more than 1 h, originated in a population of cells at the interface between the Krebs and sucrose solutions. Hexamethonium reduced the size but did not alter the time course of the synaptic potential.4. It is suggested that a higher concentration of sodium ions is required for the generation of ganglionic action potentials than for either conduction in the postganglionic axons or production of synaptic potentials.5. When lithium replaced sodium in the solution bathing the distal part of the ganglion, the synaptic potential was greatly reduced in amplitude. Impulse propagation in the postganglionic axons was only slightly impaired when lithium replaced sodium in the solution bathing the axons.6. A quantitative assessment of the potency of the ganglion-blocking drugs nicotine, pentolinium, hexamethonium and pempidine was made by measuring the depression of the synaptic potentials produced by bathing the distal part of the ganglion in flowing isotonic sucrose solution. The concentrations which produced a 50% depression were 8.1 muM nicotine, 26.5 muM pentolinium, 111 muM hexamethonium and 22.2 muM pempidine.

Animals↗
PubMed2002

Aryl cyclopentadienyl tricarbonyl rhenium complexes: novel ligands for the estrogen receptor with potential use as estrogen radiopharmaceuticals.

The need for imaging agents for estrogen receptor positive (ER+) tumors that are both cost effective and widely available, as well as the need for novel radiotherapeutic agents for the treatment of breast cancer, has prompted us to investigate cyclopentadienyl tricarbonyl metal [CpMet(CO)(3), Met=Re, Tc-99m] complexes that bind well to the ER. Thus, we have prepared a series of p-hydroxyphenyl-substituted CpRe(CO)(3) complexes and evaluated them (and, in some cases, their cyclopentadiene precursors) for binding to ER. These compounds constitute a new class of structurally integrated organometallic ligands for ER in which the CpMet(CO)(3 )organometallic unit forms the very structural core of these molecules and thus is necessarily intimately involved in their interaction with the receptor. The CpRe(CO)(3) compounds were prepared by reaction of the lithium salt of the arene-substituted cyclopentadiene with a suitable Re(CO)(3)(+) precursor, followed by deprotection of the methyl ether. The X-ray crystal structure of one of these analogues shows that it has the classical 'piano stool'-like geometry, with the alkyl groups directed upward, away from the tripodyl metal carbonyl base. The aryl-substituted CpRe(CO)(3) complexes that we have prepared all bind to the ER, some with affinity as great as 20% that of the native ligand, estradiol. In general, at least two p-hydroxyphenyl substituents and one to two alkyl groups attached to the organometallic cyclopentadienyl core are needed for high ER affinity. Where we have been able to make comparisons, the metal complexes bind to ER with an affinity greater than their cyclopentadiene precursors. The high affinity of some of these complexes indicates that the bulky Re(CO)(3) unit is able to exploit the considerable volume in the center of the ER ligand binding pocket that is not occupied by most ligands, a consideration that is supported by molecular modeling. The preparation of the best of these agents in technetium-99m labeled form is currently being investigated.

Breast Neoplasms↗
PubMed1995

Sucrose analogues modified at position 3: chemoenzymatic synthesis and inhibition studies of dextransucrases.

Conditions for the large-scale (molar) oxidation of sucrose by Agrobacterium tumefaciens were improved, thus leading to homogeneous solutions of 3-ketosucrose in 40% yield. Treatment of this solution with hydroxylamine or methoxylamine afforded the corresponding oximes 3a and 3b (isolated as acetates) in excellent yield. Dissolving-metal reduction of these oximes gave mixtures of amino disaccharides in which the gluco epimer (3-amino-3-deoxysucrose) was predominant. A more efficient approach to this amino sucrose was provided by the highly stereoselective hydrogenation of 3-ketosucrose peracetate (7), which gave exclusively the allo isomer 8 (2,4,6-tri-O-acetyl-alpha-D-allopyranosyl 1,3,4,6-tetra-O-acetyl-beta-D-fructofuranoside). Upon reaction with lithium azide, the triflate derived from 8, compound 9, afforded 3-azido-3-deoxysucrose peracetate (10) which was converted into 3-amino-3-deoxysucrose (12). The reaction of triflate 9 with potassium ethylxanthate led to a mixture of products (the expected 3-S-ethoxythiocarbonyl-3-thiosucrose derivative and the peracetates of 3-thiosucrose and of 3-thiosucrose disulfide), which could be all converted into 3-thiosucrose (17). Sucrose analogues 12 and 17 were not substrates of dextransucrases from various strains of L. mesenteroides, nor did they participate in glycosyl transfer reactions to an acceptor (maltose). Compounds 3a and 12 were found to be strong competitive inhibitors of the dextran synthesis process (dextransucrase from strain B-1397). These results indicate that 3a and 12 compete effectively with sucrose for the sucrose binding site but are unable to participate as glycosyl donors in the polymerization or glycosyl-transfer processes.

Agrobacterium tumefaciens↗
PubMed1994

Inhibitors of sterol synthesis. Synthesis and spectral properties of 3 beta-hydroxy-5 alpha-cholestan-15-one and its 17 beta-epimer and their effects on 3-hydroxy-3-methylglutaryl coenzyme A reductase activity.

3 beta-Hydroxy-5 alpha-cholestan-15-one (2a) and its 14 beta-epimer 2b were prepared from 3 beta-acetoxy-5 alpha-cholest-8(14)-ene (3). Hydroboration of 3 at 45-50 degrees C gave a mixture of 5 alpha,14 alpha-cholestane-3 beta,15 alpha-diol and 5 alpha,14 beta-cholestane-3 beta,15 beta-diol, which were separated on silica gel as their 3 beta-tert-butyldimethylsilyl ethers 5a and 5b. Oxidation of 5a with pyridinium chlorochromate, followed by desilylation with tetrabutylammonium fluoride gave 2a. Analogous transformations of 5b gave 2b contaminated with 2a. Desilylation of 5b followed by oxidation with pyridinium chlorochromate resulted in a mixture composed mainly of 5 alpha,14 beta-cholestane-3,15-dione and 2b. Successive chromatographic separations on silica gel and reversed phase media gave 2b of high purity. Compound 2a was also prepared by lithium-ammonia reduction of 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15-one (96% yield) and by selective reduction of 5 alpha-cholestane-3,15-dione with lithium tri-tert-butoxyaluminum hydride (90% yield). Isomers 2a and 2b were readily epimerized under acidic or basic conditions or under conditions used for gas chromatographic analysis. The purities of 2a and 2b were measured from nuclear magnetic resonance (NMR) spectra; chromatographic methods gave less reliable estimates of purity. NMR data also showed that ring C of the 14 beta sterols is predominantly in a chair conformation. The effects of 2a and 2b on the levels of 3-hydroxy-3-methylglutaryl coenzyme A reductase have been studied in Chinese hamster ovary cells.

Animals↗
PubMed1988

Metabolism of glucose 1,6-P2--III. Partial purification and characterization of glucose 1,6-P2 synthase from pig skeletal muscle.

1. Glycerate 1,3-P2-dependent glucose, 1,6-P2 synthase has been purified 2000-fold from pig skeletal muscle, with a yield of 75%. 2. The enzyme possesses fructose 1,6-P2-dependent glucose 1,6-P2 synthase and phosphoglucomutase activities, which represent 0.1 and 60% of the main activity, respectively. 3. Both glucose 1-P and glucose 6-P can act as acceptors of the phosphoryl group from glycerate 1,3-P2. 4. The Km values are 19 microM and 67 nM for glucose 1-P and glycerate 1,3-P2, respectively. 5. The enzyme is inhibited by glycerate 2,3-P2, fructose 1,6-P2, glycerate 3-P, phosphoenolpyruvate and lithium, the inhibition pattern varying with the compound.

Animals↗
PubMed1998

n-alkyl fluorenyl phases in chromatography. I. Synthesis and characterization.

A new class of silica gel-bound fluorene phases is described. The compounds are synthesized via reaction of fluorenyl lithium with omega-alkenyl bromides leading to 9-(5'-hexenyl)-9H- and 9-(9'-decenyl)-9H-fluorene (1 and 2), followed by hydrosilation reactions with different hydrosilanes. The resulting omega-functionalized silylalkyl fluorenes 3a(T0), 3b(T0), 4a(T0), 4b(T0) and 4c(M0) (Scheme 1) react with surface silanol groups of silica gel to generate the new fluorene phases 3a(Tn)(Qm)y, 3b(Tn)(Qm)y, 4a(Tn)(Qm)y, 4b(Tn)(Qm)y and 4c(M1)(Qm)y. The phases are characterized by employing 1H, 13C and 29Si solid-state nuclear magnetic resonance spectroscopy. Their applicability in high-performance liquid chromatography is proved by the Sander and Wise test (SRM 869). In contrast to conventional n-alkyl phases, pi-pi interactions are additionally involved in the separation process and, therefore, the retention times of the polycyclic aromatic hydrocarbons sample molecules depend on the ligand densities of the applied fluorene phases.

Chromatography, High Pressure Liquid↗
PubMed2001

Determination of sodium cromoglycate in human plasma by liquid chromatography-mass spectrometry in the turbo ion spray mode.

A highly sensitivity liquid chromatography-tandem mass spectrometry method has been developed for the quantitation of sodium cromoglycate (SCG) in human plasma. The method was validated over a linear range of 0.100-50.0 ng/ml, using 13C4 sodium cromoglycate as the internal standard. Compounds were extracted from 1.0 ml of lithium heparin plasma by methanol elution of C18 solid-phase extraction cartridges. The dried residue was reconstituted with 100 microl of 0.01 N HCl. and 30 microl was injected onto the LC-MS-MS system. Chromatographic separation was achieved on a C8 (3.5 microm) column with an isocratic mobile phase of methanol-water-0.5 M ammonium acetate (35:64.8:0.2, v/v/v). The analytes were detected with a PE Sciex API 3000 mass spectrometer using turbo ion spray with positive ionization. Ions monitored in the multiple reaction monitoring (MRM) mode were m/z 469.2 (precursor ion) to m/z 245.1 (product ion) for SCG and m/z 473.2 (precursor ion) to m/z 247.1 (product ion) for 13C4 SCG (I.S.). The average recoveries of SCG and the I.S. from human plasma were 91 and 87%, respectively. The low limit of quantitation was 0.100 ng/ml. Results from a 4-day validation study demonstrated excellent precision (C.V.% values were between 1.9 and 6.5%) and accuracy (-5.4 to - 1.2%) across the calibration range of 0.100-50.0 ng/ml.

Chromatography, High Pressure Liquid↗
PubMed2002

Theoretical studies to understand surface chemistry on carbon anodes for lithium-ion batteries: how does vinylene carbonate play its role as an electrolyte additive?

To elucidate the role of vinylene carbonate (VC) as a solvent additive in organic polar solutions for lithium-ion batteries, reductive decompositions for vinylene carbonate (VC) and ethylene carbonate (EC) molecules have been comprehensively investigated both in the gas phase and in solution by means of density functional theory calculations. The salt and solvent effects are incorporated with the clusters (EC)nLi+(VC) (n = 0-3), and further corrections that account for bulk solvent effects are added using the polarized continuum model (PCM). The electron affinities of (EC)nLi+(VC) (n = 0-3) monotonically decrease when the number of EC molecules increases; a sharp decrease of about 20.0 kcal/mol is found from n = 0 to 1 and a more gentle variation for n > 1. For (EC)nLi+(VC) (n = 1-3), the reduction of VC brings about more stable ion-pair intermediates than those due to reduction of the EC molecule by 3.1, 6.1, and 5.3 kcal/mol, respectively. This finding qualitatively agrees with the experimental fact that the reduction potential of VC in the presence of Li salt is more negative than that of EC. The calculated reduction potentials corresponding to radical anion formation are close to the experimental potentials determined with cyclic voltammetry on a gold electrode surface (-2.67, -3.19 eV on the physical scale for VC and EC respectively vs experimental values -2.96 and -2.94 eV). Regarding the decomposition mechanisms, the VC and EC moieties undergo homolytic ring opening from their respective reduction intermediates, and the energy barrier of VC is about one time higher than that of EC (e.g., 20.1 vs 8.8 kcal/mol for (EC)2Li+(VC)); both are weakly affected by the explicit solvent molecules and by a bulk solvent represented by a continuum model. Alternatively, starting from the VC-reduction intermediate, the ring opening of the EC moiety via an intramolecular electron-transfer transition state has also been located; its barrier lies between those of EC and VC (e.g., 17.2 kcal/mol for (EC)2Li+(VC)). On the basis of these results, we suggest the following explanation about the role that VC may play as additive in EC-based lithium-ion battery electrolytes; VC is initially reduced to a more stable intermediate than that from EC reduction. One possibility then is that the reduced VC decomposes to form a radical anion via a barrier of about 20 kcal/mol, which undergoes a series of reactions to give rise to more active film-forming products than those resulting from EC reduction, such as lithium divinylene dicarbonate, Li-C carbides, lithium vinylene dicarbonate, R-O-Li compound, and even oligomers with repeated vinylene and carbonate-vinylene units. Another possibility starting from the VC-reduction intermediate is that the ring opening occurs on the unreduced EC moiety instead of being on the reduced VC, via an intramolecular electron transfer transition state, the energy barrier of which is lower than that of the former, in which VC just helps the intermediate formation and is not consumed. The factors that determine the additive functioning mechanism are briefly discussed, and consequently a general rule for the selection of electrolyte additive is proposed.

Journal Article↗
PubMed1996

Lithium toxicity.

We report a case of severe lithium toxicity precipitated by a thiazide diuretic and compounded by an angiotensin converting enzyme inhibitor. There was severe vasodilatation refractory to noradrenaline.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1998

Comparative anti-mitotic effects of lithium gamma-linolenate, gamma-linolenic acid and arachidonic acid, on transformed and embryonic cells.

The effects of gamma-linolenic acid (GLA), the lithium salt of gamma-linolenic acid (LiGLA) and arachidonic acid (AA) were compared at doses of 50 microg/ml for periods of 6 and 24 h on cell cycle progression and apoptosis induction in transformed and in normal cells. In WHCO3 (oesophageal cancer) cells and on primary embryonic equine lung cells, we found LiGLA to be the most effective in apoptosis induction. After 24 h, 94% of the WHCO3 cancer cells and 44% of the primary embryonic equine lung cells exposed to LiGLA were apoptotic. The WHCO3 cancer cells were also very susceptible to the apoptosis-inducing effects of AA (56%) and GLA (44%), whereas the embryonic equine lung cells were much less affected by these two fatty acids. After 6 h exposure to all three compounds, most of the cycling WHCO3 cancer cells were blocked in S-phase. After 24 h treatment, some of the S-phase cells exposed to AA and GLA were apparently able to move into the G2/M phase, the LiGLA exposed cells were mostly apoptotic and no cycling cells were present. The primary embryonic equine lung cells were fairly resistant to the cytotoxic effects of GLA and AA. From our studies we conclude that, although LiGLA was the most toxic to the cancer cells, it is apparently less selective, compared to AA and GLA, in the killing of cancer and normal cells. It would also appear that the lithium might have added to the cytotoxic effects of LiGLA. The mechanism needs to be clarified.

Animals↗
PubMed1987

Synergism of a compound unconditioned stimulus in taste aversion conditioning.

Anti-lymphocyte serum (ALS) and lithium chloride have both previously been used successfully as unconditioned stimuli in taste aversion conditioning paradigms in rats. This report substantiates those findings but shows that when the two stimuli are given as a compound unconditioned stimulus in association with saccharin flavoured drinking solution, the conditioned taste aversion response following a second exposure to saccharin alone is more profound than that following conditioning with either ALS or LiCl alone. These results demonstrate synergism between the two stimuli when given together.

Animals↗
PubMedDate not supplied

Endogenous ethanol--its metabolic, behavioral and biomedical significance.

Ethanol is constantly formed endogenously from acetaldehyde, and level of the former can be measured in both human beings and animals. Acetaldehyde can be generated in situ from the metabolism of pyruvate, threonine, deoxyribose-5-phosphate, phosphoethanolamine, alanine and presumably from other substrates. The levels of blood and tissue endogenous ethanol change as a function of various physiologic and experimental conditions such as starvation, aging, stress, cooling, adrenalectomy, etc. and are regulated by many exogenous compounds such as antimetabolites, derivatives of amino acids, lithium salts, disulfiram, cyanamide, etc. Under free choice alcohol selection situations, the levels of endogenous ethanol in rat blood and alcohol preference by the animals are negatively correlated. Similar negative correlations have been found between the levels of blood endogenous ethanol and the frequency of delirium in alcoholic patients undergoing alcohol withdrawal. Endogenous ethanol and acetaldehyde can therefore be regarded as compounds which fulfil substrate, regulatory and modulator functions.

Alcoholism↗
PubMed2004

X-ray absorption spectroscopy study of the LixFePO4 cathode during cycling using a novel electrochemical in situ reaction cell.

The extraction and insertion of lithium in LiFePO4 has been investigated in practical Li-ion intercalation electrodes for Li-ion batteries using Fe K-edge X-ray absorption spectroscopy (XAS). A versatile electrochemical in situ reaction cell was utilized, specifically designed for long-term X-ray experiments on battery electrodes during the lithium-extraction/insertion process in electrode materials for Li-ion batteries. The electrode contained about 7.7 mg of LiFePO4 on a 20 microm-thick Al foil. In order to determine the charge compensation mechanism and structural perturbations occurring in the system during cycling, in situ X-ray absorption fine-structure spectroscopy (XAFS) measurements were conducted on the cell at a moderate rate using typical Li-ion battery operating voltages (3.0-4.1 V versus Li/Li+). XAS studies of the LiFePO4 electrode measured at the initial state (LiFePO4) showed iron to be in the Fe(II) state corresponding to the initial state (0.0 mAh) of the battery, whereas in the delithiated state (FePO4) iron was found to be in the Fe(III) state corresponding to the final charged state (3 mAh) of the battery. The X-ray absorption near-edge structure (XANES) region of the XAS spectra revealed a high-spin configuration for the two states [Fe(II), d6 and Fe(III), d5]. The XAFS data analysis confirmed that the olivine structure of the LiFePO4 and FePO4 is retained by the electrodes, which is in agreement with the X-ray diffraction observations on these compounds. The XAFS data that were collected continuously during cycling revealed details about the response of the cathode to Li insertion and extraction. These measurements on the LiFePO4 cathode show that the material retains good structural short-range order leading to superior cycling.

Electric Power Supplies↗