JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 4 2002
Erwin Buncel
Abstract Factors influencing C,H isotopic exchange rates in five-membered azoles, that is imidazoles and thiazoles, under catalysis by H+ and Mn+, especially transition metals, Pt(II) and Co(III) are discussed. Hydrogen ion catalysis through N(3) protonation of azoles 1,3 is generally the most efficient, with rate enhancements in the range 102,109 over the neutral process being attained. Metal-ion coordination also results in effective catalysis, though less so than catalysis by protons. Catalysis of C,H exchange by Mn+ can be studied through addition of the metal salts to a buffered solution of the heterocycle in which labile complexes exist, or on synthesized complexes such as 4,13 which are substitution-inert thus precluding complications from unknown dissociation equilibria. A delicate balance of factors influence the ease of C,H exchange, including: (1) the magnitude of the fractional charge located at N(3) of the heterocycle through Mn+,N(3) , bond polarization; (2) metal-to-ligand , back-bonding; (3) the electronic structure of the metal ions. These considerations have obvious consequences for deuterium- and tritium-labelling of a number of biomolecules, e.g. proteins, enzymes, nucleic acids, some vitamins, as well as drugs which incorporate five-membered azoles in their structures. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Proton and sodium MRI assessment of fluid level in calf tissue

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2006
Chun S. Zuo PhD
Abstract Purpose To investigate the feasibility of using 1H and 23Na MRI to detect fluid levels in the lower leg muscle. Materials and Methods Proton and sodium MRI was applied to detect body fluid levels in the lower leg muscles of 18 healthy young male subjects at 3T and 4T. The paradigms under investigation were a postural change from sitting upright to lying supine, and saline infusion. Results We found that the average proton MR signal in gastrocnemius and soleus muscles were reduced following the postural change by 3.5% ± 1.4% (P < 0.05) and rose following saline infusion by 3.7% ± 0.9% (P < 0.01). More dramatically, the sodium MR signal decreased by 7.1% ± 1.2% (P < 0.01) following the postural change and increased following saline infusion by 12% ± 3.8% (P < 0.05). The ratio of intra- to extracellular fluid levels was 1.6 ± 0.5 for the subjects based on the acquired proton and sodium data. Conclusion Our results indicate that proton and sodium MRI can be used to assess fluid levels in the lower extremities, and this technique may be applied to evaluate fluid retention. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source]

Underutilization of gastroprotection for at-risk patients undergoing percutaneous coronary intervention: Spain compared with the United States

ALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 5 2010
R. Casado-Arroyo
Aliment Pharmacol Ther 2010; 32: 689,695 Summary Background, Proton pump inhibitors (PPIs) are the preferred agents for the prevention of aspirin-associated upper gastrointestinal bleeding (UGIB). Data are limited to determine whether PPIs are being used to reduce UGIB risk. Aim, To evaluate the implementation of PPI treatment to reduce the GI risk in two cardiology centres from Europe and the United States. Methods, A retrospective cross-sectional study was carried out at the University of Michigan and University Hospital-Zaragoza in 429 consecutive patients hospitalized for percutaneous coronary intervention (PCI) on dual antiplatelet therapy. Results, Admission for PPI co-therapy was similar (34% vs. 30%) in both centres. At discharge, the proportion of high-risk patients receiving PPI therapy in the Spanish centre (75.4%) was higher than their American peers (55.6%) (OR: 2.5; 95% CI; 1.3,4.7). No differences in PPI prescription rates were found among Spanish patients with/without GI risk factors. The opportunity to initiate PPI co-therapy in high-risk patients was missed in 81.8% (36/44) of those not on PPI at admission in US patients vs. 24.1% (19/79) (P < 0.0001) in Spanish patients. Conclusions, There are important differences concerning PPI prescription and risk stratification in the two centres when managing PCI patients. Efforts to stratify risks and utilize appropriate strategies for UGIB prophylaxis in high-risk patients are warranted. [source]

Proton pump inhibitors as a risk factor for paediatric Clostridium difficile infection

ALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 7 2010
R. TURCO
Aliment Pharmacol Ther,31, 754,759 Summary Background, Proton pump inhibitors (PPIs) and H2 receptor antagonists (H2RAs) may play an important role on the onset of Clostridium difficile -associated disease (CDAD) in adults. The impact of Clostridium difficile on children treated with gastric acid-suppressing agents remains unknown. Aim, To investigate the relationship between CDAD and exposure to acid suppressive therapy in hospitalized paediatric patients. Methods, We reviewed the medical records of children, with a diagnosis of protracted diarrhoea and abdominal pain, whose stool was analysed for C. difficile toxins. We identified 68 patients with CDAD. For each patient, we randomly selected one control subjects with stool analysis negative for C. difficile. Comorbid illnesses, previous hospitalizations, antibiotics, corticosteroids, immunosuppressants and gastric acid suppressing exposures were recorded. Results, The use of PPI was significantly higher in C. difficile positive group compared with C. difficile negative group [odds ratio (OR): = 4.5; 95% confidence interval (CI) = 1.4,14.4]. We also found a trend for the use of H2RAs in patients infected by C. difficile compared with C. difficile negative comparison group (OR: = 3.8; 95% CI = 0.7,18.9). Conclusions, Children exposed to PPIs therapy seem to be at higher risk for the development of Clostridium difficile -associated disease. [source]

Review article: dual delayed release formulation of dexlansoprazole MR, a novel approach to overcome the limitations of conventional single release proton pump inhibitor therapy

ALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 9 2009
D. C. METZ
Summary Background, Proton pump inhibitors (PPIs) provide the most effective pharmacotherapy for treating acid-related disorders. However, PPIs do not completely control acid over 24 h with once-daily dosing. Aims, To discuss limitations inherent in the pharmacokinetics (PK) and pharmacodynamics of conventional PPI formulations, which provide a single drug release. Also, to consider approaches to extending the duration of acid suppression focusing on dexlansoprazole MR, a PPI with a novel Dual Delayed Release (DDR) formulation. Method, We reviewed the available literature regarding marketed and investigational PPIs. Results, Non-standard dosing of currently marketed PPIs has produced incremental advances in acid control. Multiple approaches are being evaluated to enhance acid suppression with PPIs. Dexlansoprazole MR is a DDR formulation of dexlansoprazole, an enantiomer of lansoprazole, with two distinct drug release periods to prolong the plasma dexlansoprazole concentration,time profile and extend duration of acid suppression. Clinical studies show that dexlansoprazole MR produces a dual-peak PK profile that maintains therapeutic plasma drug concentrations longer than lansoprazole, with a single-peak PK profile, and increases the percentage of time that intragastric pH >4. Conclusions, Novel drug delivery platforms, including the dexlansoprazole MR DDR formulation, may improve acid suppression and offer benefits over conventional single release PPI formulations. [source]

Effect of proton pump inhibition on the gastric volume: assessed by magnetic resonance imaging

ALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 8 2009
A. BABAEI
Summary Background Proton pump inhibitor (PPI) therapy is known to suppress gastric acid secretion. Thus PPI therapy may decrease gastric volume and gastric contents available for gastro-oesophageal reflux by decreasing acid secretion. Aim To determine the effect of PPI therapy on the gastric volume after a standard meal. Methods A total of nine healthy subjects were studied using magnetic resonance imaging, before and after a standard liquid meal mixed with a paramagnetic contrast to help demarcate the gastric region. Images were acquired for a total of 90 min after the meal. Studies were conducted before and following esomeprazole twice daily for 7 days. Images were analysed to determine the gastric liquid volume. Results Gastric volume, 15 min after the meal peaked to 611 ± 37 mL on the control day and 539 ± 30 mL following the PPI administration (P < 0.001). Average gastric volume remained significantly lower (56 ± 9 mL, P < 0.05) on the PPI therapy from 5 to 75 min after the meal. Conclusions Proton pump inhibitor therapy causes a significant reduction in the gastric contents volume during first 75 min after the meal. In addition to increasing the gastric pH, PPI therapy may decrease the frequency of gastro-oesophageal reflux by decreasing the volume of gastric contents. [source]

Proton pump inhibitors increase significantly the risk of Clostridium difficile infection in a low-endemicity, non-outbreak hospital setting

ALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 6 2009
B. R. DALTON
Summary Background, Proton pump inhibitors (PPI) have been linked to higher risk of Clostridium difficile infection (CDI). The relevance of this association in hospitals with low disease activity, where an outbreak strain is nondominant, has been assessed in relatively few studies. Aim, To assess the association of PPI and CDI in a setting of low disease activity. Methods, A retrospective cohort study was conducted at two hospitals. Patients admitted for ,7 days receiving antibiotics were included. Demographics, exposure to PPI, antibiotics and other drugs in relation to diagnosis of CDI were assessed by univariate and multivariate analyses. Results, Of 14 719 patients, 149 (1%) first episode CDI were documented; PPI co-exposure increased CDI [1.44 cases/100 patients vs. 0.74 cases/100 non-exposed (OR: 1.96, 95% CI: 1.42,2.72)]. By logistic regression, PPI days (adjusted OR: 1.01 per day, 95% CI: 1.00,1.02), histamine-2 blockers, antidepressants, antibiotic days, exposure to medications, age, admission service and length of admission were significant predictors. Conclusions, A statistically significant increase in CDI was observed in antibiotic recipients who received PPI, but the absolute risk increase is modest. In settings of with low rates of CDI, the benefit of PPI therapy outweighs the risk of developing CDI. These data support programmes to decrease inappropriate use of PPI in hospitalized patients. [source]

Review article: the management of heartburn in pregnancy

ALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 9 2005
J. E. RICHTER
Summary Heartburn is a normal consequence of pregnancy. The predominant aetiology is a decrease in lower oesophageal sphincter pressure caused by female sex hormones, especially progesterone. Serious reflux complications during pregnancy are rare; hence upper endoscopy and other diagnostic tests are infrequently needed. Gastro-oesophageal reflux disease during pregnancy should be managed with a step-up algorithm beginning with lifestyle modifications and dietary changes. Antacids or sucralfate are considered the first-line drug therapy. If symptoms persist, any of the histamine2 -receptor antagonists can be used. Proton pump inhibitors are reserved for women with intractable symptoms or complicated reflux disease. All but omeprazole are FDA category B drugs during pregnancy. Most drugs are excreted in breast milk. Of systemic agents, only the histamine2 -receptor antagonists, with the exception of nizatidine, are safe to use during lactation. [source]

Helicobacter pylori and dyspepsia: physicians' attitudes, clinical practice, and prescribing habits

ALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 3 2002
H. J. O'Connor
Background: Consensus guidelines have been published on the management of Helicobacter pylori infection and it is assumed that these guidelines are adhered to in clinical practice. Aim: To assess the changing attitudes of medical practitioners to H. pylori, and the impact of H. pylori infection on everyday clinical practice and prescribing patterns. Methods: Data for this review were gathered up to December 2000 from detailed review of medical journals, the biomedical database MEDLINE, and relevant abstracts. Results: Physician surveys show widespread acceptance of H. pylori as a causal agent in peptic ulcer disease. Gastroenterologists adopted H. pylori therapy for peptic ulcer earlier and more comprehensively than primary care physicians. Despite a low level of belief in H. pylori as a causal agent in nonulcer dyspepsia and gastro-oesophageal reflux disease (GERD), H. pylori therapy is widely prescribed for these conditions. Proton pump inhibitor-based triple therapy is the eradication regimen of choice by all physician groups. In routine clinical practice, there appears to be significant under-treatment of peptic ulcer disease with H. pylori therapy, but extensive use for nonulcer indications. Prescription of H. pylori treatment regimens of doubtful efficacy appears commonplace, and are more likely in primary care. Despite the advent of H. pylori therapy, the prescription of antisecretory therapy, particularly of proton pump inhibitors, continues to rise. Conclusions: Publication of consensus guidelines per se is not enough to ensure optimal management of H. pylori infection. Innovative and ongoing educational measures are needed to encourage best practice in relation to H. pylori infection. These measures might be best directed at primary care, where the majority of dyspepsia is managed. [source]

Treatment with a proton pump inhibitor promotes corpus gastritis in patients with Helicobacter pylori -infected antrum-predominant gastritis

ALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 1 2002
M. Suzuki
Background: Proton pump inhibitors have been reported to modify the level of Helicobacter pylori gastritis. Aim: To quantitatively investigate the effect of a proton pump inhibitor on the mucosal neutrophil reaction. Methods: Forty-six H. pylori -infected patients (17 duodenal ulcer, 29 gastric ulcer) were enrolled. During endoscopic examination, biopsy samples were obtained from the antrum and the corpus. The tissue content of neutrophil myeloperoxidase was measured by enzyme-linked immunoabsorbent assay, and H. pylori infection was histologically assessed. A proton pump inhibitor was administered orally for 8 weeks. Results: In the patients as a whole, antral myeloperoxidase decreased significantly after proton pump inhibitor treatment, but corpus myeloperoxidase remained largely unchanged. In duodenal ulcer patients, myeloperoxidase significantly decreased in the antrum, but increased in the corpus. In gastric ulcer patients, a significant reduction was observed in antral myeloperoxidase, but corpus myeloperoxidase remained unchanged. In the antral myeloperoxidase > corpus myeloperoxidase subgroup (n=24), antral myeloperoxidase significantly decreased, whereas corpus myeloperoxidase increased. No changes were observed at either site in the corpus myeloperoxidase > antral myeloperoxidase subgroup. Histology showed that the antral bacterial load of H. pylori decreased in all subgroups, but that it was mostly unchanged in the corpus. Conclusions: Proton pump inhibitor treatment stimulated the neutrophil reaction in the corpus mucosa of duodenal ulcer patients and of patients in whom antral neutrophil accumulation was more predominant than that of the corpus. This phenomenon may not be caused by increased bacterial density. [source]

Single Radiation-Induced Grafting Method for the Preparation of Two Proton- and Lithium Ion-Conducting Membranes

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 8 2006
Mohamed Mahmoud Nasef
Abstract Summary: Two distinct types of polymer electrolyte membranes for conducting protons and lithium ions have been prepared by a radiation-induced grafting method. The polymer electrolyte precursor (PVDF- g -PS) is obtained by the simultaneous grafting of styrene onto poly(vinylidene fluoride) (PVDF) followed by one of two specific treatments. This includes sulfonation with a chlorosulfonic acid/dichloromethane mixture to obtain proton (H+)-conducting membranes, or activation with LiPF6/EC/DC liquid electrolyte to obtain lithium ion (Li+)-conducting membranes. The chemical structure of the obtained electrolyte membranes is verified by FT-IR spectroscopy. Differential scanning calorimetry is used to examine the changes in the crystallinity and the thermal properties of both electrolyte membranes during the preparation process. The thermal stability of both electrolyte membranes is also evaluated using thermal gravimetrical analysis. The obtained polymer electrolyte membranes achieve superior conductivity values: 1.61,×,10,3 S,·,cm,1 for Li+ and 5.95,×,10,2 S,·,cm,1 for H+ at room temperature at a polystyrene content of 50%. The results of this work suggest that high quality H+ - and Li+ -conducting membranes can be obtained using a single radiation-induced grafting method. Schematic representation of the single root for preparation of Li+ - and H+ -conducting membranes started by radiation-induced grafting of styrene onto a PVDF film followed by chemical treatment. [source]

Pharmacokinetics of clarithromycin in Helicobacter pylori eradication therapy in patients with liver cirrhosis

ALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 2000
T. Azuma
Summary Background: Proton pump inhibitor triple therapy with clarithromycin and metronidazole has been widely used for Helicobacter pylori eradication. However, the efficacy and the safety of this therapy in patients with liver cirrhosis have not been established. Aim: To evaluate the effect of hepatic dysfunction on metabolism of clarithromycin as it is used for H. pylori eradication therapy in patients with liver cirrhosis, and the efficacy of eradication therapy in those patients. Methods: Serum levels of clarithromycin and its meta-bolite, 14-(R)-hydroxyclarithromycin, were examined in 18 subjects (five normal controls and 13 hospitalized patients with liver cirrhosis) on a selected day between days 7 and 10 of a 2-week course of eradication therapy. This therapy consisted of lansoprazole (30 mg, once a day) together with clarithromycin (200 mg, twice a day) and metronidazole (250 mg, twice a day). In addition, 118 H. pylori -positive out-patients, 88 with peptic ulcer and 30 with liver cirrhosis, underwent the same eradication therapy. Results: Values for the area under the 0,6 h concentration,time curve (AUC) for clarithromycin were not significantly different among the groups. However, the AUC (0,6 h) values of 14-(R)-hydroxyclarithromycin were significantly lower in the Child-Pugh C group than in either the normal controls or the Child-Pugh A/B group. The cure rate for the peptic ulcer patients was 84% on a per protocol analysis (95% CI: 80%,88%) and 81% on an intention-to-treat analysis (95% CI: 77%,85%), while in the liver cirrhosis patients it was 89% in a per protocol analysis (95% CI: 78%,99%) and 83% in an intention-to-treat analysis (95% CI: 70%,97%). Mild adverse effects were observed in 10% of the peptic ulcer patients and 13% of the liver cirrhosis patients, with none leading to premature withdrawal from the study. Conclusion: The 2-week low-dose lansoprazole-based triple therapy tested is a simple, effective and well-tolerated regimen for H. pylori eradication in patients with liver cirrhosis. [source]

Evidence from ESR studies for [Co(,-C2H4)3] produced at 77 K in a rotating cryostat,

MAGNETIC RESONANCE IN CHEMISTRY, Issue 10 2006
Lynda J. Hayton
Abstract Co atoms were reacted with ethene at 77 K and the paramagnetic products studied by electron spin resonance (ESR) at X- and K-bands. The ESR spectra of the major product at both frequencies showed eight cobalt multiplets (ICo = 7/2) indicating a mono-cobalt complex. The spectra have orthorhombic g and cobalt hyperfine tensors and were simulated by the parameters; g1 = 2.284, g2 = 2.0027, g3 = 2.1527; A1 < , 25 MHz, A2 = , 109 MHz, A3 = , 198 MHz. Proton and 13C (1% natural abundance) hyperfine couplings were lower than the line widths (<2 MHz) indicating less than 0.5 spin transfer to the ethene ligands. We assigned the spectrum to a Jahn,Teller-distorted planar trigonal mono-cobalt tris-ethene [Co(,-C2H4)3] complex in C2v symmetry. The SOMO is either a 3dx2,y2 (2a1) orbital in a T-geometry or a 3dxy (b1) orbital in a Y-geometry but there is only a spin density, a2, of 0.30 in these d orbitals. The spin deficiency of 0.70 is attributed to two factors; spin transfer from the Co to ethene ,/,* orbitals and a 4p orbital contribution, b2, to the SOMO. Calculations of a2 and b2 have been made at three levels of spin transfer, ,. At , = 0.00a2 is 0.23 and b2 is 0.78, at , = 0.25a2 is 0.25 and b2 is 0.52 and at , = 0.50a2 is 0.28 and b2 is 0.23. The other possible assignment to a mono-cobalt bis-ethene complex [Co(,-C2H4)2] cannot be discounted from the ESR data alone but is considered unlikely on other grounds. The complex is stable up to ,220 K indicating a barrier to decomposition of ,50 kJ Mol,1 Copyright © 2006 John Wiley & Sons, Ltd. [source]

Proton and electron radiation data and analysis of GaInP2/GaAs/Ge solar cells

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 6 2002
P. R. Sharps
We present electron and proton radiation data for our GaInP2/GaAs/Ge triple-junction solar cell. An analysis of the data is also done with both the relative damage coefficients (RDC) method developed at NASA-JPL, as well as the displacement damage dose (D3) method developed by the Naval Research Laboratory. We also discuss radiation tolerance of cells in the light of our development of an advanced triple-junction cell. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Anion-Exchange-Triggered 1,3-Shift of an NH Proton to Iridium in Protic N-Heterocyclic Carbenes: Hydrogen-Bonding and Ion-Pairing Effects,

ANGEWANDTE CHEMIE, Issue 5 2010
Guoyong Song Dr.
Protonenfreisetzung: IrI -Phosphan-Komplexe mit fünffach koordiniertem Ir-Zentrum und protischen N-heterocyclischen Carbenliganden wurden synthetisiert, die NH,,,Cl-Brücken enthalten (siehe Schema; cod=1,5-Cyclooctadien). Der Austausch von Cl, gegen schwächer koordinierende Anionen führt zur reversiblen 1,3-Wanderung des NH-Protons zum Iridiumatom, wahrscheinlich über einen neuartigen, wasservermittelten Protonenrelais-Mechanismus. [source]

Hexa- and Heptasubstitution in the Interaction of Octafluoronaphthalene with Lithium Dialkylamides: A New Approach to the Naphthalene "Proton Sponges".

CHEMINFORM, Issue 32 2004
Vladimir I. Sorokin
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

Proton- and Redox-Controlled Switching of Photo- and Electrochemiluminescence in Thiophenyl-Substituted Boron,Dipyrromethene Dyes

CHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2006
Holger Röhr Dipl.-Phys.
Abstract A luminescent molecular switch in which the active thiol/disulfide switching element is attached to a meso -phenyl-substituted boron,dipyrromethene (BDP) chromophore as the signalling unit is presented. The combination of these two functional units offers great versatility for multimodal switching of luminescence: 1) deprotonation/protonation of the thiol/thiolate moiety allows the highly fluorescent meso - p -thiophenol-BDP and its nonfluorescent thiolate analogue to be chemically and reversibly interconverted, 2) electrochemical oxidation of the monomeric dyes yields the fluorescent disulfide-bridged bichromophoric dimer, also in a fully reversible process, and 3) besides conventional photoexcitation, the well separated redox potentials of the BDP also allow the excited BDP state to be generated electrochemically (i.e., processes 1) and 2) can be employed to control both photo- and electrochemiluminescence (ECL) of the BDP). The paper introduces and characterizes the various states of the switch and discusses the underlying mechanisms. Investigation of the ortho analogue of the dimer provided insight into potential chromophore,chromophore interactions in such bichromophoric architectures in both the ground and the excited state. Comparison of the optical and redox properties of the two disulfide dimers further revealed structural requirements both for redox switches and for ECL-active molecular ensembles. By employing thiol/disulfide switching chemistry and BDP luminescence features, it was possible to create a prototype molecular ensemble that shows both fully reversible proton- and redox-gated electrochemiluminescence. In dieser Arbeit wird ein lumineszierender molekularer Schalter vorgestellt, bei dem das aktive Thiol/Disulfid-Schaltelement an einen meso-phenylsubstituierten Bordipyrromethen (BDP) Farbstoff als Signal gebende Komponente gekoppelt ist. Die Kombination dieser beiden funktionellen Einheiten offeriert eine hohe Vielseitigkeit für das multimodale Schalten der Lumineszenz: 1) die Deprotonierung/Protonierung der Thiol/Thiolat-Gruppe erlaubt es, das stark fluoreszierende meso-p-Thiophenol-BDP und das analoge, nicht fluoreszierende Thiolat chemisch reversibel ineinander zu überführen, 2) die elektrochemische Oxidation der monomeren Farbstoffe ergibt das fluoreszierende, disulfidverbrückte, bichromophore Dimer,dieser Prozess ist ebenfalls vollständig reversibel, und 3) neben der konventionellen Anregung mit Licht erlauben die deutlich getrennten Redoxpotenziale des BDPs ebenfalls eine elektrochemische Generierung des angeregten BDP-Zustandes, d.h., Prozesse 1) und 2) können dazu eingesetzt werden, sowohl die Photo- als auch die Elektrochemilumineszenz (ECL) des BDP zu steuern. Diese Arbeit stellt die Charakteristika der verschiedenen Zustände des Schalters vor und diskutiert die zu Grunde liegenden Mechanismen. Die Untersuchung des ortho-Analogen des Dimers vermittelte zudem Einsicht in mögliche Chromophor,Chromophor-Wechselwirkungen im Grund- wie im angeregten Zustand von solchen bichromophoren Architekturen. Der Vergleich der optischen und Redoxeigenschaften der beiden Disulfid-Dimere gab des Weiteren Aufschluss über strukturelle Voraussetzungen von Redoxschaltern sowie ECL-aktiven molekularen Ensembles. Unter Einsatz schaltbarer Thiol/Disulfid-Chemie und mit den Lumineszenzeigenschaften der BDPs war es möglich, ein erstes molekulares Ensemble zu entwickeln, das vollständig reversible protonen- als auch redoxgesteuerte Elektrochemilumineszenz zeigt. [source]

Behaviour of [PdH(dppe)2]X (X=CF3SO3,, SbF6,, BF4,) as Proton or Hydride Donor: Relevance to Catalysis

CHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2004
Michele Aresta Prof.
Abstract The synthesis, characterization and properties of [PdH(dppe)2]+CF3SO3,,0.125,THF (1; dppe=1,2-bis(diphenylphosphanyl)ethane) and its SbF6, (1,) and BF4, (1,,) analogues, the missing members of the [MH(dppe)2]+X, (M=Ni, Pd, Pt) family, are described. The Pd hydrides are not stable in solution and can react as proton or hydride donors with formation of dihydrogen, [Pd(dppe)2]2+ and [Pd(dppe)2]. Complexes 1,1,, react with carbocations and carbanions by transferring a hydride and a proton, respectively. Such H, or H+ transfer occurs also towards unsaturated compounds, for example, hydrogenation of a CC double bond. Accordingly, 1 can hydrogenate methyl acrylate to methyl propionate. Complex 1,, is an effective (hourly turnover frequency=16) and very selective (100,%) catalyst for the hydrogenation of cyclohexen-2-one to cyclohexanone with dihydrogen under mild conditions. Density functional calculations coupled with a dielectric continuum model were carried out to compute the energetics of the hydride/proton transfer reactions, which were used to rationalize some of the experimental findings. Theory provides strong support for the thermodynamic and kinetic viability of a tetracoordinate Pd complex as an intermediate in the reactions. [source]

pH-Controllable Supramolecular Systems

CHEMISTRY - AN ASIAN JOURNAL, Issue 3 2009
Ken Cham-Fai Leung Prof.
Abstract Proton, all that matters! This Focus Review surveys representative examples of pH-controllable supramolecular systems with interesting features and state-of-the-art applications, which can lead to the construction of meaningful molecular machines for electronic and biological applications that can be controlled by simple perturbation with acid and base. This Focus Review surveys representative examples of pH-controllable supramolecular systems with interesting features and state-of-the-art applications such as 1),conformational changes within individual molecules; 2),folding/unfolding of polymers; 3),simultaneous binding of cations and anions; 4),logic function; 5),ON,OFF switchable colorimetric sensing; 6),translocation of macrocycle-in-rotaxane molecules; 7),large-scale movement within molecules; and 8),regulation of the substrate flow in nanocontainers. In particular, systems will be discussed that involve: pH-induced conformational changes of a resorcinarene cavitand and a bis(iron porphyrin) complex; pH control in assembly and disassembly of supramolecular systems stabilized with different major noncovalent interactions; pH-driven movements of interlocked molecules involving rotaxanes, molecular elevators, and molecular muscles; and, finally, multicomponent supramolecular systems immobilized on solid supports as pH-responsive nanovalves for the controlled release of specific substrates. Recent advances in the understanding of pH-controllable supramolecular systems have led to the construction of meaningful molecular machines for electronic and biological applications that are amenable to control by simple perturbation with acids and bases. [source]

Pituitary and autonomic responses to cold exposures in man

ACTA PHYSIOLOGICA, Issue 4 2005
J. Leppäluoto
Abstract This review presents hormonal responses to various cold exposures and their calorigenic effects in man and some animals. Previous studies in rats have shown that cold exposures activate the hypothalamic-pituitary-thyroid axis. Increased thyroid hormone concentrations lead to heat production via general stimulation of metabolism (obligatory thermogenesis) and possibly via activation of thyroid hormone receptors and uncoupling protein 1 (UCP 1) and deiodinase enzyme genes in the brown adipose tissue (BAT). In human subjects long-term cold exposures do not seem to activate the pituitary-thyroid axis, but rather accelerate the elimination of triiodothyronine (T3), leading to low serum concentrations of free T3 hormone. In corollary to this a hypothyreotic condition with increased serum thyroid-stimulating hormone and impaired mood and cognitive performance can be observed after long-term cold exposures such as wintering. During cold exposures the sympathetic nerve system is activated and noradrenaline is released to blood circulation and to BAT, where it leads to production of cAMP, lipolysis and free fatty acids. Free fatty acids open the mitochondrial proton channel protein in BAT. Protons enter the mitochondria and inhibit ATP synthesis (uncoupling). By this way energy is transformed into heat (facultatory or adaptive thermogenesis). In adult human subjects the amount of BAT is small and adaptive thermogenesis (non-shivering thermogenesis) has a smaller role. UCP 1 with other uncoupling proteins may have other functions in the control of body weight, sugar balance and formation of reactive oxygen species. [source]

Background potassium channel block and TRPV1 activation contribute to proton depolarization of sensory neurons from humans with neuropathic pain

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2004
Thomas K. Baumann
Abstract Protons cause a sustained depolarization of human dorsal root ganglion (DRG) neurons [Baumann et al. (1996) Pain, 65, 31,38]. In the present study we sought to determine which ion channels are expressed in human DRG neurons that could mediate the sustained responses observed in the patch-clamp recordings. RT-PCR of material from the DRG tissue revealed the presence of mRNAs for a nonselective cation channel that is activated by protons (TRPV1) and background potassium channels that are blocked by protons (TASK-1, TASK-3 and Kir2.3). Highly acidic solution (pH 5.4) applied to cultured DRG neurons evoked prolonged currents that were associated with a net increase in membrane conductance. Consistent with the involvement of TRPV1, these proton-evoked currents were blocked by capsazepine and were only found in neurons that responded to capsaicin with an increase in membrane conductance. Less acidic extracellular solution (pH 6.0) evoked such currents only rarely, but was able to strongly enhance the currents evoked by capsaicin. Capsazepine (1 µm) blocked the currents evoked by capsaicin at pH 7.35, as well as the potentiated responses to capsaicin at pH 6.0. In neurons that were not excited by capsaicin, moderate extracellular acidification (pH 6.0) caused a sustained decrease in resting membrane conductance. The decrease in membrane conductance by protons was associated with inhibition of background potassium channels. This excitatory effect of protons was not blocked by capsazepine. We conclude that in most neurons the sustained depolarization in response to moderately acidic solutions is the result of blocked background potassium channels. In a subset of neurons, TRPV1 also contributes. [source]

Artificial DNA Nano-Spring Powered by Protons

ADVANCED MATERIALS, Issue 25 2010
Chunyan Wang
A novel multifunctional, proton-fueled DNA nano-spring has been constructed. By incorporation of the G-quadruplex/i-motif sequence into the assembly, the nanodevice can perform spring-like motions in response to changes in the environmental pH without permanent deformation. Nanosized objects/functional groups could be assembled/disassembled into this system in an addressable, contractile, and reversible manner. [source]

The Folding and Unfolding Kinetics of the i-Motif Structure Formed by the C-Rich Strand of Human Telomere DNA

CHEMBIOCHEM, Issue 11 2005
Yong Zhao Dr.
Return to the fold. Nucleic acids with four tandem cytidine-rich repeats can fold into a structure called the i-motif at acidic pH. The folding- and unfolding-rate constants of such a sequence in vertebrate telomere DNA were measured. Protons were found to promote i-motif formation by increasing the folding and decreasing the unfolding. [source]

The First Fulleropyrrolidine Derivative of Sc3N@C80: Pronounced Chemical Shift Differences of the Geminal Protons on the Pyrrolidine Ring.

CHEMINFORM, Issue 41 2005
Claudia M. Cardona
No abstract is available for this article. [source]

Probing the Vibrations of Shared, OH+O-Bound Protons in the Gas Phase

CHEMPHYSCHEM, Issue 5 2004
David T. Moore Dr.
Spectral signature of a proton bridge? Gas-phase infrared spectra are reported in the range of 500,1800 cm,1 for three species with short, strong hydrogen bonds, namely the proton-bound dimers of dimethyl ether (shown in the picture) and diethyl ether, and protonated 1,1,-oxybis[2-methoxyethane] (diglyme). The spectra are all quite similar, and furthermore they also strongly resemble the spectrum of the proton-bound water dimer (H5O2+), suggesting that there may be a conserved "spectral signature" for a proton bound between two oxygen atoms. [source]

Magnetization Transfer from Laser-Polarized Xenon to Protons with Spin-Diffusion Quenching

CHEMPHYSCHEM, Issue 4 2003
Hervé Desvaux
Position of the prisoner: Accurate location of xenon atoms in cage molecules (see picture) is derived by specific through-space magnetization transfer from laser-polarized gas to protons using a new NMR pulse sequence. [source]

Cation/proton antiporter complements of bacteria: why so large and diverse?

MOLECULAR MICROBIOLOGY, Issue 2 2009
Terry A. Krulwich
Summary Most bacterial genomes have five to nine distinct genes predicted to encode transporters that exchange cytoplasmic Na+ and/or K+ for H+ from outside the cell, i.e. monovalent cation/proton antiporters. By contrast, pathogens that live primarily inside host cells usually possess zero to one such antiporter while other stress-exposed bacteria exhibit even higher numbers. The monovalent cation/proton antiporters encoded by these diverse genes fall into at least eight different transporter protein families based on sequence similarity. They enable bacteria to meet challenges of high or fluctuating pH, salt, temperature or osmolarity, but we lack explanations for why so many antiporters are needed and for the value added by specific antiporter types in specific settings. In this issue of Molecular Microbiology, analyses of the pH dependence of cytoplasmic [Na+], [K+], pH and transmembrane electrical potential in the ,poly extremophile'Natranaerobius thermophilus are the context for assessment of the catalytic properties of 12 predicted monovalent cation/proton antiporters in the genome of this thermophilic haloalkaliphile. The results provide a profile of adaptations of the poly extremophilic anaerobe, including a proposed role of cytoplasmic buffering capacity. They also provide new perspectives on two large monovalent cation/proton antiporter families, the NhaC and the cation/proton antiporter-3 antiporter families. [source]

Aerosols and gaseous contrast agents for magnetic resonance imaging of the lung

CONTRAST MEDIA & MOLECULAR IMAGING, Issue 5 2008
Karim Mosbah
Abstract Magnetic resonance imaging of lungs and the investigation of pulmonary pathologies with this technique are limited by low proton spin density, degraded magnetic homogeneity and motion. Inhaled contrast agents (gases or aerosols) can improve the diagnostic value of MRI for lung. Paramagnetic contrast agents such as gadolinium chelates aerosol or dioxygen gas increase the relaxivity of proton in lung parenchyma and can be used to assess the ventilated fraction of the bronchoalveolar space. Similarly, inhalation of non proton-MRI nuclei such as perfluorinated gas or hyperpolarized gases (3He or 129Xe) can provide functional ventilation image. In this review paper, the principles, the practical implementation, the limitations and possible safety issues of these different techniques are summarized. The main pre-clinical and clinical applications of these approaches based on oral contrast agents are reviewed and illustrated with cutting-edge lung MRI studies. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Radiation induced modification of impurity-related point defects in crystalline quartz , a review

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2006
Harish Bahadur
Abstract This article presents a short review of impurity-related point defects in crystalline quartz and their radiation induced modifications. In particular, a discussion has been presented on some of the prominent aluminum related alkali and proton compensated centers. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Hantzsch 1,4-dihydropyridines containing a nitrooxyalkyl ester moiety to study calcium channel antagonist structure,activity relationships and nitric oxide release

DRUG DEVELOPMENT RESEARCH, Issue 4 2000
Jeffrey-Tri Nguyen
Abstract A group of 3-nitrooxyalkyl 5-alkyl 1,4-dihydro-2,6-dimethyl-4-(pyridyl)-3,5-pyridinedicarboxylates were prepared using a modified Hantzsch reaction that involved the condensation of a nitrooxyalkyl acetoacetate with an alkyl 3-aminocrotonate and a pyridinecarboxaldehyde. 1H NMR nuclear Overhauser enhancement (nOe) studies for 3-(3-nitrooxypropyl) 5-isopropyl 1,4-dihydro-2,6-dimethyl-4-(2-pyridyl)-3,5-pyridinedicarboxylate (17) indicates a predominant rotamer exists in solution where the pyridyl nitrogen atom is orientated above the 1,4-DHP ring system, and the pyridyl nitrogen atom is antiperiplanar to the 1,4-DHP ring H-4 proton. Variable temperature 1H NMR studies (,30 to +60°C) showed the 1,4-DHP NH proton in 17 is H-bonded in CHCl3 solution. This interaction is believed to be due to intermolecular H-bonding between the pyridyl nitrogen free electron pair and the 1,4-DHP NH proton. In vitro calcium channel antagonist (CCA) activities were determined using a muscarinic-receptor-mediated Ca+2 -dependent contraction of guinea pig ileal longitudinal smooth muscle assay. This class of compounds exhibited lower CCA activity (IC50 = 5.3 × 10,6 to 3.5 × 10,8 M range) than the reference drug nifedipine (IC50 = 1.4 × 10,8 M). For compounds having C-3 ,CH2CH2ONO2 and C-4 pyridyl substituents, the C-5 alkyl was a determinant of CCA (i -Pr > the approximately equipotent i -Bu, t -Bu, and Et analogs). The point of attachment of the isomeric C-4 pyridyl substituent was a determinant of CCA when C-3 ,CH2CH2ONO2 and C-5 i -Pr substituents were present providing the potency profile 2-pyridyl , 3-pyridyl > 4-pyridyl. CCA with respect to the C-3 nitrooxyalkyl substituent was inversely dependent on the length of the alkyl spacer. The percent nitric oxide (·NO) released in vitro by this group of compounds (range of 0.03,0.43%/ONO2 group), quantified as nitrite by reaction with the Griess reagent, was lower than that for the reference drug glycerol trinitrate (3.81%/ONO2 group). Nitric oxide release studies showed that the %·NO released was dependent on the number of ONO2 groups/molecule. A QSAR study for this group of compounds showed a correlation between the specific polarizability descriptor (SpPol) and %·NO release. Drug Dev. Res. 51:233,243, 2000. © 2001 Wiley-Liss, Inc. [source]