Search results for "Hydrogen-ion concentration"
showing 10 items of 769 documents
Scalable Constant pH Molecular Dynamics in GROMACS
2022
Molecular dynamics (MD) computer simulations are used routinely to compute atomistic trajectories of complex systems. Systems are simulated in various ensembles, depending on the experimental conditions one aims to mimic. While constant energy, temperature, volume, and pressure are rather straightforward to model, pH, which is an equally important parameter in experiments, is more difficult to account for in simulations. Although a constant pH algorithm based on the λ-dynamics approach by Brooks and co-workers [Kong, X.; Brooks III, C. L. J. Chem. Phys.1996, 105, 2414–2423] was implemented in a fork of the GROMACS molecular dynamics program, uptake has been rather limited, presumably due to…
In situ formation of steroidal supramolecular gels designed for drug release
2013
In this work, a steroidal gelator containing an imine bond was synthesized, and its gelation behavior as well as a sensitivity of its gels towards acids was investigated. It was shown that the gels were acid-responsive, and that the gelator molecules could be prepared either by a conventional synthesis or directly in situ during the gel forming process. The gels prepared by both methods were studied and it was found that they had very similar macroand microscopic properties. Furthermore, the possibility to use the gels as carriers for aromatic drugs such as 5-chloro-8-hydroxyquinoline, pyrazinecarboxamide, and antipyrine was investigated and the prepared two-component gels were studied with…
Investigation of pH-Responsiveness inside Lipid Nanoparticles for Parenteral mRNA Application Using Small-Angle X-ray Scattering.
2020
Messenger ribonucleic acid (mRNA)-based nanomedicines have shown to be a promising new lead in a broad field of potential applications such as tumor immunotherapy. Of these nanomedicines, lipid-based mRNA nanoparticles comprising ionizable lipids are gaining increasing attention as versatile technologies for fine-tuning toward a given application, with proven potential for successful development up to clinical practice. Still, several hurdles have to be overcome to obtain a drug product that shows adequate mRNA delivery and clinical efficacy. In this study, pH-induced changes in internal molecular organization and overall physicochemical characteristics of lipoplexes comprising ionizable li…
Validation of Dissolution Testing with Biorelevant Media: An OrBiTo Study.
2017
Dissolution testing with biorelevant media has become widespread in the pharmaceutical industry as a means of better understanding how drugs and formulations behave in the gastrointestinal tract. Until now, however, there have been few attempts to gauge the reproducibility of results obtained with these methods. The aim of this study was to determine the interlaboratory reproducibility of biorelevant dissolution testing, using the paddle apparatus (USP 2). Thirteen industrial and three academic laboratories participated in this study. All laboratories were provided with standard protocols for running the tests: dissolution in FaSSGF to simulate release in the stomach, dissolution in a singl…
Industrial application of selected lactic acid bacteria isolated from local semolinas for typical sourdough bread production
2016
Abstract Four obligate heterofermentative lactic acid bacteria (LAB) strains (Weissella cibaria PON10030 and PON10032 and Leuconostoc citreum PON 10079 and PON10080) were tested as single strain starters, mono-species dual strain starters, and multiple strain starter for the preparation and propagation of sourdoughs for the production of a typical bread at industrial level. The kinetics of pH and TTA during the daily sourdough refreshments indicated a correct acidification process for all trials. The concentration of lactic and acetic acid increased consistently during fermentation. The resulting molar ratios between these two organic acids in the experimental trials were lower than those o…
Acid Titrations of poly(dG-dC).poly(dG-dC) in Aqueous Solution and in a w/o Microemulsion
2005
The model polynucleotide poly(dG-dC).poly(dG-dC) (polyGC) was titrated with a strong acid (HCl) in aqueous unbuffered solutions and in the quaternary w/o microemulsion CTAB/n-pentanol/n-hexane/water. The titrations, performed at several concentrations of NaCl in the range 0.005 to 0.600 M, were followed by recording the modifications of the electronic absorption and of the CD spectra (210or = lambdaor =350 nm) upon addition of the acid. In solution, the polynucleotide undergoes two acid-induced transitions, neither of which corresponds to denaturation of the duplex to single coil. The first transition leads to the Hoogsteen type synG.C+ duplex, while the second leads to the C+.C duplex. The…
Alkaline titrations of poly(dG-dC).poly(dG-dC): microemulsion versus solution behaviour
2007
PolyGC was titrated with a strong base in the presence of increasing concentrations of NaCl (from 0.00 to 0.60M) either in water solution or with the polynucleotide solubilized in the aqueous core of reverse micelles, i.e., the cationic quaternary water-in-oil microemulsion CTAB/n-hexane/n-pentanol/water. The results for matched samples in the two media were compared. CD and UV spectroscopies and, for the solution experiments, pH measurements were used to follow the course of deprotonation. In both media the primary effect of the addition of base was denaturation of the polynucleotide, reversible by back-titration with a strong acid. In solution, the apparent pK(a) of the transition decreas…
Dissociation of theophylline uptake and inotropic effect in myocardial tissue: influence of temperature, pH and calcium.
1975
1. The myocardial uptake and the positive inotropic effect of theophylline (100 mug/ml; 0.56 mM) were studied in isolated electrically driven guinea-pig hearts perfused by the Langendorff technique under various extracellular conditions. [3H]-theophylline was used. 2. Variations in temperature, hydrogen ion and calcium ion concentrations of the perfusion media changed the time course and magnitude of the effect of theophylline on myocardial twitch tension but did not affect the time course and amount of theophylline uptake. 3. Under all conditions, the build-up of the positive inotropic effect of theophylline was about three times faster than the uptake of the drug into the heart. 4. Since …
Flow-Injection Spectrophotometric Determination of Phenolic Drugs and Carbamate Pesticides by Coupling with Diazotized 2,4,6-Trimethylaniline
1999
Abstract A flow-injection (FI) spectrophotometric system is proposed for the determination of phenols and carbamates. In the FI manifolds, the solutions of phenols or carbamates (the latter after hydrolysis with NaOH) were injected into a diazonium ion carrier stream at pH 9.5 (buffered with tetrahydroborate), which was formed by mixing 2,4,6-trimethylaniline (TMA) with nitrate in a sodium dodecyl sulfate aqueous micellar medium. Absorbance was measured at 550 nm. The system combines the advantages derived from the use of TMA for the coupling of phenols in basic micellar media, because of the inhibition of the self-coupling reaction of the reagent, with the precision and speed of the FI pro…
A proton-translocating H+-ATPase is involved in C6 glial pH regulation.
1998
AbstractGlial cells extrude acid equivalents to maintain pHi. Although four mechanisms have been described so far, pHi-control under physiological conditions is still not sufficiently explained. We therefore investigated whether a H+-translocating ATPase is involved in glial pHi homeostasis using an established glial cell line (C6 glioma). In the absence of bicarbonate, the inhibition of H+-ATPases by NEM led to a pHi decrease. The application of a more specific inhibitor (NBD-Cl) showed that the H+-ATPase involved is of the vacuolar type. Inhibition went along with delayed cell swelling. Together with the fact that glial acidification was far more pronounced in Na+-free media, this may ser…