Iodine Laser Temperature Jump Research Articles

Dynamics of AOT and AOT/Nonionic Cosurfactant Microemulsions. An Iodine-Laser Temperature Jump Study

The iodine-laser temperature jump (ILTJ) technique was used to probe the interfacial and intermicellar dynamics of water-in-isooctane microemulsions stabilized by AOT both in the presence and in the absence of a cosurfactant such as an aliphatic chained alcohol (hexanol or decanol) or poly(oxyethylene) alkyl ether (C10E4 or C10E8). These cosurfactants have been shown to induce changes in the interfacial rigidity; the former increase it, and the latter decrease it. Two relaxation times were observed, one in the microsecond range and another, previously undetected, in the millisecond range. The relaxation times obtained in the microsecond range were higher for CiEj-containing microemulsions and lower for decanol-containing ones. This is consistent with the effect of the cosurfactants on interfacial rigidity, as this relaxation is inversely proportional to the bending modulus, κ. The value of κ = 0.3 kT determined for AOT reversed micelles (Wo = 55) is in agreement with those found in the literature. The rel...

Dynamics of Micro- and Macrophase Separation of Amphiphilic Block-Copolymers in Aqueous Solution

The dynamics of purified poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO−PPO−PEO) block-copolymer micellization and phase separation in aqueous solutions were studied using the iodine laser temperature-jump and stopped flow techniques. The changes in the micellar solutions were followed by either light scattering or fluorescence of 1,6-diphenyl-1,3,5-hexatriene (DPH), which is a probe located in the micelle interior. Three different relaxation processes were observed for the temperature range covering the micro- and macrophase separation of the EO13PO30EO13 (Pluronic L64) block-copolymer. The fastest process corresponds to the incorporation of unimers into micelles which leads to larger micelles that are not thermodynamically stable. This process is followed by a relaxation with negative amplitude during which the micellar core is dehydrated and a redistribution of micellar sizes is achieved. The third relaxation process corresponds to the clustering of micelles into large...

Kinetics and equilibrium binding of phosphoenolpyruvate to phosphoenolpyruvate carboxylase from Zea mays

Phosphoenolpyruvate carboxylase (PEPC) the carbon dioxide processing enzyme of C4 plants shows different affinities for the substrate phosphoenolpyruvate (PEP) at pH 7.0 and pH 8.0. This has been demonstrated by determination of the enzymatic activity, applying fluorescence titrations and fast reaction techniques such as iodine laser temperature jump (ILTJ) and stopped flow (SF). The binding reaction of PEP to PEPC from Zeamays was measured using the fluorescence probe 2-p-toluidinonaphthalene-6-sulfonate (TNS). The kinetics are described by an allosteric mechanism with a fast reversible bimolecular binding reaction of PEP to a high affinity (tensed) form of PEPC which is in equilibrium with its low affinity (relaxed) form. The association and dissociation rate constants k+A and k-A for the fast binding reaction to the high affinity form were determined to be 1.4±0.15×104 M-1 s-1 and 17±6 s-1 at pH 8.0. The corresponding dissociation constants Kd=1.2±0.5 mM for PEP calculated from the kinetic constants, measured by ILTJ and SF, are in good agreement with Kd values achieved in our equilibrium titration experiments or from the data of Michaelis–Menten-type kinetic experiments. PEP preferentially binds to the high affinity binding site of PEPC, shifting the isomerisation equilibrium strongly towards the tensed form, with the consequence that PEPC is activated. Rate constants for the isomerisation process were obtained as kB+(0)=4.95±0.35 s-1 and kB-(0)=1.25±0.1 s-1 at pH 8. Our kinetic data are consistent with the concerted sequential allosteric mechanism introduced by Monod, Wyman and Changeux. In summary, in this study we present, for the first time, data on the kinetics of PEP binding and on the rate of the isomerisation reaction between the two allosteric forms of PEPC.

Kinetics of solute partitioning at surfactant monolayers in water-in-oil microemulsions

The time scales of the p-nitrophenol (pNP) interfacial association at the curved surfactant monolayers of a dioctyl-sulfosuccinate (AOT) water-in-oil microemulsion system were identified and quantified using the Iodine Laser Temperature Jump (ILTJ) technique. The location of the solute (pNP) was monitored spectrophotometrically as a function of time, following a rapid (≈1 μs) temperature perturbation of the system which shifted the partitioning of pNP between the water and oil phases. The characteristic time assigned to solute association and/or transport was measured to be in the range 0.1 – 1 ms. The equilibrium distribution of pNP was determined and used to identify the mechanism responsible for this relaxation time. Our preliminary results for the association of pNP from the aqueous phase to the curved surfactant interface and transport to the oil are consistent with estimates based on reported results for interfacial resistance offered by surfactants at planar interfaces. A model that accounts for mass-transfer between the water-surfactant-oil regions is proposed to describe the association and transport of species through the surfactant pseudophase and used to analyze the experimental characteristic times.

Kinetics and molecular modelling of ligand binding to ribulose 1, 5‐bisphosphate carboxylase/oxygenase (RUBISCO)

AbstractThe dye 2‐toluidinonaphthalino‐6‐sulphonate TNS is sensitive to ligand binding events at the active site of RUBISCO purified from spinach or Rhodospirillum rubrum. Equilibrium binding curves of the substrate D‐ribulose 1, 5‐bisphosphate RUBP and the inhibitor 6‐D‐phosphogluconate 6‐PG to RUBISCO from spinach were apparently biphasic. Iodine laser temperature jump (ILTJ) experiments showed a fast and a slow bimolecular binding reaction of both ligands corresponding to a strong and a weak equilibrium binding process. In Stopped Flow (SF) experiments different reaction mechanisms were observed for the binding of the transition state analogue 2‐carboxy‐D‐arabinitol 1, 5‐bisphosphate CABP to RUBISCO in the presence and absence of magnesium ions. In the absence of magnesium ions CABP binds in a reversible bimolecular binding reaction to RUBISCO. In the presence of magnesium ions an irreversible two step reaction mechanism for the CABP binding was detected. Molecular dynamic (MD) simulations of ligand binding to RUBISCO were used for modelling of the strong influence of magnesium ions on the kinetics of ligand binding to RUBISCO.

Temperature dependent intermediate structures during the main phase transition of dimyristoyl phosphatidylcholine vesicles a combined iodine laser-temperature jump and time resolved cryo-electron microscopy study

The kinetics of the main phase transition of dimyristoylphosphatidyl choline (DMPC) unilamellar vesicles were investigated in the time range from microseconds to seconds. Iodine laser-temperature jump (ILTJ) experiments showed three discrete relaxation phenomena. Time resolved cryo-electron microscopy (CEM) was applied to produce images of intermediate states typical for the relaxation times of lipid vesicles in the micro- to millisecond time window. A careful measurement of the rate of temperature decrease observed during the production of vitrified lamellae of aqueous samples on a copper grid was performed. The best conditions resulted in average rates of cooling of 3 × 10 4 K/s. By comparing the images from CEM of DMPC vesicle samples vitrified above, at, and below the phase transition temperature a structural model was designed, which explains the temperature jump relaxation times in the micro- to millisecond time range by the formation and disappearance of coexisting clusters of crystalline, intermediate, and fluid lipid areas inside the DMPC bilayers.

Percolation of Water-in-Oil Microemulsions Studied by the Iodine Laser Temperature Jump

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPercolation of Water-in-Oil Microemulsions Studied by the Iodine Laser Temperature JumpC. Petit, J. F. Holzwarth, and M. P. PileniCite this: Langmuir 1995, 11, 7, 2405–2409Publication Date (Print):July 1, 1995Publication History Published online1 May 2002Published inissue 1 July 1995https://doi.org/10.1021/la00007a015RIGHTS & PERMISSIONSArticle Views69Altmetric-Citations9LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (522 KB) Get e-Alerts Get e-Alerts

Interfacial Dynamics of Water-in-Oil Dropliets: a Temperature-Jump Investigation

AbstractThe dynamic response of water-in-oil AOT microemulsion droplets to perturbations caused by rapid energy transfer has been interpreted in terms of the surfactant interface bending rigidity. The Iodine Laser Temperature Jump technique was used to rapidly (1 μs) increase the microemulsion temperature and thus disturb the system equilibrium. The dynamic relaxation to the new equilibrium position was monitored by measuring the turbidity of the microemulsion over a I ms time interval immediately after the temperature jump. The rate and direction of the turbidity change depended on the initial temperature, size and salt content of the water droplets. We observed characteristic times of 2 to 10 μs and attributed them to the relaxation of the surfactant interface. A bending modulus of 0.4 kT was derived for the AOT interface, using a model for the shape perturbation of a spherical interface.

Aggregation kinetics of oil-in-water microemulsion droplets stabilized by C12E5

The author have measured the kinetics of aggregation of oil-in-water microemulsion droplets stabilized by the nonionic surfactant n-dodecyl pentakis(ethylene glycol) ether (C{sub 12}E{sub 5}). The rate of droplet aggregation, which is induced by increasing temperature, was determined by using an iodine laser temperature-jump (ILTJ) technique. The second-order rate constant for the droplet aggregation is found to be significantly lower than the diffusion-controlled limiting value, indicating an energy barrier of magnitude several kT must be overcome before the equilibrium aggregated state is reached. This energy barrier is found to decrease with increasing droplet size.

Kinetics of the interaction of acridine dyes with nucleic acids. An iodine-laser temperature-jump investigation

The intercalation reaction of 9-aminoacridine, acriflavine, acridine orange, proflavine and ethodin into nucleic acids has been studied kinetically using the iodine-laser temperature-jump (ILTJ) technique with fluorescence detection, avoiding interference by transient electric fields. If the interaction with calf-thymus DNA (AT-rich) is considered, two main groups of dyes may be distinguished: 9-aminoacridine, acriflavine and acridine orange showed a linear correlation of the reciprocal relaxation times with DNA phosphate concentration, while proflavine and ethodin were characterized by a levelling off of the relaxation times at large DNA concentrations. On the other hand, proflavine and ethodin showed a linear dependence when Micrococcus lysodeikticus DNA (GC-rich) was used. A model for the interpretation of the experimental results has been proposed which assumes two main types of binding sites, related to GC- or AT-base pairs, for intercalation and a two-step mechanism in both cases. Rapid external binding precedes insertion between base pairs. The outer complex appears to be mainly electrostatic when attached to GC-sites, while it is much stronger with AT-sites. The nature of this extra stabilization has been discussed, together with structure–mechanism relationships.