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J Caspers

Publications and source records attributed to J Caspers.

17 recordsLinked to original sources
PubMed1999

Lipid-Drug Interaction and Colligative Properties in Phospholipid Vesicles.

Imipramine penetration into the lipid core of a membrane was demonstrated through measurements on lipid monolayers (surface pressure and surface potential). The surface pressure measurements allow us to calculate the intrinsic binding constant (partition coefficient) for the lipid-Imipramine interaction. This latter value is in correct agreement with the results obtained by electrophoretic mobility measurements on liposomes. In addition, it was observed that the same mole fraction of "lipid-soluble drug" (Chlorpromazine or Imipramine) incorporated in a given lipidic phase (DPPC) induced the same shift in the transition temperature. Copyright 1999 Academic Press.

Journal Article↗
PubMed1998

Physico-chemical characterization of a double long-chain cationic amphiphile (Vectamidine) by microelectrophoresis.

We recently synthesized a novel cationic amphiphile (N-t-butyl-N'-tetradecyl-3-tetradecylaminopropionamidine or Vectamidine (previously described as diC14-amidine)) that associates with DNA and RNA and facilitates their entry and expression into eukaryotic cells. Among several parameters that have been shown to influence the transfection process, the surface charge density plays a key role. Quantitative information about that charge density associated to the cationic amphiphiles organized in liposomal structure is not yet available. We provide here evidence by titration and microelectrophoresis measurements that an evaluation of the intrinsic acidity constants, the surface pH and the counterion binding constants allows to determine the charge density at physiological pH of Vectamidine liposomes. The knowledge of this superficial charge is a prerequisite to a molecular understanding of the DNA-cationic amphiphile complex formation. The method described could be extended to any kind of cationic amphiphile.

Cations↗
PubMed1993

[Effect of pneumatic compression in connection with ergotherapeutic treatment of Colles' fracture. A clinical controlled trial].

We followed forty women with functional deficits in the wrist and hand after sustaining a Colles' fracture. The women participated in occupational therapy three times a week for three weeks. At the initial evaluation, after three weeks, and at a three month evaluation, we measured the following: range of joint movement, grip strength, hand volume (oedema), pain and ADL. There was significant improvement in most of the parameters measured after three weeks of occupational therapy, with a less significant improvement from three weeks to three months. Seventeen of the forty women received twenty minutes of intermittent pneumatic compression before occupational therapy. These patients showed significant improvement in wrist extension, compared with the control group of twenty-three patients. Occupational therapy is recommended for patients showing a functional deficit after Colles' fracture. Intermittent pneumatic compression is recommended as a supplement to occupational therapy.

Aged↗
PubMed1993

Effects of time pressure on the phonetic realization of the Dutch accent-lending pitch rise and fall.

The goal of this experiment is to find the most important phonetic features of Dutch accent-lending pitch movements, in terms of shape, pitch level and alignment with the segmental structure. Time pressure is used as a heuristic method to isolate important phonetic aspects of pitch movements, assuming that under time pressure the speaker will preserve those aspects. In a production experiment, accent-lending rises ('1') and falls ('A') were realized under various types of time pressure. The pitch rise is time-compressed under all pressure types, which would mean that the shape of the rise is relatively unimportant. The segmental alignment of the rise proved to be more important: the onset of the rise is synchronized with the syllable onset. For the fall no fixed synchronization point was found, but its shape was relatively invariant, indicating that shape rather than exact timing is the more important feature of the fall.

Female↗
PubMed1988

Colles fracture: does the anatomical result affect the final function?

Thirty patients who had sustained a Colles' fracture at least four years previously were examined functionally and radiographically. Seventeen had a good radiological result and 13 were considered to have malunion. Functionally the displaced group performed significantly worse than the undisplaced group. We conclude that malunion of a Colles' fracture results in a weak, deformed, stiff and probably painful wrist.

Aged↗
PubMed1987

Ionization state of amiodarone mediates its mode of interaction with lipid bilayers.

Amiodarone is a potent antianginal and antiarrhythmic drug which affects the lipid dynamics. The influence of amiodarone ionization on the lipid transition temperature and enthalpy associated to the liquid crystalline to gel state transition was studied in multilamellar vesicles (MLV) of dipalmitoylphosphatidylcholine (DPPC) by differential scanning measurements (DSC) at different pH. These data were correlated with the calculated number of charged amiodarone molecules inserted into the lipid vesicles. The procedure of calculation requires the knowledge of the intrinsic ionization constant of amiodarone and the area occupied per amiodarone molecule in the close packed state; it can be applied successfully to water insoluble amphiphilic molecules. Only the ionized form of amiodarone molecule destabilizes the lipid matrix organisation whereas no effect was observed with the uncharged form. This destabilizing effect could be explained in terms of a modification of the drug structure induced by its ionization state or in terms of its distribution in the lipid matrix, as an isolated molecule or assembled in clusters depending on its ionization state.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1982

Evaluation of the anesthetic-lipid association constant. A monolayer approach.

A new approach is presented which allows to describe the binding of different local anesthetics to lipids. Lipids (DL- alpha-dipalmitoylphosphatidylcholine, phosphatidylserine, cardiolipin) are spread at the air-water interface and the anesthetic (procaine, butacaine, tetracaine) injected into the aqueous subphase. The equilibrium constants associated to the interfacial reaction: D+ (subphase) +L- (monolayer) in equilibrium DL (monolayer) (where D+ denotes the anesthetics, L- the lipid anionic site and DL the complex) are calculated from an experimental evaluation of the surface potential of the lipid monolayer. This mode of determination is based essentially on the good correlation between the experimental values of the surface potential and the theoretical predictions from the Gouy-Chapman theory. Fluorescence measurements on liposomes are carried out in order to locate the position of the drug in the lipid layer. This method can be extended to any positively charged drug-anionic lipid interaction.

4-Aminobenzoic Acid↗
PubMed1980

Evidence of a specific complex between adriamycin and negatively-charged phospholipids.

Membrane-model systems (monolayers, small unilamellar vesicles) were used to study the interaction between adriamycin (ADM) and phospholipids. Adsorption of 3H-labeled adriamycin on different phospholipid monolayers demonstrated the specificity of adriamycin for negatively-charged phospholipids (cardiolipin, phosphatidylserine, phosphatidic acid). The stoichiometry has been found to be approx. 2 mol (1.8) adriamycin per mol cardiolipin and approx. 1 mol (0.75) adriamycin per mol phosphatidylserine and phosphatidic acid. No adsorption was detected with neutral lipids. Surface-potential measurements confirm the formation of a complex stabilized by electrostatic interactions without penetration of the drug into the lipid lipophilic phase. Some adriamycin derivatives were used to discriminate between the ionized hydrophilic and hydrophobic contributions in the complex formation. The absorption spectrum of adriamycin in the presence of cardiolipin resembles the behavior of the ADM-DNA complex. Moreover, the association constants of the two complexes are very similar (cardiolipin-ADM, 1.6 . 10(6) . M-1; ADM-DNA, 2.4 . 10(6) . M-1). To explain the high affinity of cardiolipin for adriamycin, we proposed that two essential interactions are responsible for the complex stabilization: an electrostatic interaction between the protonated amino groups of the sugar residues and the ionized phosphate residues, and an interaction between adjacent anthraquinone chromophores. These data strongly suggest competitive behavior between a membrane site and the target. Consequently, it must be assumed that the lipidic components of the cell membrane structure may be an important determinant in the behavior of adriamycin. This observation should be kept in mind in the building of new derivatives.

Calorimetry↗
PubMed1979

The effect of surface charge density on valinomycin-K+ complex formation in model membranes.

The model membrane approach was used to investigate the surface charge effect on the ion-antibiotic complexation process. Mixed monolayers of valinomycin and lipids were spread on subphases containing K+ or Na+. The surface charge density was modified by spreading ionizable valinomycin analogs on aqueous subphases of different pH or by changing the nature of the lipid (neutral, negatively charged) in the mixed film. Surface pressure and surface potential measurements demonstrated that a neutral lipid (phosphatidylcholine) or positively charged valinomycin analogs didn't enhance the anti-biotic complexing capacity. However, a maximal complexation is reached for a critical lipid concentration in the valinomycin-phosphatidylserine mixed film. The role of the surface charge on the valinomycin complexing properties was examined in terms of the Gouy-Chapman theory. As a consequence of the negative charge of the lipid monolayer, the K+ concentration near the surface is larger than the bulk concentration, by a Boltzmann factor. A good agreement was observed between the experimental results and the theoretical predictions. Conductance measurements of asymmetric bilayers containing a neutral lipid (egg lecithin) on one side and a negatively charged lipid (phosphatidyl-serine) on the other, confirm the role of the surface charge. Indeed, addition of K+ to the neutral side of the bilayer containing valinomycin had no effect on the conductance whereas addition of K+ to the charged side of the bilayer caused a 80-fold conductance increase.

Kinetics↗
PubMedDate not supplied

Experiments on the meaning of four types of single-accent intonation patterns in Dutch.

The Grammar of Dutch Intonation (GDI) provides a description of the possible intonation contours of Dutch. The GDI distinguishes accent-lending and nonaccent-lending pitch configurations, but refrains from further functional statements. This paper describes an experimental attempt to verify meaning hypotheses for four Dutch single-accent pitch patterns as postulated in the linguistic literature. The four pitch accent types were realized on proper names; the abstract meanings, in terms of the manipulation of an element of the background shared between speaker and listener, were incorporated in situational contexts, distinguishing between a "default" and a vocative use of the proper name ("orientation"). Listeners ranked the four melodic shapes from most to least appropriate in their specific context. After revision of part of the materials a second perception experiment was conducted, in which subjects had a rank four contexts from most to least appropriate for a specific pitch accent type. Results show a distinct effect of "orientation" on the appropriateness of two of the investigated pitch accent types in the various context types; the other two pitch accent types are associated with the predicted context types (and vice versa) well above chance, indicating the viability of at least two of the linguistic proposals.

Adult↗
PubMedDate not supplied

Who's next? The melodic marking of question vs. continuation in Dutch.

The present study is concerned with functional differences between the accent-lending rise followed by sustained level pitch (GDI-notation "10," cf., 't Hart, Collier, and Cohen, 1990) and the combination of the accent-lending rise and final rise ("12") in Dutch. Theoretical analyses of the meaning of Dutch intonation claim that "10" can be interpreted as a question. In contrast, recent investigations of the relevance of intonation for turn-taking indicate that "10" signals that the speaker wants to keep the turn. The main goal of the present experimental investigation is to find evidence for the idea that speakers may use contour "10" to keep the floor. Thirty subjects were presented with short utterances bearing either a "12" or a "10" contour in three perception experiments. Results support the hypothesis that "10" is not readily interpreted as a question, as opposed to contour "12," which indicates that contour "10" may play a role in signaling turn-keeping in Dutch.

Adolescent↗