In Situ Infrared Attenuated Total Reflection (IR ATR) Spectroscopy: A Complementary Analytical Tool for Drug Design and Drug Delivery

A comprehensive summary of basic relations for quantitative IR ATR spectroscopy of isotropie and oriented samples is given. Experimental requirements for detection of sub-monolayer quantities in aqueous environment are discussed. New instrumental developments such as a single-beam-sample-reference (SBSR) attachment, and FTIR modulation spectroscopy at low frequencies are presented. Examples of in situ experiments with tertiary-amine local anesthetics interacting with planar, immobilized lipid bilayers are discussed. Partition coefficients of the total amine, as well as of the protonated and deprotonated forms have been determined. Structural alterations, especially of lipids, were detected upon interaction. Adsorption isotherms revea1ed multilayer formation at the membrane surface. The onset of this process for dibucaine is at ca. 5 mm bulk concentration or even below. Preferential accumulation of dibucaine base is observed already at bulk pH 5.5 (pKa = 8.83). For peptide conformation analysis, FTIR temperature (T) modulation experiments were performed for the first time. A modulation amplitude of ΔT = ± 1° at a given mean temperature is shown to result in high-quality phase-resolved spectra enabling detailed insight into periodically induced changes of the state of the sample

Les classes à degrés multiples:: les dispositifs d’enseignement-apprentissage mis en place.

Dans mon présent travail, je m’intéresse aux classes regroupant plusieurs degrés. Dans le cadre théorique, j’ai commencé par chercher la raison de l’existence de ces classes, leurs caractéristiques ainsi que les différentes appellations qui y sont associées. Je me suis intéressée au contexte à l’intérieur de la classe, c’est-à-dire à l’hétérogénéité. J’ai ensuite pu chercher des informations concernant les pratiques mises en place par les enseignants. J’ai donc décidé de me concentrer sur les dispositifs d’enseignement-apprentissage utilisés par les enseignants dans ces classes. Comme méthode d’investigation pour récolter le corpus de données, j’ai alors choisi de mener trois entretiens semi-directifs avec trois enseignantes de l’espace BE-JU. Les trois enseignent dans des classes à degrés multiples de différents cycles: en 3-4H, en 3-4-5H (avec 6-7-8H pour certaines leçons) et 7-8H. Ensuite, j'ai réalisé une analyse thématique des entretiens, mon but étant de connaître les différents dispositifs utilisés, leur pertinence et les raisons de ces choix effectués par les enseignantes

Interactions between magnetic nanoparticles and model lipid bilayers—Fourier transformed infrared spectroscopy (FTIR) studies of the molecular basis of nanotoxicity

The toxicity of nanoparticles (nanotoxicity) is often associated with their interruption of biological membranes. The effect of polymer-coated magnetic nanoparticles (with different Fe3O4 core sizes and different polymeric coatings) on a model biological membrane system of vesicles formed by dimyristoylphosphatidylcholine (DMPC) was studied. Selected magnetic nanoparticles with core sizes ranging from 3 to 13 nm (in diameter) were characterised by transmission electron microscopy. Samples with 10% DMPC and different nanoparticle concentrations were studied by attenuated total reflectance—Fourier transform infrared spectroscopy to establish the influence of nanoparticles on the phase behaviour of model phospholipid systems

Lipid dependence of peptide-membrane interactions Bilayer affinity and aggregation of the peptide alamethicin

AbstractMembrane incorporation and aggregation of the peptide alamethicin have been investigated as a function of lipid type. Head group and acyl chain regions both contribute to modulate alamethicin incorporation. Specifically, the peptide prefers thin membranes and saturated chains; incorporation is reduced by the presence of cholesterol. Aggregation of the peptide in the bilayer is virtually insensitive to changes in lipid composition. These findings show some analogies to results obtained with intrinsic membrane proteins and cast doubt on the use of global membrane parameters for interpreting lipid-peptide interactions

Efficacy and Safety of Rivaroxaban for Postoperative Thromboprophylaxis in Patients After Bariatric Surgery: A Randomized Clinical Trial.

IMPORTANCE Venous thromboembolism (VTE) is a leading cause of morbidity and mortality after bariatric surgery. Clinical end point studies on thromboprophylaxis with direct oral anticoagulants in patients undergoing bariatric surgery are lacking. OBJECTIVE To assess the efficacy and safety of a prophylactic dose of 10 mg/d of rivaroxaban for both 7 and 28 days after bariatric surgery. DESIGN, SETTING, AND PARTICIPANTS This assessor-blinded, phase 2, multicenter randomized clinical trial was conducted from July 1, 2018, through June 30, 2021, with participants from 3 academic and nonacademic hospitals in Switzerland. INTERVENTION Patients were randomized 1 day after bariatric surgery to 10 mg of oral rivaroxaban for either 7 days (short prophylaxis) or 28 days (long prophylaxis). MAIN OUTCOMES AND MEASURES The primary efficacy outcome was the composite of deep vein thrombosis (symptomatic or asymptomatic) and pulmonary embolism within 28 days after bariatric surgery. Main safety outcomes included major bleeding, clinically relevant nonmajor bleeding, and mortality. RESULTS Of 300 patients, 272 (mean [SD] age, 40.0 [12.1] years; 216 women [80.3%]; mean body mass index, 42.2) were randomized; 134 received a 7-day and 135 a 28-day VTE prophylaxis course with rivaroxaban. Only 1 thromboembolic event (0.4%) occurred (asymptomatic thrombosis in a patient undergoing sleeve gastrectomy with extended prophylaxis). Major or clinically relevant nonmajor bleeding events were observed in 5 patients (1.9%): 2 in the short prophylaxis group and 3 in the long prophylaxis group. Clinically nonsignificant bleeding events were observed in 10 patients (3.7%): 3 in the short prophylaxis arm and 7 in the long prophylaxis arm. CONCLUSIONS AND RELEVANCE In this randomized clinical trial, once-daily VTE prophylaxis with 10 mg of rivaroxaban was effective and safe in the early postoperative phase after bariatric surgery in both the short and long prophylaxis groups. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT03522259

Phase behaviour of dehydrated phosphatidylcholines

Dehydrated DLPC, DMPC, DPPC and DSPC have been characterised at temperatures below the diacyl carbon chain-melting transition (Tm), using DSC. For the first time, the existence of pre-Tm transition processes, which are, usually, only observed in the colloidal/liposomal state of saturated phospholipids have been detected for the dehydrated phosphatidylcholines. Temperature modulated differential scanning calorimetry (TMDSC) was used to characterize the several complex, overlapping pre-Tm transition processes. Kinetic studies of the chain-melting (Tm) transition show the activation energy dependence on α (conversion rate) i.e. activation energy decreases as the transition progresses, pointing to the importance of initial cooperative (intra- and inter-molecular) mobility. Furthermore the activation energy increases with increase in diacyl chain length of the phosphatidylcholines which supports the finding that greater molecular interactions of the polymer chain and its head groups in the dehydrated solid state lead to enhanced stability of dehydrated phosphatidylcholines

PHEMTO: protein pH-dependent electric moment tools

PHEMTO (protein pH-dependent electric moment tools) is released in response to the high demand in protein science community for evaluation of electrostatic characteristics in relations to molecular recognition. PHEMTO will serve protein scientists with new advanced features for analysis of protein molecular interactions: Electric/dipole moments, their pH-dependence and in silico charge mutagenesis effects on these properties as well as alternative algorithms for electric/dipole moment computation—Singular value decomposition of electrostatic potential (EP) to account for reaction field. The implementation is based on long-term experience—PHEI mean field electrostatics and PHEPS server for evaluation of global and local pH-dependent properties. However, PHEMTO is not just an update of our PHEPS server. Besides standard electrostatics, we offer new, advanced and useful features for analysis of protein molecular interactions. In addition our algorithms are very fast. Special emphasis is given to the interface—intuitive and user-friendly. The input is comprised of the atomic coordinate file in Protein Data Bank format. The advanced user is provided with a special input section for addition of non-polypeptide charges. The output covers actually full electrostatic characteristics but special emphasis is given to electric/dipole moments and their interactive visualization. PHEMTO server can be accessed at http://phemto.orgchm.bas.bg/

Characterization of the Interactions between Fluoroquinolone Antibiotics and Lipids: a Multitechnique Approach

Probing drug/lipid interactions at the molecular level represents an important challenge in pharmaceutical research and membrane biophysics. Previous studies showed differences in accumulation and intracellular activity between two fluoroquinolones, ciprofloxacin and moxifloxacin, that may actually result from their differential susceptibility to efflux by the ciprofloxacin transporter. In view of the critical role of lipids for the drug cellular uptake and differences observed for the two closely related fluoroquinolones, we investigated the interactions of these two antibiotics with lipids, using an array of complementary techniques. Moxifloxacin induced, to a greater extent than ciprofloxacin, an erosion of the DPPC domains in the DOPC fluid phase (atomic force microscopy) and a shift of the surface pressure-area isotherms of DOPC/DPPC/fluoroquinolone monolayer toward lower area per molecule (Langmuir studies). These effects are related to a lower propensity of moxifloxacin to be released from lipid to aqueous phase (determined by phase transfer studies and conformational analysis) and a marked decrease of all-trans conformation of acyl-lipid chains of DPPC (determined by ATR-FTIR) without increase of lipid disorder and change in the tilt between the normal and the germanium surface (also determined by ATR-FTIR). All together, differences of ciprofloxacin as compared to moxifloxacin in their interactions with lipids could explain differences in their cellular accumulation and susceptibility to efflux transporters