Search

Due to their outstanding chemical and physical properties, polyimides are widely used in industrial applications. The degree of imidization of polyimides significantly influences their properties, making it an important factor in tailoring the material for specific applications. Imidization refers to the process of converting a precursor poly(amic acid) by removing water, and it is essential to analyze this process in detail to tune the final structure and properties of the material. Conventional techniques for this task include Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), or differential scanning calorimetry (DSC), but they lack the possibility of spatially and/or depth-resolved analysis or do not enable in-line monitoring capabilities. To overcome these limitations, we propose laser-induced breakdown spectroscopy (LIBS) as a powerful tool for the monitoring of the imidization reaction. To establish a measurement method, a total of 130 in-house prepared, self-synthesized samples were thermally cured to exhibit varying imidization degrees. IR spectroscopy served as a reference technique during method development, and a novel formula for calculating the degree of imidization, based on the C 2 and H signal trends, was introduced. The calculated imidization degrees of model thin films based on LIBS were in good accordance with the IR reference method although minor differences between the two methods were expected due to varying information depth and the size of the sampled area. Additionally, the robustness of the procedure was demonstrated by depth profiling of a stacked model polymer, spiking with commercially available additives and, ultimately, by analyzing industry-relevant polymer samples., (© 2024. The Author(s).)

Background: Rapid assessment of hemostasis during postpartum hemorrhage (PPH) is essential to allow characterization of coagulopathy, to estimate bleeding severity, and to improve outcome. Point of care (POC) coagulation monitors could be of great interest for early diagnosis and treatment of coagulation disorders in PPH., Methods: Women with ongoing PPH >500 mL who clinically required an assessment of coagulation with thromboelastography (TEG) were included. The primary aim of this retrospective observational cohort study was to assess the predictive accuracy of TEG parameters for the diagnosis of coagulation disorders (hypofibrinogenemia ≤2 g/L, thrombocytopenia ≤80,000/mm, prothrombin ratio ≤50%, or activated partial thromboplastin time ratio ≥1.5) during PPH. The analyzed TEG parameters were Kaolin-maximum amplitude (K-MA), Kaolin-maximum rate of thrombus generation using G (K-MRTGG), functional fibrinogen-maximum amplitude (FF-MA), and functional fibrinogen-maximum rate of thrombus generation using G (FF-MRTGG). Secondary aims of this study were (1) comparison of the time delay between classical parameters and velocity curve-derived parameters (K-MA versus K-MRTGG and FF-MA versus FF-MRTGG) and (2) evaluation of the accuracy of TEG parameters to predict severe hemorrhage estimated by calculated blood losses., Results: Ninety-eight patients were included with 98 simultaneous TEG analyses and laboratory assays. All parameters had an excellent predictive performance. For the Kaolin assay, no significant difference was evidenced between K-MA and K-MRTGG for the predictive performance for hypofibrinogenemia ≤2 g/L and/or thrombocytopenia ≤80,000/mm (respective area under the curve [AUC], 0.970 vs 0.981). For the functional fibrinogen assay, no significant difference was evidenced between FF-MA and FF-MRTGG for the predictive performance for hypofibrinogenemia ≤2 g/L (respective AUC, 0.988 vs 0.974). For both assays, the time to obtain results was shorter for the velocity parameters (K-MRTGG: 7.7 minutes [2.4 minutes] versus K-MA: 24.7 minutes [4.2 minutes], P < .001; FF-MRTGG: 2.7 minutes [2.7 minutes] versus FF-MA: 14.0 minutes [4.3 minutes], P < .001). All TEG parameters derived from the Kaolin and functional fibrinogen assays and Clauss fibrinogen were significantly predictive of severe PPH >2500 mL., Conclusions: During PPH, when coagulation assessment is indicated, TEG provides a rapid and reliable detection of hypofibrinogenemia ≤2 g/L and/or thrombocytopenia ≤80,000/mm. No difference in performance was evidenced between the velocity-derived parameters (K-MRTGG and FF-MRTGG) and the classical parameters (K-MA and FF-MA). However, velocity-derived parameters offer the advantage of a shorter time to obtain results: FF-MRTGG parameter is available within ≤5 minutes. POC assessment of hemostasis during PPH management may help physicians to diagnose clotting disorders and to provide appropriate hemostatic support.

Perioperative fluid management in paediatrics has been the subject of many controversies in recent years, but fluid management in the neonatal period has not been considered in most reviews and guidelines. The literature regarding neonatal fluid management mainly appears in the paediatric textbooks and few recent data are available, except for resuscitation and fluid loading during shock and major surgery. In the context of anaesthesia, many neonates requiring surgery within the first month of life have organ malformation and/or dysfunction. This article aims at reviewing basic physiological considerations important for neonatal fluid management and mainly focusses on fluid maintenance and replacement during surgery.

Background: In this prospective study, we compared the relationship between propofol concentrations and bispectral index (BIS) in children versus young adults anesthetized with target-controlled infusion (TCI) of propofol., Methods: Forty-five prepubertal subjects (children) and 45 postpubertal subjects (adults) were studied. All patients were anesthetized with TCI of propofol, based on the Kataria et al.'s model for children and on the Schnider et al.'s model for adults. All data from the BIS and the TCI system were continuously recorded using Rugloop software. Remifentanil was continuously administered throughout the study (0.25 microg x kg(-1) x min(-1)). In all patients, after the end of surgery, a 12-min period with a stable target plasma concentration (Ct) of propofol, randomly assigned at 2, 3, 4, 5, and 6 microg/mL, was performed. In addition, in most of the patients, another 12-min period was performed during which the BIS was targeted at 50 +/- 5. After each 12-min steady-state period, the Ct and BIS were noted and the plasma concentration of propofol was measured (Cm). The Ct and Cm corresponding to half maximal effect (BIS(50)) was determined by the Hill equation, and by targeting BIS at 50., Results: In children, as in adults, BIS values were highly correlated with the corresponding Ct or Cm of propofol following classical E(max) dose-response curves. The ECt(50) and the ECm(50), derived from the dose-response curves, were higher in children than in adults: ECm(50): 4.0 (3.6-4.5) microg/mL vs 3.3 (3.0-3.7) microg/mL [mean (95% CI)], P < 0.001; as well were the Ct and Cm clinically obtained when BIS was targeted at 50 (Cm(50): 4.3 +/- 1.1 microg/mL vs 3.4 +/- 1.2 microg/mL, (mean +/- SD) P < 0.05, children versus adults). Cm was generally under-estimated by the Ct, and the bias was higher in children than in adults: 2.6 +/- 2.6 microg/mL vs 1.7 +/- 1.6 microg/mL (P = 0.05)., Conclusions: The good relationship between propofol and BIS demonstrated in children as in adults suggested a slightly lower sensitivity to propofol in children. As the predictability of plasma propofol concentrations with the classical pharmacokinetic/pharmacodynamic models is limited in children, a cerebral pharmacodynamic feedback, such as BIS, may be useful in this population.

After 8 years of silence, dengue virus serotype 2 (DENV-2) reemerged in southeastern Senegal in 1999. Sixty-four DENV-2 strains were isolated in 1999 and 9 strains in 2000 from mosquitoes captured in the forest gallery and surrounding villages. Isolates were obtained from previously described vectors, Aedes furcifer, Ae. taylori, Ae. luteocephalus, and--for the first time in Senegal--from Ae. aegypti and Ae. vittatus. A retrospective analysis of sylvatic DENV-2 outbreaks in Senegal during the last 28 years of entomologic investigations shows that amplifications are periodic, with intervening, silent intervals of 5-8 years. No correlation was found between sylvatic DENV-2 emergence and rainfall amount. For sylvatic DENV-2 vectors, rainfall seems to particularly affect virus amplification that occurs at the end of the rainy season, from October to November. Data obtained from investigation of preimaginal (i.e., nonadult) mosquitoes suggest a secondary transmission cycle involving mosquitoes other than those identified previously as vectors.

Reverse transcriptase PCR (RT-PCR) for diagnosis of Rift Valley fever (RVF) was evaluated by using 293 human and animal sera sampled during an RVF outbreak in Mauritania in 1998. Results of the RT-PCR diagnostic method were compared with those of virus isolation (VI) and detection of immunoglobulin M (IgM) antibodies. Our results showed that RT-PCR is a specific, sensitive tool for RVF diagnosis in the early phase of the disease and that its results do not differ significantly from those obtained by VI. Moreover, the combined results of RT-PCR and IgM antibody detection were in 100% concordance with the results of VI.

Cadmium(II) interactions with multilamellar vesicles of dimyristoyl (DM)- and dipalmitoyl (DP)-phosphatidylcholine (PC), -phosphatidylserine (PS), -phosphatidic acid (PA), -phosphatidylglycerol (PG) and -phosphatidylethanolamine (PE) have been investigated both from the metal and the membrane viewpoints, respectively, by solution 113Cd-NMR and diphenylhexatriene fluorescence polarization coupled with solid-state 31P-NMR. Results can be summarized as follows. (1) Strong cadmium binding to membrane phospholipids results in a decrease of the free Cd(II) 113Cd-NMR isotropic signal and because of slow exchange, in the NMR time scale, between free and bound cadmium pools, the lipid/water partition coefficients, Klw, of the Cd(II) species can be determined in the lamellar gel (fluid) phase. It is found Klw(DMPC) approximately Klw(EggPE) approximately 2+/-2 (2+/-2); Klw(DMPA)=392+/-20 (505+/-25); Klw(DMPG)=428+/-21 (352+/-17); Klw(DMPS)=544+/-27 (672+/-34). Cadmium interactions with membrane phospholipids are therefore electrostatic in nature and the phosphate moiety is proposed as a potential binding site. (2) The presence of Cd(II) stabilizes the gel phases of PG, PA and PS lipids and leads to suppression of the main phase transition for PA and PS. These effects are reduced upon increasing salinity to 0.5 M Cl- and abolished at 1.8 M Cl-, Cd(II) being removed from the membranes due to formation of soluble CdCln species. Moving the pH from 7 to 6 also decreases Cd(II) binding to PA, because of surface charge reduction. (3) Cadmium promotes the formation of isotropic 31P-NMR lines with PG systems and of a hexagonal phase on egg PE bilayers at 24 degreesC, suggesting dramatic membrane reorganization. Properties of cadmium and calcium interacting with phospholipid model membranes are compared, and the potential roles of these interactions in the molecular mechanisms of cadmium uptake and toxicity in cells are discussed.

A nuclear magnetic resonance (NMR) spectroscopy and molecular modeling study of the interaction between alpha-cyclodextrin (alpha-CD) and phospholipids with serine, ethanolamine, or choline headgroups is presented. The experimental approach is based on 31P and 1H NMR measurements on small unilamellar vesicles (SUV), multilamellar systems (MLV), and aqueous suspensions of lipids using a direct complex preparation with alpha-CD. Molecular dynamics computer simulations are used to investigate the trajectory of alpha-CD in the vicinity of a membrane surface and the influence of the charge and dipole moment of the phospholipid headgroups. These factors of charge and orientation of dipole moment seem to play a key role in the interaction of phospholipids with alpha-CD and reflect very well the experimentally observed selectivity of the phospholipid -alpha-CD approach. However, with this approach, there is no evidence for the formation of a complex with the phospholipid headgroup (except for phosphatidylinositol) that results from electrostatic forces. Rather, after a possible extraction of the lipid from the membrane, a classical inclusion of the sn-2 chain in the cavity of alpha-CD occurs. This step depends on the alkyl chain length and saturation state of the lipids as well as on their organization (i.e., as vesicles or dispersions). Based on our results, chemical modifications of the alpha-CD molecule to control the hemolytic properties of alpha-CD are discussed.

The ability of per(3,6-anhydro) alpha cyclodextrin(3,6CD) to capture lead from a preformed glutathion (GSH)-lead complex was investigated by NMR spectroscopy. Such a removal strongly depends on the nature and pH of the buffer used in the competition experiments. It was found that an almost complete removal of lead can be achieved at pH 5.5, especially when lead nitrate is used. The capture also strongly depends on the nature of the lead species as well as of the counter ion present in the medium. These observations imply that decontamination of lead by this process should be optimal under acidic conditions, i.e. in the acidic tractus (stomach). Conversely, lead decontamination at neutral pH was of poor efficiency or required a large excess of (3,6CD). This was particularly the case when human plasma was used as solvent.

Methylmercury (CH3Hg(II)) interactions with multilamellar vesicles of dimyristoyl(DM)- and dipalmitoyl(DP)-phosphatidylcholine (PC), -phosphatidic acid (PA), -phosphatidylglycerol (PG), -phosphatidylserine (PS) and -phosphatidylethanolamine (PE) have been investigated from the metal viewpoint by solution 199Hg-NMR and from the membrane side by diphenylhexatriene fluorescence polarization and solid state 31P-NMR. Results can be summarized as follows: (1) CH3Hg(II) strong binding to membranes results in a progressive decrease of the free CH3HgOH 199Hg-NMR isotropic signal and because of a slow exchange, in the NMR time scale, between free and bound methylmercury pools the lipid/water partition coefficients, K(lw), of the CH3HgOH species can be determined in the lamellar gel (fluid) phase. It is found: K(lw)(DMPC) approximately 2 +/- 2 (2 +/- 2); K(lw)(DMPE) approximately 7 +/- 3 (16 +/- 3); K(lw)(DMPG) = 170 +/- 10 (110 +/- 10); K(lw)(DMPS) = 930 +/- 50 (1250 +/- 60); K(lw)(DMPA) = 1250 +/- 60 (300 +/- 20). CH3Hg(II) interactions with membrane phospholipids are therefore electrostatic in nature and the phosphate moiety is proposed as a potential binding site. (2) The presence of CH3HgOH stabilizes the PG gel phase and destabilizes that of PS. No effect is observed on PC, PA and PE thermotropism. (3) methylmercury promotes the formation of isotropic 31P-NMR lines with PG, PA and PE systems suggesting the presence of non-bilayer phases and hence membrane reorganization. The above effects are compared to those of inorganic mercury Hg(II) and discussed in the context of cell toxicity.

1H, 13C, 31P and 14N NMR spectroscopies were used to investigate the lipid composition of brain tumors (GL6 glioma) in rats, by comparison with controlateral hemispheres. Comparative indexes derived from NMR signal intensities were used to establish the statistical analysis. It was found that sterol metabolism and sphingolipid/glycerolipids ratio are significantly modified when a tumor is present.

The binding of inorganic mercury Hg(II) to phospholipid headgroups has been investigated by phosphorus-31 nuclear magnetic resonance of phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylcholine (PC) in water micellar and multilamellar phases. HgCl2 triggers the aggregation of phospholipid micelles, leading to a lipid-mercury precipitate that is no longer detectable by high-resolution 31P-NMR. The remaining signal area corresponds to micelles in the soluble fraction and is a non-linear function of the initial mercury-to-lipid molar ratio. Kinetics of micelle aggregation are exponential for the first 15 min and show a plateau tendency after 120 min. Apparent Hg(II) affinities for phospholipid headgroups are in the order: PE > PS > PC. The same binding specificity is observed when HgCl2 is added to (1:1) mixtures of different micelles (PE + PC; PS + PC). However, mercury binding to mixed micelles prepared with two lipids (PE/PC or PS/PC) induces the aggregation of both lipids. Hg(II) also leads to a 31P-NMR chemical shift anisotropy decrease of PC, PS and mixed (1:1) PE/PC multilamellar vesicles and markedly broadens PS spectra. This indicates that HgCl2 binding forces phospholipid headgroups to reorient and that the concomitant network formation leads to a slowing down of PS membrane collective motions. Formation of a gel-like lamellar phase characterized by a broad NMR linewidth is also observed upon HgCl2 binding to PE samples both in fluid (L alpha) or hexagonal (H(II)) phases. The PE hexagonal phase is no longer detected in the presence of HgCl2. Mixed PE/PC dispersions remain in the fluid phase upon mercury addition, indicating that no phase separation occurs. Addition of excess NaCl leads to the appearance of the non-reactive species HgCl4(2-) and induces the reversal of all the above effects.